Isolation and characterization of bacteriophage against multidrug-resistant Acinetobacter baumannii

Abstract

Multi-drug resistant (MDR) Acinetobacter baumannii has become one of the leading nosocomial pathogens worldwide. Treatment of the MDR A. baumannii infections by antibiotics has become less effective resulting in prolonged hospitalization and elevated mortality rate. According to this burden, alternative therapeutic strategies, for instance herbal therapy and phage therapy, have been brought recently into attention. In the development of phage therapy, more phages against MDR A. baumannii are still required. Therefore, this study aimed to isolate and characterize bacteriophages of MDR A. baumannii.  Ten aquatic environmental samples were collected from various locations in Khon Kaen municipal area. Eight of 10 water samples were found to contain phages. After phage enrichment and isolation, 3/B/121 and 10/D/36 were selected for characterizations. Infectivity of both phages were stable to temperatures ranging from 28-65 °C for  1 h, moreover their infectivity were stable for at least 3 months when kept at 4, 28 and -20 °C with 20% glycerol. In addition, the two phages were stable over a wide pH range (5 to 9). 3/B/121 and 10/D/36 had short latent periods (approximately 10 and 20 min, respectively) and large burst sizes (app. 450-500 and 300-350 PFU/cell, respectively). 3/B/121 and 10/D/36 were able to lyse 49 isolates (32.4%) and 33 isolates (21.8%) out of 151 MDR A. baumannii isolates, respectively. Both phages were able to eliminate A. baumannii from 10⁸ CFU/ml to 10⁵ CFU/ml within 4-6 h. Electron microscopy revealed that 3/B/121 and 10/D/36 particles had icosahedral heads of approximately 85-86 nm widths and 100-110 nm long with long contractile tails. The genomes of 3/B/121 and 10/D/36 are DNA. Based on their characteristics, the 3/B/121 and 10/D/36 possess advantageous properties and further studies on their genetic characteristics would facilitate the development of phage therapy against MDR A. baumannii.