Micro Midterm Flashcards
What color are gram positive bacteria on a typical gram stain? What about gram negative?
Gram positive: blueish or purple; gram negative: pink
Are these bacteria gram positive or gram negative?
Gram positive, note the purple color. This is bacillus.
What shape are cocci bacteria?
Typically spherical, in clusters, pairs, or chains
Can all bacteria be visualized with the gram stain?
No, some need other stains e.g. spirochetes
Do bacteria have organelles?
No, they are prokaryotes
What is the outermost coat of the gram-negative cell wall?
A phospholipid membrane (there are two of them, one for the cell well and one that functions as the plasma membrane)
What is the cell wall of gram-positive bacteria made of?
Peptidoglycan: peptide cross links between polysaccharide chains
Are lipopolysaccharides characteristic of gram positive or gram negative bacteria?
Gram negative, as they integrate into the outer phospholipid membrane
Does Staphylococcus epidermidis normally cause disease on the skin?
No, it is benign. Staph aureus is the more virulent strain that can cause acne and other skin infections.
Is the peptidoglycan layer of the cell wall thicker in gram positive or gram negative bacteria?
Gram positive bacteria have thicker peptidoglycan
Bacteria can be colonize or can cause disease. The ability to cause disease is determined by
– […] factors
– Host factors
– Environmental factors
Bacteria can be colonize or can cause disease. The ability to cause disease is determined by
– Virulence (bacterial) factors
– Host factors
– Environmental factors
Bacteria can be colonize or can cause disease. The ability to cause disease is determined by
– Virulence (bacterial) factors
– […] factors
– Environmental factors
Bacteria can be colonize or can cause disease. The ability to cause disease is determined by
– Virulence (bacterial) factors
– Host factors
– Environmental factors
Bacteria can be colonize or can cause disease. The ability to cause disease is determined by
– Virulence (bacterial) factors
– Host factors
– […] factors
Bacteria can be colonize or can cause disease. The ability to cause disease is determined by
– Virulence (bacterial) factors
– Host factors
– Environmental factors
Besides direct damage caused by the organism, what can infectious disease symptoms manifest via?
The immune response mounted by the host
What is hemolysis as it relates to bacteria?
The pattern that the colonies form on a blood agar plate, related to their ability to break down blood cells
Is this α or β hemolysis?
β: halo like growth around streaks
What kind of typing is this? Which side is positive?
Lancefield typing; left is positive
What are non-suppurative complications?
When the host response causes the clinical manifestations of the disease
What bacterium causes pharyngitis, cellulitis, impetigo, and necrotizing fasciitis?
Streptococcus pyogenes
Is Streptococcus pyogenes α or β hemolytic?
β hemolytic
What clinical manifestation is this? What bacterium is immediately suspect?
Pharyngitis; Streptococcus pyogenes
What clinical manifestation is this? What bacterium is suspected?
Erypsipelas; Streptococcus pyogenes
What skin condition is this? What bacterium is immediately suspect?
Impetigo; Streptococcus pyogenes
What does it mean to talk about suppurative complications of an infection?
Clinical manifestations directly caused by the organism itself; e.g., pharyngitis or a rash
Are acute rheumatic fever, glomerulonephritis, scarlet fever, and toxic shock suppurative or non-suppurative complications?
Non-suppurative
What does the word “suppurative” derive from (e.g. what does suppuration refer to?)
Pus formation
Is acute rheumatic fever more rare or less rare over the age of 30 than below?
It is very rare over 30
Does acute rheumatic fever associate with a preceding S. pyogenes throat infection, or a skin infection, or both?
Only throat infections
When a bacteria is said to belong to Group A, B, etc. what grouping system is being referenced?
The Lancefield grouping system
What is the Lancefield grouping system based on? Does it apply to α hemolytic or β hemolytic bacteria?
The carbohydrate composition of bacterial antigens in their cell walls; Lancefield only worked on β hemolytic bacteria
Clinical manifestations of acute rheumatic fever include:
- […]
- Carditis (heart failure, new murmur,
pericarditis)
- Sydenham’s chorea
- Erythema marginatum
Clinical manifestations of acute rheumatic fever include:
- Painful, migratory arthritis
- Carditis (heart failure, new murmur,
pericarditis)
- Sydenham’s chorea
- Erythema marginatum
Clinical manifestations of acute rheumatic fever include:
- Painful, migratory arthritis
- […] (heart failure, new murmur,
pericarditis)
- Sydenham’s chorea
- Erythema marginatum
Clinical manifestations of acute rheumatic fever include:
- Painful, migratory arthritis
- Carditis (heart failure, new murmur,
pericarditis)
- Sydenham’s chorea
- Erythema marginatum
Clinical manifestations of acute rheumatic fever include:
- Painful, migratory arthritis
- Carditis (heart failure, new murmur,
pericarditis)
- Sydenham’s […]
- Erythema marginatum
Clinical manifestations of acute rheumatic fever include:
- Painful, migratory arthritis
- Carditis (heart failure, new murmur,
pericarditis)
- Sydenham’s chorea
- Erythema marginatum
Clinical manifestations of acute rheumatic fever include:
- Painful, migratory arthritis
- Carditis (heart failure, new murmur,
pericarditis)
- Sydenham’s chorea
- […] marginatum
Clinical manifestations of acute rheumatic fever include:
- Painful, migratory arthritis
- Carditis (heart failure, new murmur,
pericarditis)
- Sydenham’s chorea
- Erythema marginatum
What is the pathogenesis of post-streptococcal glomerulonephritis?
Antibodies, complement components react with streptococcal antigens to form immune complexes which deposit in the renal glomerulus
Does post-streptococcal glomerulonephritis most often affect children or adults?
Children
What are these clinical manifestations characteristic of? Hint: this patient had a known exposure to Streptococcus pyogenes.
Scarlet fever
What toxins cause streptococcal toxic shock syndrome?
Pyrogenic exotoxins (SPEA, SPEB, SPEC)
If a patient is in shock and undergoing multi-organ system failure following a streptococcal infection, what syndrome may be occurring?
Streptococcal toxic shock syndrome
What do the exotoxins involved in streptococcal toxic shock bind to? What does this cause the release of?
T lymphocytes and class II MHC complexes of antigen-presenting cells; leads to massive cytokine release
Is Streptococcus agalactiae in group A or B? Is it α hemolytic or β hemolytic?
Group B; β hemolytic
What bacterium is highly associated with neonatal sepsis and maternal sepsis, as well as soft-tissue infection in diabetics?
Streptococcus agalactiae
Are enterococcal species more resistant or less resistant to cephalosporins and β-lactam based drugs?
More resistant
Enterococcus can cause:
- […]
- Biliary tract infection
- Peritonitis
- Bacterial endocarditis
- Nosocomial superinfection: particularly bacteremia
Enterococcus can cause:
- Urinary tract infection
- Biliary tract infection
- Peritonitis
- Bacterial endocarditis
- Nosocomial superinfection: particularly bacteremia
Enterococcus can cause:
- Urinary tract infection
- Biliary tract infection
- Peritonitis
- Bacterial […]
- Nosocomial superinfection: particularly bacteremia
Enterococcus can cause:
- Urinary tract infection
- Biliary tract infection
- Peritonitis
- Bacterial endocarditis
- Nosocomial superinfection: particularly bacteremia
Enterococcus can cause:
- Urinary tract infection
- Biliary tract infection
- Peritonitis
- Bacterial endocarditis
- Nosocomial superinfection: particularly […]
Enterococcus can cause:
- Urinary tract infection
- Biliary tract infection
- Peritonitis
- Bacterial endocarditis
- Nosocomial superinfection: particularly bacteremia
Are strep viridans species α hemolytic or β hemolytic? How are they distinguished from pneumococci?
α hemolytic; distinguished from pneumococci with the optochin test, which strep viridans are not sensitive to
What is the major agent causing bacterial endocarditis?
