| Listeria monocytogenes is an important foodborne bacterium due to its high mortality rate (30%), a tendency to persist in food processing plants, and its ability to grow at 4°C. Heat treatment is routinely used as a means to control pathogenic bacteria in food products. Therefore, the thermotolerance of L. monocytogenes and mechanisms responsible are of interest. Previous research using transposon mutagenesis yielded several heat resistant mutants, including one, named 1B4, that was mapped to a putative alcohol/acetaldehyde dehydrogenase gene, lmo1634, also identified as Listeria adhesion protein. This current research investigated the function of this gene in relation to a variety of environment stresses and in adherence and biofilm formation. Transposon insertion mutant 1B4 demonstrated significantly greater tolerance to acid (pH 2.7), 20% NaCl, and heat treatment of 52°C than the wild-type 568 strain. 1B4 (7.06 log10 CFU/cm 2) did not differ from the WT Lm568 (6.91 log10 CFU/cm 2) in attachment to stainless steel coupons. Neither 1B4 or Lm568 exhibited greater survival after desiccation (RH 43%) at room temperature for 7 days. The alcohol dehydrogenase activity of Lm568 (0.197 U/mg) was found to be significantly greater than in 1B4 (0.0458 U/mg).;1B4 was complemented in trans with WT lmo1634 and the successful transcription of lmo1634 in the complemented strain was confirmed by RT-PCR. In addition, no polar effect on the genes immediately downstream of lmo1634 in 1B4, i.e. lmo1635, lmo1636, or lmo1637, was observed. The complemented strain, however, did not completely restore the WT phenotype. Attempts to create a deletion mutant in lmo1634 ultimately proved unsuccessful. Despite these technical issues, it is clear that a mutation in lmo1634 yields a multi-stress resistant phenotype. |
