MORPHOMETRIC ANALYSIS OF ENTERIC LESIONS IN C3H HEN MICE INOCULATED WITH SERPULINA-HYODYSENTERIAE SEROTYPE-2 AND SEROTYPE-4 WITH OR WITHOUTORAL STREPTOMYCIN PRETREATMENT/

The segmental distribution and sequential progression and the role of the indigenous bacterial flora in the development of enteric lesions a ssociated with Serpulina hyodysenteriae infection in laboratory mice h ave not been defined. We examined the distribution and sequential morp hometric changes in the large intestine of mice orally inoculated with S. hyodysenteriae serotypes 2 and 4. To determine the role of coloniz ation resistance conferred by the indigenous bacterial flora, 40 femal e C3H/HeN mice were administered water alone or water containing 5 mg/ mL streptomycin sulfate ad libitum for seven days prior to orogastric inoculation either with S. hyodysenteriae or sterile trypticase soy br oth (TSB). Clinical signs were monitored daily and three mice per grou p were necropsied on postinoculation days (PLD) 7 and 14 for pathologi cal assessment of the cecum, proximal colon, transverse colon, and des cending colon, and bacteriological culture of the cecum for S. hyodyse nteriae. Weekly pooled fecal samples were collected from each group fo r determination of total numbers of anaerobe bacteria. Gross examinati on revealed soft fecal pellets on PID 7 and 14 and catarrhal typhlitis on PID 14, irrespective of streptomycin pretreatment. The recovery ra tes of S. hyodysenteriae from the ceca of serotype 2- and serotype 4-i noculated mice was 100 and 91.7%, respectively. Statistically signific ant differences in morphometric changes between TSB- and S. hyodysente riae-inoculated mice were present on PID 7 and 14 and were restricted to the cecum. Although oral administration of streptomycin for seven d ays prior to S. hyodysenteriae inoculation resulted in a significant r eduction in the numbers of fecal anaerobes, it did not affect the colo nization, distribution, severity, or progression of cecal lesions.