Experimental phage therapy against haematogenous multi-drug resistant Staphylococcus aureus pneumonia in mice

BACKGROUND: Community-acquired haematogenous Staphylococcus aureus pneumonia is a rare infection, though it can be acquired nosocomially. Currently, antibiotics used against S. aureus pneumonia have shown reduced efficacy. Thus, there is need for an alternative therapy against multidrug-resistant S. aureus (MDRSA) strains in the community. OBJECTIVE: We sought to determine the efficacy of environmentally-obtained S. aureus lytic phage against haematogenous MDRSA pneumonia in mice. METHODS: Phages and MDRSA were isolated from sewage samples collected within Nairobi County, Kenya. Isolated S. aureus bacteria were screened for resistance against ceftazidime, oxacillin, vancomycin, netilmicin, gentamicin, erythromycin, trimethroprim-sulfamethoxazole and cefuroxime. Thirty BALB/c mice aged six to eight weeks were randomly assigned into three groups: the MDRSA-infection group (n = 20), the phage-infection group (n = 5) and the non-infection group (n = 5). Mice were infected with either MDRSA or phage (108 CFU/mL) and treated after 72 hours with a single dose of clindamycin (8 mg/kg/bwt) or 108 PFU/mL of phage or a combination therapy (clindamycin and phage). The efficacy of phage, clindamycin or clindamycin with phage combination was determined using resolution of lung pathology and bacterial load in lung homogenates. RESULTS: The viable MDRSA count was 0.5 ± 0.2 log(10) CFU/gm in the phage-treated group, 4.4 ± 0.2 log(10) CFU/gm in the clindamycin-treated group and 4.0 ± 0.2 log(10) CFU/gm in the combination-treated group. The efficacy of phage therapy was significantly different from other therapeutic modes (p = 0 < 0.0001). Histology showed that the mice treated with phage did not develop pneumonia. CONCLUSION: Phage therapy is effective against haematogenous MDRSA infection. Thus, it can be explored as an alternative treatment method.