What patient demographic is classically affected by Staphylococcus saprophyticus urinary tract infections?

Young, sexually active females. It is the second most common cause of uncomplicated community-acquired outpatient UTIs after Escherichia coli.

What are the two primary exotoxins produced by Clostridioides difficile and their pathophysiologic mechanisms?

Toxin A (enterotoxin): Disrupts mucosal tight junctions, causing fluid secretion and extensive inflammation. Toxin B (cytotoxin): Depolymerizes actin filaments, causing mucosal cell death and pseudomembrane formation (pseudomembranous colitis).

What is the mechanism of Corynebacterium diphtheriae exotoxin?

Diphtheria toxin is an A-B exotoxin encoded by a beta-prophage (lysogenic conversion). Subunit A inactivates Elongation Factor-2 (EF-2) by ADP-ribosylation, arresting host cellular protein synthesis.

What are the laboratory characteristics and resistance challenges of Enterococcus faecalis and Enterococcus faecium?

Catalase-negative, gamma- or alpha-hemolytic, grow in 6.5% NaCl and 40% bile (bile-esculin positive). They exhibit intrinsic resistance to many beta-lactams and can acquire VanA plasmid-mediated resistance to Vancomycin (VRE), requiring Linezolid or Daptomycin.

Which patient populations are at high risk for invasive Listeria monocytogenes infection, and what is the preferred antibiotic?

Neonates, pregnant women, elderly, and immunocompromised patients (impaired cell-mediated immunity). Presents as meningitis or granulomatosis infantiseptica; treated with IV Ampicillin.

What antibiotic is most historically associated with Clostridioides difficile colitis, and what is first-line medical therapy today?

Historically Clindamycin (and fluoroquinolones/cephalosporins). First-line therapies for CDI are oral Fidaxomicin or oral Vancomycin (IV vancomycin does not reach therapeutic luminal colon concentrations).

What are the hallmark clinical manifestations of respiratory diphtheria?

Pharyngeal pseudomembrane (thick, gray, adherent fibrinous exudate that bleeds upon scraping), cervical lymphadenopathy ('bull neck'), myocarditis with arrhythmias, and neuropathies.

What test differentiates Staphylococcus aureus from coagulase-negative Staphylococci (Staph epidermidis and Staph saprophyticus)?

The Coagulase test. Staphylococcus aureus is coagulase-positive (converts fibrinogen to fibrin clot); S. epidermidis and S. saprophyticus are coagulase-negative.

What is the major virulence factor of Streptococcus pyogenes that inhibits complement activation and shares antigenic mimicry with human myocardium?

M protein. It prevents phagocytosis by degrading C3b; antibodies against M protein cross-react with cardiac myosin, causing Rheumatic Heart Disease (molecular mimicry).

How are Streptococcus pyogenes (Group A Strep) and Streptococcus agalactiae (Group B Strep) differentiated?

Both exhibit beta-hemolysis (complete clear zone). Streptococcus pyogenes is Bacitracin-sensitive and PYR-positive; Streptococcus agalactiae is Bacitracin-resistant and CAMP-test positive (enlarges Staph aureus beta-hemolysis arrowhead).

What clinical condition is strongly associated with Streptococcus gallolyticus (formerly Streptococcus bovis) bacteremia or endocarditis?

Occult colorectal neoplasia (adenoma or adenocarcinoma) or inflammatory bowel disease; colonoscopy is mandatory upon isolation from blood cultures.

What is the classic clinical presentation of Nocardia infection and its treatment of choice?

Pulmonary cavitary lesions (mimicking tuberculosis) in an immunocompromised host, with frequent dissemination to the brain forming cerebral ring-enhancing abscesses; treated with Trimethoprim-Sulfamethoxazole (TMP-SMX).

What initial biochemical test differentiates Staphylococcus species from Streptococcus species?

The Catalase test. Staphylococci are catalase-positive (produce bubbles with H2O2); Streptococci and Enterococci are catalase-negative.

What is the pathogenesis of Infant Botulism ('floppy baby syndrome') and how does it differ from Adult Botulism?

