What special culture medium is used to isolate Legionella pneumophila, and how is it commonly diagnosed at bedside?

Buffered Charcoal Yeast Extract (BCYE) agar supplemented with L-cysteine and iron. Rapidly diagnosed via the Legionella urinary antigen test (detects Legionella pneumophila serogroup 1).

What special growth factors are required by Haemophilus influenzae to grow on chocolate agar?

Factor X (hemin) and Factor V (NAD+). Can also grow on blood agar alongside Staphylococcus aureus ('satellitism'), which lyses RBCs to provide Factor X and secretes Factor V.

What is the characteristic motility and laboratory finding of Proteus mirabilis?

'Swarming motility' across blood agar plates; strongly urease-positive. Hydrolyzes urea to ammonia and CO2, raising urinary pH (>8.0) and precipitating magnesium ammonium phosphate (struvite / staghorn) calculi.

What are the clinical and microbiological distinctions between Salmonella enterica and Shigella dysenteriae?

Salmonella: Motile (flagella), produces H2S (black colonies on Hektoen agar), can cause bacteremia and osteomyelitis in sickle cell disease. Shigella: Non-motile, does not produce H2S, extremely low infectious dose (10–100 organisms), invades M cells of Peyer's patches, causes bloody bacillary dysentery.

What are the diagnostic tests used to identify Helicobacter pylori infection?

Stool antigen test, urea breath test (detects 13C-labeled CO2 exhaled after swallowing urea), and gastric mucosal biopsy with rapid urease testing (CLO test).

What is the clinical presentation and diagnostic hallmark of Enterohemorrhagic E. coli (EHEC / O157:H7)?

Bloody diarrhea (hemorrhagic colitis) without fever; Shiga-like toxin (verotoxin) inhibits the 60S ribosomal subunit. Can trigger Hemolytic Uremic Syndrome (HUS: microangiopathic hemolytic anemia, thrombocytopenia, acute renal failure); does not ferment sorbitol on MacConkey-sorbitol agar.

What is the classic clinical presentation, laboratory complication, and chest X-ray in Mycoplasma pneumoniae infection?

'Walking pneumonia' in military recruits and college students: dry hacking cough, bullous myringitis; CXR shows bilateral reticulonodular patchy infiltrates that look far worse than the clinical exam; high titers of cold agglutinins (IgM antibodies against RBC I-antigen) cause transient hemolysis.

What are the microbiological characteristics and pigments produced by Pseudomonas aeruginosa?

Gram-negative, obligate aerobe, oxidase-positive, catalase-positive, non-lactose fermenting rod with grape-like sweet odor. Produces blue-green pyocyanin and pyoverdine pigments, and exotoxin A (inactivates EF-2 like diphtheria toxin).

What severe cutaneous necrotic lesion is pathognomonic for Pseudomonas aeruginosa bacteremia in neutropenic patients?

Ecthyma gangrenosum: Rapidly progressing necrotic, ulcerated black eschar surrounded by an erythematous halo, caused by perivascular bacterial invasion and vascular thrombosis.

What are the microbiological features and classic clinical scenario of Klebsiella pneumoniae?

Encapsulated, non-motile, lactose-fermenting Gram-negative rod with a prominent mucoid capsule. Causes aspiration pneumonia in alcoholics and diabetics, presenting with thick 'currant jelly' sputum and cavitary right upper lobe infiltrates.

What is the Jarisch-Herxheimer reaction in the treatment of syphilis?

An acute, self-limiting febrile reaction with chills, headache, and myalgias occurring 2–24 hours after initiating Penicillin therapy, caused by massive release of endotoxin-like pyrogens from dying spirochetes.

Why are antibiotics contraindicated in acute Enterohemorrhagic E. coli (EHEC) infection?

Antibiotic therapy induces bacterial cell lysis and increases bacteriophage-mediated expression and release of Shiga-like toxin, significantly increasing the risk of developing Hemolytic Uremic Syndrome (HUS).

What is the difference between a Ghon focus and a Ranke (Ghon) complex in tuberculosis?

Ghon focus: Subpleural focus of caseating granulomatous inflammation in the mid-to-lower lung field. Ghon complex: Ghon focus combined with ipsilateral hilar lymph node calcification/involvement.

How are Gram-negative bacilli categorized based on lactose fermentation on MacConkey agar?

