Occurrence and characterization of methicillin-resistant staphylococci from bovine mastitis milk samples in Finland

Saara Salmenlinna,Satu Pyörälä,Veera Gindonis,Anna-Liisa Myllyniemi,Laura Lindholm,Suvi Taponen,Merja Rantala,Suvi Nykäsenoja

doi:10.1186/1751-0147-55-61

Abstract

BackgroundMethicillin-resistant staphylococci (MRS) are increasingly being isolated in bovine mastitis. The aim of our study was to evaluate the occurrence of MRS in Finnish mastitis milk samples and characterize the MRS isolates using molecular methods.ResultsMethicillin-resistant S. aureus (MRSA) was a rare finding in bovine mastitis in Finland. Only two out of 135 (1.5%) S. aureus isolates were positive for mec genes. One of these carried mecA and was of spa type t172, SCCmec type IV and ST375, and the other harboured mecC, being spa type t3256, and ST130. MRSA ST375 is common among human MRSA isolates in Finland, but this is the first report in the country of bovine mecC MRSA. In coagulase-negative staphylococci (CoNS) originating from bovine mastitis, methicillin resistance was more common. In the two CoNS collections studied, 5.2% (17/324) and 1.8% (2/110) of the isolates were mecA positive. Eighteen of these were methicillin-resistant S. epidermidis (MRSE), which were divided into 6 separate PFGE clusters. One pulsotype was detected in different parts of the country, indicating clonal spread. Most MRSE (13/18) were of SCCmec type IV, one was of type V and four were non-typeable. Comparison with a human staphylococcal database indicated that bovine MRSE strains were not closely related to human MRSE isolates.ConclusionsThe occurrence of MRS, especially MRSA, in bovine mastitis in Finland was low. Most methicillin-resistant bovine CoNS are MRSE, and we found evidence of a bovine MRSE strain that may spread clonally. This is the first report of a Finnish bovine isolate of MRSAmecC ST130. The study provides a baseline for further MRS monitoring.

Highlights

Methicillin-resistant staphylococci (MRS) are increasingly being isolated in bovine mastitis
Methicillin-resistant Staphylococcus aureus (MRSA) ST398 has been suggested to have developed in humans as a methicillin-sensitive S. aureus (MSSA) strain that was transferred to livestock, first to pigs and to cattle, and acquired the mecA gene [9]
Bacterial isolates To investigate the occurrence of methicillin resistance in staphylococcal species isolated from bovine mastitis, three sets of bacterial isolates were included in the study: one collection of S. aureus and two collections of coagulase-negative staphylococci (CoNS) (Table 1)

Summary

Introduction

Methicillin-resistant staphylococci (MRS) are increasingly being isolated in bovine mastitis. Methicillin-resistant Staphylococcus aureus (MRSA) was first reported in cows in 1972, when Devriese and co-workers found 5.2% of Belgian dairy farms MRSA positive [2]. Livestock-associated MRSA (LA-MRSA) strains of MRSA ST398 and strains carrying MRSAmecC have emerged in humans [5,6,7]. These have been isolated in bovine mastitis [5,8]. MRSA ST398 has been suggested to have developed in humans as a methicillin-sensitive S. aureus (MSSA) strain that was transferred to livestock, first to pigs and to cattle, and acquired the mecA gene [9]. MRSAmecC, was first found in both human and bovine samples in 2011, and several different sequence type lineages of MRSAmecC have been recognized [5,10]

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