Tiamulin is a pleuromutilin derivative used in veterinary practice for the control and specific therapy of infections in swine. This report summarizes studies to establish standardized susceptibility testing methods, interpretive criteria, and reagent details for use in veterinary methods recently developed by the National Committee for Clinical Laboratory Standards (NCCLS) (standards M31-A and M37-A, NCCLS, Wayne, Pa., 1999). A total of 636 fastidious and nonfastidious animal and human pathogens were processed by using media and procedures described by the NCCLS. Tiamulin disk diffusion tests used a 30-g disk concentration, and the proposed MIC breakpoints corresponding to levels achievable in animal target tissues (lung) were <4 g/ml for susceptibility and >32 g/ml for resistance. Correlate zone diameters for specific nonfastidious species were as follows: for Pasteurella multocida and staphylococci tested on Mueller-Hinton agar, susceptibility at >19 mm and resistance at <11 mm, and for Actinobacillus suis, Erysipelothrix rhusiopathiae, and Streptococcus suis tested on enriched chocolate Mueller-Hinton agar, susceptibility at >16 mm and resistance at <8 mm. When Actinobacillus pleuropneumoniae was tested, a susceptibility breakpoint of <16 g/ml (>9 mm) was suggested for veterinary fastidious medium broth and enriched chocolate Mueller-Hinton agar. Absolute categorical agreement between NCCLS dilution and disk diffusion test results with these criteria ranged from 90.5 to 96.2%. Tiamulin susceptibility testing methods appear to be accurate in their categorical classification for indicated species, and their availability will allow immediate testing of animal isolates to guide therapy via appropriate levels of dosing and to monitor the development of resistance for agents in this unique class.Tiamulin is a pleuromutilin derivative antimicrobial used in the control and treatment of veterinary gram-positive and gram-negative pathogens, with a particular emphasis on infections in swine (11). It has exceptional activity (MIC, Յ1 g/ml) against anaerobic bacterial species, intestinal spirochetes, and Mycoplasma spp. (3,12,13). The present study was initiated in order to document the sustained antimicrobial activity of tiamulin against indicated bacterial species and rapidly growing and fastidious animal pathogens and to establish choices of diagnostic reagents. MIC and disk diffusion zone diameter correlates were determined in order to ensure the precision and accuracy of the susceptibility testing procedures performed according to National Committee for Clinical Laboratory Standards (NCCLS) guidelines for susceptibility testing of veterinary antimicrobial agents (5, 6). MATERIALS AND METHODSOrganisms tested. The organisms tested were isolates from various types of infections and included both human and veterinary pathogens. A total of 636 strains were processed, each identified by routine methods at the institution of initial isolation and confirmed by reference testing at a referral location (CAST Laboratories, Iow...

No abstract

The use of in-feed antimicrobials is coming under increased pressure in food animal production. Five field studies examined the impact of vaccines to stimulate protective immunity against pathogens commonly controlled with in-feed antimicrobials (Lawsonia intracellularis, a common enteric pathogen causing ileitis). Grow-finish pigs were immunized and various levels of infeed antimicrobials used to control or prevent Lawsonia were removed. Performance was compared between vaccinated and matched, continuously medicated barns. Performance was improved in vaccinated/reduced medication pigs while allowing for a 50% or greater reduction in in-feed antimicrobials targeting ileitis. More than six grams of tylosin and 20 grams of tetracycline per pig were removed from finishing feeds. Up to 50% of the time period in vaccinated finishing pigs occurred without any medications in feed. Large amounts of in-feed antimicrobials were successfully removed while improving growing and finishing pig performance.

Food borne Salmonella Typhimurium is a valid concern for the global pork industry. An attenuated oral swine Salmonella Choleraesuis vaccine has proven to be an effective tool for the pre-harvest reduction of carrier rates for multiple Salmonella spp. Serum antibody assays are available to monitor exposure to wild-type Salmonella infection. This clinical study assessed protection induced by an attenuated oral Salmonella Choleraesuis vaccine against challenge infection with S. Typhimurium in swine. A serologic antibody assay was concurrently evaluated for its ability to differentiate vaccinated pigs from those challenged with Salmonella Typhimurium. Vaccination significantly improved clinical scores, pyrexia, and enteric lesion prevalence, while numerically improving average daily weight gain, and group body weight variation in comparison to unvaccinated/challenged pigs. Vaccination, while protecting pigs against disease, did not generate detectable serum antibodies prior to challenge. No vaccinated animals became seropositive prior to challenge, indicating that conventional ELISA tests could be used in vaccinated pigs to monitor wild-type exposure. Following challenge, there was no detectable difference between vaccinated/challenged and non-vaccinated/challenged animals. All strict control pigs remained serum antibody negative. These findings support the use of this vaccine to protect swine against S. Typhimurium, without confounding pre-harvest Salmonella serologic monitoring programs.