Info

20 40 0 3 6 9 10 12 14 (b) Injury (min) Repair (h) Fig. 7.1 Behavior of Listeria monocytogenes (Scott A) after exposure to 100 ppm NaNO2 for 40 min (98.5 injury) and after enrichment with (a) LRB ( ) or (b) UVM ( ) plated on ( ) TP A and (---) TP AN (from Ngutter and Donnelly, 2003). (Reprinted with permission from Journal of Food Protection. Copyright held by the International Association for Food Protection, Des Moines, Iowa, USA.) use of selective agents. The selective agents added into...

T

Stress-adaptation and cross-protection D-value of stress-adapted cells challenged against single or multiple stresses Fig. 6.1 Examples of methods to detect stress adaptation and cross-protective responses at different levels of gene expression in microorganisms. (Adapted from Yousef and Courtney, 6.6.1 Detection of stress-response genes Detection of genes encoding for proteins involved in stress adaptation could be used to predict the capacity of microorganisms to respond to stress, as well as...

Pathogenicity and virulence

Horizontally transferred DNA has contributed significantly to both pathogenicity and virulence, and genome analyses are aiding our understanding of these developments. For example, the sequences of the genomes of two strains of O157 H7 Escherichia coli have identified the existence of a large number of insertions compared with the genome of E. coli K12 (Hayashi et al., 2001 Perna et al., 2001). The basic gene order of the genomes of the O157 H7 and K12 organisms is conserved and the two...

Types of microbial stress adaptation

The mechanisms of bacterial defense against adverse environmental conditions can be divided into two classes, limited and multiple adaptive responses (De Angelis and Gobbetti, 2004). A limited or specific adaptive response results from microbial exposure to a sublethal dose of a physical, chemical or biological stress, which protects cells against subsequent lethal treatment with the same stress (De Angelis and Gobbetti, 2004 Sanders et al., 1999). A multiple adaptive response, also known as...

I

Fig. 1.1 The traditional deductive cycle of knowledge and the hypothesis generation different biological systems or even between different states of a system may be useful in understanding cellular processes, even when a complete knowledge of the genetic make-up of the system is not available. In this regard, fingerprinting approaches are discussed that provide proteomic and metabolomic 'snapshots' and offer potential for rapid assessment of biological systems at the functional level. Although...

Factors affecting virulence expression

Even before a foodborne pathogen adheres to its target host tissue, it begins to sense a variety of signals that indicate to the bacterium that it has entered a host environment. The signals induce many changes in bacterial gene expression, including changes that prepare the bacterium to survive host-associated stress conditions, and changes that begin the infectious processes. Some of these signals are well known and commonly studied, but many of the factors that influence stress response and...

Introduction heterogeneity in cellular response to stress

Although in an exponentially growing bacterial culture there is an assumption of homogeneity, in fact cells are growing and dividing in a non-synchronous manner. This heterogeneity in expressed phenotype may become vital when cells are challenged with a stress condition many cells within the population may die but a small proportion will survive because their exact physiological conditions at the time of exposure fitted them for survival. That such survivors show only transient physiological...

Detecting and quantifying crossprotection

There are many approaches to detect and quantify stress adaptation, which vary depending on the goal of the study and the stress-induced molecules monitored (Fig. 6.1). Improvements in analytical methods have made it possible to study physiological changes during adaptation of the microbial cells to stress. Genome comparison, in microorganisms in which the genome has been well characterized, permits the identification of stress-related genes expression of these genes can be determined primarily...

Bioinformatics and in silico approaches

The availability of experimental data on proteomes and metabolomes, albeit in partial formats, enables the structuring of the data for future mining of information. The science of archiving such data into databases (Table 1.1), after proper curation, and that of retrieval of these data, forms the basis of the field of bioinformatics. Several in silico approaches have been developed and are increasingly appearing in the literature for mining the vast amount of information that is currently...

