Colonization of beef muscle surfaces by Pseudomonas fluorescens and Pseudomonas fragi

Attached and unattached cell densities were determined for Pseudomonas fluorescens and Pseudomonas fragi growing on the surface of beef muscle stored at 4 and 25 degrees C, in presence of NaCl, KCl and CaCl2. A mechanical rinsing procedure was developed for this purpose. Both species colonized the surface at both temperatures and were enhanced at low (4 degrees C) temperature. Attached cells represented up to 90% of the total until a density of 10(5)-10(6) CFU cm-2 was reached. At that point, a proportion of attached cells to unattached cells declined but colonization of the surface continued. In presence of CaCl2, ratios of attached to unattached cells did not decline, suggesting a significant role for the calcium ion in colonization. Ability to colonize meat surfaces may be a significant competitive advantage for meat spoilage bacteria such as Pseudomonas fragi and Pseudomonas fluorescens