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1 Esherichia coli Gram-negative rod Facultative anaerobe Named for Theodor Escherich German physician (ca. 1885) Demonstrated that particular strains were.

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Presentation on theme: "1 Esherichia coli Gram-negative rod Facultative anaerobe Named for Theodor Escherich German physician (ca. 1885) Demonstrated that particular strains were."— Presentation transcript:

1 1 Esherichia coli Gram-negative rod Facultative anaerobe Named for Theodor Escherich German physician (ca. 1885) Demonstrated that particular strains were responsible for infant diarrhea and gastroenteritis Normal flora of the mouth and intestine Protects the intestinal tract from bacterial infection Assists in digestion Produces small amounts of vitamins B 12 and K Colonizes newborns GI tract within hours after birth There are more than 700 different serotypes of E. coli Distinguished by different surface proteins and polysaccharides

2 2 Escherichia Escherichia coli –coli- large intestine, colon –Mammalian large intestine Escherichia blattae –blattae. L. n. blatta cockroach –Hindgut of cockroach Blatta orientalis Bergey’s Manual of Systematic Bacteriology

3 3 Escherichia coli K-12 strain The original E. coli strain K-12 was obtained from a stool sample of a diphtheria patient in Palo Alto, CA in 1922 Strain K-12 was used for biochemical and genetic studies for many years –Metabolism –F + plasmids –Bacteriophages –Operons –Genome sequencing

4 4 Many strains O antigen –Somatic (on LPS) –171 antigens H antigen –Flagella –56 antigens K antigen –Capsule and or fimbrial antigen –80 antigens Serotypes Antibody – antigen rxn O18ac:H7:K1 18 th O antigen 1 st K antigen 7 th H antigen

5 5 EPEC Enteropathogenic E. coli ETEC Enterotoxigenic E. coli EIEC Enteroinvasive E. coli Bergey’s Manual of Systematic Bacteriology

6 6 Summary of the virulence factors of pathogenic strains of E. coli Fimbriae (Pili) Hemolysins Siderophores Flagella Toxins Endotoxin LPS Capsules K antigens LPS Antigenic variation Drug resistance plasmids Toxin and other virulence plasmids Thermolabile toxin (LT) Thermostable toxin (ST) Found alone or together Both are plasmid borne

7 7 Pathogenic Agent Urinary Tract Infections Sepsis / neonatal meningitis Enteric / diarrheal diseases

8 8 Uropathogenic E. coli UPEC Most common form of extraintestinal E. coli infection Acute symptomatic UTI –12% of all men –10-20% of women –100,000 patients hospitalized for renal infections

9 9 Urovirulence Factors Adherence Fimbriae Aerobactin Siderophore Hemolysis   Capsule K antigens Resist phagocytosis Resist complement proteins Endotoxin

10 10 Neonatal Meningitis E. coli NMEC Meningitis in an infection of the fluid and membranes that cover the brain and spinal cord –Bacteria –Viruses –Fungi E. coli incites between 1/4 and 1/3 of meningitis cases in newborns – Less than 2% of cases of meningitis at all other ages Approximately 1 out of 5 newborns with E. coli meningitis dies –Survivors frequently sustain permanent brain damage The majority of cases occur in premature babies K-1 –80% of NMEC E. coli strains produce K-1 capsular antigens –K1 capsular polysaccharide –O18ac:H7:K1 –Inhibits phagocytosis Siderophore production –Sequesters Fe Endotoxin

11 11

12 12 Enteric / diarrheal diseases E. coli can adhere to the mucosa of the large intestine

13 13 Combinations of the O & H antigens identify the serotype Clinical Microbiology Reviews 1998 11:142-201 ETEC Enterotoxigenic E. coli EPEC Enteropathogenic E. coli EHEC Enterohemorrhagic E. coli EAEC Enteroaggregative E. coli EIEC Enteroinvasive E. coli

14 14 Enterotoxigenic E. coli ETEC Adhere to intestinal mucosa by fimbriae Produce enterotoxins –Plasmids contain genes for enterotoxins –Cause leakage of intestinal epithelial cells Loss of electrolytes & water Attach by fimbriae Cause diarrhea in children & adults Toxins increase intracellular levels of cAMP Causes cell leakage Traveler’s diarrhea Weanling diarrhea

