COMPREHENSIVE MICROBIOL MBIM 720
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This 6 page Class Notes was uploaded by Salvatore Runolfsson IV on Monday October 26, 2015. The Class Notes belongs to MBIM 720 at University of South Carolina - Columbia taught by Staff in Fall. Since its upload, it has received 16 views. For similar materials see /class/229602/mbim-720-university-of-south-carolina-columbia in Microbiology at University of South Carolina - Columbia.
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Date Created: 10/26/15
Course Medical Microbiology MBIM 650720 Lecture 34 and 35 20022003 Topic Ente39robacte39riaceae Vib39rio Campylobacte39r and Helicobacte39r Suggested reading Murray Fourth Edition Chapters 29 31 Faculty Dr on Phone 733 3288 E mail afofomedscedu Office C 19 Blg 2 KEY WORDS Opportunistic Diarrhea Dysentery Urinary tract infections Lactose positivenegative API strip Enteropathogenic E coli Enterotoxigenic E coli Heat stable toxin Heat lable toxin Enteroinvasive E coli Enterohemorrhagic E coli Vero toxin Shiga like Shigella Bacillary dysentery Shiga toxin Salmonella enteritidis salmonellosis Salmonella Choleraesui5 Salmonella typhi Vi antigen Typhoid Vib39rio Cholerae Cholera Choleragen cholera toxin Ye39rsinia ente39rcolitica Hemolysin Campylobacter jejuni Adhesive pili Helicobacter pylori ENTEROBACTERIACEAE General Comments This group of organisms include several that cause primary infections of the human gastrointestinal tract Thus they are referred to as enterics Affecting the gastrointestinal tract include certain strains of E coliSalmonella all 4 species of Shigella and Ye39rsinia ente39rcolitica The rheumatic disease Reiter39s syndrome associated with HLA B27 can result from prior exposure to Salmonella Shigella or Yetsinia Other organisms that are not members of the Entetobactetiacae including Campylobactet and Chlamydia are also causative agents of Reiter s syndrome Yetsina pestis the cause of Hplague will be considered separately with other zoonotic organisms Members of this family are major causes of opportunistic infection including septicemia pneumonia meningitis and urinary tract infections Examples of genera that cause opportunistic infections are Citrobacte39r Ente39robacte39r Escherichia Hafnia Morganella Provideneia and Serratia Selection of antibiotic therapy is complex due to the diversity of organisms However some additionally cause community acquired disease in otherwise healthy people Klebsiella pneumoniae is often involved in respiratory infections The organism has a prominent capsule aiding pathogenicity The commonest community acquired ascending urinary tract infection is caused by E coli The vast majority of urinary tract infections are ascending often from fecal contamination Proteus is another common cause of urinary tract infection the organism produces a urease that degrades urea producing an alkaline urine Isolation and identification of Enterobacteriaceae These are Gram negative facultative anerobic rods They lack cytochrome oxidase and are referred to as oxidase negative They are often isolated from fecal matter on agar containing lactose and a pH indicator Colonies which ferment lactose will produce sufficient acid to cause a color shift in the indicator E coli is a fermenter of lactose while Shigella Salmonella and Yersinia are non fermenters quotNon pathogenic strains of E coli and other lactose positive enterics are often present in normal feces Since they are difficult to differentiate from pathogenic E coli lactose negative colonies are often the only ones identified in feces All Enterobacteriaceae isolated from other sites which contain low numbers of bacteria eg urine or are normally sterile e g blood are identified biochemically eg the API ZOE system see LAB HANDOUT Important serotypes can be differentiated by their 0 lipopolysaccharide H agellar and K capsular antigens However serotyping is generally not performed in the routine clinical laboratory Gastroenteritis diarrhea and dysentery i Escherichia coli Genetically E coli and Shigella are indistinguishable For practical reasons primarily to avoid confusion they are not placed in the same genus Not surprisingly there is a lot of overlap between diseases caused by the two organisms 1 Enteropathogenic E coli EPEC Certain serotypes are commonly found associated with infant diarrhea The use of gene probes has confirmed these strains as different from other groups listed below There is a characteristic morphological lesion with destruction of microvilli without invasion of the organism which suggests adhesion is important Clinically one observes fever diarrhea vomiting and nausea usually with non bloody stools 2 Enterotoxigenic E coli ETEC produce diarrhea resembling cholera but much milder in degree Also cause Htravellers diarrhea Two types of plasmid encoded toxins are produced a Heat labile toxins which are similar to choleragen