Observations by Electron Microscopy on Pig Muscle Inoculated and Incubated with Pseudomonas fragi1

Abstract

Myofibrils from pig muscle inoculated and incubated with Pseudomonas fragi showed an extremely disrupted appearance as compared to uninoculated controls. There was an almost complete absence of material in the H zone, marked disruption of the A band (probably myosin), and some loss of dense material from the Z line. These changes indicated that marked proteolysis had occurred. Bacteria observed in spoiled muscle tissue exhibited protrusions or blebs on the outer surface of the cell walls. The blebs appeared to form detached globules that migrated into the muscle mass. Bacteria grown in non-muscle-containing media did not produce blebs, which indicates the blebs were induced by growth on muscle tissue. The possibility that the blebs and globules may contain a proteolytic enzyme responsible for myofibrillar disruption is discussed.

The Predominance of Psychrotrophic Pseudomonads on Aerobically Stored Chilled Red Meat

“…Pseudomonas fragi secreted aldolase, glyceraldehyde phosphate dehydrogenase, lactic dehydrogenase, and creatine kinase in the sarcoplasm of rabbit and porcine muscles, which led to muscle breakdown (Hasegawa et al, 1970). Early electron microscopic images of P. fragi growth on porcine muscle have depicted extensive degradation of myofibrils compared to the uninoculated controls (Dutson, Pearson, Price, Spink, & Tarrant, 1971). Authors also reported marked proteolysis where there was a severe loss of material in the H zone and marked disruption of the A band, as well as loss of dense material from the Z line of the porcine skeletal muscle tissue (Dutson et al, 1971;Hasegawa et al, 1970).…”

“…Early electron microscopic images of P. fragi growth on porcine muscle have depicted extensive degradation of myofibrils compared to the uninoculated controls (Dutson, Pearson, Price, Spink, & Tarrant, 1971). Authors also reported marked proteolysis where there was a severe loss of material in the H zone and marked disruption of the A band, as well as loss of dense material from the Z line of the porcine skeletal muscle tissue (Dutson et al, 1971;Hasegawa et al, 1970). Enzymatic activity of P. fragi has a deleterious effect on the color of meat stored at chilled temperatures.…”

“…Another interesting observation is that when P. fragi cells colonize the muscle tissue, globular protrusions or "bleb"-like structures appear on the outer cell wall surfaces (Dutson et al, 1971;Thompson, Naidu, & Pestka, 1985) (Figure 1). Electron microscopic observations have shown that these structures are covered with multiple layered membranes identical to the cell wall and they form into detached globules that migrate into the muscle mass (Thompson et al, 1985).…”

“…Similar "bleb" structures were observed in the human pathogen Pseudomonas aeruginosa in which those structures seem to aid in the penetration of the bacterium into the infected tissues (Kadurugamuwa & Beveridge, 1995) and this could be a mechanism facilitating the efficient invasion of the tissues to be degraded. Some studies have reported that, despite being a highly proteolytic organism, P. fragi is unable to excrete proteases when grown in vitro (Dutson et al, 1971;Labadie, 1999;Molin & Ternström, 1982). It was assumed that meat proteins or peptides are necessary for the secretion of proteases into the extracellular medium (Labadie, 1999).…”

Protein Changes Caused by Bacterial Growth on Beef

“…They were able to demonstrate changes in both the sarcoplasmic and myofibrillar proteins of minced pork meat inoculated with pure cultures of several different bacteria and incubated at refrigeration temperatures. Pseudomonas fragi produced the greatest changes and its activity in minced pork muscle was studied further by (a) comparing the appearance of its extracellular proteinase with the onset of spoilage odours and protein breakdown (Tarrant, Pearson, Price & Lechowich, 1971); (b) examining myofibrillar structure during storage by electron microscopy (Dutson et al, 1971) and (c) following the effect of partially purified proteinase on ground muscle and on isolated myofibrillar and sarcoplasmic proteins (Tarrant, Jenkins, Pearson & Dutson, 1973). In most of these experiments, slime and spoilage odours were apparent at the earliest sampling times used and no data relating to the prespoilage period of storage were reported.…”