Microbiology of organic and conventionally grown fresh produce

ABSTRACT Fresh produce is a generalized term for a group of farm-produced crops, including fruits and vegetables. Organic agriculture has been on the rise and attracting the attention of the food production sector, since it uses eco-agricultural principles that are ostensibly environmentally-friendly and provides products potentially free from the residues of agrochemicals. Organic farming practices such as the use of animal manure can however increase the risk of contamination by enteric pathogenic microorganisms and may consequently pose health risks. A number of scientific studies conducted in different countries have compared the microbiological quality of produce samples from organic and conventional production and results are contradictory. While some have reported greater microbial counts in fresh produce from organic production, other studies do not. This manuscript provides a brief review of the current knowledge and summarizes data on the occurrence of pathogenic microorganisms in vegetables from organic production.

Microbiology of organic and conventionally grown fresh produce

Fresh produce is a generalized term for a group of farm-produced crops, including fruits and vegetables. Organic agriculture has been on the rise and attracting the attention of the food production sector, since it uses eco-agricultural principles that are ostensibly environmentally-friendly and provides products potentially free from the residues of agrochemicals. Organic farming practices such as the use of animal manure can however increase the risk of contamination by enteric pathogenic microorganisms and may consequently pose health risks. A number of scientific studies conducted in different countries have compared the microbiological quality of produce samples from organic and conventional production and results are contradictory. While some have reported greater microbial counts in fresh produce from organic production, other studies do not. This manuscript provides a brief review of the current knowledge and summarizes data on the occurrence of pathogenic microorganisms in vegetables from organic production.(AU)

Bacteriocinogenic Lactococcus lactis subsp. lactis DF04Mi isolated from goat milk: Application in the control of Listeria monocytogenes in fresh Minas-type goat cheese

Listeria monocytogenes is a pathogen frequently found in dairy products. Its control in fresh cheeses is difficult, due to the psychrotrophic properties and salt tolerance. Bacteriocinogenic lactic acid bacteria (LAB) with proven in vitro antilisterial activity can be an innovative technological approach but their application needs to be evaluated by means of in situ tests. In this study, a novel bacteriocinogenic Lactococcus lactis strain (Lc. lactis DF4Mi), isolated from raw goat milk, was tested for control of growth of L. monocytogenes in artificially contaminated fresh Minas type goat cheese during storage under refrigeration. A bacteriostatic effect was achieved, and counts after 10 days were 3 log lower than in control cheeses with no added LAB. However, this effect did not differ significantly from that obtained with a non-bacteriocinogenic Lc. lactis strain. Addition of nisin (12.5 mg/kg) caused a rapid decrease in the number of viable L. monocytogenes in the cheeses, suggesting that further studies with the purified bacteriocin DF4Mi may open new possibilities for this strain as biopreservative in dairy products.(AU)

Bacteriocinogenic Lactococcus lactis subsp: lactis DF04Mi isolated from goat milk: Evaluation of the probiotic potential

Lactic acid bacteria capable of producing bacteriocins and presenting probiotic potential open innovative technological applications in the dairy industry. In this study, a bacteriocinogenic strain (Lactococcus lactis subsp. lactis DF4Mi) was isolated from goat milk, and studied for its probiotic potential. Lc. lactis DF4Mi was resistant to acidic pH and oxbile, presented co-aggregation with Listeria monocytogenes, and was not affected by several drugs from different generic groups, being sensitive to most tested antibiotics. These properties indicate that this Lc. lactis strain can be used for enhancement of dairy foods safety and quality, in combination with potential probiotic properties.

Bacteriocinogenic Lactococcus lactis subsp. lactis DF04Mi isolated from goat milk: characterization of the bacteriocin

Lactic acid bacteria capable of producing bacteriocins and presenting probiotic potential open innovative technological applications in the dairy industry. In this study, a bacteriocinogenic strain (Lactococcus lactis subsp. lactis DF4Mi) was isolated from goat milk, and studied for its antimicrobial activity. The bacteriocin presented a broad spectrum of activity, was sensitive to proteolytic enzymes, resistant to heat and pH extremes, and not affected by the presence of SDS, Tween 20, Tween 80, EDTA or NaCl. Bacteriocin production was dependent on the components of the culture media, especially nitrogen source and salts. When tested by PCR, the bacteriocin gene presented 100% homology to nisin Z gene. These properties indicate that this L. lactis subsp. lactis DF4Mi can be used for enhancement of dairy foods safety and quality.