15 15 Enteropathogenic E. coli EPEC Attaching & effacing –Effacement of microvilli –Adherence between bacterium and epithelial cells –Unique histopathology –Locus of enterocyte effacement Clinical Microbiology Reviews 1998 11:142-201

16 16 Clinical Microbiology Reviews 1998 11:142-201

17 17 Enteroaggregative E. coli EAEC Adhere to HEp-2 cells –Human laryngeal carcinoma cells Bacterial cells autoagglutinate –Stick to one another Do not secrete enterotoxins Clinical Microbiology Reviews 1998 11:142-201

18 18 Clinical Microbiology Reviews 1998 11:142-201

19 19 Enteroinvasive E. coli EIEC Biochemically, genetically, and pathogenetically closely related to Shigella spp. Cause watery diarrhea –Not bloody EIEC cells invade intestinal epithelial cells, lyse the phagosomal vacuole, spread through the cytoplasm and infect adjacent cell –Shigella does the same thing Plasmid encoding a gene for a K surface antigen –Attach and invade mucosal cells

20 20 Clinical Microbiology Reviews 1998 11:142-201

21 21 Enterohemorrhagic E. coli EHEC Severe gastrointestinal distress Hemorrhagic colitis –Crampy abdominal pain –Watery diarrhea –Little or no fever –Bloody diarrhea New serotype O157:H7 –1983 –Undercooked hamburgers

22 22 E. coli 015:H7 Distinguished by serology Cannot be distinguished from all other strains of E. coli using other standard microbiological tests

23 23 E. coli 015:H7 157 th somatic O antigen 7 th flagellar H antigen Hemorrhagic colitis –Abdominal cramps, blood stools, with minor or no fever Post diarrheal hemolytic ureamic syndrome –Acute renal injury –Thrombocytopenia An abnormal decrease in the number of platelets in circulatory blood. –Microangiopathic hemolytic anemia The fragmentation of red blood cells because of narrowing or obstruction of small blood vessels. Enterohemorrhagic E. coli –EHEC Among the most dangerous enteric pathogens The Lancet 1998 352:1207-1212

24 24 Reservoir Healthy cattle are the major reservoir for human infection –Deer, sheep, goats, horses, dogs, birds and flies Bacterial cells can survive in manure and water troughs Infection is more common during the summer in both the northern and southern hemisphere

25 25 Transmitted via food –Ground beef –Raw milk –Lamb meat –Venison jerky –Salami and other fermented dried meat products –Lettuce, spinach, alfalfa sprouts –Unpasteurized apple cider Transmitted via water –Drinking and swimming in unchlorinated water Direct person to person contact –Diaper changing –Improper sanitation –Day care & chronic adult care facilities

26 26 Clinical Features Average interval between exposure & illness is 3 days Most patients recover with 7 days 70% of patients report bloody stools 30-60% of patients report vomiting Approx 5% of patients develop HUS The Lancet 1998 352:1207-1212 Sequelae A condition following as a consequence of a disease. Proteinuria Excess protein in the urine.

27 27 Identification MacConkey agar (SMAC) –Does not ferment sorbitol rapidly –Forms colorless colonies on sorbitol containing MacConkey agar Serology –Colorless colonies on SMAC are screened for the 0157 antigen

28 28 Shiga Toxins Exotoxin Very similar to toxin produced by Shigella dysenteriae –Inhibits protein synthesis in host cell –A subunit inactivates the 60S ribosomal subunit Shiga toxin producing E. coli (STEC) –Verotoxins Most OH157 strains produce Shiga toxin 2 –25% produce Shiga toxin 1 Identical to Shigella toxin A B exotoxin –A subunit exists on a temperate bacteriophage

29 29 Cells leak Na +, Cl -, K +, HCO 3 - and water Watery diarrhea Cramps Nausea Vomiting Bloody stool

30 30 Virulence Factors Virulence plasmid (pO157) –Encodes a hemolysin –O157 strains can use iron from blood released into the intestine Locus of enterocyte effacement –Adhesion proteins

31 31

32 32 Non O157 Shiga Toxin Producing E. coli Several other serotypes of E. coli produce Shiga toxins –O111:nonmotile –O26:H11 –O132:H2 Incite diarrhea, hemorrhagic colitis & HUS Labs generally not prepared to identify these strains –Many times go undetected

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