In Vitro Induction of Chlorhexidine-and Benzalkonium-Resistance in Clinically Isolated Pseudomonas aeruginosa

Abstract

A study was made on the MIC distributions of chlorhexidine and benzalkonium chloride againstclinically isolated 178 strains of Pseudomonas aeruginosa to find out the existence of strains resistantto those disinfectants and also on the in vitro induction of resistance to both drugs.
The MIC of chlorhexidine gluconate was found to be distributed from 78 to 625μg/ml with asingle peak at 312μg/ml. All 178 strains of clinical isolates were sensitive to chlorhexidine and nonecould be induced to become chlorhexidine resistant in vitro, suggesting that P. aeruginosa can noteasily acquire chlorhexidine resistance.
On the other hand, the MIC of benzalkonium chloride was distributed in two peaks; one peak wasbenzalkonium sensitive at 625μg/ml (150 strains/178 strains: 84.3%) and the another peak wasbenzalkonium resistant at 5, 000μg/ml (28 strains/178 strains; 15.7%). Six (4.0%) of the 150benzalkonium sensitive strains acquired benzalkonium resistance by in vitro induction of resistance;the MIC of 5 strains increased from 625 μg/ml to 2, 500μg/ml and that of the residual 1 strain increasedfrom 312μg/ml to 1, 250μg/ml. However, no change of MIC was observed in 28 benzalkonium-resistantstrains of clinically isolated P. aeruginosa by in vitro resistance induction. Strains with MIC more than5, 000μg/ml could not be obtained at all. The results suggest that the benzalkonium resistance can beintroduced in P.aeruginosa whereas the resistance-acquiring rate is low.
These results suggest that chlorhexidine gluconate is the first choice for prevention of Pseudomonas infection in the hospital and benzalkonium is also useful in 0.5% solution is used.