Oral Microbiology and Immunology

Richard J. Lamont, George N. Hajishengallis, Hyun (Michel) Koo, Howard F. Jenkinson, Richard J. Lamont, George N. Hajishengallis, Hyun (Michel) Koo, Howard F. Jenkinson

• Publisher: ASM Press
• Year: 2019
• ISBN:
  9781683672906
• Edition: 3
• Topic: Médecine
• Subtopic: Microbiologie et parasitologie médicales

The field of oral microbiology has seen fundamental conceptual changes in recent years. Microbial communities are now seen as the fundamental etiological agent in oral diseases through their interface with host inflammatory responses. Study of structured microbial communities has increased our understanding of the roles of each member in the pathogenesis of oral diseases, principles that apply to both periodontitis and dental caries.

Against this backdrop, the third edition of Oral Microbiology and Immunology has been substantially expanded and rewritten by an international team of authors and editors. Featured in the current edition are:

• links between oral infections and systemic disease
• revised and updated overview of the role of the immune system in oral infections
• thorough discussions of biofilm development and control
• more extensive illustrations and Key Points for student understanding

Graduate students, researchers, and clinicians as well as students will find this new edition valuable in study and practice. The field of oral microbiology has seen fundamental conceptual changes in recent years. Microbial communities are now seen as the fundamental etiological agent in oral diseases through their interface with host inflammatory responses. Study of structured microbial communities has increased our understanding of the roles of each member in the pathogenesis of oral diseases, principles that apply to both periodontitis and dental caries.

SECTION I

GENERAL PRINCIPLES OF ORAL MICROBIOLOGY AND IMMUNOLOGY

1 General Microbiology

2 The Immune System and Its Functions

3 The Oral Environment

4 Isolation, Classification, and Identification of Oral Bacteria

5 Oral Microbial Ecology

6 Oral Microbial Physiology

7 Genetics and Molecular Biology of Oral Microorganisms

8 Applied Molecular Biology and the Oral Microbes

9 Population Genetics of Oral Bacteria

10 Immunology of the Oral Cavity

1

General Microbiology

HOWARD F. JENKINSON

Introduction

Biological Classification Scheme

Bacterial Classification

Bacterial Architecture

Membranes

Cell Wall Peptidoglycan

Lipopolysaccharides

Lipoteichoic Acids

Other Important Components Produced by Bacteria

Capsule

Fimbriae and Pili

Fibrillar Layers

Flagella

Vesicles

Surface Layers

Endospores

Genetic Organization in Bacteria

The Bacterial Chromosome

Chromosome Replication in Bacteria

Gene Transfer in Bacteria

Bacterial Growth and Nutrition

Growth

Nutrient Acquisition

Environmental Sensing

Secretion

Introduction to Fundamental Concepts in Oral Microbial Ecology

Microbial Biofilms

Microbial Cooperativity

Microbial Antagonism

Polymicrobial Communities

Ecology of the Oral Microbiota and Development of Oral Diseases

KEY POINTS

INTRODUCTION

Antonie van Leeuwenhoek was a Dutch scientist who made the first microscopic observations of bacteria and microorganisms, which he named “animalcules.” In 1683, van Leeuwenhoek scraped material from his own teeth, describing “a little white matter, which is as thick as if ’twere batter.” He wrote, “I then most always saw…that in the said matter there were many very little living animalcules.” When observing a sample from an old man who had not cleaned his teeth, van Leeuwenhoek found “an unbelievably great company of living animalcules, a-swimming more nimbly than any I had ever seen up to this time.” These observations of dental plaque were among the first recorded sightings of live bacteria. Nowadays, we appreciate that the human oral cavity is a highly dynamic ecosystem that supports the life of a tremendous number of very diverse microorganisms. In fact, there are roughly a million bacteria present per milliliter of saliva. These bacteria have been shed from the surfaces of hard or soft tissues of the oral cavity and nasopharynx, on which they normally grow, and they multiply in retained pools of saliva. The use of conventional microbiological techniques, coupled with new more sophisticated and sensitive technologies in molecular biology, has helped gain an appreciation for the enormous diversity in the oral microbiota. Recent estimates suggest that there are 700 to 1,000 different species of bacteria that may be found in the oral cavity. Better understanding of the genetics, physiology, and biochemistry of the oral microbiota has revealed that the normal microbial colonizers are a critical component in oral health, and that oral ecology plays a major role in the development of diseases.

To comprehend how oral microorganisms persist and, under certain circumstances, cause disease, it is necessary to have knowledge of the structure, function, and biological activities of the oral microbiota. Why? Recognition of the structural components of a microorganism is important because determinants on the cell surface, such as adhesin proteins, dictate which tissues the organisms can colonize. In addition, many components that contribute to the ability of the organisms to cause disease and damage host tissues, such as enzymes and polysaccharides, are located on the cell surface. It is also important to have an appreciation for the wide variety of biological and biochemical activities that oral microorganisms possess. The metabolic capabilities of the cells, such as their abilities to degrade the substances secreted into saliva and ingested in the diet, are of major importance in oral health and disease. How effectively microorganisms utilize the available nutrients determines whether the organisms will establish and compete effectively at particular sites in the mouth. Moreover, the end products of metabolism of these nutrients, such as organic acids, have harmful effects on the tissues of the mouth. The following sections of this chapter highlight key features of the classification, structure, and functions of bacteria. The aim is to provide a foundation for the more detailed descriptions of oral microbes, oral microbial ecology, growth of the oral microbiota, and the virulence mechanisms used by oral pathogens that are presented in the following chapters.

