Microbiology: Basic Bacteriology Flashcards
What color pigment does Pseudomonas aeruginosa produce?
Blue-green (aeruginosa: arugula is green)
Coxiella is considered an obligate intracellular pathogen. Name other bacteria in this class.
Rickettsia, Chlamydia, &; COxiella are intracellular (stay inside [cells] when it is Really CHilly &; COld)
What component of the cell envelope extends from the membrane to the exterior and induces TNF-α and IL-1 on gram-positive bacteria?
Lipoteichoic acid (in gram positive) bacteria
Anaerobic bacteria usually smell bad, are difficult to culture, and produce CO2 and H2 in tissue. What causes the foul smell?
Short-chain fatty acids
When an anticoagulated tube of blood from a man with fever cools, precipitate forms. Mycoplasma pneumoniae is found. What medium was used?
Eaton agar; M pneumoniae requires cholesterol
Your microbiology lab advisor wishes to use a special silver stain. What organisms may he be looking for?
Legionella, Helicobacter pylori, and fungi (eg, Coccidioides, Pneumocystis jirovecii)
Exotoxins are typically destroyed at 60°C. What are the exceptions?
Staphylococcal enterotoxin and Esherichia coli heat-stable toxin are exceptions
In patients with pharyngitis, what protein from group A Streptococcus species prevents phagocytosis by the body’s immune cells?
M Protein
What type of toxin causes sepsis and meningococcemia?
Endotoxin
What bacteria usually utilize a type III secretion system?
Gram ⊖ bacteria such as Pseudomonas, Salmonella, Shigella, and Escherichia coli
What is the chemical composition of the bacterial cytoplasmic membrane, and what are the membrane’s 2 main enzymatic functions?
The membrane comprises a phospholipid bilayer with embedded proteins; its main enzymatic functions are oxidation and transportation
What component of the cell envelope induces TNF on gram-negative bacteria?
Lipid A (also induces IL-1)
IgA protease allows bacteria to colonize mucous membranes. Describe its mechanism of action.
IgA protease cleaves IgA, allowing bacteria to adhere to mucous membranes
What cell wall structures do gram ⊖ and gram ⊕ bacteria have in common?
Both gram ⊕ and gram ⊖ bacteria have flagella, pili, capsules, peptidoglycans, and cytoplasmic membranes
Catalase degrades H2O2, preventing conversion to microbicidal products by myeloperoxidase (enzyme). Name 7 catalase-⊕ organisms.
Nocardia, Pseudomonas, Listeria, Aspergillus, Candida, Escherichia coli, Staphylococci, Serratia, Burkholderia cepacia, Helicobacter pylori (Cats Need PLACESS to Belch Hairballs)
What cheaper and sensitive stain is used in lieu of the Ziehl-Neelsen stain to screen for mycobacteria?
Auramine-rhodamine stain
When autoclaving surgical equipment, what temperature and time setting should be used to kill bacterial spores?
Equipment must be autoclaved for 15 minutes at 121°C because bacterial spores are highly resistant to heat and chemicals
A man with an Escherichia coli infection has significant fever, hypotension, and edema. What component of the bacteria is responsible for his symptoms?
Lipopolysaccharide (LPS) in the outer membrane of gram ⊖ bacteria (eg, E coli); activates macrophages, complement, and tissue factor
What is a type III secretion system?
A special protein appendage produced by gram ⊖ bacteria that allows direct delivery of toxins
A patient with scarlet fever has erythrogenic toxins in her blood. What toxin is to blame for her symptoms?
Exotoxin A, which causes toxic shock-like syndrome (rash, fever, shock) and is released by Streptococcus pyogenes
A man recovering from trauma has a foul-smelling, necrotic skin lesion with crepitus. Mechanism of action of the causative toxin?
The alpha toxin of Clostridium perfringens, a phospholipase, degrades phospholipids, causing tissue and cell membrane necrosis (myonecrosis)
A child with whooping cough has an infection with bacteria having which mechanism of virulence?
Bordetella pertussis toxin overactivates adenylate cyclase, disables Gi, and impairs phagocytosis, permitting survival of the microbe
In endotoxin-based complement activation, which complement(s) cause(s) hypotension/edema and histamine release?
C3a and C5a
Endotoxin activation of macrophages causes release of cytokines (IL-1, IL-6, TNF-α). What are their functions?
