Characterization, Antibiofilm, and Depolymerizing Activity of Two Phages Active on Carbapenem-Resistant Acinetobacter baumannii

Abstract

Acinetobacter baumannii is a leading cause of healthcare-associated infections worldwide. Its various intrinsic and acquired mechanisms of antibiotic resistance make the therapeutic challenge even more serious. One of the promising alternative treatments that is increasingly highlighted is phage therapy, the therapeutic use of bacteriophages to treat bacterial infections. Two phages active against nosocomial carbapenem-resistant A. baumannii strain 6077/12, vB_AbaM_ISTD, and vB_AbaM_NOVI, were isolated from Belgrade wastewaters, purified, and concentrated using CsCl gradient ultracentrifugation. The phages were screened against 103 clinical isolates of A. baumannii from a laboratory collection and characterized based on plaque and virion morphology, host range, adsorption rate, and one-step growth curve. Given that phage ISTD showed a broader host range, better adsorption rate, shorter latent period, and larger burst size, its ability to lyse planktonic and biofilm-embedded cells was tested in detail. Phage ISTD yielded a 3.5-and 2-log reduction in planktonic and biofilm-associated viable bacterial cell count, respectively, but the effect was time-dependent. Both phages produced growing turbid halos around plaques indicating the synthesis of depolymerases, enzymes capable of degrading bacterial exopolysaccharides. Halos tested positive for presence of phages in the proximity of the plaque, but not further from the plaque, which indicates that the observed halo enlargement is a consequence of enzyme diffusion through the agar, independently of the phages. This notion was also supported by the growing halos induced by phage preparations applied on pregrown bacterial lawns, indicating that depolymerizing effect was achieved also on non-dividing sensitive cells. Overall, good rates of growth, fast adsorption rate, broad host range, and high depolymerizing activity, as well as antibacterial effectiveness against planktonic and biofilm-associated bacteria, make these phages good candidates for potential application in combating A. baumannii infections.

A temperate phage 5W infecting multidrug-resistant Acinetobacter baumannii

“…baumannii activities. Together, these ndings demonstrate that phages and their lysins and depolymerases are potential therapeutic agents for the prevention and control of drug-resistant A. baumannii, and highlight the need of further research on phages (Vukotic et al 2020).…”

Gram-Negative Bacteria Holding Together in a Biofilm: The Acinetobacter baumannii Way

“…Phages and phage-associated enzymes have been extensively studied as strategies for biofilm prevention and eradication. The phage ISTD, isolated from Belgrade wastewaters, yielded a 2-log reduction in A. baumannii biofilm-associated viable bacterial cell count [ 190 ]. However, the effect was time-dependent, thus indicating that phage treatment provides a window in which bacteria might be eradicated by some other antimicrobial agent, presumably another phage, or an antibiotic.…”

Bacteriophage as a Novel Therapeutic Weapon for Killing Colistin-Resistant Multi-Drug-Resistant and Extensively Drug-Resistant Gram-Negative Bacteria

“… There was a reduction in bacterial load and efficacy was observed against all bacteria [ 90 ] Blasco et al 2019 ElyA1 and ElyA2 endolysins [from phage Ab1051Φ and Ab1052Φ] Colistin-resistant MDR P. aeruginosa , MDR A. baumannii , and carbapenemase-producing K. pneumoniae isolates ElyA1 illustrated antibacterial activity and combination of colistin and ElyA1 decreased the MIC of colistin in all isolates [ 93 ] Bernasconi et al 2017 PYO, INTESTI, and Septaphage MDR carbapenemase-producers, colistin-resistant E. coli and Proteus spp . isolates Although Septaphage had no antibacterial activity, carbapenemase producers and colistin-resistant isolates were susceptible to PYO and INTESTI [ 94 ] Aslam et al 2019 AB‐PA01, AB‐PA01 m1, Navy phage cocktail1, and Navy phage cocktail2 for patient one, AB‐PA01 for patient two, and single lytic phage for patient three Colistin-resistant MDR P. aeruginosa and B. dolosa Phage therapy was well related to clinical recovery in lung transplant recipients with MDR Gram-negative bacterial infections [ 95 ] Vukotic et al 2020 vB_AbaM_ISTD and vB_AbaM_NOVI Colistin-resistant A. baumannii Two colistin-resistant isolates were also sensitive to both NOVI and ISTD phages [ 96 ] Schirmeier et al 2018 Artilysin Art-175 Colistin-resistant mcr-1 -positive E. coli isolates Art-175 showed a high antimicrobial activity against all mcr-1 colistin-resistant E. coli isolates and the number of bacteria was reduced [ 97 ] Defraine et al 2016 Artilysin Art-175 MDR colisti...…”