General Microbiology Exam 3 Review

Comprehensive practice flashcards for General Microbiology Exam 3 covering bacterial pathogens, virulence factors, clinical pathology, diagnostics, and therapeutics.

What are the primary general characteristics of the genus Staphylococci regarding Gram reaction, spore formation, morphology, and catalase activity?

Staphylococci are Gram-positive, non-endospore-forming, catalase-positive cocci arranged in clusters (staphylo-), lack flagella, may possess a capsule, and are pyogenic (pus-forming).

What are the optimal growth temperature and colony appearance of Staphylococcus aureus?

Colonies are large, round, and opaque, with an optimum growth temperature of $37^\bot\text{C}$.

How does Protein A function as a virulence factor in Staphylococcus aureus?

Protein A binds to the Fc region of host IgGs, interfering with normal opsonization and phagocytosis.

What is the role of coagulase produced by Staphylococcus aureus?

It promotes blood clot formation by converting fibrinogen to fibrin.

What genetic mechanism is responsible for methicillin resistance in MRSA (methicillin-resistant Staphylococcus aureus)?

The mecA gene encodes a novel penicillin-binding protein (PBP) that confers resistance to all beta-lactam antibiotics.

What structural differences distinguish VISA from VRSA?

VISA (Vancomycin-intermediate Staphylococcus aureus) has a thicker cell wall, whereas VRSA (Vancomycin-resistant Staphylococcus aureus) possesses altered peptide cross-linkers.

What are the incubation period and common clinical manifestations of Staphylococcus aureus food intoxication?

Caused by ingesting heat-stable enterotoxins, it causes nausea, vomiting, abdominal cramps, and mild fever with an incubation period of $1\text{--}6\,\text{hours}$ and duration of $24\text{--}48\,\text{hours}$.

What cutaneous condition is caused by S. aureus exfoliative toxins?

Staphylococcal scalded skin syndrome (SSSS), characterized by red flush, blisters, and desquamation of the epidermis (with a localized variant known as bullous impetigo).

Which Staphylococcus species is coagulase-positive?

Staphylococcus aureus.

Which coagulase-negative Staphylococcus species is a common cause of urinary tract infections in sexually active young women?

Staphylococcus saprophyticus.

Which coagulase-negative Staphylococci typically colonize around apocrine sweat glands?

Staphylococcus hominis and Staphylococcus haemolyticus.

How do Staphylococci and Streptococci differentiate on a catalase test?

Staphylococci are catalase-positive, whereas Streptococci are catalase-negative (possessing peroxidase).

What is the basis of the Lancefield classification scheme for Streptococci?

Cell wall carbohydrate antigens (recognized by specific antibodies), dividing them into 17 groups (e.g., Group A, Group B, Group C).

What are the three patterns of hemolysis observed in Streptococci and their visual appearances on blood agar?

$\alpha$ (alpha) hemolysis produces greenish bruising/partial clearing; $\beta$ (beta) hemolysis produces complete clearing; $\gamma$ (gamma) hemolysis produces no lysis.

What specific surface virulence factors are found on Streptococcus pyogenes (Group A Streptococcus)?

C-carbohydrates (protect from lysozymes), fimbriae (adherence), M-protein (resists phagocytosis and blocks C3b), hyaluronic acid capsule (mimics host tissue), and C5a protease.

What toxin produced by lysogenized Streptococcus pyogenes causes scarlet fever?

Streptococcal pyrogenic exotoxin (SPE), an erythrogenic toxin that induces fever and a sandpapery red rash.

What are the two major non-suppurative post-streptococcal sequelae of Streptococcus pyogenes infection?

Rheumatic fever (causes carditis, valve damage, arthritis, chorea) and acute glomerulonephritis (immune complexes causing increased blood pressure and potential kidney failure).

What bacterium is classified as Lancefield Group B Streptococcus, and what severe conditions does it cause in neonates?

Streptococcus agalactiae (GBS); it causes neonatal pneumonia, sepsis, and meningitis.

