Scanning electron microscope study of Pseudomonas fragi on intact and sarcoplasm-depleted bovine longissimus dorsi muscle.

Intact bovine longissimus dorsi muscle strips used 24 h postmortem were washed to remove sarcoplasmic fluid or left intact and were either left uninoculated or inoculated with Pseudomonas fragi ATCC 4973. The effects of decreased sarcoplasm concentration on growth of P. fragi and consequent microstructural changes of beef muscle during aerobic storage at 4 degrees C for 12 days were evaluated. P. fragi grew slower on washed muscle than on intact muscle. Scanning electron micrographs revealed surface degradation of both intact inoculated and washed inoculated muscle only in areas of localized colonization. Extracellular fibrils appeared to mediate adhesion of P fragi to the muscle surface as well as cell-to-cell attachment within microcolonies. P. fragi was also observed growing between muscle fibers.