Isolation of bacteriophages specific to bovine mastitis-causing bacteria and characterization of their lytic activity in pasteurized milk

Background and Aim

Bovine mastitis is one of the most serious issues in dairy production. It is caused by contagious and coliform pathogens such as Staphylococcus spp., Escherichia coli, and Klebsiella pneumoniae. In addition, the emergence of drug-resistant bacteria raises urgent concerns in the field of drug treatment, thus requiring the exploration of alternative treatments. Bacteriophage therapy has been shown to be a promising alternative approach for the control of antibiotic-resistant pathogens. In this study, we aimed to isolate phages specific to contagious mastitis and coliform mastitis, characterize the isolated phages, and examine their ability to lyse bacteria in pasteurized milk samples.

Materials and Methods

The Staphylococcus phage vB_Sau-RP15 isolated from raw milk in our previous study was used in this study. Other three phages, vB_Eco-RN12i1, vB_Kpn-RN14i1, and vB_Ssc-RN20i3, were isolated from wastewater using E. coli 5823, K. pneumoniae 194, and Staphylococcus sciuri MM01 as hosts, respectively. The host range and efficiency of plating (EOP) were determined following phage isolation. Moreover, the lysis activities of these phages against their hosts were investigated in pasteurized milk using a multiplicity of infections (MOIs) of 10 and 100 at 37°C. Phages were applied using individual and combination phages.

Results

According to the EOP results, all phages showed high specificity to their respective hosts. They are tailed phages with distinct morphologies. Individual phage treatments in spiked pasteurized milk with their respective bacterial hosts significantly reduced the bacterial counts in both MOI conditions during the first 2 h of the treatment (approximately 1-8 log reduction compared to the control). Although these phages specifically infected only their hosts, the phage cocktail resulted in a better result compared to the use of individual phage. However, bacterial regrowth was observed in all experiments, which may be related to the development of phage-insensitive mutants.

Conclusion

Our findings suggest that the application of phages could be used to treat bovine mastitis. Phage cocktail is suitable to promote the efficacy of phage treatment in pasteurized milk. However, when considering the use of phages in dairy cows, certain phage properties in raw milk and in vivo and ex vivo should be highlighted to ensure their effectiveness as biocontrol agents for bovine mastitis treatment.

A novel Staphylococcus phage, vB_Sau-RP15, and its application in contaminated milk

The vB_Sau-RP15 phage, selected for its potential use as a phage treatment in milk, was isolated from raw milk using Staphylococcusaureus NP01 as the host. The host range test revealed that the phage was able to lyse 12 strains of Staph. aureus from raw milk. This phage was stable at 4-37°C and pH 6-9 for at least 1 h. The adsorption rate was ~78% within the first 3 min. A low frequency of phage-insensitive mutant induction (4.6 × 10-6) was observed. Genomic analyses revealed that the vB_Sau-RP15 represented a novel species in the genus Silviavirus. Even though no virulence or antibiotic resistance genes were detected, the phage genome carried lysogenic-associated genes. Phage treatments (108 PFU per ml) in pasteurized milk contaminated with low (104 CFU per ml) and high (107 CFU per ml) concentrations of Staph. aureus confirmed the proficiency of the phage in the diminishing of the number of bacterial cells at 4°C and ambient temperature. A Staphylococcus phage, vB_Sau-RP15, could be a promising agent for controlling Staph. aureus contamination in milk.

Bacteriophage efficacy in controlling swine enteric colibacillosis pathogens: An in vitro study

Background and Aim

Swine enteric colibacillosis caused by Escherichia coli is a major problem in the swine industry, causing diarrhea among swine and resulting in substantial financial losses. However, efforts to counter this disease are impeded by the increase in antimicrobial resistance (AMR) worldwide, so intensive research is being conducted to identify alternative treatments. This study isolated, characterized, and evaluated the efficacy of bacteriophages to control pathogens causative of swine enteric colibacillosis.

Materials and Methods

Five sewage samples were collected from different areas of a swine farm in Suphanburi province, Thailand and the bacteriophages were enriched and isolated, followed by purification by the agar overlay method using E. coli RENR as the host strain. The selected phages were characterized by evaluating their morphology, while their specificity was verified by the host range test. The efficiency of plating and multiplicity of infection (MOI) were also determined.

Results

Four selected phages, namely, vB_Eco-RPNE4i3, vB_Eco-RPNE6i4, vB_Eco-RPNE7i1, and vB_Eco-RPNE8i3, demonstrated different patterns of host range and phage efficiency. They significantly decreased E. coli concentration at the tested MOIs (0.01-100) from 1 h onward. However, bacterial regrowth was observed in all phage treatments.

Conclusion

This study shows the potential of using phages as an alternative treatment for swine enteric colibacillosis. The obtained results demonstrated that the selected phages had a therapeutic effect against pathogens causative of swine enteric colibacillosis. Therefore, phages could be applied as an alternative treatment to control specific bacterial strains and reduce AMR arising from the overuse of antibiotics.

