2 ENTEROBACTERIACEAERod-Shaped Bacterium, E. coli (division) (SEM x22,245) E. coli (0157:H7)a rod prokaryote.
3 Antigenic Structure of Enterobacteriaceae S. typhiO antigen side chain(Fimbriae)
4 Family Enterobacteriaceae Certain E .coli strains can be considered true pathogensTrue pathogen(nonmotile)(nonmotile)True pathogenTrue pathogen
5 Incidence of Enterobacteriaceae Associated with Bacteremia
6 Sites of Infections with Members of the Enterobacteriaceae
7 General Information:This group of organisms include several that cause primaryinfections of the human gastrointestinal tract.They are referred to as enterics (regardless of whether theycause gut disorders).Bacteria that affect the gastrointestinal tract include certainstrains of E. coli and Salmonella, all 4 species of Shigella,and Yersinia entercolitica.
8 The rheumatic disease, Reiter's syndrome (associated with HLA-B27), can result from prior exposure to Salmonella,Shigella, or Yersinia.Other organisms that are not members of theEnterobacteriacae, including Campylobacter and Chlamydia,are also causative agents of Reiter's syndrome.Yersina pestis (the cause of "plague") will be consideredseparately with other zoonotic organisms.
9 Members of this family are major causes of opportunistic infection (including septicemia, pneumonia, meningitis andurinary tract infections).Examples of genera that cause opportunistic infections are:1. Citrobacter2. Enterobacter3. Escherichia4. Hafnia5. Morganella6. Providencia7. SerratiaSelection of antibiotic therapy is complex due to the diversityof organisms.
10 Some members of the Enterobacteriaceae cause community acquired disease in otherwise healthy people.Klebsiella pneumoniae is often involved in respiratoryinfections. The organism has a prominent capsule aidingpathogenicity.The most common community acquired ("ascending")urinary tract infection is caused by E. coli.The vast majority of urinary tract infections are ascendingoften from fecal contamination.Proteus is another common cause of urinary tractinfection; the organism produces a urease that degradesurea producing an alkaline urine.
11 Isolation and identification of Enterobacteriaceae Gram negative facultative anerobic rods2. Lack cytochrome oxidase (oxidase negative)
12 Isolated from fecal matter on agar containing lactose and a pH indicatorColonies which ferment lactose will producesufficient acid to cause a color shift in theindicator.E. coli ferments lactoseShigella, Salmonella and Yersinia arenon-fermenters"Non-pathogenic" strains of E. coli (and otherlactose-positive enterics) are often present innormal feces.
13 "Non-pathogenic" strains of E. coli are difficult to differentiate from "pathogenic" E. coli. Lactose-negativecolonies are often the only ones identified in feces.All Enterobacteriaceae isolated from other siteswhich contain low numbers of bacteria [e.g. urine]sterile [e.g. blood]are identified biochemically [e.g. the API 20E system]Important serotypes can be differentiated by their:O (lipopolysaccharide)H (flagellar) antigensK (capsular) antigensHowever, serotyping is generally not performed in theroutine clinical laboratory.
15 (i) Escherichia coli 1. At the species level, E. coli and Shigella are indistinguishable.For practical reasons (primarily to avoidconfusion), they are not placed in the same genus.There is a significant amount of overlapbetween diseases caused by the two organisms.
16 Enteropathogenic E. coli (EPEC). Certain serotypes are commonly found associatedwith infant diarrhea.The use of gene probes has confirmed these strainsas different from other groups listed below.There is a characteristic morphological lesion withdestruction of microvilli without invasion of theorganism which suggests adhesion is important.Clinically one observes fever, diarrhea, vomitingand nausea usually with non-bloody stools.
17 2) Enterotoxigenic E. coli (ETEC) Produce diarrhea resembling cholera but muchmilder in degree.ETEC is also cause "travellers diarrhea".
18 Two types of plasmid-encoded toxins are produced. a) Heat labile toxins which are similar to choleragen.Adenyl cyclase is activated with production ofcyclic AMP and increased secretion of water andions.b) Heat stable toxinsGuanylate cyclase is activated which inhibits ionicuptake from the gut lumen.Watery diarrhea,feverand nausearesult in both cases.
19 3) Enteroinvasive E. coli (EIEC ) Produce a dysentery which isclinically indistinguishable fromshigellosis.
20 4) Enterohemorrhagic E. coli (EHEC). These are usually serotype O157:H7.Transmission electronmicrograph ofEscherichia coli O157:H7
21 Chronology of E. coli O157:H7 infections, an emerging type of foodborne illness. CDC 1982: First recognized as a pathoghen1985: Associated with hemolytic uremic syndrome1990: Outbreak from drinking water1991: Outbreak from apple cider1993: Multi-state outbread from fast food hamburgers1995: Outbread from fresh produce1996: Outbread in JapanMulti-state outbreak from unpasteurized apple juice
22 These organisms can produce a hemorrhagic colitis (characterized by bloody and copiousdiarrhea with few leukocytes in afebrilepatients).However, they are taking increasing importancewith the recognition of outbreaks caused bycontaminated hamburger meat.The organisms can disseminate into thebloodstream producing systemichemolytic-uremic syndrome (hemolytic anemia,thrombocytopenia and kidney failure).
