Enhanced killing of multiresistant strains of Staphylococcus aureus and Acinetobacter baumannii through a combined action of antibiotics and bacteriocins

Abstract

A search for multidrug-resistant bacteria was conducted in 1,143 clinical samples in Morocco from which 244 isolates were tested against 29 different antibiotics. This showed a prevalence of resistant strains of 68.4%. The spectra of resistance ranged from 1 to 21. Ampicillin, Ticarcilin, Amoxicillin, Piperacillin and Ciproflaxin were the most frequently resisted. Eight antibiotics were tested against two selected strains, S. aureus 400037 from conjunctive mucosa and A. baumannii 280291 urine, which showed resistance to concentrations up to 240 µg.ml-1. A. baumannii 280291 also resisted the two bacteriocins nisin A and pediocin PA-1, while S. aureus 400037 showed relative sensitivity to nisin A with a MIC of 125 µg.ml-1 but was insensitive to pediocin PA-1. However, the combined use of antibiotics and bacteriocins showedpotentiating effects of bacteriocins on antibiotics or synergistic effects between the two antimicrobials. Combinations with nisin A resulted for instance in a sensitisation of S. aureus 400037 to penicillin G, amoxicillin, ampicillin, cefaclor and ciprofloxacin with MIC values as low as 0.19; 0.78; 0.31; 3.75 and 0.62 µg.ml-1 respectively. Against A. baumannii 280291, the MIC value of gentamycin decreased from 60 to 3.75 µg.ml-1, in the presence of nisin. Similar results were obtained when antibiotics were combined with pediocin PA-1 and such effects were even stronger when both bacteriocins were used along with antibiotics. The present study shows that pathogenic bacteria that developed high levels of resistance to a wide array of antibiotics can be rendered sensitive to the same antibiotics simply by combining them with bacteriocins.