PATHOGENICITY OF 3 STRAINS OF SERPULINA-PILOSICOLI IN PIGS WITH A NATURALLY ACQUIRED INTESTINAL FLORA

Serpulina pilosicoli is an anaerobic spirochete which has been isolate d from the colons of pigs with enteric disease, The clinical and patho logic features of experimental infections of conventional pigs (born b y normal farrowing with a naturally acquired intestinal flora) with th ree strains of S. pilosicoli were determined in order to confirm the e nteropathogenicity of this species, Strains were derived from the colo ns of British pigs with colitis and passaged 8 to 10 times during expa nsion and purification in vitro, Eighteen ten-week-old Large White-Lan drace cross pigs were each inoculated once orally with 0.7 x 10(9) to 1.6 x 10(9) of one of three strains of S. pilosicoli. Six pigs were ch allenged with each strain, Control pigs were dosed with uninfected bro th medium or with 1.8 x 10(7) cells of the nonpathogenic Serpulina inn ocens, Eight pigs (two to four per S. pilosicoli challenge group) deve loped soft or diarrheic feces (fecal dry matter < 24%) between 3 and 8 days after challenge, which persisted for 7 to 8 days or until necrop sy at 14 days after challenge, Average weight gains in two of the thre e groups challenged with S. pilosicoli were significantly less than co ntrols. The feed conversion ratios of all the groups challenged with S . pilosicoli were impaired compared to controls, The mean values for d aily liveweight gain (and feed conversion ratio) for the three groups challenged with S. pilosicoli were 0.799 (2.13), 0.783 (2.05), and 0.8 44 kg (2.10), respectively, while that of the uninoculated controls wa s 0.944 kg (1.70), Gross lesions with slight mucosal thickening, conge stion, and multifocal erosions were evident in seven of eight diarrhei c pigs, The relative weights of the large intestines of pigs challenge d with S. pilosicoli were significantly less than controls, Histologic lesions with an increase in mucosal height, infiltration of the lamin a propria with mononuclear cells, mucosal erosion with mixed inflammat ory cell infiltration, and goblet cell hyperplasia in colonic glands w ere evident in 15 of the 18 challenged pigs. S. pilosicoli was recover ed on bacterial culture of the colon from all except one of the pigs w ith these histologic lesions, Serpulina sp. was clearly visible within the colonic glands of these affected pigs in silver-stained sections of the gut, Clinical and pathologic findings in control pigs were unre markable, with no diarrhea or colonic lesions evident, The results pro vide further evidence that S. pilosicoli is a specific enteric pathoge n for conventional pigs, It is capable of colonizing the large intesti ne and causing mucosal damage, which although mild is sufficient to re sult in significant adverse effects on growth.