very resistant to low pH, with high survival rates at pH
3.0 for 1 hr. On the other hand, studies have shown that
Bifidobacterium spp. isolates are very sensitive to pH 2.0
and pH 3.0 [4]. Lactic acid bacteria are acidophilic, which
means they are tolerant to low pH. However, this needs to
be differentiated from a condition of high concentration
of free acids (H+), because the free acids may cause
growth inhibition [19]. Probiotic bacteria need to survive
passage through the stomach, where the pH can be as
low as 1.5 to 2.0 [20], and stay alive for 4 hr or more
[5] before they move to the intestinal tract. However, the
feed passage rate for birds is faster than for other animals,
especially mammals; therefore, bacterial acid tolerance
is not as critical in chickens as it is in other animals [21].
Both strains grew at 15 and 45°C at 2 and 4 hr of
incubation (Table 3). Wouters et al. [22] demonstrated
reduced glycolytic activity leading to reduced production
of lactic acid in Lactococcus lactis at low temperature.
According to Ibourahema et al. [23], the bacterial
capability to grow at high temperature is a good
characteristic, as it could be interpreted as indicating
an increased rate of growth and lactic acid production.
Moreover, a high fermentation temperature decreases
contamination by other microorganisms [23]. Both strains
were also able to tolerate high osmotic concentrations of
NaCl (Table 3). This examination gave an indication of
the osmotolerance level of the LAB strains. According to
Ibourahema et al. [23], bacterial cells cultured with a high