Changes in the Dependence of Pseudomonas aeruginosa O Serogroup Strains and Their Resistance to Antibiotics in a University Hospital During a 5-year Period

The aim of our study was to determine the changes in antibiotic resistance and O serogroup dependence of P. aeruginosa strains isolated from lower respiratory tract specimens of patients in 2003 and 2008; the patients were treated in intensive care units of the biggest treatment facility in Lithuania (Hospital of Lithuanian University of Health Sciences, HLUHS, former Hospital of Kaunas University of Medicine)
Material and Methods. The study included 90 P. aeruginosa strains serotyped in 2003 and 101 P. aeruginosa strains serotyped in 2008, which were randomly selected. The resistance of P. aeruginosa strains was determined by the disc diffusion method based on the standard guidelines. The sizes of inhibition zones were interpreted according to the National Committee for Clinical Laboratory Standards (M2-A6). Isolates were serotyped using sera with specific antibodies against the O antigens of P. aeruginosa (Bio-Rad, France).
Results. Comparison of changes in the distribution of P. aeruginosa serogroups in 2003 and 2008 showed that P. aeruginosa strains of serogroups O:1, O:2, and O:3 were more prevalent in 2003 as compared with 2008 (23.3%, n=21; 27.8%, n=25; 12.2%, n=11 vs. 9.9%, n=10; 10.9%, n=11; 4.0%, n=4, P<0.05). P. aeruginosa strains of serogroups O:6 and O:11 were isolated more frequently in 2008 than 2003 (26.7%, n=27; 34.7%, n=35 vs. 4.4%, n=4; 10.0%, n=9, P<0.001). The results showed that 18 of the 90 P. aeruginosa strains in 2003 and 25 of the 101 P. aeruginosa strains in 2008 were resistant to three or more antibiotics tested, i.e., they were multidrug-resistant. Analysis of the distribution of serogroups among these P. aeruginosa strains isolated in 2003 and 2008 revealed a significantly higher frequency of O:11 serogroup than other serogroups. Meanwhile, in the group of nonmultidrug-resistant P. aeruginosa strains, P. aeruginosa O:11 serogroup strains were identified less frequently and accounted only for 2.8% (n=2, P<0.001) of the isolates in 2003 and 27.6% (n=21, P<0.01) in 2008.
Conclusions. During the 5-year period, the isolation rate of P. aeruginosa strains belonging to serogroup O:11 increased. P. aeruginosa strains isolated in 2003 and 2008 belonging to serogroup O:11 were more frequently multidrug resistant. The increasing resistance of P. aeruginosa to reserve antibiotics of carbapenem group was observed.