Food microorganisms and parasites play a critical role in nutrition and dietetics, particularly in Kenya where food safety and public health are major concerns. Understanding the physiology, genetics, and biochemical behavior of these organisms helps nutrition professionals prevent foodborne diseases and improve dietary outcomes. This chapter examines the detailed anatomy and physiology of microorganisms and parasites relevant to food microbiology and parasitology, equipping students with the knowledge to identify, control, and manage these agents in food environments.

2.1 Microorganisms' Anatomy and Physiology

Microorganisms relevant to nutrition and dietetics include bacteria, fungi, viruses, and protozoa, many of which influence food quality and safety. In Kenya’s food sector, from informal markets to hospitals, knowledge of their structure and function aids in designing effective interventions against contamination and spoilage. This section explores their cellular anatomy and physiological processes that affect their survival, growth, and pathogenicity.

2.1.1 Anatomy of Microorganisms

The anatomy of microorganisms determines their interaction with food substrates and host organisms. Their structural components provide protection, enable reproduction, and facilitate nutrient absorption.

Cellular Structure and Organization

Most microorganisms are unicellular with simple organization. Bacteria have a cell wall composed of peptidoglycan, differentiating Gram-positive and Gram-negative types, which influences their susceptibility to disinfectants. Fungi possess chitin in their cell walls, offering resistance to environmental stress. Viruses lack cellular structure but have a protein coat (capsid) enclosing genetic material. Protozoa have complex cellular organelles enabling motility and feeding.

Cell Wall and Membrane Composition

The cell wall provides shape and mechanical support. In bacteria, the thickness and chemical composition determine staining properties and pathogenic potential. Fungal cell walls contain glucans and chitin, aiding in adherence to food surfaces. The cytoplasmic membrane controls nutrient uptake and waste expulsion, critical for microbial metabolism.

Genetic Material and Reproduction Structures

Microorganisms carry DNA or RNA as genetic material. Bacteria have circular DNA and may possess plasmids carrying antibiotic resistance genes. Viruses contain either DNA or RNA genomes, which hijack host machinery for replication. Some microorganisms form specialized reproductive structures: bacterial endospores enable survival under adverse conditions, while fungal spores facilitate dispersal.

Appendages and Motility

Flagella, pili, and fimbriae are appendages that assist in movement, attachment to surfaces, and exchange of genetic material in bacteria. Motility enhances colonization of food matrices and host tissues, influencing infection risk. Protozoa use cilia or flagella for locomotion, impacting their distribution in contaminated food or water.

2.1.2 Physiology of Microorganisms

Microbial physiology explains how these organisms metabolize nutrients, reproduce, and respond to environmental conditions, directly affecting food safety and spoilage in Kenyan contexts.

Metabolic Pathways and Energy Production

Microorganisms utilize diverse metabolic pathways including aerobic respiration, anaerobic respiration, and fermentation. For example, lactic acid bacteria ferment carbohydrates producing acids that preserve fermented foods like Kenyan mursik. Metabolic flexibility allows survival in varied food environments.

Growth Requirements and Environmental Adaptations

Microbial growth depends on factors such as temperature, pH, oxygen availability, and moisture. Psychrotrophic bacteria spoil refrigerated foods, while thermophiles survive cooking temperatures. Acid-tolerant microbes thrive in fermented foods. Understanding these adaptations informs food storage and processing protocols in hospitals and markets.

Enzyme Production and Biochemical Activities

Microorganisms produce enzymes like proteases, lipases, and amylases that degrade food components, impacting texture and flavor. Pathogenic bacteria produce toxins and enzymes that damage host tissues, contributing to foodborne illnesses. Enzymatic profiles aid in identifying microbial species in clinical nutrition labs.

Genetic Regulation and Mutation

Microbial genes regulate physiological responses such as sporulation, biofilm formation, and antibiotic resistance. Spontaneous mutations and horizontal gene transfer contribute to microbial evolution, complicating infection control. Monitoring genetic changes in pathogens like Salmonella helps Kenyan clinics adapt treatment strategies.

Chapter Summary

This chapter explored the anatomy and physiology of microorganisms, detailing their shapes, arrangements, cell cytology, and specific structures such as sporulation and cell arrangements like cocci, bacillus, and spiral chains. It also examined physiological aspects including metabolic processes, growth and reproduction, cell structure and function, adaptation mechanisms, genome structure, horizontal gene transfer, mutation, evolution, and genetic manipulation. The anatomy and physiology of parasites were similarly covered, focusing on their shapes, arrangements, metabolic activities, growth patterns, cell functions, and adaptation strategies. Factors influencing the growth and activity of food microorganisms and parasites were analyzed, distinguishing between intrinsic factors like nutrient content, water activity, pH, antimicrobial substances, and biological structures, and extrinsic factors such as temperature, oxygen concentration, and relative humidity. The chapter further explained the growth patterns of microorganisms and parasites through the stages of microbial growth and the microbial growth curve. Finally, the Gram staining method was discussed as a key technique for identifying and understanding microorganisms involved in food fermentation processes.