Some coagulase negative Staphylococcus spp. isolated from buffalo can be misidentified as Staphylococcus aureus by phenotypic and Sa442 PCR methods

Camila C De Almeida,Glenn A Soltes,Fernando A De Ávila,Lucas J L Pizauro,Janet I Macinnes,Durda Slavic,João M Pizauro

doi:10.1186/s13104-018-3449-8

Camila C De Almeida, Glenn A Soltes + Show 5 more

Open Access

https://doi.org/10.1186/s13104-018-3449-8

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Abstract

ObjectiveStaphylococcus aureus is a commonly reported cause of buffalo mastitis. However, its prevalence may be overestimated. The aim of this study was to compare S. aureus identification by conventional phenotypic and genotypic assays versus Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) and novel real-time quantitative PCR tests for the cytochrome oxidase subunit D II (cydB) and staphylocoagulase (coa) genes.ResultsFrom 408 samples obtained from buffalo milk/milking environment, 32 putative S. aureus strains were identified based on characteristic growth on Baird Parker agar, positive catalase reaction, ability to clot rabbit plasma, and positive Sa442 PCR assay. However, in further testing, only 10 of these strains were positive in latex agglutination tests and by MALDI-TOF MS, only eight of the 32 strains were S. aureus while the rest were S. chromogenes (19), S. agnetis (3), S. cohnii (1), or S. xylosus (1). All eight strains identified as S. aureus by MALDI-TOF analysis and confirmed by 16S RNA gene sequencing were positive in a S. aureus-specific cydB PCR test. As well, 7/8 S. aureus strains were PCR positive in a real-time coa PCR test as were 2/69 S. chromogenes and the lone S. xylosus strain tested.

Highlights

Buffalo milk and its derivatives have become increasingly important worldwide [1] and Staphylococcus aureus is one of the most significant pathogens responsible for contagious mastitis in dairy buffaloes [2]
We describe how common testing approaches can lead to misidentification of “non-S. aureus” strains as S. aureus and the development of new a cytochrome oxidase subunit D II (cydB) realtime polymerase chain reaction (PCR) assay that can be used for accurate S. aureus identification
Staphylococcus chromogenes and Streptococcus suis DNAs and water were used in negative control reactions and S. aureus strains COL, NewMan, MW2, Mu50 and ATCC 25923 were used as positive controls

Summary

Introduction

Buffalo milk and its derivatives have become increasingly important worldwide [1] and Staphylococcus aureus is one of the most significant pathogens responsible for contagious mastitis in dairy buffaloes [2]. Antibiotic treatment of S. aureus mastitis is often unsuccessful and treatment failures can lead to spread of the infection. Animals with chronic S. aureus infection are often culled [3]. The initial identification of S. aureus is based on culture and phenotype on specific media; other assays commonly de Almeida et al BMC Res Notes (2018) 11:346

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