MAP is of concern in dairy products because it can survive
pasteurization of milk (Grant et al., 2002), and thus can be
transmitted to humans. Its high tolerance to low pH values has been
also documented (Sung and Collins, 2003). In our study, changes in
MAP viability during SMP fermentation containing living LAB cultures
producing bacteriocins were examined.
In the pre-experimental phase, the growth of different MAP
isolates has been tested on different culture media with and without
decontamination (data not shown). Following from these results, two
field isolates of MAP and two different culture media with different
decontamination methods were used in this study. The presence of
MAP in SMP did not affect the pH when compared with the negative
control. The pH was identical within all replicate controls and
artificially contaminated SMPs and no influence resulting from the
addition of MAP isolates was recorded (data not shown). The pH
change during the fermentation of all SMP showed a declining
tendency in all products except for Yogurt 1 (Fig. 1). It did not reach
the desired pH value probably due to the fact that the LAB culture
of Yogurt 1 is extremely sensitive to the veterinary antimicrobial
residues, which might be present in milk. Therefore, Yogurt 1 was
taken as a control product with inhibited LAB compared to the rest
of the normally fermented products in the experiment. Also
M7H10-PANTA agar was not able to inactivate the LAB in Kefir
culture, which resulted in massive growth of LAB and therefore the
results could not be interpreted.