Abstract
Aim
Virulent bacteriophages are known to be an effective therapy against various human bacterial infections. The aims of the study are to evaluate i) the killing activity of an antistaphylococcal phage lysate (ASPL), available in the Czech Republic for topical application, against Staphylococcal aureus (Sa) strains isolated in orthopedic infections; ii) the antimicrobial activity of ASPL against biofilm-embedded cells of a methicillin-resistant Sa (MRSA) standard strain.
Method
The susceptibility of 25 MRSA and 18 methicillin-sensitive Sa (MSSA) strains to the ASPL was evaluated by spot assay. In addition, susceptibility of four laboratory MRSA strains, including ATCC 43300, ATCC 33591, Mu3 (MRSA/hetero vancomycin intermediate resistant Sa) and Mu50 (MRSA/vancomycin-resistant Sa) was also tested. The activity of ASPL against planktonic and biofilm-embedded MRSA ATCC 43300 was evaluated in real-time by isothermal microcalorimetry. The minimum heat inhibitory concentrations (MHIC) was defined as the lowest antimicrobial concentration leading to the lack of heat flow production after 24h for both planktonic and biofilm-embedded cells. The viability of bacterial cells was assessed by plating and colony counting. The minimum bactericidal concentration (MBC) was defined as the lowest antimicrobial concentration leading the reduction of 3 log CFU compared to the untreated control.
Results
Around 34 out of 43 (79%) Sa strains were susceptible to the ASPL, including 17 MRSA and 17 MSSA strains. Both Mu3 and Mu50 (vancomycin intermediate and resistant MRSA, respectively) strains were also susceptible. Microcalorimetric evaluation of the activity of ASPL against planktonic cells of MRSA ATCC 43300 revealed the MHIC and the MBC were 104 PFU/ml and 105 PFU/ml, respectively. ASPL tested at 105 PFU/ml was able to suppress the heat produced by biofilm bacterial cells, although this titer was not able to completely eradicate MRSA biofilm.
Conclusions
ASPL showed a broad host spectrum among MRSA and MSSA strains associated with infections on implants, including strains that are resistant to vancomycin as well. ASPL exhibits a lytic activity against planktonic and biofilm MRSA and a titer of phage higher than 105 PFU/ml is needed in order to achieve a complete eradication of MRSA biofilm. In conclusion, the antistaphylococcal phage lysate shows an excellent potential treatment of implant-related infections caused by Sa strains.