Fast lactose fermenters (pink colonies): Escherichia coli, Klebsiella pneumoniae, Enterobacter. Slow lactose fermenters: Citrobacter, Serratia. Non-lactose fermenters (white/colorless): Pseudomonas, Salmonella, Shigella, Proteus.

What are the three clinical stages of Lyme Disease (Borrelia burgdorferi) transmitted by Ixodes ticks?

Stage 1 (Early localized): Erythema migrans ('bull's-eye' rash), flu-like symptoms. Stage 2 (Early disseminated): Bilateral Bell's palsy, AV heart block, migratory arthralgias. Stage 3 (Late): Chronic asymmetric mono/oligoarthritis (knee), encephalopathy.

What organism is transmitted by dog and cat bites, and what rapid infection does it produce?

Pasteurella multocida (small Gram-negative coccobacillus with bipolar staining). Causes cellulitis with rapid onset (<24 hours) and potential osteomyelitis; treated with Amoxicillin-Clavulanate.

What are the characteristic extrapulmonary signs of Legionnaires' disease?

Atypical pneumonia accompanied by high fever, confusion/neurological signs, watery diarrhea/gastrointestinal symptoms, and marked hyponatremia (due to SIADH or renal tubule wasting).

What are the microbiological features and classic clinical presentation of Campylobacter jejuni?

Comma- or S-shaped Gram-negative rod, motile, oxidase-positive, grows at 42°C ('Campy loves the fire'). Transmitted via undercooked poultry; causes bloody inflammatory diarrhea; major trigger for Guillain-Barré syndrome and reactive arthritis.

What organism causes Cat-Scratch Disease and Bacillary Angiomatosis in HIV patients?

Bartonella henselae. In immunocompetent patients, causes subacute regional lymphadenopathy; in immunocompromised/AIDS patients, causes vascular proliferations resembling Kaposi sarcoma (bacillary angiomatosis).

What food ingestion and clinical risks are associated with Vibrio vulnificus?

Ingestion of raw oysters or exposure of open wounds to warm seawater, especially in patients with chronic liver disease/hemochromatosis. Causes fulminant septicemia with hemorrhagic bullous skin lesions and necrotizing fasciitis.

What clinical syndrome is caused by Bordetella pertussis and what are its three clinical phases?

Whooping cough (pertussis). 1. Catarrhal stage (mild URI, highly contagious); 2. Paroxysmal stage (violent coughing spasms with inspiratory 'whoop' and post-tussive emesis); 3. Convalescent stage (gradual recovery over months). Marked by prominent lymphocytosis.

What organism causes Weil Disease, and what are its clinical features and exposure history?

Leptospira interrogans (spirochete with hooked ends). Transmitted through water contaminated with infected animal (rodent) urine. Weil disease is severe leptospirosis: jaundice, acute renal failure, hepatic dysfunction, and pulmonary hemorrhage.

What is the intracellular mechanism of Pertussis toxin?

ADP-ribosylates and disables the Gi protein subunit, preventing inhibition of adenylyl cyclase, leading to elevated intracellular cAMP, impaired neutrophil chemotaxis, and massive lymphocytosis.

What is the difference between non-treponemal (VDRL, RPR) and treponemal tests (FTA-ABS, TP-PA) for syphilis?

Non-treponemal (VDRL/RPR) tests detect anticardiolipin antibodies; used for screening and monitoring treatment response (titers fall after therapy), but have false positives (SLE, pregnancy, leprosy). Treponemal tests detect specific treponemal antibodies; remain positive for life.

What virulence factor of Neisseria meningitidis correlates directly with the severity of septic shock and DIC (Waterhouse-Friderichsen syndrome)?

Lipooligosaccharide (LOS), an endotoxin that sheds outer membrane blebs, triggering massive inflammatory cytokines, petechial/purpuric rash, DIC, and bilateral adrenal hemorrhage.

What are the clinical manifestations of Primary, Secondary, and Tertiary Syphilis?

Primary: Painless indurated genital chancre. Secondary: Diffuse maculopapular rash including palms and soles, condylomata lata. Tertiary: Gummas, thoracic aortic aneurysm (obliterative endarteritis of vasa vasorum), tabes dorsalis, Argyll Robertson pupils.

