Acinetobacter baumannii is one of the most important pathogens leading to infections in burn patients. Control of
A. baumannii infections in these patients is a major challenge due to the proliferation of MDR strains [
25]. In the current study, all isolates were identified as MDR strains. Also in accordance with other studies, we found that all our
A. baumannii strains were carbapenem resistant [
26]. Similarly to our study, 94.5% of
A. baumannii isolated from burn patients were resistant to carbapenems in the study by Pournajaf et al., [
5], suggesting that the mentioned group of antibiotics is no longer suitable for the treatment of infections caused by this bacterium. Determination of resistance by MIC showed that all strains were sensitive to colistin. These data are in agreement with those of Tarashi et al., [
27] and previous studies [
17], and show that colistin is still an effective antibiotic against MDR
A. baumannii. In our study,
blaVIM was identified as the most common gene encoding MBLs in the vast majority of isolates, followed by
blaIMP. According to the literature, a wide distribution of VIM type metallo-β-lactamase has been reported at Middle East CRAB [
22]. An association between class 1 integrons and MBLs genes, particularly
blaIMP and
blaVIM, has been reported in other studies [
17]. However, our findings showed that the
blaIMP and
blaVIM genes were not located on the class 1 integrons and no association was found between MBL genes and the presence of class 1 integrons among studied isolates. The reason could be that these genes may have been located on the other region of bacterial DNA.
The analysis of integrons content revealed that 79.0% of studied integron class 1 positive
A. baumannii strains carried at least one gene cassette, while 21.0% had no cassettes and carried empty integrons. Considering that strains with empty integrons have the potential to capture cassettes carrying resistance genes, this result could be remarkable. The most common integron cassettes identified among integron-positive
A. baumannii strains were
arr2,
cmlA5, qacE1, which encode rifampin ADP -ribosyltransferase, chloramphenicol transporter and quaternary ammonium resistance protein leading to resistance to rifampicin, chloramphenicol and quaternary ammonium compounds, respectively. Rifampin resistance due to the
arr-2 gene carried by class 1 integrons has been documented in
A. baumannii strains [
28]. Also other variants of
cmlA gene have been reported in other studies and it seems that this is the first report of detecting
cmlA5 and
cmlA7 variants in
A. baumannii strains in Iran [
24]. Other cassettes, including
aadA1 and
aac(3)-Ic encoding aminoglycoside adenylase and aminoglycoside acetyltransferase respectively were found to be less common in the present study. In researches conducted in other parts of the world, including Taiwan, mainland China, and France, different variants of the
aadA gene such as
aadA1,
aadA2 and
aadA6 have been identified in multidrug-resistant
A. baumannii strains [
23,
24,
29]. The identification of
aadA1 and
aac(3)-Ic genes in cassettes of class 1 integrons could explain the high resistance to aminoglycosides in the present study. Despite the high resistance to antibiotics such as ceftazidime, ciprofloxacin, and trimethoprim/sulfamethaxazole, no gene cassette encoding resistance to these antibiotics was found in the present study. Therefore, the development of resistance to mentioned antibiotics may depend on the presence of genetic elements other than integrons.