Kan Kültüründen İzole Edilen Acinetobacter Baumannii ve Pseudomonas Aeruginosa Suşlarında Karbapenem Heterodirencinin Fenotipik ve Moleküler Yöntemlerle Araştırılması
Özet
Since heteroresistance (HR) was first detected in Haemophilus influenzae in 1947, it has been described in many bacterial species and against different antibiotic classes. Briefly, HR is defined as the presence of bacterial subpopulations with different susceptibilities within a susceptible bacterial population.
In addition to the fact that heteroresistance protects the bacteria from the effect of bactericidal antibiotic exposure, HR may also be an evolutionary intermediate stage in the development of antibiotic resistance in bacteria. With the increasing prevalence of infections caused by multidrug and pandrug resistant bacteria, the presence of high prevalence of heteroresistance against different antimicrobials in many bacterial species supports this hypothesis.
A total of 408 non-fermentative bacterial strains (256 A.baumannii and 152 P.aeruginosa strains) isolated from the blood cultures sent to The Central Bacteriology Laboratory of Hacettepe University Hospital between January 2014 and July 2018, were included in the study. Imipenem (IMP) and meropenem (MEM) susceptibilities of the isolates were determined by broth microdilution (BMD) method. In our study, according to the CLSI susceptibility breakpoints; 11.3% (n=29) of 256 A.baumannii isolates were found as IMP-susceptible, 0.4% (n=1) as IMP “intermediate” and 88.3% (n=226) as IMP-resistant; 11.7% (n=30) of the isolates were found as MEM-susceptible, 0.8% (n=2) as MEM “intermediate”, and 87.5% (n=224) as MEM-resistant. Of the 152 P.aeruginosa isolates, 37.5% (n=57) were found as IMP-susceptible, 19.1% (n=29) as IMP “intermediate” and 43.4% (n=66) as IMP-resistant; 38.1% (n=58) of the isolates were found as MEM-susceptible, 15.1% (n=23) as MEM “intermediate” and 46.8% (n=71) as MEM-resistant.
The presence of carbapenem HR was investigated in the isolates which were determined as IMP or MEM susceptible by BMD test. HR was investigated by disc diffusion, antibiotic gradient test and population analysis profiling (PAP) method. In our study, the rates of IMP-HR and MEM-HR in A.baumannii isolates were found as 24.1% and 30%, respectively. However, in P.aeruginosa isolates the rate of IMP-HR was 57.9% and MEM-HR was 13.8%.
In order to determine the epidemiology of carbapenem resistance in carbapenem-resistant strains, the presence of carbapenemase genes was investigated by polymerase chain reaction (PCR) method. blaOXA-51 was detected in all carbapenem-resistant A.baumannii isolates. Although, blaOXA-23 was detected in 86.3% (n=195), blaOXA-24 in 0.9% (n=2), blaOXA-58 in 0.9% (n=2) and blaNDM in 0.9% (n=2) of carbapenem-resistant A.baumannii isolates. In carbapenem-resistant P.aeruginosa isolates, blaIMP was detected in 4.2% (n=3), blaOXA-10 in 26.8% (n=19) and blaOXA-2 in 1.4% (n=1) of.
In order to determine the presence of heteroresistance by genotypic methods, the presence of carbapenemase genes in carbapenem-resistant subpopulations was investigated by PCR. In carbapenem-resistant A.baumannii subpopulations, blaOXA-51 was detected in %100 and blaOXA-23 was amplified in 75% of the isolates. Carbapenemase genes were not amplified in carbapenem-resistant P.aeruginosa subpopulations.
Detection of HR is of great clinical importance, as heteroresistant bacterial populations can cause persistent and recurrent infections, especially in immunocompromised individuals. The PAP test, which is accepted as the gold standard method for HR detection, can not be applied in routine microbiology laboratories as it is a labor-intensive and laborious test. Although in some of the studies, using diffusion tests was recommended for detection of HR in routine microbiology laboratories, in our study the sensitivity and specificity of diffusion based tests were found too low for detection of carbapenem HR. Therefore, there is still no reliable test other than PAP method that can be used to detect HR isolates.
