Mutations in Genes Encoding Penicillin-Binding Proteins and Efflux Pumps Play a Role in {beta}-Lactam Resistance in Helicobacter cinaedi [PublishAheadOfPrint]

β-Lactams are often used to treat Helicobacter cinaedi infections; however, the mechanism underlying β-lactam resistance is unknown. In this study, we investigated β-lactam resistance in a H. cinaedi strain, MRY12-0051 (MIC of AMX and CRO: 32 and 128 μg/ml; obtained from human feces). Based on a comparative whole genome analysis of MRY12-0051 and the CRO-susceptible H. cinaedi strain MRY08-1234 (MIC of AMX and CRO: 1 and 4 μg/ml; obtained from human blood), we identified five mutations in genes encoding penicillin-binding proteins (PBPs), including two in pbpA, one in pbp2, and two in ftsI. Transformation and penicillin-binding assays indicated that CRO resistance was mainly associated with mutations in pbpA; mutations in ftsI also led to increased resistance to AMX. Knocking out cmeB and cmeD, which encode resistance-nodulation-division-type efflux pump components, in H. cinaedi type strain CCUG18818 (AMX MIC: 4--8 μg/ml) resulted in an 8- and 64-fold decrease, respectively, in the AMX MIC. Hence, MICs of AMX in H. cinaedi become similar to those of H. pylori isolates in the absence of cmeD. In conclusion, the difference in susceptibility to β-lactams between H. pylori and H. cinaedi is explained by differences in efflux pump components. Mutations in pbpA are the primary determinant of high resistance to β-lactams in H. cinaedi.

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