Methods: K. pneumoniae isolates (n=139) were evaluated for antimicrobial resistance and biofilm formation (CDC, Providence VA Med. Ctr., Rhode Island Hosp., BEI, and ATCC). Susceptibility was based predominantly on 2017 CLSI (Clinical and Laboratory Standards Institute) breakpoints. Isolates were categorized as multidrug-resistant (MDR: resistant to ≥ 1 antimicrobial in ≥ 3 out of 16 antimicrobial categories) or extensively drug-resistant (XDR: resistant to ≥ 1 antimicrobial in all but ≤ 2 out of 16 antimicrobial categories) based on expert consensus criteria for Enterobacteriaceae (European CDC (ECDC)/CDC, 2012). We collapsed antimicrobial categories described by the ECDC/CDC consensus group into 9 categories: penicillins, cephalosporins, monobactam, carbapenems, protein synthesis inhibitors, fluoroquinolones, folate pathway inhibitors, fosfomycin, and colistin. Biofilm formation was assessed using a modified crystal violet method (OD570) and defined by tertile cut-points. Antimicrobial resistance was compared for weak (n=47) versus strong (n=46) biofilm formation by chi-square or Fisher’s exact test. Predictors of strong biofilm formation were identified using logistic regression.
Results: MDR isolates were more common among weak (n=46/47, 97.9%) versus strong biofilm formers (n=35/46, 76.1%; p=0.002), whereas XDR was similar between groups (n=12/47, 25.5% vs. n=13/46, 28.3% p=0.77). Resistance to penicillins, cephalosporins, monobactams, carbapenems, protein synthesis, or fluoroquinolones were more common among weak biofilm formers (p<0.05). Carbapenem resistance was inversely associated with strong biofilm formation (odds ratio 0.09; 95% confidence interval 0.02-0.33).
Conclusion: Carbapenem resistant K. pneumoniae were 91% less likely to form strong biofilm. Potential trade-off mechanisms between antimicrobial resistance and biofilm formation require further exploration.
M. Luther, None
V. Lopes, None
A. Caffrey, Merck: Grant Investigator , Research grant . The Medicine's Company: Grant Investigator , Research grant . Pfizer: Grant Investigator , Research grant .
K. LaPlante, Merck: Grant Investigator , Research grant . Pfizer Pharmaceuticals: Grant Investigator , Research grant . Allergan: Scientific Advisor , Honorarium . Ocean Spray Cranberries, Inc.: Grant Investigator and Scientific Advisor , Honorarium and Research grant . Achaogen, Inc.: Scientific Advisor , Honorarium . Zavante Therapeutics, Inc.: Scientific Advisor , Honorarium .