Identification of Staphylococcus aureus small colony variant by MALDI-TOF MS

Abstract

Objective To explore the feasibility of using matrix-assisted laser desorption/ ionization time of flight mass spectrometry (MALDI-TOF MS) to study the variation of Staphylococcus aureus colony, and to study the characteristic protein fingerprint of bacteria in depth. Methods Traditional biochemical identification, 16S rRNA gene sequencing and MALDI-TOF MS were used to identify the isolate. The MS for the Staphylococcus aureus SCV strain was obtained by vitek MS, and the m/z expression intensity of Staphylococcus aureus agr and sigB systems was analyzed. Phylogenetic tree based on peak spectrum of mass spectrum was constructed by SARAMIS software. Results The isolate was identified as Staphylococcus aureus by MALDI-TOF MS, the results obtained from the other two methods mentioned above including traditional biochemical identification and 16S rRNA gene seqencing were consistant with the MALDI-TOF MS. The colony morphology was in line with the characteristic of typical SCV strain, and the expression intensity related with biofilm formation was 100% for PSMα3 (m/z 2634.4); 76.1% for PSMα1 (m/z 2286.8) and 32.3% for PSMα4 (m/z 2198.6). The delta toxin intensity of agr regulatory system reflecting acute early infection was only 10%. The relative intensity of peak spectrum of sigB regulatory system reflecting chronic and recurrent infection was less than 25%. The phylogenetic tree approximation of the strain and SCV was more than 70%. Conclusions MALDI-TOF MS technology not only can identify the atypical Staphylococcus aureus, quickly and accurately, but also can preliminarily indicate the infection status of the strain in the host, and thus this technology has great application prospect. Key words: Matrix-assisted laser desorption/ionization time of flight mass spectrometry; Accessory gene regulator(agr), delta toxin, sigB gene; Staphylococcus aureus; Small colony variants