Comparative genomic analyses of Lactococcus garvieae isolated from bovine mastitis in China

Abstract

ABSTRACTLactococcus garvieae is an emerging zoonotic pathogen, but there are few reports regarding bovine mastitis. The recent prevalence of L. garvieae poses an increasing disease threat and global public health risk. A total of 39 L. garvieae isolates were obtained from 2899 bovine clinical mastitis milk samples in 6 provinces of China from 2017 to 2021. Five clonal complexes were determined from 32 MLST types of L. garvieae; ST46 was the predominant sequence type and 13 novel MLST types were identified. All isolates were resistant to chloramphenicol and clindamycin, but susceptible to penicillin, ampicillin, amoxicillin-clavulanic acid, imipenem, ceftiofur, enrofloxacin, and marbofloxacin. Based on genomic analyses, L. garvieae had 6310 genes, including 1015, 3641 and 1654 core, accessory and unique genes. All isolates had virulence genes coding for collagenase, fibronectin-binding protein, Glyceraldehyde-3-phosphate dehydrogenase, superoxide dismutase and NADH oxidase. Most isolates had lsaD and mdtA AMR genes. Based on COG results, the functions of defense, transcription and replication, recombination and repair were enhanced in unique genes, whereas functions of translation, ribosomal structure and biogenesis were enhanced in core genes. The KEGG functional categories enriched in unique genes included human disease and membrane transport, whereas COG functional categories enriched in core genes included energy metabolism, nucleotide metabolism and translation. No gene was significantly associated with host specificity. In addition, core genome SNPs analysis suggested potential host adaptation of some isolates in several sequence types. Therefore, this study characterized L. garvieae isolated from mastitis and assessed host adaptation of L. garvieae to various hosts.IMPORTANCEThis study provides important insights on bovine mastitis key topic pathogen Lactococcus garvieae, which constitutes mastitis concerns. However, comprehensive genomic analyses of L. garvieae from dairy farms have not been performed. This study gives a detailed and comprehensive novel feature in L. garvieae, an important but poorly characterized bacterium, recovered in the past 5 years in 6 Chinese provinces. We documented diverse contributory genetic processes, including predominant sequence type ST46 and 13 novel MLST types. L. garvieae had 6310 genes, including 1015, 3641 and 1654 core, accessory and unique genes. All isolates had virulence genes coding for collagenase, fibronectin-binding protein, Glyceraldehyde-3-phosphate dehydrogenase, superoxide dismutase and NADH oxidase, and resistant to chloramphenicol and clindamycin. Most isolates had lsaD and mdtA antimicrobial resistance genes. No gene was significantly associated with host specificity. This is the first absolute quantification of L. garvieae isolated from mastitis and identified host adaptation of L. garvieae to various hosts.