see cholera section below Adenyl cyclase is activated with production of cyclic AMP and increased secretion of water and ions b Heat stable toxins Guanylate cyclase is activated which inhibits ionic and water uptake from the gut lumen Watery diarrhea fever and nausea result in both cases 3 Enteroinvasive E coli EIEC produce a dysentery indistinguishable clinically from shigellosis see bacillary dysentery below 4 Enterohemorrhagic E coli EHEC These are usually serotype 0157 H7 These organisms can produce a hemorrhagic colitis characterized by bloody and copious diarrhea with few leukocytes in afebrile patients However importance with the recognition of outbreaks caused by contaminated hamburger meat The organisms can disseminate into the bloodstream producing systemic hemolyticvuremic syndrome hemolytic anemia thrombocytopenia and kidney failure Production of Vero toxin biochemically similar to shiga toxin thus also known as Hshiga like is highly associated with this group of organisms encoded by a phage Hemolysins plasmid encoded are also important in pathogenesis As noted above there are at least 4 etiologically distinct diseases However in the diagnostic laboratory generally the groups are not differentiated and treatment would be on symptomatology Generally uid replacement is the primary treatment Antibiotics are generally not used except in severe disease or disease that has progressed to a systemic stage e ghemolytic uremia syndrome Two major classes of pili are produced by E coli mannose sensitive and mannose resistant pili The former bind to mannose containing glyocoproteins and the latter to cerebrosides on the host epithelium allowing attachment This aids in colonization by E coli n Shigella Shigella 4 species S exneri S boydii S sonnei S dysenteriae all cause bacillary dysentery or shigellosis bloody feces associated with intestinal pain The organism invades the epithelial lining layer but does not penetrate Usually within 23 days dysentery results from bacteria damaging the epithelium lining layers of the intestine often with release of mucus and blood found in the feces and attraction of leukocytes also found in the feces as Hpus Shiga toxin chromosomally encoded which is neurotoxic enterotoxic and cytotoxic plays a role The toxin inhibits protein synthesis acting on the 705 ribosome and lysing 285 rRNA This 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 adult food handlers contaminating food The source in each case is unwashed hands Man is the only quotreservoirquot Patients with severe dysentery are usually treated with antibiotics eg ampicillin In contrast to salmonellosis patients respond to antibiotic therapy and disease duration is diminished iii Salmonella Based on genetic studies there is a single species of Salmonella Salmonella enterica At the other extreme using appropriate antibodies more than 2000 antigenic types have been recognized There are however only a few types that are commonly associated with characteristic human diseases most simply referred to as S enteritidis S Choleraeduis and S typhi Salmonellosis the common salmonella infection is caused by a variety of serotypes most commonly S enteritidis and is transmitted from contaminated food such as poultry and eggs It does not have a human reservoir and usually presents as a gastroenteritis nausea vomiting and non bloody stools The disease is usually self limiting 25 days Like Shigella they invade the epithelium and do not produce systemic infection In uncomplicated cases of salmonellosis which are the vast majority antibiotic therapy is not useful S Choleraeduis seen much less commonly causes septicemia after invasion In this case antibiotic therapy is required The severest form of salmonella infections typhoid enteric fever caused by Salmonella typhi is rarely seen in the US Although it is one of the historical causes of widespread epidemics and still is in the third world The organism is transmitted from a human reservoir or in the water supply if sanitary conditions are poor or in contaminated food It initially invades the intestinal epithelium and during this acute phase gastrointestinal symptoms are noted The organisms penetrates usually within the first week and passes into the bloodstream where it is disseminated in macrophages Typical features of a systemic bacterial infection are noted The septicemia usually is temporary with the organism finally lodging in the gall bladder Organisms are shed into the intestine for some weeks At this time the gastroenteritis including diarrhea is noted again The Vi capsular antigen plays a role in the pathogenesis of typhoid A carrier state is common thus one person eg a food handler can cause a lot of spread Antibiotic therapy is essential Vaccines are not widely effective and not generally used see comments on cholera 1V Ye rsinia Yersinia ente rcolitica is a major cause of gastroenteritis the main clinical symptom in