MICROBIAL DRUG RESISTANCE Volume 8, Number 2, 2002 © Mary Ann Liebert, Inc. Characterization of Antimicrobial Resistance Among Escherichia coli O111 Isolates of Animal and Human Origin D.G. WHITE, 1 S. ZHAO, 1 P.F. MCDERMOTT, 1 S. AYERS, 1 S. GAINES, 1 S. FRIEDMAN, 1 D.D. WAGNER, 1 J. MENG, 2 D. NEEDLE, 3 M. DAVIS, 3 and C. DEBROY 3 ABSTRACT Fifty isolates of Escherichia coli serogroup O111 recovered from humans and various animal species over a 24-year period (1976–1999) were examined for typical virulence-associated factors and susceptibilities to an- timicrobials of human and veterinary significance. Nine H (flagellar) types were identified including nonmotile (n 5 24), 32 (n 5 12), negative (n 5 5), and 56 (n 5 3). Thirty-five (70%) isolates possessed at least one Shiga- toxin-producing E. coli (STEC)-associated virulence determinants (eae, stx1, stx2, hlyA) via PCR analysis. Of these 35 isolates, 20 possessed eae, stx1, and hlyA genes, whereas three isolates possessed eae, stx1, stx2, and hylA genes. Multiple antibiotic resistance was observed in 70% of the 50 E. coli O111 isolates. The majority of isolates displayed resistance to streptomycin, sulfamethoxazole, tetracycline, and kanamycin. Bacterial re- sistance to ampicillin, gentamicin, chloramphenicol, trimethoprim and apramycin was also observed. Inte- grons were identified in 23 (46%) of the E. coli isolates assayed, with a 1-kb amplicon being most frequently observed. DNA sequencing of these integrons revealed the presence of the aadA gene, encoding resistance to streptomycin. Two integrons of 1.5 and 2 kb contained the aadA2 and either dfrI or dfrXII genes, encoding resistance to streptomycin and trimethoprim, respectively. Integrons were also identified from isolates dating back to 1982. Isolates were further genetically characterized via ribotyping, which identified 15 distinct ri- bogroups, with 62% of isolates clustering into four major ribogroups. Certain riboprint patterns from dif- ferent animal species, including humans, were observed in isolates spanning the 24-year collection period, sug- gesting the dissemination of specialized pathogenic O111 clones. 139 INTRODUCTION D ISEASE CAUSED BY Shiga-toxin-producing Escherichia coli (STEC) is increasingly being reported worldwide. STEC infection produces a range of illnesses, including diarrhea with abdominal cramping that often develops into hemorrhagic col- itis (HC). The illness usually resolves in 7–10 days, but in about 10% of patients it progresses to hemolytic uremic syndrome (HUS). 18 In the United States, approximately 73,000 cases are attributed to E. coli serotype O157:H7, and 36,000 to non- O157:H7 serotypes, resulting in over 100 deaths each year. 1,2 E. coli 0157:H7 strains were first recognized as a distinct class of pathogenic E. coli in 1982 when E. coli O157:H7 caused two outbreaks of HC associated with consumption of undercooked ground beef. 34 The most important virulence factors associated with STEC infection are the potent cytotoxins: Shiga toxins 1 and 2 encoded by stx1 and stx2 genes, respectively. In addition to the cytotoxins, virulence is a function of the acquired abil- ity to adhere closely to the cells lining the intestinal mucosa. 4,21 Enterohemorrhagic strains also typically produce a plasmid- borne hemolysin (encoded by hlyA) 28 and many produce in- timin, a 97-kDa attachment-and-effacement protein (encoded by eaeA), 15 as well as other putative virulence factors. While E. coli O157:H7 is currently the predominant serotype of STEC infections, non-O157 are being increasingly recognized as a cause of HC and HUS in many countries. 17 More than 100 serotypes of E. coli isolated from humans, animals, food, and other sources have been identified as STEC. 1 In addition, more than 60 serotypes of STEC have been isolated from stool sam- ples of patients with HC or HUS. 12 Among non-O157 strains, serotypes O26 and O111 are most commonly associated with human disease. 5,32 Since the diarrheal phase of illnesses asso- 1 Center for Veterinary Medicine, U.S. Food and Drug Administration, Laurel, MD, 20708. 2 Department of Nutrition and Food Science, University of Maryland, College Park, MD 20742. 3 The Gastroenteric Disease Center, The Pennsylvania State University, University Park, PA, 16802.