Genotypic characterization by polymerase chain reaction of Staphylococcus aureus isolates associated with bovine mastitis

doi:10.1016/j.vetmic.2011.05.042

Veterinary Microbiology

Volume 153, Issues 3–4, 15 December 2011, Pages 285-292

https://doi.org/10.1016/j.vetmic.2011.05.042 Get rights and content

Abstract

Staphylococcus aureus is recognized worldwide as a pathogen causing many serious diseases in humans and animals, and is the most common aetiological agent of clinical and subclinical bovine mastitis. The importance of evaluating the combination of S. aureus virulence factors has been emphasized both in human and veterinary medicine, and knowledge about the genetic variability within different S. aureus populations would help in the design of efficient treatments.

The aim of the present study was to determine the genetic profiles of S. aureus strains isolated from milk of cows suffering from clinical and subclinical mastitis in Belgium. The presence of about forty virulence-associated genes was investigated by specific polymerase chain reaction (PCR) amplification.

A high number of genotypic subtypes were observed, demonstrating further the large variation in the presence of virulence genes in S. aureus isolates and the considerable diversity of strains populations that are able to cause mastitis in cows. In accordance with other studies, we showed that some genes are associated with mastitis-causing S. aureus isolates, whereas others are absent or rarely present. We also further highlighted the presence of conserved gene combinations, namely the enterotoxigenic egc-cluster and the bovine pathogenicity island SaPIbov. Importantly, the presence of isolates carrying genes coding for toxins involved in important human infections makes the milk of cows with mastitis a potential reservoir for these toxins, and therefore a potential danger in human health, which strengthens the importance to consider raw milk consumption and its processing very carefully.

Introduction

Staphylococcus aureus (S. aureus) is a worldwide pathogen causing many serious diseases in humans and animals. It is the most common aetiological agent of clinical and subclinical bovine mastitis (Watts, 1988), with relevant losses in the dairy industry as it reduces milk quality and production.

S. aureus isolates produce several virulence factors that can contribute in different ways to their pathogenicity (Dinges et al., 2000, Peacock et al., 2002, Sutra and Poutrel, 1994). These factors can be divided into different groups, including surface-associated factors, degradative enzymes and superantigenic toxins. Furthermore, there is a high redundancy within the classes of S. aureus exotoxins. Indeed, there are, at least, 4 distinct bicomponent leukocidins, approximately 20 different enterotoxins, 3 exfoliative toxins, and 6 haemolysins. Thus, this diversity and the large variations in the presence of these genes may influence the pathogenesis of S. aureus infections in cattle (Peacock et al., 2002, Zecconi et al., 2006).

The importance of evaluating the combination of S. aureus virulence factors has been recently emphasized both in human and veterinary medicine (Jarraud et al., 2002, Peacock et al., 2002, von Eiff et al., 2004, Zecconi et al., 2006), and knowledge about the genetic variability within different S. aureus populations would help in the design of efficient treatments. Although staphylococcal virulence factors have been identified in many S. aureus collections isolated from cases of bovine intramammary infection (IMI), it is not yet known which factors are specifically associated with mastitis.

Section snippets

Bacterial isolates

A total of 229 bovine S. aureus isolates, originating from different areas of the Walloon Region of Belgium, were virulotyped. All isolates were collected from bovine cases of mastitis (2005–2008) and were either obtained from the Association Régionale de Santé et d’Identification Animales (ARSIA), which performs the majority of the bacterial analyses on cow milk in Walloon Region, or isolated from milk samples directly received at the Bacteriology lab. These isolates were cultured on Columbia

Results

The relative frequency of the 38 genes whose presence was investigated by PCR among the 229 isolates of the collection is reported in Table 2 as % of positive isolates. Inasmuch as a high number of properties was studied and because numerous combinations were obtained among the whole collection of isolates, the results are presented hereafter by groups of related genes: the surface factor genes coding for adherence and anti-opsonophagocytosis factors, the leukocidin and haemolysin genes coding

Discussion

Based on these results, the prevalence of the surface factor-, leukocidin-, haemolysin-, protease- or superantigen-encoding genes among the isolates of our collection was compared to other published results, when available. To the best of our knowledge, the number of isolates (n = 229) that were here considered is the largest of all similar studies in other countries.

In agreement with other studies, we observed that about one third of the isolates harbour the cna gene (van Leeuwen et al., 2005,

Acknowledgements

This study was funded by the Walloon Region (SPW-DGTRE, convention 415897 and SPW-DGARNE, convention D31-1231), and by grants of the Fonds de la Recherche Scientifique (FRS-FNRS, Crédits aux chercheurs, n° 1642 and n° 1363). We thank the Association Régionale de Santé et d’Identification Animales (ARSIA) for providing us the bovine mastitis-associated S. aureus isolates.

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¹: These authors contributed equally to this work.

²: Present address: Department of Food Science, Microbiology, Faculty of Veterinary Medicine, University of Liège, Sart-Tilman, Bât B43b, B-4000 Liège, Belgium.

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Genotypic characterization by polymerase chain reaction of Staphylococcus aureus isolates associated with bovine mastitis

Abstract

Introduction

Section snippets

Bacterial isolates

Results

Discussion

Acknowledgements

Adv. Microb. Physiol.

Vet. Microbiol.

Vet. Microbiol.

J. Dermatol. Sci.

Vet. Microbiol.

Vet. Microbiol.

Vet. Microbiol.

Vet. Microbiol.

Diagn. Microbiol. Infect. Dis.

Vet. Microbiol.

Microb. Pathog.

FEMS Microbiol. Lett.

Vet. Microbiol.

Toxin genes and other characteristics of Staphylococcus aureus isolates from milk of cows with mastitis

Clin. Diagn. Lab. Immunol.

Exotoxins of Staphylococcus aureus

Clin. Microbiol. Rev.

Characterization of a putative pathogenicity island from bovine Staphylococcus aureus encoding multiple superantigens

J. Bacteriol.