Characterization of class 1 integrons and antibiotic resistance genes in multidrug-resistant Salmonella enterica isolates from foodstuff and related sources

In recent years, an increase in the occurrence of antimicrobial resistance among Salmonella enterica has been observed in several countries, which is worrisome because S. enterica is one of the most common causes of human gastroenteritis worldwide. The aim of this study was to characterize class 1 integrons and antibiotic resistance genotypes in Salmonella enterica isolates recovered from foodstuff and related sources. Nineteen multidrug-resistant (MDR) Salmonella enterica isolates were recovered. Higher resistance rates to tetracycline (90%), streptomycin (80%), sulfamethoxazole-trimethoprim (80%), ampicillin (60%) and nalidixic acid (70%) were related to the presence of the tetA, aadA, sul1/sul2, blaTEM-1 genes, and a codon mutation at position 83 of the gyrA gene, respectively. Class 1 integrons harboring aadA, blaTEM-1, sul1 or dhfr1 genes were detected in nine (45%) Salmonella enterica strains belonging to serotypes Brandenburg, Panama, Agona, Mbandaka and Alachua. Finally, clonal dissemination of S. Panama, S. Derby and S. Mbandaka was confirmed by PFGE. Detection of clonally related MDR Salmonella enterica suggests that endemic serotypes can be supported by class 1 integron-borne gene cassettes and/or mutations in drug targets. Emergence and dissemination of multidrug-resistant Salmonella enterica can have a major public health impact in an environment where large-scale suppliers ship their products.

Behaviour of L. monocytogenes in sliced, vacuum-packed mortadella

This study evaluated the growth of naturally occurring L. monocytogenes in sliced, vacuum-packed mortadella samples during storage at 5ºC until the expiration date. Tukey's test indicated that counts of L. monocytogenes on 0, 10, 20, 30 and 40 days of storage were significantly different (p 0.05), indicating growth during shelf life. In three trials, the mean increase was 1.72 log cycles. Vacuum packing and storage under refrigeration were not effective in controlling the growth of L. monocytogenes in sliced mortadella, indicating that good manufacturing practices and implemented HACCP programs are essential to assure safety of this product.

O presente trabalho avaliou a multiplicação de L. monocytogenes naturalmente presente em mortadelas fatiadas, embaladas a vácuo e estocadas a 5ºC durante sua vida de prateleira. O teste Tukey indicou que as populações de L. monocytogenes nos tempos 10, 20, 30 e 40 dias diferiram significativamente (p 0,05) indicando multiplicação durante o armazenamento. Em três repetições, o aumento médio foi de 1,80 ciclos log. A embalagem a vácuo e estocagem sob refrigeração não foram suficientes para o controle da multiplicação de L. monocytogenes em mortadelas fatiadas, indicando que as boas práticas de fabricação e um sistema HACCP implantado são fundamentais para assegurar a segurança desse produto.

Performance of two ready-to-use systems for enumeration of aerobic mesophilic microorganisms in frozen goat milk

Enumeration of aerobic microorganisms in Brazilian pasteurized bovine milk using PetrifilmTM AC and SimplateTM TPC was shown to be influenced by the nature of autochthonous microbiota. This study was conducted to assess if the same occurs in pasteurized goat milk. Pasteurized frozen goat milk (n=62) was purchased in retail stores in São Paulo, SP, Brazil, and submitted to mesophilic aerobic counts using PetrifilmTM AC and SimplateTM TPC, comparing results with those of conventional pour-plates. Correlation indexes above 0.90 were ranked "excellent"; those between 0.80 and 0.89, "good", those from 0.79 to 0.50, "fair", and those below 0.50, "poor". Correlation indexes for PetrifilmTM AC counts were "good", but "poor" using SimplateTM TPC. Comparison of PetrifilmTM AC and SimplateTM TPC also produced "poor" correlation indexes. Results suggest that autochthonous microbiota have little, if any, influence on the performance of these two systems, since good correlations were achieved using PetrifilmTM AC.

Foi demonstrado que a enumeração de microrganismos aeróbios em leite bovino brasileiro pasteurizado utilizando-se as placas PetrifilmTM AC e SimplateTM TPC pode ser influenciada pela microbiota autóctone. O presente estudo foi conduzido para se determinar se o mesmo ocorreria com leite de cabra pasteurizado. Foram analisadas 62 amostras de leite pasteurizado e congelado, vendidas no comércio varejista de São Paulo, SP. As amostras foram submetidas à contagem de microrganismos aeróbios mesófilos utilizando-se placas PetrifilmTM AC e SimplateTM TPC, comparando-se os resultados com a semeadura em profundidade. Um índice de correlação acima de 0,90 foi classificado como "excelente", entre 0,80 e 0,89 como "bom", entre 0,79 e 0,50 como "fraco", e abaixo de 0,50, como "ruim". O índice de correlação para as contagens em placas PetrifilmTM AC foi "bom", mas foi "ruim" quando se usou as placas SimplateTM TPC. A comparação entre os resultados obtidos com as placas PetrifilmTM AC e SimplateTM TPC também produziu um índice de correlação "ruim". Os resultados sugerem que a microbiota autóctone têm pouca ou nenhuma influência sobre a performance destes dois sistemas, pois boas correlações foram obtidas com o uso das placas PetrifilmTM AC.

