Which of the following is FALSE regarding Enterobacteriacae?
Ans. b (They are oxidase positive) (Ref. Ananthnaryan microbiology, 6th ed., 270)# Characteristics of E. coli - All members of Enterobacteriaceae family have in common the fact that they- Ferment glucose,- Oxidase negative, and- Reduce nitrates to nitrites.ENTEROBACTERIACEAEIntroduction# E. coli is the most commonly found aerobic, gram-negative bacilli in the GI tract of humans.# E. coli is responsible for over 80 percent of UTIs, and others like gastroenteritis, sepsis, and neonatal meningitis.# Most of these cause a self-limited diarrhea with the exception of enterohemorrhagic E. coli, frequently known as E. coli serotype O157:H7. which is usually acquired from eating poorly cooked meat from an infected cow.# Complications of infection with this organism include hemolytic uremic syndrome (HUS).# Hemolysin HlyA is particularly important in producing an inflammatory response in the urinary tract, whereas most of the other exotoxins are more pathogenic in the GI tract.# E. coli are divided into serogroups based on the O antigen found on the lipopolysaccharide (LPS) of the cell membrane and the H antigen found on the flagella.Diagnosis# A quantitative urine culture from a symptomatic patient should demonstrate greater than 105 colony-forming units (CFUs) bacteria/mL urine to be considered significant.# E. coli would appear as pink colonies on MacConkey agar indicating fermentation of lactose. A rapid spot indole test would give a preliminary identification of E. coli, which would be confirmed by biochemical analysis.Treatment and Prevention# Common antimicrobials chosen include trimethoprim-sulfamethoxazole, or a fluoroquinolone.# Most E. coli are resistant to ampicillin and penicillin.Additional Educational points:FactorFunctionOrganismsAll capsulesAntiphagocyticStreptococcus pneumoniae, Klebsiella pneumoniae, Haemophilus influenzae, Pseudomonas aeruginosa, Neisseria meningitidis, Cryptococcus neoformans (mnemonic: some killers have pretty nice capsules) and many moreM proteinAntiphagocyticGroup A streptococciA proteinAntiphagocyticStaphylococcus aureusLipoteichoic acidAttachment to host cellsAll gram-positive bacteriaAll piliAttachmentMany gram-negativePili of N. gonorrhoeaeAntiphagocytic, antigen variationN. gonorrhoeaHyaluronidaseHydrolysis of ground substanceGroup A streptococciCollagenaseHydrolysis of collagenClostridium perfringens, Prevotella melaninogenicaUreaseIncrease local pH(contributes to kidney stones)Proteus, Ureaplasma, Nocardia, Cryptococcus, Helicobacter (mnemonic: PUNCH)KinasesHydrolysis of fibrinStreptococcus, StaphylococcusLecithinaseDestroys cell membranesClostridium perfringensHeparinaseThrombophlebitisBacteroidesCatalaseDestroys hydrogen peroxide (major problem for CGD patients)# Most important; Staphylococcus. Pseudomonas, Aspergillus, Candida, Enterobacteriaceae# Most anaerobes lack diseaseIgADestroy IgA, promote colonization of mucosal surfacesNeisseria, Haemophilus, Sterptococcus pneumoniaeOxidasePossession of cytochrome C oxidaseNeisseria and most gram-negatives, except EnterobacteriaceaeCoagulaseProduces fibrin clotStaphylococcus aureus and Yersinia pestis
Non-fastidious growth
They are oxidase positive
They are catalase positive
They reduce nitrates
Bacteria