IL-1 and IL-6 cause fever; TNF-α causes both fever and hypotension
A 56-year-old goat herder discovers a painless, black ulcer on his arm. What is the mechanism of the likely underlying bacterial toxin?
Edema toxin, released by Bacillus anthracis, mimics adenylate cyclase (↑ cAMP), causing edematous borders of black eschar
On what part of the CNS does the Clostridium tetani toxin tetanospasmin act?
Renshaw cells in the spinal cord (toxin prevents release of inhibitory neurotransmitters, leading to spastic paralysis)
A 20-year-old man recently had a splenectomy. Why should he receive Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitis vaccines?
Encapsulated bacteria are opsonized and cleared by the spleen; a patient without a spleen has ↓ opsonizing ability and is at risk for infection
What is the purpose of autoclaving surgical equipment?
To kill bacterial spores
A chest x-ray obtained from a patient with reactivated tuberculosis shows apical infiltrates in both lungs. Explain the location of these findings.
The lung apices have the highest partial pressure of oxygen; M tuberculosis (and all obligate aerobes) require oxygen to make ATP
On what 2 medical products are Staphylococcus epidermidis likely to grow on?
Catheters and prosthetic devices
Name 5 bacterial toxins coded for in a lysogenic phage.
Group A strep erythrogenic toxin, Botulinum toxin, Cholera toxin, Diphtheria toxin, Shiga toxin (ABCD’S)
What are endotoxins composed of?
The lipid A component of lipopolysaccharide (a bacterium’s structural part); lysis releases it
A 16-year-old boy has a foot infection caused by bacteria that avoid opsonization and phagocytosis through a particular virulence factor. What protein promotes this virulence?
Protein A; prevents opsonization and phagocytosis of S aureus by binding the Fc region of immunoglobulins
Name the segment of DNA that can jump from one location to another, can transfer genes from plasmid to chromosome, and vice versa.
Transposon
A catheterized pt has bacterial sepsis. Which bacterial structure, composed of polysaccharides, enabled the adhesion of the bacteria?
Slime (S) layer
How do the cell walls of gram ⊕ and gram ⊖ bacteria compare?
Gram ⊕: thick peptidoglycan layer and lipoteichoic acid
Gram ⊖: thin peptidoglycan layer, porin, endotoxin, lipopolysaccharide, and periplasmic space
In a gram-positive bacterium you identify a specialized structure composed of dipicolinic acid and peptidoglycan. What is it?
Most likely a spore
Name 3 toxins produced by Staphylococcus aureus and their associated symptoms.
Toxic shock syndrome toxin (symptom: rash, fever, shock); exfoliative toxin (symptom: scalded-skin syndrome); enterotoxin (symptom: diarrhea, vomiting)
What is the difference between enterohemorrhagic Escherichia coli and Shigella manifestations?
Unlike Shigella (Shiga toxin), enterohemorrhagic E coli does not invade host cells; its Shiga-like toxin inactivates 60S ribosomes and causes cytokine release → HUS/dysentery
Which pleomorphic gram ⊖ bacteria can be identified with a Giemsa stain?
Chlamydia and Rickettsia species
An Escherichia coli infection overactivates cellular guanylate cyclase. Describe the mechanism by which the responsible toxin causes diarrhea
Heat-stable toxin of enterotoxigenic E coli (ETEC) ↓ reabsorption of NaCl and water in the gut
What is the mechanism by which superantigens cause toxic shock syndrome?
Superantigens bind MHC II molecules and T-cell receptors; overwhelming release of IFN-γ, IL-2, IL-1, and TNF-α, causing shock
You find an intracellular organism that can live both within and outside of the host cell. Which bacteria might you identify?
Salmonella, Neisseria, Brucella, Mycobacterium, Listeria, Francisella, Legionella, Yersinia pestis (Some Nasty Bugs May Live FacultativeLY)
An unimmunized 1-year-old boy is irritable, sluggish, and has a stiff neck. How do you culture the causative agent, Haemophilus influenzae?
On chocolate agar with factors V (NAD+) and X (hematin); the patient likely has H influenzae meningitis
A girl has rice-water diarrhea and is dehydrated. A toxin is to blame. What is its mechanism of action?
