Mauro Faber de Freitas Leitão

Growth of Salmonella Enteritidis in melon, watermelon and papaya pulp stored at different times and temperatures

Abstract The ability of Salmonella Enteritidis to grow on melon (Cucumis melo), watermelon (Citrullus vulgaris) and papaya (Carica papaya) pulp stored at different times and temperatures was investigated. Fruit pulp portions with an average pH of 5.87, 5.50 and 4.87 for melon, watermelon and papaya, respectively, were obtained aseptically, homogenized, weighed and inoculated with suspensions (approximately 102 CFU/g) of Salmonella Enteritidis. Viable populations of Salmonella were determined by the pour plate technique using of test portions on TSA agar. The test organism increased in numbers at all tested temperatures. The generation times for melon at 10, 20 and 30 °C were respectively 7.31, 1.69 and 0.69 h, for watermelon were 7.47, 1.60 and 0.51 h and for papaya 16.61, 1.74 and 0.66 h. The results showed that Salmonella Enteritidis can grow on low acid fruit pulp, and that refrigeration at 10 °C, although reducing the generation rate, does not inhibit its growth.

Detection and characterization of bacteriocin-producing Lactococcus lactis strains

One hundred sixty seven strains of Lactococcus lactis were screened for bacteriocin production by well diffusion assay of GM17 agar. Fourteen (8.4%) produced antimicrobial activity other than organic acids, bacteriophages or hydrogen peroxide. The frequency of bacteriocin production ranged from 2% in L. lactis subsp. cremoris up to 12% in L. lactis subsp. lactis. Antimicrobial activities were not observed in any strain of L. lactis subsp. lactis var. diacetylactis. Among thirteen bacteriocin-producing strains and two nisin-producing strains (L. lactis subsp. lactis ATCC 11454 and L. lactis subsp. lactis CNRZ 150), eight (53%) were characterized as lactose-positive (Lac+) and proteinase-negative (Prt-). The bacteriocin-producing cultures were also characterized on the basis of plasmid content. All strains had 2 to 7 plasmids with molecular weights varying from 0.5 to 28.1 Mdal. Four strains (ITAL 435, ITAL 436, ITAL 437 and ITAL 438) showed identical profiles and the other were quite distinct.

Ocorrência de Bacillus sporothermodurans em leite UAT/UHT brasileiro e a influência do tratamento térmico

Bacillus sporothermodurans (BSP) has been isolated worldwide, but mainly in European contries as an usual contaminant of milk by the UHT system. Even being non pathogenic, generally its presence results in product rejection based on international microbiological standards limiting the counts to a maximum of 100 cfu/ml. In this research work, the occurrence of BSP was evaluated in UHT milk samples produced in different regions of Brazil (Central, South and Southeast) and processed by the indirect thermal treatment system (plate or tube exchangers) or by the direct system (steam infusion or steam injection). A total of 100 commercial samples were analysed both quantitatively by spread plate technique using Brain Heart Infusion Esculin Agar (BHI-E agar) and qualitatively after thermal shock treatment (115°C/7min), followed by incubation and plating in that medium. The results showed a total of 45% of the examined samples with counts above 100 cfu/ml, varying from 2 .104 and 9,5 .105 cfu/ml. However, 71.4% of the samples processed by indirect system were above limits, while none of the samples heat treated by the direct system, that allows a more drastic temperature condition, were rejected. A similar picture was observed in the qualitative evaluation, with contamination levels of 71,7 and 22,2% for the indirect and direct system, respectively. A total of 300 cultures were isolated from contaminated samples, showing cultural, morphological and biochemical patterns similar to BSP, except a late glucose fermentation capacity showed by most of the isolated strains. When 24 representative strains were submitted to PCR-RAPD evaluation and compared to the reference BSP strain (DSMZ 10599), they were confirmed as Bacillus sporothermodurans based on their DNA pattern.O Bacillus sporothermodurans (BSP) tem sido isolado em todo o mundo, principalmente nos paises europeus, como um contaminante usual do leite processado pelo sistema UAT/UHT. Embora o BSP nao seja patogenico, o leite contaminado fica fora dos padroes da legislacao, que fixa o limite de contagem de microrganismos aerobios mesofilos em 100ufc/ml. Tal bacilo foi pesquisado em amostras de leite UAT produzido nas regioes Sul, Sudeste e Centro-Oeste do Brasil, processado pelos sistemas de aquecimento indireto (trocadores a placas ou tubulares) e direto (injecao ou infusao de vapor). Foi analisado um total de 100 amostras, avaliadas quantitativamente pela tecnica de espalhamento superficial no meio diferencial agar infusao de cerebro e coracao - esculina (agar BHI-E). Na analise qualitativa as amostras foram submetidas a choque termico (115oC/7min), incubadas e plaqueadas no referido agar. Os resultados revelaram um total de 45% de amostras com contagens acima do limite toleravel (100ufc/ml), oscilando entre 2x104 e 9,5x105ufc/ml. No entanto, em funcao do tipo de sistema de aquecimento, as variacoes foram muito acentuadas, sendo que na avaliacao quantitativa os indices de rejeicao foram de 71,4% nas amostras aquecidas indiretamente e naquelas processadas diretamente. Isto se deve, provavelmente, as condicoes mais drasticas de tratamento termico utilizada pelos laticinios com sistema direto de aquecimento. Na analise qualitativa, os indices de rejeicao foram de 71,7 e 22,2%, respectivamente. Trezentas culturas foram isoladas das amostras contaminadas, revelando caracteristicas culturais, morfologicas e bioquimicas similares as de BSP, exceto pela capacidade de fermentacao lenta da glicose evidenciada pela maioria delas. Deste total, 24 cepas tiveram seu DNA cromossomico avaliado pelo metodo PCR-RAPD, sendo que os perfis obtidos foram muito similares ao de BSP referencia (DSMZ 10599) confirmando tratar-se de Bacillus sporothermodurans.

