Vibrio, Aeromonas & Plesiomonas
Similarities to Enterobacteriaceae Gram-negative Facultative anaerobes Fermentative bacilli Differences from Enterobacteriaceae Polar flagella Oxidase positive Formerly classified together as Vibrionaceae Primarily found in water sources Cause gastrointestinal disease Shown not closely related by molecular methods General Characteristics of Vibrio, Aeromonas and Plesiomonas
Comma-shaped (vibrioid) bacilli V. cholerae, V. parahaemolyticus, V. vulnificus are most significant human pathogens Broad temperature & pH range for growth on media 18-37 C pH 7.0 - 9.0 (useful for enrichment) Grow on variety of simple media including: MacConkey’s agar TCBS ( T hiosulfate C itrate B ile salts S ucrose) agar V. cholerae grow without salt Most other vibrios are halophilic Morphology & Physiology of Vibrio
Vibrio spp. (Family Vibrionaceae) Associated with Human Disease
Vibrio spp. (including V. cholerae ) grow in estuarine and marine environments worldwide All Vibrio spp. can survive and replicate in contaminated waters with increased salinity and at temperatures of 10-30 o C Pathogenic Vibrio spp. appear to form symbiotic (?) associations with chitinous shellfish which serve as an important and only recently recognized reservoir Asymptomatically infected humans also serve as an important reservoir in regions where cholera is endemic Epidemiology of Vibrio spp.
Taxonomy of Vibrio cholerae >200 serogroups based on somatic O-antigen O1 and O139 serogroups are responsible for classic epidemic cholera O1 serogroup subdivided into Two biotypes: El Tor and classical (or cholerae ) Three serotypes: ogawa, inaba, hikojima Some O1 strains do not produce cholera enterotoxin (atypical or nontoxigenic O1 V. cholerae ) Other strains are identical to O1 strains but do not agglutinate in O1 antiserum (non-cholera (NCV) or non-agglutinating(NAG) vibrios) (non-O1 V.cholerae ) Several phage types
Epidemiology of Vibrio cholerae Cholera recognized for more than two millennia with sporadic disease and epidemics Endemic in regions of Southern and Southeastern Asia; origin of pandemic cholera outbreaks Generally in communities with poor sanitation Seven pandemics (possible beginning of 8 th ) since 1817 attributable to increased world travel Cholera spread by contaminated water and food Human carriers and environmental reservoirs
Recent Cholera Pandemics 7 th pandemic: V. cholerae O1 biotype El Tor Began in Asia in 1961 Spread to other continents in 1970s and 1980s Spread to Peru in 1991 and then to most of South & Central America and to U.S. & Canada By 1995 in the Americas, >10 6 cases; 10 4 dead 8 th pandemic (??) V. cholerae O139 Bengal is first non-O1 strain capable of causing epidemic cholera Began in India in 1992 and spread to Asia, Europe and U.S. Disease in humans previously infected with O1 strain, thus no cross-protective immunity
Pathogenesis of V.cholerae Incubation period: 2-3 days High infectious dose: >10 8 CFU 10 3 - 10 5 CFU with achlorhydria or hypochlorhydria (lack of or reduced stomach acid) Abrupt onset of vomiting and life-threatening watery diarrhea ( 15-20 liters/day ) As more fluid is lost, feces-streaked stool changes to rice-water stools: Colorless Odorless No protein Speckled with mucus
Pathogenesis of V.cholerae (cont.) Cholera toxin leads to profuse loss of fluids and electrolytes (sodium, potassium, bicarbonate) Hypokalemia (low levels of K in blood) Cardiac arrhythmia and renal failure Cholera toxin blocks uptake of sodium & chloride from lumen of small intestine Death attributable to: Hypovolemic shock (due to abnormally low volume of circulating fluid (plasma) in the body) Metabolic acidosis (pH shifts toward acid side due to loss of bicarbonate buffering capacity)
Treatment & Prevention of V. cholerae Untreated: 60% fatality Treated: <1% fatality Rehydration & supportive therapy Oral Sodium chloride (3.5 g/L) Potassium chloride (1.5 g/L) Rice flour (30-80g/L) Trisodium citrate (2.9 g/L) Intravenous (IV) Doxycycline or tetracycline (Tet resistance may be developing) of secondary value Water purification, sanitation & sewage treatment Vaccines