AB toxin activates Gs protein and stimulates adenylate cyclase, increasing Cl- (and water) secreted in the gut (this is Vibrio cholerae)
A patient tests ⊕ for tetanospasmin. Low activity of what neurotransmitters underlies the patient’s symptoms?
Glycine and GABA; tetanospasmin blocks inhibitory release by cleaving SNARE proteins, which mediate vesicle fusion
The inner leaflet of the outer membrane is composed of what?
Phospholipids
A 10-year-old girl is found to have whooping cough caused by Bordetella pertussis. How can the organisms be cultured?
B pertussis grows on Bordet-Gengou (potato) agar (Bordet for Bordetella) or Regan-Lowe medium (charcoal, blood, and antibiotic)
A 20-year-old military recruit has a headache and cough caused by Mycoplasma. Why do these bacteria not Gram stain well?
Mycoplasma species do not have cell walls
Which spirochete can be identified with Giemsa stain?
Borrelia
Deoxyribonuclease is added to a Petri dish growing Neisseria. Which process of gene transfer among bacteria will be halted?
Transformation (deoxyribonuclease lyses the naked DNA, thus preventing transformation)
Cholera toxin is encoded in a phage. Describe how the phage helps the toxin gene undergo transduction.
A lysogenic phage infects bacteria, inserts viral DNA into chromosomes; viral (and bacterial) DNA are excised into the capsid and can infect other bacteria
In patients with Pseudomonas infections, how does the catalase enzyme make these bacteria more pathogenic?
Catalase degrades H2O2 → H2O and O2 before myeloperoxidase can convert it to microbicidal products
Where in the cell wall of gram ⊖ bacteria are β-lactamases located?
The periplasmic space, which is only present in gram ⊖ bacteria
Which part of the body do bacteria that secrete IgA protease tend to colonize?
The respiratory mucosa; these bacteria are S pneumoniae, H influenzae type B, Neisseria (SHiN)
Facultative anaerobes may use O2 as a terminal electron receptor to generate ATP, but may also use what other pathways?
Fermentation and other pathways that are not O2-dependent
A patient receives a pneumococcal conjugate vaccine (PCV). How does a PCV work to promote a T-cell response?
In encapsulated bacteria vaccines, protein and polysaccharide are conjugated to promote a T-cell response and class switching as a result
An elderly woman is vaccinated only against nonconjugated polysaccharide antigens. Why is this patient at greater risk for infection when compared to conjugated vaccines?
Polysaccharide antigens alone are not presented to T cells; this prompts a weaker immune response, in comparison to conjugated vaccines
A patient has otitis media. What biofilm-producing bacteria are most likely responsible for the infection?
Nontypeable (unencapsulated) Haemophilus influenzae
What is the typical composition of the cytoplasmic membrane in gram-negative bacteria?
Phospholipid bilayers with embedded proteins and enzymes; only in gram-positive bacteria does lipoteichoic acid extend into the exterior
What are the most commonly found pleomorphic bacteria?
Anaplasma, Ehrlichia, Chlamydiae, Rickettsiae, Mycoplasma, Ureaplasma
Coxiella is considered an obligate intracellular pathogen. How does this organism get energy?
It obtains ATP from its host cell
A man is infected with bacteria that produce exotoxin A, which induces host cell death. Identify the pathogen and the exotoxin mechanism.
The pathogen is Pseudomonas aeruginosa; exotoxin A inactivates elongation factor (EF-2) to trigger host cell death
In a culture plate, some colonies representing enteric bacteria turn pink. What medium was used to identify the bacteria?
MacConkey agar, which is used to identify lactose-fermenting enterics (eg, Escherichia coli)
A patient presents with struvite stones. What is the underlying biochemical reaction that leads to the formation of such stones
Urease hydrolyzes urea, with release of ammonia and CO2; the increased urine pH encourages ammonium magnesium phosphate stone formation
Name 4 aerobes.
Nocardia, Pseudomonas aeruginosa, Mycobacterium tuberculosis, Bordatella pertussis (Nagging Pests Must Breathe)
What are the 2 distinguishing components in the outer layer of Mycobacteria?
Mycolic acid and high lipid content
An agar plate infected with multiple bacteria is treated with alcohol. Which bacteria would survive?
Spore-forming bacteria (Bacillus and Clostridium); spores are resistant to alcohol
What type of toxin causes tetanus, botulism, and diphtheria?