Infants ingest Clostridium botulinum spores (often from raw honey or dusty soil), which germinate in the immature colon and produce toxin in vivo. Adults ingest preformed botulinum toxin in improperly canned foods.

What is the mechanism of action of Clostridium tetani neurotoxin (tetanospasmin)?

Retrogradely transported via motor axons to spinal cord inhibitory interneurons (Renshaw cells); cleaves synaptobrevin (SNARE protein), blocking the release of inhibitory neurotransmitters GABA and glycine, producing spastic paralysis, trismus (lockjaw), and risus sardonicus.

What is the classic microscopic appearance and primary virulence factor of Streptococcus pneumoniae?

Lancet-shaped Gram-positive diplococci in pairs. Its primary virulence factor is a polysaccharide capsule, which inhibits phagocytosis (demonstrated by positive Quellung capsular reaction).

How are Staphylococcus epidermidis and Staphylococcus saprophyticus distinguished in the laboratory?

Novobiocin sensitivity testing: Staphylococcus epidermidis is Novobiocin-sensitive; Staphylococcus saprophyticus is Novobiocin-resistant ('NO Staph SAPs').

How are Streptococcus pneumoniae and Streptococcus viridans distinguished on blood agar and laboratory tests?

Both display alpha-hemolysis (partial greening). Streptococcus pneumoniae is Optochin-sensitive and bile-soluble; Viridans streptococci (e.g., S. mutans, S. mitis) are Optochin-resistant and bile-insoluble.

What is the mechanism of action of Toxic Shock Syndrome Toxin-1 (TSST-1) produced by Staphylococcus aureus?

TSST-1 functions as a superantigen that cross-links the MHC Class II receptor on antigen-presenting cells to the V-beta region of T-cell receptors, triggering massive, polyclonal T-cell activation and cytokine storm (IL-1, IL-2, TNF-alpha, IFN-gamma).

Which late non-suppurative complication of Streptococcus pyogenes follows pharyngitis but NOT impetigo?

Acute Rheumatic Fever follows only streptococcal pharyngitis. In contrast, Poststreptococcal Glomerulonephritis (PSGN) can develop after either pharyngeal or cutaneous streptococcal infection.

What clinical syndrome and classic chest radiograph findings characterize inhalation anthrax ('wool-sorters' disease')?

Inhalation of B. anthracis spores leads to hemorrhagic mediastinitis, widened mediastinum on chest X-ray, bilateral pleural effusions, rapid respiratory collapse, and septic shock.

What are the morphologic characteristics and two primary toxins of Bacillus anthracis?

Large, spore-forming, boxcar-shaped Gram-positive rod with a unique poly-D-glutamic acid polypeptide capsule. Produces Edema Factor (adenylyl cyclase that increases cAMP) and Lethal Factor (zinc metalloprotease that cleaves MAP kinase kinase).

What is the mechanism of action of Clostridium botulinum toxin and its classic clinical triad?

Cleaves SNARE proteins at presynaptic neuromuscular junctions, preventing acetylcholine release. Presents with symmetric descending flaccid paralysis, cranial nerve palsies (diplopia, dysphagia, dysarthria, ptosis), and clear sensorium.

What toxin is produced by Clostridium perfringens and what is its role in Gas Gangrene (clostridial myonecrosis)?

Alpha-toxin (lecithinase / phospholipase C). It degrades cell membrane phospholipids, causing widespread cell lysis, tissue necrosis, intravascular hemolysis, and gas production in muscle beds.

What temperature and motility characteristics distinguish Listeria monocytogenes?

Facultative intracellular Gram-positive motile rod that exhibits 'tumbling motility' at room temperature (22–25°C) and can multiply at refrigerated temperatures (4°C, 'cold enrichment'); forms 'rocket tails' by actin polymerization to move cell-to-cell.

What organism is the leading cause of neonatal sepsis, pneumonia, and meningitis, and when are pregnant women screened?

Streptococcus agalactiae (Group B Streptococcus / GBS). All pregnant individuals are screened at 36 0/7 to 37 6/7 weeks of gestation via rectovaginal swab; intrapartum IV Penicillin G or Ampicillin is administered if positive.

What clinical syndrome is caused by Actinomyces israelii, and what is its first-line antibiotic treatment?

