Novel phage vB_CtuP_B1 for controlling Cronobacter malonaticus and Cronobacter turicensis in ready-to-eat lettuce and powered infant formula

Abstract

Cronobacter spp. are important foodborne pathogens that are a threat to people of all ages, but especially neonates and infants. Bacteriophages are biological agents that are potentially useful for the control of foodborne pathogens. However, there has been little research on the control of C. malonaticus and C. turicensis using bacteriophages. In the present study, a novel lytic phage vB_CtuP_B1 (hereafter referred to as B1)-which can simultaneously lyse C. malonaticus and C. turicensis- was isolated from river water in Guangzhou, China, and was used in the control of Cronobacter contaminated food. The phage has a short tail, and has been identified as a new species of Kayfunavirus based on genomic and phylogenetic analyses. One-step growth and stability assays revealed that phage B1 has a very short latent period (<5 min) and a large burst size (4006 pfu/cell), and is highly stable between 25 and 60 °C and between pH 5 and 11. Its genome encodes two lytic proteins, but does not contain any genes responsible for antibiotic resistance and virulence factors. In broth, the phage B1 completely inhibited the growth of C. malonaticus cro2475W and C. turicensis cro1541A1-1 for up to 6 h. On lettuce, phage B1 reduced the viable count of C. turicensis cro1541A1-1 to below the detection limit for bacteria on lettuce (<10 cfu/mL) after 6 h at 4 °C and 2 h at 25 °C, and also significantly reduced the viable count of C. malonaticus cro2475W at those temperatures. In powdered infant formula, the viable counts of both the phage-treated bacterial hosts were significantly reduced after 2 h of storage at 4 °C or 37 °C. Furthermore, phage B1 reduced the viable count of C. turicensis cro1541A1-1 to below the detection limit (<10 cfu/mL) from 4 h to 24 h at 37 °C. It significantly inhibited the growth of C. turicensis cro1541A1-1 than that of C. malonaticus cro2475W (P < 0.05). In conclusion, phage B1 with high stability and strong lytic ability is potentially useful for controlling C. malonaticus and C. turicensis.

Keywords: Bacteriophage; Biocontrol; Cronobacter; Food security; Lettuce; Powdered infant formula.