Inactivation of Escherichia coli O157:H7 in hamburgers by gamma irradiation

Escherichia coli O157:H7 causes bloody diarrhoea, haemorrhagic colitis and life-threatening complications like haemolytic uremic syndrome and thrombotic thrombocitopenic purpura. Among foods associated with outbreaks caused by this pathogen, hamburger is the most common one. The aim of this research was to determine the radiation dose to reduce the population of E. coli O157:H7 in hamburgers to non-detectable levels in order to render a safer product. Hamburgers, inoculated with Escherichia coli O157:H7, were exposed to gamma radiation (60Co) treatment, with doses ranging from 0 to 0.7 kGy. The average temperature during the process was 5.6ºC. Non-inoculated hamburgers were submitted to sensory evaluation after being exposed to irradiation doses of 0.8 kGy and 1.0 kGy. The D10 for the pathogen varied from 0.17 kGy to O.27 kGy in hamburger. Considering the highest D10 value in hamburger, a dose of 1.08 kGy would be sufficient to reduce E. coli O157:H7 contamination in 4 log cycles, without affecting the sensory attributes of the product.

Escherichia coli O157:H7 causa colite hemorrágica que pode evoluir para síndrome urêmica hemolítica e síndrome púrpura trombótica trombocitopênica. Entre os alimentos mais envolvidos nos surtos causados por essa bactéria destacam-se os hambúrgueres de carne bovina. Esta pesquisa teve como objetivo determinar o valor D10 de E. coli O157:H7 em hambúrgueres e sugerir uma dose que torne o alimento seguro em relação à essa bactéria e sem alterar suas características sensoriais. Amostras de hambúrgueres industrializados foram inoculados com Escherichia coli O157:H7 e submetidos à radiação com raios gama (60Co). A temperatura média durante o processo foi de 5,6ºC. O valor D10 no hambúrguer variou de 0,17 a 0,27 kGy. Considerando o maior valor D10 obtido, a dose de 1,08 kGy seria suficiente para reduzir a população de Escherichia coli O157:H7 em 4 ciclos logarítmicos, sem que houvesse rejeição do produto pelo painel treinado de analistas.

Biochemical characteristics of typical and atypical Staphylococcus aureus in mastitic milk and environmental samples of Brazilian dairy farms

This study reports results on the biochemical characteristics of 274 Staphylococcus aureus strains isolated from mastitic milk, hands of milkmen and milking machines. Features included colony morphology on Baird Parker agar (BPA), catalase, coagulase and thermonuclease tests. API-Staph (bioMérieux, France) was used as reference identification system. 39.4% of the colonies on BPA identified as S.aureus were atypical. They were more frequent in milk samples (94.4%). All S.aureus strains were coagulase positive but intensity of the test varied according to the source: environmental strains were 3+ or 4+, while 17.1% of strains isolated from milk presented only 1+ or 2+ results. The majority of atypical S.aureus strains presented a 4+ coagulase result. 2.2% of S.aureus strains were thermonuclease negative. Sixteen thermonuclease positive and coagulase positive strains were identified as S.hyicus.

Esse trabalho relata as características bioquímicas de 274 cepas de Staphylococcus aureus isoladas de leite mastítico, de mãos de ordenhadores e de ordenhadeiras mecânicas. Foram avaliadas as características morfológicas em agar Baird Parker (BPA) e os resultados para os testes de catalase, coagulase e termonuclease. API-Staph foi empregado como sistema de referência para identificação. 39,4% das colônias em BPA identificadas como S.aureus apresentaram morfologia atípica, sendo mais freqüentes em leite (94,4%). Todas as cepas identificadas como S.aureus foram coagulase positivas mas a intensidade da reação variou de acordo com a fonte: cepas isoladas de amostras ambientais foram 3+ ou 4+, enquanto 17,1% daquelas isoladas de leite foram apenas 1+ ou 2+. A maioria das cepas de S aureus com morfologia atípica em agar Baird-Parker apresentaram coagulase 4+. 2,2% das cepas de S.aureus foram termonuclease negativas. 16 cepas termonuclease positivas e coagulase positivas foram identificadas como S.hyicus.