Cervicofacial actinomycosis ('lumpy jaw') forming chronic, indurated, non-tender granulomatous abscesses with draining sinus tracts discharging sulfur granules, often following dental procedures; treated with high-dose IV Penicillin G for prolonged courses.

What virulence factor enables Staphylococcus epidermidis to adhere to prosthetic heart valves, orthopedic joints, and central IV catheters?

Extracellular polysaccharide biofilm (slime layer) production, which protects embedded bacteria from antibiotics and host phagocytic defenses.

What clinical food-borne illness syndromes are caused by Bacillus cereus?

Emetic type (nausea/vomiting 1–5 hours after eating reheated fried rice, mediated by preformed heat-stable cereulide toxin); Diarrheal type (watery diarrhea/cramping 8–18 hours later, mediated by heat-labile enterotoxin formed in gut).

What are the morphologic and staining differences between Nocardia asteroides and Actinomyces israelii?

Both are branching, filamentous Gram-positive rods. Nocardia is an aerobe and partially/weakly acid-fast (modified Ziehl-Neelsen positive). Actinomyces is a strict anaerobe, non-acid-fast, and forms visible yellow 'sulfur granules'.

What virulence factor of Staphylococcus aureus binds the Fc region of IgG to inhibit opsonization and phagocytosis?

Protein A. It prevents complement activation and Fc receptor-mediated phagocytosis by binding IgG antibodies in the reverse orientation.

What culture media are specifically used to grow and identify Corynebacterium diphtheriae?

Löffler coagulated serum medium (showing metachromatic granules on methylene blue) and Cystine-Tellurite blood agar (forming black/gray colonies). Toxin production is confirmed via the Elek immunodiffusion test.

Medical Microbiology — Gram-Positive Bacteria (Staph, Strep, Bacillus, Clostridium, Listeria)

Catalase, coagulase, hemolysis patterns, exotoxins, spore-formers, branching rods, and clinical syndromes of Gram-positive organisms.

Level: basic
Languages: en → en
Cards: 32
Markdown: Medical Microbiology — Gram-Positive Bacteria (Staph, Strep, Bacillus, Clostridium, Listeria) (.md)

Flashcards (32)

