Objectives: Carbapenem-resistant Klebsiella pneumoniae has emerged as a major cause of healthcare-associated infections, driven by the global dissemination of high-risk clones. Because chlorhexidine is widely used for infection prevention in healthcare settings, we investigated whether multidrug-resistant K. pneumoniae lineages display reduced chlorhexidine susceptibility. Methods: Chlorhexidine susceptibility was evaluated in 110 invasive KPC-2 carbapenemase-producing K. pneumoniae bloodstream isolates collected from a Brazilian tertiary-care hospital cohort. Chlorhexidine MICs, time-kill assays, whole-genome sequencing, and genetic complementation experiments were performed to identify and validate mechanisms associated with reduced susceptibility. Results: Chlorhexidine MICs were higher in the strains belonging to this local ST258 sublineage compared with other sequence types (STs) (MIC 50 64 vs. 16 µg/mL). Time-kill assays showed that a representative ST258 isolate survived exposure to 0.02% chlorhexidine, a concentration that achieved ≥3–6 log 10 killing in control strains. Whole-genome sequencing revealed that all 42 ST258 isolates carried a 7-nucleotide deletion in smvR , the TetR-like repressor of the SmvA efflux pump. Genetic complementation with wild-type smvR , but not with the frameshift allele, restored lower chlorhexidine MICs, confirming causality. The effect of smvR inactivation was specific to chlorhexidine susceptibility and did not confer cross-resistance to colistin. Conclusions: This study identifies smvR inactivation as an important mechanism of reduced chlorhexidine susceptibility in multidrug-resistant K. pneumoniae . Although MICs remained below in-use concentrations, survival at low chlorhexidine levels could facilitate environmental persistence and potentially contribute to nosocomial transmission. Our results support the integration of antiseptic susceptibility monitoring into infection-control surveillance frameworks targeting multidrug-resistant pathogens.
Objectives: Candida infections remain a major challenge in intensive care units (ICUs), where host factors, invasive interventions, broad-spectrum antimicrobial use, and ICU-related selective pressures promote fungal colonization and invasive disease. We investigated yeast colonization dynamics, species distribution, antifungal susceptibility, and associated risk factors in 329 critically ill patients. Methods: We recovered 880 yeast isolates; 207 were identified by both matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and internal transcribed spacer (ITS) sequencing, demonstrating high concordance (96.7%, κ = 0.93). Longitudinal analysis of 568 isolates showed a significant shift in species composition over time (p 0.031), despite stable alpha diversity, with modest but significant changes in beta diversity. Results: Overall, 262 patients (79.6%) became colonized with Candida spp, and candidiasis developed in 26 (7.9%). C. albicans, C. tropicalis , and C. parapsilosis predominated. Most taxa declined at follow-up, with variation across anatomical sites. In 78% of candidiasis cases, the causative species had been detected during prior colonization, with higher predictive value when detected closer to disease onset. Overall, 11.2% of isolates showed resistance to at least one antifungal agent according to clinical breakpoints, whereas most exhibited a wild-type phenotype according to epidemiological cutoff values. Conclusions: These findings indicate that ICU Candida colonization is highly prevalent, temporally dynamic, and clinically informative, with site-specific and time-dependent shifts that anticipate invasive disease. Integrated longitudinal surveillance and accurate species-level identification may improve risk stratification, inform antifungal stewardship, and support infection prevention strategies in critically ill patients.