What are the key microbiological characteristics of Neisseria meningitidis versus Neisseria gonorrhoeae?

Both are oxidase-positive Gram-negative diplococci growing on Thayer-Martin medium. N. meningitidis ferment maltose and glucose and possess a polysaccharide capsule. N. gonorrhoeae ferments only glucose, lacks a capsule, and has hypervariable pili.

What organism causes Cholera, and what is the intracellular mechanism of Cholera toxin?

Vibrio cholerae (curved, comma-shaped Gram-negative rod growing on TCBS agar). Cholera toxin permanently ADP-ribosylates Gs-alpha, continuously stimulating adenylyl cyclase to increase cAMP, opening CFTR channels and producing massive secretory 'rice-water' diarrhea.

Why are beta-lactam antibiotics completely ineffective against Mycoplasma pneumoniae?

Mycoplasma pneumoniae completely lacks a peptidoglycan cell wall; its cell membrane contains sterols (cholesterol) acquired from the host. Beta-lactams that target peptidoglycan synthesis have no drug target.

What makes Mycobacterium tuberculosis acid-fast on Ziehl-Neelsen staining?

High content of mycolic acids (long-chain beta-hydroxy fatty acids) and complex lipids in the cell wall, which resist decolorization with acid-alcohol.

What organism causes Tularemia and what are its classic reservoirs and vectors?

Francisella tularensis (highly infectious intracellular Gram-negative coccobacillus). Reservoirs are wild rabbits, hares, and rodents; vectors include Dermacentor ticks and deer flies; causes ulceroglandular disease.

What organism causes Syphilis and what microscopic technique is used to view it from a primary chancre?

Treponema pallidum (spirochete). Visualized directly using Darkfield Microscopy or direct fluorescent antibody (DFA) staining, because it cannot be cultured on standard bacteriologic media.

Medical Microbiology — Gram-Negative Bacteria, Enterics, Spirochetes, Mycobacteria & Atypicals

Lactose fermenters, zoonoses, enteric pathogens, spirochetal staging, Mycobacterium tuberculosis pathogenesis, and cell-wall deficient atypical bacteria.

Level: basic
Languages: en → en
Cards: 32
Markdown: Medical Microbiology — Gram-Negative Bacteria, Enterics, Spirochetes, Mycobacteria & Atypicals (.md)

Flashcards (32)

