Food Safety & Microbial Physiology Group (FSMP)
       
   

 
     
   

 
 
 

We are interested in diverse but interrelated areas in microbiology including food safety, bacterial stress responses and dairy starters. In pursuing all these aspects, we hold the belief that basic knowledge in microbiology is a necessity to better exploit useful microorganisms and eradicate harmful ones. Our research can be categorized into the following disciplines:

Courtesy of Dr. Roy Sleator

  • Food Safety

Our food safety research involves surveillance and characterization of emergent foodborne pathogens. Those include Enterobacter sakazakii, Campylobacter and Arcobacter. While extensive research has been carried out to characterize these food-associated microorganisms in Western food safety/public health laboratories, there is a real need to pursue this work in developing countries.  A prime reason for this is the fact that foods are produced and distributed under different environmental conditions in different countries, which could  be reflected in variable distribution and characteristics of foodborne pathogens in different countries.

We are also interested in the lab on a chip area as to develop nanodevices for the detection of pathogenic bacteria in foods.

  • Bacterial Stress Responses

The study of the behaviour of bacteria under environmental stress is directly related to food safety and fermentation industries given the frequent exposure of bacteria to stressful conditions during food processing and preservation, e.g. heat, salt, low pH, and cold temperatures. The need for pursuing research within this area is highlighted by the recent emergence of pathogens unusually capable of surviving food preservation conditions. Examples include the ability of Escherichia coli O157:H7 to survive acidic conditions and salt tolerance of Listeria monocytogenes, which also increases in numbers on exposure to low temperatures. Equally serious is the ability of a number of foodborne bacteria to tolerate severe stress following their exposure to mildly adverse conditions. This actually coincides with a recent consumers' trend favouring minimally-processed foods produced under minimum preservative conditions, which may enable bacterial adaptation to stress.  The emergence of these phenomena raises the need for more in-depth studies that examine the involvement of cell components in the behaviour of foodborne  bacteria under environmental stress conditions. These studies will improve our understanding of stress adaptation and resistance in bacteria and will enable the development of effective food preservation regimes. Carrying out these studies may also provide better understanding of the mechanisms of human infection by bacteria, which may lead to drug discoveries. This stems from the fact that pathogenic bacteria are exposed to stress conditions during the course of human infection. Successful pathogens are those being able to resist adverse conditions such as low pH in the stomach, high temperature associated with fever and/or osmotic stress provoked by the release of perspiration in the skin infections. It was interesting to note that acid-resistant strains of the pathogen Shigella had lower infectious doses than other acid-sensitive strains of the same pathogen. This was ascribed to the ability of acid-resistant strains to tolerate gastric acidity.

The study of bacterial stress responses is also important for better exploitation of industrial bacteria such as lactic acid bacteria (LAB). During the preparation of fermented foods, LAB may also experience diverse stresses.  For example, during the making of several cheese varieties, milk is fermented by the addition of appropriate LAB “starter” cultures such as Lactococcus. lactis, Streptococcus thermophilus that acidify milk. The resultant curd (coagulum) is progressively heated to elevated temperatures and finally pressed to eliminate moisture. Curd/cheese is also salted by the addition of dry salt (NaCl) or soaking in a  brine solution. Employing these procedures, LAB are thus exposed to acid, heat and osmotic stresses.  Even when LAB are prepared for commercial distribution in the form of lyophilised starter cultures, they encounter freezing and drying stresses.  Developing adaptive strategies to cope with these environmental hardships is therefore essential for LAB to pose their functional characteristics in food fermentation. While LAB have been reported to display stress-adaptive mechanisms to cope with adverse conditions, the regulation of these mechanisms remains to be elucidated. To this end, we are interested in studying the roles of two-component signal transduction systems (see El-Sharoud, 2005: Science Progress 88: 203-228) and ribosome-associated proteins (El-Sharoud, 2004: Science Progress 87:137-152) in regulating stress-responses in LAB.

Examples of stressful situations encountered by LAB. During their passage through the digestive channel, included within fermented foods, LAB are exposed to severe acidity in the stomach and free short fatty acids in the intestine (right figure). LAB are also exposed to acid, heat and osmotic stresses during the cheese-making process (left figure) (El-Sharoud, 2005; Science Progress 88: 203-228).

  • Dairy Starters

We are currently interested in isolating and characterizing lactic acid bacteria (LAB) from traditional Egyptian dairy products. This work is aimed to end up with the selection of LAB strains of improved performance in dairy industries and biotechnological applications. Selection criteria involve metabolic activities and stress-tolerance of isolated LAB strains. We are also interested in characterizing exopolysacchride-producing LAB recovered from traditional dairy products.

 

 

 
Food Safety & Microbial Physiology Group (FSMP)