Population Structure ofStaphylococcus aureusIsolated from Bulk Tank Goat's Milk

Abstract

The presence of Staphylococcus aureus in raw milk can represent a potential threat to human health, due to the introduction of pathogenic strains into dairy food supply chain. The present study was performed to investigate the genetic variation among S. aureus strains isolated from bulk tank goat's milk. The virulence profiles were also assessed to link the isolates with the potential source of milk contamination. A population study was performed on 60 strains using distance-based methods such as pulsed-field gel electrophoresis (PFGE), and the output was analyzed using Structure statistical software (University of Chicago; http://pritch.bsd.uchicago.edu/structure.html ). This Bayesian clustering model tool allows one to assign individuals into a population with no predefined structure. In order to assess partition of genetic variability among isolates, groups obtained by Structure were also investigated using analysis of molecular variance. S. aureus was recovered in 60 out of 78 samples (76.9%) collected from 26 farms. According to PFGE analysis, the strains were divided into 25 different pulsotypes and grouped into two main clusters. Restriction profiles, analyzed by Structure, allowed us to identify two distinct S. aureus genetic groups. Within each group, the strains showed a high coefficient of membership. A great part of genetic variability was attributable to within-groups variation. On the basis of the virulence profile, 45% of the isolates were linked to "animal" biovar, while 6.7% could be assigned to "human" biovar. Out of 60 strains, 27 were characterized by in vitro production of either enterotoxins A (5.0%), C (38.3%), or D (1.7%). The present study showed a high prevalence of bulk tank goat's milk contamination with S. aureus of animal origin. The presence in goat's milk of S. aureus strains able to produce enterotoxins and their potential introduction into dairy chain may represent a serious threat to human health.

Prevalence and characterization of Staphylococcus aureus isolated from goat milk powder processing plants

“…In contrast, a higher contamination rate of S. aureus was found in raw goat milk, tank milk, and workers' samples than that in other processing sites. This was confirmed in previous reports (Bianchi et al, 2014;Intrakamhaeng, Komutarin Schlegelova et al, 2010;Spanu et al, 2013). Our results indicated that S. aureus was common in different goat milk powder processing plants.…”

“…Their potential introduction into the dairy supply chain may represent a serious threat to human health. The tst and sec genes of S. aureus from goat and ovine milk are usually detected together (Lyra et al, 2013;Rosengren, Fabricius, Guss, Sylven, & Lindqvist, 2010;Spanu et al, 2013), which was in agreement with our study, suggesting that these genes may exist together. Pvl is associated with human infections (Chen, Hiramatsu, Huang, Wang, & Lauderdale, 2009) and goat mastitis (Unal et al, 2012).…”

“…Pvl, tst and sec were frequently detected in the isolates from raw goat milk, while ser, seb, pvl, and sec were frequently found in the isolates from processing plants. The sec gene is often reported as the most frequent enterotoxin gene in S. aureus from goat milk (Chu, Yu, Lee, & Su, 2012;Lyra et al, 2013;Spanu et al, 2013). It was confirmed in this study.…”

Phenotypic antimicrobial resistance profile of isolates causing clinical mastitis in dairy animals

“…Unsurprisingly the most prevalent species was Staphylococcus aureus (20.14% in sheep and 44.44% in goat) whose presence in sheep and goat milk has been widely demonstrated in Italy: Cortimiglia et al (2015) evidenced in bulk tank sheep’s milk a Staphylococcus aureus prevalence of 43%, Spanu et al (2013) in bulk tank goat’s milk showed a prevalence of 76%. On the other hand, the predominant bacterial genera isolated from cow samples was Streptococcus spp.…”

Enterotoxin genes, enterotoxin production, and methicillin resistance in Staphylococcus aureus isolated from milk and dairy products in Central Italy

“…In Italy, MRSA have been sporadically identified in bovine milk (Antoci, Pinzone, Nunnari, Stefani, & Cacopardo, 2013;Normanno et al, 2007;Pilla et al, 2012), while they have never been detected in surveys conducted on ovine, caprine or bubaline milk (Cremonesi et al, 2013;Morandi, Brasca, Andrighetto, Lombardi, & Lodi, 2010;Perillo et al, 2012;Spanu et al, 2013;Virdis et al, 2010). At a global level, only a few data are available on the presence of MRSA in dairy products.…”