The effect of sodium chloride concentration and pH on the growth of Salmonella typhimurium colonies on solid medium

Abstract

The growth of Salmonella typhimurium colonies on a model food system (agar solidified culture medium) was followed. Colony radius, determined using computer image analysis (IA) techniques, and viable cell number per colony were measured as indices of colony growth, and the effect of [NaCl] (0.5-3.5% (w/v)) and pH (7.0-5.0) on colony growth at 30 degrees C was observed; colonies were point inoculated from serial dilutions. Colony growth (between 13 and 26 h after inoculation) was linear when expressed in terms of radius, and exponential when expressed in terms of viable cell number per colony. Overall, both increasing the [NaCl] and decreasing the pH had little effect on colony growth, other than to delay the onset of linear radial growth. Initial specific growth rate (mu) ranged from 0.73 to 0.87 h-1. Thin films of agar medium on microscope slides allowed the growth of microcolonies to be observed after just 4 h incubation. A greater understanding of the growth kinetics of bacterial colonies, and the effects of environment on such data, may enable better control of foodborne bacterial pathogens, and consequently an improvement in food product safety.

Influence of a gel microstructure as modified by gelatin concentration on Listeria innocua growth

“…Katsaras and Leistner (1991) also studied the development of bacteria in fermented sausages. Measurements in or on food model experimental systems have included agar gels (Cooper, Dean, & Hinshelwood, 1968;McKay & Peters, 1995;Mitchell & Wimpenny, 1997;Stecchini, Del Torre, Donda, & Maltini, 2000), gelatin gels (Brocklehurst, Mitchell, & Smith, 1997; and dextran solutions (Hills, Buff, Wright, Sutcliffe, & Ridge, 2001). It has been reported that bacterial growth occurs as discrete colonies in gels and gelled regions of food (Dodd, 1990;Dodd & Waites, 1991;Wimpenny et al, 1995).…”

Modeling Surface Growth of Escherichia coli on Agar Plates

“…Here, the substances needed for microbial growth such as nutrients and water passed through the membrane from the agar plate to cells. Some investigators inoculated bacterial cells directly on the surface of an agar plate (2,21,24). The membrane filter method has several technical advantages.…”

A simple mathematical model that describes the growth of the area and the number of total and viable cells in yeast colonies

“…The proportionality factor, C s (cell‐surface coefficient), was calculated as described in , and its value for each species was 5·71·10 6 ± 1·48·10 5 for S. cerevisiae , 5·20·10 6 ± 1·25·10 5 for Debaryomyces fabryi , 8·22·10 6 ± 3·85·10 5 for Rhodotorula glutinis and 2·26·10 6 ± 9·44·10 4 for Zygosaccharomyces rouxii , in cells mm −2 . Several types of equations, relating the logarithm of the number of cells and the area or radius of the colony, have been published for bacteria (McKay and Peters ; Harrison et al . ; Guillier et al .…”

“…More complex descriptions of the early development of colonies were published, mainly for bacteria (Palumbo et al . ; Reyrolle and Letellier ; Lewis and Wimpenny ; McKay and Peters ; Panikov et al . ; Theys et al .…”