Basic Bacteriology Flashcards
Many guests, especially the elderly, have developed high fever and pneumonia after 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 is typically found in the core of a bacterial spore?
Dipicolinic acid
What is the chemical composition of an endotoxin?
Lipopolysaccharide (LPS)
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)
In endotoxin-based complement activation, which complement(s) cause(s) hypotension/edema and histamine release?
C3a and C5a
What bacterial structural appendage, composed of protein, is known to help provide motility?
Flagellum
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)
Bacteria with thin peptidoglycan layers turn what color(s) with counterstain on Gram staining?
Red or pink, and are gram ⊖
After examining a patient suspected of having Clostridium difficile infection, you clean your hands with soap and water rather than the alcohol sanitizer. Why?
Spore-forming bacteria ( like Bacillus and Clostridium) are resistant to alcohol and can only be killed with soap and water
Which spirochete can be identified with Giemsa stain?
Borrelia
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
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)
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
What are the commonly encountered spore-forming bacteria, and what diseases do they cause?
Bacillus & Clostridium: B anthracis (anthrax), B cereus (food poisoning), C botulinum (botulism), C difficile (pseudomembranous colitis), C perfringens (gas gangrene), C tetani (tetanus)
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
What color pigment does Pseudomonas aeruginosa produce?
Blue-green (aeruginosa: aerugula is green)
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
What are endotoxins composed of?
The lipid A component of lipopolysaccharide (a bacterium’s structural part); lysis releases it
What stain is useful to identify Tropheryma whipplei in a patient suspected to have Whipple disease?
Periodic acid-Schiff stain, that stains glycogen, and mucopolysaccharides (PaSs the sugar)
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
In which component of the cell envelope are oxidative and transport enzymes located?
Cytoplasmic membrane
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)
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
A patient presents with contact lens-associated keratitis. What biofilm-producing bacteria are the cause?
Pseudomonas aeruginosa
A man is infected with bacteria that produce exotoxin A, which induces host cell death. Identify the pathogen and the mechanism of exotoxin A.
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)
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
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
Escherichia coli grows on MacConkey agar, producing a color change. Describe the medium and how it works.
MacConkey agar is a pH indicator (or differential) medium; it responds with a color change after conversion of lactose to acidic metabolites by E coli
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)
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
In a gram-positive bacterium you identify a specialized structure composed of dipicolinic acid and peptidoglycan. What is it?
A Spore
Diagnostic test for rheumatic fever uses antibodies against what part of the causative agent?
Antibodies against Streptococcus toxin, streptolysin O (anti-streptolysin O)
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
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)
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)
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
Which strain of Escherichia coli has a toxin that overactivates adenylate cyclase?
Enterotoxigenic E coli (heat-labile toxin)
A male patient with many sexual partners has purulent penile discharge from Neisseria gonorrhoeae. How is the causative organism cultured?
On Thayer-Martin agar, a selective medium containing vancomycin, trimethoprim, colistin, and nystatin (antibiotics that inhibit the growth of other organisms except for Neisseria)
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
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
A patient with pneumonia is receiving ventilatory assistance. This patient is at risk for infection with which biofilm-producing bacteria?
Pseudomonas aeruginosa
Name 4 aerobes.
Nocardia, Pseudomonas aeruginosa, Mycobacterium tuberculosis, Bordetella pertussis
Coxiella is considered an obligate intracellular pathogen. How does this organism get energy?
It obtains ATP from its host cell
Where are genes coding for the exotoxin of the bacteria located?
In the plasmid or bacteriophage
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)
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
A patient with lockjaw 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 diagnosis is tetanus)
Your microbiology lab advisor wishes to use a special silver stain. What organisms may he be looking for?
Legionella, Helicobacter pylori, or fungi (eg, Coccidioides, Pneumocystis jirovecii)
A 10-year-old girl has a severe cough that is accompanied by an inspiratory whoop. What is the mechanism of the offending toxin?
Bordetella pertussis disables the Gi protein (overactivates adenylate cyclase), impairing phagocytosis and allowing bacteria to survive
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
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
A patient has otitis media. What biofilm-producing bacteria are most likely responsible for the infection?
Nontypeable (unencapsulated) Haemophilus influenzae
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 (antigenic targets) similar to those of human cellular proteins, a phenomenon known as molecular mimicry
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, Pneumocystis jirovecii, Giardia, and Cryptosporidium
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)
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
In the microbiology lab, you notice that some Sabouraud agar is growing pathogens. What is likely growing
Fungi (Sab’s a fun guy!)
