Immune response and use of organic acids in broilers challenged with Salmonella Minnesota.

Background: Salmonella control in poultry industry is of great importance to prevent foodborne diseases in humans. The intense control of Salmonella Enteritidis caused an increased isolation of other serotypes as Salmonella Minnesota (SM), and it cannot be affirmed that additives used to control Salmonella Enteritidis showed the same efficacy to control of other serovars. Therefore, the aim of this study was to evaluate the pathogenesis of SM in challenged broilers and the use of different organic acids for SM control in broilers. Materials, Methods & Results: In the present study, three experiments were conducted. In the first experiment an in vivo study to evaluate the pathogenesis of the SM in broilers where the birds were divided into 4 treatments with 15 animals each: T1 - animals inoculated orally with SM, T2 - animals inoculated through feed with SM, T3 - "in-contact" birds caged with SM challenged birds and T4 - negative control. At 12, 24 and 48 h after the challenge, the crop, duodenum, cecum and liver were collected to detect SM. It was also collected fragments of jejunum, ileum and cecum for histopathological and immunohistochemistry analysis. At the microbiological evaluation 12 h after inoculation, it has already been possible to observe the presence of SM in the crop, duodenum and cecum of birds challenged orally and through feed. Twenty-four h after contact with the challenged birds, the in-contact group have already shown the presence of SM in crop and duodenum. It was observed a significant increase of goblet cells in the jejunum 24 h post inoculation (PI) in the orally inoculated birds, and in the ileum 48 h PI in the feed challenged birds. In immunohistochemical evaluation, 12 h PI the birds challenged orally have already shown a significant increase in the number of CD3+ cells in the jejunum and 24 h PI a significant increase of these cells in the ileum and cecum. In the second experiment an in vitro study was also performed to assess the minimum inhibitory concentration (MIC) of four organic acids against Salmonella Minnesota (SM). The MIC results were: organic acid A: 3.12%, organic acid B: 0.78%, organic acid C: 1.56%, organic acid D: 0.39%. In the third experiment it was evaluated the efficacy of different organic acids via water and food in chickens challenged with SM, where 30 broilers from 1st to 28th days of age were divided into six treatments with five animals each: T1 - negative control not challenged with SM, T2 - positive control challenged with SM, T3 - birds challenged with SM and treated with organic acid A in the feed, T4 - birds challenged with SM and treated with organic acid A in the feed and organic acid B in the water, T5 - birds challenged with SM and treated with organic acid C in the feed, T6 - birds challenged with SM and treated with organic acid C in the feed and organic acid D in the water. For microbiological evaluation cloacal swabs were collected 48 h PI and the crop and cecum were collected 7 days after inoculation. Only a significant reduction of SM in the crop of challenged birds was observed. Discussion: Based on the results it was observed that SM has spread rapidly in the gastrointestinal tract of poultry and it could be isolated 12 h after oral inoculation. In histopathological analysis of intestinal segments it was possible to observe an initial increase of goblet cells and subsequent increase of lymphocytes T in challenged birds. In the experiments where the organic acids were used to control SM it was observed that the recommended dosage by the manufacturer is below that the indicated by the MIC, which may have resulted in the low efficiency of the acids tested in the challenged animals.