RAPID DETECTION OF CARBAPENEMASE-PRODUCING Enterobacteriaceae IN CLINICAL ISOLATES

The increasing occurrence of resistance to last-resort drugs in Gram-negative bacteria is one of the major public health concerns, particularly in Enterobacteriaceae. Carbapenems are among those last-resort antibiotics, because of their wide range of activity, but their effectiveness may be compromised by the production of carbapenemases. Acquired carbapenemases in Enterobacteriaceae belong to three different Ambler classes, with class A including the serine carbapenemases KPC, NMC/IMI and SME, the class B including the metallo-ß-lactamases VIM, IMP and NDM, and the class D including OXA-48-like ß-lactamases (with OXA-48 and OXA-181 variants being predominant). In order to evaluate the efficacy of phenotypic tests for the detection of carbapenemases in enterobacteria, we studied 126 bacteria isolates of clinical samples from the University Hospital of Londrina, who presented resistance to carbapenems. Most of the microorganisms were isolated from the urine samples (41.35%), with Klebsiella pneumoniae being the most prevalent enterobacterium (81.90%). All strains were submitted to the phenotypic test and compared to the genotype test, considered reference test. O modified Hodge test, was positive for 88 (69.84%) samples and presented 95.9% sensitivity and 90.7% specificity. In the phenylboronic acid (PBA) inhibition test, 41 (32.54%) samples were positive for imipenem and 85 (67.46%) for meropenem, respectively, 91.4% - 95.7% sensitive and 95.7% - 91.4% specific. The test of Carba NP (Nordmann and Poirel) presented a positive test for 103 (81.75%) isolated, being 96.48% sensitive and 85.18% specific. The search for the blakpc gene was positive for 82 (78.85%) being considered reference test. The high sensitivity for detection of KPC using boronic acid and its derivatives could also be observed by others authors. Even so specificity problems can arise in isolates with reduced sensitivity to carbapenems due to the high level of expression of ampC, generating false -positive. Overall, the Carba NP method was easy to perform, inexpensive, and, in most cases, easy to interpret, particularly on KPC. However, some genes, like OXA-48, may not be detected, affecting the sensitivity of the method. The Carba NP test was an accurate and cost-effective method to rapidly identify potential carrier isolates which could then be further confirmed by molecular methods such as PCR; the test thus obviates the need for other less accurate and/or more time-consuming phenotypic screening methods such as the modified Hodge test or combined disk tests, optimizing and increasing the chance of effectiveness of the patient's treatment.