Which diagnostic tests differentiate Group A Streptococcus (S. pyogenes) from Group B Streptococcus (S. agalactiae)?

GAS is sensitive to bacitracin; GBS is bacitracin-resistant and tests positive on the CAMP test.

What clinical conditions are commonly associated with viridans group streptococci (e.g., S. mutans, S. oralis)?

Dental caries, tooth abscesses, and subacute bacterial endocarditis (especially in individuals with pre-existing heart disease).

What is the cellular morphology and hemolysis of Streptococcus pneumoniae?

Small, lancet-shaped Gram-positive cocci arranged in pairs (diplococci) and short chains displaying $\alpha$-hemolysis.

What diagnostic test visualizes the capsule of Streptococcus pneumoniae using specific anticapsular antibodies?

The Quellung test (capsular swelling reaction).

What are the primary differences between Streptococcus pneumoniae and Enterococcus on bile and optochin tests?

S. pneumoniae is optochin-sensitive and bile-soluble, whereas Enterococci are optochin-resistant and grow in the presence of bile esculin.

What are the three exotoxin components produced by Bacillus anthracis?

Protective antigen (PA, which forms a heptameric pore), Edema factor (EF, an adenylate cyclase that increases intracellular cAMP), and Lethal factor (LF, a metalloprotease that cleaves MAP kinase kinases).

What is the unique composition of the capsule in Bacillus anthracis?

A polypeptide capsule composed of poly-D-glutamic acid.

What distinguishes the emetic form of Bacillus cereus food poisoning from the diarrheal form?

The emetic form is an intoxication associated with fried rice, mediated by a heat-stable enterotoxin with short incubation and duration; the diarrheal form is associated with meat and vegetables, mediated by a heat-labile enterotoxin that stimulates cAMP after bacterial replication.

What organism causes gas gangrene (myonecrosis), and what is its primary lethal virulence factor?

Clostridium perfringens; its primary virulence factor is alpha toxin, a lecithinase (phospholipase C) that lyses erythrocytes, platelets, leukocytes, and endothelial cells.

Why is Clostridium difficile infection (CDI/CDAD) commonly associated with broad-spectrum antibiotic treatment?

Antibiotic therapy eradicates the normal competing colonic flora, allowing antibiotic-resistant C. difficile to superinfect and produce enterotoxins that cause pseudomembranous colitis.

What is the mechanism of action of tetanospasmin produced by Clostridium tetani?

It is retrogradely transported along axons to the spinal cord, where it cleaves proteins regulating the release of the inhibitory neurotransmitters glycine and GABA, causing uncontrolled spastic muscle contractions.

How does botulinum toxin cause flaccid paralysis?

It remains at the peripheral neuromuscular junction and cleaves proteins required for acetylcholine release from motor neurons, blocking muscle contraction.

Why should pasteurized honey not be given to infants under one year of age?

Honey can contain Clostridium botulinum spores that can germinate in an infant's immature gastrointestinal tract, causing infant botulism.

What characteristic features of Listeria monocytogenes enable it to survive and disseminate within host cells?

It is a facultative intracellular coccobacillus that uses listeriolysin O and phospholipases to escape the phagolysosome and ActA to polymerize host actin for propulsion between cells.

What food products are most frequently associated with Listeria monocytogenes outbreaks?

Unpasteurized dairy products, soft cheeses, cold cuts/deli meats, poultry, and raw vegetables.

What zoonotic infection is caused by Erysipelothrix rhusiopathiae in butchers and fish handlers?

Erysipeloid (a localized inflammatory cutaneous lesion accompanied by pain and swelling).

What is the mechanism of action of the Corynebacterium diphtheriae exotoxin?

The A subunit inactivates elongation factor 2 (EF-2) by ADP-ribosylation, halting host cell protein synthesis; the B subunit binds to heparin-binding EGF-like growth factor receptors.

What diagnostic test evaluates Corynebacterium diphtheriae for exotoxin production using antitoxin-impregnated paper?

The Elek test (immunoprecipitation assay).

What characteristic respiratory sign can cause asphyxiation in respiratory diphtheria?