Future trends

There is a drive to direct significant analytical efforts towards capturing changes in proteomes and the metabolomes, thanks to an increasing realization that not all transcribed genes contribute to cell function and that cellular activities are mediated by processes beyond transcription. Current analytical efforts are more focused on unravelling the mysteries of the proteome. Even here, several challenges remain to be surmounted with respect to increasing the number of proteins detected per...

Predicting and controlling pathogenicity

Predicting pathogenicity is fraught with uncertainty, but investigations of changes in pathogens over time allow certain trends to be recognized. Understanding the molecular mechanisms that drive the capacity of bacteria to adapt and change, and understanding how bacteria benefit from increasing virulence are critical aspects of approaches to predicting and controlling pathogenicity. Gaining a better understanding of circumstances that are mutually beneficial to pathogen and host is one...

Contents

Contributor contact details Introduction Part I Understanding virulence, stress response and resistance mechanisms 1 Understanding the behaviour of pathogenic cells proteome and metabolome analyses S. Vaidyanathan and R. Goodacre, The University of Manchester, UK 1.2 Rationale behind analysing proteomes and metabolomes 1.3 Strategies for proteome analyses 1.5 Proteomic and metabolomic fingerprinting and footprinting 1.6 Bioinformatics and in silico approaches 1.7 Applications in understanding...

Genetic exchange and the development of pathogenicity

The genetic changes that result in pathogenicity or increased virulence fall into one of two categories, namely, changes in existing bacterial DNA and acquisition of new DNA from other microorganisms. Changes in the bacterium's DNA typically result in small changes that accumulate over a long period of time, although recombination events can sometimes cause large changes to occur. Mutations are highly significant in bacteria because their high numbers and short generation times allow for...

Introduction

As discussed in other chapters, the behaviour of microbial populations (growth, survival or decline) is determined by the effects of the physicochemical environment in the food (e.g. temperature, pH, water activity) both in terms of those conditions at any particular time and also the sequences and rates of change of environmental conditions experienced by the microbial cells. It would be of immense practical value to be able to predict the effect of environmental conditions in foods on the...

Conclusions

In this chapter, some of the main techniques currently used in predictive microbiology are discussed. Until recently, studies were focused mostly on the predictions of the bacterial growth rate. As they are usually developed with unstressed cells, growth rate models do not take into account the effects of stress on bacterial population growth kinetics. However, as shown in this chapter, the effect of stress on the bacterial lag time can be taken into account through parameters related to the...

Sources of further information and advice

The reference list includes several reviews that will be valuable to readers interested in further information on development of pathogenicity in foodborne pathogens. Additional sources of information are HACKER J, Kaper J B (2002), Pathogenicity Islands & the Evolution of Pathogenic Microbes, Springer-Verlag Telos. Hacker J, Kaper J B, Compans R W, Cooper M , Ito Y, Koprowski H, Melchers, F, OLDSTONE M, OLSNES, S, POTTER M (2002), Pathogenicity Islands & the Evolution of Pathogenic...

References

DOORES, S. (1999) Food safety Current status and future needs. A report from the American Academy of Microbiology. 4 March 2005. HELMS, M., Vastrup, P., Gerner-Scmidt, P. AND M0LBAK, K. (2003) Short and long term mortality associated with foodborne bacterial gastrointestinal infections registry based study. British Medical Journal 326, 357-360. MEAD, P.S., Slutsker, L., Dietz, V., McCaig, L.F., Bresee, J.S., SHAPIRO, C., Griffin, P.M. AND TAUXE, R.V. (1999) Food related illness and death in the...

Chapter

Dr Christine Dodd School of Biosciences University of Nottingham Sutton Bonington Campus Loughborough LE12 5RD UK email christine.dodd nottingham.ac.uk Professor Ahmed E. Yousef* Department of Food Science and Technology Ohio State University 2015 Fyffe Road Columbus OH 43210 USA Donnelly Department of Nutrition and Food University of Vermont Burlington Vermont 05405 USA email David.Nyachuba uvm.edu email Catherine.Donnelly uvm.edu

Cellular stage of growth and bacterial resistance

In E. coli, entry into the stationary phase of growth is accompanied by a host of cellular changes. Cells become shorter and rounder, the mode of metabolism alters, there are changes in membrane and cell wall structure, and cells show increased resistance to a number of stresses including oxidative, near-UV irradiation, acid and osmotic stress and starvation. Central to these changes is the expression of a central regulator of stationary phase gene expression, the sigma factor os or RpoS....

