Abstract
Subclinical mastitis is a persistent problem in dairy farms worldwide. Environmental Escherichia coli is the bacterium predominantly responsible for this condition. In Thailand, subclinical mastitis in dairy cows is usually treated with various antibiotics, which could lead to antibiotic resistance in bacteria. E. coli is also a reservoir of many antibiotic resistance genes, which can be conveyed to other bacteria. In this study, the presence of E. coli in milk and water samples was reported, among which enteropathogenic E. coli was predominant, followed by enteroaggregative E. coli and enterohemorrhagic E. coli, which was found only in milk samples. Twenty-one patterns of antibiotic resistance were identified in this study. Ampicillin- and carbenicillin-resistant E. coli was the most common among the bacterial isolates from water samples. Meanwhile, resistance to ampicillin, carbenicillin, and sulfamethoxazole-trimethoprim was the pattern found most commonly in the E. coli from milk samples. Notably, only the E. coli from water samples possessed ESBL phenotype and carried antibiotic resistance genes, blaTEM and blaCMY-2. This indicates that pathogenic E. coli in dairy farms is also exposed to antibiotics and could potentially transfer these genes to other pathogenic bacteria under certain conditions.
Highlights
In dairy farms, mastitis is a persistent problem resulting in economic losses and premature culling of cows
Thirty-eight milk samples were collected in sterile falcon tubes from cows with subclinical mastitis, which had an somatic cell count (SCC) of >200,000 cells/ml in milk, after the teats had been disinfected with 70% ethanol and 4–5 streams of milk had been removed
We found the extended spectrum beta-lactamase (ESBL) phenotype (12/185, 6.5%) in six E. coli isolates each from water and milk samples
Summary
Mastitis is a persistent problem resulting in economic losses and premature culling of cows. Subclinical mastitis, which is defined as a somatic cell count (SCC) of >200,000 cells/mL in milk, is usually caused by gram negative bacteria, such as Escherichia coli (E. coli), Klebsiella pneumoniae, and Serratia marcescens (Schukken et al, 2012; Azevedo et al, 2016). These bacteria are commonly found in environmental settings, such as bedding, clothes, farmers’ hands, and water used on farms (Perkins et al, 2009; Iraguha, Hamudikuwanda & Mushonga, 2015; Azevedo et al, 2016). In Uruguay, E. coli was second only to S. aureus in bovine subclinical mastitis cases (Gianneechini et al, 2002), whereas in China, it was one of the leading types of coliform bacteria found in milk from cows with subclinical mastitis (Memon et al, 2013; Wang et al, 2015)
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