Phumthanakorn Nathita, Thanasak Jitkamol
Department of Preclinic and Applied Animal Science, Faculty of Veterinary Science, Mahidol University, Nakhon Prathom, 73170, Thailand.
Department of Clinical Sciences and Public Health, Faculty of Veterinary Science, Mahidol University, Nakhon Prathom, 73170, Thailand.
Transl Anim Sci. 2025 Jun 16;9:txaf081. doi: 10.1093/tas/txaf081. eCollection 2025.
In Thailand, small- to medium-scale (SM) dairy farms typically have fewer than 100 cows. They are often family-owned or independently operated, and vary in infrastructure and mechanization depending on their size. In contrast, large-scale (L) farms, with more than 100 cows, are more industrialized, utilizing advanced technology, higher production systems, and usually employ multiple workers. To date, few studies have reported the prevalence of methicillin-resistant staphylococci (MRS) and methicillin-susceptible staphylococci (MSS) and their antimicrobial resistance (AMR) at different farm scales. This study aimed to investigate the prevalence of , MRS, MSS and their AMR as well as their genetic backgrounds on SM and L dairy farms in Thailand. A total of 157 mastitis milk samples were collected from 106 cows on 42 SM farms, and 65 samples from 37 cows on one L farm, all located in Kanchanaburi Province. Antimicrobial susceptibility testing was conducted by determining the minimum inhibitory concentration. Whole-genome sequencing and analysis were performed for genetic characterization. There was a significant difference in the prevalence of spp. on L farm (26.2%) and SM farms (14%) ( = 0.031, χ² test). The phenotypic resistance of trimethoprim/sulfamethoxazole in L farm (58.8%) was significantly greater than that in SM farms (27.3%) ( = 0.049, χ² test). Six methicillin-resistant staphylococci (27.3%), including sequence type (ST) 3 (N = 1) and ST42 (N = 3) and ST59 (N = 2) were discovered on SM farms, whereas a single ST398 (5.9%, N = 1) was found on an L farm. These strains were multidrug-resistant and carried multiple, diverse antimicrobial resistance genes, including β-lactam resistance genes (, ), tetracycline resistance genes [(K), (M)], and macrolide resistance genes [(A), (C)]. Compared with MRS, MSS carried fewer diverse antimicrobial resistance genes and had distinct STs at both farm scales. At each farm scale, a particular type of resistance may originate from a certain species or specific ST. In conclusion, the prevalence of spp. and their resistance traits and genetic background on SM and L farms differ according to different production farm scales. The specific management and monitoring of the information on spp. circulated on each farm type could help to limit the spread of antimicrobial-resistant staphylococci.
在泰国，中小型奶牛场通常饲养不到100头奶牛。这些农场多为家庭所有或独立经营，基础设施和机械化程度因规模而异。相比之下，拥有100多头奶牛的大型农场工业化程度更高，采用先进技术和更高的生产系统，通常雇佣多名工人。迄今为止，很少有研究报道不同规模农场中耐甲氧西林葡萄球菌（MRS）和甲氧西林敏感葡萄球菌（MSS）的流行情况及其抗菌药物耐药性（AMR）。本研究旨在调查泰国中小型和大型奶牛场中MRS、MSS及其AMR的流行情况以及它们的遗传背景。总共从北碧府的42个中小型农场的106头奶牛中采集了157份乳腺炎乳样，从一个大型农场的37头奶牛中采集了65份样本。通过测定最低抑菌浓度进行抗菌药物敏感性试验。进行全基因组测序和分析以进行遗传特征鉴定。大型农场（26.2%）和中小型农场（14%）的葡萄球菌属流行率存在显著差异（P = 0.031，χ²检验）。大型农场中甲氧苄啶/磺胺甲恶唑的表型耐药率（58.8%）显著高于中小型农场（27.3%）（P = 0.049，χ²检验）。在中小型农场中发现了6株耐甲氧西林葡萄球菌（27.3%），包括序列类型（ST）3（N = 1）、ST42（N = 3）和ST59（N = 2），而在一个大型农场中发现了1株ST398（5.9%，N = 1）。这些菌株具有多重耐药性，携带多种不同的抗菌药物耐药基因，包括β-内酰胺耐药基因（blaZ、blaM）、四环素耐药基因[tet(K)、tet(M)]和大环内酯耐药基因[erm(A)、erm(C)]。与MRS相比，MSS携带的不同抗菌药物耐药基因较少，并且在两个农场规模上都有不同的ST。在每个农场规模上，特定类型的耐药性可能源自某个物种或特定的ST。总之，中小型和大型农场中葡萄球菌属的流行情况及其耐药特征和遗传背景因生产农场规模不同而有所差异。对每种农场类型中传播的葡萄球菌属信息进行具体管理和监测，有助于限制耐抗菌药物葡萄球菌的传播。