Streptococci, in particular strep viridans
Can Staphylococcus aureus cause bacterial endocarditis?
Yes
Are streptococcal strains gram positive or negative?
Gram positive
S. mutans and S. sanguis are both streptococcal bacteremia that comprise what group?
Strep viridans, or α hemolytic streptococci
How many kinds of hemolysis are there for a bacterial culture on blood agar? What are they?
Three: α, β, γ
Is Streptococcus pyogenes sensitive to bacitracin? Does an antibody to M protein enhance immune response?
Yes, it is sensitive to bacitracin; yes, antibody to M protein is protective
What are three pyogenic consequences of streptococcus pyogenes infection?
Pharyngitis, cellulitis, impetigo
What does “pyogenic” mean?
Causes creation of pus
What genus do E. faecalis and E. faecium belong to?
Enterococcus
How are enterococci divided by Lancefield grouping?
They are divided into group D and non-group D
What streptococcal bacteria normally colonize the oropharynx?
Strep viridans
What bacterium most typically causes dental caries (cavities)?
S. mutans
What is the hardest genus of streptococcus to kill with antibiotics?
Enterococcus
What is a mnemonic for three common causes of S. pyogenes based on “PH”?
PHaryngitis to rheum PHever and glomerulonePHritis
What is a mnemonic for rheumatic fever symptoms?
JONES:
- Joints
- Heart (is round like an O)
- Nodules
- Erythema marginatum (pink rings on the trunk)
- Syndenham’s Chorea (abnormal involuntary movement disorder)
Is Staphylococcus aureus gram positive or negative? Does it form chains or clusters?
Positive; clusters
Is S. aureus coagulase positive or negative?
Positive
What bacteria are these?
Staphylococcus aureus; clusters + gram positive
Virulence factors for S. aureus include […], surface factors, and secreted proteins.
Virulence factors for S. aureus include biofilm, surface factors, and secreted proteins.
Virulence factors for S. aureus include biofilm, […], and secreted proteins.
Virulence factors for S. aureus include biofilm, surface factors, and secreted proteins.
Virulence factors for S. aureus include biofilm, surface factors, and […] proteins.
Virulence factors for S. aureus include biofilm, surface factors, and secreted proteins.
What protein in S. aureus correlates with virulence and binds to the Fc terminal of IgG inhibiting complement fixation? What else does this inhibit?
Protein A; phagocytosis
S. aureus can surround their cell walls with a […] capsule, which inhibits opsonization.
S. aureus can surround their cell walls with a polysaccharide capsule, which inhibits opsonization.
S. aureus can surround their cell walls with a polysaccharide capsule, which inhibits […].
S. aureus can surround their cell walls with a polysaccharide capsule, which inhibits opsonization.
What part of S. aureus is protein A integrated into?
The cell wall
Are coagulase positive staphylococci more or less virulent than coagulase-negative ones?
More virulent
Do staphylocci infections typically produce pus?
Yes
What is the primary host immune response to staphylococcus infection?
Primarily mechanical and in the epidermis, but opsonization and neutrophil phagocytosis are also significant
Can S. aureus cause skin and soft tissue infections? What about endocarditis? Septic arthritis?
Yes to all
What toxin does S. aureus produce that causes toxic shock syndrome?
TSST1
What bacteria produces an abscess like this?
S. aureus
Can impetigo be caused by S. aureus?
Yes
What color is the crust around impetigo lesions?
Golden
What is skin infection is this picture characteristic of?
Cellulitis, probably by S. aureus
What is this infection called? Is this the same as a stye? What bacterium is it associated with?
Chalazion; it is different from a stye (it is a cyst blocking a tarsal gland, not a sebaceous gland); S. aureus
What are these?
Microemboli associated with endocarditis
What are serious neurologic targets of metastatic infection caused by S. aureus?
Brain abscesses or spinal epidural abscess
Can S. aureus cause knee arthritis?
Yes, it can infect it causing septic arthritis
What does “nosocomial” mean?
Hospital-acquired (usually referring to an infection)
What does MRSA stand for? What infection source is it associated with?
Methicillin-resistant Staphylococcus aureus; nosocomial infections
What bacteria commonly causes acute food poisoning? How long does this illness last?
Staphylococcus aureus; 24 hours
How long is an S. aureus bacteremia usually treated? What is the reasoning behind this?
4 weeks; undertreating a bacteremia can lead to the development of a resistant strain
How do you treat MRSA?
Synthetic cell-wall active penicillins: Oxacillin, nafcillin, cefazonin; or vancomycin
Does vancomycin work on gram positive or gram negative bacteria?
Gram positive
Is S. epidermidis coagulase positive or negative?
Negative
Does S. epidermidis typically cause any disease while inhabiting the skin?
No, but it is important in association with medical devices
What is the thick, multilayered slime created by *S. epidermidis *that covers catheters during invasion and protects it from antibiotics called?
Biofilm
What bacterium is associated with infections from intravascular devices?
S. epidermidis
What location of infection is S. saprophyticus commonly associated with?
Urinary tract infection
*S. saprophyticus *most likely has unique surface proteins that permit it to bind to which receptors in the genitourinary tract?
Mucosal receptors
What drug is this?
Vancomycin
Wha tis the mechanism of Vancomycin?
It inhibits bacterial cell wall synthesis by binding firmly to D-ala-D-ala of the peptidoglycan, preventing elongation and cross-linking
What are two mechanisms of resistance to vancomycin?
- Altered peptidoglycan binding site: D-ala-D-ala to D-ala-D-lactate
- Thickened cell wall
Is vancomycin active against gram-positive or gram-negative bacteria or both?
Gram-positive
What is the drug of choice for treating MRSA and penicillin-resistant pneumococcus?
Vancomycin
What are two major toxic side effects of vancomycin?
Nephrotoxicity and hypersensitivity (red man syndrome or anaphylaxis)
Why is vancomycin given slowly?
To avoid histamine reactions resulting from rapid infusion, such as red man syndrome
Why might a pretreatment of antihistamine be used before a rapid infusion of vancomycin?
To avoid anaphylaxis or red man syndrome
Is vancomycin bactericidal or bacteriostatic?
Slowly bactericidal, mostly bacteriostatic
What drug is this?
Daptomycin
Does daptomycin act against gram-positive or gram-negative bacteria?
Gram-positive
What is the mechanism of daptomycin?
It binds the cytoplasmic membrane and causes rapid depolarization
Is daptomycin bactericidal or bacteriostatic?
Rapidly bactericidal
Does daptomycin have gram-negative activity?
No
What ion does daptomycin use to bind to the cytoplasmic membrane?
Ca++
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If an enterococcus is vancomycin resistant, what cyclic lipopeptide antibacterial can be used?
Daptomycin
What is the interaction between daptomycin and pulmonary surfactant? Can daptomycin be used to treat pneumonias?
Pulmonary surfactant breaks it down; no
Does daptomycin have adverse musculoskelatal effects?
Yes, including myalgias, weakness, rhabdomyolysis, and cramps
What serum levels can be measured to monitor musculoskeletal adverse effects of daptomycin?
Creatinine phosphokinase
What is a protein synthesis inhibitor in gram-positive cocci that acts on…
- Initiation?
- Elongation?
- Transpeptidation?
- Initiation: linezolid
- Elongation: doxycycline
- Transpeptidation: clindamycin
Are protein synthesis inhibitors for gram positive cocci bactericidal or bacteriostatic?
Bacteriostatic
What drug family do doxycycline, minocycline, and demeclocycline belong to? What is their mechanism?
Tetracycline; inhibitor against protein elongation
What dietary substance should not by consumed with doxycycline?
Dairy, because it forms nonabsorbable chelates with Ca++
Doxycycline binds to which tissues undergoing calcification?
Teeth and bones
Is doxycycline excreted in the urine? Metabolized in the liver?
Yes to both
What effect on teeth can occur with doxycycline?
