2026. Phenotypic and Molecular Characterization of Drug Resistance and Biofilm Production in Stenotrophomonas maltophilia Obtained in a 10-Year Period from a Mexican Hospital

Background Stenotrophomonas maltophilia is an emerging drug-resistant opportunistic pathogen related with healthcare-associated infections. The aim was to perform a phenotypic and molecular characterization of drug resistance and biofilm formation in S. maltophilia obtained in a 10-year period from a Mexican Hospital. Methods S. maltophilia isolates from a 10-year period from a tertiary care hospital in Mexico were identified by MALDI-TOF MS. Antimicrobial susceptibility was determined by the broth microdilution method. Drug resistance-associated genes were analyzed by PCR. Biofilm formation and its composition was assessed by crystal violet staining, and detachment assays, respectively. Biofilm production-associated genes were analyzed by PCR. MALDI-TOF mass spectra patterns were analyzed to search markers of drug resistance and biofilm production using the ClinProTools software. Results In the 10-year study period, 258 S. maltophilia isolates were identified, with high resistance detected for ceftazidime (48.4%), cefepime (31.6%), ciprofloxacin (25.0%), trimethoprim-sulfamethoxazole (18.8%), and lower resistance to chloramphenicol (13.6%) and levofloxacin (2.2%). Drug resistance was not associated to the presence of the sul1 (4.1%), sul2 (0.5%), sul3 (0.0%) or ISCR (0.0%) genes. Overexpression of the SmeABC efflux pump was associated to higher drug resistance (P < 0.05). Overall, 97.7% isolates were biofilm producers, i.e., 41.7% were strong producers; 32.0% were moderate, and 26.2% were weak producers. Biofilm composition analysis showed similar percentages for carbohydrates, proteins and DNA in all isolates (36.0, 39.7 and 40.9%, respectively). Biofilm-associated genes fsnR, rmlA, rpfF, xanB and spgM were detected in 94.0, 75.3, 28.6, 17.2% and 0.0% of isolates, respectively. Four potential biomarker peaks were detected in rmlA positive biofilm-producing isolates (P < 0.05). Conclusion Most of S. maltophilia clinical isolates showed high antimicrobial resistance levels and were able to produce biofilm. Biofilm biomass composition of these isolates showed a similar proportion of polysaccharides, proteins, and DNA. The presence of the rmlA gene was associated with biofilm production. Four potential markers of the presence of the biofilm production-associated rmlA gene were detected by mass spectrometry. Disclosures All authors: No reported disclosures.