Comparison of stained smears and culturing for identification of Treponema hyodysenteriae

Abstract

A comparative study was made of stained fecal smears and cultured fecal swabs for identification of the large spirochetes Treponema hyodysenteriae and Treponema innocens. Feces were obtained by swabbing rectums, colons, and stools of nonexposed swine and swine experimentally exposed to swine dysentery. In this study there was a significant (P < 0.001) correlation between the observation of one or more large spirochetes on stained slides and obtaining either a strong or a weak beta-hemolytic reaction in culture. A significant (P < 0.001) correlation was also found between the observation of one or more large spirochetes on stained smears or obtaining either a strong or a weak beta-hemolytic reaction in culture and the occurrence of either nonhemorrhagic or hemorrhagic diarrhea in the swine. In the diarrheic swine at the time of swabbing, 157 of 393 samples (40%) were negative for both the presence of large spirochetes on stained smears and the production of either a strong or a weak beta-hemolytic reaction; in nondiarrheic swine, 42 of 278 samples (15.1%) were positive in stained smears and 32 of 268 samples (11.9%) were positive by culturing. In swine infected with swine dysentery, 17 of 1,011 samples produced weak beta-hemolytic reactions, and in swine infected with nonpathogenic large spirochetes of T. innocens, three of 34 samples produced strong beta-hemolytic reactions. It was concluded from this study that neither staining rectal smears nor culturing rectal swabs is sufficient, either together or alone, for the diagnosis of swine dysentery; however, these laboratory methods could be highly supportive of a diagnosis of swine dysentery in swine with clinical signs and lesions of the disease.

Enhanced isolation of Serpulina hyodysenteriae by using sliced agar media

“…The spirochetes isolated on sliced blood agar from the two samples of swine not exposed to SD but having a soft stool (source 11; Table 1) migrated similarly to that of S. hyodysenteriae but produced a weak beta-hemolysis similar to that of S. innocens (2,5). However, only 1 of the 2 samples produced weak beta-hemolysis with conventional streaking.…”

“…A total of 151 rectal and colonic swab samples were collected and tested for S. hyodysenteriae from swine experimentally or farm exposed to SD, swine with soft stools, and nondiarrhetic swine not exposed to SD (Table 1). With each rectal or colonic sample, 3 swabs were collected: one swab for the count of large spirochetes per oil immersion field (OIF), one swab for streaking the sliced agar, and one swab for conventional streaking (5). From swine with acute SD diarrhea, 20 rectal samples were collected from 20 live swine, 16 colonic samples from 16 dead swine, 2 rectal samples of 2 swine from 2 farm outbreaks, and 20 colonic samples from 2 frozen colons.…”

“…The second swab was streaked perpendicular to the cuts on the sliced blood agar. The third swab was streaked and restreaked conventionally on unsliced blood agar (5). The blood agar medium consisted of trypticase soy agar (Becton Dickins Microbiology Systems, Cockeysville, Md.)…”

“…The SBJ medium contained the following antibiotics: spectinomycin, spiramycin, rifampin, vancomycin, and colistin. The plates were incubated anaerobically at 42ЊC in an atmosphere of 80% H 2 and 20% CO 2 as previously described (5). A pint jar one-third full of water was kept in the anaerobic jar to maintain a proper level of humidity and prevent drying of media.…”

“…In the sliced agar plates, the interpretation of the growth and type of hemolysis was made by observing the edge of the cut. If areas of beta-hemolysis developed in the conventionally streaked plates, plugs of agar were removed with a 1-ml sterile Pasteur pipette and the plates were reincubated anaerobically and reex-amined 24 h later for the type of beta-hemolysis around the edge of the holes (5). A strong beta-hemolytic reaction produced by S. hyodysenteriae was characterized by a high intensity of brightness along the edge of the cut or around the hole and with a more discrete and defined edge where it ended, whereas a weak beta-hemolytic reaction produced by S. innocens was characterized by a lower intensity of brightness along the edge of the cut or around the hole and with a poorly defined boundary where it ended (5).…”