| A model system for studying Salmonella within an animal's intestinal gut community was developed and challenged with a variety of antibiotic, chemical and microbial treatments including lactose, anaerobic cultures, chloramphenicol, neomycin, novobiocin, streptomycin, pyruvate and lactate. Biofilm formation, including Salmonella colonization, was achieved through a time-zero mechanism of "infecting" the model. This approach served to portray the immediate exposure of newly-hatched chicks to Salmonella during normal intestinal colonization. An antibiotic-sensitive and an antibiotic-resistant strain of Salmonella were compared throughout these studies. Established biofilms were also challenged with Salmonella and were shown to be much more resistant to invasion during both initial and re-infection modes. Daily "feeding" of the model biofilm enabled the establishment of a representative feeding cycle which supplied nutrients, eliminated surface waste materials, and created a flow across the biofilm's surface, as well as providing a means for introducing the treatments to the bacterial niches within the model environment. To enumerate and follow Salmonella populations, several methods of quantitation were attempted. The use of various selective media and growth curve extrapolation proved to be futile. However, selective media supplemented with vancomycin and other antibiotic(s), were effective in inhibiting competitive bacterial populations of the intestinal tract and quantitating the Salmonella. When antibiotics were administered to time-zero infected biofilms, continuous antibiotic exposure only provided minimal benefit to the Salmonella reduction effort, with possible serious adverse effects to the biofilm community itself. Conversely, dramatic Salmonella population declines were observed upon incorporation of either pyruvate or lactate into the feeding media. Although the exact modes of action of lactate and pyruvate are not known, the findings suggested that the presence of these compounds either inhibited key metabolic pathways within Salmonella and/or generated growth-inhibiting substances. |