Discoloration of teeth or stunting of growth
Does clindamycin affect enterococcal bacteria?
No
Does clindamycin affect aerobic or anaerobic bacteria?
Anaerobic
Can clindamycin treat an infection in the CNS?
No, it does not reach therapeutic levels in CSF
The disc on the left is erythromycin, and the one on the left is clindamycin. What is significant about the flattened part of the area of impeded growth facing the erythromycin disc? Is this bacteria resistant to clindamycin?
This indicates that erythromycin is activating genes that provide resistance to clindamycin; therefore, this bacteria is inducibly clindamycin resistant.
What are two side effects of clindamycin?
Rash and clostridium difficile colitis
What is the bioavailability of oral linezolid?
100%
What is the mechanism of linezolid?
Inhibits protein synthesis initiation in gram positive bacteria
What are three main safety concerns with linezolid?
Thrombocytopenia/neutropenia, metabolic acidosis, serotonin syndrome
What side effect of linezolid is characterized by mental status changes, fever, hypertension, tachycardia, hyperreflexia, myoclonus, and tremor?
Serotonin syndrome
Is hyperthermia a more severe toxicity finding than altered mental status?
Yes
What is the mechanism of trimethoprim-sulfamethoxazole?
It is a folic acid antagonist
How do humans acquire folic acid? How do bacteria acquire folate?
Humans ingest it; bacteria synthesize it
What synthesis process requires folate-derived cofactors in bacteria?
Synthesis of DNA and RNA
Are folic acid antagonists bacteriostatic or bactericidal?
Bacteriostatic
What is the drug of choice for treatment of Pneumocystis jirovecii and Nocardia?
TMP-SMX, a combo of sulfamethoxazole and trimethoprim
Can TMP-SMX reach the CSF?
Yes
Side effects of TMP-SMX include: […], rashes, hemolytic anemia, and kernicterus (a bilirubin-induced brain dysfunction)
Side effects of TMP-SMX include: hypersensitivity, rashes, hemolytic anemia, and kernicterus (a bilirubin-induced brain dysfunction)
Side effects of TMP-SMX include: hypersensitivity, […], hemolytic anemia, and kernicterus (a bilirubin-induced brain dysfunction)
Side effects of TMP-SMX include: hypersensitivity, rashes, hemolytic anemia, and kernicterus (a bilirubin-induced brain dysfunction)
Side effects of TMP-SMX include: hypersensitivity, rashes, hemolytic […], and kernicterus (a bilirubin-induced brain dysfunction)
Side effects of TMP-SMX include: hypersensitivity, rashes, hemolytic anemia, and kernicterus (a bilirubin-induced brain dysfunction)
Side effects of TMP-SMX include: hypersensitivity, rashes, hemolytic anemia, and […] (a bilirubin-induced brain dysfunction)
Side effects of TMP-SMX include: hypersensitivity, rashes, hemolytic anemia, and kernicterus (a bilirubin-induced brain dysfunction)
What bacterium causes this skin infection?
Staphylococcus aureus
What genus of bacterium causes this infection?
Staphylococcus species
What six antibacterials can be used to treat MRSA?
Vancomycin, daptomycin, clindamycin, doxycycline, linezolid, TMP-SMX
What is the common mechanism for penicillin, cephalosporin, carbapenems, and monobactam?
They are inhibitors of peptidoglycan crosslinking
Which side is gram +, and which is gram -?
Left is gram + (thick peptidoglycan); right is gram - (two cell membranes)
What drugs are these?
Top: penicillin; bottom: cephalosporin. Notice the CH3R1 group and six-membered ring on cephalosporin, distinguishing it from other β-lactams. Penicillin has a five-membered ring with a dimethyl group.
What drug derived from mold acts on this crosslinking process in peptidoglycan? What enzyme is being inhibited?
Penicillin; a transpeptidase
What is the most common method of resistance to penicillin?
Beta-lactamase, a gene that breaks penicillin down
Where does beta-lactamase cleave penicillin?
The beta-lactam four atom ring
Can plasmids contain multiple resistance factors?
Yes
What channels do β-lactams use to enter the peptidoglycan layer of gram negative bacteria?
Porin channels
What is the mechanism of vancomycin and bacitracin?
Both inhibit peptidoglycan synthesis
Do vancomycin and bacitracin inhibit peptidoglycan crosslinking?
No, they inhibit polymerization of the peptide to the polysaccharide chain
Are gram negative and gram positive bacteria equally susceptible to vancomycin treatment? Why or why not?
Gram negative are intrinsically resistant; vancomycin cannot cross the outer membrane
What do enterococci synthesize instead of the terminal D-ala-D-ala on peptidoglycan to prevent vancomycin from binding?
D-ala-D-lactic acid
What is another name for transpeptidases in bacteria named after the drug that affects them?
Penicillin-binding proteins
What class of drugs does erythromycin belong to? What is their mechanism? How is resistance generated?
Macrolides; they inhibit protein synthesis by acting on the bacterial ribosome; the 50S subunit is modified so the drug cannot bind
How can resistance to tetracyclins be generated by bacteria?
They actively transport it out of the cell
What is the mechanism of metronidazole?
It enters bacteria and is metabolized by bacterial enzymes that allow it to cause DNA damage
What are two antibiotics that are DNA-dependent RNA polymerase inhibitors?
Rifampicin and actinomycin D (the latter is only a laboratory reagent)
Why do folic acid antimetabolites like sulfonamides and trimethoprim have antibacterial activity?
Bacteria need to metabolize folic acid to synthesize nucleotides (humans can acquire them from the diet)
How might resistance to trimethoprim develop, unrelated to modifications in the target enzyme itself?
Overproduction of the target enzyme can prevent the inhibitor from sufficiently affecting folic acid metabolism
What kind of antibiotic-antibiotic interaction is this? (The y-axis is log bacterial cell count)
Indifference
What kind of antibiotic-antibiotic interaction is this?
Antagonism
What is the best possible antibiotic-antibiotic interaction?
Synergy
Can aminoglycosides still kill bacteria without protein synthesis?
No
What antibiotic (whose mechanism is still unclear) is used against TB?
Isoniazid
Is the number of antibiotics discovered per year increasing or decreasing?
Decreasing
Why is it less profitable to build a new antibiotic than, for instance, a new anti-cholesterol drug?
Antibiotics are usually not taken chronically and so patients and hospitals will almost always spend less on them than other drugs
What experiment did Avery et al. perform in 1944 to show that bacterial virulence is a genetic property?
Virulent bacteria could be non-encapsulated and mixed with encapsulated non-virulent bacteria which would then be able to infect and kill mice
Are bacteria typically haploid or diploid?
Haploid
How do bacteria normally exchange genetic material with other cells, conferring antimicrobial resistance?
Plasmids
What is the spontaneous frequency of a mutation that knocks out or knocks in an operon in bacteria, per replication?
10-6
What are three methods of genetic exchange used by bacteria?
Transformation, conjugation, and transduction
Could mutations alone explain the rapidity at which bacteria acquire resistance to drugs?
No, the exchange of genetic material is also significant
Can all bacteria use transformation to take up DNA from the environment?
No
How is bacterial conjugation different from transformation?
During conjugation, an extension of the membrane from one bacterium to another (a pillus) whereby the cytoplasms of the two cells can mix allows genetic material to move from one cell to the other. Transformation involves uptake of extracellular DNA.
As double-stranded DNA enters the bacterium during transformation, what happens to it?
One strand of it is degraded, and then it forms a triple-strand with genomic DNA
During conjugation of two bacteria, are the cell walls of each organism interrupted?
Yes
What process is being observed here via EM? What is the significance of one cell looking “hairy” while the other is not?
Conjugation of bacteria; the hairy cell is the F+ cell and the other is the F- cell
Can plasmids be exchanged during conjugation?
Yes, along with chromosomes
What structures allow transduction to occur between bacteria?
