Comparison of Salmonella species recovered from Irish liquid milk production holdings with temporal clinical veterinary isolates.

The presence of microbiological hazards in foodstuffs including, Salmonella, form a major source of food-borne diseases in humans. In-line milk filters from 97 liquid milk production holdings in Cork, the largest dairy region in Ireland, were surveyed for the presence of Salmonella species at herd level over a 2-year period (September 2001-September 2003). Each dairy farm was visited 6 times at 4 monthly intervals (denoted by cycles A-F). Six of the 97 herds (6%) were positive. Ten isolates were detected based on culture methods. These included five (5%) Salmonella Typhimurium DT104, 4 (4%) Salmonella Dublin, and 1 (1%) Salmonella Agona from a total of 556 filters. During cycle C, in addition to the milk filters, a bulk tank milk (BTM) sample was procured from each dairy holding and analysed but no Salmonella were isolated. For comparison purposes a further 26 temporal veterinary clinical isolates (21 S. Typhimurium of varying phage type, and 5 S. Dublin) were procured from the Cork Veterinary Clinical Diagnostic Laboratory, Cork. The study collection showed resistance to one or more antimicrobial agents. During the study, Salmonella spp. were isolated from five of the herds prior to any clinical signs in the farm animals. Pulsed-field gel electrophoresis (PFGE) profiles indicated clonality among the isolates pre- and post-clinical illness. A phenotypic and genotypic database for Salmonella spp. has been developed and used for comparative purposes.