#	Front (Term / Question)	Back (Definition / Answer)
1	What special culture medium is used to isolate Legionella pneumophila, and how is it commonly diagnosed at bedside?	Buffered Charcoal Yeast Extract (BCYE) agar supplemented with L-cysteine and iron. Rapidly diagnosed via the Legionella urinary antigen test (detects Legionella pneumophila serogroup 1).
2	What special growth factors are required by Haemophilus influenzae to grow on chocolate agar?	Factor X (hemin) and Factor V (NAD+). Can also grow on blood agar alongside Staphylococcus aureus ('satellitism'), which lyses RBCs to provide Factor X and secretes Factor V.
3	What is the characteristic motility and laboratory finding of Proteus mirabilis?	'Swarming motility' across blood agar plates; strongly urease-positive. Hydrolyzes urea to ammonia and CO2, raising urinary pH (>8.0) and precipitating magnesium ammonium phosphate (struvite / staghorn) calculi.
4	What are the clinical and microbiological distinctions between Salmonella enterica and Shigella dysenteriae?	Salmonella: Motile (flagella), produces H2S (black colonies on Hektoen agar), can cause bacteremia and osteomyelitis in sickle cell disease. Shigella: Non-motile, does not produce H2S, extremely low infectious dose (10–100 organisms), invades M cells of Peyer's patches, causes bloody bacillary dysentery.
5	What are the diagnostic tests used to identify Helicobacter pylori infection?	Stool antigen test, urea breath test (detects 13C-labeled CO2 exhaled after swallowing urea), and gastric mucosal biopsy with rapid urease testing (CLO test).
6	What is the clinical presentation and diagnostic hallmark of Enterohemorrhagic E. coli (EHEC / O157:H7)?	Bloody diarrhea (hemorrhagic colitis) without fever; Shiga-like toxin (verotoxin) inhibits the 60S ribosomal subunit. Can trigger Hemolytic Uremic Syndrome (HUS: microangiopathic hemolytic anemia, thrombocytopenia, acute renal failure); does not ferment sorbitol on MacConkey-sorbitol agar.
7	What is the classic clinical presentation, laboratory complication, and chest X-ray in Mycoplasma pneumoniae infection?	'Walking pneumonia' in military recruits and college students: dry hacking cough, bullous myringitis; CXR shows bilateral reticulonodular patchy infiltrates that look far worse than the clinical exam; high titers of cold agglutinins (IgM antibodies against RBC I-antigen) cause transient hemolysis.
8	What are the microbiological characteristics and pigments produced by Pseudomonas aeruginosa?	Gram-negative, obligate aerobe, oxidase-positive, catalase-positive, non-lactose fermenting rod with grape-like sweet odor. Produces blue-green pyocyanin and pyoverdine pigments, and exotoxin A (inactivates EF-2 like diphtheria toxin).
9	What severe cutaneous necrotic lesion is pathognomonic for Pseudomonas aeruginosa bacteremia in neutropenic patients?	Ecthyma gangrenosum: Rapidly progressing necrotic, ulcerated black eschar surrounded by an erythematous halo, caused by perivascular bacterial invasion and vascular thrombosis.
10	What are the microbiological features and classic clinical scenario of Klebsiella pneumoniae?	Encapsulated, non-motile, lactose-fermenting Gram-negative rod with a prominent mucoid capsule. Causes aspiration pneumonia in alcoholics and diabetics, presenting with thick 'currant jelly' sputum and cavitary right upper lobe infiltrates.
11	What is the Jarisch-Herxheimer reaction in the treatment of syphilis?	An acute, self-limiting febrile reaction with chills, headache, and myalgias occurring 2–24 hours after initiating Penicillin therapy, caused by massive release of endotoxin-like pyrogens from dying spirochetes.
12	Why are antibiotics contraindicated in acute Enterohemorrhagic E. coli (EHEC) infection?	Antibiotic therapy induces bacterial cell lysis and increases bacteriophage-mediated expression and release of Shiga-like toxin, significantly increasing the risk of developing Hemolytic Uremic Syndrome (HUS).
13	What is the difference between a Ghon focus and a Ranke (Ghon) complex in tuberculosis?	Ghon focus: Subpleural focus of caseating granulomatous inflammation in the mid-to-lower lung field. Ghon complex: Ghon focus combined with ipsilateral hilar lymph node calcification/involvement.
14	How are Gram-negative bacilli categorized based on lactose fermentation on MacConkey agar?	Fast lactose fermenters (pink colonies): Escherichia coli, Klebsiella pneumoniae, Enterobacter. Slow lactose fermenters: Citrobacter, Serratia. Non-lactose fermenters (white/colorless): Pseudomonas, Salmonella, Shigella, Proteus.
15	What are the three clinical stages of Lyme Disease (Borrelia burgdorferi) transmitted by Ixodes ticks?	Stage 1 (Early localized): Erythema migrans ('bull's-eye' rash), flu-like symptoms. Stage 2 (Early disseminated): Bilateral Bell's palsy, AV heart block, migratory arthralgias. Stage 3 (Late): Chronic asymmetric mono/oligoarthritis (knee), encephalopathy.
16	What organism is transmitted by dog and cat bites, and what rapid infection does it produce?	Pasteurella multocida (small Gram-negative coccobacillus with bipolar staining). Causes cellulitis with rapid onset (<24 hours) and potential osteomyelitis; treated with Amoxicillin-Clavulanate.