A dense, pseudomembrane (white-grayish film of fibrin, dead tissue, and inflammatory cells) adhering firmly to the tonsils, pharynx, or larynx.

What are the Gram stain morphology and oxidase reaction of the genus Neisseria?

Gram-negative, bean-shaped diplococci that are oxidase-positive.

Why does no protective vaccine exist for Neisseria gonorrhoeae?

N. gonorrhoeae lacks a capsule and exhibits extensive antigenic variation in its surface structures (pili, Opa proteins).

Which Neisseria meningitidis capsular serogroup is poorly immunogenic and historically not contained in the standard capsular polysaccharide vaccine?

Serogroup B.

What antibiotics are recommended for chemoprophylaxis in close contacts of individuals with Neisseria meningitidis meningitis?

Rifampin, ciprofloxacin (for adults), or ceftriaxone.

What is the characteristic clinical lesion of primary syphilis caused by Treponema pallidum?

A hard, painless chancre at the site of inoculation accompanied by regional lymphadenopathy.

What is a hallmark diagnostic dermatologic sign of secondary syphilis?

A non-pruritic maculopapular red or brown rash occurring prominently on the palms of the hands and soles of the feet, along with condylomata lata in moist areas.

What febrile, systemic reaction can occur within $2\text{--}8\,\text{hours}$ of initiating penicillin treatment for syphilis?

The Jarisch-Herxheimer reaction.

What are the nontreponemal serological screening tests that detect host cardiolipin antibodies in syphilis?

RPR (Rapid Plasma Reagin) and VDRL (Venereal Disease Research Laboratory) tests.

What organism causes Lyme disease, what is its vector, and what is the characteristic early rash?

Borrelia burgdorferi; transmitted by Ixodes ticks; presents with an expanding bull's-eye rash known as erythema migrans.

What mechanism enables Borrelia recurrentis to cause relapsing episodes of fever?

Antigenic variation of its outer surface proteins (OSPs) during infection.

What is Weil disease, and what spirochete is responsible for it?

A severe form of leptospirosis caused by Leptospira interrogans, characterized by renal failure, hepatic failure (jaundice), vasculitis, and myocarditis.

What unique lipid component of the Mycobacterium cell wall imparts acid-fastness and antibiotic resistance?

Mycolic acids (long-chain fatty acids containing $70\text{--}90$ carbons).

What is the Mantoux test for Mycobacterium tuberculosis?

An intradermal injection of purified protein derivative (PPD) read at $48\text{--}72\,\text{hours}$ to evaluate for induration resulting from a delayed-type (T cell) hypersensitivity response.

What are the two major clinical forms of leprosy (Hansen disease) caused by Mycobacterium leprae?

Tuberculoid leprosy (paucibacillary, strong TH1 response, localized asymmetrical lesions with nerve damage and sensory loss) and lepromatous leprosy (multibacillary, TH2 response, deeply nodular lesions with widespread tissue destruction).

What presentation of Mycobacterium avium complex (MAC) infection is known as Lady Windermere syndrome?

A chronic pulmonary disease seen in elderly women who chronically suppress their voluntary cough reflexes.

What are the three clinical stages of whooping cough caused by Bordetella pertussis?

Catarrhal stage (cold-like symptoms, highest communicability), paroxysmal stage (repetitive severe coughing fits ending with an inspiratory whoop), and convalescent stage (gradual reduction of cough).

What are the primary growth factors required by Haemophilus influenzae present in heated blood (chocolate) agar?

X factor (hemin) and V factor (nicotinamide adenine dinucleotide, NAD).

What sexually transmitted infection is caused by Haemophilus ducreyi, and how does its ulcer differ from syphilis?

Chancroid; it presents as painful, soft chancres (in contrast to the painless, hard chancre of syphilis).

What organism commonly found in the normal oral flora of cats and dogs causes rapid cellulitis after bite wounds?

Pasteurella multocida.

What are the biochemical hallmarks of the family Enterobacteriaceae?

Gram-negative rods, facultative anaerobes, oxidase-negative, catalase-positive, and fermenters of glucose.

