Multiplex PCR study of nosocomial Pseudomonas aeruginosa for genes of Metallo Beta -Lactamases: could such enzymes bring us to end of antibiotics?

ABSTRACT

Metallo- beta lactamases [MBLs] have been increasingly recognized from bacterial isolates worldwide where they are considered to be one of the most worrisome antibiotic resistance mechanisms. They differ from other beta-lactamases in their need of metallic cofactor for enzymatic activity which could be inhibited by metallic chelators, in their ability to resist beta-lactamase inhibitors and in being able to hydrolyze all beta lactams including carbapenems. In the present study, the most common MBLs- genes [the VIM and IMP genes] were detected using multiplex polymerase chain reaction [PCR] in nosocomial isolates of 40 Imipenem [IPM] resistant and 20 Imipenem sensitive Pseudomonas aeruginosa. The results revealed that none of the Imipenem sensitive isolates had any MBLs-gene while 16/40 [40%] of the Imipenem resistant isolates were positive for MBL-VIM gene and none of them had MBL-IMP gene. So, MBL-VIM gene was found to be significantly associated with IPM resisting than IPM sensitive isolates [P<0.001]. Among the IPM resisting P. aeruginosa, isolates which had the VIM gene were found to be more prevalent in blood [87.5 %] and sputum [60 %] than urine [20 %] and infected post operative wounds or burns [8.3 %]. It was also found that VIM positive isolates were more resistant to Amikacin [75% versus 66.7%, P 1.000], Ceftazidime [93.8% versus 45.8 %, P 0.034], Ciprofloxacin [100% versus 29.2%, P 0.000], Gentamycin [87.5% versus 50%, P 0.020] and Tobramycin [81.3% versus 41.7%, P 0.022], and less resistant to Piperacillin [50% versus 75%, P 0.205] than VIM negative isolates. Moreover, case fatality rate was found to be significantly higher in patients infected with VIM positive isolates than those infected with VIM negative isolates [50 % versus 8.4 %, P 0.005]. It could be concluded that isolates of IPM - resistant P. aeruginosa which had MBL-gene [MBL-producers] were more resistant to antibiotics and more associated with serious infections and higher mortality rate than those which have other mechanisms of beta lactam resistance. So, as it is thought that emergence of such enzymes could bring us to feared end of antibiotics, it has to be recommended that all IPM-resistant isolates should be tested for MBLs production. This will ensure the early recognition of an outbreak and introduction of appropriate infection control measures to prevent further nosocomial spreading of such multiresistant highly virulent strains