Adaptation of Lactobacillus alimentarius to environmental stresses.
Lactobacillus alimentarius BJ33 has been tested for its biopreservative capacities to improve quality and safety in many meat products. The combination of different preservatives such as NaCl, glucono-delta-lactone and citric acid with this protective culture during the manufacture of sausages represent an interesting alternative to control microbial spoilage and to extend product shelf life. The use of these preservatives may also limit the growth of L. alimentarius. In this study, the sublethal doses of these preservatives were determined and tested in combination to verify if the organism was able to adapt to these stresses. The sublethal doses of gluconic acid, citric acid, and NaCl were 100-110 mM, 50-55 mM and 8%, respectively. When the culture was first grown in MRS broth containing citric acid (50 or 55 mM) or gluconic acid (100 or 110 mM) and then transferred in MRS broth containing NaCl (8%), only limited growth was observed (O.D.(600 nm) = 0.2-0.3) after 6 days at 30 degrees C. However, when the culture was first grown in NaCl and then transferred in MRS broth containing gluconic or citric acid, growth was observed after 1 day (O.D.(600 nm) = 0.4-0.5) and after 5 days an O.D.(600 nm) of 0.8 was reached. Cell filamentation was also observed under electron microscopy when cells were grown for 2 days in presence of gluconic and citric acid at their sublethal doses and with a combination of 18 mM gluconic acid and 37 mM citric acid, but cellular elongation was not observed with cultures exposed to 8% NaCl. These results suggest that two different adaptation mechanisms are induced in L. alimenatrius when treated with organic acids and NaCl.