土井 洋平

BACKGROUND: Carbapenem-resistant Gram-negative bacilli (CR-GNB) are a major public health threat, traditionally linked to hospital settings. However, infections are increasingly reported in the community, and the clinical distinctions between community-associated (CA) and healthcare-associated (HA) infections remain unclear. METHODS: We conducted a prospective multicenter study of hospitalized patients with CR-GNB infections across 13 Japanese tertiary hospitals between April 2019 and March 2024. Infections were categorized as CA, HA, or hospital-onset (HO) using standardized criteria. We compared patient demographics, microbiological findings, infection sites, and clinical outcomes based on the setting of onset. RESULTS: Among 425 patients, 43 had CA, 59 HA, and 323 HO infections. Pseudomonas aeruginosa was the predominant pathogen in all groups. Aeromonas species were more frequently associated with CA than HO cases (23.3% of CA vs 2.2% of HO cases), whereas Stenotrophomonas maltophilia was detected almost exclusively among HO cases. Hospital-onset infections were associated with longer median hospital stays compared with CA infections (68 vs 17 days) and a trend toward higher 30-day mortality (23.9% vs 9.5%). In contrast, HA infections demonstrated no significant differences from CA infections in either hospital length of stay (23 vs 17 days) or 30-day mortality rate (10.3% vs 9.5%). CONCLUSIONS: Community-associated CR-GNB infections are an emerging concern in Japan, showing distinct pathogen profiles and infection sites compared to HO cases. Importantly, HA infections resembled CA infections in terms of clinical characteristics and outcomes, suggesting a need to reexamine the clinical relevance of current HA classification criteria for guiding therapy and risk stratification.

Antibiotic resistance is a threat to human health, yet recent work highlights how loss of resistance may drive pathogenesis in some bacteria. In two recent studies, we found that β-lactam antibiotics and nutrient stresses faced during infection selected for genetic inactivation of the Pseudomonas aeruginosa antibiotic efflux pump mexEFoprN. Unexpectedly, efflux pump mutations increased P. aeruginosa virulence during infection; however, neither the prevalence of mexEFoprN inactivating mutations in real human infections, nor the mechanisms driving increased virulence of efflux pump mutants are known. We hypothesized that human infection would select for virulence enhancing mutations. Using genome sequencing of clinical isolates, we show that mexEFoprN efflux pump inactivating mutations are enriched in P. aeruginosa isolates from cystic fibrosis infections relative to isolates from acute respiratory infections. Combining RNA-seq, metabolomics, genetic approaches, and infection models we show that efflux pump mutants have elevated quorum sensing driven expression of elastase and rhamnolipids which increase P. aeruginosa virulence during acute and chronic infections. Restoration of the efflux pump in a representative respiratory isolate and the notorious cystic fibrosis Liverpool epidemic strain reduced their virulence. These findings suggest that mutations inactivating antibiotic resistance mechanisms could lead to greater patient mortality and morbidity.