Oxacillin sensitization of methicillin-resistant Staphylococcus aureus and methicillin-resistant Staphylococcus pseudintermedius by antisense peptide nucleic acids in vitro.
BMC Microbiol. 2015 Nov 11;15(1):262.
Goh S1, Loeffler A2, Lloyd DH2, Nair SP3, Good L4.
1Pathology and Pathogen Biology, Royal Veterinary College, Hawkshead Lane, Hatfield, Hertfordshire, UK. firstname.lastname@example.org
2Clinical Sciences and Services, Royal Veterinary College, Hawkshead Lane, Hatfield, Hertfordshire, UK.
3Department of Microbial Diseases, UCL Eastman Dental Institute, University College London, London, UK.
4Pathology and Pathogen Biology, Royal Veterinary College, Royal College Street, London, UK.
Antibiotic resistance genes can be targeted by antisense agents, which can reduce their expression and thus restore cellular susceptibility to existing antibiotics. Antisense inhibitors can be gene and pathogen specific, or designed to inhibit a group of bacteria having conserved sequences within resistance genes. Here, we aimed to develop antisense peptide nucleic acids (PNAs) that could be used to effectively restore susceptibility to β-lactams in methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus pseudintermedius (MRSP).
Antisense PNAs specific for conserved regions of the mobilisable gene mecA, and the growth essential gene, ftsZ, were designed. Clinical MRSA and MRSP strains of high oxacillin resistance were treated with PNAs and assayed for reduction in colony forming units on oxacillin plates, reduction in target gene mRNA levels, and cell size. Anti-mecA PNA at 7.5 and 2.5 μM reduced mecA mRNA in MRSA and MRSP (p<0.05). At these PNA concentrations, 66 % of MRSA and 92 % of MRSP cells were killed by oxacillin (p<0.01). Anti-ftsZ PNA at 7.5 and 2.5 μM reduced ftsZ mRNA in MRSA and MRSP, respectively (p≤0.05). At these PNA concentrations, 86 % of MRSA cells and 95 % of MRSP cells were killed by oxacillin (p<0.05). Anti-ftsZ PNAs resulted in swelling of bacterial cells. Scrambled PNA controls did not affect MRSA but sensitized MRSP moderately to oxacillin without affecting mRNA levels.
The antisense PNAs effects observed provide in vitro proof of concept that this approach can be used to reverse β-lactam resistance in staphylococci. Further studies are warranted as clinical treatment alternatives are needed.