A Competitive Microflora Increases the Resistance of
            <i>Salmonella typhimurium</i>
            to Inimical Processes: Evidence for a Suicide Response

Aldsworth, Timothy G.; Sharman, Rachel; Dodd, Christine E. R.; Stewart, Gordon S. A. B.

doi:10.1128/aem.64.4.1323-1327.1998

Cited by 49 publications

(31 citation statements)

References 22 publications

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“…In the field of food microbiology, specific recovery media and procedures that allow maximal recovery of sublethally injured cells have been developed. A factor that seems to be particularly important during recovery is oxidative stress (Aldsworth et al 1998;Dodd and Aldsworth 2002). Oxidative stress in bacterial cultures is caused by reactive oxygen species (ROS), which include hydrogen peroxide (H 2 O 2 ), the superoxide radical (O À 2 ), the hydroxyl radical (OH°) and singlet oxygen ( 1 O 2 ).…”

Section: Introductionmentioning

confidence: 99%

Source of tryptone in growth medium affects oxidative stress resistance in Escherichia coli

et al. 2004

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Aims: To investigate the influence of the source of tryptone in the growth medium on the resistance of Escherichia coli to various types of oxidative stress. Methods and Results: Cultures of Escherichia coli MG1655 were grown in Luria-Bertani (LB) medium at 37°C to stationary phase, harvested, and subsequently subjected to various types of oxidative stress. A marked difference in oxidative stress sensitivity was observed depending on the origin of the tryptone in the LB medium used to grow the cultures. Cells harvested from LB containing tryptone from source x (LBx) were more sensitive to inactivation by the superoxide generating compound plumbagin and by t-butyl peroxide, and to growth inhibition by the lactoperoxidase enzyme system, than cells harvested from LB containing tryptone from source y (LBy). By monitoring expression of a panel of stress gene promotors linked to the gfp (green fluorescent protein) gene, and using D2-22 alkaline phosphatase as a probe for disulphide bridge formation from protein sulphydryl groups, it was demonstrated that a greater cytoplasmic oxidative stress existed in cells during growth in LBy than in LBx. Conclusions: Depending on the source of tryptone, bacteria may experience different levels of oxidative stress in tryptone-containing nonselective growth media. Although these levels of oxidative stress are subinhibitory, they may trigger a stress response that makes the bacteria more resistant to a subsequent exposure to a lethal or inhibitory level of oxidative stress. Significance and Impact of the Study: This work highlights the importance of controlling very subtle differences in composition of nonselective growth media in studies on bacterial physiology.

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Section: Introductionmentioning

confidence: 99%

Source of tryptone in growth medium affects oxidative stress resistance in Escherichia coli

et al. 2004

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“…The induction time for RpoS-mediated gene expression was determined as described previously (Aldsworth et al 1998) and the results are recorded in Table 1.…”

Section: Resultsmentioning

confidence: 99%

“…Standardized mid-exponential phase Salm. typhimurium LT2[pSB367] cultures were prepared as previously described (Aldsworth et al 1998) and inoculated into 50 ml volumes of each type of medium to an initial density of 10 5 cfu ml −1 . The cultures were then incubated aerobically at 37°C and 200 rev min −1 in an orbital incubator, and the bioluminescence and optical density at 600 nm were monitored at 30 min intervals using a Turner TD20e luminometer (Turner Designs Inc., Mount View, USA) and Gallenkamp Visi-Spec spectrophotometer, respectively.…”

Section: Detection Of Rpos-mediated Gene Expressionmentioning

confidence: 99%

Induction ofrpoSinSalmonella typhimuriumby nutrient‐poor and depleted media is slower than that achieved by a competitive microflora

Aldsworth

Dodd

Stewart

1999

Letters in Applied Microbiology

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The presence of a viable competitive microflora, at greater than 108 cfu ml−1, is known to advance the induction of RpoS‐mediated gene expression in a sub‐population of Salmonella typhimurium. As starvation is known to induce RpoS, one action of the competitive microflora could be to cause depletion of essential nutrients. The aim of the current experiments was to determine whether this was the case by examining RpoS induction in Salm. typhimurium in reduced nutrient media. RpoS‐mediated gene expression in Salm. typhimurium was not advanced so significantly in ‘conditioned’ or diluted medium as it was in the presence of competitors, which indicates that nutrient depletion was not the responsible mechanism. The effect of a competitive microflora has implications for models of bacterial survival during food processing, as RpoS ultimately regulates both stress resistance and virulence.

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“…Typhimurium cells behaving more like stationary phase cells with respect to enhanced resistance to heat and freeze injury (Duffy et al . 1995; Aldsworth et al . 1998).…”

Section: Discussionmentioning

confidence: 99%

Cell-cell interactions influence resistance and survival of Salmonella serotype Typhimurium to environmental stress

et al. 2003

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Aims: The aim of this work was to study the effects of prolonged nutrient stress on survival, cell interactions and resistance to inimical processes in Salmonella serotype Typhimurium. Methods and Results: Salmonella Typhimurium cells were subjected to prolonged incubation in the stationary phase of growth and the properties of starved cells (old) were investigated with reference to those of exponentiallygrowing cells (young). Competition experiments between old and young cells revealed cell-cell interactions that influenced stationary phase survival and response of the bacterium to heat stress. During prolonged incubation of cells, cycles of resistance and sensitivity to heat stress were identified. Competition experiments between old and young cells revealed that the resistance of young cells to heat increased to levels more like those of stationary phase cells than growing cells. The presence of old cells influenced the phenotype of young cells, possibly by means of cell-cell interactions. There was no evidence for the involvement of any extracellularly-produced factors in this phenomenon, but a requirement that the old competitor cells be viable could be demonstrated. Conclusions: It is proposed that the complex interactions within stationary phase cultures of Salm. Typhimurium may be due to cycles of mutation in concert with an as yet undefined interaction between old cells and growing ones. Significance and Impact of the Study: This study provides evidence for active and diverse responses to nutrient stress within populations of Salm. Typhimurium that promote survival and that may be important for the success of this bacterium as a pathogen.

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A Competitive Microflora Increases the Resistance of Salmonella typhimurium to Inimical Processes: Evidence for a Suicide Response

Cited by 49 publications

References 22 publications

Source of tryptone in growth medium affects oxidative stress resistance in Escherichia coli

Source of tryptone in growth medium affects oxidative stress resistance in Escherichia coli

Induction ofrpoSinSalmonella typhimuriumby nutrient‐poor and depleted media is slower than that achieved by a competitive microflora

Cell-cell interactions influence resistance and survival of Salmonella serotype Typhimurium to environmental stress

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