Bacteriophages
What are these? What genetic exchange process for bacteria do they facilitate?
Bacteriophages; transduction
When bacteriophages add DNA to a bacterium, is it necessarily killed?
No, it is only killed in the lytic cycle, not the lysogenic cycle
What are phages capable of only the lytic cycle called?
Virulent
Can all phage species undergo the lytic cycle? What happens to the bacterium in this cycle?
Yes; it is killed
If bacteriophages create and replicate their own DNA during the lytic cycle, how could it be used to transfer host genetic material to another bacterium (transduction)?
Host genetic material (e.g. part of a chromosome) could be packaged by accident into a phage created within a bacterium, which goes on to inject it into another cell
What genetic studies can be facilitated by measures of cotransduction?
Linkage, or an estimate of how far apart two bacterial genes are to each other on a chromosome
What are DNA sequences that can jump from one position to another called?
Transposons
How long are insertion sequences (IS elements), a type of transposon? What is encoded by them?
1-3kb; a transposase protein that facilitates the transposition action, along with regulatory proteins
What sort of DNA element is this?
A transposon, specifically an insertion sequence (note IS elements)
What are DNA elements that encode a site-specific recombinase along with its recognition region called? What public health issue are they relevant for?
Integrons; multiple antibiotic resistance
What can destroy DNA that enters a bacterium?
Nucleases, or it can be inherently unstable and self-destruct
What type of recombination does RecA facilitate?
Homologous recombination
What is the most frequent cause of genetic variation in bacteria? How frequently does it occur per generation?
Homologous recombination, with a frequency of 10-1 to 10-2 per generation
Is plasmid transfer in bacteria more frequent per generation than transposition?
Generally more frequent
What was the first bacterial genome sequenced?
Haemophilus influenzae in 2003
Are aminoglycosides, fluoroquinolones and lipopeptides like daptomycin time-dependent or concentration-dependent?
Concentration-dependent
For concentration-dependent drugs, is a large bolus administered, or frequent smaller doses?
A large bolus
What is the minimum inhibitory concentration of an antibiotic/bacteria combination?
The lowest concentration that will inhibit the visible growth of bacteria in vitro
Can broth microdilution measure minimum inhibitory concentration (MIC)?
Yes
What method is microdilution (to measure minimum inhibitory concentration) based on?
Broth macrodilution
Is the epsilometer more or less accurate than broth macrodilution at measuring minimum inhibitory concentration (MIC)?
Less
Does Kirby Bauer disc diffusion produce the minimum inhibitory concentration of a drug-bacteria combination?
No
Is the zone size measured by Kirby Bauer proportional to bacterial resistance or susceptibility?
Proportional to susceptibility
Can an antibiotic be bactericidal against some organisms and bacteriostatic against others?
Yes, e.g., vancomycin
Would a person already severely ill from bacterial infection preferably receive a bactericidal or bacteriostatic agent?
Bactericidal
What is the identifying prefix for cephalosporin antibiotics?
Cef- or Ceph-
What are the four families of β-lactam antibiotics?
Penicillins, cephalosporins, carbapenems, and monobactams
What is the unifying suffix for penicillin-class β-lactam antibiotics?
NAME?
Name the two rings in this generalized antibiotic structure. What family does this structure describe?
Top, thiazolidine ring; bottom, β-lactam ring; penicillins (identified by the thiazolidine ring)
Where is penicillin-binding protein located within a bacterium?
The cell membrane (the inner one, for gram-negative bacteria)
Do natural penicillins have activity against streptococci? What about staphylococci?
Yes against streptococci; usually not against staphylococci
Are there synthetic penicillins that act against staphylococci?
Yes
What penicillin is very completely absorbed after oral administration?
Amoxicillin
Which penicillin is not cleared renally?
Nafcillin
What diagnoses are penicillin still used for today?
Group A and Group B Strep, caused by *S. pyogenes *and S. agalactiae, respectively, and syphilis, caused by Treponema pallidum
What is the oral formulation of pencillin called? What is the IV forumation called?
Penicillin V - oral; penicillin G - intravenous
What bacteria causing skin infections is mostly resistant to penicillin because of the production of β-lactamases?
Staphylococcus aureus
Can anti-staphylococcal penicillins be cleaved by β-lactamases (penicillinases)?
Usually, no.
What are three anti-staphylococcal penicillins? What is the route of administration?
NOD: Nafcillin, oxacillin, dicloxacillin; oral
Is methicillin still used clinically?
Usually no, because of nephrotoxicity
What common infection are NOD (Nafcillin, oxacillin, dicloxacillin) used to treat?
Skin or bloodstream infections with Staphylococcus aureus
What is another name for extended-spectrum penicillins?
Amino-penicillins
What are two extended-spectrum penicillins taken orally?
Ampicillin and amoxicillin
Do ampicillin and amoxicillin have gram-negative activity?
Yes, although Klebsiella is resistant
What penicillins have good activity against enterococci?
Amino-penicillins like ampicillin and amoxicillin
What is the drug of choice for listeria monocytogenes?
Amino-penicillins: ampicillin, amoxicillin
What should this 12 year old patient be tested for? What is the treatment for the common infection that results in this appearance of the tonsils?
Strep type A (S. pyogenes); it can be treated with penicillin or amoxicillin
Why is Mycoplasma resistant to penicillins?
It has no cell wall
What two penicillin resistance strategies can a gram-negative bacteria develop that a gram-positive bacteria cannot?
Change in the outer membrane porins, or an efflux pump in the outer membrane
What mutation commonly causes the resistance to penicillins seen in MRSA?
An alteration to penicillin-binding protein (transpeptidases) that decreases affinity for β-lactams
What drug is this? What bond would be broken by a β-lactamase?
Ampicillin; this bond would be broken:
What is the point of a β-lactamase inhibitor?
It inhibits the β-lactamases that break down β-lactam antibiotics, so the β-lactam can inhibit transpeptidases
What class of drugs do clavulanic acid, sulbactam, and tazobactam belong to?
β-lactamase inhibitors
What three drugs can be combined with penicillins to increase gram-negative activity by inhibiting β-lactamases?
Clavulanic acid, sulbactam, and tazobactam
What does the sulbactam in an ampicillin-sulbactam combination do?
It inhibits β-lactamases that would break down the ampicillin
What does the clavulanic acid in the amoxicillin-clavulanic acid combination formulation do?
It is a β-lactamase inhibitor that inhibits breakdown of the amoxicillin
What are two common adverse reactions to penicillin that present as skin symptoms?
Hypersensitivity and rash
Can penicillins cause anaphylaxis?
Yes
What is this patient experiencing after administration of penicillin?
Angioedema, an adverse reaction do to hypersensitivity of the immune system
Are rash and hypersensitivity reactions to penicillin common? What other drug allergies can be suspected after such a reaction?
Yes; increased chance of reactivity to other β-lactams (cephalosporins, carbapenems) excepting monobactams
Almost 100% of patients with what viral infection develop a maculopapular rash to amoxicillin?
EBV-associated mononucleosis
What kidney-related adverse reaction can occur with penicillins? What antibiotic is no longer used because of this risk?
Nephritis (acute kidney injury); methicillin
What kind of colitis can result from penicillin administration?
Clostridium difficile colitis
What type of antibiotic is this? What are its identifying features?
Cephalosporin; β-lactam 4-membered ring in center, and 6-membered dihydrothiazine ring to the right
How many generations of cephalosporins have been made? What increases over the generations?
5; gram-negative activity
Can cephalosporins cross the blood-brain barrier?
Yes, after the 3rd and 4th generation
Do cephalosporins treat Enterococcus or Listeria?
No
Can cephalosporins treat MRSA?
Only the “5th” generation, ceftaroline
What is the 1st generation cephalosporin? What is its oral formulation called?
Cefazolin; cephelexin is the oral formula
Can cefazolin be used against group A and group B strep, and S. viridans?
