Isolation and characterization of Listeria species from rodents in natural environments in China

Abstract

Listeria is ubiquitous in a variety of environments and can be isolated from a wide range of animal hosts. Rodents are capable of carrying pathogenic bacteria in their intestines, such as Listeria, and can disseminate those pathogens into the natural environment and to where human activity occurs. In this study, we investigated the occurrence and antimicrobial susceptibility of Listeria spp. isolated from wild rodents found in natural environments in China. We collected 341 intestinal fecal samples of rodents from five different regions of China, all representing different rodent habitats. The antimicrobial susceptibility of the Listeria spp. isolates obtained were firstly assessed using the Kirby-Bauer disk diffusion method. Thirty-one samples were positive for Listeria spp., of which 11 were positive for Listeria monocytogenes and seven were positive for Listeria ivanovii. Other species identified include Listeria innocua, Listeria fleischmannii and Listeria floridensis. All Listeria spp. isolates were sensitive to the majority of the antimicrobials tested, but largely resistant to oxacillin (94.1%) and cefuroxime (70.6%). All L. monocytogenes isolates were further characterized by serotyping, multi-locus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). L. monocytogenes strains were grouped into three serotypes, five sequence types and five pulsotypes (PTs) by serotyping, MLST and PFGE, respectively. Almost half of the isolates (five of 11) belonged to serotype 1/2b, ST87 and PT1. This study determined that Listeria is carried in the intestinal tracts of wild rodents from multiple regions at a low rate, filling an epidemiological data gap on Listeria in natural environments in China.

Figure 1

(A) Pulsed-field gel electrophoresis-based dendrogram representing L. monocytogenes strains isolated from rodents of wild fields in China. The 11 L. monocytogenes isolates were divided into two lineages by serotyping, MLST and PFGE. The corresponding data, including the name of the isolate (isolate_id), region, serotype, pulsotype and ST are shown. (B) The minimum spanning tree of the five sequence types of L. monocytogenes isolates from rodents in wild environments in China. The corresponding sequence type and isolated region are displayed within the circles. The size of each circle corresponds to the isolate count, and the color within the circles represents the species of the rodents. multi-locus sequence typing, MLST; pulsed-field gel electrophoresis, PFGE; sequence type, ST.