Comparative resistomic analyses of Lysobacter species with high intrinsic multidrug resistance

Ubiquitous Gram-negative Lysobacter species are known to confer intrinsic antibiotic resistance and are being considered as new sources for novel anti-methicillin-resistant Staphylococcus aureus (MRSA) antibiotics. This study aimed to determine the intrinsic antibiotic resistance profiles of Lysobacter enzymogenes strain C3 (LeC3) and Lysobacter antibioticus strain ATCC29479 (LaATCC29479), and to in silico identify their intrinsic resistomes and compare with Xanthomonas campestris, a close relative and plant pathogen.

The intrinsic resistant profiles of LeC3 and LaATCC29479 were determined by minimum inhibitory concentration (MIC) and disk diffusion assays. Resistance Gene Identifier (RGI) in the Comprehensive Antibiotic Resistance Database (CARD) was used to predict resistomes. Selected resistance genes were mutated and their roles in resistance to antibiotics were determined by spot dilution assays.

MIC and disk diffusion assays revealed that both LeC3 and LaATCC29479 exhibited high levels of multidrug resistance to 12 common antibiotics. Comparative resistomic analyses using the RGI revealed possible antibiotic resistance genes (ARGs) related to the antibiotic resistance profiles in LeC3 and LaATCC29479, and the core resistome of Lysobacter spp. Functional studies confirmed that three ARGs (bla, aac and sph) conferred antibiotic resistance in LeC3, and also in X. campestris when expressed in trans.

The findings show that LeC3 and LaATCC29479 exhibited multidrug resistance at very high levels and the resistomes of Lysobacter strains were more abundant than those of X. campestris, which might provide novel targets for studies in the intrinsic antibiotic resistance of Lysobacter and other environmental bacterial species.