Enhanced antibacterial effect of the novel T4-like bacteriophage KARL-1 in combination with antibiotics against multi-drug resistant Acinetobacter baumannii

Abstract

The continuing rise of infections caused by multi-drug resistant bacteria has led to a renewed interest in bacteriophage therapy. Here we characterize phage vB_AbaM-KARL-1 with lytic activity against multi-drug resistant clinical isolates of Acinetobacter baumannii (AB). Besides genomic and phenotypic phage analysis, the objective of our study was to investigate the antibacterial outcome when the phage acts in concert with distinct antibiotics. KARL-1 belongs to the family of Myoviridae and is able to lyse 8 of 20 (40%) tested clinical isolates. Its double-stranded DNA genome consists of 166,560 bp encoding for 253 open reading frames. Genome wide comparison suggests that KARL-1 is a novel species within the subfamily Tevenvirinae, sharing 77% nucleotide identity (coverage 58%) with phage ZZ1. The antibacterial efficacy at various multiplicities of infection (MOI) was monitored either alone or in combination with meropenem, ciprofloxacin, and colistin. A complete clearance of liquid cultures was achieved with KARL-1 at an MOI of 10 and meropenem (>128 mg/l). KARL-1 was still effective at an MOI of 10, but antibacterial activity was significantly augmented with meropenem. While ciprofloxacin did generally not support phage activity, the application of KARL-1 at an MOI of 10 and therapeutic doses of colistin significantly elevated bacterial suppression. Hence, KARL-1 represents a novel candidate for use against multi-drug resistant AB and the therapeutic outcome may be positively influenced by the addition of traditional antibiotics.

Bacteriophage Therapeutics: A Primer for Clinicians on Phage‐Antibiotic Combinations

“…The other in vitro studies evaluated did use differing phage inoculums, and the optimal “dose” of phage likely depends on the phage itself, its respective bacterial host, and the antibiotic combination. A prime example was demonstrated in which the antibiotic and phage combinations exposed a dose‐dependent effect that differed for each phage inoculum and each tested antibiotic concentration.…”

Phage-Antibiotic Combination Treatments: Antagonistic Impacts of Antibiotics on the Pharmacodynamics of Phage Therapy?

“…4.1.9. Jansen et al, 2018, Acinetobacter baumannii, Ciprofloxacin, Colistin, and Meropenem Jansen et al [104] followed broth cultures of A. baumannii for 16 h in the presence of phage KARL-1 added at various starting MOIs (all less than 1, the highest being 0.1) and various concentrations of the antibiotics ciprofloxacin, colistin, or meropenem (ranging from less than to more than MIC; the bacterial isolate used is described as multi-drug resistant, but nevertheless antibiotic concentrations used in experiments exceeded MICs, so this study is included here). With antibiotics alone there was substantial resulting culture turbidity at all treatment concentrations, though especially with ciprofloxacin there was some increasing reduction in turbidity with increasing antibiotic concentration.…”

Investigating Bacteriophages Targeting the Opportunistic Pathogen Acinetobacter baumannii

“…A BLASTn [33] search against the NCBI database using vPhT2 genome as a query resulted in the identification of the five most closely related genomes, AbTZA1, AM101, KARL-1 [34], vB_ApiM_fHyAci03 [35] and ZZ1 [36] (Table 4), all of which were Acinetobacter infecting bacteriophages. At the nucleotide level, the vPhT2 genome was only genetically very similar to Israeli isolate AbTZA1, where an average nucleotide identity (ANI) of 95.34% was calculated (with a cut-off of >95% to represent being of the same species).…”