Oral Presentations Oral Presentations

ORAL PRESENTATIONS Discussion: Cross-resistance to different antibacterial agents including quinolones and nalidixic acid, chloramphenicol, trimethoprim and in some cases b-lactam antibiotics is a common phenomenon in Gram-negative bacteria (Gutmann et al., 1995). In this study adaptive resistance in Salmonella enterica and E. coli O157, O55 and K-12 was readily achieved by passage in sublethal concentrations of antibacterial agents, which conferred cross-resistance to other antibiotics and biocides. Interestingly, adaptive resistance to TLN by E. coli O157 appeared to confer a marked increased sensitivity to AMC, AMX and IPM and to a lesser degree to CHL, CS and GEN. Differences between the adaptiveand cross-resistance profiles between K-12, O55 and O157 suggest that strain-specific rather than global mechanisms are underlying the resistance observed, some of which may be facilitated by the additional genes O157 is known to possess over K-12 and potentally O55 (Perna et al., 2001). No obvious correlation could be drawn between Salmonella serotype and resistance to a particular class of antibiotics or group of biocides, however, this does not detract from the finding that in particular strain / antibiotic / biocide combination strong evidence of cross-resistance was observed.