Clinical characteristics and antimicrobial susceptibility of Aerococcus urinae isolates recovered from urine and blood cultures at a Japanese tertiary care hospital.

BACKGROUND

Aerococcus urinae is an emerging uropathogen frequently misidentified as "other Gram-positive cocci", with limited data on its clinical characteristics and antimicrobial susceptibility, particularly in Japan. In this study, we investigated the clinical features and antimicrobial susceptibility of A. urinae isolates recovered from urine and blood cultures.

METHODS

This retrospective study was conducted at a tertiary care hospital between January 2013 and August 2023. Aerococcus urinae isolates were identified using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry. Antimicrobial susceptibility was determined using a commercial broth microdilution system. Minimum inhibitory concentrations were interpreted according to the Clinical and Laboratory Standards Institute M45 criteria. For the primary analysis, only the first isolate per patient was included.

RESULTS

Two hundred and sixty-eight patients (median age, 82 years; 124 [46.3%], male) were included in this study. Among these, 89 patients (33.2%) were diagnosed with urinary tract infection (UTI), whereas 179 (66.8%) were considered to be colonized. Three hundred thirty-nine A. urinae isolates (333 urine and 6 blood) were recovered from these patients. Aerococcus urinae was considered the primary pathogen in 8 patients (3.0%) and a possible pathogen in 81 (30.2%). Penicillin G, ceftriaxone, and levofloxacin susceptibility rates were 100%, 98.9%, and 76.8%, respectively. All patients with bacteremia exhibited complicated UTI and achieved clinical cure after antimicrobial therapy and source control.

CONCLUSIONS

Aerococcus urinae was more commonly identified as a possible rather than a primary urinary pathogen. The high susceptibility to β-lactam antibiotics supports their continued use as appropriate treatment options for suspected A. urinae UTI.