Chapter 20

• Vibrio are commonly found in aquatic environments
• Four Vibrio spp. most commonly isolated

  • V. cholerae
  • V. parahaemolyticus
  • V. vulnificus
  • V. alginolyticus

  
• Factors of a possible Vibrio infection

  • Recent consumption of raw seafood (oysters)
  • Recent immigration or foreign travel
  • Gastroenteritis with cholera-like or rice-water stools
  • Accidental trauma during contact with fresh, estuarine, or marine water or associated products
• Vibrio

  • Asporogenous, "curved" gram-negative rods
  • Possess polar, sheathed flagella (broth) or peritrichous, unsheathed flagella (solid media)
• Vibrio


  • Oxidase positive
  • Able to reduce nitrate to nitrite
  • Susceptible to vibriostatic compound O/129 (150μg)
  • Positive string test (mucoid "stringing" reaction with 0.5% sodium desoxycholate)
  • Halophilic (except for V. cholerae and V. mimicus)
• Three major subgroups of V. cholerae


  • V. cholerae O1
  • V. cholerae O139
  • V. cholerae non-O1

  
• Serotypes of V. cholerae O1


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

  
• Cholera


  Acute diarrheal disease spread mainly through contaminated water (also improperly preserved and handled foods)

  
• Cholera toxin or choleragen


  Enterotoxin produced by V. cholerae that stimulates production of adenylate cyclase, leading to accumulation of cAMP and hypersecretion of electrolytes and water out of the cell

  
• Two biogroups of epidemic V. cholerae O1 strains


  • Classic
  • El Tor

  
• V. parahaemolyticus


  Second most common species implicated in gastroenteritis, number one cause of "summer diarrhea" in Japan
• Kanagawa phenomenon


  Virulence of V. parahaemolyticus is associated with the production of heat-stable hemolysin that lyses human RBCs in Wagatsuma agar
• V. vulnificus

  "Lactose-positive" Vibrio, second most serious type of Vibrio-associated infections, causes primary septicemia and wound infections
• V. alginolyticus


  Least pathogenic, most infrequently isolated, strict halophile (at least 1% NaCl)
• Laboratory diagnosis of Vibrio

  • Vibrios are non-fastidious
  • Culture medium should contain at least 0.5% salt
  • SBA or CHOC: Medium to large colonies that are smooth, opaque, and iridescent with a greenish hue
  • MAC: Nonlactose-fermenters except V. vulnificus
  • TCBS agar differentiates sucrose-fermenting (yellow) and nonsucrose-fermenting (green) species
• Organisms that can be confused with Vibrio

  • Aeromonas
  • Plesiomonas
  • Enterobacteriaceae
  • Pseudomonas
• Aeromonas


  • Ubiquitous, oxidase-positive, glucose-fermenting, gram-negative rods
  • Straight rods, most are motile by means of a single polar flagellum
  • Two groups: mesophilic (37°C) and psychrophilic (22° to 25°C)
• Diarrheal presentations of Aeromonas infections


  • Acute, secretory diarrhea with vomiting
  • Acute, dysenteric form similar to shigellosis
  • Chronic diarrhea lasting more than 10 days
  • Cholera-like disease
  • Nebulous syndrome referred as "traveler's diarrhea"
• Aeromonas colonies


  • Large round, raised, opaque colonies with an entire edge and a smooth, mucoid surface
  • Extremely strong odor
  • Pigmentation ranges from translucent and white to buff colored
• Plesiomonas


  Oxidase-positive, glucose-fermenting, facultatively anaerobic, gram-negative bacilli, motile by polar flagella, only oxidase-positive member of Enterobacteriaceae
• Clinical types of Plesiomonas gastroenteritis

  • More common watery or secretory diarrhea
  • Subacute or chronic disease (14 days to 2-3 months)
  • More invasive, dysenteric form
• Plesiomonas


  • Straight, gram-negative bacilli, do not form spores or capsules, motile by monotrichous or 2-5 lophotrichous flagella, shares identical biochemical and antigenic features with Shigella
• Campylobacter


  Known to cause abortion in domestic animals, Campylobacter jejuni is the most common cause of bacterial gastroenteritis worldwide, transmission is through direct contact with animals or consumption of contaminated water and food, plays a role in Guillain-Barré syndrome
• Helicobacter pylori


