Renate Schöbitz

Effects of a bacteriocin-like inhibitory substance from Carnobacterium piscicola against human and salmon isolates of Listeria monocytogenes.

The aim of this study was to characterize the antagonism of a bacteriocin-like inhibitory substance (BLIS) produced by Carnobacterium piscicola L103 against Listeria monocytogenes strains isolated from salmon and human samples. The inhibitory effect of the BLIS was evaluated in Tryptic soy agar (TSA) during different growth phases of L. monocytogenes at 5 degrees C, using the well diffusion method. Also, the type of inhibition, either bacteriostatic or bactericidal of the BLIS in Tryptic soy broth (TSB), was studied and the development of resistant cells investigated. Results showed an antagonistic effect of the BLIS on all the strains of L. monocytogenes. Four selected strains presented a higher sensitivity to the BLIS in the exponential growth phase and were more resistant in the stationary phase. In TSB, the inhibitory substance showed a partially bactericidal effect on L. monocytogenes. After inactivation of the BLIS with a protease, however, a regrowth of L. monocytogenes was found. The isolate most affected by the action of the BLIS was one of salmon origin. From the 86 isolated colonies that grew in the presence of the BLIS, 93% showed total resistance and 7% partial resistance, which was maintained through five consecutive culture cycles in the absence of the BLIS.

Bacteriocin like substance production by Carnobacterium piscicola in a continuous system with three culture broths. Study of antagonism against Listeria monocytogenes on vacuum packaged salmon

Tres meios de cultura foram avaliados quanto a producao de substâncias semelhantes a bacteriocinas (SSB) por Carnobacterium piscicola L 103, utilizando um sistema continuo de cultura. A eficacia da substância antagonista contra Listeria monocytogenes foi testada em salmao embalado a vacuo. As SSB foram produzidas em bioreator de 1.0 L, em cultura continua e em cultura estacionaria, utilizando D-MRS, mod. D-MRS e APT como meios de cultivo. Files de salmao foram inoculados com SSB (200 AU mL-1 e 800 AU mL-1) e L. monocytogenes (8.0 x 101 ufc cm-2) e mantidos a 4oC. O crescimento de L. monocytogenes foi verificado a cada 5 dias, durante 15 dias. C. piscicola L 103 antigiu a fase estacionaria depois de 12 h de incubacao em cultivo em batelada, sendo a atividade SSB de 800 AU mL-1 nos meios D-MRS e mod. D-MRS e de 400 AU mL-1 no caldo APT. Durante a cultura continua, a atividade SSB aumentou ate 6400 AU mL-1 nos dois tipos de caldo MRS, ao passo que no caldo APT esta atividade diminuiu a 50 AU mL-1, indicando uma clara vantagem de uso dos dois primeiros meios de cultura e do sistema de crescimento continuo. SSB mostrou efeito bacteriostatico sobre L. monocytogenes quando inoculada em salmao, com contagens de 6,0 x 103 ufc cm-2 apos 15 dias. Nao foram encontradas diferencas significantes entre as duas atividades utilizadas. No ensaio controle, sem SSB, a contagem de L. monocytogenes aumentou ate 1,0 x 106 ufc cm-2 apos 15 dias de estocagem.