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MICROBIOLOGY

Slightly Curved Bacilli

Members of this genus share many characteristics with enteric bacteria such as Escherichia and Salmonella

Found in water environments worldwide (among the most common bacteria in surface waters).

Vibrio cholerae is the most common species to infect humans

Vibrio cholerae serogroup O1 (Ogawa & Inaba serotypes)

It has 2 biotypes: classical and ElTor

Causes cholera

Humans become infected with V. cholerae by ingesting contaminated food and water

Found most often in communities with poor sewage and water treatment

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 environment

Cholera toxin (enterotoxin) is the most important virulence factor of V. cholerae

Vibrio

GM1

Some infections are asymptomatic or cause mild diarrhea

Incubation period id 1-4 days

Can cause severe disease resulting in abrupt watery diarrhea and vomiting (20-30L/day)

“Rice-water stool” is characteristic

Results in severe fluid and electrolyte loss, dehydration, shock, acidosis, anuria

Can progress to coma and death

Mortality rate in untreated cases is 60%

Cholera Pathology

Diagnosis

Usually based on the characteristic diarrhea

Selective medium : TCBS (thiosulphate, citrate, bile salt, sucrose agar) pH 8.5-9.5

Vibrio cholerae is a sucrose fermenter

Vibrio parahemolyticus is a non-sucrose fermenter

Diagnosis, Treatment, and Prevention

Treatment

Treatment

Fluid and electrolyte replacement

Antimicrobial drugs are not as important because they are lost in the watery stool

Tetracyclines reduce stool output and shorten the period of excretion of vibrios

Resistance via plasmids is developing

An attack is followed by immunity of unknown duration

Prevention

Adequate sewage and water treatment can limit the spread of V. cholerae

Epidemiology

Epidemics caused by classical biotype through the early 1960s

El Tor biotype prevailed in the late 1960s

It is endemic in Southeast Asia

Ships have carried it to ports all around the world in ballast water

It is spread by person to person contact, water, food, and flies

There are seldom carriers

Vibrio parahaemolyticus

It is halophilic and does not ferment sucrose

Results from ingestion of shellfish or raw fish

Incubation period is 12-24 hours

Causes cholera-like gastroenteritis

Vibrio vulnificus

Causes septicemia following consumption of contaminated shellfish

Infections can result from washing wounds with contaminated seawater (skin lesions)

Other Diseases of Vibrio

Gram negative rods with comma, S or “gull wings” shapes

Motile with a single polar flagellum, non-sporing.

One of the most common cause of gastroenteritis in the developed world

Many animals serve as reservoirs for the bacteria where they cause sepsis, abortion or enteritis

Humans become infected by consuming contaminated food, milk, or water

Infections produce bloody and frequent diarrhea that is self-limiting

Spread of the bacteria can be reduced by proper food handling and preparation

Campylobacter

Campylobacter jejuni

A common human pathogen causing enteritis

Poultry is the most common source of infection

The source of infection may be food, drink, contact with infected animals or humans and their excreta

Organisms multiply in the small intestine, invade the epithelium and produce inflammation causing appearance of RBCs and WBCs in stools resembling shigellosis.

Culture

Selective medium is Skirrow’s medium (VPT). Colonies are colourless or grey (tear drop) or watery or round

Incubation atmosphere: microaerophilic with reduced O2 (5%) and added CO2 (10%)

Incubation temperature 42-43ºC

Oxidase and catalase positive

Treatment

Self limited

Erythromycin: shortens the duration of fecal shedding of bacteria

Other CampylobactersOther species include Campylobacter fetus

(cattle & sheep), Campylobacter coli (pigs) and Campylobacter lari (animals and birds).

Campylobacter fetus can cause systemic infections in immunocompromised patients.

Was originally placed with campylobacters but it has sheathed flagella and is urease positive

Slightly helical, Gram-negative highly motile bacterium that colonizes the stomach of its hosts

It is present on the gastric mucosa of 20% of persons under 20 years and increases up to 80% in adults in developing countries

The natural history of infection is not well known but it is likely that person to person transmission and common source infections occur

Once acquired, infection persists for years or for life.

Helicobacter pylori

Virulence factors

H.pylori produces numerous virulence factors that enable it to colonize the stomach

It is a strong producer of urease

Flagella that enable the pathogen to burrow through the mucous lining the stomach

Adhesins facilitate binding to gastric cells

H. pylori also produces a protease that modifies the gastric mucous and further reduces the ability of acid to diffuse through the mucous.

Toxins and lipopolysaccharide

A toxin that inhibits acid production by stomach cells

Pathogenesis

Associated with antral gastritis

Important in Peptic ulcer (duodenal)

Warren-MarshalL & Koch’s postulates

Optimum pH 6-7, killed at low pH

Gastric mucous is relatively impermeable to acid and has a strong buffering capacity.

On the lumen side of the mucous, pH is low 1-2

While on the epithelial side the pH is about 7.4

H. pylori is found deep in the mucous layer near the epithelial surface

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 surface

H. pylori invades the epithelial cell surface to a limited degree

Toxins and lipopolysaccharide may damage the cells also

IgM, IgG & IgA are produced and persist in chronic infections

Phagocytosed bacteria survive in leukocytes by catalase and superoxide dismutase

Diagnosis

Mainly histologically (biopsy)

Presence of H. pylori can be demonstrated by a positive urease test

Biochemical tests provide a definitive identification

Treatment

Antimicrobial drugs are used in combination with drugs that inhibit acid production (triple therapy)

Prevention

Prevention is difficult because the exact mode of transmission is unknown

Diagnosis, Treatment, and Prevention