Combined Application of Bacteriophages and Carvacrol in the Control of Pseudomonas syringae pv. actinidiae Planktonic and Biofilm Forms

Abstract

Pseudomonas syringae pv. actinidiae (Psa) is the causative agent of the bacterial canker of kiwifruit (Actinidia spp.). Phage therapy has been suggested as a viable alternative approach to controlling this disease, but its efficacy is limited by the emergence of phage-resistant mutants. Carvacrol is an essential oil that may be useful for the control of Psa. Combination therapies can be used to overcome resistance development. Here, the combination of phages (single phage suspensions of phages PN05 and PN09, and a cocktail of both phages) and carvacrol was investigated in controlling Psa planktonic and biofilm forms in vitro. The phage therapy alone (with phages PN05 and PN09), and the carvacrol alone (minimum inhibitory concentration 2.0 mg/mL), inhibited Psa growth, but the combined effect of both therapies was more effective. The phages alone effectively inhibited Psa growth for 24 h, but Psa regrowth was observed after this time. The carvacrol (2.0 mg/mL) alone prevented the biofilm formation for 48 h, but did not destroy the pre-formed biofilms. The combined treatment, phages and carvacrol (2.0 mg/mL), showed a higher efficacy, preventing Psa regrowth for more than 40 h. In conclusion, the combined treatment with phages and carvacrol may be a promising, environment-friendly and cost-effective approach to controlling Psa in the kiwifruit industry.

Molecular Characterization and Taxonomic Assignment of Three Phage Isolates from a Collection Infecting Pseudomonas syringae pv. actinidiae and P. syringae pv. phaseolicola from Northern Italy

“…Phage cocktail persistence in the open field could be improved with specific formulations [ 9 ] and their action can be increased in synergy with the addition with other compounds such as carvacrol [ 20 ] and garlic extract [ 24 ]. Additionally, the phages we isolated can be a useful source of endolysins as an alternative Psa and Pph biocontrol method [ 78 ]; the vast number of functionally uncharacterized ORFs they encode could contribute to further control approaches once their role is elucidated, urging a vast effort to assign function to the unprecedented proteomic diversity harbored by phages [ 67 , 79 , 80 ].…”

“…syringae pathovars porri [ 11 ], aesculi [ 12 ] and morsprunorum [ 13 , 14 ]. Several studies have described phages that could potentially be used to control Psa [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ] and Pph [ 23 , 24 , 25 ].…”

A Hundred Years of Bacteriophages: Can Phages Replace Antibiotics in Agriculture and Aquaculture?

“…In addition, the commercially available phage Φ6 was also effective, both in vitro and ex vivo, particularly against two highly aggressive Psa strains [92]. Similarly interesting, in a recent study, it has been shown that the combination of phages PN05 and PN09 and the natural antimicrobial carvacrol (2.0 mg/mL) controlled Psa regrowth for more than 40 h, preventing the emergence of phage-resistant mutants and controlling biofilm development [93].…”

Transcriptome Analysis on the Mechanism of Ethylicin Inhibiting Pseudomonas syringae pv. actinidiae on Kiwifruit

“…According to the method of Ni [ 30 ], Psa was incubated to OD 600 values of 0.6–0.8. Different treatment solutions were mixed with 300 µL of bacterial suspension in 96-well plates to give the final concentrations of ethylicin of 0, 1.80, 2.70, 3.60, and 4.50 μg/mL at 28 °C for 72 h to form biofilms, and each treatment was repeated six times.…”