Yes
Are cephalosporins affected by β-lactamases?
No, they are not β-lactam drugs
Is cefazolin more active against gram-positive or gram-negative bacteria?
Gram-positive
Can cefazolin be used for UTIs and skin infections?
Yes
Do cephalosporins have similar adverse reactions as penicillin?
Yes
What is the cross-reactivity of cephalosporins with people that have penicillin allergies? Should they be used in a patient that has had hives in reaction to penicillin?
About 1-10%; no
What does this patient have on his arm, given the following culture?
Staphylococcus aureus
If a patient who has a history of IV drug abuse has high fevers and a methicillin susceptible S. aureus infection, what are some reasonable treatments?
Anti-staphylococcal penicillins: Nafcillin
Cephalosporins: Cefazolin
These will kill methicillin-susceptible S. aureus, and both drugs are unaffected by penicillase (most S. aureus harbors penicillase)
Besides age and allergies, what else should be evaluated before prescribing β-lactam or cephalosporin antibiotics?
Kidney function
If a skin infection has gram positive cocci that are identified as β hemolytic, what bacterium related to the one causing strep throat should be suspected?
S. pyogenes
What are examples of non-suppurative consequences of a S. pyogenes infection?
Scarlet fever, acute rheumatic fever, glomerulonephritis
Are penicillins bacteriostatic or bactericidal?
Bactericidal
What potential problem when treating abscesses with oral antibiotics, assuming the right one was prescribed at the right dosage and the organism is susceptible?
Distribution of the drug into the abscess, since the neutrophils surrounding the abscess can block access of the antibiotic to the area with the most bacteria
When the serum C3 complement level is measured as low, what does this indicate?
It has been consumed (broken down to C3b and C3a), so the immune system was exposed to an antigen that activated the complement pathway (alternatively: there is a C3 deficiency, but this is rare)
Acute rheumatic fever is most often associated with streptococcal strains rich in what protein?
Protein M
Are streptococcal strains rich in M protein more or less virulent? Why?
They are relatively resistant to phagocytosis and multiply quickly in tissues
What exotoxin is secreted by extra-virulent S. pyogenes that causes necrotizing fasciitis? What life-threatening syndrome can this exotoxin cause?
Superantigen, which hyperactivates T cells; it can cause toxic shock syndrome
What is the course of treatment for necrotizing fasciitis?
Aggressive surgical debridement, and secondarily, IV antibiotics
Which researcher on tuberculosis developed postulates that led to a new understanding of infectious disease and a Nobel?
Robert Koch
What is the property of tuberculosis bacteria’s cell wall that makes it resistant to disinfectants and traditional stains?
It is lipid rich
What is the major component of mycobacterium’s cell wall?
Mycolic acid
Why do mycobacteria clump together?
Hydrophobicity of the cell wall
Are mycobacteria motile? Are they spore-forming?
No to both
What is the gram staining of mycobacteria?
Gram null to weakly gram positive
What kind of staining, also called Ziehl-Neelsen or Kinyoun, reveals mycobacteria?
Acid fast staining
Of the four Runyon classes of mycobacteria, which grows fastest?
Runyon class IV
Is mycobacterium tuberculosis in a Runyon class? If so, which one?
No, it is not in a class.
Do mycobacteria encourage or discourage phagocytosis by immune cells? What happens to a phagosome containing a mycobacteria?
Phagosome formation is encouraged; phagosome maturation is blocked, so the bacterium can survive
What fusion event is inhibited after phagocytosis of mycobacteria to allow them to survive?
Phagosome-lysosome fusion is inhibited
What immune proteins that normally surround intruders to aid in their destruction are rendered ineffective by mycobacterium?
Antibody and complement proteins
Is the incidence of TB in the United States among native-born persons still declining?
Yes
Approximately what fraction of the world’s population carries mycobacterium tuberculosis?
One third
The spread of what disease in the 1980’s led to an uptick in tuberculosis infection?
HIV/AIDS
What can a tuberculosis patient do to expose other people to the bacterium, besides blood-to-blood contact? Can TB bacilli remain infectious in the air?
Coughing, sneezing, speaking, or singing; yes, it can remain suspended in the air for several hours
During the primary infection process for mycobacterium tuberculosis, is there a host immune response?
No, the bacteria replicate freely in alveolar macrophages
What channels does the tuberculosis bacterium use to spread after infection of the alveoli?
Lymphatics and bloodstream
What immune response (humoral or cell-mediated) contains the primary infection by TB? What histological immune structures form in the lungs during the killing of the bacilli?
Cell-mediated immune response; granulomas
What is this histological feature, characteristic of TB infection?
A granuloma
Within caseating centers of granulomas, does TB replicate faster or slower? Why?
Slower; because of the lower pH and the anoxic environment.
In 90% of patients, what is the endpoint of primary tuberculosis? Is it symptomatic?
Latent tuberculosis; usually it is not
Is latent tuberculosis contagious?
No
What is the common test for latent TB infection? What is a requirement for this test, without which it will return a false negative?
PPD (the tuberculin skin test); you need a functional immune system
How long does it take for delayed hypersensitivity reactions to tuberculins to be detectable by a PPD after the initial infection? How long are the tuberculins implanted in the skin before reading?
6-8 weeks; 48-72 hours
What is a more sensitive assay for past exposure to tuberculosis bacterium? How does it work?
Interferon γ release assay; it is an ELISA test that detects release of interferon γ from sensitized patients after incubation with two peptides from TB
What is the standard approach to latent tuberculosis?
Chest x-ray, sputum analysis, and Isoniazid for 9 months
What are the common presenting symptoms of active tuberculosis?
Cough, hemoptysis (bloody cough), night sweats, anorexia, weight loss
Can tuberculosis infect tissues besides the longs?
Yes, including the bones, lymph nodes, brain, GI tract…
This sample is from a TB patient. What has occurred that is characteristic of its pathology?
Caseating necrosis
What staining is used here to visualize bacteria? Which bacterium is this characteristic of?
Acid fast staining; mycobacterium, particularly tuberculosis
What is common in HIV patients with tuberculosis infections?
It spreads to other tissues quickly, e.g., the fingers
What is visible on a CT scan of the lungs of most tuberculosis patients?
Nodules (they can be bilateral or unilateral and in any lobe, as the following CT shows)
What is the mnemonic for the 4-drug regimen to treat active tuberculosis?
RIPE:
- Rifampin
- Isoniazid
- Pyrazinamide
- Ethambutol
Which part of the bacterium does isoniazid act upon?
The cell wall
What dietary warning is given to people on prolonged isoniazid for tuberculosis infection?
Do not consume alcohol
What is the mechanism of Rifampin? Is it bactericidal or bacteriostatic?
It inhibits DNA-dependent RNA polymerase in mycobacteria; bactericidal
What is the primary adverse effect of Rifampin? Why?
Hepatotoxicity; it induces hepatic cytochrome p450 enzymes
What is the primary adverse affect of isoniazid, requiring a dietary warning?
Hepatotoxicity
Production of what component of mycobacterium is inhibited by isoniazid? Is it bacteriostatic or bactericidal?
Mycolic acid synthesis, the main component of the cell wall; bactericidal
Is pyrazinamide bacteriostatic or bactericidal? What globally common infection is it used to treat?
Bacteriostatic; tuberculosis
What does ethambutol inhibit that makes it a good treatment for tuberculosis? Is it bacteriostatic or bacteriocidal?
Cell wall polysaccharide synthesis
What is the primary adverse effect of ethambutol?
Optic neuritis
Are certain strains of TB resistant to isoniazid and/or rifampin?
Yes
What can be used to supplement treatment for MDR or XDR tuberculosis?
Other antibacterials: streptomycin, linezolid, fluoroquinolones, kanamycin, …
Why are multiple antibiotics administered concurrently to eradicate a TB infection in a patient?
To prevent development of a resistant strain
What is the most significant gram-negative microbe in the GI tract?
