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Chapter V Discussion
compounds are known to have bacteriostatic properties at least in vitro (Suskovic et al.,
1997). Hence, if they also present this bacteriostatic activity in vivo, bacteria tolerant to
phenols might have more chances of survival than those which were not. In contrast to the
high phenol resistance (resistance to 0.4% phenol) which was previously reported by
Xanthopoulus et al. (2000) and Suskovi et al. (1997) for L. acidophilus strains, the L. casei
LAM-1 strain was highly resistant towards this compound. The results of this study on the
phenol resistance of all Lactobacilli strains suggested that they were moderately tolerant.
A major requirement for probiotic strains is that they should be safe for human
consumption. In order to assure the safety of bacteria used in food, the European Food Safety
Authority (EFSA) has initiated a ‘Qualified Presumption of Safety’ concept, similar to the
GRAS system in the USA, has the purpose of allowing strains with long history of safe use
and status to enter the market without extensive testing requirements (EFSA, 2004).
Antibiotic resistance is one of the safety concerns included in the QPS concept to determine a
strain’s QPS status. The reason for this is the hypothesis that food bacteria may act as
reservoirs for antibiotic resistance genes (Chesson et al., 2002; Danielsen and Wind, 2003;
Franz et al., 2005). In a survey of 62 Lactobacillus starter strains, Danielsen and Wind (2003)
found a high level of resistance to aminoglycosides for all investigated Lactobacilli. Similar
results were also found by Charteris et al. (1998) and Katla et al. (2001). These authors
concluded that resistance to aminoglycosides among Lactobacilli is natural, i.e. intrinsic trait,
which has been attributed to the absence of a cytochrome-mediated electron transport which
mediates the uptake of aminoglycosides (Charteris et al., 2001). Danielsen and Wind (2003)
also suggested that resistance to ciprofloxacin appeared to constitute a natural or intrinsic
resistance. In view of these deliberations, antibiotic resistances observed for the strains in this
study, i.e. resistance towards ciprofloxacin and aminoglycosides may consider being intrinsic