Abstract
Simple SummaryStaphylococci are one of the main microorganisms responsible for intramammary infections in sheep—a syndrome causing important economic losses to farmers. Additionally, eventual staphylococcal contamination of milk could cause significant health problems in humans, especially by the consumption of dairy products made with raw milk containing toxic compounds, such as biogenic amines or antibiotic resistant bacteria. This study aims to check the presence and safety of staphylococci in bulk tank ewe’s milk from different farms, and to determine the relationship between the presence of these staphylococci with farming practices. We found that among the indigenous staphylococcal population in bulk tank ewe’s milk, there were multidrug-resistant and aminobiogenic isolates. Additionally, it was observed that some farming practices, especially those related to the hygienic-sanitary conditions, affect the risk of finding antibiotic-resistant and biogenic amine-producing Staphylococcus isolates in milk. Therefore, farmers should make stronger efforts not only to prevent animals from suffering an intramammary infection but also to avoid compromising consumers’ health and to stop the spread of antibiotic-resistant bacteria.Staphylococci are one of the main microorganisms responsible for intramammary infections in sheep, causing important economic losses for farmers and eventually health problems in humans, especially by the consumption of dairy products made with raw milk containing toxic compounds, such as biogenic amines or antibiotic resistant bacteria. This study aimed to check the presence and safety of staphylococci in bulk tank ewe’s milk from different farms, and to determine the relationship between the presence of these staphylococci and farming practices, by applying nonlinear canonical correlation models (OVERALS). Two-hundred and fifty-nine staphylococci from milk samples from eighteen farms were genotyped and representative isolates of the major clusters were identified as belonging to Staphylococcus (S.) aureus, S. epidermidis, S. arlettae, S. lentus, S. simulans, and S. chromogenes species. Identified isolates were assayed in terms of their safety, by evaluating resistance to antimicrobial drugs and the aminobiogenic capacity, using both phenotypic and genetic assays. Antibiotic resistance phenotypic assay revealed that 82.9% were resistant to some antibiotics, although in the genotypic assay only the genes tetM, ermB, ermC, and grlA were detected. Fifty-three percent were high biogenic amine (BA) producers, being putrescine the most produced amine. A lowered risk of finding antibiotic-resistant and BA-producing staphylococci is related to some farming methods such as enrolling in a breeding program, use of good farming practices, postdipping teat disinfection, hygienic livestock housing, or periodic check of the milking machine.
Highlights
Staphylococci are one of the main microorganisms responsible for intramammary infections in ewes—a syndrome causing significant economic losses to farmers by decreased milk yields, death and early culling of animals, or the necessary administration of antibiotics [1]
Different species have been reported to be present in these infections, and while Staphylococcus (S.) aureus, a coagulase-positive staphylococci (CPS) species, is frequently isolated from clinical mastitis, coagulase-negative staphylococci (CNS) are more frequent in subclinical mastitis, the main type of intramammary infections in ewes [2]
In addition to the above-mentioned problems, another important aspect that should be considered is that eventual staphylococcal contamination of milk could cause significant health problems in humans, especially by the consumption of dairy products made with raw milk [3], including those related to antibiotic resistance transmission between bacteria or the presence of biogenic amines (BA) in milk [4]
Summary
Staphylococci are one of the main microorganisms responsible for intramammary infections in ewes—a syndrome causing significant economic losses to farmers by decreased milk yields, death and early culling of animals, or the necessary administration of antibiotics [1]. In addition to the above-mentioned problems, another important aspect that should be considered is that eventual staphylococcal contamination of milk could cause significant health problems in humans, especially by the consumption of dairy products made with raw milk [3], including those related to antibiotic resistance transmission between bacteria or the presence of biogenic amines (BA) in milk [4]. Since the ability of microorganisms to decarboxylate amino acids is highly variable, being in most cases a strain-dependent property, the detection of bacteria possessing this activity in raw milk is relevant because it could have an important impact in the quality of artisanal cheese. Some studies on raw milk Manchego cheese corroborate the presence of BAs in high quantities [8,9]
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