Objectives: To test whether reduced susceptibility to biocides (RSB) in extended-spectrum ß-lactamase-producing Klebsiella pneumoniae (ESBL-Kp) is associated with i) increased antimicrobial resistance (co-resistance), ii) clone type (epidemic vs non-epidemic), iii) fitness cost, and/or iv) changes in expression of the genes encoding acrB, an AcrAB efflux pump component, and OmpK35 and OmpK36 porins.

Results: Reduced susceptibility to SOD and TRI was associated with increased MICs of ciprofloxacin, nalidixic acid and nitrofurantoin (p<0.05). The MICs of CHX, BZK and TRI against isolates adapted to growth with these biocides were >4 dilutions higher than those observed against isolates not adapted to biocides. Adaptation to biocides was also significantly associated with increased MICs of imipenem, colistin, norfloxacin and tigecycline. The only significant association between RSB and clone type was observed with ET, detected in 43% of isolates with epidemic behaviour and 19% of isolates showing non-epidemic behaviour (p=0.04). Mean generation times ranged from 23.1 to 32.7 min, and were similar before and after biocide adaptation. Isolate exposure to CHX or BZK was associated with increased relative expression of acrB, whereas TRI had no significant effect. Exposure to TRI decreased expression of ompK35 and ompK36. Conclusions: In the ESBL-Kp tested, acquisition of reduced susceptibility to some biocides, such as SOD or TRI, is associated with increased resistance to imipenem, norfloxacin, tigecycline and colistin. Acquisition of RSB is not associated with a significant fitness cost. Isolates with epidemic behaviour are more tolerant to ET than those showing non-epidemic behaviour. CHX and BZK can upregulate acrB expression, whereas TRI can downregulate ompK35 and ompK36 expression. Significance and Impact of the study: The results obtained in the present study will be very useful in the design of appropriate infection control and surveillance measures in order to avoid the dissemination of isolates of ESBL-producing K. pneumoniae