BIOLOGICAL CLASSIFICATION SCHEME

The system that is commonly used for classification of life on Earth is derived from that developed by Carl Linnaeus in the 18th century. This classification scheme, originally intended for systematics of plants and animals, was useful in accommodating new forms of life as they were discovered through the centuries. Today, life on Earth is divided into three primary domains: Eukarya, which are eukaryotes, and Bacteria and Archaea, which are prokaryotes, the oldest and most diverse forms of life on the planet (Table 1). Archaea, sometimes referred to as archaebacteria, differ genetically and metabolically from true bacteria. In fact, archaea are considered to bridge a major gap in evolution between prokaryotes and eukaryotes. Prokaryotes are distinguished from eukaryotes most notably by lack of a nuclear membrane, which in eukaryotes separates the chromosomal DNA of the cell from the cytoplasmic contents. Eukaryotes also possess a variety of organelles and subcellular structures, such as mitochondria, the Golgi apparatus, and the endoplasmic reticulum, that are lacking in prokaryotes. There are other fundamental differences between these two general classes of life, some of which are summarized in Table 1. Among the more notable differences, the transcription of DNA to mRNA and the translation of RNA to protein occur in separate compartments in eukaryotes, but not in prokaryotes.

TABLE 1 General differences between prokaryotes and eukaryotes

Members of each of the domains may be found in the oral cavity, but bacteria form numerically the vast majority of cells present within the oral microbiota. While archaea have been detected in the oral cavity, current indications are that they appear to represent a small minority of the total organisms present on oral soft or hard tissues. Protozoa, which are single-cell eukaryotes, graze on bacteria that are growing on surfaces. Fungi, which are also eukaryotic microorganisms, are often present in the mouth, but generally they are there in low numbers. Some fungi, for example, Candida species, flourish well when there is a restriction of saliva availability or a reduction in immunological competence. Because bacteria comprise the overwhelming majority of oral microorganisms, most of this introductory chapter focuses on bacteria.

BACTERIAL CLASSIFICATION

Most bacteria can be divided into two categories, either Gram positive or Gram negative, based upon a differential staining technique developed by the Danish bacteriologist Christian Gram. The Gram stain reveals a major structural difference between the two groups of bacteria based upon the thickness and degree of cross-linking of their cell wall polymers. Detailed molecular studies have established that this relatively simple staining reaction also discloses a major evolutionary split between two major classes of bacteria. Among the bacteria, there are microorganisms that cannot appropriately be classified on the basis of Gram staining. For example, the agent of tuberculosis, Mycobacterium tuberculosis, has a cell envelope made up of mycolic acids and waxes that do not stain. Instead of Gram staining, mycobacteria can be stained by the Ziehl-Neelsen staining technique, which is also called acid-fast staining. In contrast, Mycoplasma species and closely related organisms are completely devoid of a cell wall. Consequently these organisms are negative in the Gram reaction, even though genetically they are more closely related to Gram-positive bacteria. Gram staining and similar techniques remain useful for bacterial identification, but the phylogenetic relationships (i.e., the evolutionary connections of bacteria) are now based almost exclusively on comparisons of nucleotide and protein sequences of organisms. Chapters 4 and 9 explain in detail many of the techniques used to assign bacteria to species, and they also outline current phylogenetic relationships of the oral microbiota.

One of the most fascinating aspects of microbiology is the tremendous diversity in microbial structure and metabolic capacities and in the environments in which microbes can thrive. In nature, there are bacteria that grow optimally at pH values around 2, designated acidophiles (acid loving), while others will only grow well at pH values near 10 (alkalophiles). Bacteria that can survive acidic conditions, but not necessarily grow under those conditions, are designated aciduric (acid tolerant). Some prokaryotes grow very poorly at temperatures above 15°C (termed psychrophiles), whereas there are other bacteria that thrive at 100°C in hydrothermal vents miles below the surface of the ocean (thermophiles). Some microorganisms can grow with jet fuel or kerosene as the primary carbon and energy source, others create tiny internal magnets to use for directed movement, some emit light, and others detoxify mercury in the environment. A variety of bacteria can corrode metals, and many (e.g., Streptomyces) synthesize products of significant economic importance, such as antibiotics or complex polysaccharides that are used in foods or pharmaceuticals.

Bacteria within and upon the human body outnumber the total cells composing the body by about 10 to 1. The number of bacterial species that colonize humans is fairly low compared to the total number of known bacterial species, and the number that routinely cause disease is substantially smaller still. Interestingly, the oral microbial community is among the most diverse group of organisms colonizing the various environments of a human host. To begin to become familiar with the organisms that comprise the oral microbiota in health and disease, some of the more abundant or significantly important oral microorganisms are listed in Table 2.

TABLE 2 Microorganisms of importance in the oral cavity

BACTERIAL ARCHITECTURE

Most bacterial cells are about 1 to 5 mm across the largest dimension of the cell, although there are some interesting exceptions, including a few unusual marine bacteria that are as large as 100 mm in diameter. A bacterial colony roughly 3 mm in diameter that forms on an agar plate can contain upward of 100 million organisms. Bacteria also come in a wide variety of shapes: coccoid, or spherical; bacillary, or rod shaped; fusiform, or long, thin rods that taper at the ends; helical, or corkscrew shaped; curved; irregular; or a combination of shapes, termed pleomorphic. In addition, many bacteria can form complex, multicellular structures or can differentiate into alternative shapes, for example, spores with clearly distinct func...