A. baumanii, a bacterium with multidrug resistance, is considered a highly important pathogen that can endanger human health. This organism is the cause of numerous infections in human that occur mainly in the people with immunodeficiency or underlying disease. The infections due to A. baumanii is treated with broad-spectrum antibiotics .However, the antibiotic resistance due to this microorganism has unfortunately been is the on the rise, including carbapenem resistance that is increasingly spreading across the world . Carbapenems including imipenem and meropenem are drugs of choice for A. baumanii infection, but recently, the emergence of MBLs (carbapenemase), belonging to the classes D and B of beta-lactamases, has led to the hydrolysis of these drugs and therefore A. baumanii resistance to them [22, 23]. It is therefore highly useful to early detect these genes in carbapenem resistant bacteria to control and prevent the spread of these bacteria in hospitals and to help the physicians to make appropriate prognosis and prescribe suitable antibiotic regimens . In this study, we investigated the prevalence of the most important MBL genes that have been identified in A. baumanii
We observed that 85 (85%) isolates were resistant to meropenem and imipenem, and the prevalence of the IMP-1 and VIM-1 genes were derived 3% and 23%, respectively.
Nouri et al. studied the prevalence of MBLs in A. baumanii in Tehran with the most strains isolated from tracheal samples as with our study. Such high prevalence rate can therefore represent an association between this infection and artificial respiratory system and that sterilization of respiratory tubes is one of the most important ways to prevent development of this infection in these tubes . In our study, the phenotypic tests AmpC disk, CD, EDS, modified Hodge, and E-Test MBL showed that, out of the 100 isolates, respectively, 46, 59, 50, 65, and 65 isolates were MBL-producing, and out of the positive isolates, only 23 isolates carried the VIM-1 gene and three isolates did the IMP-1 gene. This inconsistency in the findings can be attributed to the presence of other MBL genes or other mechanisms such as defects of porins or decreased expression of outer membrane proteins .
However, consistent results with ours have also been reported regarding the difference in the results of phenotypic and genotypic tests. For example, Shoja reported that 55% of the isolates were positive by DDS test but did not find any MBL producing gene, which is consistent with the studies of  and Hu.
Peymani et al. observed that out of the 63 carbapenem-resistant A. baumanii strains, 31 (49%) strains contained MBL, out of which 19 (61%) carried bla VIM-1 and the rest did bla IMP-1 (31%), which is consistent with our study with respect to the prevalence of the VIM-1 gene but inconsistent with respect to the prevalence of IMP-1 that was higher in the study of Peymani et al.. The study of Kouyama et al. showed that out of the 598 A. baumanii strains isolated from the patients in the hospitals in different cities of Japan, 4.5% were resistant to imipenem and meropenem, which is a lower prevalence rate compared to different regions. This can be attributed to the genetic and climatic conditions in that region of the world . A. baumanii resistance rate to imipenem and meropenem is heterogeneous in East Asia such that it has been reported 9.26% in Korea , 49% in Taiwan , 50-52.4% in China , and 4.5% in Japan, possibly representing the effects of geographical differences.
Turner et al. conducted a large study in Europe that showed that imipenem resistance rate of A. baumanii isolates at the hospital level was 22-26% .
Sung et al. reported that out of the 31 carbapenem-resistant A. baumanii strains, 15 (48.4%) isolates carried the bla IMP-1 gene, which is comparatively higher than our finding . Taken together, the spread and prevalence of both genes are increasing. However, the lower prevalence of bla IMP-1 in the region studied in the current study and also the high prevalence and importance of bla VIM-1 should be paid special attention.
The coexistence of different carbapenemases is considered a serious health issue for which alternative and newer therapeutic strategies, stricter measures of infection control, and continuous monitoring should be planned. The continuous monitoring of the prevalence of carbapenem resistance and associated mechanisms in A. baumanii strains helps to develop appropriate therapeutic strategies against nosocomial infections.
The lack of investigation on others resistance mechanisms in A. baumanii isolates can be mentioned as one of the main limitations of the present study.