Bacillus cereus: produção de metalloproteinases na cadeia produtiva de lácteos e avaliação da proteólise da kappa-caseína em leite pasteurizado
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Data
2018-05-04
Autores
Aguilar, Carlos Eduardo Gamero [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
As espécies do grupo do Bacillus cereus estão na cadeia produtiva do leite associadas a problemas tecnológicos por produzirem metaloproteínases. O controle deste microrganismo se faz necessário devido aos prejuízos causados por perdas. Com o objetivo de verificar a presença do gene npr (produção de metaloproteínases), Plcr (regulador pleitrópico) e cspa (assinatura psicrotrófica), avaliar fenotipicamente os isolados quanto à capacidade proteolítica e mensurar a atividade deteriorante da mencionada enzima sobre a kappa-caseína, foram isolados da cadeia produtiva de lácteos, identificados e sequenciados genomicamente, microrganismos pertencentes ao grupo do Bacillus cereus que comprovadamente possuiam características proteolíticas e psicrotróficas. De 466 amostras, obteve-se 69 isolados de Bacillus cereus, sendo que o gene npr, fenótipo proteolítico e Plcr estavam presentes em, respectivamente, 97,1%, 92,7% (64) e 88,4% (61) das amostras. O gene cspa foi identificado em 100% das amostras. Entretanto, fenotipicamente apenas um isolado comportou-se como tal, sugerindo a existência de outros fatores para expressão desta característica. A concentração de ácido siálico elevou-se durante o tempo de prateleira do produto, na média, de 3,99 µg/mL para 4,45 µg/mL no primeiro e último dia, respectivamente. Assim, devido a ampla distribuição do Bacillus cereus associada a sua resistência térmica e a elevada frequência de características proteolíticas, faz-se necessário a obtenção higiênica do leite, minimizando contaminações, para que produtos de qualidade possam ser elaborados.
The species included in Bacillus cereus group are widespread in the dairy production chain and are often associated with technological failures in dairy products, due to the production of metalloproteinases. Controlling this microorganism is necessary due to economic losses. In order to assess the presence of npr gene (metalloproteinases production), Plcr (pleiotropic regulator) and cspa (psychotropic signature), proteolytic activity on plates and the spoilage potential of the enzyme on kappa-casein, Bacillus cereus samples which had proteolytic and psychotropic characteristics were isolated from dairy production chain and sequenced. A set of 69 isolates were obtained from 466 samples and the frequency of npr gene, proteolytic activity and Plcr were observed in, respectively, 97.1%, 92,7% and 88,4% of the samples. The cspa gene was present in all samples. However, only one sample demonstrated the psychotropic phenotype, suggesting the existence of other factors involved in the expression of this characteristic. Concentration of free sialic acid during the shelf life of pasteurized milk ranged from 3,99 µg/ml to 4.45 µg/ml in the first and last days of the storage period, respectively. Therefore, due to the wide distribution of Bacillus cereus associated with thermal resistance and high frequency of proteolytic features, hygienic milking practice is critical to decrease contamination and produce milk with higher quality.
The species included in Bacillus cereus group are widespread in the dairy production chain and are often associated with technological failures in dairy products, due to the production of metalloproteinases. Controlling this microorganism is necessary due to economic losses. In order to assess the presence of npr gene (metalloproteinases production), Plcr (pleiotropic regulator) and cspa (psychotropic signature), proteolytic activity on plates and the spoilage potential of the enzyme on kappa-casein, Bacillus cereus samples which had proteolytic and psychotropic characteristics were isolated from dairy production chain and sequenced. A set of 69 isolates were obtained from 466 samples and the frequency of npr gene, proteolytic activity and Plcr were observed in, respectively, 97.1%, 92,7% and 88,4% of the samples. The cspa gene was present in all samples. However, only one sample demonstrated the psychotropic phenotype, suggesting the existence of other factors involved in the expression of this characteristic. Concentration of free sialic acid during the shelf life of pasteurized milk ranged from 3,99 µg/ml to 4.45 µg/ml in the first and last days of the storage period, respectively. Therefore, due to the wide distribution of Bacillus cereus associated with thermal resistance and high frequency of proteolytic features, hygienic milking practice is critical to decrease contamination and produce milk with higher quality.
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biologia molecular, microbiologia, sequenciamento genômico, leite experimentalmente contaminado, genomic sequencing, microbiology, molecular biology