- Most urine specimens are obtained from adult patients via the clean-catch midstream technique.
- Bacteriuria can be detected microscopically using Gram staining of uncentrifuged urine specimens, Gram staining of centrifuged specimens, or direct observation of bacteria in urine specimens.
- On staining, E coli appear as non-spore-forming, Gram-negative rod-shaped bacterium
- Routine urine cultures should be plated using calibrated loops for the semi-quantitative method.
Note: The most commonly used criterion for defining significant bacteriuria is the presence of ⩾105 CFU per milliliter of urine.
- The types of media used for routine cultures should be limited to blood agar and MacConkey’s agar.
- Urine cultures should be incubated overnight at 35°C–37°C in ambient air before being read.
E. coli typically produce positive test results for indole, lysine decarboxylase, lactose, and mannitol fermentation and produces gas from glucose. An isolate from urine can be quickly identified as E. coli by its hemolysis on blood agar, typical colonial morphology with an iridescent “sheen” on differential media such as EMB agar, and a positive spot indole test result. More than 90% of E. coli isolates are positive for β-glucuronidase using the substrate 4-methylumbelliferyl-β-glucuronide (MUG).
- ETEC: commercial immunoassays available for detecting ST in clinical specimens and cultures; PCR assays used with clinical specimens.
- EPEC: Characteristic adherence to HEp-2 or HeLa cells; probes and amplification assays developed for the plasmid-encoded bundle-forming pili and gene targets on the “locus of enterocyte effacement” pathogenicity island.
- EAEC: Characteristic adherence to HEp-2 cells; DNA probe and amplification assays developed for conserved plasmid.
- STEC: Screen for O157: H7 with sorbitol MacConkey agar; confirm by serotyping; immunoassays (ELISA, latex agglutination) for detection of the Stx toxins in stool specimens and cultured bacteria; DNA amplification assays developed for Stx genes.
- EIEC: Sereny (guinea pig keratoconjunctivitis) test; plaque assay in HeLa cells; probes and amplification assays for genes regulating invasion (cannot discriminate between EIEC and Shigella).
- The sulfonamides, ampicillin, cephalosporins, fluoroquinolones, and aminoglycosides have marked antibacterial effects against the enterics, but variation in susceptibility is great, and laboratory tests for antibiotic susceptibility are essential.
- E. coli meningitis requires antibiotics, such as third-generation cephalosporins (eg, ceftriaxone).
- E. coli pneumonia requires respiratory support, adequate oxygenation, and antibiotics, such as third-generation cephalosporins or fluoroquinolones.
- In most cases of diarrheal disease, antibiotics are not prescribed. The best way to treat E coli infection is to drink plenty of fluids to avoid dehydration and to get as much rest as possible. However, patients should avoid dairy products because those products may induce temporary lactose intolerance, and therefore make diarrhea worse.
Prevention and Control
- It is widely recommended that caution be observed in regard to food and drink in areas where environmental sanitation is poor and that early and brief treatment (eg, with ciprofloxacin or trimethoprim-sulfamethoxazole) be substituted for prophylaxis.
- Their control depends on handwashing, rigorous asepsis, sterilization of equipment, disinfection, restraint in intravenous therapy, and strict precautions in keeping the urinary tract sterile (ie, closed drainage).
- Murray, P. R., Rosenthal, K. S., & Pfaller, M. A. (2013). Medical microbiology. Philadelphia: Elsevier/Saunders
- Sastry A.S. & Bhat S.K. (2016). Essentials of Medical Microbiology. New Delhi: Jaypee Brothers Medical Publishers.
- Scaletsky, I. C., Fabbricotti, S. H., Carvalho, R. L., Nunes, C. R., Maranhão, H. S., Morais, M. B., & Fagundes-Neto, U. (2002). Diffusely adherent Escherichia coli as a cause of acute diarrhea in young children in Northeast Brazil: a case-control study. Journal of clinical microbiology, 40(2), 645-8.