Exotoxin
Certain bacteria, such as Corynebacterium diphtheriae, have adenosine diphosphate- (ADP) ribosylating AB toxins. Name the functions of the A and B components.
B component Binds and triggers endocytosis; A component (taken up) is Active (eg, ADP ribosyltransferases and other enzymatic activities)
What are the effects and characteristics of an endotoxin?
ENDOTOXINS: Edema, Nitric oxide, DIC/Death, Outer membrane, TNF-α, O-antigen, eXtremely heat stable, IL-1/IL-6, Neutrophil chemotaxis, Shock
Legionella, Bartonella, and Ehrlichia all share what property that makes them suboptimal for Gram stain?
They are all primarily intracellular bacteria
A man presents with a new heart murmur after a recent bout of pharyngitis. What would confirm the most likely diagnosis?
The presence of anti-streptolysin O (ASO) antibodies (he likely has rheumatic fever)
In which type of transduction is viral DNA incorporated into the host DNA?
Specialized transduction (involves a lysogenic phage)
How does Thayer-Martin agar work in the infectious disease lab to test for Neisseria?
It is a selective medium (contains antibiotics that permit selective growth of Neisseria by preventing the growth of other organisms)
Transposition is done between a plasmid from vancomycin-resistant Enterococcus & S aureus. How does S aureus become vancomycin resistant?
Flanking chromosomal DNA is incorporated into plasmid, then into another bacterium (eg, vanA gene from Enterococcus to S aureus)
A gram-positive bacterium produces offspring with a special keratin-like coat. How do these offspring survive?
By resisting dehydration, heat, and chemicals (the offspring are spores)
A patient with a fever and rash subsequently goes into shock. What are 2 commonly tested gram ⊕ bacteria that can cause a rash and septic shock?
Staphylococcus aureus (via toxic shock syndrome toxin) and Streptococcus pyogenes (via exotoxin A)
Chlamydia do not Gram stain well because they are intracellular and have ↓ levels of what acid in their cell wall?
Muramic acid, resulting in suboptimal staining of peptidoglycan
What characteristic of the structure of the cell wall in bacteria provides rigid support?
The cell wall is composed of peptidoglycans that provide rigid support
Excessive stimulation of the coagulation cascade by tissue factor can cause what condition?
Disseminated intravascular coagulation (DIC)
A painless black ulcer develops on the arm of a 56-year-old goat herder. What unique molecule does the capsule of the bacterium contain?
Poly-D-glutamate, which is only found in Bacillus anthracis (diagnosis: cutaneous anthrax)
Two plates grow the same lactose-fermenting bacteria. One is pink; the other has a green metallic sheen. What medium was used on each plate
Escherichia coli turns MacConkey agar pink; E coli also grows colonies with a green metallic sheen on eosin-methylene blue (EMB) agar
Where can endotoxin be found in the cell?
Outer membrane of gram ⊖ bacteria (endotoxin is an integral part of the outer membrane of gram-negative bacteria)
A plasmid is transferred from one bacterium to another. What is this transfer of information called?
Conjugation
What is typically found in the core of a bacterial spore?
Dipicolinic acid
What is the mechanism of diphtheria toxin?
Inactivates elongation factor 2 via adenosine diphosphate- (ADP) ribosylation, leading to necrosis in the pharynx, cardiac, and CNS tissue; this is Corynebacterium diphtheriae
A teacher with unvaccinated students has had a persistent cough for 3 months. Identify the exotoxin involved.
Pertussis toxin, produced by Bordetella pertussis, which overactivates adenylate cyclase (causing a “100-day cough” in adults)
Diagnostic test for rheumatic fever uses antibodies against what part of the causative agent?
Antibodies against Streptococcus toxin, streptolysin O (anti-streptolysin O)
An unimmunized 7-year-old boy has a sore throat and fever. Exam reveals gray pseudomembranes in his throat. What medium should be used for culture?
Tellurite agar with Löffler medium (organism is likely Corynebacterium diphtheriae)
List the structures unique to gram ⊕ bacteria and those unique to gram ⊖ bacteria.
Gram ⊕: lipoteichoic acid; gram ⊖: porin, periplasmic space, and outer membrane formed by endotoxins/lipopolysaccharides
What characteristic of Mycobacterium makes it visible on Ziehl-Neelsen staining?