#	Front (Term / Question)	Back (Definition / Answer)
1	What patient demographic is classically affected by Staphylococcus saprophyticus urinary tract infections?	Young, sexually active females. It is the second most common cause of uncomplicated community-acquired outpatient UTIs after Escherichia coli.
2	What are the two primary exotoxins produced by Clostridioides difficile and their pathophysiologic mechanisms?	Toxin A (enterotoxin): Disrupts mucosal tight junctions, causing fluid secretion and extensive inflammation. Toxin B (cytotoxin): Depolymerizes actin filaments, causing mucosal cell death and pseudomembrane formation (pseudomembranous colitis).
3	What is the mechanism of Corynebacterium diphtheriae exotoxin?	Diphtheria toxin is an A-B exotoxin encoded by a beta-prophage (lysogenic conversion). Subunit A inactivates Elongation Factor-2 (EF-2) by ADP-ribosylation, arresting host cellular protein synthesis.
4	What are the laboratory characteristics and resistance challenges of Enterococcus faecalis and Enterococcus faecium?	Catalase-negative, gamma- or alpha-hemolytic, grow in 6.5% NaCl and 40% bile (bile-esculin positive). They exhibit intrinsic resistance to many beta-lactams and can acquire VanA plasmid-mediated resistance to Vancomycin (VRE), requiring Linezolid or Daptomycin.
5	Which patient populations are at high risk for invasive Listeria monocytogenes infection, and what is the preferred antibiotic?	Neonates, pregnant women, elderly, and immunocompromised patients (impaired cell-mediated immunity). Presents as meningitis or granulomatosis infantiseptica; treated with IV Ampicillin.
6	What antibiotic is most historically associated with Clostridioides difficile colitis, and what is first-line medical therapy today?	Historically Clindamycin (and fluoroquinolones/cephalosporins). First-line therapies for CDI are oral Fidaxomicin or oral Vancomycin (IV vancomycin does not reach therapeutic luminal colon concentrations).
7	What are the hallmark clinical manifestations of respiratory diphtheria?	Pharyngeal pseudomembrane (thick, gray, adherent fibrinous exudate that bleeds upon scraping), cervical lymphadenopathy ('bull neck'), myocarditis with arrhythmias, and neuropathies.
8	What test differentiates Staphylococcus aureus from coagulase-negative Staphylococci (Staph epidermidis and Staph saprophyticus)?	The Coagulase test. Staphylococcus aureus is coagulase-positive (converts fibrinogen to fibrin clot); S. epidermidis and S. saprophyticus are coagulase-negative.
9	What is the major virulence factor of Streptococcus pyogenes that inhibits complement activation and shares antigenic mimicry with human myocardium?	M protein. It prevents phagocytosis by degrading C3b; antibodies against M protein cross-react with cardiac myosin, causing Rheumatic Heart Disease (molecular mimicry).
10	How are Streptococcus pyogenes (Group A Strep) and Streptococcus agalactiae (Group B Strep) differentiated?	Both exhibit beta-hemolysis (complete clear zone). Streptococcus pyogenes is Bacitracin-sensitive and PYR-positive; Streptococcus agalactiae is Bacitracin-resistant and CAMP-test positive (enlarges Staph aureus beta-hemolysis arrowhead).
11	What clinical condition is strongly associated with Streptococcus gallolyticus (formerly Streptococcus bovis) bacteremia or endocarditis?	Occult colorectal neoplasia (adenoma or adenocarcinoma) or inflammatory bowel disease; colonoscopy is mandatory upon isolation from blood cultures.
12	What is the classic clinical presentation of Nocardia infection and its treatment of choice?	Pulmonary cavitary lesions (mimicking tuberculosis) in an immunocompromised host, with frequent dissemination to the brain forming cerebral ring-enhancing abscesses; treated with Trimethoprim-Sulfamethoxazole (TMP-SMX).
13	What initial biochemical test differentiates Staphylococcus species from Streptococcus species?	The Catalase test. Staphylococci are catalase-positive (produce bubbles with H2O2); Streptococci and Enterococci are catalase-negative.
14	What is the pathogenesis of Infant Botulism ('floppy baby syndrome') and how does it differ from Adult Botulism?	Infants ingest Clostridium botulinum spores (often from raw honey or dusty soil), which germinate in the immature colon and produce toxin in vivo. Adults ingest preformed botulinum toxin in improperly canned foods.
15	What is the mechanism of action of Clostridium tetani neurotoxin (tetanospasmin)?	Retrogradely transported via motor axons to spinal cord inhibitory interneurons (Renshaw cells); cleaves synaptobrevin (SNARE protein), blocking the release of inhibitory neurotransmitters GABA and glycine, producing spastic paralysis, trismus (lockjaw), and risus sardonicus.
16	What is the classic microscopic appearance and primary virulence factor of Streptococcus pneumoniae?	Lancet-shaped Gram-positive diplococci in pairs. Its primary virulence factor is a polysaccharide capsule, which inhibits phagocytosis (demonstrated by positive Quellung capsular reaction).
