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Biochemical and ultrastructural changes occurring in chicken pectoralis muscle inoculated with pseudomonas fragi Sage, Gilbert


Chicken pectoralis muscle was inoculated with Pseudomonas fragi and incubated at room temperature. Alterations in the nonprotein nitrogen, water-soluble protein nitrogen, and salt-soluble protein nitrogen fractions were studied and attempts were made to relate these changes to structural changes observed by scanning and transmission electron microscopy. A significant decrease in myofibrillar protein solubility was found in the inoculated muscle during the protein extract-ability study. Results of the gel filtration study indicated that proteolysis of the sarcoplasmic proteins occurred and that the nonprotein nitrogen fraction increased due to growth of P. fragi. Alterations were observed in the disc gel electrophoretic patterns of the sarcoplasmic and myofibrillar protein fractions. Arginine, threonine, serine, proline and tyrosine were selectively utilized by P. fragi. Scanning electron micrographs indicated that proteolysis of the endomysium occurred after 2 days of incubation at 25°C. Proteolysis of the endomysium became more extensive as incubation time increased. After 4 days of incubation the myofibrils showed evidence of disruption as a result of bacterial growth. Disruption of the muscle fiber was limited to a depth of 2 to 4 micrometers after 9 days of incubation. Bacteria were observed growing between the muscle fibers. Proteolysis was not as extensive in samples incubated at 5°C. Electron micrographs prepared from thin sections of myofibrils inoculated with P. fragi showed marked disruption of the myofibrils due to bacterial growth. A clear zone, devoid of structural detail, surrounded the bacterial cell. A region of disrupted tissue exists between the clear zone and intact myofibrils. Cellular protrusions were observed on the surface of the bacteria.

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