Vibrio, Aeromonas, Campylobacter and Campylobacter like species

What family does the genus Vibrio belong to?

Vibrionaceae

What key biochemical characteristics define Vibrio species?

Oxidase-positive, glucose-fermenting, gram-negative bacilli.

On which agar can Vibrio grow?

MacConkey agar.

What environments are typical reservoirs for Vibrio species?

Freshwater, brackish/estuarine water, and marine/saltwater environments.

What is a major risk factor for acquiring Vibrio infections?

Consumption of raw or undercooked shellfish (especially oysters), especially in warmer months.

What are the four Vibrio species most often encountered clinically?

V. cholerae (O1 and non-O1), V. parahaemolyticus, V. vulnificus, and V. alginolyticus.

What is the typical shape of Vibrio species under microscopy?

Curved (comma-shaped), gram-negative rods; highly pleomorphic.

Are Vibrio species facultative or obligate anaerobes?

Facultative anaerobes.

What is the oxidase and catalase result for most Vibrio species?

Positive for both.

Which Vibrio species is negative for oxidase, catalase, and nitrate reduction?

Vibrio metschnikovii.

Do Vibrio ferment inositol?

No, they do not ferment inositol.

What is the purpose of the string test in Vibrio identification?

To detect a mucoid “stringing” reaction with 0.5% sodium desoxycholate—positive in Vibrio spp.

Which Vibrio species are not halophilic?

V. cholerae and V. mimicus.

What vibriostatic compound is used to differentiate Vibrio spp.?

O/129 (2,4-diamino-6,7-diisopropylpteridine).

What media can be used for O/129 susceptibility testing?

Mueller-Hinton or trypticase soy agar.

A fisherman sustains a cut while handling oysters and develops a rapidly spreading wound infection. What organism should be suspected?

Vibrio vulnificus.

A traveler from a coastal region presents with rice-water stools and severe dehydration. What is the likely diagnosis?

Cholera due to Vibrio cholerae O1.

A patient presents with gastroenteritis after eating raw oysters. What Vibrio species is most likely responsible?

Vibrio parahaemolyticus.

Which Vibrio species is associated with rapidly progressing sepsis in patients with liver disease or immunosuppression?

Vibrio vulnificus.

What disease is caused by Vibrio cholerae?

Cholera, a severe diarrheal disease.

What is the route of transmission for V. cholerae?

Fecal-oral route, often due to poor sanitation.

What toxin is responsible for the watery diarrhea in cholera?

Cholera toxin (CT or choleragen).

What is the hallmark stool appearance in cholera?

“Rice water stools” (fluid with mucous flecks).

What pili help V. cholerae attach to mucosal cells?

Toxin-coregulated pili (TCP).

What does the zona occludens toxin (Zot) do?

Disrupts tight junctions in intestinal epithelium, increasing permeability.

What is the incubation period of cholera?

1–4 days.

What are the three major subgroups of V. cholerae?

O1, O139, and non-O1/non-O139.

Which subgroups are associated with epidemics and pandemics?

O1 and O139.

What are the O1 serotypes of V. cholerae?

Ogawa (A, B), Inaba (A, C), Hikojima (A, B, C).

What are the two biotypes of V. cholerae O1?

Classic and El Tor.

Which biotype of V. cholerae is more virulent and widespread?

El Tor.

Name 3 characteristics of the El Tor biotype.

Hemolysin producer, VP positive, polymyxin B resistant.

What medium is used to transport stool samples suspected of Vibrio?

Cary-Blair medium.

What kind of stool sample is preferred for Vibrio cholerae culture?

Mucous flecks from stool.

Name 2 rapid tests for cholera toxin in stool.

ELISA, Latex agglutination (e.g., SMART II Cholera O1).

What is the motility type of V. cholerae under the microscope?

Rapid, darting (“shooting-star”) motility.

What is the selective medium for Vibrio isolation?

TCBS agar (Thiosulfate Citrate Bile Salts Sucrose).

What is the colony appearance of V. cholerae on TCBS agar?

Yellow colonies (sucrose fermentation).

What is the purpose of the string test?

To differentiate Vibrio (positive) from Aeromonas (negative).

What modern technologies can rapidly identify Vibrio species?

MALDI-TOF MS, VITEK MS.

What medium is used for enrichment before plating on TCBS?

Alkaline Peptone Water (pH 8.5 with 1% NaCl).

What is the most common presentation of V. parahaemolyticus infection?

Gastroenteritis (self-limiting).

What symptoms are seen in V. parahaemolyticus gastroenteritis?

Watery diarrhea, cramps, vomiting, mild/no fever.

What region is known for summer diarrhea due to V. parahaemolyticus?

Japan.

What pandemic strain of V. parahaemolyticus caused global outbreaks?

O3:K6.

What is the salt requirement for V. parahaemolyticus growth?

1%–8% NaCl.

What foods are common sources of V. parahaemolyticus infection?

Oysters, clams, shrimp, crabs, scallops, sardines.

What virulence test is used for V. parahaemolyticus?

Kanagawa phenomenon (hemolysis on Wagatsuma agar).

What are the two main clinical presentations of V. vulnificus infection?

Primary septicemia and wound infections.

How is primary septicemia acquired?

Consumption of raw/undercooked shellfish, especially oysters.

What history is common in V. vulnificus wound infections?