Mycolic acid in the cell wall
A male patient with many sexual partners has purulent penile discharge from Neisseria gonorrhoeae. How is the causative organism cultured?
N gonorrhoeae grows on Thayer-Martin agar, a selective medium that contains vancomycin, trimethoprim, colistin, and nystatin
What components of the cell envelope are found only in gram-negative bacteria?
Outer membrane, periplasm
A febrile man with septic shock has poorly antigenic toxins in his blood found on the outer cell membrane of gram ⊖ bacteria. Induction of which cytokines caused this condition?
TNF, IL-1, and IL-6 (induced by endotoxin)
Shiga-like-toxin (SLT) causes hemolytic-uremic syndrome (HUS). What is the toxin’s mechanism of action?
Causes enhanced cytokine release
How does an indicator (differential) medium work? Give an example of such a medium.
A color change results in response to some organisms’ metabolites; Escherichia coli changes color on MacConkey agar (pH indicator) due to lactose conversion to acidic metabolites
In endotoxin-based complement activation, which complement promotes neutrophil chemotaxis?
C5a
What are exotoxins composed of?
Polypeptides
A patient with cystic fibrosis has a chronic cough and confirmed biofilm-producing bacterial growth. Identify the bacteria.
Pseudomonas aeruginosa
A company would like to target the Escherichia coli endotoxin with a new antibiotic. Where is this endotoxin found?
The outer membranes of cells of gram ⊖ bacteria (both cocci and rods)
What glycoprotein-derived structure allows bacteria to adhere to the cell surface?
The fimbria (pilus)
Bacteria with thin peptidoglycan layers turn what color(s) with counterstain?
Red or pink, and are gram ⊖
In what scenario is a fluorescent antibody stain typically used?
To confirm syphylis (FTA-ABS); it can also be used to identify many bacteria and viruses
Where is endotoxin (lipopolysaccharide) located in gram-negative bacteria?
Outer leaflet of the outer membrane
What bacterial structural appendage, composed of protein, is known to help provide motility?
Flagellum
Why do Clostridium, Bacteroides, Fusobacterium, and Actinomyces israelii have increased susceptibility to oxidative damage?
They lack the enzymes catalase and superoxide dismutase, and are thus susceptible to oxidative damage (anaerobes Can’t Breathe Fresh Air)
A 10-year-old girl has had coughing fits, after which she fights to catch her breath, for 2 months. What is the mechanism of the offending toxin?
Bordetella pertussis disables the Gi protein (overactivates adenylate cyclase), impairing phagocytosis and allowing bacteria to survive
Which strain of Escherichia coli has a toxin that overactivates adenylate cyclase?
Enterotoxigenic E coli (heat-labile toxin)
What is the chemical composition of endotoxin?
Lipopolysaccharide (LPS)
A drug company wishes to target β-lactamases. In which compartment of the bacteria would they be?
In the periplasm, the space between the cytoplasmic membrane and the outer membrane in gram-negative bacteria
You are studying the effects of the lipid A component in lipopolysaccharide (LPS). How does this endotoxin differ from an exotoxin based on its release from the cell?
An endotoxin is released on cell lysis or by living cells (blebs detach from the outer surface membrane); exotoxins are actively secreted
A terrified patient presents with risus sardonicus, spasticity, and lockjaw. What is the likely mechanism of the causative exotoxin?
Cleavage of soluble NSF attachment protein receptor (SNARE), needed for release of inhibitory neurotransmitters (exotoxin is tetanospasmin)
In the microbiology lab you find bacteria that produce yellow “sulfur” granules (sand). What are the granules made of?
Bacterial filaments; the bacteria are Actinomyces israelii (israel has yellow sand)
One pathogen can be visualized using India ink and mucicarmine. Describe the part of the organism that is stained.
The thick polysaccharide capsule of Cryptococcus neoformans stains red with mucicarmine
An unmarked bacterial plate is producing urease. What organisms could be growing on the plate?
Proteus, Cryptococcus, Helicobacter pylori, Ureaplasma, Nocardia, Klebsiella, Staphylococcus epidermidis, Staphylococcus saprophyticus (Pee CHUNKSS)
A patient presents with contact lens-associated keratitis. What biofilm-producing bacteria are the cause?
Pseudomonas aeruginosa
Which 5 organisms can be visualized with Giemsa stain?
