Impact of Incremental Antiseptic Selection on Antibiotic Cross-Resistance and Enhanced Biofilm Formation in Escherichia coli and Acinetobacter baumannii: In Vitro.

Chlorhexidine, cetrimide, chloroxylenol, and povidone iodine, in various combinations and concentrations are widely used antiseptics in clinical settings for skin antisepsis and hand hygiene in India. Evidences suggest that exposure of bacterial pathogens to antiseptics over a period of time can result in adaptation of bacteria resulting in tolerance and cross-resistance towards antiseptics and antibiotics. Given the crucial role that antiseptics play in reducing infection and preventing the spread of AMR, understanding the adaptation to antiseptics becomes a critical element in using them effectively. This study is aimed at determining the behavior of two clinically relevant species Escherichia coli and Acinetobacter baumannii adapted to chlorhexidine (CHG), cetrimide, chloroxylenol (PCMX), and povidone iodine (PVP-I). In particular, we have evaluated changes in minimum inhibitory concentration (MIC), cross-tolerance/resistance to both antibiotics and antiseptics and biofilm formation capability post the evolution study towards respective biocides. Both the studied bacterial species adapted to concentrations of antiseptics higher than their initial MICs. Among the adapted strains, E. coli cetrimide showed tolerance to cetrimide with a 16-fold increase in MIC. Similarly, a 4-fold increase in MIC against PVP-I was observed in A. baumannii PVP-I strain, indicating tolerance to PVP-I. Cross-adaptation studies indicated cross-tolerance of E. coli CHG and E. coli cetrimide to cetrimide and CHG, respectively. Among seven antibiotics tested, A. baumannii PCMX showed antibiotic resistance towards tetracycline and imipenem. A concomitant change in biofilm formation, indicated by an increased specific biofilm formation value was also observed. Moreover, CHG, cetrimide and PVP-I adapted A. baumannii strains showed sensitivity towards antibiotics, gentamicin, piperacillin, and tetracycline, a functional trade-off for survival at high antiseptic concentrations. Collectively, these in vitro findings suggest that the decision to use appropriate antiseptics should be based not solely on antiseptic and antibiotic susceptibility data, but also on pathogens to be neutralized, and specific phenotypic factors like bacterial fitness and biofilm-formation capabilities. Thus, frequent clinical microbiological monitoring with respect to antiseptic usage is crucial in controlling infection and spread of AMR.