E. coli
Can E. coli cause neonatal sepsis or meningitis?
Yes
What bacterium is this?
E. coli, identified by gram negative rods and fermentation of lactose on MacConkey agar
There are 3 important surface antigens on E coli. How are they named?
O, H, and K
In the strain serotype E. coli O157:H7, what is the meaning of the second part of this name?
It refers to surface antigens O and H
When a patient complains of dysuria and changes in frequency of urination, a UTI is suspected. What is significant about a co-presentation with flank pain and cost-vertebral angle tenderness?
An upper UTI may be suspected as opposed to a lower UTI. This might include e.g. pyelonephritis
What is the most common cause of UTIs?
E. coli
What does dysuria mean?
Painful urination
Which pili on E. coli allows certain strains to adhere to the urinary epithelium?
P-pili
What is the typical IV therapy for pyelonephritis?
Fluroquinolones (e.g. Ciprofloxacin) or ceftriaxone
What is the typical course of treatment for a lower UTI?
Fluoroquinolones, ceftriaxone, or trimethoprim-sulfamethoxazole
What is the typical cause of “traveler’s diarrhea”?
E. coli, caused by a lack of immunity to bacteria in the local water
ETEC, EPEC, EIEC, EHEC, STEC, and EAEC are all strains of…
Diarrhea-causing E. coli
In enterotoxigenic E. coli, is the mucosa of the GI tract disrupted?
No
What long structures surround E coli, mediating its attachment to various surfaces?
Pili
Which pili mediates adhesion of ETEC to the GI tract?
CF pili
What other microbial toxin is the Heat Labile Toxin of ETEC similar to?
Cholera toxin
What enzyme is stimulated by Heat Labile Toxin and what doe sthis cause? What organism secretes this toxin?
Adenylate cyclase, causing export of Na+, K+, and water into the GI lumen (diarrhea); enterotoxigenic E. coli (ETEC)
What enzyme is stimulated by Heat Stable Toxin, released by enterotoxigenic E. coli?
Guanylate cyclase
Enterotoxigenic E. coli secretes two toxins abbreviated LT and ST. What are their full names?
Heat labile toxin and heat stable toxin
What does the stimulation of guanylate cyclase by heat stable toxin cause? What organism secretes it as an exotoxin?
Secretion of Cl-, HCO3- and water; ETEC (enterotoxigenic E. coli)
What organism causes hemolytic-uremic syndrome (HUS)?
Enterohemorrhagic E. coli
What has happened to these RBCs? What strain of E. coli can do this?
Fragmentation (happens in small blood vessels); Enterohemorrhagic E. coli
How is enterohemorrhagic E. coli acquired?
Consumption of raw beef, food contaminated by animal feces, or animal contact
What is the hallmark symptom of enterohemorrhagic E. coli infection?
Bloody diarrhea
What are two common abbreviations for the organism that causes hemolytic uremic syndrome?
EHEC or STEC, both referring to enterohemorrhagic E. coli
What toxin is produced by EHEC that triggers hemolytic uremic syndrome?
Shigatoxin
What is the best way to test for EHEC infection?
Test for Shiga toxin in the stool
Can sorbital agar reliably identify EHEC?
It can only identify the O157:H7 strain—it will not identify other strains of EHEC
Where are the typical genomic locations for virulent factors of E. coli strains, like exotoxins?
Phages, plasmids, or pathogenicity islands
What does enteroinvasive E. coli cause (EIEC)?
Dysentery
When E. coli is suspected for a case of dysentery, what can be used on the stool to diagnose it?
A stool smear to reveal WBCs
Is there disruption of the mucosa in EIEC?
Yes, bacteria invade the enterocytes (enteroinvasion)
What do enteroaggregative E. coli form on the wall of the GI epithelium?
A biofilm, inhibiting proper absorption across the intestinal membrane
Why is bacterial neonatal sepsis and meningitis treated with ampicillin in addition to cefotaxime?
Cefotaxime is for E. coli, but the ampicillin is intended to kill listeria, another top bacterial etiology for these symptoms
What is notable about the strains of E. coli that cause nosocomial infections?
They are typically resistant to many antibiotics
What bacterium is seen here, in this sampling of CSF from a patient with altered mental status?
Gram negative; probabably meningococcus
Is meningitis more common in children or adults?
Children under 2 years of age
Removal of what organ can cause in increase in risk for meningitis?
Spleen
How is neisseria meningitidis transmitted?
Respiratory droplets, which is why it is more likely to cause epidemics in overcrowded conditions
What is “meningococcus” an abbreviation for?
Neisseria meningitidis
What does N. meningitidis secrete to allow survival in the respiratory tract?
IgA protease
What is the function of the pili on N. meningitidis in the respiratory tract, besides conjugation?
Attachment to the respiratory epithelium
What is the capsule of N. meningitidis made of?
Polysaccharides
What form of endotoxin is secreted by N. meningitidis that can cause sepsis?
Lipooligosaccharide
What is the defining feature of the rashes caused by meningococcemia?
They are all non-blanching
Which serogroup of N. meningitidis has no vaccine? Why not?
Serogroup B, because it has a polysaccharide capsule similar to human sialic acid
Is LOS different from LPS? If so, how?
Yes; they are a subtype of LPS present in bacteria that colonize mucosal surfaces not bathed in bile, such as N. meningitidis
What is the difference with the conjugate vaccine for meningitis as opposed to the polysaccharide vaccine?
The conjugate vaccine has proteins, which are more immunogenic
Does N. meningitidis produce β-lactamases?
No
What can be used to treat N. meningitidis?
Penicillin works, but ceftriaxone is more common
Empiric treatment of bacterial meningitis in adults when nothing is seen on gram stain consists of what drugs?
Ceftriaxone (against meningococcus, Haemophilus and pneumococcus), vancomycin (against β-lactam pneumocci), and sometimes ampicillin (against Listeria monocytogenes)
Is Listeria gram positive or negative? What is its shape?
Gram positive; rod (bacillus)
What is the motility style of Listeria?
Tumbling, end over end
Which age groups does Listeria affect? What other population is particularly at risk?
Infants and the elderly (bimodal); the immunocomprised, such as pregnant women
Is ceftriaxone used to treat L. monocytogenes?
No, ampicillin is more reliable
What can be used to prevent spread of meningitis to those in close contact?
Chemoprophylaxis
What is a nickname for N. gonorrhoeae?
Gonococcus
What is the difference in the capsule between N. meningitidis and N. gonorrhoeae?
N. gonorrhoeae does not have a true polysaccharide capsule
What is the energy source for N. gonorrhoeae in culture? Is this different from N. meningitidis?
Glucose only; yes, N. meningitidis can also use maltose
What part of N. gonorrhoeae makes development of a vaccine difficult?
Antigenic variability of the pili
Is the age distribution of N. gonorrhoeae infections modal or bimodal?
Modal, with the highest range around 15-25 years of age
What inflammatory disease can be caused by chronic N. gonorrhoeae infection?
Pelvic inflammatory disease
Which diagnostic tool is used most often in clinical practice for gonococci?
DNA amplification probes
What is the mainstay of therapy for N. gonorrhoeae? Do they have β-lactamase? What co-infection is assumed?
Cephalosporins, e.g., ceftriaxone; yes; Chlamydia
When a patient presents with respiratory symptoms, and a cultured bacterium grows on chocolate agar and with VX factor, what organism is suspected?
Haemophilus influenzae
What is this feature seen on a blood agar plate? What organism is it significant for?
Satellite colonies; Haemophilus influenzae
Is the present vaccine for Haemophilus influenzae a polysaccharide vaccine or a conjugate vaccine?
Conjugate
Does the Haemophilus genus cause any STDs?
Yes, chancroid, by Haemophilus ducreyii. It is characterized by painful fluid-filled lesions on the genitals
What can Moraxella catarrhalis cause? Is it gram negative, or gram positive? Is it anaerobic or aerobic?
