Enterococcus spp. are pathogens that cause environmental mastitis and are difficult to eliminate owing to their resistance to antibiotics. To compare the virulence characteristics of isolates from bovine mastitis milk (BMM) and bovine normal raw milk (NRM), we isolated Enterococcus spp. from 39 dairy farms in South Korea from 2015–2020. A total of 122 Enterococcus spp. were identified, with Enterococcus faecalis (73.8%) accounting for the majority, followed by Enterococcus faecium (26.2%). E. faecalis isolated from BMM harbored gelE, asa1, esp, and cylA genes with a prevalence of 85.7, 71.4, 54.3, and 30.0%, respectively. These genes were significantly more abundant in BMM than in NRM, except for asa1 (p < 0.0001). Interestingly, strong biofilm and gelatinase formation was predominately observed for BMM isolates and this was significantly correlated to the presence of esp and gelE genes (p < 0.05). BMM isolates demonstrated higher resistance to tetracycline (59.3%), followed by chloramphenicol (21.0%), rifampicin (18.5%), doxycycline (4.9%), ciprofloxacin (1.2%), and nitrofurantoin (1.2%), than those from NRM. E. faecalis harboring esp, gelE, and cylA may be causative agents for bovine mastitis and act as a reservoir for the transmission of virulence factors to humans.

Three aerobic, rod-shaped actinobacterial strains, designated MMS17-SY117^T, MMS17-SY207-3^T and MMS17-SY213^T, were isolated from soil and their taxonomic positions were analysed using a polyphasic approach. The isolates showed best growth at 30 °C, pH 7 and 0–1 % (w/v) NaCl. On the basis of 16S rRNA gene sequence similarity, the isolates were affiliated to the genus Nocardioides , and the closest species to MMS17-SY117^T, MMS17-SY207-3^T and MMS17-SY213^T were Nocardioides aestuarii JC2056^T (97.76%), Nocardioides currus IB-3^T (97.41%) and Nocardioides exalbidus RC825^T (98.71%), respectively. Each isolate formed a distinct cluster within the Nocardioides clade in the phylogenetic tree. The orthologous average nucleotide identity and digital DNA–DNA hybridization values were in the range of 74.4–85.7 % and 16.6–39.2 %, respectively, with the type strains of related species. The major polar lipids in all three strains were phosphatidylinositol, phosphatidylglycerol and diphosphatidylglycerol. The predominant fatty acids were iso-C_16 : 0 and C_17 : 1 ω8c. MK-8(H₄) was the major isoprenoid quinone and ll-DAP was the major diamino acid. Galactose, glucose and rhamnose were present in the whole-cell hydrolysate, and MMS17-SY213^T also contained mannose and ribose. The DNA G+C contents of MMS17-SY117^T, MMS17-SY207-3^T and MMS17-SY213^T were 72.2, 70.4 and 71.5 mol%, respectively. The phylogenetic, phenotypic and chemotaxonomic data supported the classification of each strain as representing a new species of Nocardioides , for which the names Nocardioides euryhalodurans sp. nov. (MMS17-SY117^T=KCTC 49175^T=JCM 32831^T), Nocardioides seonyuensis sp. nov. (MMS17-SY207-3^T=KCTC 49176^T=JCM 32832^T) and Nocardioides eburneiflavus sp. nov. (MMS17-SY213^T=KCTC 49177^T=JCM 32833^T) are proposed accordingly.

Methicillin-resistant Staphylococcus aureus (MRSA) is a drug-resistant pathogen causing subclinical and clinical bovine mastitis. This study examined the molecular properties, biofilm formation, virulence genes, and antimicrobial susceptibility of MRSA isolates from mastitis-infected dairy cow milk in South Korea. Whole-genome sequencing of an ST22-SCC mec IV MRSA strain positive for Panton–Valentine leukocidin (PVL) and toxic shock syndrome toxin-1 (TSST-1) was also performed. Of the 488 S . aureus isolates, 30 (6.1%) were identified as MRSA, harboring the mecA gene. MRSA exhibited the highest resistance to kanamycin (66.7%) among non-beta-lactam antibiotics. Multidrug resistance was observed in 83.3% of MRSA isolates. All MRSA strains had the capacity to form biofilm and harbored biofilm-related genes. The primary virulence genes included hla , hlb , lukED , seg , sei , sem , sen , and seo . The ST72-t324-SCC mec IV genotype was the most prevalent. Of note, three ST22-SCC mec IV isolates were positive for PVL and TSST-1. Our findings suggest that the majority of MRSA isolates from milk obtained from dairy cows with mastitis are multidrug-resistant, capable of forming robust biofilms, and harbor multiple virulence genes. The presence of PVL- and TSST-1-positive ST22-SCC mec IV isolates in mastitis-infected bovine milk highlights the need for persistent monitoring to mitigate possible public health risks. IMPORTANCE: This study reports on the presence and characteristics of methicillin-resistant Staphylococcus aureus strains in milk from mastitis-infected cows. To our knowledge, this is the first report of a Panton–Valentine leukocidin- and toxic shock syndrome toxin-1-positive ST22-SCC mec IV strain in South Korea.