23 Production of Vero toxin (biochemically similar to shiga toxin thus also known as "shiga-like") ishighly associated with this group of organisms;encoded by a lysogenic phage.Hemolysins (plasmid encoded) are alsoimportant in pathogenesis.
24 There are at least 4 etiologically distinct diseases caused by E. coli.The diagnostic laboratory generally does notdifferentiate the groups and treatment is based onsymptomatology.Generally fluid replacement is the primarytreatment.Antibiotics are generally not used except in severedisease or disease that has progressed to asystemic stage (e.g.hemolytic-uremia syndrome).
25 Two major classes of pili are produced by E. coli; mannose sensitive and mannose resistant pili.The former bind to mannose containingglyocoproteins and the latter to cerebrosides onthe host epithelium allowing attachment.This aids in colonization by E. coli.
26 (ii) ShigellaShigella sonnei - rod prokaryote; causes shigellosis (bacterial dysentery)
27 Shigella 4 Species; S. flexneri, S. boydii, S. sonnei, S. dysenteriae All cause bacillary dysentery or shigellosis.Shigellosis is bloody feces associated withintestinal pain.
28 The organism invades the epithelial lining layer but does not penetrate.Usually within 2-3 days, dysentery results frombacteria damaging the epithelium lining layers ofthe intestine.Also seen is a release of mucus and blood in thefeces as well as the appearance of “pus” from theattraction of leukocytes into the bowel.Watery diarrhea is frequently observed with noevidence of dysentery.
29 Shiga toxin 1. Chromosomally encoded 2. Neurotoxic 3. Enterotoxic 4. CytotoxicEnterotoxicity can make the disease clinicallyappear as a diarrhea.The toxin inhibits protein synthesis (acting on the60S ribosome and lysing 28S rRNA).
30 Shigellosis is primarily a disease of young children occurring by fecal-oral contact.Adults can catch this disease from children.Although it can be transmitted by infected adultfood handlers contaminating food.The source in each case is unwashed hands.Man is the only "reservoir".
31 Managing dehydration is of primary concern. Mild diarrhea is often not recognized as shigellosis.Patients with severe dysentery are usually treatedwith antibiotics (e.g. ampicillin).In contrast to salmonellosis, patients respond toantibiotic therapy and disease duration isdiminished.
33 Based on genetic studies there is a single species of Salmonella (Salmonella enterica).Using appropriate antibodies more than 2000antigenic "types" have been recognized.Only a few types that are commonly associatedwith characteristic human diseases -1. S. enteritidis2. S. cholerae-suis3. S. typhi
34 1. Salmonellosis,the common salmonella infection,is caused by a variety of serotypes (mostcommonly S. enteritidis) and is transmitted fromcontaminated food (such as poultry and eggs).2. It does not have a human reservoir.3. It usually presents as a gastroenteritisnauseavomitingnon-bloody stool4. The disease is usually self-limiting (2 - 5 days).
35 Like Shigella, salmonella invade the epithelium and do not produce systemic infection.In uncomplicated cases of salmonellosis, whichare the vast majority, antibiotic therapy is notuseful.S. cholerae-suis (seen much less commonly)causes septicemia after invasion.In this case, antibiotic therapy is required.
36 The severest form of salmonella infections is called "typhoid" or enteric fever.Typhoid is caused by Salmonella typhi.This disease is rarely seen in the US.Typhoid is one of the historical causes ofwidespread epidemics and still causes epidemics inthe third world.
37 Salmonella typhi The organism is transmitted from: 1. a human reservoir2. in the water supply (if sanitary conditionsare poor)3. in contaminated foodIt initially invades the intestinal epithelium andduring this acute phase, gastrointestinalsymptoms are noted.
38 The organisms penetrates (usually within the first week) and passes into the bloodstreamwhere it is disseminated in macrophages.Typical features of a systemic bacterial infectionare noted.The septicemia usually is temporary with theorganism finally lodging in the gall bladder.Organisms are shed into the intestine for someweeks.
39 At this time the gastroenteritis (including diarrhea) is noted again.The Vi (capsular) antigen plays a role in thepathogenesis of typhoid.A carrier state is common; thus one person e.g.a food handler can cause a lot of spread.Antibiotic therapy is essential.Vaccines are not widely effective and notgenerally used.
40 (iv) Yersinia Yersinia entercolitica is a major cause of gastroenteritis.The organisms are invasive (usually withoutsystemic spread).
41 Typically the infection is characterized by: 1. diarrhea2. fever3. abdominal painSystemic symptoms, after bacteremia, are seen.This organism can be transmitted by fecalcontamination of:1. water or milk by domestic animals2. from eating meat products
42 It is best isolated by "cold" enrichment; when refrigerated this organism surviveswhile others do not.A similar, but less severe, disease is caused byY. pseudotuberculosis.Antibiotic therapy is recommended.
43 Conclusion Sanitary measures protect the water supply, avoiding contamination with sewage.This is the primary reason that epidemics withlife-threatening pathogens (e.g cholera andtyphoid) are rarely seen in the US but arecommonly seen in the third world.
44 Other less severe diseases (e.g. salmonellosis, EHEC) are still common from eatingcontaminated animal products, which has beenless well controlled.Shigella, which has a human host, would beeven more difficult to eradicate.Vaccination is rarely used and indeed is anexpensive way to go compared to sewagetreatment.
45 In severe diarrhea, fluid replacement is essential.Antibiotic therapy is used in severe localinfection and always in systemic disease.