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3 Cards in this Set
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Most important species human pathogen Gram-ve rods Facultative anaerobes O(capsule),H(flagella) and K antigens Aerobe in human gut Remain viable for some days after excretion in feces; responsible for recent contamination of water Survive at 44degrees Peritrichous flagella Motile Capsulated O, K and H antigens Indole positive Fermenters of mannitol Catalase negative Oxidase negative
Colonies.
MacConkey- pink colonies
Eosin methylene blue agar- metallic shine appearance on colonies
Virulence factors
P pili Binds galactoside disaccharide receptor if urinary tract epithelium
Type I pili Bind D mannose receptor on epithelial cells surface(not easily flushed out) Colonizing factors antigen Bind to enterocytesIntimin/ non fimbrial adhesin Attach on lesions Siderophores Iron sequestration Capsule (K antigen)K1 capsule in neonatal meningitis Decrease antibodies and complement bacterial surface, inhibit phagocytosis O antigen Outer membrane Endotoxin H antigens (flagella) Motility and Invasive disease Alpha hemolysins Pore forming on membrane Lyse lymphocytes, beta hemolysins inhibit phagocytosis and chemotaxis of neutrophils
Colonizing factors antigen Bind to enterocytes Type 3 secretion System Inject E coli secretory proteins Intimin/ non fimbrial adhesin Attach on lesion O antigen Outer membrane Endotoxin H antigens (flagella) Motility and Invasive disease Alpha hemolysins Pore forming on membrane Lyse lymphocytes, beta hemolysins inhibit phagocytosis and chemotaxis of neutrophils Exotoxins LT(heat labile) Produced by enterotocigenic E coli Resemble cholera toxin in it's functions
Has two fragments A and B Active A fragment causes ADP ribosylation of G protein- upregulates adenylate cyclase- increase cAMP-increase water and electrolytes secretion- diarrhea
Fragment B is inactive and binds GM1 ganglioside receptor on intestinal epithelium
It's plasmid coded Detected by: ligated ileal loop test, skin test, Chinese hamster ovary cells
ST(heat stable) Produced by enterotocigenic E coli
Binds guanylate cyclase- increase cGMP- diarrhea Plasmid coded
Verocytotoxin/shiga-like toxin
Produced by enterohemorrhagic E coli It's cytotoxic to Vero cell lines Has A and B fragment Fragment B binds to globotriosyl ceramide (Gb3) receptor on intestinal epithelium
Fragment A is active fragment, inhibit protein synthesis by inhibiting 28S ribosome Cause hemolytics uremic syndrome By O 157 H7 serotype
It's bacteriophage coded
Epidemiology
Human bowel colonized within 40hrs after birth 700 serotypes Most common cause of UTI 2nd most common cause of neonatal meningitis Leading cause of infantile bacterial diarrhea
Transmission UTI- Intestinal e coli- perianal-urethra Neonatal meningitis- birth canal Intestinal disease-contaminated food and water
Extra intestinal disease UTI Neonatal meningitis Pneumonia Septicemia
Intestinal disease EPEC ETEC EIEC EHEC EAEC
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ENTEROINVASIVE E COLI
Similar to Shigella Lower dose to cause infections Atypical E coli Non motile Non lactose fermenting Sereny test positive
Virulence factors Outer membrane proteins
Common serotypes O28, O122, O114, O124, O136,O152
Epithelial cell invasion due to plasmid coded antigen called virulence marker antigen (VMA)
Causes ulceration of bowel, dysentery
ENTEROTOXIGENIC E COLI
Cause travellers diarrhea in all ages Infective dose more than 10'9 Not transmitted Food and water borne Causes acute watery diarrhea in adults and infants Along with abdominal cramps Onset 1+2 days Watery diarrhea similar to cholera
Non inflammatory non invasive
Common serotypes O6,8,15,25,27,153,159
Toxins Heat labile-highly antigenic;increase cAMP Heat stable- increase cGMP
Self limited disease-resolves within 3-4days
Virulence factors Colonization factor antigen LT ST
