Identification by 16S ribosomal RNA gene sequencing of an Enterobacteriaceae species from a bone marrow transplant recipient

Aims - To ascertain the clinical relevance of a strain of Enterobacteriacea e isolated from the stool of a bone marrow transplant recipient with diarrh oea. The isolate could not be identified to the genus level by conventional phenotypic methods and required 16S ribosomal RNA (rRNA) gene sequencing f or full identification. Methods-The isolate was investigated phenotypically by standard biochemical methods using conventional biochemical tests and two commercially availabl e systems, the Vitek (GNI+) and API (20E) systems. Genotypically, the 16S b acterial rRNA gene was amplified by the polymerase chain reaction (PCR) and sequenced. The sequence of the PCR product was compared with known 16S rRN A gene sequences in the GenBank database by multiple sequence alignment. Results-Conventional biochemical tests did not reveal a pattern resembling any known member of the Enterobacteriaceae family. The isolate was identifi ed as Salmonella arizonae (73%) ana Escherichia coli (76%) by the Vitek (GN I+) and API (20E) systems, respectively. 16S rRNA sequencing showed that th ere was only one base difference between the isolate and E coli K-12, but 4 8 and 47 base differences between the isolate and S typhimurium (NCTC 8391) and S typhi (St111), respectively, showing that it was an E coli strain. T he patient did not require any specific treatment and the diarrhoea subside d spontaneously. Conclusions-16S rRNA gene sequencing was useful in ascertaining the clinica l relevance of the strain of Enterobacteriaceae isolated from the stool of the bone marrow transplant recipient with diarrhoea.