Pseudomonas aeruginosa and Acinetobacter spp. are common causes of life threatening infections mainly in hospitalized patients. Further, the biofilm production and the metallo-β-lactamase production among these bacteria have further aggravated the problem. Infections with multidrug resistant P. aeruginosa and Acinetobacter spp. are of serious concern mainly in admitted patients .
In this study, 16.4% of P. aeruginosa were metallo β-lactamase producers which was in agreement with the finding by Kali et al. (16.3%) . Similar rate of MBL production among Acinetobacter spp. as in our study was also reported by Lee et al. (15.1%) .
Polymyxin B and colistin have been reported to demonstrate reasonable success in treatment of infections caused by MBL producing Acinetobacter spp. and P. aeruginosa. However, due to their high toxicity, polymyxins are used for the treatment of only serious infections caused by pan-resistant Gram negative bacilli . A study in Thailand showed that all the multidrug resistant P. aeruginosa and Acinetobacter spp. were susceptible to polymyxin B and colistin .
Very high rates of biofilm production in comparison to our study were reported by Rewatkar and Wadher among the strains of P. aeruginosa (90% by Congo red agar method and 83.33% by tube adherence method)  and by Badave and Kulkarni among the isolates of Acinetobacter spp. (65.2%) .
In our study, no statistically significant association between biofilm production and metallo beta-lactamase production along with antimicrobial resistance could be established, which was in contrast to the findings by Heydari and Eftekhar  and Singhai et al. . However, higher rates of drug resistance were seen among biofilm producers in comparison to biofilm non producers. Though higher numbers of biofilm producers were detected by tube adherence method in comparison to Congo red agar method but the correlation was statistically insignificant. The lack of significance might be due to small sample size taken in our study.
Though the higher numbers of biofilm producers were detected by tube adherence method in our study, due to the simplicity and cost effectiveness of the Congo red agar method  in comparison to tube adherence method, it is more appropriate for laboratory use in the developing countries like Nepal. In addition, its sensitivity and specificity have been reported to be 89% and 100% respectively, when compared to polymerase chain reaction as standard . Similarly, those for tube adherence method were 100% .