Acinetobacter baumannii clones resistant to phage AP22 were formed at the rate of 10−6 per a cell. A total of 50 phage-resistant clones of

A. baumannii 1053 were analyzed to determine whether they are phage-resistant mutants or lysogens with inserted prophage. To reveal possible spontaneous induction, bacterial suspensions of each clone treated with chloroform were spotted on bacterial lawn of sensitive strain. Besides, the resistant clones were grown in the presence of different concentrations of mitomycin C to show possible presence of the phage in concentrated preparation by EM procedure. In both cases, there was no presence of the phage in the samples. A possibility of the prophage presence in genomic DNA of resistant compound screening assay ABT-737 supplier clones was estimated by PCR with two pairs of primers specific to the phage DNA. It was shown the absence

of prophage DNA in genomic DNA of resistant clones (Fig. 5). Lytic activity and host specificity of the phage were tested against 130 identified A. baumannii genotype-varying MDR strains. These strains were isolated from patients of burn units, units of selective and emergency surgery, therapeutics units, intensive care units, and urology units in 2005–2010. Most of them were resistant to diverse groups of antibiotics, including aminoglycosides, fluoroquinolones, third- and forth-generation cephalosporins, and also cefoperazone sulbactam and carbapenems. All strains were divided into 10 groups by RAPD analysis. RAPD groups A1 and B1 predominated with 48% and

35% of the investigated strains, respectively, and were spread in clinics of a variety of Russian cities. Unlike some other known A. baumannii phages, bacteriophage AP22 was found to have a broad range of lytic activity against A. baumannii multidrug-resistant clinically relevant strains. The phage was shown to specifically infect and lyse 68% (89 of 130) of A. baumannii strains by forming clear zones. Of many particular interest is that the phage lysed 83% (88 of 106) of A. baumannii strains from those two RAPD groups that were dominating in some Russian hospitals between 2005 and 2010 (Table 1). Wound, tissue sampling, sputum, bronchopulmonary lavage, pleural fluid, urine, bile, blood, and hospital environmental rinses Chelyabinsk, Moscow, St. Petersburg Wound, tissue sampling, sputum, bronchopulmonary lavage, pleural fluid, urine, bile, blood, rinses of drainage and intravenous catheters, and hospital environmental rinses Chelyabinsk, N-Novgorod, Moscow, St. Petersburg Chelyabinsk, N-Novgorod, Moscow, St. Petersburg Wound, sputum, and rinses of intravenous catheters Chelyabinsk, N-Novgorod, St. Petersburg The phage was also tested against some other representatives of the genus Acinetobacter (A. lwoffii, A. anitratus, and A. calcoaceticus), as well as several other gram-negative microorganisms such as P. aeruginosa, E. coli, Y. pseudotuberculosis, Y. enterocolitica, K.