2 VibrioMembers of this genus share many characteristics with enteric bacteria such as Escherichia and SalmonellaFound in water environments worldwide (among the most common bacteria in surface waters).Vibrio cholerae is the most common species to infect humansVibrio cholerae serogroup O1 (Ogawa & Inaba serotypes)It has 2 biotypes: classical and ElTorCauses choleraHumans become infected with V. cholerae by ingesting contaminated food and waterFound most often in communities with poor sewage and water treatmentThere are 100 O serogroups. Many vibrios share a single heat labile flagellar H Ag
7 Vibrio They are curved aerobic rods motile by a polar flagellum A large inoculum (108) is required to cause disease because the bacteria are susceptible to the acidic stomach environmentCholera toxin (enterotoxin) is the most important virulence factor of V. choleraeLemon drops during epidemics
9 Cholera PathologySome infections are asymptomatic or cause mild diarrheaIncubation period is 1-4 daysCan cause severe disease resulting in abrupt watery diarrhea and vomiting (20-30L/day)“Rice-water stool” is characteristicResults in severe fluid and electrolyte loss, dehydration, shock, acidosis, anuriaCan progress to coma and deathMortality rate in untreated cases is 60%
10 Diagnosis, Treatment, and Prevention Usually based on the characteristic diarrheaSelective medium : TCBS (thiosulphate, citrate, bile salt, sucrose agar) pHVibrio cholerae is a sucrose fermenterVibrio parahemolyticus is a non-sucrose fermenter
12 Treatment Treatment Prevention Fluid and electrolyte replacement Antimicrobial drugs are not as important because they are lost in the watery stoolTetracyclines reduce stool output and shorten the period of excretion of vibriosResistance via plasmids is developingAn attack is followed by immunity of unknown durationPreventionAdequate sewage and water treatment can limit the spread of V. cholerae
13 EpidemiologyEpidemics caused by classical biotype through the early 1960sEl Tor biotype prevailed in the late 1960sIt is endemic in Southeast AsiaShips have carried it to ports all around the world in ballast waterIt is spread by person to person contact, water, food, and fliesThere are seldom carriers
17 Other Diseases of Vibrio Vibrio parahaemolyticusIt is halophilic and does not ferment sucroseResults from ingestion of shellfish or raw fishIncubation period is hoursCauses cholera-like gastroenteritisVibrio vulnificusCauses septicemia following consumption of contaminated shellfishInfections can result from washing wounds with contaminated seawater (skin lesions)
18 Campylobacter Gram negative rods with comma, S or “gull wings” shapes Motile with a single polar flagellum, non-sporing.One of the most common causes of gastroenteritis in the developed worldMany animals serve as reservoirs for the bacteria where they cause sepsis, abortion or enteritisHumans become infected by consuming contaminated food, milk, or waterInfections produce bloody and frequent diarrhea that is self-limitingSpread of the bacteria can be reduced by proper food handling and preparation
19 Campylobacter jejuni A common human pathogen causing enteritis Poultry is the most common source of infectionThe source of infection may be food, drink, contact with infected animals or humans and their excretaOrganisms multiply in the small intestine, invade the epithelium and produce inflammation causing appearance of RBCs and WBCs in stools resembling shigellosis.
22 CultureSelective medium is Skirrow’s medium (VPT). Colonies are colourless or grey (tear drop) or watery or roundIncubation atmosphere: microaerophilic with reduced O2 (5%) and added CO2 (10%)Incubation temperature 42-43ºCOxidase and catalase positive
23 Treatment Self limited Erythromycin: shortens the duration of fecal shedding of bacteria
24 Other Campylobacters Other species include Campylobacter fetus (cattle & sheep), Campylobacter coli (pigs)and Campylobacter lari (animals and birds).Campylobacter fetus can cause systemicinfections in immunocompromised patients.
25 Helicobacter pyloriWas originally placed with campylobacters but it has sheathed flagella and is urease positiveSlightly helical, Gram-negative highly motile bacterium that colonizes the stomach of its hostsIt is present on the gastric mucosa of 20% of persons under 20 years and increases up to 80% in adults in developing countriesThe natural history of infection is not well known but it is likely that person to person transmission and common source infections occurOnce acquired, infection persists for years or for life.
29 Virulence factorsH.pylori produces numerous virulence factors that enable it to colonize the stomachIt is a strong producer of ureaseFlagella that enable the pathogen to burrow through the mucous lining the stomachAdhesins facilitate binding to gastric cellsH. pylori also produces a protease that modifies the gastric mucous and further reduces the ability of acid to diffuse through the mucous.Toxins and lipopolysaccharideA toxin that inhibits acid production by stomach cells
30 Pathogenesis Associated with antral gastritis Important in Peptic ulcer (duodenal)Warren-MarshalL & Koch’s postulatesOptimum pH 6-7, killed at low pHGastric mucous is relatively impermeable to acid and has a strong buffering capacity.On the lumen side of the mucous, pH is low 1-2While on the epithelial side the pH is about 7.4H. pylori is found deep in the mucous layer near the epithelial surface
31 Pathogenesis (cont.)H. pylori also produces a potent urease which yields ammonia and further buffers the acid.H. pylori is quite motile even in mucous and is able to find its way to the epithelial surfaceH. pylori invades the epithelial cell surface to a limited degreeToxins and lipopolysaccharide may damage the cells alsoIgM, IgG & IgA are produced and persist in chronic infections
32 Phagocytosed bacteria survive in leukocytes by catalase and superoxide dismutase
33 Diagnosis, Treatment, and Prevention Mainly histologically (biopsy)Presence of H. pylori can be demonstrated by a positive urease testBiochemical tests provide a definitive identificationTreatmentAntimicrobial drugs are used in combination with drugs that inhibit acid production (triple therapy)PreventionPrevention is difficult because the exact mode of transmission is unknown