Virulence Factors Associated with Vibrio cholerae O1 and O139
Two Broad Classes of Bacterial Exotoxins Intracellular Targets : A-B dimeric (two domain) exotoxins: (prototype is diphtheria toxin of Corynebacterium diphtheriae ): Bipartite structure: Binding domain (B) associated with absorption to target cell surface and transfer of active component (A) across cell membrane; once internalized, domain (A) enzymatically disrupts cell function Receptor-mediated endocytosis (host cell uptake and internalization of exotoxin) ADP-ribosylation of intracellular target host molecule Cellular Targets : Cytolytic exotoxins (usually degradative enzymes) or cytolysins: hemolysis, tissue necrosis, may be lethal when administered intravenously
Cholera Toxin (A2-5B)(Vibrio cholerae) Chromosomally-encoded; Lysogenic phage conversion; Highly conserved genetic sequence Structurally & functionally similar to ETEC LT B-subunit binds to GM 1 ganglioside receptors in small intestine Reduction of disulfide bond in A-subunit activates A 1 fragment that ADP-ribosylates guanosine triphosphate (GTP)-binding protein (G s ) by transferring ADP-ribose from nicotinamide adenine dinucleotide (NAD) ADP-ribosylated GTP-binding protein activates adenyl cyclase leading to an increased cyclic AMP (cAMP) level and hypersecretion of fluids and electrolytes
Mechanism of Action of Cholera Toxin 1 4 3 2 NOTE: In step #4, uptake of Na + and Cl - from the lumen is also blocked. HCO 3 - = bicarbonate which provides buffering capacity.
Mechanism of Action of Cholera Toxin
Heparin-binding epidermal growth factor on heart & nerve surfaces
Summary of Vibrio parahaemolyticus Infections
Summary of Vibrio vulnificus Infections
Virulence Factors Associated with Non-cholerae Vibrios (Kanagawa positive)
Laboratory Identification of Vibrios Transport medium - Cary-Blair semi-solid agar Enrichment medium - alkaline peptone broth Vibrios survive and replicate at high pH Other organisms are killed or do not multiply Selective/differential culture medium - TCBS agar V. cholerae grow as yellow colonies Biochemical and serological tests
Characteristics and Epidemiology of Aeromonas (Family Aeromonadaceae) Gram-negative facultatively anaerobic bacillus resembling members of the Enterobacteriaceae Motile species have single polar flagellum (nonmotile species apparently not associated with human disease) 16 phenospecies: Most significant human pathogens A. hydrophila, A. caviae, A. veronii biovar sobria Ubiquitous in fresh and brackish water Acquired by ingestion of or exposure to contaminated water or food
Associated with gastrointestinal disease Chronic diarrhea in adults Self-limited acute, severe disease in children resembling shigellosis with blood and leukocytes in the stool 3% carriage rate Wound infections Opportunistic systemic disease in immunocompromised Putative virulence factors include: endotoxin; hemolysins; eneterotoxin; proteases; siderophores; adhesins Clinical Syndromes of Aeromonas
Afimbriated Aeromonas hydrophila Nonadherent Afimbriated Bacterial Cells and Buccal Cells
Adherent Fimbriated Bacterial Cells and Buccal Cells Fimbriated Aeromonas hydrophila
Characteristics of Plesiomonas Formerly Plesiomonadaceae Closely related to Proteus & now classified as Enterobacteriaceae despite differences: Oxidase positive Multiple polar flagella ( lophotrichous ) Single species: Plesiomonas shigelloides Isolated from aquatic environment (fresh or estuarine) Acquired by ingestion of or exposure to contaminated water or seafood or by exposure to amphibians or reptiles Self-limited gastroenteritis : secretory, colitis or chronic forms Variety of uncommon extra-intestinal infections
Epidemiological Features Aeromonas Plesiomonas Natural Habitat Source of Infection Fresh or brackish water Contaminated water or food Fresh or brackish water Contaminated water or food Clinical Features Diarrhea Vomiting Abdominal Cramps Fever Blood/WBCs in Stool Present Present Present Absent Absent Present Present Present Absent Present Pathogenesis Enterotoxin (??) Invasiveness Characteristics of Aeromonas and Plesiomonas Gastroenteritis
