Fluoroquinolones are commonly used against broad range of bacteria, including staphylococci. However, already since 1990s, many staphylococcal clinical specimens were found to be resistant to ciprofloxacin. In general, resistance could be acquired by mutational change or by the acquisition of resistance-encoding genetic material through horizontal gene transfer.
Here we provide the first report on ciprofloxacin resistance transfer in staphylococci by bacteriophage.
Two Staphylococcus aureus strains (S. aureus 57, ciprofloxacin sensitive clinical strain and S. aureus #14 environmnetal isolate), and bacteriophage Sa 92 isolated from the Black Sea in Spring 2015, have been selected for transduction experiments. Several sets of experiments with different phage/bacteria ratios (1/10, 1/100, 1/1000, 1/10000) have been conducted. Influence of low ciprofloxacin concentration (0.5µg/ml) on transduction frequency has also been estimated. Tryptic soy agar supplemented with ciprofloxacin 5µg/ml was used for selection of transductants.
It was shown that phage Sa 92 transduced ciprofloxacin resistance from the donor S. aureus 14 to the recipient S. aureus 57 strain at the frequency of 2.25×10-7 per PFU. Transduction frequency was inversely proportional to the multiplicity of infection (MOI). Interestingly, low concentration of ciprofloxacin increased transduction frequency twice that may indicate possible influence of low antibiotic concentrations on intensity of horizontal gene transfer in the environments.
Randomly selected transductants showed resistance to the phage Sa92 possibly due to lysogenization of the strains, though so far, no phage was obtained by mytomycin C induction. The studies are ongoing to detect the genes responsible for ciprofloxacin resistance in bacterial strains as well as in the putative transducing phage.
The obtained data confirm the role of bacteriophages, along with the significance of selective pressure caused by the overuse and misuse of antibiotics, in the spread of antibiotic resistance.