Clinical importance of A.baumannii arises from prompt global emergence of multi-drug resistant strains resulted in high rate of mortality and difficulties for health organization. Regarding the mentioned facts, epidemiological findings could be helpful to recognize the susceptibility profiles of A.baumannii cause infections in different area. Current study evaluated the distribution of integrons and antimicrobial susceptibility patterns among A.baumanii isolates in south area of Iran. Obtained data showed a high percentage of MDR phenotypes and integrons existence in clinical isolates which implicate the importance of integrons in dissemination of antibiotic resistance genes in the environment (13, 14).
Our findings showed that a half of A.baumannii isolates (50.9 %) were obtained from hospitalized patients in the ICU wards. This result is in accordance with those of previous studies about the role of A. baumannii in ICU infections (15, 16).
Screening for MDR phenotype among A. baumannii isolates showed an alarming trend of increasing resistance to multiple antibiotics. Several studies have also shown emergence of MDR strains and it is likely due to improper use of antimicrobial agents, which limits therapeutic protocols (17-19).
Several cases of MDR A. baumannii have been reported from hospitals in the United Arab Emirates, Bahrain, Saudi Arabia, Palestine and Lebanon(12, 20).
The MDR frequency among tested isolates is similar to that stated previously in Poland (100%) (21), Greece (100%)(22) , China (93 %)(23, 24) and also, this is considerably higher than those reported in other recent reports from Thailand (21.1%) (25)and China (61.3%)(26). This aspect should be considered in the treatment of the relevant infections in order to prevent the inappropriate use of broad-spectrum antibiotics which could cause more implication during sickness.
It should be noted that resistant to Carbapenems including Imipeneme and Meropeneme had dramatically increased in comparison with previous study in Shiraz by Japoni et al. In accordance with our results, Carbapenem‑resistant A.baumanii isolates were detected in a recent study in Shiraz by investigating Metallo‑beta‑lactamase (MβL) enzymes production(27).
In comparison with previous reports, our findings showed significantly higher resistance rates to Cephalosporins and Aminoglycosides agents. So, prescription of these antimicrobial groups should be reviewed in nosocomial infections management.
As the results shown, Polymixins (PMb ) are the most effective antimicrobial agents in agreement with previous reports .Although the efficacy of Polymixins have declared in studies ,their prescription are confined because of its neurotoxic or nephrotoxic side effects(28, 29).Acquisition of foreign genetic elements such as integrons leads to emerge the resistant phenotypes. The spread of these mobile elements between species causes the extension of resistance in health-care settings. We found a remarkable increase in presence of class 1 and 2 integrons compared to the previous study in the same area. This trend is acceptable considering the changes in resistance patterns of isolates compared to the previous study. Also, our results are in consistence with the results of the other studies represented higher prevalence of integron class 1 compared to class 2 ,and rarely class 3 (30, 31).
Statistical analysis showed a significant association between the presence of integrons and resistance to antimicrobial agents including Ampicillin-Sulbactam, Cephalosporins, Gentamycin and Tetracyclin. So, it should be remembered that other mechanisms are involved in resistance to antibiotics in addition to integrons acquisition. (32, 33). The prevalence of class 1 integrons are higher than the rate found in other areas of country(34, 35). Since the presence of class I integron in the present study is significantly associated with Ampicillin-Sulbactam resistance, the increase in resistance to this class of antibiotics is consistent with the increase in the presence of class I integron compared to the previous study(35).
Whereas none of the isolates in previous study harboring the class 3 integrons (35, 36), 12.1 % of our isolates contained this class of integron genes. As we found a significant correlation, existence the class 3 integron gene could be associated with increased resistance of our isolates to Cephalosporins. Indeed, prescription these group of antimicrobial agents should be given more attention considering the global resistant dissemination(37) Also, in accordance with a previous study in Iran By Japoni-Nejad, resistant to Aminoglycosides were reported.
Moreover, the acquisition of class 3 integron gene may be resulted in activated efflux pumps and resistance to Tetracyclin(38) .
Present study is also first investigation of the gene cassettes among isolates of A. baumannii in Shiraz.
According to the PCR method 7 different sizes of integron class 1gene cassettes were detected. Sequencing method for identification the types of gene cassettes indicates two different types of class I integron gene cassettes which both of them previously reported: aadA2 and dfrA12.
DfrA12 is related to expression of Dihydrofolate reductase gene which is contributed to resistance to Trimethoprim. In this study 90.8% of isolates were resistant to Cotrimoxazole (Trimethoprim- Sulfamethoxazole). These gene cassette previously reported in studies in Iran and other countries(31, 39).
AadA2 is related to expression of Aminoglycoside adenylyl transferase gene which is responsible for resistant to Aminoglycoside antibiotics (in this study: Amikacin and Gentamycin).Our results determined that 98.2% and 95.4% of isolates were resistant to Gentamycin and Amikacin respectively. This gene cassette is reported in other region in Iran(31, 40, 41)and other countries(18, 42).
Considering our results, resistant isolates to Trimethoprim- Sulfamethoxazole contained the DfrA12 gene cassettes. Also, the presence of AadA2 gene cassettes is in consistent with resistance to Gentamycin and Amikacin. So, it is worth noting to declare that there is a significant association between the presence of gene cassette and a reduced susceptibility to antibiotics.