What do the O, K, and H surface antigens represent in serotyping Enterobacteriaceae?

O = somatic cell wall lipopolysaccharide (LPS); K = capsular antigen (Vi in Salmonella); H = flagellar protein antigen.

What clinical syndrome is caused by Enterohemorrhagic E. coli (EHEC, such as O157:H7), and what serious systemic complication can arise?

Hemorrhagic colitis (bloody diarrhea) mediated by Shiga-like toxin (STEC), which can progress to hemolytic uremic syndrome (HUS, causing acute renal failure).

Which pathogenic group of E. coli is the most common cause of traveler's diarrhea through the action of LT and ST enterotoxins?

Enterotoxigenic E. coli (ETEC).

What bacterium causes typhoid fever, and in which organ do chronic carriers harbor the bacteria?

Salmonella enterica serovar Typhi; chronic carriers harbor bacilli in the gallbladder.

What cellular receptor does Shiga toxin bind to, and what is its intracellular mechanism of toxicity?

The B subunits bind to the Gb3 glycolipid receptor on intestinal villi and renal endothelial cells; the internalized A subunit inactivates the 28S rRNA of the 60S eukaryotic ribosomal subunit, halting protein synthesis.

What enteric organism causes mesenteric lymphadenitis with right lower quadrant pain that can closely mimic appendicitis?

Yersinia enterocolitica.

What organism causes the plague, and what are its primary vector and safety morphology?

Yersinia pestis; transmitted by the flea vector (e.g., Xenopsylla); exhibits pronounced bipolar staining (safety-pin appearance).

What water-soluble pigments and characteristic odor are produced by Pseudomonas aeruginosa?

Pyocyanin (blue-green pigment) and pyoverdine; colonies often produce a sweet, grape-like or fruity odor.

What is the mechanism of action of Exotoxin A (ETA) produced by Pseudomonas aeruginosa?

It halts host cell protein synthesis by ADP-ribosylating and inactivating elongation factor 2 (EF-2), functioning identically to diphtheria toxin.

What is the cellular morphology and flagellar arrangement of Vibrio cholerae?

Comma-shaped, Gram-negative rod possessing a single polar flagellum (monotrichous).

What is the intracellular effect of cholera toxin (CT) on intestinal epithelial cells?

It binds GM1 ganglioside receptors via B subunits, allowing the A subunit to ADP-ribosylate the Gs regulatory protein, activating adenylate cyclase and leading to elevated cAMP and massive hypersecretion of water and electrolytes ('rice-water stools').

Which Vibrio species is notorious for causing rapidly spreading, severe wound infections and septicemia following exposure to warm coastal waters or raw oysters?

Vibrio vulnificus.

What autoimmune neurological condition characterized by ascending paralysis is a recognized post-infectious sequela of Campylobacter jejuni gastroenteritis?

Guillain-Barré syndrome.

How does Helicobacter pylori protect itself from the acidic pH of the stomach lumen?

It produces large amounts of urease, which hydrolyzes urea into carbon dioxide and ammonia ($\text{NH}_3$), creating a neutralizing alkaline microenvironment.

What unique structural feature distinguishes Mycoplasma and Ureaplasma from almost all other bacteria?

They naturally lack a peptidoglycan cell wall and have membranes stabilized by sterols.

What clinical disease is caused by Mycoplasma pneumoniae?

Tracheobronchitis and atypical or 'walking pneumonia'.

Which antiviral drugs function by competitive inhibition of viral DNA polymerase to treat Herpes simplex and Varicella-zoster virus infections?

Acyclovir, valacyclovir, famciclovir, and penciclovir.

What is the mechanism of action of the influenza antivirals oseltamivir and zanamivir?

They are neuraminidase inhibitors that prevent the enzymatic cleavage of sialic acid, preventing the release and dissemination of progeny virions.

What are the entry/fusion inhibitor antivirals used in the treatment of HIV, and what molecules do they target?

Enfuvirtide (blocks viral gp41 fusion) and maraviroc (antagonist of host CCR5 co-receptor).