|Bradner, Laura -|
|Beitz, Donald -|
|Robbe-Austerman, Suelee -|
Submitted to: Iowa State University Animal Industry Report
Publication Type: Review Article
Publication Acceptance Date: January 20, 2013
Publication Date: February 4, 2013
Citation: Bradner, L., Stabel, J.R., Beitz, D.C., Robbe-Austerman, S. 2013. Treatment with antibiotics is detrimental to the recovery of viable Mycobacterium avium subsp. paratuberculosis cultured from milk and colostrum of dairy cows. Iowa State University Animal Industry Report. A.S. Leaflet No. R2792. Interpretive Summary: Johne's disease is a chronic, debilitating intestinal disorder in cattle characterized by diarrhea, reduced feed intake, weight loss and death. Cattle usually become infected as young calves by ingesting feces containing the causative bacteria. However, symptoms of disease do not usually present themselves until the animals reach 3 to 5 years of age or even older. During this time the animal is infected and may be shedding the organism in its feces without showing any clinical signs of disease. In addition to reduced production by these animals through reduced milk production, they also present a potential infective threat to the rest of the herd. Shedding of this bacterium into the milk of infected dams is one mode of transmission to young calves. However, there is very little data to determine how much shedding occurs. This is due to the difficulty in culturing the bacterium from milk and colostrum. The present study evaluates the addition of antibiotics to the decontamination protocol prior to culture of milk for optimal recovery of the bacterium. These results are critical for diagnostic laboratories so that proper methods can be employed to assess exposure of calves on-farm.
Technical Abstract: Antibiotic cocktails are frequently used as secondary decontaminants prior to the culture of Mycobacterium avium subsp. paratuberculosis (MAP). This study investigated whether secondary incubation with an antibiotic cocktail containing vancomycin, nalidixic acid, and amphotericin B after primary exposure to N-acetyl-L-cysteine-1.5% sodium hydroxide affected the recovery of viable MAP from milk experimentally spiked with 102 to 106 cfu/ml. Results indicated that incubation with this antibiotic cocktail did reduce the incidence of contamination in culture media but it was also highly detrimental to the recovery of viable MAP. This effect was not advantageous given the low numbers of MAP naturally shed into milk and colostrum of infected cows. These results demonstrate that secondary incubation with antibiotics during the decontamination procedure could potentially lead to false-negative culture results due to their detrimental effect on the viability of MAP.