DETECTION AND CHARACTERIZATION OF SALMONELLA-TYPHIMURIUM FROM A DAIRY-HERD IN NORTH-DAKOTA

Nasal secretions, faecal samples and buffy coats were obtained from 10 2 cattle from a North Dakota dairy herd with a history of calf scours. Treated buffy coats, faecal samples and nasal secretions were inocula ted into tetrathionate broth (TB), incubated at 37 degrees C overnight , and plated onto brilliant green agar medium with novobiocin (BGAN). The TB was left at room temperature for 5 days and then used to inocul ate fresh TB. The fresh TB was incubated at 37 degrees C over night an d plated onto BGAN medium All the plates were incubated at 37 degrees C over night and observed for Salmonella-like growth. Suspect colonies were further tested and Salmonella isolates were serotyped by the Nat ional Veterinary Services laboratory. Twenty-two of the 36 calves samp led harboured S. typhimurium in their faeces, but no samples from cows were positive. No Salmonella were isolated from the buffy coats, but 4 calves were shown to have Salmonella in their nasal secretions. Exte nded enrichment of the faecal cultures in TB resulted in a significant increase in Salmonella isolations, although 2 samples mere positive f ollowing the initial enrichment period and not after secondary enrichm ent. The typical. Salmonella isolate detected from this herd contained a transmissible R-plasmid encoding resistance to tetracycline, kanamy cin, sulphisoxazole and ampicillin. This study confirmed that delayed secondary enrichment in TB is superior to primary enrichment for detec tion of Salmonella from cattle.