Predicting antimicrobial resistance of Lactococcus garvieae: PCR detection of resistance genes versus MALDI-TOF protein profiling

Abstract

This study examined the antimicrobial susceptibility and multidrug resistant (MDR) Lactococcus garvieae isolated from rainbow trout, and determined the correlation between resistance phenotype, genotype, and proteomic profile. Eighty-two L. garvieae strains were tested by the disc diffusion method, typed by PCR for detection of six antimicrobial resistance genes (ARGs) and analysed by MALDI-TOF-MS. Disc diffusion antimicrobial susceptibility assay showed resistance of the isolates to trimethoprim-sulfamethoxazole and flumequine (100% resistance), enrofloxacin (67%), oxytetracycline (44%) amoxicillin (23%), chloramphenicol (18%) and florfenicol (13%). PCR identified several antimicrobial resistance genes (ARGs) with tet(B) showing the highest prevalence (85%), followed by FloR (78%), Tet(A) (61%), Tet(S) (13%) and Tet(K) (9%). The tet(B) and FloR genes were detected in 100% of isolates of L. garvieae resistants to oxytetraclycine and florfenicol. Furthermore, 83% of L. garvieae tested were MDR, being the most relevant combination tetA + tetB (56% of the strains tested), tetA + FloR and tetB+ FloR (51%) and teA + tetB + FloR (48%). MALDI-TOF-MS has proven to be an effective and rapid method for the identification of putative protein biomarkers of resistance to oxytetracycline (5 peaks) and to florfenicol (8 peaks) of L. garvieae isolates. This study provides a starting point for the establishment of surveillance systems for antimicrobial resistance in aquaculture.