br Methods br Results br Discussion

Methods
Results
Discussion A. baumannii remains one of the most common nosocomial pathogens and frequent causes of outbreaks in burn wound infections. Unfortunately, most of the isolates are resistant to antimicrobial agents. β-Lactamases are microbial enzymes that hydrolytically inactivate β-lactam antibiotics and these enzymes, due to the emergence of pathogenic bacteria resistant to β-Lactamases are microbial enzymes that hydrolytically inactivate β-lactam antibiotics and these enzymes can cause resistance to β-lactam antibiotics, including carbapenems, penicillins and cephalosporins. Based on Ambler classification, these enzymes are belonging to four molecular classes: A, B, C, and D. Class D serine carbapenemases belong to the OXA (oxacillinase) family, and are most prevalent in A. baumannii isolates. The ability of OXA enzymes to hydrolyze the isoxazolyl penicillin oxacillin is faster than classical penicillins (benzylpenicillin). Provisionally, they can be grouped into six subclasses; however, today, based on amino A 804598 cost sequence analysis, Class D carbapenemases are reclassified into 12 subgroups: OXA-23, OXA-24/40, OXA-48, OXA-51, OXA-58, OXA-134a, OXA-143, OXA-211, OXA-213, OXA-214, OXA-229, and OXA-235. In addition, they include 232 enzymes with few variants and the same carbapenemase activity. In burn patients, the resistance rate of A. baumannii against carbapenems has been reported from 33.33% to 98%. In our study, according to susceptibility test results, a considerable proportion of A. baumannii isolates (92.5%) were resistant to carbapenems, and this finding suggests that carbapenems are not appropriate for the treatment of A. baumannii infections in burn patients hospitalized at Taleghani hospital. In the present study, there was a difference between imipenem E-test results and imipenem disk diffusion. This indicated that imipenem disk could not detect 25% of resistant isolates and use of this disk for antimicrobial susceptibility could lead to false susceptible results. In contrast to imipenem, meropenem disk was the same as using the E-test, and detected all resistant isolates. It seems that meropenem disk is more appropriate than imipenem disk for identification of resistant isolates. Among the tested antibiotics, colistin and polymyxin B were the most effective agents in vitro, and 97.5% and 100% of isolates were susceptible, respectively. While colistin-resistant isolates have been reported worldwide, no colistin-resistant isolates were obtained from burn patients. Ampicillin-sulbactam is another treatment option, and 72.5% of the isolates were susceptible to this drug in vitro. It has been proposed that ampicillin-sulbactam is an effective and inexpensive treatment for nosocomial infection due to ampicillin-sulbactam susceptible A. baumannii. However, it has been suggested that OXA carbapenemase plays an important role in carbapenem resistance in A. baumannii. Outbreaks of carbapenem-resistant A. baumannii carrying blaOXA-23-like were discovered in different countries, and the range of blaOXA-23-like has been reported from 31% to 100% worldwide. In our study, the vast majority of isolates (70%) were positive for blaOXA-23-like. Moreover, we found that 20% of isolates harbor blaOXA-24-like, and this rate is inconsistent with previous studies globally, which reported the rate of blaOXA-24-like from 0% to 85.43%. While several studies demonstrated the blaOXA-58-like gene in A. baumannii, it has been detected from 2% to 84.92% in different parts of the world, In contrast, however, in our study, no isolate was positive for the blaOXA-58-like gene. Based on the DDS and E-test results, 55.6% and 97.3% of isolates were MBL producers. In spite of phenotypic test, no amplicon was detected for studied MBL genes. While MBL genes, blaIMP, blaVIM, blaNDM, and blaSPM have been reported sporadically in A. baumannii, we could not detect any of these genes among our isolates. Similar to our results, different studies have been reported that A. baumannii isolates were MBL producers by phenotypic tests, but no MBL encoding genes were detected. One probable reason for these positive MBLs may be due to the bactericidal activity of EDTA, which may lead to an increased inhibition zone, but this increase is false positive and not associated with true MBL production. By contrast, these results may be true positive associated with another MBL gene. Other studies have indicated that false-negative results often occurred, in particular when a low level of resistance is observed and phenotypic detection tests are time-consuming. Furthermore, one isolate of A. baumannii was carbapenem -resistant, but it had only the blaOXA-51-like gene, and other genes were not detected. The mechanism of carbapenem-resistance in this isolate may be in relation to the modification of penicillin binding proteins, loss of porins and decreased permeability, AmpC stable derepression, overexpression of efflux pump, or insertion of ISAba1 in upstream of blaOXA-51-like. In addition, further research is needed to identify different carbapenem-resistant mechanisms in this isolate. Since we found only blaOXA-23-like andblaOXA-24-like, we therefore suppose that carbapenem resistance in our isolates is mostly due to these genes. REP-PCR is a useful tool for typing of A. baumannii and provides information about the epidemiology of this bacterium in the hospitals. In order to investigate the clonality of A. baumannii in different wards, REP-PCR was done and analysis of REP-PCR revealed that four clones (A, B, C, and D) are circulating in different wards. Consistent with our study, in a study on burn isolates of A. baumannii, Mahdian et al reported that 11 clones were detected, of which four occurred most frequently. In the present study, Clones B and C were the most epidemic ones and it seems these clones were possibly interward spread and caused infection in burn patients.