Impact of sublethal injury on recovery of foodborne pathogens

Sublethal injury has been reported for many of the bacteria of interest to the food microbiologist including L. monocytogenes, Salmonella spp., Campylobacter spp., E. coli, Clostridium spp., Staph. aureus, B. cereus, Vibrio spp., and Aero-monas hydrophila (Ray and Adams, 1984 Palumbo, 1986 Donnelly, 2002 Ngutter and Donnelly, 2003). More sensitive detection and or recovery methods need to be developed and continuously refined to ensure safety of food products that undergo processing treatments....

Microbial stress adaptation and crossprotection

Microbial cells sense stress (e.g. disruption of ribosomes as a result of heat or changes in cell membrane fluidity during cold shock), and this triggers protective responses against the sensed deleterious conditions. These responses involve physiological adaptations, which counterbalance stress damage and allow the cells to continue their growth and ensure their survival. Microorganisms also respond to stress induced by inherent physiological change. Entry into the stationary phase, for...

Blocking infection

Although prevention of foodborne disease is preferable to treating it, we are still far from achieving this admirable goal. Furthermore, resistance to the frontline antibiotics is spreading among foodborne pathogens, making treatment of infections more difficult (McDermott et al., 2002 White et al., 2002). Continued research into prevention and treatment strategies for foodborne pathogens is, thus, a necessity. Some of the alternative strategies to blocking infection being pursued include the...

Pathogenic cell adhesion and invasion 431 Adhesion

Just as the human host has evolved multiple mechanisms to prevent infection by pathogenic microorganisms, the microorganisms themselves have evolved diverse and effective mechanisms that thwart their host's defense mechanisms to enable successful infection. As previously mentioned, for example, many bacteria have evolved stress response systems that enable them to survive highly acidic conditions such as those encountered during passage through the human stomach. After reaching the intestine,...

Primary models

2.3.1 Dynamics of bacterial population growth Dynamics of a bacterial population of size x as a function of time can be seen as a succession of three phases (Fig. 2.1) 1. A lag phase which is associated with the physiological adaptation of the cells to their new environment, prior to growth. 2. An exponential growth phase where the logarithm of the bacterial population increases linearly with time. The slope of this linear portion, when the natural logarithm of the bacterial concentration is...

Processing conditions producing sublethal injury

Foods and food ingredients may be subjected to a variety of processes to achieve preservation against microbiological spoilage and pathogenic microorganisms or toxins. The treatments may result in viable microorganisms that are physiologically deficient or injured because of the stress to which the cells have been subjected Ray and Adams, 1984 Budu-Amoako et al., 1992 . Concern has been expressed about the ability of heat-injured foodborne pathogens to resuscitate during processing treatments,...

Host defense mechanisms and pathogen survival strategies

4.2.1 Non-specific human host defense mechanisms There are multiple human host defense mechanisms acting all along the human gastrointestinal tract that help prevent infection by foodborne bacterial pathogens. These include non-specific defenses against all bacteria as well as defenses specific to particular pathogens that are part of an adaptive immune response. Some of the body's non-specific defenses include the acidic pH and proteolytic enzymes in the stomach, detergents and flushing action...

Woodhead Publishing Limited

Published by Woodhead Publishing Limited, Abington Hall, Abington, Published in North America by CRC Press LLC, 6000 Broken Sound Parkway, NW, Suite 300, Boca Raton, FL 33487, USA First published 2005, Woodhead Publishing Ltd and CRC Press LLC The authors have asserted their moral rights. This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. Reasonable efforts have been made to publish...