Selection and characterization of bacteriophages specific to Salmonella Choleraesuis in swine

Background and Aim

Salmonella Choleraesuis is the most common serotype that causes salmonellosis in swine. Recently, the use of bacteriophages as a potential biocontrol strategy has increased. Therefore, this study aimed to isolate and characterize bacteriophages specific to S. Choleraesuis associated with swine infection and to evaluate the efficacy of individual phages and a phage cocktail against S. Choleraesuis strains in simulated intestinal fluid (SIF).

Materials and Methods

Three strains of S. Choleraesuis isolated from pig intestines served as host strains for phage isolation. The other 10 Salmonella serovars were also used for the phage host range test. The antibiotic susceptibility of the bacterial strains was investigated. Water samples from natural sources and drain liquid from slaughterhouses were collected for phage isolation. The isolated phages were characterized by determining the efficiency of plating against all Salmonella strains and the stability at a temperature range (4°C-65°C) and at low pH (2.5-4.0) in simulated gastric fluids (SGFs). Furthermore, morphology and genomic restriction analyses were performed for phage classification phages. Finally, S. Choleraesuis reduction in the SIF by the selected individual phages and a phage cocktail was investigated.

Results

The antibiotic susceptibility results revealed that most Salmonella strains were sensitive to all tested drugs. Salmonella Choleraesuis KPS615 was multidrug-resistant, showing resistance to three antibiotics. Nine phages were isolated. Most of them could infect four Salmonella strains. Phages vB_SCh-RP5i3B and vB_SCh-RP61i4 showed high efficiency in infecting S. Choleraesuis and Salmonella Rissen. The phages were stable for 1 h at 4°C-45°C. However, their viability decreased when the temperature increased to 65°C. In addition, most phages remained viable at a low pH (pH 2.5-4.0) for 2 h in SGF. The efficiency of phage treatment against S. Choleraesuis in SIF showed that individual phages and a phage cocktail with three phages effectively reduced S. Choleraesuis in SIF. However, the phage cocktails were more effective than the individual phages.

Conclusion

These results suggest that the newly isolated phages could be promising biocontrol agents against S. Choleraesuis infection in pigs and could be orally administered. However, further in vivo studies should be conducted.

In vivo assessment of bacteriophages specific to multidrug resistant Escherichia coli on fecal bacterial counts and microbiome in nursery pigs

Escherichia coli is the most common cause of economic loss in swine industry. Nowadays, bacteriophages have been proven as good candidates for controlling bacterial infections. In this study, 6 phages were isolated and selected based on their high efficacy against 11 stains of E. coli isolated from diarrheal pigs. Six groups of weaned piglets were assigned (control, bacterial control (BC), two phage control (PC) and two phage treatment (PT) groups). Two titers (2 × 10⁹ PFU/animal and 2 × 10¹⁰ PFU/animal) of phage cocktails consisting of these phages were tested in the PC and PT groups via oral gavage at 24, 48, and 72 h against an E. coli cocktail (2 × 10⁹ CFU/animal) that was given to the piglets at 0, 12, 24, and 48 h of the trial. A significant reduction of fecal E. coli counts was observed in both PT groups from day 1 to 7 following the final phage dosage when compared to those of the BC group. Microbiomes in feces obtained 24 h after the final phage administration revealed phage therapy with both dosages could restore the gut's bacterial composition. Moreover, the given phage cocktails resulted in a significantly higher average daily gain of piglets during the first few weeks in both PC groups and the PT group receiving a higher phage dosage. These findings suggest that bacteriophages might be a potential alternative to antibiotics in the treatment of pathogens. In addition, they could also be utilized to improve pig growth performance.

Characterization of Salmonella bacteriophages and their potential use in dishwashing materials

AIMS

The aims of this study were to isolate and characterize novel Salmonella phages and to evaluate the effectiveness of phage cocktails used as antibacterial agents in dishwashing materials.

METHODS AND RESULTS

The effective phages, vB_STy-RN5i1 and vB_STy-RN29, were isolated from drain water samples collected from open markets using Salmonella Typhimurium as the host strain. These phages were identified as members of Podoviridae and Siphoviridae, respectively. Both phages infected at least six Salmonella serovars and rapidly lysed their host within one hour. They were stable at 4-45°C and at pH 6-9 for at least an hour while being evaluated in this study. The phage application results indicated that bacterial cells were reduced by 3⋅1 and 2⋅7 log CFU per ml at room temperature when they encountered the phage cocktail on scouring pads (SPs) and dishwashing sponges (DSs), respectively.

CONCLUSIONS

The isolated Salmonella phages, vB_STy-RN5i1 and vB_STy-RN29, had potential against Salm. Typhimurium and could reduce the occurrence of bacterial-cross-contamination from dishwashing materials, which have been reported to be a source of bacteria, to other kitchen utensils and food.

SIGNIFICANCE AND IMPACT OF THE STUDY

The successful reduction of bacterial contamination in dishwashing materials by the phage cocktail consisting of vB_STy-RN5i1 and vB_STy-RN29 reveals its potential to be an alternative antimicrobial agent for SPs and DSs.