The presence of Salmonella and Campylobacter spp. in rodents and insectivores (n  282) was investigated

on organic farms. Infections were encountered in house mice (8 of 83 Campylobacter positive and 1 of 83

Salmonella sp. strain Livingstone positive) and brown rats (1 of 8 Campylobacter positive) but not in other

species. No shared Campylobacter genotypes were found between rodent and pig manure isolates. Effective

on-farm rodent management is recommended

B. G., Meerburg

W. F., Jacobs-Reitsma

English

Organic Eprints

APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Jan. 2006, p. 960–962 Vol. 72, No. 10099-2240/06/$08.000 doi:10.1128/AEM.72.1.960–962.2006Copyright © 2006, American Society for Microbiology. All Rights Reserved.Presence of Salmonella and Campylobacter spp. in Wild SmallMammals on Organic FarmsB. G. Meerburg,1* W. F. Jacobs-Reitsma,1 J. A. Wagenaar,1 and A. Kijlstra1,2Animal Sciences Group, Wageningen University and Research Centre, Lelystad, The Netherlands,1and Department of Ophthalmology, Eye Research Institute Maastricht,University of Maastricht, Maastricht, The Netherlands2Received 30 August 2005/Accepted 27 October 2005The presence of Salmonella and Campylobacter spp. in rodents and insectivores (n  282) was investigatedon organic farms. Infections were encountered in house mice (8 of 83 Campylobacter positive and 1 of 83Salmonella sp. strain Livingstone positive) and brown rats (1 of 8 Campylobacter positive) but not in otherspecies. No shared Campylobacter genotypes were found between rodent and pig manure isolates. Effectiveon-farm rodent management is recommended.Salmonella and Campylobacter spp. are the most importantcauses of bacterial gastroenteritis in humans and are respon-sible for 24% of food-borne diseases caused by known patho-gens in the United States (11, 15). Food from animal origin isone of the main sources of infection (15). Prevention of theintroduction of zoonotic agents in the primary production isstrongly dependent on the level of biosecurity. Wild rodentsmay spread zoonotic bacteria between farms (5, 6, 10, 14). Thisrisk may be even greater in organic production, where contactwith livestock is more likely and rodenticides are used lessoften.Rodents and insectivores were trapped on ten organic farms(nine pig farms, one broiler farm) by using live-traps betweenAugust and October 2004. Farms were subdivided into ﬁveareas: feeding passage (near the feed trough), storage (insidethe stable), outdoor area (next to the stable, solid/slatted con-crete ﬂoor, sometimes roofed), pasture, and “nature area”(further from stable, wild vegetation). After CO2 euthanasia,trapped animals were taken to the laboratory within hours.Upon arrival, their ceca and colons were processed.Pig manure samples were collected on 6 of 10 farms inOctober 2004. Four farms were omitted because the livestockbatch had meanwhile changed. On each farm, ﬁve fresh ma-nure samples (10 g) were taken throughout the stables. Thesesamples were pooled and analyzed for the presence of Salmo-nella and Campylobacter.Rodent intestinal contents or pig manure were directlystreaked on CCDA Campylobacter-selective agar plates (OxoidCM739  SR155) by using cotton swabs. These swabs weresubsequently transferred to 5 ml of Preston enrichment broth(Oxoid CM67  SR84  SR204) without blood (8). Enrich-ment broth was incubated for 24 h at 41.5°C under microaero-bic conditions and plated onto CCDA plates. All CCDA plateswere incubated for 48 h at 41.5°C under microaerobic condi-tions and examined for presence of characteristic colonies ofCampylobacter. Conﬁrmation was performed by checking mor-phology and motility microscopically. The ampliﬁed fragmentlength polymorphism (AFLP) method was used for speciesidentiﬁcation and genotyping (3, 4).For Salmonella detection, a swab containing 0.1 to1go frodent intestinal content or pig manure was added to 9 ml ofnonselective preenrichment medium, buffered peptone water(Biotrading K168B009). After preenrichment for 18 h at 37°C,3 drops were transferred to Modiﬁed Semi-Solid RappaportVassiliadis agar plates (MSRV; Lab M, Lab150). MSRV plateswere incubated at 41.5°C for 24 h. Growth on MSRV platessuspected to be Salmonella sp. was streaked on Brilliant GreenAgar (Oxoid CM329) and examined for presence of suspectedcolonies after incubation for 18 to 24 h at 37°C. A suspectedcolony was then agglutinated with polyvalent anti-speciﬁc Oantisera (Oxoid) and speciﬁc ﬂagellar H antisera. Each isolatewas biochemically conﬁrmed (triple sugar iron [Oxoid] agar,urease, and lysine decarboxylase).In total, 282 animals were examined, and 9 were positive forCampylobacter spp. (8 of 83 house mice, 1 of 8 brown rats).One Salmonella sp. strain Livingstone-positive house mousewas detected. Positive animals were only found in the storage,feeding passage and outdoor areas (Table 1). On three farms(A, B, and C), three single rodent isolates were obtained. Onfarm A, 1 of 6 (16.7%) house mice was positive (Campylobactercoli). On farm B, 1 of 8 (12.5%) brown rats caught was positive(C. coli). On farm C, 1 of 30 (3.3%) house mice was positive(Campylobacter spp.). This