Clinical characteristics of Providencia rettgeri bacteraemia and antimicrobial susceptibility patterns

Providencia rettgeri is an opportunistic gram-negative pathogen associated with healthcare-associated infections and is characterised by intrinsic and acquired antimicrobial resistance. However, clinical and microbiological data on P. rettgeri infections in Japan remain limited.

We conducted a retrospective observational study to investigate the clinical characteristics and antimicrobial susceptibility patterns of P. rettgeri isolates, with a particular focus on phenotypic findings suggestive of antimicrobial resistance, recovered from blood and urine cultures at a tertiary care hospital between January 2017 and January 2023.

In total, 106 P. rettgeri isolates were identified during the study period. Seven patients had isolates recovered from blood and urine, suggesting a close association between urinary tract infection and subsequent bacteraemia. Most patients had significant underlying conditions, including cerebrovascular disease and the presence of indwelling urinary catheters. Antimicrobial susceptibility testing showed limited activity of several β-lactam agents consistent with the known intrinsic resistance profile of Providencia species, whereas susceptibility to piperacillin/tazobactam and meropenem was largely preserved. Aminoglycosides demonstrated good activity against most isolates. Extended-spectrum β-lactamase-producing and metallo-β-lactamase-screen-positive isolates were detected based on phenotypic testing, although their prevalence was low. Importantly, no substantial differences in antimicrobial susceptibility profiles were observed between isolates recovered from blood and urine.

These findings indicate that P. rettgeri remains an uncommon but clinically relevant pathogen in healthcare settings and underscore the importance of continuous surveillance to monitor emerging antimicrobial resistance.