title: Population structure of Staphylococcus aureus isolated 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.
authors: Department of Veterinary Medicine, University of Sassari, Sassari, Italy. cspanu@uniss.it
authors: Vincenzo
authors: V
authors: Spanu
authors: Christian
authors: C
authors: Scarano
authors: Salvatore
authors: S
authors: Virdis
authors: Sara
authors: S
authors: Melito
authors: Carlo
authors: C
authors: Spanu
authors: Enrico Pietro Luigi
authors: EP
authors: De Santis
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics; D015373:Bacterial Typing Techniques; D001499:Bayes Theorem; D016000:Cluster Analysis; D004269:DNA, Bacterial / Q000235:genetics; D016521:Electrophoresis, Gel, Pulsed-Field; D004768:Enterotoxins / Q000235:genetics / Q000302:isolation & purification; D005506:Food Contamination / Q000032:analysis; D005516:Food Microbiology; D006041:Goats; D008892:Milk / Q000382:microbiology*; D046915:Penicillin-Binding Proteins; D016133:Polymerase Chain Reaction; D013211:Staphylococcus aureus / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification*; D037521:Virulence Factors / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004768:Enterotoxins; D046915:Penicillin-Binding Proteins; D037521:Virulence Factors; C487789:mecA protein, Staphylococcus aureus