Identification of Arcobacter cryaerophilus isolated from a traffic accident victim with bacteremia by 16S ribosomal RNA gene sequencing

Traditional ways of identifying slow growing bacteria is slow and often difficult. In this study, a small, Gram-negative, facultative anaerobic, slow growing bacillus was isolated from the blood culture of a 7-year old traffic accident victim. The bacterium was non-hemolytic, catalase and oxidase positive. An attempt to use the Vitek system (GNI+) and the API system (20NE) to identify the strain was unsuccessful as the growth controls showed negative results. 16S ribosomal RNA gene sequencing showed that there was 1 base difference between the isolate and Arcobacter cryaerophilus (GenBank Accession no. U25805), 1 base difference between the isolate and A. cryaerophilus (GenBank Accession no. U34387), 10 base differences between the isolate and A. cryaerophilus (GenBank Accession no. L14624), 34 base differences between the isolate and A. butzleri (GenBank Accession no. U34386), 34 base differences between the isolate and A. butzleri (GenBank Accession no. U34387), and 38 base differences between the isolate and A. butzleri (GenBank Accession no. L14626), indicating that the isolate most closely resembled a strain of A. cryaerophilus. Identification of the isolate in our case by conventional methods was difficult, as the absence of a curved morphology has made it confused with other Gram-negative non-fermentative bacteria, and the slow growth rate has made it unidentifiable by both the Vitek and API systems. Although the exact source of infection and route of transmission in our case remains elusive, we speculate that the bacteria were transmitted through the respiratory tract while the boy was suffocated in the mud. The present report represents an example of showing the usefulness of 16S rRNA gene sequencing for identification of slow growing bacteria.