Antimicrobial activity of combinations of carbapenem with other antimicrobial agents against pseudomonas aeruginosa and its resistant molecular profile(In vitro study)

Pseudomonas aeruginosa (P. aeruginosa) is one of the leading gram-negative organisms associated with nosocomial infections. The increasing frequency of multidrug-resistant Pseudomonas aeruginosa (MDRPA) strains is concerning as efficacious antimicrobial options are severely limited. In this prospective study, twenty nine clinical isolates of bacteria from AL-Kadhimia teaching hospital were identified as Pseudomonas aeruginosa using morphological characteristics, biochemical testing and by Vitek 2 compact system and their identification was confirmed by detection of 16SrDNA gene using PCR technique. The isolates were recovered from patients with multiple types of infections: 13(44.8%) from wound, 6(20.6%) ear, 3(10.3%) urine, 3(10.3%) burn, 2(6.89%) eye and 1(3.4%) for both CSF and sputum. The antibiotic resistance profiles of the isolates were determined against ten antibiotics belonging to different classes. DNA was extracted from each strain using commercially available DNA extraction kit. The 16S rDNA gene specific for Pseudomonas aeruginosa was amplified and considered as identifying gene and internal control. In order to identify the genes implicated in antimicrobial resistance mechanisms, resistance genes PstS, blaOXA-50, blaOXA-2 and IMP-13 were amplified using specific primers each. The results showed that difference in number of strains identified by vitek2 and 16SrDNA was not statistically significant (P value= 1.000). It showed also that the percentages of resistant strains to tested antibiotics were as follows: Imipenem, Cefepime, Amikacin, Tobramycin, Ciprofloxacin and Levofloxacin (24.14%), Ceftazidime and Gentamicin (27.59%). The highest resistance percentage was for Ceftriaxone (96.55%) and the lowest resistant was (17.24%) for Meropenem. Seven strains were identified as a multidrug resistance strain. The study did not identify the presence of blaoxa-2 or blaIMP 13 at any of the tested strains of P. aeruginosa. It determined instead the PstS and detected the presence of OXA type genes, namely OXA-50. There were no significant relationship between blaOXA-50 presence and resistance to Meropenem, Imipenem, Ceftazidime and Cefepim (p value 1.000, 1.000, 0.474, and 0308).Antibiotics combinations were studied and revealed that antipseudomonal β-lactam (Meropenem, Imipenem, Ceftazidime, Cefepime) with Amikacin against MDR strains of P. aeruginosa showed a synergistic effect.
This study reported the presence of PstS and blaOXA50 in P. aeruginosa strains. The presence of blaOXA-50 is important in order to identify and track the spread of multidrug-resistant P. aeruginosa clones since that blaOXA-50 may be potential clonality marker, Meropenem is the most effective antibiotic and can be considered as the drug of choice against tested P.aeruginosa strains also synergisim were found in the combinations of Meropenem, Ceftazidime or Cefepime with Amikacin against multidrug resistance strains.