EFFECT OF SEVERAL DECONTAMINATION PROCEDURES ON LISTERIA-MONOCYTOGENES GROWING IN BIOFILMS

Listeria monocytogenes is a pathogenic bacterium which has been implic ated in several foodborne illnesses. This microorganism grows into bio films attached to the surfaces in food-processing plants, increasing i ts resistance to antimicrobial agents. The present work was realized t o investigate the attachment of L.monocytogenes isolates to glass surf aces and to find a decontamination procedure to remove these bacteria in biofilms. Three-day biofilms were prepared by growing L. monocytoge nes isolates from food plant environments on glass surfaces. Sixteen d econtamination treatments at different pHs, temperatures, and times of exposure were tested against L. monocytogenes biofilms. The most effi cient treatments were those applied at 63 degrees C. Combinations of d econtamination treatments applied at 55 degrees C for 30 min provided different results according to the other factors used. In general, L., monocytogenes biofilms were found to be not very susceptible to high o smolarity (10.5% NaCl), and the interaction of sodium chloride and aci d did not seem to have important effects in inactivating these bacteri a (from a 1.3- to a 1.9-log-CFU/cm(2) reduction). The combination of N aOH (pH 10.5; 100 mM) and acetic acid (pH 5.4; 76.7 mM) applied sequen tially at 55 degrees C for even 5 min was shown to be the most effecti ve treatment to remove L. monocytogenes from biofilms (at least a 4.5- to 5.0-log-CFU/cm(2) decline).