Identification of slide coagulase positive, tube coagulase negative Staphylococcus aureus by 16S ribosomal RNA gene sequencing

Abstract

Aims - To ascertain the clinical importance of a strain of slide coagulase positive but tube coagulase negative staphylococcus species isolated from the blood culture of a 43 year old patient with refractory anaemia with excessive blasts in transformation who had neutropenic fever. Methods - The isolate was investigated phenotypically by standard biochemical methods using conventional biochemical tests and two commercially available systems, the Vitek (GPI) and API (Staph) systems. Genotypically, the 16S ribosomal RNA (rRNA) gene of the bacteria was amplified by the polymerase chain reaction (PCR) and sequenced. The sequence of the PCR product was compared with known 16S rRNA gene sequences in the GenBank by multiple sequence alignment. Results - Conventional biochemical tests did not reveal a pattern resembling a known staphylococcus species. The Vitek system (GPI) showed that it was 94% S simulans and 3% S haemolyticus, whereas the API system (Staph) showed that it was 86.8% S aureus and 5.1% S warneri. 16S rRNA gene sequencing showed that there was a 0 base difference between the isolate and S aureus, 28 base difference between the isolate and S lugdunensis, 39 base difference between the isolate and S schleiferi, 21 base difference between the isolate and S haemolyticus, 41 base difference between the isolate and S simulans, and 23 base difference between the isolate and S voarneri, indicating that the isolate was a strain of S aureus. Vancomycin was subsequently prescribed and blood cultures taken four days after the start of treatment were negative. Conclusions - 16S rRNA gene sequencing was useful in ascertaining the clinical importance of the strain of slide coagulase positive but tube coagulase negative staphylococcus species isolated from blood culture and allowing appropriate management.