17	How are Staphylococcus epidermidis and Staphylococcus saprophyticus distinguished in the laboratory?	Novobiocin sensitivity testing: Staphylococcus epidermidis is Novobiocin-sensitive; Staphylococcus saprophyticus is Novobiocin-resistant ('NO Staph SAPs').
18	How are Streptococcus pneumoniae and Streptococcus viridans distinguished on blood agar and laboratory tests?	Both display alpha-hemolysis (partial greening). Streptococcus pneumoniae is Optochin-sensitive and bile-soluble; Viridans streptococci (e.g., S. mutans, S. mitis) are Optochin-resistant and bile-insoluble.
19	What is the mechanism of action of Toxic Shock Syndrome Toxin-1 (TSST-1) produced by Staphylococcus aureus?	TSST-1 functions as a superantigen that cross-links the MHC Class II receptor on antigen-presenting cells to the V-beta region of T-cell receptors, triggering massive, polyclonal T-cell activation and cytokine storm (IL-1, IL-2, TNF-alpha, IFN-gamma).
20	Which late non-suppurative complication of Streptococcus pyogenes follows pharyngitis but NOT impetigo?	Acute Rheumatic Fever follows only streptococcal pharyngitis. In contrast, Poststreptococcal Glomerulonephritis (PSGN) can develop after either pharyngeal or cutaneous streptococcal infection.
21	What clinical syndrome and classic chest radiograph findings characterize inhalation anthrax ('wool-sorters' disease')?	Inhalation of B. anthracis spores leads to hemorrhagic mediastinitis, widened mediastinum on chest X-ray, bilateral pleural effusions, rapid respiratory collapse, and septic shock.
22	What are the morphologic characteristics and two primary toxins of Bacillus anthracis?	Large, spore-forming, boxcar-shaped Gram-positive rod with a unique poly-D-glutamic acid polypeptide capsule. Produces Edema Factor (adenylyl cyclase that increases cAMP) and Lethal Factor (zinc metalloprotease that cleaves MAP kinase kinase).
23	What is the mechanism of action of Clostridium botulinum toxin and its classic clinical triad?	Cleaves SNARE proteins at presynaptic neuromuscular junctions, preventing acetylcholine release. Presents with symmetric descending flaccid paralysis, cranial nerve palsies (diplopia, dysphagia, dysarthria, ptosis), and clear sensorium.
24	What toxin is produced by Clostridium perfringens and what is its role in Gas Gangrene (clostridial myonecrosis)?	Alpha-toxin (lecithinase / phospholipase C). It degrades cell membrane phospholipids, causing widespread cell lysis, tissue necrosis, intravascular hemolysis, and gas production in muscle beds.
25	What temperature and motility characteristics distinguish Listeria monocytogenes?	Facultative intracellular Gram-positive motile rod that exhibits 'tumbling motility' at room temperature (22–25°C) and can multiply at refrigerated temperatures (4°C, 'cold enrichment'); forms 'rocket tails' by actin polymerization to move cell-to-cell.
26	What organism is the leading cause of neonatal sepsis, pneumonia, and meningitis, and when are pregnant women screened?	Streptococcus agalactiae (Group B Streptococcus / GBS). All pregnant individuals are screened at 36 0/7 to 37 6/7 weeks of gestation via rectovaginal swab; intrapartum IV Penicillin G or Ampicillin is administered if positive.
27	What clinical syndrome is caused by Actinomyces israelii, and what is its first-line antibiotic treatment?	Cervicofacial actinomycosis ('lumpy jaw') forming chronic, indurated, non-tender granulomatous abscesses with draining sinus tracts discharging sulfur granules, often following dental procedures; treated with high-dose IV Penicillin G for prolonged courses.
28	What virulence factor enables Staphylococcus epidermidis to adhere to prosthetic heart valves, orthopedic joints, and central IV catheters?	Extracellular polysaccharide biofilm (slime layer) production, which protects embedded bacteria from antibiotics and host phagocytic defenses.
29	What clinical food-borne illness syndromes are caused by Bacillus cereus?	Emetic type (nausea/vomiting 1–5 hours after eating reheated fried rice, mediated by preformed heat-stable cereulide toxin); Diarrheal type (watery diarrhea/cramping 8–18 hours later, mediated by heat-labile enterotoxin formed in gut).
30	What are the morphologic and staining differences between Nocardia asteroides and Actinomyces israelii?	Both are branching, filamentous Gram-positive rods. Nocardia is an aerobe and partially/weakly acid-fast (modified Ziehl-Neelsen positive). Actinomyces is a strict anaerobe, non-acid-fast, and forms visible yellow 'sulfur granules'.
31	What virulence factor of Staphylococcus aureus binds the Fc region of IgG to inhibit opsonization and phagocytosis?	Protein A. It prevents complement activation and Fc receptor-mediated phagocytosis by binding IgG antibodies in the reverse orientation.
32	What culture media are specifically used to grow and identify Corynebacterium diphtheriae?	Löffler coagulated serum medium (showing metachromatic granules on methylene blue) and Cystine-Tellurite blood agar (forming black/gray colonies). Toxin production is confirmed via the Elek immunodiffusion test.