Scandinavia and elsewhere and is seen in the US The organisms are invasive usually without systemic spread Typically characterized by diarrhea fever and abdominal pain However systemic symptoms after bacteremia are seen This organism can be transmitted by fecal contamination of water or milk by domestic animals or from eating meat products Best isolated by cold enrichment when refrigerated this organism survives while others do not A similar but less severe disease is caused by Y pseudombe39rculosis Antibiotic therapy is recommended VIBRIOS Gram negative rods comma shaped facultative anaerobe which are oxidase positive The most important vibrio Vibrio cholerae is the causative agent of cholera It has simple nutritional requirements and is readily cultivated V cholerae is found in the feces of an infected individual and ends up in the water supply if the sewage is untreated The organism is thus transmitted by drinking contaminated water The organism survives in fresh water and like other vibrios in salt water Food after water contamination is another means of transmission Thus it is primarily a disease of the third world In the US it is observed in the occasional international traveler Although it is sometimes seen after ingestion of seafood Once in the gut the organism adheres to the epithelium of the intestine without penetration Adhesion to the microvilli is thus important in pathogenesis Cholera toxin is then secreted Choleragen cholera toxin is chromosomally encoded and contains two types of subunit A and B The B subunit binds to gangliosides on epithelial cell surfaces allowing internalization of the A subunit B subunits provide a channel through which A penetrates The A subunit catalyses ADP ribosylation of a regulator complex which in turn activates adenylate cyclase present in the cell membrane of the epithelium of the gut The overproduction of cyclic AMP in turn stimulates massive secretion of ions and water into the lumen Dehydration and death without treatment result Thus uid replacement is the major component of treatment Antibiotic therapy including tetracycline is additionally used in therapy Vaccination is only partially effective and not generally recommended It is most commonly used by international travelers Vibrio parahenwlyticus is usually transmitted by ingestion of raw seafood and thus is not commonly seen in the US The organism grows best in high concentrations of salt Not as severe as cholera but a non bloody diarrhea is observed Aemmonas and Plesiomonas are other water borne organisms causing gastrointestinal disease CAMPYLOBACTER AND HELICOBACTER The two groups of Gram negative organisms are both curved or spiral shaped and are genetically related The most common of the Campylobacter causing human disease is C jejuni The organism infects the intestinal tract of several animal species including cattle and sheep and is a major cause of abortions The organism is transmitted to man in milk and meat products Watery diarrhea predominates but dysentery is common The organism is invasive but generally less so than Shigella Malaise fever and abdominal pain are other disease features Bacteremia is observed in a small minority of cases The organism is microaerophilic and grows best at 42 C under these conditions and using selective media is now frequently isolated Can be treated with antibiotics but is usually a self limiting disease Helicobacter pylori is the major cause of stomach ulcers where it colonizes The organism chronically lives in and on the stomach mucosa of man Culture is the preferred method of diagnosis but may miss a number of cases The organism characteristically produces a urease which generates ammonia and carbon dioxide This aids in detecting and identifying the isolated organism Urease is produced in such large amounts that can be directly detected in mucosa sampled after endoscopy Alternatively 13C or 14C labeled CO2 is detected in the breath after feeding labeled urea Production of ammonia is a factor in pathogenesis in locally neutralizing stomach acid Antibiotic therapy eliminates the organism peptic ulcers heal and relapses are generally avoided Concluding statement on gastrointestinal diseases Sanitary measures protect the water supply avoiding contamination with sewage This is the primary reason that epidemics with life threatening pathogens e g cholera and typhoid are rarely seen in the US but are commonly seen in the third world Other less severe diseases eg salmonellosis EHEC are still common from eating contaminated animal products which has been less well controlled Shigella which has a human host would be even more difficult to eradicate Vaccination is rarely used and indeed is an expensive way to go compared to sewage treatment In severe diarrhea uid replacement is essential Antibiotic therapy is used in severe local infection and always in systemic disease
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