Combine thermal processing with polyvalent phage LPEK22 to prevent the Escherichia coli and Salmonella enterica contamination in food

Thermal processing is the most frequently used method to destruct bacteria in food processing. However, insufficient thermal processing may lead to the outbreak of foodborne illness. This study combined thermal processing with thermostable phage to prevent food contamination. The thermostable phages were screened which can retain activity at 70 °C for 1 h. Among them, the polyvalent phage LPEK22 was obtained to lyse Escherichia coli and Salmonella enterica, especially several multi-drug resistant bacteria. In milk (liquid food matrix), LPEK22 significantly reduced the E. coli by 5.00 ± 0.18 log₁₀ CFU/mL and S. enterica by 4.20 ± 0.23 log₁₀ CFU/mL after thermal processing at 63 °C for 30 min. For beef sausage (solid food matrix), LPEK22 significantly reduced the E. coli by 2.34 ± 0.17 log₁₀ CFU/cm² and S. enterica by 1.54 ± 0.13 log₁₀ CFU/cm² after thermal processing at 66 °C for 90 s. Genome analysis revealed that LPEK22 was a novel phage with a unique tail spike protein belonging to the family of Ackermannviridae. LPEK22 did not contain lysogenic, drug-resistant, and virulent genes that may compromise the safety of food application. These results determined that LPEK22, a novel polyvalent Ackermannviridae phage, could combine with thermal processing to prevent drug-resistant E. coli and S. enterica both in vitro and in foods.

The antagonistic interactions between a polyvalent phage SaP7 and β-lactam antibiotics on combined therapies

Phage therapy is a promising alternative antibiotic strategy to combat multidrug-resistant bacteria infections. Most studies focus on the synergistic effects, while the antagonistic interactions between phage and antibiotics is rarely studied. Here, we isolated and identified a novel polyvalent phage SaP7, which is capable of infecting multidrug-resistant Salmonella S7 and several E. coli strains. Morphology via electron microscopy showed that SaP7 belonged to the Myoviridae family. Genomic analysis revealed that the genome of SaP7 lacked any genes associated with antibiotic resistance, toxins, lysogeny, and virulence factors. We discovered the antagonism efficacy of SaP7 combined amoxicillin/potassium clavulanate (AMC) in counteracting Salmonella S7 in piglet-models by bacterial loads in feces and tissues. The consistent result as above between SaP7 and amoxicillin (AMX) was further verified in BALB/c mice-models. Furthermore, in vitro, plaque assay and minimum inhibitory concentration (MIC) determinations showed that AMX or AMC or cefepime (FEP) inhibited SaP7 plaque formation respectively and SaP7 decreased bacterial susceptibility of Salmonella S7 to AMX, AMC and FEP. And the negative interference of SaP7 with the bacteriostasis to Salmonella S7 of these three β-lactam antibiotics was observed in planktonic cultures via microtiter plates, but could not prevent the bacteriostasis of high titer of phage or high concentration of antibiotics. Finally, our research suggested that a polyvalent phage SaP7 existed antagonism with several β-lactam antibiotics. It is therefore crucial to fully and cautiously evaluate phage/antibiotic interactions and probable outcomes to avoid antagonistic impacts and failure of antibiotic and phage combination therapy.

Comparing polyvalent bacteriophage and bacteriophage cocktails for controlling antibiotic-resistant bacteria in soil-plant system

Antibiotic resistant pathogenic bacteria (ARPB) residual in soil-plant system has caused serious threat against public health and environmental safety. Being capable of targeted lysing host bacteria, phage therapy has been proposed as promising method to control the ARPB contamination in environments. In this study, microcosm trials were performed to investigate the impact of various phage treatments on the dissipation of tetracycline resistant Escherichia coli K-12 and chloramphenicol resistant Pseudomonas aeruginosa PAO1 in soil-carrot system. After 70 days of incubation, all the four phage treatments significantly decreased the abundance of the pathogenic bacteria and the corresponding antibiotic resistance genes (tetW and cmlA) in the soil-carrot system (p < 0.05), following the order of the cocktail phage treatment (phages ΦYSZ1 + ΦYSZ2) > the polyvalent phage (ΦYSZ3 phage with broad host range) treatment > host-specific phage (ΦYSZ2 and ΦYSZ1) treatments > the control. In addition, the polyvalent phage treatment also exerted positive impact on the diversity and stability of the bacterial community in the system, suggesting that this is an environmentally friendly technique with broad applications in the biocontrol of ARPB/ARGs in soil-plant system.