17	What are the characteristic extrapulmonary signs of Legionnaires' disease?	Atypical pneumonia accompanied by high fever, confusion/neurological signs, watery diarrhea/gastrointestinal symptoms, and marked hyponatremia (due to SIADH or renal tubule wasting).
18	What are the microbiological features and classic clinical presentation of Campylobacter jejuni?	Comma- or S-shaped Gram-negative rod, motile, oxidase-positive, grows at 42°C ('Campy loves the fire'). Transmitted via undercooked poultry; causes bloody inflammatory diarrhea; major trigger for Guillain-Barré syndrome and reactive arthritis.
19	What organism causes Cat-Scratch Disease and Bacillary Angiomatosis in HIV patients?	Bartonella henselae. In immunocompetent patients, causes subacute regional lymphadenopathy; in immunocompromised/AIDS patients, causes vascular proliferations resembling Kaposi sarcoma (bacillary angiomatosis).
20	What food ingestion and clinical risks are associated with Vibrio vulnificus?	Ingestion of raw oysters or exposure of open wounds to warm seawater, especially in patients with chronic liver disease/hemochromatosis. Causes fulminant septicemia with hemorrhagic bullous skin lesions and necrotizing fasciitis.
21	What clinical syndrome is caused by Bordetella pertussis and what are its three clinical phases?	Whooping cough (pertussis). 1. Catarrhal stage (mild URI, highly contagious); 2. Paroxysmal stage (violent coughing spasms with inspiratory 'whoop' and post-tussive emesis); 3. Convalescent stage (gradual recovery over months). Marked by prominent lymphocytosis.
22	What organism causes Weil Disease, and what are its clinical features and exposure history?	Leptospira interrogans (spirochete with hooked ends). Transmitted through water contaminated with infected animal (rodent) urine. Weil disease is severe leptospirosis: jaundice, acute renal failure, hepatic dysfunction, and pulmonary hemorrhage.
23	What is the intracellular mechanism of Pertussis toxin?	ADP-ribosylates and disables the Gi protein subunit, preventing inhibition of adenylyl cyclase, leading to elevated intracellular cAMP, impaired neutrophil chemotaxis, and massive lymphocytosis.
24	What is the difference between non-treponemal (VDRL, RPR) and treponemal tests (FTA-ABS, TP-PA) for syphilis?	Non-treponemal (VDRL/RPR) tests detect anticardiolipin antibodies; used for screening and monitoring treatment response (titers fall after therapy), but have false positives (SLE, pregnancy, leprosy). Treponemal tests detect specific treponemal antibodies; remain positive for life.
25	What virulence factor of Neisseria meningitidis correlates directly with the severity of septic shock and DIC (Waterhouse-Friderichsen syndrome)?	Lipooligosaccharide (LOS), an endotoxin that sheds outer membrane blebs, triggering massive inflammatory cytokines, petechial/purpuric rash, DIC, and bilateral adrenal hemorrhage.
26	What are the clinical manifestations of Primary, Secondary, and Tertiary Syphilis?	Primary: Painless indurated genital chancre. Secondary: Diffuse maculopapular rash including palms and soles, condylomata lata. Tertiary: Gummas, thoracic aortic aneurysm (obliterative endarteritis of vasa vasorum), tabes dorsalis, Argyll Robertson pupils.
27	What are the key microbiological characteristics of Neisseria meningitidis versus Neisseria gonorrhoeae?	Both are oxidase-positive Gram-negative diplococci growing on Thayer-Martin medium. N. meningitidis ferment maltose and glucose and possess a polysaccharide capsule. N. gonorrhoeae ferments only glucose, lacks a capsule, and has hypervariable pili.
28	What organism causes Cholera, and what is the intracellular mechanism of Cholera toxin?	Vibrio cholerae (curved, comma-shaped Gram-negative rod growing on TCBS agar). Cholera toxin permanently ADP-ribosylates Gs-alpha, continuously stimulating adenylyl cyclase to increase cAMP, opening CFTR channels and producing massive secretory 'rice-water' diarrhea.
29	Why are beta-lactam antibiotics completely ineffective against Mycoplasma pneumoniae?	Mycoplasma pneumoniae completely lacks a peptidoglycan cell wall; its cell membrane contains sterols (cholesterol) acquired from the host. Beta-lactams that target peptidoglycan synthesis have no drug target.
30	What makes Mycobacterium tuberculosis acid-fast on Ziehl-Neelsen staining?	High content of mycolic acids (long-chain beta-hydroxy fatty acids) and complex lipids in the cell wall, which resist decolorization with acid-alcohol.
31	What organism causes Tularemia and what are its classic reservoirs and vectors?	Francisella tularensis (highly infectious intracellular Gram-negative coccobacillus). Reservoirs are wild rabbits, hares, and rodents; vectors include Dermacentor ticks and deer flies; causes ulceroglandular disease.
32	What organism causes Syphilis and what microscopic technique is used to view it from a primary chancre?	Treponema pallidum (spirochete). Visualized directly using Darkfield Microscopy or direct fluorescent antibody (DFA) staining, because it cannot be cultured on standard bacteriologic media.