In vitro antimicrobial activity against reference strains and field isolates of Treponema hyodysenteriae

Abstract

The in vitro susceptibilities of eight isolates of Treponema hyodysenteriae from pigs naturally infected with swine dysentery between 1976 and 1983 were determined by an agar dilution technique. Carbadox, olaquindox, tiamulin, metronidazole, furazolidone, and monensin were the most active against these field isolates regardless of the year of recovery. The influence of inoculum size on the MICs against four reference strains of T. hyodysenteriae was studied. Various degrees of activities of ampicillin and lincomycin were found, depending on the inoculum size. The effect of successive in vitro subcultures on the susceptibility of a reference strain of T. hyodysenteriae was examined. The strain resistant to tylosin became susceptible to the drug.Treponema hyodysenteriae is considered the primary causative agent of swine dysentery, a disease characterized by severe bloody diarrhea (8,24). Determination of the susceptibility of T. hyodysenteriae to antimicrobial agents is of great importance in the selective use of chemotherapeutics, the evaluation of new antimicrobial agents, and the development of drug resistance through continuous use of antimicrobial agents against field isolates (10,15,18,26,27). A commonly used method for in vitro susceptibility testing of the organism is an agar dilution technique (15, 27). However, the MICs are sometimes markedly influenced by the test conditions (4, 23). Inoculum size would be a key factor affecting the amount of antimicrobial agent required to inhibit the organism in vitro, because a large inoculum is required for the propagation of T. hyodysenteriae (13). Because the reference strain, as an indicator strain for MIC determination, should usually be maintained in vitro, successive subcultures in vitro may also affect its MICs since successive subcultures often cause decreased pathogenicity in vivo (12).The purpose of the present study was to determine the in vitro activities of antimicrobial agents currently in medicinal and veterinary use and to investigate the influence of inoculum size and the effect of in vitro subcultures on the susceptibility of T. hyodysenteriae. were used to study the influence of inoculum size and the effect of successive subcultures on in vitro susceptibilities. Eight field isolates were examined for the activities of antimicrobial agents. These isolates were individually isolated from mucosal scrapings of colons or diarrheal feces with mucus and blood from pigs naturally infected with swine dysentery at different localities in Japan. Four isolates were recovered during sporadic outbreaks from 1976 to * Corresponding author.1979, and four others were recovered from 1980 to 1983. They were maintained in vitro in our laboratory. Eight field isolates underwent less than 10 successive subcultures; S73/2, ATCC 31212, and ATCC 27164 underwent less than 50 successive subcultures; and DJ70 underwent both less than 50 and more than 150 successive subcultures. Prophylactic and therapeutic regimens for swine dysentery are unknown.Media. An anaerobic diluent ...

In Vitro Activity of Four Antimicrobial Agents against North American Isolates of Porcine Serpulina Pilosicoli

“…When compared with the MIC 90 of S. hyodysenteriae strains against tiamulin, the North American isolates of S. pilosicoli were similar. 2,15,16,20,21,29,30,38 Thus, as previously shown for S. hyodysenteriae, 8,[15][16][17]20,21,29,30,38 S. pilosicoli is highly sensitive to tiamulin.…”

“…2,8,9,[14][15][16][17][20][21][22]29,30,38,39 Because S. pilosicoli was recognized only recently, little information is available about the in vitro antimicrobial susceptibility of this spirochete. 8,9,14,21,29,30 The results of the present in vitro study indicated that 100% of the isolates were susceptible to carbadox and tiamulin, whereas the suceptibility to lincomycin and gentamicin differed among the isolates.…”

Antimicrobial Susceptibility Testing of Porcine Brachyspira ( Serpulina ) Species Isolates

“…The solid medium most commonly used for the antimicrobial susceptibility testing of B. hyodysenteriae is Trypticase soy agar with 5% ox or ssheep blood (8,14,23,26,29). In general, the MIC is reported as the lowest concentration of the antimicrobial agent that prevents growth or hemolysis.…”

“…The antimicrobial agents most frequently used in Sweden and many other countries for the treatment of the disease are tylosin and tiamulin. Widespread resistance to tylosin, a 16-membered macrolide antibiotic, in B. hyodysenteriae has been reported in several countries (2,14,17,23). This resistance is caused by a point mutation in the 23S rRNA gene (9).…”

Susceptibility of Brachyspira hyodysenteriae Isolates to Doxycycline using Agar Dilution and Epsilometer Test

“…To determine susceptibility of B. hyodysenteriae to doxycycline, the ADM was used. In most laboratories, quantitative susceptibility testing of brachyspiras is commonly done by diluting the antibacterial substance in agar media (Kitai et al 1987;Ronne and Szancer 1990;Smith et al 1991;Trott et al 1996;D uhamel et al 1998;Hommez et al 1998;Fossi et al 1999) or by the broth dilution method (Hayashi et al 1988;Buller and Hampson 1994;Karlsson et al 2002). Apart from applying the agar dilution method, which has been used by our laboratory on a daily basis for several years, a semi-quantitative method, namely the Epsilometer test for B. hyodysenteriae susceptibility to doxycycline, was analyzed.…”