Identification of ovine-associated staphylococci by MALDI-TOF mass spectrometry

Abstract

The objective of this study was to use matrix-assisted laser desorption ionisation–time of flight mass spectrometry (MALDI-TOF MS) for the identification of ovine-associated staphylococci. Presumptive Staphylococcus isolates were recovered from ovine udder surface (US), individual raw milk, bulk tank milk, and cheese samples and were characterised by conventional phenotypic methods. A total of 69 bacterial isolates were further confirmed by MALDI-TOF MS. Forty-two (60.9%) of 69 isolates were successfully identified on genus and species level. Two thirds (n 5 28) of the 42 identified isolates were shown to be Staphylococcus spp. These 28 staphylococcal isolates formed two clusters, one consisting of 22 Staphylococcus aureus strains and the other composed of 6 non-aureus staphylococci, including S. simulans (n 5 3), S. auricularis, S. equorum, and S. haemolyticus. MALDI-TOF MS has proven to be a reliable tool for the identification of staphylococci from raw sheep’s milk, especially bulk tank milk; however, currently it appears to be less useful for the identification of bacterial isolates originating from ovine US samples. This is the first study to evaluate the applicability of MALDI-TOF MS for identification of Staphylococcus spp. in ovine raw milk, cheese, and US samples in Hungary.