Trauma with aquatic exposure (e.g., fishhooks, saltwater cuts).

What serious complication can result from wound infection?

Necrotizing fasciitis, multi-organ failure.

What is the fatality rate for wound-related infections with V. vulnificus?

20%–30%.

What lab tests are used for diagnosing V. vulnificus?

Blood cultures, Gram stain, creatine kinase.

Which Vibrio species is the least pathogenic to humans?

Vibrio alginolyticus.

What is the NaCl requirement for V. alginolyticus?

Requires ≥1% NaCl; tolerates up to 10%.

What types of infections are caused by V. alginolyticus?

Extraintestinal: ear, eye, wound, and burn infections.

What is the gram stain and morphology of Aeromonas spp.?

Gram-negative straight rods or coccobacilli, occurring singly, in pairs, or short chains.

Are Aeromonas spp. oxidase and catalase positive or negative?

Both oxidase-positive and catalase-positive.

What type of hemolysis is observed with Aeromonas on blood agar?

β-hemolysis.

At what temperature do motile strains of Aeromonas grow best?

37°C

At what temperature do nonmotile Aeromonas strains grow best?

22°C

What are common sources of Aeromonas spp. in the environment?

Freshwater, estuarine and marine environments, and animal meat products.

What is the indole reaction of Aeromonas spp.?

Indole positive.

Which species is most often linked to gastrointestinal infections in neonates and children?

Aeromonas caviae

A child has blood and mucus in stool, and culture yields β-hemolytic, oxidase-positive rods. What is the likely pathogen?

Aeromonas spp.

What are common complications of Aeromonas infections?

Hemolytic-uremic syndrome (HUS) and kidney disease.

Name three Aeromonas species commonly isolated from wounds.

A. hydrophila subsp. hydrophila, A. veronii, and A. dhakensis.

Which test can help differentiate Aeromonas from Plesiomonas?

Inositol fermentation: Aeromonas is negative; Plesiomonas is positive.

On CIN agar, how can Aeromonas be misidentified?

It may be mistaken for Yersinia enterocolitica; use oxidase test to differentiate (Aeromonas is oxidase positive).

Which carbohydrate does Aeromonas ferment to distinguish it from Pseudomonas?

Glucose (Aeromonas ferments it; Pseudomonas does not).

What medium can differentiate Aeromonas using D-xylose?

Aeromonas agar.

What is the morphology and oxygen requirement of Chromobacterium violaceum?

Facultatively anaerobic, motile, gram-negative rod or cocci.

What is the natural habitat of Chromobacterium violaceum?

Soil and water.

What is a key pigment produced by Chromobacterium violaceum?

Violacein – a violet pigment.

What odor is associated with Chromobacterium violaceum colonies?

Almond or ammonium cyanide-like odor.

What serious infections can Chromobacterium violaceum cause?

Cellulitis progressing to systemic abscesses and septic shock.

A wound exposed to tropical soil becomes purple-pigmented and necrotic. What rare organism should be suspected?

Chromobacterium violaceum

What is the only species of Plesiomonas?

Plesiomonas shigelloides

Is Plesiomonas shigelloides oxidase-positive or negative?

Oxidase-positive.

How does Plesiomonas shigelloides differ from most Enterobacteriaceae?

It does not produce gas from glucose and is oxidase-positive.

What is the primary clinical presentation of Plesiomonas shigelloides?

Diarrheal illness.

What are the three types of gastroenteritis caused by Plesiomonas shigelloides?

Secretory/watery, subacute/chronic, and dysenteric colitis-like diarrhea

What environments are Plesiomonas shigelloides typically found in?

Soil and aquatic environments

What is the morphology of Plesiomonas under a microscope?

Gram-negative bacilli in singles, pairs, chains, or filamentous forms.

What type of flagella does Plesiomonas use for motility?

Monotrichous or lophotrichous flagella.

Can Plesiomonas ferment lactose?

Yes.

What selective agar can be used to isolate Plesiomonas?

Inositol brilliant green bile agar.

How do Plesiomonas colonies appear on inositol brilliant green bile agar?

White to pink.

What appearance do Plesiomonas colonies have on CIN agar?

Opaque colonies with an apron-like appearance.

Is Plesiomonas shigelloides susceptible or resistant to ampicillin?

Susceptible.

A returning traveler develops watery diarrhea, and the stool culture reveals oxidase-positive, lactose-fermenting gram-negative rods. What is a likely pathogen?

Plesiomonas shigelloides

What is the gram stain and morphology of Campylobacter spp.?

Gram-negative, small curved or seagull-winged bacilli.

Are Campylobacter spp. motile? If yes, what type of motility do they show?

Yes, they exhibit “darting” motility.

Are Campylobacter spp. oxidase and catalase positive?

Yes, most are oxidase- and catalase-positive.

What is the oxygen requirement for Campylobacter spp.?

Microaerophilic (5–10% O₂).

Are Campylobacter spp. asaccharolytic or saccharolytic?

Asaccharolytic (do not ferment sugars).

What are common sources of human infection with C. jejuni and C. coli?

Contaminated food (especially undercooked chicken), water, and unpasteurized milk.

What animals may carry Campylobacter spp.?

Poultry, cattle, sheep, pigs, and domestic pets.

Which Campylobacter species have humans as the only known reservoir?

C. concisus, C. rectus, C. curvus, C. showae.