Efeito e modo de ação das bacteriocinas produzidas por Lactococcus lactis subsp. lactis ITAL 383, ATCC 11454 e CNRZ 150 contra Listeria innocua LIN 11

The effect and mode of action of the bacteriocin produced by L. lactis subsp. lactis ITAL 383 and CNRZ 150 are similar to the nisin produced by L. lactis subsp. lactis ATCC 11454. It was clearly bactericidal, and caused lysis of a strain of L. innocua LIN 11 detected by the decrease of absorbance values and the cell viability. Their lethal effect was considerably higher during the logarithmic growth when compared to the stationary phase. Adsorption developed rapidly and was influenced by the pH value of the suspension medium. Maximum adsorption was observed at pH 6,0 and immediately after initial contact and loss at pH 2,0.

Occurrence of Bacillus sporothermodurans and the influence of the thermal processing procedure on its presence in brazilian UHT milk

Bacillus sporothermodurans (BSP) has been isolated worldwide, but mainly in European contries as an usual contaminant of milk by the UHT system. Even being non pathogenic, generally its presence results in product rejection based on international microbiological standards limiting the counts to a maximum of 100 cfu/ml. In this research work, the occurrence of BSP was evaluated in UHT milk samples produced in different regions of Brazil (Central, South and Southeast) and processed by the indirect thermal treatment system (plate or tube exchangers) or by the direct system (steam infusion or steam injection). A total of 100 commercial samples were analysed both quantitatively by spread plate technique using Brain Heart Infusion Esculin Agar (BHI-E agar) and qualitatively after thermal shock treatment (115°C/7min), followed by incubation and plating in that medium. The results showed a total of 45% of the examined samples with counts above 100 cfu/ml, varying from 2 .104 and 9,5 .105 cfu/ml. However, 71.4% of the samples processed by indirect system were above limits, while none of the samples heat treated by the direct system, that allows a more drastic temperature condition, were rejected. A similar picture was observed in the qualitative evaluation, with contamination levels of 71,7 and 22,2% for the indirect and direct system, respectively. A total of 300 cultures were isolated from contaminated samples, showing cultural, morphological and biochemical patterns similar to BSP, except a late glucose fermentation capacity showed by most of the isolated strains. When 24 representative strains were submitted to PCR-RAPD evaluation and compared to the reference BSP strain (DSMZ 10599), they were confirmed as Bacillus sporothermodurans based on their DNA pattern.O Bacillus sporothermodurans (BSP) tem sido isolado em todo o mundo, principalmente nos paises europeus, como um contaminante usual do leite processado pelo sistema UAT/UHT. Embora o BSP nao seja patogenico, o leite contaminado fica fora dos padroes da legislacao, que fixa o limite de contagem de microrganismos aerobios mesofilos em 100ufc/ml. Tal bacilo foi pesquisado em amostras de leite UAT produzido nas regioes Sul, Sudeste e Centro-Oeste do Brasil, processado pelos sistemas de aquecimento indireto (trocadores a placas ou tubulares) e direto (injecao ou infusao de vapor). Foi analisado um total de 100 amostras, avaliadas quantitativamente pela tecnica de espalhamento superficial no meio diferencial agar infusao de cerebro e coracao - esculina (agar BHI-E). Na analise qualitativa as amostras foram submetidas a choque termico (115oC/7min), incubadas e plaqueadas no referido agar. Os resultados revelaram um total de 45% de amostras com contagens acima do limite toleravel (100ufc/ml), oscilando entre 2x104 e 9,5x105ufc/ml. No entanto, em funcao do tipo de sistema de aquecimento, as variacoes foram muito acentuadas, sendo que na avaliacao quantitativa os indices de rejeicao foram de 71,4% nas amostras aquecidas indiretamente e naquelas processadas diretamente. Isto se deve, provavelmente, as condicoes mais drasticas de tratamento termico utilizada pelos laticinios com sistema direto de aquecimento. Na analise qualitativa, os indices de rejeicao foram de 71,7 e 22,2%, respectivamente. Trezentas culturas foram isoladas das amostras contaminadas, revelando caracteristicas culturais, morfologicas e bioquimicas similares as de BSP, exceto pela capacidade de fermentacao lenta da glicose evidenciada pela maioria delas. Deste total, 24 cepas tiveram seu DNA cromossomico avaliado pelo metodo PCR-RAPD, sendo que os perfis obtidos foram muito similares ao de BSP referencia (DSMZ 10599) confirmando tratar-se de Bacillus sporothermodurans.