By: Aditi Rungta *
The journey of food microbiology initially started with the discovery of canning by Nicolas Appert in 1810 followed by Louis Pasteur’s conclusive demonstration of the relation between food spoilage and microorganisms, some 50 years later, now known as Pasteurisation. This led to a cascade of events which ultimately established the food microbiology as we know of today. Food is the source of nutrients for microorganisms which makes it vulnerable to spoilage and also may have an impact on the health of the person ingesting spoilt food. Food microbiology is dynamic and has evolved a lot over the past 200 years and also various new technologies have emerged. Not only the technology has undergone evolution, but the microorganisms have become deadlier and more resistant. The emergence of these microorganisms such as: E. Coli O157H7 (Shiga toxin producing strain); Vibrio vulnificus; Cyclospora cayetanensis; etc. leads to a need for rapid detection of these food borne pathogens to prevent outbreaks.
Advancements in Microbiology
There have been a lot of advancements in the areas of isolation, detection and enumeration of microorganisms. When we talk about the area of sample preparation for any microbiological experiments Stomacher and Pulsifiers, which homogenize the samples inside a sterile disposable bag, are the most widely used instruments. Dilution is another tedious and laborious task to be done after sample preparation. Gravimetric diluters which inject the appropriate amount of diluents in the samples are available for this purpose. Spiral Plating Systems are being increasingly employed for plating a fixed amount of sample on solidified agar plates for determination of total viable counts.
Identification and Detection of Microorganisms
Detection Kits: For identification and detection of microorganisms, scientists have been working on the development of miniaturised kits to reduce the volumes being used. One of the most successful detection kits being used is the VITEK kits which comprise of 30 tiny wells in which reagents are added. The addition of culture changes colour and the colour scheme can be used for identification of the culture. Several such detection kits have been developed for the detection of specific microorganisms.
Immunology: This is an upcoming field using antigen-antibody reactions as a microbial detection technique. Any antigen associated with microorganisms when introduced into an animal’s body generates antibodies which are isolated from them. This forms the basis for immunological tests. Sandwiched ELISA is the most commonly used test.
Lateral Flow Technology: It is another technology being used to detect food borne pathogens by incubating the food overnight which changes colour on detecting the presence of any pathogenic microorganism.
Instrumental Analysis: Instruments are also being used to analyse microbial growth kinetics such as pH, ATP changes, turbidity, colour etc. of a microbial population. These parameters are directly related to the viable cell count which makes the detection easier. Liquid and semi-solid samples can be analysed in such a way. The detection time will depend on the growth rate of microorganisms.
DNA Bar-coding System: This can also be used for detection of the kind of microorganisms contaminating the food. This comprises of a 100-1000 base pair (bp) long DNA fragment representative of the microorganism which is amplified using Polymerase Chain Reaction and is matched with the DNA fragment extracted from the food.
Biosensor: Biosensor is a group of biological molecules attached to a signal recognition material. When the analyte comes in contact with the biosensor a signal is generated which can be detected and reported in an instrument. Sometimes the whole cell can be used as a biosensor to recognise toxins, pathogens, carbohydrates, etc. Whole cells are good alternative biosensors as compared to enzymes, as they are easy to maintain and have a low cost. Electrochemical and optical techniques can be used to detect signals generated by the biosensor.
Nanotechnology: Nanotechnology comprises the study, design, creation, synthesis, manipulation, and application of materials and devices usually at a nanoscale. The nanotechnology is a promising approach in the field of food microbiology; e.g. the use of nano sensors in the food production facility or food packaging. The nano sensors are used to detect/control internal and external conditions of food such as the presence of pathogenic microorganisms in food. Combining biology and nanotechnology can only lead to an enhancement in the sensitivity of detection. A bio analytical nanosensor can detect one pathogenic microorganism, even before it starts to multiply. This can be even used to prevent the growth of that pathogen in the food. Thus, nanotechnology offers a very cheap and effective alternative to the tedious, old techniques which have been used for a long time.
As there are several new deadly strains of microorganisms being discovered every day, the techniques of detection are also becoming very advanced. There will be a time soon when consumers will have their very own personal kits for detection of pathogens in their food decreasing the risk of food poisoning and toxicity. It can be said that the field of food microbiology has come a long way and has a tremendous potential for growth further in making the food safe for consumption.
* Placement Coordinator, Institute of Chemical Technology, Mumbai