Antibiotic Susceptibility Patterns of Yerslnla enterocolltlca

Antibiotic susceptibility patterns for Yersinia enterocolitica strains involving 10 different serotypes were analyzed and compared. All Y. enterocolitica were susceptible to colistin, gentamicin, kanamycin, neomycin and doxycycline, whereas all isolates displayed resistance to penicillin G, methicillin (derivative of penicillin), novobiocin, and clindamycin. The antibiograms for the Y. enterocolitica isolates were in some instances related to the somatic serotypes, especially serotype 0:8 for which the antimicrobial susceptibility pattern displayed the greatest disparity. By eliminating the antibiograms for the four serotype 0:8 strains, antimicrobial susceptibility patterns for atypical and typical strains were similar. Numerous Yersinia enterocolitica serotypes and strains possessing a diversity of biochemical reactions have been isolated with increasing frequency from various foods (11,19), environmental sources (12,14) and humans (3). Different Y. enterocolitica enrichment procedures and plating media have been shown to isolate certain strains or serotypes at various frequencies, indicating differences in sensitivity to selective agents and environmental situations among strains and/or serotypes (4,19). In recent years, an increase in isolations have occurred of atypical (environmental) or Y. enterocolitica-Iike strains from human (5,6) and a variety of nonhuman sources including vacuum-packaged beef (1 1), raw and pasteurized milk (19) and water (12). These strains differ from the typical strains by their acid production from melibiose, rhamnose, raffinose or salicin, use of citrate and/or failure to ferment sucrose. Further, the rhamnose-positive atypical Y. enterocolitica strains possess a more extensive profile of temperaturedependent biochemical and physiological responses than the typical strains (4). Invasiveness of HeLa cells was demonstrated to occur for typical clinical strains of Y. enterocolitica while none of the esculinand salicinpositive or food and water atypical isolates adhered to or invaded HeLa cells (15). In addition, enterotoxin production is much more prevalent in strains isolated from humans (including serotypes 0:3, 0:8, 0:9, 0:5, 27 and 0:6, 30) than isolates from animals, water, raw milk and food (17). Therefore, enterotoxigenicity could be another characteristic that may be common to a large majority oftypical Y. enterocolitica strains but scarce in atypical strains. In addition, Bottone (4) has suggested that the atypical or Y. enterocolitica-Iike strains not be designated as Y. enterocolitica but placed in a new species such as Y ersinia rhamnophilica. Further, according to deoxyribonucleic acid (DNA) homology studies, Brenner et al. (7) demonstrated that the rhamnose-positive atypical strains are not closely related to typical Y. enterocolitica strains and placed these atypical strains into separate DNA relatedness groups. Some Y. enterocolitica serotypes display a dramatic geographical distribution. Serotype 0:8 is isolated from humans almost exclusively in the United States (4) while 0:3 (phage type 96), 0:5, 27 and 0:6, 30 are the predominant serotypes of Y. enterocolitica isolates from Canada (20). In Japan, serotypes 0:3 and 0:5 are the most common isolates from animal and clinical sources (1,21) while in European countries serotype 0:3 is the dominant Y. enterocolitica isolate, with 0:9 the next most commonly encountered strain from nonhuman and human sources (16). Similar to serotype distribution, indole production in Y. enterocolitica is variable, with most European and Japanese isolates reported as indole-negative as compared to the United States isolates where most are indole-positive (4). Further, Knapp and Thai (13) have proposed that indole-positive and -negative strains be placed in separate species, Y. enterocolitica and Y ersinia enteritidis, respectively. Since Y. enterocolitica is not a homogenous species and comparisons of antibiotic sensitivity testing among species are scarce (3,10,18), antibiograms of various strains isolated from different geographical locations in the world were determined and compared. MATERIALS AND METHODS