New products may be sought by modifying older fermentation products, exemplified by the semisynthetic antibiotic tilmicosin and other derivatives of tylosin. Another approach is to screen fermentation broths, exemplified by the discovery of the structurally-unique insecticidal macrolide spinosad. The polyketide class of fermentation products encompasses a wide diversity of chemical structures a...

OBJECTIVES To determine how resistance to macrolides is conferred in field isolates of Pasteurella multocida and Mannheimia haemolytica that lack previously identified resistance determinants for rRNA methylation, efflux and macrolide-modifying enzymes. METHODS Isolates of P. multocida and M. haemolytica identified as being highly resistant (MICs >64 mg/L) to the macrolides erythromycin, gami...

A comparative in vivo pharmacokinetic (PK) study of tilmicosin (TIL) was conducted in 6 crossbred healthy pigs and 6 crossbred pigs infected with Haemophilus (H.) parasuis following oral administration of a single 40 mg/kg dose. The infected model was established by intranasal inoculation and confirmed by clinical signs, blood biochemistry, and microscopic examinations. Plasma TIL concentration...