S1. E. Coli, klebsiella & proteus Flashcards
common characteristics of the 3 groups?
- normal flora of intestinal tract (colon)
- belong to the family ( Enterobacteriaceae)
- grow on simple media (enteric medium & macConkey agar)
- gram -ve, non spore formers
- aerobe & faculatative anaerobe
- motile ( W/ PERITRICHOUS FLAGELLAE) or non- motile
- ferment glucose w/ or w/out gas production
- reduce nitrate to nitrite
- comprise pathogens and non-pathogens
- possess somatic (O) antigen, flagellar (H) antigen, fimbrial (P, F, CS) antigens or capsular (K) antigens
What do u know about E, coli?
- most abundant aerobic flora in COLON
- indicator of FEACAL POLLUTION of food and water
- gram -ve, motile, grows on mcConkey agar producing NON-MUCOID PINK COLONIES ( DUE TO LACTOSE- FERMENTATION) ferment-sugar producting ACID( makes the colonies pink) and gas
Diff parts of the bacterium act as diff antigens, what antigens does e, coli possess?
Possess LPS ( somatic) (O) antigen, flagellar (Hoo(o antigen), capsular (K antigen) or fimbrial antigens
What are the intestinal / extra-intestinal diseases caused by e.coli ?
Intestinal—> diarrhea
Extra-intestinal —> UTI, neonatal meningitis, septicaemia, wound infection, septic shock (severe infection causing drop in BP affecting function of organs-kidney, heart, brain etc. leading to death)
What’re the virulence factors of E.coli?
1- strains causing NEONATAL INFECTION possess capsular (K) antigens !(K1,K5)! Capsule protects the organism from bactericidal effect of complement & phagocytes
2- strains causing UTI possess ! type 1 and P fimbirae !
3- HAEMOLYSIN, CYTOTOXIN & SIDEROPHORES causing ! extra-intestinal infections !
Pathotypes (virotypes) of diarrhoeagenic (cause diarrhea) E.coli?
- Enterotoxigenic E.coli. (ETEC)
- Enteroinvasive E.coli. (EIEC)
- Enteropathogenic E.coli. (EPEC)
- Enterohaemorrhagic E.coli (EHEC)
- Enteroaggregative E.coli. (EEAC)
What pathotype E coli causes persistent diarrhea?
EAEC
What pathotype of e.coli causes watery, cholera like diarrhea?
ETEC
What pathotype of e.coli causes traveller’s diarrhea and mediated by what?
ETEC, mediated by Heat-labile entertoxin (LT) o heat-stable enterotoxin (ST)
What are heat-labile (LT) and heat-stable (ST) entertoxins?
LT: -degraded by heat -elevate cAMP ST: - not degraded by heat -elevate cAMP * both cause diarrhea ( travellar’s)
What diarrhea does EPEC cause and mediated by?
in children up to 2 yrs
mediated by attaching to and destroying the small intestinal epithelial cells
Other names of EHEC are?
- verocytooxin producing E.coli (VTEC)
- shiga toxin-producing E.coli (STEC)
what diarrhea EHEC causes and mediated by?
ranging from mild ,watery to diarrhea w/ large amounts of fresh blood (haemorrhagic colitis) w/ some ppl developing haemolytic uraemic syndrome ( HUS- heaemolytic anaemia, uraemia ( kidney failure), thrombocytopenia)
* mediated by shiga virus (VT)(1&2); predominant serotype was O157:H7
What is the reservois of infection?
intestinal tracts of cattle and other animals (carriers only)
disease transmitted thru contaminated meat ( this e.coli nicknamed hamburger e.coli)
transmission also by contaminated salads and unpasteurised fruit juices
what does EIEC cause?
causes dysentery ( stool w blood, mucus & pus) in all ages by invading the colonic mucosa. This e.coli very closely related to shigella spp. that also causes dysentery
What does EAEC cause?
Causes persistent diarrhea > 14 days in children by adherence of bacterial aggregates to colonic mucosa also causes travellers doarrhea and diarrhea in HIV/AIDS patients
What are the laboratory diagnosis of e.coli infections?
- clinical specimens ( body fluid, swab, diarrheal stool) on McConkey agar
- lactose fermenting pink colony confirmed by biochemical reaction ( Vitek, API-20E-commercial tests)
- specific antigens (K1) pr serotypes ( O,H antigens) identified by aggulnation test w specific specimen
- diarrhoeagenic e.coli identified by PCR tests based on distinct virulence genes
Klebsiella characterestics?
Gram -ve, non-motile, polysaccrhide capsule (80 types), produce lactose fermenting (pink) MUCOID colonies ( due to polysaccride capsule ) on mcConkey agar
Diseases caused by klebsiella?
- nosocomial infections, UTI, resp.tract infection (bronchopneumonia) , wound infection, bacteriaemia
- rhinoscleroma ( by K.rhinoscleromatis) - granulomatous infiltration of submucosa affecting nose, larynx, throat, trachea
- ozaena (by k.ozaenae) - arrophic rhinitis ( wasting of nasal mucosa)
- some cases of antibiotic-associated haemorrhagic colitis (by k.granulomatis causes donovosis, a sexually transmitted disease)
Virlulence factors of klebsiella?
- long chain LPS protects from opsonisation (coating by antibody for elimination by phagocyte) and killing by serum complement
- capsule protects against phagocytosis
- fimbriae (type 1 fimbria) promote adhesion to tissues
- iron acquisition by SIDEROPHORE production
- hypermucoviscosity ( excess polysaccharide capsule production) comfers high serum resistence & correlates w high invasive infection (liver abscess)
- ESBL (extended specturum B-lactamase) & carbapenamase- producing Klebsiella sp-. Virulent & produce outbreaks
Laboratory diagnosis of klebsiella species infections?
- clinical specimen on mcConkey agar
- pink, mucoid colonies comfirmed as klebsiella by biochemical reactions using Vitek test or API-20E test
- capsular types determined by capsular swelling reaction by aggulnation specifc antidsera (Quellung reaction, german word for swelling-capsule swells by binding w antibody)
Proteus species characterestics?
gram -ve, motile, produse lactose-nonfermenting, pale colonies on mcConkey agar.
produce striking swarming effect on blood sugar, characterized by expanding waves of organism. have ability to deaminate amino acids (Phenyl alanine converted to phenyl pyruvic acid by deaminase) produce UREASE, splitting urea into ammonia and carbon dioxide
another bacteria that produces urease?
helicobacter pylori :)
What are the medically imp species?
Proteus mirabilis, Proteus vulgaris & Proteus rettgeri
* cell wall antigens of certain strains p.vulgaris (OX-2,OX-19, OX-K) cross-react w certain species of rickettsiae (gram -ve bacteria causing spotted & typhus fevers). These proteus antigens detect antibodies to rickettsiae in patients serum. This test is called WEIL-FELIX test