The emergence of antibiotic resistance in foodborne pathogens isolated from meat pro-ducts and their producing environment has been an increasing and leading threat to public health. The aim of the study was to identify pathogens and their antimicrobial resistance isolated from pig production to pork meat distribution phases. Through this study, food spoilage and foodborne or clinical pathogenic bacteria were isolated and identified from pork (belly and neck) meat product and its related environmental samples that include pig swabs, diets, feces, liquid manure, workers’ gloves, dust fan swabs, carcass swabs, floor swabs, and drain water in the affiliated farm, slaughterhouse, meat processing plant, and in retail stores. All carcasses at the slaughterhouse and meat products at the meat processing plant were tracked from pigs at a targeted farm. Nine different selective media agars were used to effectively isolate various pathogenic bacteria. A total of 283 presumptive pathogenic bacteria isolated from 126 samples were selected and identified using MALDI-ToF MS. Twenty-three important foodborne pathogens were identified, and some of them, Shiga-toxin-producing E. coli (STEC), Listeria monocytogenes, Staphylococcus aureus, and Yersinia enterocolitica, were further confirmed using PCR. The PFGE patterns of 12 STEC isolates were grouped by sample source or site. All the foodborne pathogens used in the study were not resistant to amoxicillin/clavulanate, ciprofloxacin, and gentamicin, whereas some of the STEC, L. monocytogenes, and S. aureus isolates were resistant to various antibiotics, including ampicillin, erythromycin, tetracycline, and vancomycin. The most common antimicrobial resistance pattern in the pathogenic STEC isolates was AMP-KAN-STR-SXT-TET. Consequently, this study provides valuable information for the distribution of antimicrobial-resistant pathogens along the pork meat production chain and can assist farmers and stakeholders to develop a systematic strategy for reducing the current emergence and spread of antimicrobial resistance in the different phases of pig production and distribution.

Klebsiella pneumoniae , a zoonotic agent, is a causative pathogen of bovine mastitis. Despite its clinical relevance in dairy farms, studies on K. pneumoniae in bovine mastitis remain limited. Additionally, studies on K. pneumoniae ’s genetic diversity and virulence characteristics in South Korea remain limited. Therefore, in this study, we aimed to elucidate the genetic diversity, antimicrobial resistance, virulence genes, and biofilm-forming capacity of 29 K . pneumoniae strains isolated from bovine mastitis milk samples in South Korea between 2017 and 2023. Multilocus sequence typing revealed 23 sequence types, four of which were novel, indicating substantial genetic heterogeneity and the absence of a dominant clonal lineage. Excluding intrinsic resistance, the highest resistance rates were observed for tetracycline (34.5%) and sulfisoxazole (31.0%), whereas resistance to the other antibiotics tested ranged from 0% to 20.7%. In addition, multidrug resistance (MDR) was noted in 20.7% of isolates. Virulence gene analysis revealed that most isolates carried the ureA , uge , wabG , and fimH genes, whereas allS , rmpA , iucB , and iroNB were not detected. Two isolates exhibited a hypermucoviscous phenotype, and one belonged to the capsular serotype K2. All isolates demonstrated biofilm-forming ability, with moderate-to-strong production observed in over 89.0% of cases, indicating potential for persistence and treatment challenges. In conclusion, K. pneumoniae isolates from mastitis milk carried multiple virulence genes and showed MDR as well as robust biofilm formation. Therefore, continued surveillance and further characterization of K. pneumoniae are needed to support mastitis control and protect public health. IMPORTANCE: Klebsiella pneumoniae is an emerging environmental pathogen associated with clinical mastitis in dairy cows, raising concerns regarding antimicrobial resistance and public health. To the best of our knowledge, this study provides the first comprehensive characterization of K. pneumoniae isolates from mastitis milk in South Korea, including analyses of genetic diversity, antimicrobial resistance, virulence factors, and biofilm formation. The findings advance our current understanding of K. pneumoniae associated with bovine mastitis and highlight the need for continued surveillance that will contribute to mastitis control efforts and safeguard public health.

Hye Jeong Kang, Serim Hong, Dasom Park, Ha-Young Kim, Jin-San Moon. Korean J. Vet. Serv. 2022;45:181-9. https://doi.org/10.7853/kjvs.2022.45.3.181