Adaptation of Lactobacillus alimentarius to environmental stresses

Lactobacillus alimentarius BJ33 has been tested for its biopreservative cap acities to improve quality and safety in many meat products. The combinatio n of different preservatives such as NaCl, glucono-delta-lactone and citric acid with this protective culture during the manufacture of sausages repre sent an interesting alternative to control microbial spoilage and to extend product shelf life. The use of these preservatives may also limit the grow th of L. alimentarius. In this study, the sublethal doses of these preserva tives were determined and tested in combination to verify if the organism w as able to adapt to these stresses. The sublethal doses of gluconic acid, c itric acid, and NaCl were 100-110 mM, 50-55 mM and 8%, respectively. When t he 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 contai ning 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 day s an O.D.(600) (nm) of 0.8 was reached. Cell filamentation was also observe d 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 o f 18 mM gluconic acid and 37 mM citric acid, but cellular elongation was no t observed with cultures exposed to 8% NaCl. These results suggest that two different adaptation mechanisms are induced in L. alimenatrius when treate d with organic acids and NaCl. (C) 2000 Elsevier Science B.V. All rights re served.