isolate was lost in follow-up andcould not be speciated. On farm D, 1 C. hyointestinalis,2C.coli, and 3 C. jejuni strains were isolated from 6 of 15 (40%)house mice that were caught. The Salmonella sp. strain Living-stone-positive house mouse (also positive for C. jejuni) wascaught here. Salmonella and Campylobacter spp. were not iso-lated from the pig manure at this farm. Overall, Campylobacterstrains was isolated from pig manure on three of six farms(farms A, B, and E), but Salmonella strains were not encoun-tered.AFLP analysis revealed no direct shared genotypes ofCampylobacter isolates from rodents and those from pigs atfarms A and B (Fig. 1; a cutoff point of 95% similarity to deﬁneidentical isolates was chosen). Campylobacter strains in twohouse mice caught at the same time at exactly the same trap-* Corresponding author. Mailing address: Animal Sciences Group,Wageningen University and Research Centre, P.O. Box 65, NL-8200AB Lelystad, The Netherlands. Phone: 31 (320)238238. Fax: 31(320)238050. E-mail: Bastiaan.Meerburg@wur.nl.960ping point on farm D were indistinguishable (Fig. 1, numbers244 and 245). Further examination of this particular farmshowed that almost all (ﬁve of six) Campylobacter-positive an-imals were found in one pig stable. The sixth infected animalwas trapped in the feeding passage of another stable, only 25meters away. No infections were encountered elsewhere.Although we realize the limitations concerning the numberof herds and their microbiological status, our study shows thaton Dutch organic farms two rodent species were found to becarriers of Salmonella and Campylobacter strains. Salmonellaprevalence was limited, a ﬁnding similar to a previous study(13) in which fecal pellets from house mice caught on-farmwere analyzed (0 of 222 animals infected). However, Salmo-nella prevalence may increase when rodents are caught near aSalmonella sp.-positive herd or ﬂock. The Campylobacter spe-cies found in rodents in the present study were C. jejuni, C. coli,and C. hyointestinalis subsp. hyointestinalis.Although no shared Campylobacter genotypes in rodents andpigs were found, horizontal transmission by infected rodentscannot be excluded. Pigs can carry multiple Campylobacterstrains (mixed infections), a phenomenon also observed inpoultry (1, 7). In turn, this phenomenon may facilitate geneticexchange between different Campylobacter strains in the piggastrointestinal tract under normal farm conditions. Such ge-netic instability under natural conditions could undermine theapplication of genetic subtyping (2). Hypothetically, infectedrodents and pigs can acquire their infection from the samesource or by infecting each other after having acquired theinfection from some other source. For example, this couldresult from the consumption of an infected rodent by a pig orby a mouse foraging through infected pig manure.Understanding of epidemiology of pathogens is important toensure livestock health and food safety. Here, house mice andbrown rats were found to carry Salmonella and Campylobacterstrains, but rodents can also transmit other pathogens, such asToxoplasma gondii (9). Transmission risks might be limited, buta reliable assessment is necessary to quantify the risks posed byrodents. Organic farmers should apply effective rodent man-agement that is in line with organic principles to protect live-stock and human health (12).This study was supported by grants from the Dutch Ministry forAgriculture, Nature, and Food Quality and the European Union In-tegrated Project Quality Low Input Food.We thank the participating farmers, the pig production group ofBiologica, the Dutch Society for the Study and Conservation of Mam-mals, Frans-Freddy Putirulan, Arie Hoogendoorn, Jan Cornelissen,Albert de Boer, Nico Bolder, Fimme Jan van der Wal, Bryan Jones,and Davy Duijsings.FIG. 1. AFLP analysis of Campylobacter strains identiﬁed in the study, linked to farms of origin. M, house mouse; R, rat; P, pig.TABLE 1. Cross-tabulation of animal species (n  283), their numbers, and the area in which they were encounteredSpecies Latin name Total no.No. found in (area of farm)a:Feed passage Storage Outdoor area Pasture Nature areaWhite-toothed shrew Crocidura russula 119 4 20 29 23 43Common shrew Sorex araneus 10 0 0 0 2 8House mouse Mus musculus 83 37 (2*) 21 (1*) 14 (5*,1†) 7 4Common vole Microtus arvalis 31 1 2 2 12 14Wood mouse Apodemus sylvaticus 19 0 1 0 3 15Brown rat Rattus norvegicus 8 8 (1*) 0 0 0 0Harvest mouse Micromys minutus 60 00 0 6Field vole Microtus agrestis 30 00 2 1Bank vole Clethrionomys glareolus 30 00 2 1Northern voleb Microtus oeconomus 10 00 0 1a Numbers indicate number of animals captured; numbers of positives are between parentheses (, Campylobacter positive; †, Salmonella positive).b This animal was released again because of its endangered status in The Netherlands.VOL. 72, 2006 SALMONELLA AND CAMPYLOBACTER SPP. IN SMALL MAMMALS 961REFERENCES1. Bang, D. D., E. M. Nielsen, K. 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Presence of Salmonella and Campylobacter spp. in Wild Small Mammals on Organic Farms

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