Effects of increasing Mg++ ion concentration on the PKU monitoring assay

Comparison of liquid and agar-solidified defined media regarding the physiological mechanism by which beta-2-thienylalanine inhibits growth of Escherichia, Shigella, and Salmonella cultures

Growth comparisons were made, using Shigella, Escherichia, and Salmonella cultures, in liquid and agar-solidified defined media containing beta-2-thienylalanine (beta-2-t). The comparisons were performed to determine the nature of growth inhibition by beta-2-t under different physical growth conditions. In a plate assay, with increasing beta-2-t mixed into the agar, inhibition of Escherichia and Shigella increased. However, Salmonella cultures were not inhibited even at the highest beta-2-t concentrations used. With beta-2-t added to liquid cultures, however, dose-response growth relationships were exhibited by all three genera. The differences occurring in beta-2-t inhibition between liquid and plate assay conditions were not due to composition of culture plates, time of challenge of cultures with beta-2-t, availability of oxygen and associated differences in ratios of volume of media to available surface area, selection of mutants in the plate assay, or to extractable substances from the agar. However, when beta-2-t diffusion into the liquid medium was delayed by using agar plug diffusion cultures, a physiological mechanism was demonstrable which largely protected Salmonella cultures, but not Escherichia and Shigella cultures, from growth inhibition.

The assay on a defined medium of the effects of beta-2-thienylalanine on the growth of anaerobic bacterial isolates from phenylketonuric patients

Faecal samples were taken from three diet-managed phenylketonuric children to determine effects of beta-2-thienylalanine (beta-2-t) on indigenous bacteria. From sample swabs, 127 anaerobes were identified and tested for beta-2-t inhibition on a phenylalanine (Phe)-free medium, Anaerobe Inhibition Test (AIT) agar. Of the isolates, 77.9% grew sufficiently to assay reactions on at least 25% of AIT plates. Using Phe-containing Columbia agar, 86.5% of the strains could be assayed. None of 28 Bacteroides cultures was inhibited by beta-2-t on AIT. Of the genera, Bifidobacterium, Eubacterium, Lactobacillus, Peptostreptococcus, and Propionibacterium, no isolates which would grow on AIT were inhibited. At least one isolate of each of the genera Peptococcus, Fusobacterium, and Clostridium was inhibited. Of 127 total isolates, only nine were inhibited by beta-2-t on AIT, and inhibition was abolished on Columbia agar. Thirty-nine "aerobes" were isolated from the same patients. Strains of the genera tested reacted similarly to previously tested strains from non-PKU sources. Also, anaerobically isolated Excherichia coli were inhibited, while Streptococcus faecalis cultures were not, confirming results on aerobically-isolated non-PKU cultures of the same species. These studies, the first dealing with beta-2-t and anaerobic bacteria, suggest that little change in intestinal bacterial populations might be expected during in vivo beta-2-t treatment.

Colonization by Salmonella typhimurium and Shigella flexneri III of the gastrointestinal tract of mice treated with beta-2-thienylalanine and streptomycin

Mice fed beta-2-thienylalanine (beta-2-T) by oesophageal tube were no more susceptible to gastrointestinal tract colonization by Salmonella typhimurium or Shigella flexneri III than control mice fed water. In both beta-2-T-fed and water-fed groups, the increasing dosage of S. typhimurium, in logarithmic increments to groups of mice, resulted in increasing numbers of these bacteria detectable on dilution plates from organ homogenates. Colonization by S. flexneri III only occurred at a dosage of 10(8) bacteria for both groups. Pretreatment with 50 mg streptomycin allowed 10(3) Salmonella or 10(4) Shigella to colonize both beta-2-T and water-fed groups. Coliforms, inhibited by beta-2-T under certain conditions in vitro, were found in equal numbers in both groups. No obvious differences were noted in either types of other bacteria detected or numbers recovered from the two groups. No gross behavioural changes were noted in mice fed beta-2-T and not challenged with pathogenic bacteria, and no pathological changes were noted in hepatic or splenic tissues. With increasing Salmonella dosage, collections of polymorphonuclear leucocytes, which were almost focal, and increased numbers of giant cells were noted in splenic red pulp areas, in both groups.