Broad-host-range Salmonella bacteriophage STP4-a and its potential application evaluation in poultry industry

Abstract

Salmonella is regarded as the predominant cause of foodborne illnesses worldwide, and the increase of these antimicrobial-resistant strains makes it more difficult to prevent. On this occasion, bacteriophages (phages) stand out as an alternative biocontrol agent with high efficiency and low mutation rates. Salmonella phages have confronted challenges to counteract with more than 2,500 serovars of Salmonella spp. and overcome the universality of antibiotics to different species, and thus, broad-host-range phages infecting Salmonella spp. are urgently required to realize precise poultry treatment or clinical therapy. First, phage STP4-a was screened to have a broad host range through bioinformatics analysis, and then the host range assay proved that phage STP4-a could inhibit 88 out of 91 Salmonella strains. Then, in silico analysis excluded the possibility of phage STP4-a possessing any known lysogeny factors, toxins, pathogen-related genes, or foodborne allergens, and oral toxicity studies further ensured the safety of unknown factors or suspected risks. In addition, strong inhibition effects of phage STP4-a were seen on both single Salmonella strain and multiple Salmonella strains in vitro, reducing 3-5 log in 30 min. Phage STP4-a could survive and keep more than 50% activity in simulated stomach or intestine environments in vitro. In terms of antimicrobial activities in chickens, pretreatment with phage STP4-a was the most efficient approach to Salmonella biocontrol, non-detectable in feces during the 14-day experimental period. Therefore, phage STP4-a was an extremely broad-host-range and safe biocontrol agent, performing its potential as a food additive or therapeutic drug in poultry industry.

Keywords: Salmonella bacteriophage; antimicrobial activity; broad-host-range; poultry industry; safety.

Figure 1

Histological observations of different organs in different groups. (A) Liver (H.E × 400), (B) spleen (H.E × 200), (C) kidney (H.E × 400), (D) stomach (H.E × 200), (E) intestine (H.E × 200), (F) heart (H.E × 200).

Figure 1

Histological observations of different organs in different groups. (A) Liver (H.E × 400), (B) spleen (H.E × 200), (C) kidney (H.E × 400), (D) stomach (H.E × 200), (E) intestine (H.E × 200), (F) heart (H.E × 200).

Figure 2

The in vitro antimicrobial activities of phage STP4-a and its stability in simulated environments for different time intervals. (A) In vitro antimicrobial activity for a single strain, Salmonella Typhimurium ATCC 14028. (B) In vitro antimicrobial activity for 6 Salmonella strains. (C) The stability of phage STP4-a in simulated environments. Borders with blue color represented titers of phage in 12 mL simulated digestion preparations (4 mL simulated saliva and 8 mL simulated gastric juice, abbr. “SA + GA”) for 0, 1 h; Borders with red color represented titers of phage 8 mL simulated gastric juice (abbr. “GA”) for 0, 1, 2 h. Borders with green color represented titers of phage 12 mL simulated intestinal fluid (abbr. “IN”) for 0, 3 h.

Figure 3

Bacteria counts in feces among Salmonella-infected groups during the 2-week experiments. Data in the same day with different letters (a, b, c) are significantly different (P < 0.05).