Nonparallel secretion of antibacterial activity and protein in porcine pancreatic juice.

The antimicrobial activity of exocrine pancreatic juice is an important component of gastrointestinal tract innate defenses, yet little is known about whether secretion is regulated in parallel with digestive enzymes. In this study, we used 8 pigs with pancreatic catheters to quantify antibacterial activity and measure protein content (indicator of enzyme secretion) of pancreatic juice collected hourly from 0700 to 1900, with the animals adapted to being fed at 0800 and 1600. Antibacterial activity in the samples of pancreatic juice was quantified by comparing the growth inhibition of Staphylococcus aureus subsp. aureus strain ATCC 6538P relative to a known concentration of gentamicin. Antibacterial activity (U/mL and /min) was highest in samples collected 1 hour prior to feeding (equivalent to 0.6 microgram gentamicin/mL), declined as the meal was consumed, and was lower (P < 0.05) in samples collected while the meals were being digested (0.41 microgram gentamicin/mL). Protein content was negatively correlated with antibacterial activity, with protein secretion lower (mg/mL and /min) before feeding, with an increase as the pigs ate and digested the meals (P < 0.05). The results indicate that the antibacterial activity in pancreatic juice is not secreted in parallel with protein secretion, suggesting that regulation involves alternative signaling pathways or contrasting responses to shared signals.

A kinetic microplate method for quantifying the antibacterial properties of biological fluids.

The microplate assay for measuring antibacterial activity was adapted by incorporating a known concentration range of gentamicin as an internal standard. Staphylococcus aureus subsp. aureus strain ATCC 6538P, Escherichia coli ATCC 25922, and Lactobacillus spp. were used as target organisms, although other indicator organisms and antibiotics can be examined. Assay range and sensitivity were dependent on the species and density of indicator organism, and conditions (e.g., type, concentration, and pH of growth medium). Plotting the area under the growth curve (AUGC) versus gentamicin concentration (log transformed) yielded a linear curve that was used to quantify in units of gentamicin the antibacterial activity of a secretory fluid (SCF; pancreatic juice) and for comparisons of samples collected at different times, analysed on different days, and from different studies. This adaptation of the microtiter broth method will be useful for investigating man-made compounds, and the antibacterial activity of secretory fluids and the influences of age, diet, and health status.

Use of Double-Gradient Plates To Study Combined Effects of Salt, pH, Monolaurin, and Temperature on Listeria monocytogenes †.

This study evaluated the combined effects of pH, NaCl, incubation temperature, and sublethal concentrations of monolaurin on the survival of Listeria monocytogenes using the double-gradient diffusion technique. L. monocytogenes tolerance to NaCl was greatest (>78 g/liter) at neutral pH (6.8 to 7.2) and increased in the pH range 7.0 to 5.4 as the incubation temperature was lowered. Monolaurin at 2 µg/ml lowered the salt tolerance of L. monocytogenes to 60 g/liter independently of pH. At 4 µg of monolaurin per ml, salt tolerance was reduced to approximately 40 g/liter with no growth occurring at pH 6.0 to 5.4 and 25 g of NaCl per liter. At 8 µg of monolaurin per ml, only a subpopulation of the initial inoculum tolerated 25 g of NaCl per liter at neutral pH (6.5 to 7.5). Monolaurin reduced the tolerance of L. monocytogenes to NaCl and low pH.