RLP, a bacteriophage of the family Podoviridae, rescues mice from bacteremia caused by multi-drug-resistant Pseudomonas aeruginosa.

Antimicrobial resistance is a serious threat to public health around the globe. According to the World Health Organization, there will be a return to the pre-penicillin era by 2050 if no new antimicrobials are discovered. It is therefore necessary to find new antimicrobials and alternatives. Pseudomonas aeruginosa exhibits resistance against many antibiotics and causes a variety of infections in immunocompromised individuals and especially in those with burn wounds and lung infections. Bacteriophage RLP against P. aeruginosa strain PA-1 was isolated from the Ravi River near Lahore. It showed marked stability at different pH values and temperatures, with the maximum storage stability at 4 °C. It demonstrated the ability to inhibit bacterial growth for up to 20 h, replicated in 25 min, and produced 154 virions per infected cell. RLP showed a broad host range, infecting 50% (19/38) of the multiple-drug-resistant (MDR) P. aeruginosa strains that were tested. The 43-kbp-long genome of RLP is a double-stranded DNA molecule that encodes 56 proteins in total: 34 with known functions, and 22 with no homolog in the gene databases. A cascade system of lytic machinery is also present in the form of four genes (R/z, R/z1, holin and endolysin). Therapeutic studies of RLP in bacteremic mice infected with P. aeruginosa strain PA-1 demonstrated a 92% survival rate in the treated group compared with 7.4% in the untreated group, and this result was statistically significant. Based on its physiological and genetic properties, ability to cause a reduction in bacterial growth in vitro and its in vivo therapeutic efficacy, RLP could be a good candidate for use in phage therapy.