Resistance to pH, temperature and sodium chloride
A basal MRS medium was used in these series of in
vitro studies. An overnight culture of each isolate was
used as the inoculum, with the cells being centrifuged
and resuspended in 0.9% sterile saline. The suspension
(100 µL) was inoculated into 10 mL of MRS broth in
each test tube. Two incubation time points, i.e., two and
four hours, were evaluated for each of the variables (pH,
temperature and sodium chloride - NaCl). The rationale
for these two points was mainly based on food matter
passage time through the gastrointestinal tract of poultry.
The temperatures tested were 15°C and 45°C, and
the concentrations of NaCl tested were 3.5 and 6.5%
(w/v). The LAB were tested for survivability using two
different pHs (2.0 and 3.0). The tubes were incubated
with reciprocal shaking at the specific test temperatures
or at 37°C for the tests on pH and concentrations of NaCl.
At the time points evaluated, each sample was streaked
onto MRS agar to determine the presence or absence
of growth, which was used to confirm livability of the
strains. The turbidity of each tube was also noted as an
indication of growth or no growth. Each treatment was
tested with triplicate tubes.