Otitis, sinusitis, and pneumonia (particularly with underlying emphysema); gram positive; aerobic
What is the gram negative coccobacillus that causes whooping cough?
Bordetella pertussis
Which vaccine was built to eliminate Bordetella pertussis?
DPT: diphtheria, pertussis, tetanus
Are incidents of pertussis on the rise or declining since the introduction of the DPT vaccine?
They are still rising
What capsulated bacterium produces a purpuric, petechial rash?
N. meningitidis
How many capsule serogroups of N. meningitidis are there? Does the vaccine cover all of them?
13; no, the vaccine covers 4 of the most common
What is the vaccine protecting against Haemophilus influenzae called?
HiB vaccine
Are N. gonorrhoeae susceptible to quinolones?
No, resistance has developed
What is used to combat B. pertussis in severe cases of whooping cough?
Azithromycin
What type of organisms is the spleen an important defense organ for?
Encapsulated organisms, e.g. N. meningitidis and Listeria
Can fats and sugars within the outer membrane of a gram negative bacterium trigger a fatal response?
Yes, because of inflammation
What is notable about this CT that is suggestive of S. pneumoniae?
The infection is well contained to one lobe
What bacterium is this?
Strep pneumoniae: a gram-positive, encapsulated diplococci, note the thick cell wall.
What is the hemolysis pattern of S. pneumoniae? Is it optochin sensitive or resistant? Does it have a Lancefield antigen?
α hemolysis; optochin sensitive; no Lancefield antigen
How is S. pneumoniae transmitted? What is colonized transiently that leads to no symptoms in most adults? Is smoking a risk factor?
Through droplets; the nasopharynx; Yes
What is the distribution of ages for S. pneumoniae infection? What other significant risk factor must be considered, which e.g. asplenia could contribute to?
Very young and very old; immunosuppression
Besides age, immunosuppression, and smoking, what are two other risk factors for S. pneumoniae infection?
CSF leaks and cochlear implants
How many serotypes of S. pneumoniae exist?
Over 90
Did a vaccine for pneumococcus exist in 1998?
No
What is serotyping of S. pneumoniae based on? Are antibodies against these molecules protective?
The capsular polysaccharide; Yes
Do symptoms of S. pneumoniae present acutely or chronically compared to a TB patient?
Acutely
What are nuchal rigidity, Kernig and Brudzinsky signs all indicative of?
Meningitis
What infection with a high mortality can cause fever, photophobia, headache, and altered mental status?
Meningitis
What physical exam procedure is this? What does it test for?
Kernig sign; meningitis
What physical exam technique is this? What is it testing for?
Brudzinski sign; meningitis
What is this a picture of? What condition is present?
The eardrum; otitis media. The following is a normal eardrum:
Can S. pneumonia cause bacteremia, sinusitis, and peritonitis?
Yes
What type of antibody can prevent adherence of S. pneumoniae, preventing infection?
Secretory IgA (sIgA)
What is the main virulence factor of S. pneumoniae?
The capsule
What is binding of the pneumococcus to an epithelial cell mediated by?
Adhesins
What can pneumococci secrete to defeat secreted IgA and adhere to epithelial cells anyway?
IgA protease
Which pathway for complement activation is inhibited by the capsule of S. pneumoniae?
The alternate pathway
What bacterium contains pneumolysin? Where is it stored in the bacterium? What is its function?
S. pneumonia; in the cytoplasm; it lyses phagocytic cells
Which system unrelated to the capsular specific antibodies is critical for clearing S. pneumoniae from the bloodstream?
The lymphoreticular system of the spleen
Why is the spleen more important for clearing capsulated organisms?
Phagocytosis by neutrophils is less efficient, so filtration in the spleen is a more significant way for these organisms to be cleared
What class of drugs is used to treat S. pneumoniae? How does resistance usually present?
β-lactams; resistance is usually from altered penicillin binding proteins
Do clavulinic acid or sulbactam help β-lactam treatment of S. pneumoniae that are becoming β-lactam resistant? Why or why not?
No; they are β-lactamase inhibitors, but this is not the typical way that resistance develops in S. pneumoniae
Can you overcome the weak binding of β-lactams to PBP’s in somewhat resistant S. pneumoniae by increasing the dose?
Sometimes, yes
Which β-lactams are most often used against S. pneumoniae?
Amoxicillin, ampicillin, cefotaxime and ceftriaxone
Why is ceftriaxone particularly effective against S. pneumoniae, particularly with regard to preventing serious complications?
It can get into the CSF, and does well against the three most common causes of bacterial meningitis
What cause of meningitis is not covered by cephalosporins?
Listeria monocytogenes
Can ceftriaxone be administered orally? Can vancomycin be administered orally?
No to both
How is ceftriaxone excreted?
Biliary ducts
How is cefotaxime excreted? Does it have a shorter or longer half-life than ceftriaxone?
Kidneys; shorter half-life (8h) compared to ceftriaxone (12-24h)
What do fluoroquinolones inhibit causing bacterial death? Which fluoroquinolone cannot be used against respiratory infections?
Bacterial topoisomerase and DNA gyrase, thereby inhibiting DNA synthesis; Ciprofloxacin has no activity against gram positive organisms and thus is not indicated for respiratory infections (where S. pneumoniae is suspect)
What athletic activity is dangerous during administration of fluoroquinolones?
Weight lifting and running, because of the adverse effect of tendonitis and/or tendon rupture
If S. pneumoniae is resistant to β-lactams, what antibiotic can be used? Is it active against gram negatives, gram positives, or both?
Vancomycin
What is the empiric treatment for bacterial meningitis?
Vancomycin and ceftriaxone, which both reach the CSF and in conjunction combat β-lactam sensitive and resistant gram positive and gram negative bacteria
What oral treatment is given for pneumococcal pneumonia?
Amoxicillin and/or azithromycin, and levofloxacin
If an IV drug user comes in and reports symptoms indicating bacterial pneumonia, what else must be suspected?
Immunodeficiency, e.g. AIDS
What would otitis media or sinusitis with a suspected bacterial cause be treated with?
Amoxicillin (oral)
Why isn’t the pneumovax vaccine immunogenic in children under 2? What vaccine is given to them instead, and why does that one work better?
It is a purified capsular polysaccharide antigen, which children of this age will not recognize as foreign (it is a T-cell independent antigen); the PCV-13 (Prevnar-13) vaccine has the polysaccharide conjugated to a diphtheria toxoid (T-cell dependent antigen), which the immune system will recognize as foreign at this age
After recommendation of the PCV7 vaccine in 2000, did rates of S. pneumoniae decrease in children, or across all age groups? What is this phenomenon called?
All age groups; herd immunity
What are environmental sources of pseudomonadaceae?
Soil, water, plant material, and environmental surfaces
What is this bacterium, which grows aerobically in immunocompromised hosts, particularly within burn injuries?
Pseudomonadaceae (gram negative bacilli)
Does P. aeruginosa ferment lactose?
No (right), which is different from E. coli (left)
Does Pseudomonas produce oxidase?
Yes
Is this a positive or negative oxidase test?
Positive
What is this morphology on agar to the right called?
Mucoid: it indicates formation of a biofilm
What features of P. aeruginosa are shown here?
Unipolar flagellum and adherence mediating pili
What can render a host particularly susceptible to Pseudomonas infections?
Neutropenia (e.g. by chemotherapy), severe burns, diabetes/foot ulcers, cystic fibrosis
What kind of Pseudomonas infection is most likely to manifest in a neutropenic patient?
Bacteremia or sepsis
What risk factors for P. aeruginosa infection associate a respiratory infection?
Cystic fibrosis or mechanical ventilation
What organism is associated with “hot tub folliculitis”?
P. aeruginosa
What condition caused by P. aeruginosa is seen here?