Rickettsia, Chlamydia, Trypanosomes, Plasmodium, Borrelia, Helicobacter pylori (Ricky got Chlamydia as he Tried to Please the Bored “Geisha”)
In a patient with acute rheumatic fever, what bacterial virulence factor may be responsible for the autoimmune response?
M protein by group A streptococci; it has epitopes similar to those of human cellular proteins, a phenomenon known as molecular mimicry
Many guests, especially the elderly, have developed high fever and pneumonia after a staying in a hotel with central AC. What medium is used to culture the causative organism?
Charcoal yeast extract agar buffered with cysteine and iron (the causative organism is Legionella)
What glycoprotein-derived bacterial structure is known to help form an attachment between 2 bacteria during conjugation?
Sex pilus
What is the primary toxic component of an endotoxin?
Lipid A
What type of toxin is typically heat stable?
Endotoxins are stable at 100°C for 1 hour
Proteus and Klebsiella are both urease-⊕ organisms. By what mechanism do these bacteria increase pH?
Urease hydrolyzes urea, resulting in release of ammonia and CO2. Ammonia reacts with the medium to increase pH
Identify the chemical composition and the 2 main functions of the peptidoglycan layer in bacteria
It has a sugar backbone with cross-linked peptide side chains; it provides rigid support and protection against osmotic pressure damage
A patient who has had a splenectomy is at risk for infection with encapsulated bacteria. Name 4 vaccines he should receive.
Pneumococcal (PCV13 and PPSV23), Haemophilus influenzae type B, and meningococcal vaccines
What defines a pleomorphic bacteria?
No rigid cell walls
Vaccines can be created for exotoxins but not for endotoxins. Why?
Exotoxins are highly antigenic (unlike endotoxins); they are able to induce antibody production, and their toxoids can be used to make vaccines
What biofilm-producing bacteria are associated with dental plaque and infective endocarditis?
Viridans streptococci (Streptococcus mutans, Streptococcus sanguinis)
Shigella and enterohemorrhagic Escherichia coli share a mechanism for causing gastrointestinal mucosal damage and dysentery. What is it?
Both Shiga toxin and Shiga-like toxin cleave host cell rRNA, inactivating the 60S ribosomal subunit by removing adenine from rRNA
A 56-year-old man with diabetes has a foul-smelling foot ulcer with palpable crepitus. Which antibiotic must not be used to treat it? Why?
AminO2glycosides, which require O2 to enter a bacterial cell, are ineffective against anaerobes (the patient likely has an anaerobic skin infection)
In the microbiology lab, you notice that some Sabouraud agar is growing pathogens. What is likely growing?
Fungi (Sab’s a fun guy!)
Drug X is known to target polysaccharides from the bacterial capsule. What function of the bacteria is most likely affected?
Protection from phagocytosis
What color pigment does Serratia marcescens produce?
Red (Serratia: think red Sriracha hot sauce)
A patient has a gram ⊖ bacterial infection. On cell lysis, the release of endotoxin activates what components of the immune system?
Macrophages (via TLR4–CD14 interaction), complement (C3a and C5a), and tissue factor
A homeless man is febrile and coughing up blood. A chest x-ray shows a cavitary lesion. You consider tuberculosis. What medium should be used for culture?
Löwenstein-Jensen agar (Mycobacterium tuberculosis is likely the causative organism)
What components of the outer membrane are antigenic?
O polysaccharide component & most outer membrane proteins
A patient tests ⊕ for tetanospasmin. What symptoms does he likely have?
Spastic paralysis, risus sardonicus, or trismus (lockjaw) from Clostridium tetani
Name the 3 types of facultative anaerobic bacteria.
Streptococci, staphylococci, and enteric gram-negative bacteria
A 30-year-old man has a painless syphilitic penile chancre. Why does the causative organism not react to Gram stain?
Treponema is too thin to be visualized on Gram staining
What color pigment does Actinomyces israelii produce?
Yellow; sulfur granules appear yellow (Israel has yellow sand)
IgA protease is secreted by which 3 bacterial species?
S pneumoniae, H influenzae type B, Neisseria (SHiN), which normally colonize the respiratory mucosa
One type of conjugation process does not involve the transfer of chromosomes. How does it work?
In F+ to F- conjugation, plasmids are transferred from the F+ cell through a conjugal bridge; no chromosomal DNA is transferred
Endotoxin activation of macrophages causes release of which intermediate leading to hypotension?
