A study on the prevalence of gram-negative bacteria in bulk tank milk

Bulk tank milk from 131 dairy herds in eastern South Dakota and western Min nesota were examined for coliforms and noncoliform bacteria. Coliforms were detected in 62.3% of bulk tank milk samples. Counts ranged from 0 to 4.7 l og(10) cfu/ml. The mean count was 3.4 log(10) cfu/ml. Gram-negative noncoli form bacteria were observed in 76.3% of bulk tank milk. Counts ranged from 0 to 6.2 log(10) cfu/ml. The mean count was 4.8 log(10) cfu/ml. A total of 234 isolates from bulk tank milk were examined to species level; 205 isolat es belonged to 28 species. Coliforms and gram-negative noncoliform bacteria accounted for 32.9 and 67.1% of the total isolates, respectively. Organism s such as Agrobacterium radiobacter, Bordetella spp., Comamonas testosteron i, Listonella damsela, Ochrobactrum anthropi, and Oligella urethralis were isolated from bulk tank milk in this study. These organisms have not been r eported previously in bulk tank milk. A total of 116 isolates of Pseudomona s spp. were isolated from raw milk; 98 isolates belonged to nine Pseudomona s spp., and the remaining 18 isolates could not be identified to their spec ies level. Pseudomonas was the most predominant genus. Pseudomonas fluoresc ens was the most predominant species isolated from bulk tank milk and accou nted for 29.9% of all isolates examined. The results of the study suggest t hat counts of coliforms and noncoliform bacteria in bulk tank milk vary con siderably. The isolates represent a wide variety of Gramnegative bacterial species. Examination of bulk tank milk for coliforms and noncoliform bacter ia could provide an indication of current and potential problems associated with bacterial counts and milk quality.