Sewage and sewage-contaminated environments are the most prominent sources to isolate phages against Pseudomonas aeruginosa

Abstract

Background: P. aeruginosa is the primary source of hospital-acquired infections. Unfortunately, antibiotic resistance is growing to precariously high levels, making the infections by this pathogen life-threatening and hard to cure. One possible alternative to antibiotics is to use phages. However, the isolation of phages suitable for phage therapy- be lytic, be efficient, and have a broad host range -against some target bacteria has proven difficult. To identify the best places to look for these phages against P. aeruginosa we screened hospital sewages, soils, and rivers in two cities.

Results: We isolated eighteen different phages, determined their host range, infection property, and plaque morphology. We found that the sewage and sewage-contaminated environments are the most reliable sources for the isolation of Pseudomonas phages. In addition, phages isolated from hospital sewage showed the highest efficiency in lysing the bacteria used for host range determination. In contrast, phages from the river had larger plaque size and lysed bacteria with higher levels of antibiotic resistance.

Conclusions: Our findings provided additional support for the importance of sewage as the source of phage isolation.

Keywords: Antibiotic resistance; Host-range; Phage isolation; Phage therapy; Pseudomonas aeruginosa.

Fig. 1

a Map showing the fraction of phages isolated at different sites. The ratio of phages isolated on each site is in blue. Pie diagrams at 37° 16′ 33″ N, 49° 35′ 19″ E shows Rasht and 34° 47′ 57″ N, 48° 30′ 52″ E indicates Hamadan. b Z scores of EOP values of different phages on P. aeruginosa isolates- different colors represent different phages. c Z scores of phages’ EOP values— grouped based on their isolation source. Sewage phages showed the highest EOP values against bacteria used for host range determination

Fig. 2

Multiple Factor Analysis of the phages host range, infection property, source of isolation, and bacterial host characteristics. a MFA ordination of quantitative variables. b and c The contribution of each quantitative variable to dimensions 1 and 2 of the MFA. c MFA ordination of qualitative variables. e and f The contribution of each qualitative variable to dimensions 1 and 2 of the MFA. Quantitative variables include antibiotic resistance, plaque size, host range, EOP value, phages latency period, and burst size- quantitative data were scaled. Qualitative variables include plaque morphology, source and location of isolation, and Pulsed-field Gel Electrophoresis (PFGE) type of the host

Fig. 3

The correlation matrix of quantitative variables. Pearson’s correlation coefficient was used to measure the correlation between different quantitative variables (PFGE type, antibiotic resistance pattern, plaque size, host range, EOP value, latency period, and burst size). The diagonal shows distribution of each variable: on the top, the values of the correlations are displayed, while on the bottom, the bivariate scatters plots with a fitted line are shown