Primarily due to nitric oxide release; can also be secondary to TNF-α or C3a release
A 30-year-old man recently underwent splenectomy and then required several specialized vaccines. What organisms should he be vaccinated against?
Neisseria meningitidis, Streptococcus pneumonia, and Haemophilus influenzae; patients with asplenia (No Spleen Here) have ↓ opsonizing ability and need vaccines for protection
Which type of transduction does not retain the altered DNA in the subsequent generations of the bacteria?
Generalized transduction (phage DNA is not incorporated into the chromosome, and bacterial cell is lysed afterward)
A patient with pneumonia is receiving ventilatory assistance. This patient is at risk for infection with which biofilm-producing bacteria?
Pseudomonas aeruginosa
A toddler has rheumatic fever. Anti-streptolysin O titers are ⊕. What is the mechanism of by which this toxin acts?
Streptolysin O degrades cell membranes and lyses RBCs, causing β-hemolysis
What are conjugate vaccines made of?
Capsular polysaccharide and a protein conjugate
What color pigment does Staphylococcus aureus produce?
Yellow (Aureus in Latin = gold)
A trauma victim has foul-smelling necrotic skin lesions with myonecrosis and crepitus. How does the infecting agent appear on blood agar?
Forms a double zone of hemolysis on blood agar by the alpha toxin of Clostridium perfringens, which causes gas gangrene by phospholipid degradation
In an experiment, you see a cell incorporating an F+ plasmid into its own chromosomes. Name the result of this bacterial genetics process.
High-frequency recombination (Hfr) cell, a subtype of conjugation
What are the mechanisms of the heat-labile and heat-stable toxins of enterotoxigenic Escherichia coli (ETEC)?
Heat-labile overactivates adenylate cyclase (more Cl-, H2O secretion); heat-stable overactivates guanylate cyclase (less NaCl, H2O resorption)
Where are genes coding for the endotoxin of the bacteria located?
Bacterial chromosome
You conduct an experiment in which DNA segments are transferred between chromosomes & plasmids in the same cell. Name the process.
Transposition
A patient has a cough and a culture grows a gram ⊖ rod that has a positive silver stain. What is the most likely pathogen?
Legionella
A baby exhibits flaccid paralysis (mainly facial) after being fed honey. What is the mechanism of the causative agent?
Botulinum toxin inhibits release of stimulatory acetylcholine at the neuromuscular junction by cleaving SNARE
What is lipopolysaccharide (LPS) composed of?
O antigen, lipid A (the toxic component), and core polysaccharide
Where are genes coding for the exotoxin of the bacteria located?
In the plasmid or bacteriophage
Bacteria with thick peptidoglycan layers retain what dye and are deemed to be gram ⊕?
Crystal Violet
A patient with rice-water stool diarrhea has an adenosine diphosphate- (ADP) ribosylating AB toxin whose primary action is overactivation of adenylate cyclase. Diagnosis?
Vibrio cholerae infection
What purpose does the capsule of Streptococcus pneumoniae serve?
Antiphagocytic virulence factor
An F+ bacterium & an F- bacterium participate in high-frequency recombination. What is the result for the F- bacterium?
The recipient cell (F-) has received new genes from the F+ cell but remains F-
Escherichia coli grows on MacConkey agar, producing a color change. Describe the medium and how it works.
MacConkey agar is a pH indicator medium; it responds with a color change after conversion of lactose to acidic metabolites by E coli
Some bacteria can take up naked DNA from the environment. Which 3 bacteria perform this process most often?
Streptococcus pneumoniae, Haemophilus influenzae, & Neisseria (SHiN) perform transformation most often
In which component of the cell envelope are oxidative & transport enzymes located?
Cytoplasmic membrane
Although anaerobes are pathogenic in most tissues, where are they most commonly part of the normal flora?
The GI Tract
How will Ureaplasma present on Gram stain?
No staining; Ureaplasma lack a cell wall (similar to Mycoplasma) and do not Gram stain well
What factor causes endotoxins to activate the coagulation cascade?
Tissue Factor
A 16-year-old girl has recurrent Staphylococcus aureus, Pseudomonas, and Candida infections. What enzyme deficiency is likely?
NADPH oxidase deficiency, which increases susceptibility to infections with catalase-⊕ bacteria
