The influence of seasonality and antimicrobial resistance genes on biofilm formation in hospital-acquired resistant bacteria

Background Hospital-acquired resistant infections (HARI) are difficult to manage due to limited treatment options and to their ability to further resistance stress conditions by producing biofilm. This work aimed to assess the distribution of HARI-associated bacterial species in north Israel and to investigate associations between biofilm formation and extended beta-lactamase (ESBL) genes, bacterial and patient characteristics, and hospitalization length, season and year. Methods Methicillin-resistant Staphylococcus aureus (MRSA), multidrug-resistant (MDR) P. aeruginosa and A. baumannii , ESBL-producing Escherichia coli (ESBL- E. coli ), Klebsiela pneumoniae (ESBL- K. pneumoniae ) and Proteus mirabilis (ESBL- P. mirabilis ) were isolated from 569 blood, urine, wound and respiratory samples of patients with HARI hospitalized during 2020–2022 in north Israel. Biofilm-formation capacity was assessed by the crystalline violet method. ESBL genes were detected by real-time PCR. Data regarding season, time to infection, bacterial species, patient demographics, year, and hospital department, were collected from medical records. Results HARI rates were significantly lower in 2022 compared to 2020. ESBL- K. pneumoniae was the most prevalent (31.6%) bacteria. Strong biofilms were produced by 346 (60.8%), and were most common among ESBL- K. pneumoniae samples (46.2%). bla _CTX−M was the most commonly detected ESBL gene (87.7%). Most strains (61.3%) carried more than one ESBL gene. Hospitalization season had a notable impact on biofilm production, with a heightened risk of infection by robust biofilm producers during spring, summer and autumn compared to winter. Furthermore, the presence of bla _SHV and bla _TEM genes were significantly associated with enhanced biofilm production. Bacteria harboring all three ESBL genes exhibited the highest biofilm production capacities, compared to those carrying fewer than three. Conclusions Biofilm-production intensity differs across bacterial species and seasons and is influenced by the presence of ESBL genes.