REVIEW
Vibrio spp. (Family Vibrionaceae) Associated with Human Disease REVIEW
Vibrio spp. (including V. cholerae ) grow in estuarine and marine environments worldwide All Vibrio spp. can survive and replicate in contaminated waters with increased salinity and at temperatures of 10-30 o C Pathogenic Vibrio spp. appear to form symbiotic (?) associations with chitinous shellfish which serve as an important and only recently recognized reservoir Asymptomatically infected humans also serve as an important reservoir in regions where cholera is endemic Epidemiology of Vibrio spp. REVIEW
Taxonomy of Vibrio cholerae >200 serogroups based on somatic O-antigen O1 and O139 serogroups are responsible for classic epidemic cholera O1 serogroup subdivided into Two biotypes: El Tor and classical (or cholerae ) Three serotypes: ogawa, inaba, hikojima Some O1 strains do not produce cholera enterotoxin (atypical or nontoxigenic O1 V. cholerae ) Other strains are identical to O1 strains but do not agglutinate in O1 antiserum (non-cholera (NCV) or non-agglutinating(NAG) vibrios) (non-O1 V.cholerae ) Several phage types REVIEW
Epidemiology of Vibrio cholerae Cholera recognized for more than two millennia with sporadic disease and epidemics Endemic in regions of Southern and Southeastern Asia; origin of pandemic cholera outbreaks Generally in communities with poor sanitation Seven pandemics (possible beginning of 8 th ) since 1817 attributable to increased world travel Cholera spread by contaminated water and food Human carriers and environmental reservoirs REVIEW
Summary of Vibrio cholerae Infections REVIEW
Summary of Vibrio cholerae Infections (cont.) REVIEW
Pathogenesis of V.cholerae (cont.) Cholera toxin leads to profuse loss of fluids and electrolytes (sodium, potassium, bicarbonate) Hypokalemia (low levels of K in blood) Cardiac arrhythmia and renal failure Cholera toxin blocks uptake of sodium & chloride from lumen of small intestine Death attributable to: Hypovolemic shock (due to abnormally low volume of circulating fluid (plasma) in the body) Metabolic acidosis (pH shifts toward acid side due to loss of bicarbonate buffering capacity) REVIEW
Virulence Factors Associated with Vibrio cholerae O1 and O139 REVIEW
Mechanism of Action of Cholera Toxin REVIEW
Summary of Vibrio parahaemolyticus Infections REVIEW
Summary of Vibrio vulnificus Infections REVIEW
Virulence Factors Associated with Non-cholerae Vibrios (Kanagawa positive) REVIEW
Characteristics and Epidemiology of Aeromonas (Family Aeromonadaceae) Gram-negative facultatively anaerobic bacillus resembling members of the Enterobacteriaceae Motile species have single polar flagellum (nonmotile species apparently not associated with human disease) 16 phenospecies: Most significant human pathogens A. hydrophila, A. caviae, A. veronii biovar sobria Ubiquitous in fresh and brackish water Acquired by ingestion of or exposure to contaminated water or food REVIEW
Associated with gastrointestinal disease Chronic diarrhea in adults Self-limited acute, severe disease in children resembling shigellosis with blood and leukocytes in the stool 3% carriage rate Wound infections Opportunistic systemic disease in immunocompromised Putative virulence factors include: endotoxin; hemolysins; eneterotoxin; proteases; siderophores; adhesins Clinical Syndromes of Aeromonas REVIEW
Characteristics of Plesiomonas Formerly Plesiomonadaceae Closely related to Proteus & now classified as Enterobacteriaceae despite differences: Oxidase positive Multiple polar flagella ( lophotrichous ) Single species: Plesiomonas shigelloides Isolated from aquatic environment (fresh or estuarine) Acquired by ingestion of or exposure to contaminated water or seafood or by exposure to amphibians or reptiles Self-limited gastroenteritis : secretory, colitis or chronic forms Variety of uncommon extra-intestinal infections REVIEW
Characteristics of Aeromonas and Plesiomonas Gastroenteritis REVIEW
