Identification of Aerococcus spp. in blood cultures: Report of bacteremia caused by Aerococcus spp. at our hospital

Abstract

Aerococcus spp. are facultative anaerobic gram-positive cocci that often cause urinary tract infections in older men with a history of urological diseases. These species have been reported to rarely cause bacteremia or endocarditis. In our hospital, we encountered three cases of bacteremia in older men with urological diseases; one of these cases was infective endocarditis. Aerococcus spp. have the same characteristics as Staphylococcus spp. on Gram staining of blood culture media. However, on blood agar medium, they show alpha-hemolytic colonies and resemble alpha-hemolytic Streptococcus and Enterococcus spp. Therefore, Aerococcus spp. may be misidentified as α-Streptococcus. In addition, during the use of identification test kits and automatic analyzers, some strains are difficult to identify owing to insufficient databases of these instruments. In fact, in all three cases in our hospital, the results of the urine culture performed by an outsourced laboratory identified the causative organisms as Streptococcus spp. However, they were all re-identified as Aerococcus spp. using an automatic analyzer, an identification kit such as API20Strep, and a mass spectrometer. For the identification of Aerococcus spp., a thorough understanding of their characteristics is important. Furthermore, identification should be confirmed by MALDI-TOF-MS or genetic testing for future accumulation of information.