  Major cause of type B gastritis (chronic superficial gastritis), important risk factor for gastric carcinoma
• Laboratory diagnosis of Campylobacter and Helicobacter

  • Buffered glycerol-saline is toxic for transport
  • Tissue samples may be transported in cysteine-Brucella broth with 20% glycerol and frozen at -70°C
  • Culture media for Campylobacter: CAMPY-BAP, Butzler medium, Skirrow's medium, CCDA
  • Incubation for Campylobacter: 42°C for C. jejuni, 37°C for C. fetus subsp. fetus, in microaerophilic and capnophilic environment
  • Presumptive identification of Campylobacter: curved, non-spore forming rods
• Campylobacter

  Plays a role in Guillain-Barré syndrome (acute paralysis)
• Helicobacter pylori


  • Major cause of type B gastritis (chronic superficial gastritis)
  • Important risk factor for gastric carcinoma
• Laboratory Diagnosis

  1. C. fetus subsp. fetus – Blood culture

  2. Campylobacter spp. that cause enteric illness – Stool

  3. Buffered glycerol-saline is toxic

  4. H. pylori – Gastric biopsy

  5. Tissue samples may be transported in cysteine-Brucella broth with 20% glycerol and frozen at -70°C
• Culture Media (Campylobacter)

  • CAMPY-BAP: contains Brucella agar base, 10% SRBCs, and antimicrobials
  • Butzler medium
  • Skirrow's medium
  • CCDA (Charcoal cefoperazone deoxycholate agar)
• Incubation

  1. C. jejuni – 42°C

  2. C. fetus subsp. fetus – 37°C

  3. Microaerophilic and capnophilic environment

  4. Campylobacter – 5% O2, 10% CO2, 85% N2

  5. Helicobacter – 5% to 10% O2 and 5% to 12% CO2
• Campylobacter


  • Curved, non-spore-forming, gram-negative rods
  • Enteric campylobacters – long spirals, S shapes, or seagull-wings shape
  • Carbolfuchsin is recommended as a counterstain
  • "Darting" motility
  • Moist, "runny-looking," and spreading colonies; nonhemolytic; some are tan or slightly pink
• Definitive Identification (Campylobacter)

  1. Oxidase positive

  2. Motility: Brucella or tryptic soy broth

  3. Positive hippurate hydrolysis
• Definitive Identification (Helicobacter)

  1. Rapid urease reaction

  2. Christensen's urea medium and incubate at 37°C for 2 hrs

  3. Urea breath test (13C or 14C-labeled urea orally)

  4. 13CO2 or 14CO2 in exhaled breath is detected by scintillation counter
• Nonfermenting and Miscellaneous Gram-Negative Bacilli

  • They fail to acidify O-F media when overlaid with mineral oil or fail to acidify TSI agar
  • Oxidizers – oxidize carbohydrates
  • Nonoxidizers or asaccharolytic – inert or biochemically inactive
  • Motile
  • Pigmentation
  • Most are oxidase positive
  • Ubiquitous (moist environments)
• Risk factors for clinical infections

  • Immunosuppression
  • Trauma
  • Foreign body implantation
  • Infused fluids
• Biochemical Characteristics and Identification

  • Thin, gram-negative bacilli or coccobacilli
  • Oxidase positive
  • Nonreactivity in 24 hrs in commercial systems for Enterobacteriaceae
  • No acid production in the slant or butt of TSI or KIA
  • Resistance to a variety of antimicrobial agents
• Clinically Significant Nonfermentative Gram-Negative Bacilli

  • Fluorescent Pseudomonad Group
  • Acinetobacter
  • Stenotrophomonas maltophilia
  • Burkholderia
  • Moraxella and Oligella
• Pseudomonas


  • Gram-negative bacilli or coccobacilli
  • Motile with polar or polar tufts of flagella except Burkholderia mallei
  • Oxidase and catalase positive
  • Grows on MAC
  • Oxidizer or asaccharolytic
• Pseudomonas aeruginosa


  • Most commonly isolated species
  • Leading cause of nosocomial respiratory tract infections
• Clinical disease (Pseudomonas aeruginosa)

  • Bacteremia with ecthyma gangrenosum of the skin
  • Wound infections
  • Pulmonary disease (CF)
  • Nosocomial UTI
  • Endocarditis
  • Burn or trauma infections