Growth and Protelytic Activity of Pseudomonas fluorescens in Eggs and Egg Products^a

Abstract

SUMMARY The growth characteristics and proteolytic activities of 3 strains of Pseudomonas fluorescens were determined in blended fresh egg white (initial pH 7.8–8.0), egg white adjusted to pH 7.4, egg white with added yolk, 30‐day‐old egg white (pH 9.0), and various egg media at the 2% protein level. In all cases the number of viable cells increased markedly during the first l–2 weeks of incubation. Under certain conditions of incubation, strains 5 and 17 showed proteolytic activity in blended fresh egg white, and strain 10 in egg white adjusted to pH 7.4 and in egg white with added egg yolk. Growth and proteolytic activity were also observed in the 30‐day‐old egg white (pH 9.0). All strains showed growth and proteolytic activity in the spray‐dried egg white growth medium (pH 7.4, autoclaved). Proteolysis was also determined on solid media with various egg constituents as substrate.

Changes in microbial, physiochemical, and functional properties of pasteurized liquid whole egg during refrigerated storage

“…On the fourth day, there was a sudden increase in the PS count, possibly due to the strong growth ability of these bacteria at low temperatures. The ability of certain strains of Pseudomonas to cause proteolysis of LWE may also be an important factor in assisting the bacteria to multiply in LWE . Later, the growth of some other species of bacteria may inhibit the growth of Pseudomonas , which resulted in a certain decrease in the PS count.…”

Some Characteristics of a Proteolytic Enzyme System of Pseudomonas fluorescensa

“…Furthermore, others (Garibaldi, 1960 ;Feeney and Nagy, 1952) have reported that the growth of some microorganisms in eggs may be retarded because of the iron-binding properties of conalbumin. Recent studies (Hurley et a.l., 1962), however, have shown that marked increases in the viable population of various strains of P. fluorescens can occur in egg white without added iron and without prior adjustment of pH. The lack of iron available for activation of enzyme activity, however, may explain the lack of proteolysis in blended egg white at high levels of viable cells even after extensive periods of incubation.…”

“…In the present study, proteolysis was : a) absent or slight until the level of viable pol%ilation had reached a maximuni (after 5 clays), and b) greater, at the higher temperatures of incubation. Several factors may be directly or indirectly responsible for these differences in results : a) a difference in growth medium (nutrient broth versus tryptone-glucose-meat extract broth) ; the possibility exists that the protein in the growth medium may have tied up iron so that the amount available during the early stages of growth was insufficient; b) differences in substrates and methods of analysis to detect proteolysis, hq~oglobin, spray-dried egg white, and blended fresh egg white versus casein (Peterson and Gunderson, 1960) ; and c) strain differences (Long and Hammer, 1941 ;Vanclerzant and Nelson, 1953 ;Vanderzant, 1957;Hurley et al, 1962). With respect to strain differences, numerous studies with many species of bacteria have shown that certain strains may possess high proteolytic act,ivity, others medium, ancl still others little or none at all.…”