Journal of Medical Microbiology (2005), 54, 273–278 DOI 10.1099/jmm.0.45908-0 45908 & 2005 SGM Printed in Great Britain 273 Correspondence Tadashi Shimamoto tadashis@hiroshima-u.ac.jp Received 27 September 2004 Accepted 26 November 2004 Molecular characterization of a multidrug-resistant strain of enteroinvasive Escherichia coli O164 isolated in Japan Ashraf M. Ahmed, 1 Shin-ichi Miyoshi, 2 Sumio Shinoda 2 and Tadashi Shimamoto 1 1 Laboratory of Food Microbiology and Hygiene, Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima 739-8528, Japan 2 Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan Enteroinvasive Escherichia coli (EIEC) O164 strain RIMD05091045 was isolated from a travelling patient suffering from diarrhoea at the Osaka airport quarantine facility in Japan. The strain showed multidrug resistance against streptomycin, spectinomycin, co-trimoxazole (trimethoprim/ sulfamethoxazole) and ampicillin, and reduced susceptibility to ciprofloxacin. Molecular characterization of the multidrug-resistance phenotype revealed the presence of a class 1 integron containing three genes, a dihydrofolate reductase type XII gene, dfrXII, which confers resistance to trimethoprim, an aminoglycoside adenyltransferase gene, aadA2, which confers resistance to streptomycin and spectinomycin, and an ORF of unknown function. Southern blot hybridization and conjugation experiments showed that the class 1 integron was located on a transferable plasmid that was less than 90 kb in size. The resistance of EIEC O164 to ampicillin was found to be due to the presence of TEM-1 â-lactamase. On the other hand, a single mutation that has not previously been described, P158-to-S, was detected downstream of the quinolone-resistance-determining region of parC of topoisomerase IV and may be responsible for the reduced susceptibility to ciprofloxacin in this strain. INTRODUCTION Bacillary dysentery, which is mainly caused by Shigella and enteroinvasive Escherichia coli (EIEC), is responsible for a substantial proportion of acute diarrhoeal diseases world- wide (Taylor et al., 1986). EIEC outbreaks are usually food- or water-borne (Marier et al., 1973; Snyder et al., 1984). However, outbreaks of EIEC diarrhoea through person-to- person transmission have also been reported (Harris et al., 1985). E. coli serotype O164 is the most prevalent serotype among the EIEC in Bulgaria and is annually isolated in sporadic, as well epidemic, cases (Todorova et al., 1990). In Japan, EIEC serotype O164 is rare and was responsible for a case of food poisoning in 1992 (Yamamura et al., 1992). Epithelial cell invasion is a key virulence factor for EIEC, and thus dysentery is characterized by painful abdominal cramps and frequent defecation of blood and mucus attributed to the penetration and destruction of colonic epithelia (Nataro & Kaper, 1998). EIEC strains are closely biochemically, geneti- cally and pathogenetically related to Shigella species (Nataro & Kaper, 1998). Antimicrobial resistance associated with diarrhoea is an issue of great significance for public health at the global level. Moreover, it is of particular concern if the causative agents have multidrug resistance (MDR). In the last two decades, MDR phenotypes have spread widely among Gram-negative bacteria. One of the most important tools for this spread is the recently discovered genetic element known as an integron (Jones et al., 1997). Integrons are natural genetic engineering systems that incorporate circularized ORFs, called gene cassettes, and convert them into functional genes (Rowe-Magnus & Mazel, 2001). The most notable gene cassettes identified within integrons are those conferring resistance to antibiotics (Rowe-Magnus & Mazel, 2001). Integron platforms are incapable of self-transposition, but this defect is often complemented through association with an insertion Abbreviations: CCCP, carbonyl cyanide m-chlorophenylhydrazone; EIEC, enteroinvasive Escherichia coli; ETEC, enterotoxigenic Escherichia coli; MDR, multidrug resistance; QRDR, quinolone resistance-determining region. The GenBank/EMBL/DDBJ accession numbers for the class 1 integron sequence, including the dfrXII and aadA2 genes and an unknown ORF, and the blaTEM-1 gene sequence of EIEC O164 strain RIMD05091045 are AB154407 and AB194682, respectively.