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)
Immunoglobulin (Ig) A protease allows bacteria to colonize mucous membranes. Describe its mechanism of action.
IgA protease cleaves IgA, allowing bacteria to adhere to mucous membranes
What are exotoxins composed of?
Polypeptides
Legionella, Bartonella, and Ehrlichia all share what property that makes them suboptimal for Gram stain?
They are all primarily intracellular 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
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)
Where in the cell wall of gram ⊖ bacteria are β-lactamases located?
The periplasmic space, which is only present in gram ⊖ bacteria
What is the difference between pneumococcal vaccines PCV13 and PPSV23 vaccines?
PCV13 is a cojugate vaccine, whereas PPSV23 is a pneumococcal polysaccharide vaccine with no conjugated protein (hence has weaker immune response)
Name 2 bacterial disease that are typically caused by endotoxins.
Gram ⊖ rod sepsis and meningococcemia
How will Ureaplasma present on Gram stain?
No staining; Ureaplasma lack a cell wall (similar to Mycoplasma) and do not Gram stain well
What cheaper and sensitive stain is used in lieu of the Ziehl-Neelsen stain to screen for acid-fast bacteria?
Auramine-rhodamine stain
Where are genes coding for the endotoxin of the bacteria located?
Bacterial chromosome
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
Which pleomorphic gram ⊖ bacteria can be identified with a Giemsa stain?
Chlamydia and Rickettsia species
A homeless man is febrile and coughing up blood. A chest x-ray shows a cavitary lesion in the upper lobe. What medium should be used for culture of the suspected organism?
Löwenstein-Jensen agar (Mycobacterium tuberculosis is likely the causative organism)
An F+ bacterium and 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-
What are the most commonly found pleomorphic bacteria?
Anaplasma, Ehrlichia, Chlamydiae, Rickettsiae, Mycoplasma, Ureaplasma
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)
You conduct an experiment in which DNA segments are transferred between chromosomes and plasmids in the same cell. Name the process.
Transposition
A patient tests ⊕ for tetanospasmin. What symptoms does he likely have?
Spastic paralysis, risus sardonicus, or trismus (lockjaw) from Clostridium tetani
Name 4 bacterial diseases that are typically caused by exotoxins.
Cholera, tetanus, botulism, and diphtheria
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, Bordetella pertussis
Transposition is done between a plasmid from vancomycin-resistant Enterococcus and Staphylococcus aureus. How does S aureus become vancomycin resistant?
Flanking chromosomal DNA is incorporated into plasmid, then into another bacterium (eg, Tn1546 with vanA gene from Enterococcus to S aureus)
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
What glycoprotein-derived structure allows bacteria to adhere to the cell surface?
The fimbria (pilus)
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
A plasmid is transferred from one bacterium to another. What is this transfer of information called?
Conjugation
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)
In patients with pharyngitis, what protein from group A Streptococcus species prevents phagocytosis by the body’s immune cells?
M Protein
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 type of toxin (exotoxin or endotoxin) is typically heat stable?
Endotoxins are stable at 100°C for 1 hour
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
An unimmunized 1-year-old boy is irritable, sluggish, and has a stiff neck. How do you culture the likely causative agent, Haemophilus influenzae?
On chocolate agar with factors V (NAD+) and X (hematin); the patient likely has H influenzae meningitis
Coxiella is considered an obligate intracellular pathogen. Name other bacteria in this class.
Rickettsia, Chlamydia, and COxiella are intracellular (stay inside [cells] when it is Really CHilly & COld)
What is the mechanism of diphtheria toxin?
Inactivates elongation factor 2 via adenosine diphosphate (ADP) ribosylation, leading to necrosis in the pharyngeal and cardiac tissues; this is Corynebacterium diphtheriae
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 GABA and glycine (exotoxin is tetanospasmin)
What is the purpose of autoclaving surgical equipment?
To kill bacterial spores
What color pigment does Staphylococcus aureus produce?
Yellow (Aureus in Latin = gold)
In which type of transduction is viral DNA incorporated into the host DNA?
Specialized transduction (involves a lysogenic phage)
On what 2 medical products are Staphylococcus epidermidis likely to grow on?
