Conventional and Novel Rapid Methods for Detection and Enumeration of Microorganisms

Microbiological analysis of food traditionally involves examination of a representative sample for the presence, numbers, and types of microorganisms and/or their products, and is necessary to assess safety, spoilage, quality, suitability, and shelf-life of food. Conventional methods for the detection, isolation, and enumeration of foodborne microorganisms mostly rely on the cultural methods involving growth of microorganisms. Identification and characterization of spoilage or pathogenic microorganisms is based on enrichment-serology involving pre- and selective enrichment, selective and differential plating, confirmation, and strain typing. Conventional methods which are usually simple, reliable, and well-established are often regarded as the “Gold standard”. However, they are labor and material intensive, imprecise, time-consuming, retrospective, and often subjective in nature. During the past 40 years, advances in the areas of immunology, molecular biology, computer science, miniaturization, and automation have resulted in the development of many microbiological methods for rapid detection, enumeration, and characterization of foodborne microorganisms, especially emerging pathogens. These methods include modified conventional methods, microscopy- based methods, immunology-based methods, nucleic acid-based methods, molecular methods, and biosensors, and microarray-based methods. More recently, genomic-based methods for characterization of pathogens have been used by the regulatory agencies for investigating foodborne illness outbreaks and recalls of food contaminated with pathogens such as Salmonella and Listeria. These improved diagnostic technologies reduce the total time needed to detect, isolate, enumerate, identify, and characterize pathogenic microorganisms. While the rapid methods are labor- and time saving and yield accurate results with high degree of sensitivity and specificity, they require specific and often proprietary material, consumables, equipment, software, and trained analysts. In this chapter, the conventional and rapid methods used today in food microbiology are discussed.