Downloaded from www.microbiologyresearch.org by IP: 174.129.184.250 On: Wed, 17 Aug 2016 01:58:07 J. Med. Microbiol. - Vol. 40 (1994), 241-245 0 1994 The Pathological Society of Great Britain and Ireland Diagnosis of infections with Shiga-like toxin-producing Escherichia cob by use of enzyme-linked immunosorbent assays for Shiga-like toxins on cultured stool samples D. LAW, A. A. HAMOUR?, D. W. K. ACHESON$, H. PANIGRAHItj, LEELA A. GANGULI and D. W. DENNING"? Department of Microbiology and * Department of Medicine, Hope Hospital, Eccles Old Road, Salford M6 8HD, t University of Manchester, Regional Department of Infectious Diseases and Tropical Medicine, Monsall Hospital, Newton Heath, Manchester M70 8WR, $ Department of Medicine, Division of Geographic Medicine and Infectious Diseases, 750 Washington Street, NEMCH + 4 7, Boston, MA, USA and 0 Department of Microbiology, Monsall and North Manchester General Hospitals, Manchester M8 6RB Summary. Shiga-like toxin-producing (SLT) Escherichia coli, particularly those belonging to serogroup 0 157, are responsible for haemorrhagic colitis, haemolytic uraemic syndrome and some cases of gastro-enteritis. The rapid and reliable diagnosis of all these infections is necessary for correct patient management and for epidemiological reasons, but is rarely possible with present methods. We compared the efficacy of two methods, (i) the culture of faeces in broth that contained mitomycin C followed by enzyme-linked immunosorbent assay (ELISA) for SLTs, and (ii) the culture of faeces on sorbitol MacConkey agar (SMA), in the detection of infections caused by SLT-producing E. coli. SLT-producing E. coli 0 157 strains were isolated on SMA from 42 of 475 faecal samples, but SLTs were detected by ELISA in culture supernates or lysates of 54 of 475 samples. SLT-producing E. coli strains were isolated subsequently from 11 of 12 ELISA-positive, SMA culture-negative samples by a colony blot technique. In four cases, SLT-producing E. coli of serogroups other than 0157 were isolated and in seven cases E. coli 0157 was isolated in small numbers. The ELISA is a rapid and sensitive technique for the diagnosis of SLT-producing E. coli infection, especially where low numbers of the organism are present in faeces and when the infection is caused by a serogroup other than 0157. Introduction Human infections associated with strains of Escheri- chia coli that produce Shiga-like toxin (SLT) or verotoxin present as non-bloody diarrhoea, bloody diarrhoea or haemorrhagic colitis (HC).l* Haemolytic uraemic syndrome (HUS) and thrombotic thrombo- cytopaenic purpura are also associated with infection with SLT-producing E. coli.f~3~4 Although one sero- type, 01 57 : H7, predominates in most human infec- tions with SLT-producing E. coli, infections can be caused by at least 30 0 serogroups of E. ~ oli.~ The true incidence of SLT-producing E. coli infection is prob- ably underestimated because of the limitations of the currently available diagnostic tests. The culture on sorbitol MacConkey agar (SMA) as used by many laboratories only detects E. coli strains of serogroup 0157 that do not ferment sorbitol, whereas most other E. coli serotypes ferment sorbit01.~ Moreover, the numbers of SLT-producing E. coli in the faeces of patients with HC and HUS decreases markedly as the Received 26 April 1993; revised version accepted 1 Oct. 1993. diseases progress and this reduces the probability of isolating the infecting organism later in the diseases.' Shiga-like toxins can be detected in faeces and from cultures of E. coli with cytotoxicity assays5. ' and toxin- neutralising antibodies are required to ensure spec- ificity. DNA probes that hybridise with SLT-I or SLT-I1 have been developeds and have proved useful in clinical st~dies.~-l' The polymerase chain reaction (PCR) has also been applied to the detection of SLT- producing E. coli in clinical samples.12 At present these techniques are not widely available in routine clinical microbiology laboratories. Immunological techniques for detecting SLTs, such as enzyme-linked immunosorbent assays (ELISA), have been described.13* l4 Recently, we developed a diagnostic system based on the culture of faecal samples in broth containing mitomycin C, followed by ELISA for SLT-I and -II.15This assay is based on the principle that the toxins produced in most human SLT-producing E. coli infections are mediated by bacteriophage and are, therefore, inducible with mito- mycin C.16 This method amplified toxin production and allowed detection of low numbers (< 1 in 1000) of 17 24 1 JMM 40