Biomedical subjects
Publications and source records attributed to G Suarez Fernandez.
Factor sera against Listeria O antigens (serologic reference strains) were produced. The results confirm the validity of the O antigenic scheme established for Listeria, but show slight discrepancies in strains of serovars 4b, 4ab and 6b.
Cross-agglutination and absorption studies indicated that two serological reference strains of Listeria grayi and Listeria murrayi differed in at least one O factor. The serological analysis revealed that the unshared O factors are not present in other Listeria serovars. These results are not in accordance with the antigenic structure previously reported for L. grayi and L. murrayi, then a new O antigen formulation is proposed for these species: L. grayi (III), XII, XIV and XVI; L. murrayi (III), XII, XIV and XVII.
Raw milk was inoculated with Listeria monocytogenes and heat at 69 degrees C to 73 degrees C. The organism was recovered from 46.6% of the heated samples, but not from samples heated at 73 degrees C, after variable periods at refrigeration temperature. The results suggest that a low number of listeriae survive thermal treatments, but cold enrichment is necessary to repair the thermally injured cells.
A cross-agglutination study between somatic antigens from reference strains of Listeria grayi and Listeria murrayi with rabbit antisera was done. L. murrayi antisera reacted, at low titres, with L. grayi but L. grayi antisera did not react with L. murrayi antigen. These results, together with agglutinin-absorption tests, led to the conclusion that the serologic relationship between L. grayi and L. murrayi is not as close as is thought. The two species seem to differ in at least one somatic factor, that might be designated O-XVI for L. grayi and O-XVII for L. murrayi. The serologic relationship of L. grayi and L. murrayi with other serovars of Listeria is discussed. The agglutination titre of 180 healthy ruminants against O-antigens of L. grayi and L. murrayi was also investigated; almost all the sera reacted with the antigens of these species, with similar titres (that reached 640) to those detected against O-antigens of serogroups 1/2 and 4.
The survival of Listeria monocytogenes in raw milk treated in a pilot plant size pasteurizer was investigated. Raw milk was inoculated with different initial concentrations of L. monocytogenes and heated at temperatures ranging from 69 degrees to 73 degrees C. Listerias were not isolated from any of the milk samples immediately after thermal treatment. They were isolated, however, from 46.6% of heated samples (none from samples heated at 73 degrees C) after variable periods at refrigeration temperature. The results suggest that a low number of listerias survive some thermal treatments, but a cold enrichment is necessary to repair the thermally injured cells and detect these organisms in milk. The importance of the isolation technique in the recovery of listerias from pasteurized milk samples is discussed.
Because the hemolysis produced by Listeria monocytogenes and Listeria seeligeri on blood agar is frequently difficult to interpret, we developed a microplate technique for the routine determination of hemolytic activity with erythrocyte suspensions. This microtechnique is a simple and reliable test for distinguishing clearly between hemolytic and nonhemolytic strains and could be used instead of the CAMP (Christie-Atkins-Munch-Petersen) test with Staphylococcus aureus in the routine typing of Listeria strains. Furthermore, our results suggest that the quantitation of the hemolytic activity of the Listeria strains, along with the D-xylose, L-rhamnose, and alpha-methyl-D-mannoside acidification tests, allows the differentiation of L. monocytogenes, L. seeligeri, and Listeria ivanovii. We also observed that the treatment of erythrocytes with crude exosubstances of rhodococcus equi, Pseudomonas fluorescens, Acinetobacter calcoaceticus, and S. aureus enhanced the hemolytic activity of all Listeria strains with this characteristic.
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