Catheters and prosthetic devices
In endotoxin-based complement activation, which complement(s) promote(s) neutrophil chemotaxis?
C5a
Excessive stimulation of the coagulation cascade by tissue factor can cause what condition?
Disseminated intravascular coagulation (DIC)
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 to the exterior
A pharmaceutical 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
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 Hot “Geisha”)
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 Staphylococcus aureus by binding the Fc region of immunoglobulins
Where is endotoxin (lipopolysaccharide) located in gram-negative bacteria?
Outer leaflet of the outer membrane
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
ImmunoglobuIin (Ig) A protease is secreted by which 3 bacterial species?
Streptococcus pneumoniae, Haemophilus influenzae type B, Neisseria (SHiN), which normally colonize the respiratory mucosa
The release of endotoxin in a gram-negative bacterial infection activates what components of the immune system?
Macrophages (via TLR4–CD14 interaction), complement (C3a and C5a), and tissue factor
Exotoxins are typically destroyed at 60°C. What are the 2 notable exceptions?
Staphylococcal enterotoxin and Esherichia coli heat-stable toxin are exceptions
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
Some bacteria can take up naked DNA from the environment. Which 3 bacteria perform this process most often?
Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria (SHiN) perform transformation most often
A 30-year-old man has a painless penile chancre. Why does the likely causative organism not react to Gram stain?
Treponema is too thin to be visualized on Gram staining (the patient likely has syphilis
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 is lipopolysaccharide (LPS) composed of?
O antigen, lipid A (the toxic component), and core polysaccharide
Although anaerobes are pathogenic in most tissues, where are they most commonly part of the normal flora?
GI tract
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
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 16-year-old girl has recurrent Staphylococcus aureus, Pseudomonas, and Candida infections. What genetic enzyme deficiency is likely?
Reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase deficiency, which increases susceptibility to infections with catalase ⊕ bacteria
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
A catheterized patient has bacterial sepsis. Which bacterial structure, composed of polysaccharides, enabled the adhesion of the bacteria?
Slime (S) layer
What factor causes endotoxins to activate the coagulation cascade?
Tissue factor
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 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 biofilm-producing bacteria are associated with dental plaque and infective endocarditis?
Viridans streptococci (Streptococcus mutans, Streptococcus sanguinis)
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
What is the differentiating feature between F+ X F- conjugation and Hfr X F- conjugation?
F+ X F- conjugation does not involve transfer of chromosomal DNA, while Hfr X F- does involve transfer of some bacterial genes
A 56-year-old goat herder discovers a painless, black ulcer on his arm. What is the mechanism of the likely underlying bacterial toxin?
Anthrax toxin, released by Bacillus anthracis, mimics adenylate cyclase (↑ cAMP), causing edematous borders of black eschar
What components of the outer membrane are antigenic?
O polysaccharide component and most outer membrane proteins
What are conjugate vaccines made of?
Capsular polysaccharide and a protein conjugate
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 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)
Shiga-like-toxin (SLT) causes hemolytic-uremic syndrome (HUS). What is the toxin’s mechanism of action?
Causes enhanced cytokine release by inactivating 60S ribosome by removing adenine from rRNA
Name the segment of DNA that can jump from one location to another, can transfer genes from plasmid to chromosome, and vice versa.
Transposon
Why do Clostridium, Bacteroides, Fusobacterium, and Actinomyces israelii have increased susceptibility to oxidative damage?
They lack the enzymes catalase and superoxide dismutase, making them susceptible to oxidative damage (anaerobes Can’t Breathe Fresh Air)
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
What components of the cell envelope are found only in gram-negative bacteria?
Outer membrane, periplasm
A 20-year-old man involved in a motor vehicle accident required a splenectomy. Which bacterial vaccines should he receive and why?
S pneumoniae, H influenzae, and N meningitis vaccines; these bacteria are opsonized and cleared by the spleen; ↓ opsonizing ability → ↑ infection risk with asplenia
What purpose does the capsule of Streptococcus pneumoniae serve?
Antiphagocytic virulence factor
Name the 3 types of facultative anaerobic bacteria.
Streptococci, staphylococci, and enteric gram-negative bacteria
What component of the cell envelope induces tumor necrosis factor (TNF)-α on gram-negative bacteria?
Lipid A (also induces interleukin [IL]-1)
What glycoprotein-derived bacterial structure is known to help form an attachment between 2 bacteria during conjugation?
