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, and appearances 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 of this microorganism has potentially been increased, like carbapenem resistance is spreading across the world . Carbapenems including imipenem and meropenem are drugs of choice for A. baumanii 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 gain resistance to them [22, 23]. It is highly useful to early detection of these genes in carbapenem resistant bacteria to control and prevent the spread of these bacteria in hospitals. These data can also 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 strains.
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 that is similar to our study. So, 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 46, 59, 50, 65, and 65 isolates in order were MBL-producing, and only 23 isolates carried the VIM-1 gene and three isolates had 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, results of phenotypic and genotypic tests in several investigations have also consistence with our result. 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 Manageiro  and Hu.
Peymani et al. observed that among 63 carbapenem-resistant A. baumanii strains, 31 (49%) strains contained MBL which 19 (61%) carried bla VIM-1 and the rest had bla IMP-1 (31%). These statistics are 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. indicated 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. 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 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 . In regard to these statistics, the spread and prevalence of both genes are increasing. On the other hand, 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 that have remarkable effects on alternative and newer therapeutic strategies, stricter measures of infection control, and new design for continuous monitoring. The continuous monitoring of the prevalence of carbapenem resistance and associated mechanisms in A. baumanii strains can help 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.