1、Lecture 12BIOL 5331EnterobacteriaceaeBIOL 533Lecture 12Medical MicrobiologyLecture 12BIOL 5332Enterobacteriaceae Diversity of species Ecology Found worldwide in soil,water,vegetation,and microbial flora of animals and humans Some are always associated with disease e.g.,Shigella,Salmonella,Yersinia p
2、estis Some are normal flora that can become opportunistic pathogens e.g.,E.coli,K.pneumoniae,P.mirabilisLecture 12BIOL 5333Enterobacteriaceae Epidemiology Animal reservoir:most Salmonella infections Human carrier:Salmonella typhi,Shigella Endogenous spread in a susceptible patient Can involve all bo
3、dy sites 5%hospitalized patients develop nosocomial infections,primarily caused by Enterobacteriaceae such as Escherichia Sites of infectionLecture 12BIOL 5334Microbial Physiology and Structure Cell morphology Moderate-sized Gram rods Non-spore-forming Motile(with peritrichous flagella)or non-motile
4、 Physiology All are facultative anaerobes Simple nutritional requirements:Ferment glucose Reduce nitrates to nitritesLecture 12BIOL 5335Distinguishing Characteristics Oxidase:Distinguishes among other fermentative and non-fermentative Gram bacilli Lactose fermentation(red colonies on MacConkey agar)
5、Separate Escherichia,Klebsiella,Enterobacter from other lactose EnterobacteriaceaeLecture 12BIOL 5336Distinguishing Characteristics Resistance to bile salts Separate Shigella and Salmonella from normal flora in this group Eosin Methylene Blue(EMB)Lactose,eosinY,methylene blue;Lac+;grow with green sh
6、eenLecture 12BIOL 5337Virulence Factors Antigens Somatic“O”LPS Major cell wall Ag;heat stable Specific“O”antigens associated with each genus;however,cross reactions are commonSalmonella and CitrobacterEscherichia and ShigellaLecture 12BIOL 5338Virulence Factors Capsular K Either protein or polysacch
7、aride Heat-labile May interfere with detection of“O”Removed by boiling organisms Capsular antigen of Salmonella typhi referred to as Vi antigenLecture 12BIOL 5339Virulence Factors Capsular K,continued Shared by different genera both inside and outside of family Cross reactionsE.coli K1 with N.mening
8、itidis and Haemophilus meningitidisK.pneumoniae with S.pneunomiae Organisms with specific antigens have been associated with increased virulence (e.g.,E.coli K1 with neonatal meningitis)Lecture 12BIOL 53310Virulence Factors Flagella H Heat-labile proteins Can be absent or undergo antigenic variation
9、(present in two phases)Specific H antigens assocated with diseaseLecture 12BIOL 53311Virulence Factors General role in pathogenesis of“O,”“K,”and“H”antigens Specific antigens associated with meningitis,gastroenteritis,and urinary tract infections Role that Ags play in these diseases is not clear Som
10、e capsular Ag are poor immunogens Protect against antibody-mediated phagocytosis Flagellar Ag probably play a role in adherenceLecture 12BIOL 53312Virulence Factors Pili Attachment to host cellsLecture 12BIOL 53313Pathogenesis of EscherichiaE.coli present in gastrointestinal tract in normal flora Ba
11、cterial sepsis(multiplication in blood)Primary focus-infection of urinary tract or spread from gastrointestinal tract Death can occur in immunocompromised patients and infections resulting from intestinal perforationLecture 12BIOL 53314Pathogenesis of Escherichia Neonatal meningitisE.coli and group
12、B streptococci most common 75%E.coli possess Capsular K1 antigen Colonization of infants with E.coli at delivery is common;disease is notLecture 12BIOL 53315Pathogenesis of Escherichia Urinary tract infections(80%community and most nosocomial)Originate from gastrointestinal tract Important virulence
13、 factors Resistance to serum-killing Production of hemolysins Pili-mediated binding(not demonstrated in vivo)Production of slime layer that participates in cell adhesionLecture 12BIOL 53316Pathogenesis of Escherichia Gastroenteritis(countries with poor hygiene)Enterotoxigenic(ETEC)Mediated by heat-l
14、abile(like cholera)and heat-stable exotoxins(activates guanylate cyclase and stimulates secretion of fluid)Both are coded from plasmid-borne genes World-wide:both adults and children Incubation 1-2 days;persists 3-4 days Mild symptoms,including cramps,nausea,vomiting,watery diahrreaLecture 12BIOL 53
15、317Pathogenesis of Escherichia Gastroenteritis,continued Enteroinvasive(EIEC)Invade and destroy colonic epithelium Fever and cramps with blood and leukocytes in stool Uncommon;often food-borne Enteropathogenic(EPEC;childhood diarrhea)Organism adheres to enterocyte plasma membrane and causes destruct
16、ion of microvilli producing watery diarrhea Adhesiveness mediated by plasmid-encoded piliLecture 12BIOL 53318Pathogenesis of Escherichia Gastroenteritis,continued Enteropathogenic(continued)Infants 1 year affected Enterohemorrhagic(EHEC;hemorrhagic colitis)Produces cytotoxin(verotoxin)Severe abdomin
17、al pain,bloody diarrhea,little or no fever Warm months of year;affects children 5 yearsLecture 12BIOL 53319Pathogenesis of Escherichia Gastroenteritis,continued Enteroaggregative(EaggEC;watery diarrhea)Infants 90%dieLecture 12BIOL 53357Pathogenesis of Yersinia enterocolitica Associated with Contamin
18、ated meat or milk Colder climates during winter monthsLecture 12BIOL 53358Pathogenesis of Yersinia enterocolitica Gastroenteritis Diarrhea,fever,abdominal pain Lasting for 1-2 weeks Chronic form can persist for months or year Can mimic appendicitis,particularly in children Adults can have septicemia
19、,arthritis,intrabdominal abscess,hepatitis,and osteomyelitisLecture 12BIOL 53359Pathogenesis of Klebsiella pneumoniae Associated pneumonia Frequently associated with Necrotic destruction of alveolar spaces Production of blood-tinged sputum Can also cause wound,soft tissue,and urinary tract infection
20、sLecture 12BIOL 53360Pathogenesis of Proteus mirabilis Urinary tract infections Produce large amounts urease Urea into carbon dioxide and ammonia Changes renal pH Facilitates formation of stones Also toxic for uroepithelium Presence of pili may decrease virulence Better phagocytosisLecture 12BIOL 53
21、361Prevention and Control Difficult,because enterobacteria are normal flora Prevention Plague Effective vaccines Prophylactic use of tetracycline for medical workers in contact with pneumonic plague Vaccines for Salmonella typhiLecture 12BIOL 53362Prevention and Control Treatment Use of antibiotic susceptibility testingE.coli and Proteus normally respond well to antibiotic treatmentLecture 12BIOL 53363Lecture 12 Questions?Comments?Assignments.