Sex pilus
A teacher with unvaccinated students has had a persistent cough for 3 months. Identify the most likely exotoxin responsible for the prolonged cough.
Pertussis toxin, produced by Bordetella pertussis, which inactivates inhibitory G subunit and overactivates adenylate cyclase, cAMP (causing a “100-day cough” in adults)
What component of the outer layer of Mycobacteria is stained with the Ziehl-Neelsen stain?
Mycolic acid
What color pigment does Serratia marcescens produce?
Red (Serratia: think red Sriracha hot sauce)
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)
In a patient with scarlet fever who has erythrogenic toxins in her blood, what specific toxin is to blame for her symptoms?
Exotoxin A, which causes toxic shock-like syndrome (rash, fever, shock) and is released by Streptococcus pyogenes
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 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)
Bacteria with thick peptidoglycan layers retain what dye and are deemed to be gram ⊕?
Crystal violet
Drug X is known to target polysaccharides from the bacterial capsule. What function of the bacteria is most likely affected?
Protection from phagocytosis
The inner leaflet of the outer membrane of a bacteria is composed of what molecule?
Phospholipids
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
What commonly pathogenic organisms can be cultured on charcoal yeast extract agar?
Brucella, Francisella, Legionella, Pasteurella
What are the commonly encountered encapsulated bacteria?
Pseudomonas aeruginosa, Streptococcus pneumoniae, Haemophilus influenzae type b, Neisseria meningitidis, Escherichia coli, Salmonella, Klebsiella pneumoniae, group B Strep
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)
Name 2 common gram ⊕ bacteria that can cause a rash and septic shock.
Staphylococcus aureus (via toxic shock syndrome toxin) and Streptococcus pyogenes (via exotoxin A)
What is the primary toxic component of an endotoxin?
Lipid A
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)
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)
A patient with cystic fibrosis has a chronic cough and confirmed biofilm-producing bacterial growth. Identify the bacteria.
Pseudomonas aeruginosa
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
How does an 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
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 lytic phage infects a bacterial cell, cleaving its DNA into bits; the DNA is packed in a phage capsid, which infects another cell. Name the process (image).
Generalized Transduction
A man presents with signs of acute respiratory distress. A silver stain of his sputum is shown (image). Identify the pathogen.
Coccidioides
Bacteria exchange plasmid genes via sex pilus as shown in the image. What is the process called?
F+ × F- conjugation
These bacteria (image) are seen at the end of their stationary phase. How is this process beneficial to bacterial survival?
Spore formation enables survival in nutrient-poor settings; spores are highly resistant to heat and chemicals and not metabolically active
An unimmunized 7-year-old boy has a sore throat and fever. Examination of his throat is shown in the image. What medium should be used for culture of the causative agent?
Tellurite agar, Löffler medium (organism is likely Corynebacterium diphtheriae)
A culture plate has organisms visualized with a Ziehl-Neelsen stain (image). What is the main component of this stain?
Carbol Fuchsin
A stain of the stool specimen of a patient with diarrhea and abdominal pain is shown (image). What is the pathogen?
Trypanosomes
Bacteria exchange chromosomal genes via sex pilus as shown in the image. What is the process called?
High-frequency recombination (Hfr), a subtype of conjugation
Bacteria are able to import short pieces of naked bacterial DNA (from bacterial cell lysis) as shown in the image. What is it called?
Transformation
Describe how specialized transduction takes place.
A lysogenic phage infects a bacterium; viral DNA incorporates into bacterial DNA. During excision, flanking bacterial DNA is excised with the phage DNA and packaged into the capsid
A lysogenic phage infects a bacterium (image); viral DNA incorporates into the bacterial DNA. During excision, DNA is packed in the phage. Name this process.
Specialized transduction
A 50-year-old patient with pneumonia has sputum stained as shown (image). How does the capsule help in the virulence of this organism?
Capsule is antiphagocytic
In case of generalized transduction, what happens after a lytic phage infects a bacterium?
A lytic phage infects a bacterium and cleaves bacterial DNA. Bacterial DNA segments may be packaged in a phage capsid. When the phage infects other bacteria, the DNA is transferred
Staphylococcus aureus is noted to produce bubbles when treated with hydrogen peroxide in an artificial medium as shown (image). What causes this?
Catalase degrades H2O2 → H2O and O2, which forms bubbles