Ecthyma gangrenosum, a result of bacteremia
What are these two manifestations of P. aeruginosa, from left to right?
Hot tub folliculitis and infected pressure sore
What manifestation of P. aeruginosa is this?
Otitis externa
What injurious infection of P. aeruginosa can be seen here, which follows trauma to the eye, including that caused by contact lenses?
Corneal ulcers or endophthalmitis
What is the clinical (not genetic) marker of cystic fibrosis, which relates especially to P. aeruginosa?
They present with chronic lung infections and inflammation
With chronic infection by P. aeruginosa in cystic fibrosis patients, what are the two typical infections that precede it? Does the mucoid P. aeruginosa precede the non-mucoid, in the sequence of infections or the other way around?
S. aureus and H. influenzae; non-mucoid is typically first
Are cephalosporins useful against Pseudomonas aeruginosa? What about carbapenems? Monobactams? Fluoroquinolones?
Yes to all, with various resistance factors seen in the wild
What two organisms (excepting P. aeruginosa) are linked to catheter-associated bacteremia and ventilator-associated pneumonia?
Burkholderia cepacia and Stenotrophomonas maltophilia
What classes of bacteria are aminoglycosides useful for treatment? Are they usually used as primary or secondary therapy?
Gram negative, aerobic bacteria, e.g. P. aeruginosa; usually secondary to another antibiotics
What is the basic structure of an aminoglycoside?
Amino sugar linked to a central hexose
What are the host cell entry, CSF, and tissue penetration characteristics of aminoglycosides? Why is this?
All are poor; they are polycationic and highly polar
What is the mechanism of action of aminoglycosides?
Interference with bacterial protein synthesis (initiation, see the A pathway here)
What is the most common mechanism of resistance to aminoglycosides?
Drug modification (acetylation or adenylation of parts of the drug by the bacterium)
What kind of antibiotic is kanamycin? Is it currently administered?
Aminoglycoside; no longer used
What is a common topical aminoglycoside?
Neomycin
What class of drugs are streptomycin, gentamicin, tobramycin, and amikacin?
Aminoglycosides
What are four aminoglycosides that can be administered intramuscularly? Are oral forms available?
Streptomycin, gentamicin, tobramycin, and amikacin; no
What are the main adverse toxicities of aminoglycosides?
Nephrotoxicity and ototoxicity, along with neuromuscular blockade
Important agents of nosocomial infection include:
– […] (e.g., RSV, Parainfluenza, Influenza, Adenovirus)
– Methicillin-resistant Staphylococcus aureus
– Vancomycin-resistant Enterococcus faecium
– Multiresistant Gram-negative bacilli
– Clostridium difficile
Important agents of nosocomial infection include:
– Respiratory Viruses (e.g., RSV, Parainfluenza, Influenza, Adenovirus)
– Methicillin-resistant Staphylococcus aureus
– Vancomycin-resistant Enterococcus faecium
– Multiresistant Gram-negative bacilli
– Clostridium difficile
Important agents of nosocomial infection include:
– Respiratory Viruses (e.g., RSV, Parainfluenza, Influenza, Adenovirus)
– […]-resistant Staphylococcus aureus
– Vancomycin-resistant Enterococcus faecium
– Multiresistant Gram-negative bacilli
– Clostridium difficile
Important agents of nosocomial infection include:
– Respiratory Viruses (e.g., RSV, Parainfluenza, Influenza, Adenovirus)
– Methicillin-resistant Staphylococcus aureus
– Vancomycin-resistant Enterococcus faecium
– Multiresistant Gram-negative bacilli
– Clostridium difficile
Important agents of nosocomial infection include:
– Respiratory Viruses (e.g., RSV, Parainfluenza, Influenza, Adenovirus)
– Methicillin-resistant Staphylococcus aureus
– […]-resistant Enterococcus faecium
– Multiresistant Gram-negative bacilli
– Clostridium difficile
Important agents of nosocomial infection include:
– Respiratory Viruses (e.g., RSV, Parainfluenza, Influenza, Adenovirus)
– Methicillin-resistant Staphylococcus aureus
– Vancomycin-resistant Enterococcus faecium
– Multiresistant Gram-negative bacilli
– Clostridium difficile
Important agents of nosocomial infection include:
– Respiratory Viruses (e.g., RSV, Parainfluenza, Influenza, Adenovirus)
– Methicillin-resistant Staphylococcus aureus
– Vancomycin-resistant Enterococcus faecium
– […] bacilli
– Clostridium difficile
Important agents of nosocomial infection include:
– Respiratory Viruses (e.g., RSV, Parainfluenza, Influenza, Adenovirus)
– Methicillin-resistant Staphylococcus aureus
– Vancomycin-resistant Enterococcus faecium
– Multiresistant Gram-negative bacilli
– Clostridium difficile
Important agents of nosocomial infection include:
– Respiratory Viruses (e.g., RSV, Parainfluenza, Influenza, Adenovirus)
– Methicillin-resistant Staphylococcus aureus
– Vancomycin-resistant Enterococcus faecium
– Multiresistant Gram-negative bacilli
– […] difficile
Important agents of nosocomial infection include:
– Respiratory Viruses (e.g., RSV, Parainfluenza, Influenza, Adenovirus)
– Methicillin-resistant Staphylococcus aureus
– Vancomycin-resistant Enterococcus faecium
– Multiresistant Gram-negative bacilli
– Clostridium difficile
What two major classes of gram-negative bacilli are associated with nosocomial infections?
Enterobacteriaceae and Pseudomonodaceae
What units are most at risk for nosocomial infections?
Burn units, NICU, MICU/SICU, and oncology
What is the mean attributable cost to the hospital of a nosocomial bloodstream infection?
$36k
What standard precaution must be taken by all hospital workers with all patients to prevent nosocomial infections?
Hand hygiene
How long should we wash our hands with soap and water or Purell to prevent nosocomial infections?
>15 seconds
What is the usual suspect for “typical” pneumonia?
Streptococcus pneumoniae
Is there a productive cough and copious sputum with typical or atypical pneumonia?
Typical pneumonia
What extrapulmonary symptoms typically manifest in atypical pneumonia? Do most patients seek medical care?
Muscle aches and headache, low fever; most do not
Is an elevated WBC more indicative or typical or atypical pneumonia?
Typical
What are the three major suspect bacteria for atypical pneumonia?
Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Legionella
What bacterium causing atypical pneumonia is seen in this EM?
Mycoplasma pneumoniae
What is the incubation period of M. pneumoniae?
2-3 weeks
How is M. pneumoniae transmitted? Can it spread between people across a room?
Respiratory droplet; no, it requires close contact
What structural feature makes M. pneumoniae an unusual bacterium?
It lacks a cell wall
What is the shape of M. pneumoniae? Is it visible on a gram stain?
Short and rod-shaped; invisible on gram stain
Is M. pneumoniae easy to grow quickly in culture?
No, it has a long doubling time (6h)
Why was M. pneumoniae initially assumed to be a virus, in 1918?
It could pass through filters that only viruses could pass through
What is the age distribution of typical M. pneumoniae infections?
Unimodal, around adolescents and young adults
Do most patients survive M. pneumoniae infection without treatment?
Yes
Does M. pneumoniae grow inside or outside of cells?
Inside of them
What blood cell abnormality is a risk factor for Mycoplasma pneumoniae?
Sickle cell
Why does sickle cell predispose patients to M. pneumoniae?
Cold-agglutinins produced by polyclonal T cells and B cells during the immune response to M. pneumoniae bind to the I antigen on the RBC surface area, which is smaller for patients with sickle cell
What skin manifestation is associated with M. pneumoniae?
Erythema multiforme
Can M. pneumoniae cause meningitis?
Yes
Where in the respiratory tract does M. pneumoniae infection start?
Usually in the upper part, but it can spread anywhere within the tract
Is a cold-agglutinin test useful in diagnosing M. pneumoniae?
No, it is not sensitive or specific enough
