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Scanning electron microscope study of Pseudomonas fragi on intact and sarcoplasm-depleted bovine longissimus dorsi
Abstract:
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.
Insights
Washing beef muscle to reduce sarcoplasmic fluid slows the growth of Pseudomonas fragi (P. fragi). This bacterial growth causes microstructural surface degradation on beef during refrigerated storage.
Area of Science:
- Food Microbiology
- Meat Science
- Microbial Physiology
Background:
- Pseudomonas fragi (P. fragi) is a common spoilage bacterium in meat.
- Sarcoplasmic fluid in muscle may influence bacterial growth and spoilage.
- Understanding microbial interactions with meat microstructure is crucial for food safety.
Purpose of the Study:
- To investigate the impact of sarcoplasmic fluid concentration on P. fragi growth on beef.
- To examine the microstructural changes in beef muscle caused by P. fragi.
- To elucidate the role of extracellular fibrils in bacterial adhesion and colonization.
Main Methods:
- Bovine longissimus dorsi muscle strips were prepared 24 h postmortem.
- Muscle strips were either washed to remove sarcoplasmic fluid or left intact.
- Strips were inoculated with P. fragi and stored aerobically at 4°C for 12 days.
- Scanning electron microscopy (SEM) was used to analyze microstructural changes.
Main Results:
- P. fragi exhibited slower growth on washed muscle compared to intact muscle.
- SEM revealed localized surface degradation on both intact and washed inoculated muscle.
- Extracellular fibrils were identified as mediators of bacterial adhesion and microcolony formation.
- P. fragi was observed colonizing the spaces between muscle fibers.
Conclusions:
- Reduced sarcoplasmic fluid concentration inhibits P. fragi growth on beef.
- P. fragi causes microstructural damage to beef muscle, primarily in areas of colonization.
- Bacterial adhesion and aggregation are facilitated by extracellular fibrils.
- P. fragi can penetrate and grow within the muscle fiber architecture.