Isolation and relationship analysis of Listeria phages with various serotype hosts and morphological characterization

Abstract

Listeriosis, caused by Listeria monocytogenes (Lm), is a severe foodborne illness with a high fatality rate. Listeria phages specifically target and lyse Lm, offer a promising alternative for biocontrol and phage therapy. However, most existing studies focus on the lytic characteristics of Listeria phages using limited sample sizes. In this study, a large number of Listeria phages were isolated from diverse sources, and their lytic profiles and morphology were characterized. A total of 317 Listeria phages were isolated from 90 food-related environmental samples and 196 natural environmental samples collected across seven provinces. The phages were tested for lytic activity against 35 Lm strains representing nine serotypes, and their morphology was characterized using transmission electron microscopy (TEM). Statistical analysis was conducted to evaluate the lytic patterns of phages. The phages were classified into three groups based on their total lysis ratios. Broad Host Range Phages (BHRP) were primarily members of the Myoviridae-like phages and demonstrated the ability to lyse a vast majority of nine serotype host strains. Medium Host Range Phages (MHRP) comprised both Siphoviridae-like and Myoviridae-like phages, and demonstrated lysis of 6-9 serotype strains. Narrow Host Range Phages (NHRP) belonged to the Siphoviridae-like phages and exhibited effective lysis of serotype 4 strains. Furthermore, phages isolated from food-related environmental sources demonstrated greater lytic activity against Listeria serotypes 1/2b, 4a, and 4c compared to those derived from natural environmental sources. The study first isolated a multitude of Listeria phages, elucidated their lytic patterns and ecological distribution, and provided a valuable resource for future research.

Keywords: Listeria monocytogenes; Listeria phage; Ecological distribution; Lytic profiles; Morphology.

Fig. 1

Lysis Profiles of Broad Host Range Phages (BHRP) (n = 33). Left labels indicate phage sources and sample types, while right labels denote provinces of origin. Columns represent host strains, annotated with their serotypes

Fig. 2

Lysis Profiles of Medium Host Range Phages (MHRP) (n = 204). Left labels indicate phage sources and sample types, while right labels denote provinces of origin. Columns represent host strains, annotated with their serotypes

Fig. 3

Lysis Profiles of Narrow Host Range Phages (NHRP) (n = 56). Left labels indicate phage sources and sample types, while right labels denote provinces of origin. Columns represent host strains, annotated with their serotypes

Fig. 4

Comparison of the phage lysis activities by sample environmental sources. A Broad Host Range Phages (BHRP) (n = 33). B Medium Host Range Phages (MHRP) (n = 204). C Narrow Host Range Phages (NHRP) (n = 56). The bars represent the mean + SD. FE, Food-related environment; NE, Natural environment. Statistical analyses were conducted using the Wilcoxon rank-sum test, with the following significance levels: *P<0.05; ** P < 0.01 and ***P < 0.001

Fig. 5

Transmission electron microscopy images of isolated Listeria monocytogenes phages. Phages 17, 33, 263, 19, 225, 102, 62, and 251 belong to the Siphoviridae-like phage. Phages 211, 144, 201, 189, 130, 39, 208, and 222 belong to the Myoviridae-like phage family

Fig. 6

Lytic profiles and morphological characteristics of isolated Listeria monocytogenes phages. The numerical values within each cell represent the lysis ratio of each phage against the corresponding serotype strains. FE, Food-related environment; NE, Natural environment