Comparison of sorbitol MacConkey agar and a two-step method which utilizes enzyme-linked immunosorbent assay toxin testing and a chromogenic agar to detect and isolate enterohemorrhagic Escherichia coli.
Enterohemorrhagic Escherichia coli (EHEC) and specifically serotype O157:H7 are a significant cause of hemorrhagic gastrointestinal disease and the hemolytic uremic syndrome. Methods currently used in clinical microbiology labs, such as sorbitol-MacConkey (SMAC) agar, reliably detect only O157:H7. We have evaluated a two-step method that has the potential to identify and isolate all EHEC serotypes, including serotype O157:H7. This method utilizes a chromogenic selective-differential medium for the isolation of E. coli together with an enzyme-linked immunosorbent assay (ELISA) that detects the Shiga-like toxins Stx1 and Stx2. Both are commercially available and usable in a wide range of clinical microbiology laboratories. Compared to a Vero cell cytotoxic assay, SMAC had sensitivities of 23.5% for the identification of all EHEC serotypes and of 50.0% for the identification of O157:H7 alone. The two-step method had sensitivities of 76.5 and 100%, respectively. The ELISA alone had a sensitivity of 82.4% in the detection of Stx1 and Stx2. The specificity was 100% in all cases. Overall, 14 EHEC isolates were obtained: 8 (58%) O157:H7, 2 (14%) O26, 2 (14%) O111:NM, 1 (7%) O103:H2, and 1 (7%) O121:H19. All but one were isolated during the months of May to September. The two-step method was found to be considerably more expensive than SMAC for both positive and negative samples.
Novicki
T J
TJ
Department of Pathology, University of Utah School of Medicine and ARUP Laboratories, Salt Lake City, Utah 84113, USA. tnovicki@fhcrc.org
Daly
J A
JA
Mottice
S L
SL
Carroll
K C
KC
D000362:Agar; D000818:Animals; D001427:Bacterial Toxins / Q000276:immunology / Q000378:metabolism*; D015373:Bacterial Typing Techniques; D002522:Chlorocebus aethiops; D002863:Chromogenic Compounds / Q000378:metabolism; D003470:Culture Media / Q000191:economics; D003601:Cytotoxicity Tests, Immunologic; D004797:Enzyme-Linked Immunosorbent Assay / Q000191:economics / Q000379:methods*; D004926:Escherichia coli / Q000145:classification* / Q000302:isolation & purification* / Q000378:metabolism; D004927:Escherichia coli Infections / Q000175:diagnosis / Q000453:epidemiology / Q000382:microbiology*; D006801:Humans; D012703:Serotyping; D022603:Shiga Toxins; D014709:Vero Cells
D001427:Bacterial Toxins; D002863:Chromogenic Compounds; D003470:Culture Media; D022603:Shiga Toxins; D000362:Agar