A critical issue on microbiological cut-off value of ampicillin resistance in Lactiplantibacillus plantarum

Aim Comprehensive evaluation of antibiotic susceptibility patterns in Lactiplantibacillus plantarum strains isolated from grape marc, based on genomic and phenotypic assessment. Methods and results We assessed the antibiotic resistance-susceptibility patterns of 20 L. plantarum strains for 16 antibiotics. Genomes of relevant strains were sequenced for in silico assessment and comparative genomic analysis. Results showed high MIC values for spectinomycin, vancomycin, and carbenicillin, indicating natural resistance to these antibiotics. Besides, these strains revealed MIC values for ampicillin higher than previously established by the EFSA, indicating the possible presence of acquired resistance genes in the genomes. However, genomic analysis by complete genome sequencing did not reveal presence of ampicillin resistance genes. Conclusion Comparative genomic analysis between our strains and other L. plantarum genomes present in the literature showed several substantial genomic differences, and suggested the need to adjust the cut-off value for ampicillin in L. plantarum. However, further sequence analysis will reveal how these strains have acquired antibiotic resistance.