Identification of Enterococcus spp. and Lactococcus spp. Strains Isolated from Bovine Mastitis by MALDI-TOF MS and Evaluation of Antimicrobial Resistance Profiles

Abstract

Mastitis is an important problem affecting animal health, welfare, and economy. Bacterial agents play a dominant role in the disease. The role of enterococcal and lactococcal species among environmental bacterial agents in mastitis has been underestimated due to inadequate identification. The aim of this study was to isolate and identify Enterococcus spp. and Lactococcus spp. from mastitic bovine milk and to evaluate the agents phenotypically in terms of antimicrobial resistance. A total of 108 milk samples from cattle with suspected mastitis were analyzed for enterococci and lactococci by standard microbiological techniques and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). By standard microbiological methods, 38 (35%) Enterococcus spp. and 13 (12%) Lactococcus spp. were isolated and identified from 51 milk samples. In species-level identification with MALDI-TOF MS, six different enterococci and three different lactococci were identified within acceptable score ranges. In antibiogram tests performed with the standard Kirby-Bauer method using 10 antimicrobials, 26% of the Enterococcus spp. and 46% of the Lactococcus spp. were resistant to at least 50% of the antimicrobials tested. In Enterococcus spp., the highest resistance rates were observed for enrofloxacin (79%) and ampicillin + cloxacillin (71%), while the best sensitivity (100%) was obtained for penicillin and ampicillin. In Lactococcus spp., the highest resistance rate was observed for enrofloxacin (85%) and amoxicillin + clavulanic acid (70%) and the best sensitivity (100%) was obtained for penicillin, ampicillin, and gentamicin. As a result, it was concluded that the diversity and high rate of antimicrobial resistance of enterococcal and lactococcal species in mastitis isolates poses a serious potential threat to animal and public health.