Enteropathogenic E coli
It is non toxigenic and non invasive Cause infantile bacterial diarrhea Rarely adults diarrhea
Non watery diarrhea
Virulence EPEC adherence factor/bundle forming antigen- adhere to cap like structures in the intestinal lumen Adhesion to the intestinal lumen mediated by plasmid coded bundle forming pili Intimin- on cell membrane, cause polymerization on adhesion lesions causing diarrhea
20% diarrhea in bottle fed infants less than 1yrs
Transmission Formites, drinking water, meat products
Infective dose for infants very low
Virulence factors
Intimin- attach to TAR receptors E coli secretory proteins Translocated intimin receptor- polymerization of actin molecules Attachment erosive lesion Apoptosis of cells
Enterohemorrhagic E coli
Associated serotypes O157 H7, O26, H11,O6,4)55,91,103,103,113 Transmitted by contaminated food and water Commonest causes of diarrhea associated hemolytics Zoonosis Undercooked group beef Prevalence in industrialized nations
Fimbria mediated toxin- colonization factor antigen; plasmid coded; attachment to intestinal mucosa
Self limited disease-resolves within 3-4days
Reservoir are infected cattles,beef products, lettuce , sprouts
Virulence Intimin- attach to secretory TAR receptors causing attach lesions Shiga like toxin- damage blood vessels leading to microangiopathy
Symptoms Watery diarrhea, severe cramps progress to bloody diarrhea Low grade fever
Complications Hemolytics uremic syndrome Thrombocytopenic purpura Renal failure Microangiopathic hemolytics anemia Antibiotics may induced increase in shiga like toxin
Verocytotoxin has predilection for endothelial cells causing capillary microangiopathy leading to hemorrhagic colitis: manifests gross as bloody diarrhea, abdominal pain , fecal leukocytosis and no fever
More common in children
Diagnosis
EHEC does not ferment sorbitol Show pale colonies in sorbitol MacConkey agar Toxin detection in Vero cell lines,fecal toxin antigen detection by ELISA,or PCR to detect gene coding for verocytotoxin Low infective dose less than 102.cfu can initiate infections
Diagnosis EHEC does not ferment sorbitol Show pale colonies in sorbitol MacConkey agar More common in children
Toxin detection in Vero cell lines,fecal toxin antigen detection by ELISA,or PCR to detect gene coding for verocytotoxin
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Enteroaggregative E coli
Adheres to HEp-2 cells in a stacked brick fashion Most strains are O antigen and H antigen Cause chronic diarrhea in malnourished pple
Pathogenesis Colonization mediated by aggregative adhesion fimbriae I, regulated by aggR gene) Produce Enteroaggregative heat stable enterotoxin
Manifestation Persistent and acute diarrhea are common: developing countries
Diagnosis Isolation by culture of HEp-2 cells that form brick fashion
Uropathogenic E coli
Cause urinary tract infections Account for 85-95% of all UTI cases UPEC serotypes O1,2,4,6,7,75
Route of spread Ascending - after colonization periurethral area, it ascends to bladder and kidney
Descending - hematogenous seeding of E coli into kidney resulting in polynephritis
Types Upper UTI Lower UTI Neonatal meningitis 2nd most common Transmission via birth canal Virulence factors-K antigen Fever irritability constipation poor feeding bulging fontanelle seizures Neonatal pneumonia Birth canal Respiratory symptoms Septicemia When gain entry into blood
Predisposing factors Females due to short urethra and close proximity to anus Pregnancy- physiological obstruction of urinary tract due to growing fetus leading to prolonged stasis of urine and asymptomatic bacteriuria Presence of urinary catheter Urinary stones Prostate enlargement
Laboratory diagnosis Clean mid stream urine Suprapubic aspiration for coma patients Catheterised patient from catheter tube not bag
E coli is the most common cause of neonatal sepsis |
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