Avaliação fenotípica, genotípica e termorresistência de leveduras isoladas do leite in natura
Milk is considered an excellent culture medium because it is conducive to the growth of several microorganisms. Thus, ingestion of fresh milk may constitute a potential route of transmission of zoonoses, which justifies the need for microbiological analysis for human consumption. Among the main c...
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| Formato: | Dissertação |
| Idioma: | pt_BR |
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| Endereço do item: | https://repositorio.ufrn.br/jspui/handle/123456789/27258 |
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| Resumo: | Milk is considered an excellent culture medium because it is conducive to the growth of
several microorganisms. Thus, ingestion of fresh milk may constitute a potential route of
transmission of zoonoses, which justifies the need for microbiological analysis for human
consumption. Among the main contaminants of fresh milk, yeasts of the genus Candida,
which are associated with infections in humans and animals, and other species also
capable of causing opportunistic mycoses such as Kluyveromyces marxianus, Pichia
manshurica, Kodamaea ohmeri. In this study, 23 samples of fresh milk type B, collected
by manual or mechanical milking were collected and stored in collective refrigeration tanks
of farms located in the Metropolitan Region of Natal and nearby. Twenty samples of fresh
milk commercially traded in the city of Ceará-Mirim/RN were also analyzed. In order to
establish the phenotypic, genotypic, quantitative and thermo-resistant characterization of
yeasts isolated from fresh milk, we also sought to trace the susceptibility profile of the
isolates to the antifungal agents. Positive samples were analyzed for quantification by
count of Colony Forming Units (CFU). All isolated species were treated by slow
pasteurization (62-64 ° C / 30 minutes) and fast (72-75 ° C / 20 seconds), as well as by
boiling. Fifty yeast strains of the species were characterized: C. tropicalis 14 (28%), C.
parapsilosis 7 (14%), C. albicans 6 (12%), C. glabrata 5 (10%), C. krusei 5 (10%),
Kluyveromyces. marxianus 5 (10%), C. guilliermondii 4 (8%), C. rugosa 1 (2%), C.
orthopsilosis 1 (2%), Pichia manshurica 1 (2%), Kodamaea ohmeri 1 (2%). Five isolates
showed resistance to the antifungal agents tested. A global median of 37 x 102 CFU / mL
was obtained, 33 x 102 UFC / mL in the milk collected by manual milking and 80.5 x 102
UFC / mL in the milk collected by mechanical milking. The milk in natura marketed in
Ceará-Mirim/RN showed a median of 20 x102 CFU / mL. Of the isolates submitted to heat
treatment, 80% were resistant to fast pasteurisation and 60% to boiling, but none of them
resisted slow pasteurisation. It was concluded that the milk collected through mechanical
milking and stored in collective cooling tanks, presented higher rates of yeast
contamination, compared to milk samples collected by manual milking and kept under the
same storage conditions. Boiling, as well as rapid pasteurization, which are procedures
widely used to reduce the contamination of milk and its derivatives, have not proved to be
efficient for this purpose. On the other hand, the slow pasteurisation proved to be 100%
efficient for the elimination of contaminating yeasts from the evaluated milk samples. |
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