β-Lactamase-Mediated β-Lactam Resistance in Campylobacter Species: Prevalence of Cj0299 ( bla OXA-61 ) and Evidence for a Novel β-Lactamase in C . jejuni

Abstract

Fifty-two percent of 1,288 poultry isolates of campylobacters were ampicillin resistant, and resistance was more common among Campylobacter coli isolates (67.4%) than among Campylobacter jejuni isolates (47.5%). Production of β-lactamase was typically associated with resistance to ampicillin, amoxicillin (amoxicilline), penicillin, and ticarcillin. Regardless of β-lactamase production, all isolates were resistant to piperacillin (MICs ≥ 256 μg/ml), and most were resistant to carbenicillin, cloxacillin, and cephalosporins. Of all ampicillin-resistant campylobacters tested, 91% (347/380) carried the bla _OXA-61 gene, and 77% (136/175) of those tested with nitrocefin produced a β-lactamase, presumably OXA-61. The isoelectric point (pI) of OXA-61 was 8.7, and the molecular mass was 31.0 kDa. Insertional inactivation of bla _OXA-61 in C . jejuni NCTC 11168 and two ampicillin-resistant isolates resulted in increased susceptibility to ampicillin, co-amoxiclav (amoxicillin and clavulanic acid), penicillin, carbenicillin, oxacillin, and piperacillin, but the effects on MICs of cephalosporins and imipenem were negligible. Some C . jejuni isolates that lacked bla _OXA-61 produced a β-lactamase, CjBla2, with a pI of 9.2 and molecular mass of 32.4 kDa. Mass spectrometry confirmed that the most prevalent β-lactamase was the product of bla _OXA-61 , but CjBla2 was not identified. OXA-61 is prevalent among Campylobacter spp. of veterinary origin and is similar to the β-lactamase previously reported in human isolates. Production of OXA-61 was associated with resistance to penams but not cephalosporins. Co-amoxiclav remained active against all isolates tested.