Vibrio Cholerae Lecture Notes 2019-2020 PDF

Vibrio cholerae Dr. Rania T. Abdel Haleem Lecturer of medical microbiology and immunology 104 (2019-2020)  Objectives Identify the morphology, cultural characters, biochemical reactions, and serologic characters of vibrio cholerae List virulence factors of...

Vibrio cholerae Dr. Rania T. Abdel Haleem Lecturer of medical microbiology and immunology 104 (2019-2020)  Objectives Identify the morphology, cultural characters, biochemical reactions, and serologic characters of vibrio cholerae List virulence factors of vibrio cholerae and their mode of action Define cholera Explain the pathogenesis, diagnosis, treatment and prophylaxis of cholera 104 (2019-2020) Vibrios Comma shaped Gram negative bacilli Some are saprophytes in water and soil The most clinically important species is vibrio cholerae (V.cholerae) 104 (2019-2020)  V.cholerae Morphology Gram negative curved or comma shaped rods Motile with single terminal flagellum (darting motility) Note: Darting means move or run somewhere suddenly or rapidly 104 (2019-2020) V.cholerae Cultural characters Highly aerobic Grow on simple media Growth is favored by alkaline PH (8-9) On alkaline peptone water it form surface pellicle whithin 8 hours (due to affinity for oxygen) On TCBS produce yellow colonies (due to succrose fermentation) 104 (2019-2020) On alkaline peptone water V. cholerae form surface pellicle whithin 8 hours Pellicle 104 (2019-2020) 104 (2019-2020) On TCBS V. cholerae produce yellow color 104 (2019-2020)  Biochemical reaction They ferment glucose, maltose, mannite and sucrose with with production of acid only Indole positive Oxidase positive Reduce nitrate On TSI gives yellow slant, yellow butt with no gas 104 (2019-2020)  Biochemical reaction Gas Derham’s tube V. cholerae ferment glucose with production of acid only Media contain phenol red indicator 104 (2019-2020) Biochemical reaction Indole test positive 104 (2019-2020)  Biochemical reaction Nitrate reduction positive Nitrate reduction 104 (2019-2020) Biochemical reaction TSI V.cholerae Triple sugar iron (TSI) 104 (2019-2020)  Biochemical reaction Oxidase positive Oxidase positive due to presense of enzyme cytochrome oxidase 104 (2019-2020) String test positive 104 (2019-2020) Serologic characters H flagellar antigen is shared by all vibrios V. cholerae O lipopolysaccarides (O antigen) are specific which classify vibrio cholerae into at least 206 serogroups (e.g. O1,………..O139,…….) Serogroups O1 and O139 cause classic epidemic cholera in humans Occasionally non O1-non O139 V. cholerae cause sporadic cholera like disease and some of them are invasive and may cause septic infections O1 serogroup include 2 biotypes  V.cholerae  V. El Tor O1 serogroup includes 3 serotypes: Ogawa, Inaba,Hikojima 104 (2019-2020)  Serologic characters Differentiation between classic V.cholerae and V. el tor biotypes by biochemical activity V. El Tor :  Voges Proskauer’s positive  Lyse sheep RBCs  Agglutinate chicken RBCs  Resistant to Polymyxin B  Lysis by cholera phage IV Classic V.Cholerae has opposite reactions V. cholerae 0139 is similar to El Tor, it differs in being capsulated 104 (2019-2020) 104 (2019-2020)  Virulence factors V. cholerae enterotoxin is a heat labile enterotoxin Result in hypersecretion of water and electrolytes in the lumen of the intestine and severe diarrhoea occurs leading to dehydration, which, if not promptly treated, leads to acidosis, shock and death. Mucinase enzyme dissolves the protective glycoprotein coating over the intestinal cells helping adherence to the cells of the brush border of the gut. 104 (2019-2020) Pathogenesis of vibrio cholerae 104 (2019-2020)  Cholera The disease is endemic in indian subcontinent and tend to occur in worlwide epidemics Acute infectious disease Characteried by: severe vomiting Watery diarrohae ( rice water stool) resulting in dehydration and collapse IP; 1-4 days 104 (2019-2020)  Pathogenesis of cholera It is transmitted by faecal contamination of water and food, primarily from human cases or from carriers during the incubation period or convalescence. Marine shell-fish e.g. shrimp and oysters are the main animal reservoirs. Their ingestion without adequate cooking can transmit the disease. Infection is restricted to the intestine with no blood invasion. 104 (2019-2020) Pathogenesis of cholera For infection to occur, a large number of bacteria must be ingested because the organism is sensitive to gastric acidity. The organisms attach to the microvilli of the brush border of epithelial cells in the intestine, where they multiply and liberate cholera enterotoxin, which exerts the above mentioned effects. Convalescent carriers occur but chronic carriers are rare. 104 (2019-2020) Diagnosis of cholera Diagnosis of first case of cholera in non endemic area Any comma-shaped motile organisms detected in a stool sample from the first case suspected to be cholera in a non-endemic area should be thoroughly identified before giving a report as positive for cholera. 1- Mucous flecks from stools are inoculated on alkaline peptone pH 8.5. 2- Subcultures are made from the surface pellicle after 6-8 hrs on TCBS or alkaline agar. 104 (2019-2020)  Diagnosis of cholera Diagnosis of first case of cholera in non endemic area The growing colonies are identified by: A wet mount which is examined for the characteristic darting motility. Smears stained with Gram show Gram negative comma- shaped bacilli. Biochemical activities; oxidase, sugar fermentation, indole, nitrate, string test, TSI inoculation Agglutination with specific anti-O 1 and anti O- 139 cholera sera. 104 (2019-2020) Diagnosis of cholera Diagnosis of secondary case of cholera during epidemic: In an established epidemic, cases can be diagnosed by microscopic examination of stools for comma- shaped bacilli with characteristic motility, which can be immobilized by adding specific anti-O cholera sera. Direct methods for detection of V. cholerae O1 and O139 in stools are available including fluorescent antibody staining, coagglutination and immunoassay. PCR assays have been developed for detection of cholera toxin genes, which are found on the chromosome. 104 (2019-2020)  Treatment Correction of fluid and electrolyte imbalance is the most important Antibiotic has secondary role Tetracycline is the most effective 104 (2019-2020)  Prophylaxis  Public health measures that ensure clean water and food supply and proper sewage disposal to prevent faeco-oral transmission.  Chemoprophylaxis  Vaccines Gives 50 % protection and only for 6 months. An extract of killed bacteria A recombinant live attenuated oral vaccine is available. Oral vaccine that combines purified B subunit and killed whole cells is used in some countries and appears to be safe and protective 104 (2019-2020) V. parahaemolyticus Halophilic (salt loving) marine organism Cause gastroenteritis following ingestion of sea food The disease is self limited IP; 6-30 hours Virulent strains produce a haemolysin and are urease positive. The disease is characterized by mild to severe watery diarrhoea, nausea, vomiting, abdominal cramps and fever Treatment : only correction of fluid and electrolyte imbalance 104 (2019-2020)  Aeromonas Aeromonas Species are gram negative bacilli found in water, soil, food, animals and human faeces. A. hydrophila causes wound infection and diarrhoea which may be cholera or desentry-like. In immunocompromised patients it causes bacteraemia and septicaemia. It is oxidase positive, catalase positive and is differentiated from vibrios by being string test negative. It is motile in distilled water while vibrios are not. It is resistant to the compound 0/129 to which vibrios are susceptible. 104 (2019-2020) 104 (2019-2020)