Identification and antimicrobial susceptibility of bacterial species
isolated from cows with mastitis in southern Chile.
Abstract
Bovine mastitis is characterized by pathological alterations of the
mammary tissue and physical and chemical changes in the milk causing
large economic losses in the dairy industry. The most common etiological
agents include a variety of bacteria that may be either contagious or
environmental. Furthermore, antibiotic treatment has lost effectiveness,
leading to residues in milk and activation of resistance mechanisms in
bacteria. Therefore, improving the knowledge about the variety,
prevalence, and antimicrobial susceptibility of mastitis-causing
bacteria may assist in the development of new strategies to optimize
mastitis control. This study aimed to characterize bacterial species
causing mastitis from geographically related dairy plants in southern
Chile. To do this, milk samples obtained from milking cows diagnosed
with clinical mastitis (n=50) and from apparently healthy animals (n=25)
were cultured for microbiological characterization, including species
identification and antibiotic susceptibility. Morphological
identification and Gram staining showed Gram (+) cocci, Gram (-)
bacilli, and Gram (+) bacilli. A large diversity of bacteria was
detected in both mastitis and non-mastitis samples. The most frequently
isolated species were Corynebacterium spp., Staphylococcus haemoliticus,
and Staphylococcus aureus. Besides, Staphylococcus haemoliticus and
Escherichia coli showed complete resistance and intermediate antibiotic
resistance, respectively. Conclusions: the most prevalent variety of
bacterial species associated with mastitis in southern Chile are
coagulase-negative staphylococci. Furthermore, sampling the entire herd,
provides a broader view of the etiological agents causing bovine
mastitis. The results of the present study provide an update regarding
etiological agents and sampling management of bovine mastitis in
southern Chile.