Isolation and Characterization of Bacteriophages Active against Pseudomonas aeruginosa Strains Isolated from Diabetic Foot Infections

Diabetic foot infection has become one of the most important public health concerns and is a growing problem. Pseudomonas aeruginosa is an important opportunistic multidrug-resistant bacterium in diabetic foot infections. In the absence of antibiotics active against MDR strains of P. aeruginosa, phage therapy becomes a key way to deal with P. aeruginosa infections. Out of 185 samples collected from diabetic foot ulcers, 50 (27.02%) isolates were identified as P. aeruginosa. The incidence increases with older ages, and males (n=34, 68%) predominated in all age groups. The tested isolates showed maximum susceptibility towards colistin (80%), imipenem (72%), amikacin (66%), and piperacillin/tazobactam (62%), while these isolates showed moderate susceptibility towards ceftazidime (58%), cefepime (52%) and gentamicin (46%). However, it showed complete resistance (100%) to ampicillin, cefaclor, and sulphamethoxazole/trimethoprim and highly resistance to clindamycin (90%) and amoxicillin/clavulanic acid (84%). Two bacteriophages (ϕPAE1 and ϕPAE2) isolated from sewage samples showed a broad host range against P. aeruginosaa clinical strains. ϕPAE2 infected 74% (37/50) and ϕPAE2 58% (29/50). Furthermore, both phages were host-specific, infecting only P. aeruginosa strains and could not infect other bacterial species in the cross-infectivity studies. Both phages were found to be relatively heat stable as over a period of 1 h, after exposure to a temperature range of 37–50°C, no significant loss in phage activity was observed. On the other hand, the lowest activity was observed at 70°C (39.15%) for ϕPAE1 whereas it was inactivated at 75°C while the lowest activity was observed at 75°C (38.01%) for ϕPAE2 whereas it was inactivated at 80°C. Isolated phages were able to survive and lyse host bacteria over a wide pH range. The optimum pH range for infection was from 6 to 8. Furthermore, ϕPAE1 lost its ability to lyses at pH 2, 3, 11 and 12, whereas; ϕPAE2 lost its infectivity at pH 2, 3 and 12. Chloroform was the most effective solvent that reduced the infectivity of ϕPAE1 and ϕPAE2 to 63.27% and 77.88%, respectively. On the other hand, petroleum ether showed the lowest effect on the infectivity of ϕPAE1 and ϕPAE2; it was reduced to 96.4% and 97.48%, respectively, followed by acetone and ethyl alcohol. The ability of P. aeruginosa phages to form plaques after different storage temperatures (4°C, 30°C, 37°C and 44°C) for a month was slightly affected. The storage of ϕPAE1 and ϕPAE2 at 4ºC showed the least effect on its infectivity, and the storage at 44ºC showed the highest reduction in its infectivity. Moreover, Phage counts were slightly decreased by increasing storage period and temperature.