On-farm monitoring of mouse-invasive Salmonella enterica serovar enteritidis and a model for its association with the production of contaminated eggs

Abstract

Mice (Mus musculus) captured in henhouses were assessed for the presence of salmonellae in spleens. Of 621 and 526 spleens cultured during the first and second years of collection, 25.0 and 17.9%, respectively, were positive for Salmonella enterica serovar Enteritidis. Contaminated eggs were cultured from nine houses during the first year of sampling, and for eight of these houses, serovar Enteritidis was recovered from the spleens of mice. Rank sum statistical analysis of positive mouse spleens indicated that three overlapping bacterial populations were present. This pattern of infection was repeated when lipopolysaccharide (LPS) variants were used to infect chicks, and the worst infections were associated with isolates producing high-molecular-weight (HMW) LPS. Mouse isolates were capable of producing unprecedented amounts of HMW LPS as indicated by compositional analysis of six isolates that swarmed across 2% agar, which is a type of bacterial migration dependent upon production of HMW LPS. It is suggested that monitoring serovar Enteritidis cultured from the spleens of mice caught on farms will detect strains that are enhanced in their ability to contaminate eggs, in part because they are able to produce HMW LPS.

Patterns of infection by Salmonella and Yersinia spp. in commensal house mouse (Mus musculus domesticus) populations

“…Although Salmonella is commonly transmitted to humans from poultry and pigs, house mice are often claimed to be the initial reservoir (Hart et al 1997), and Davies and Wray (1995) have reported Salmonella in 48á7% of house mice from poultry units. However, comparisons by Henzler and Opitz (1992) and Guard-Petter et al (1997) show that the prevalence tends to be lower in units with no history of Salmonella in poultry (6á0% and 0á4% in the two studies, respectively) compared with those with recent Salmonella infections (31á8% and 31á5%). This suggests that although house mice may have been the initial source of pathogenic Salmonella in poultry¯ocks (Ba Èumler et al 2000), it is probably now infected livestock (especially poultry) that are infecting the mice, which then serve as a reservoir for re-infection (Henzler and Opitz 1992;Davies and Wray 1995).…”

“…There was a high rate of turnover in the house mouse population (only 21% of individuals were recaught from one month to the next), making long-term persistence of infections less likely. However, some Salmonella strains have been found to persist within commensal rodent populations for months or even years (Sato et al 1970 1 ;Henzler and Opitz 1992;Guard-Petter et al 1997). Due to the high population turnover, few mice were tested on more than one occasion, so no conclusions can be drawn about the pattern of infection in an individual.…”

“…Although this excretion drops rapidly after a few weeks, Salmonella may continue to be excreted for months and may be harboured in the liver, leading to intermittent excretion during times of stress (Davies and Wray 1995). Transmission of Salmonella within the close-knit populations of house mice can be rapid (Welch et al 1941), and strains can persist in individual populations for years (Henzler and Opitz 1992;Guard-Petter et al 1997), although due to the spatial subdivision of mouse populations, these infections may remain extremely localized (Henzler and Opitz 1992). Since house mice can act as reservoirs of infection and can re-infect poultry with Salmonella, their control needs to be considered where there are Salmonella-prone livestock (Henzler and Opitz 1992;Rose et al 2000).…”

Lipopolysaccharide O‐chain microheterogeneity of Salmonella serotypes Enteritidis and Typhimurium

“…There are three major theories concerning the origin of Salmonella illness associated with egg contamination. First, clonal expansion of an unusual strain, which results in more contaminated eggs in the marketplace owing to an enhanced ability of the organism to be invasive in chickens or otherwise to reach and survive within the internal contents of eggs (Petter, 1993;Guard-Petter et al, 1997;Guard-Petter, 1998) may be a factor; secondly, waning flock immunity to Salmonella enterica serovar Pullorum, an avian-adapted salmonellae that also contaminates eggs internally, might have provided an ecological niche for the expansion of S. Enteritidis (Rabsch et al, 2000); thirdly, Salmonella infections in rodents may have been the cause of a change in infection dynamics, resulting in the emergence of S. Enteritidis in flocks kept in houses that have resident infected mice (Henzler and Opitz, 1992;Henzler et al, 1998). The first theory suggests that it should be possible to identify biological markers unique to egg-contaminating S. Enteritidis, whereas the last two theories argue that host factors are of primary importance.…”

Persistence of Salmonella Enteritidis Phage Type 4 in the environment and arthropod vectors on an empty free‐range chicken farm

“…Mice are important in the epidemiology of Salmonella on farms as not only do they act as potential long-term carriers of the organism but also they may amplify numbers of organisms in the environment, deposit highly contaminated faeces directly into feeders. Passage of S. Enteritidis in mice may also selectively amplify more virulent and egg invasive strains (Humphrey et al ., 1996;Guard-Petter et al ., 1997;Henzler et al ., 1998;Guard-Petter, 2001). Carriage of Salmonella by arthropods has also been reported previously (Graffar and Mertens, 1950;Fischer, 1999;Olsen and Hammack, 2000) but the seasonal appearance of contaminated ground beetles and their larvae in one of the empty poultry houses during two consecutive summers was unexpected.…”