8: Microbiology and Immunology

CHAPTER 8 Microbiology and Immunology


Microorganisms are life forms that normally CANNOT be seen with the unaided human eye. Possess characteristics common to ALL cellular life in terms of physiology, morphology, reproduction. Inhabit MOST niches of environment. Normal inhabitants of human body (normal flora). A medically IMPORTANT microorganism is one that inhabits human host and is considered a pathogen (causes disease).

Microbiology Classification

Microbiology spectrum includes prokaryotes, eukaryotes, viruses. Classification of prokaryotes and eukaryotes employs Latin binomial system of genus and species. Ultrastructures have important MAIN differences.

Microbial Metabolism

Microbial metabolism includes sum total of all biochemical reactions that occur in the cell.

See Chapter 3, Anatomy, Biochemistry, and Physiology: body metabolism.
G. Respiration: energy-efficient process that results in production of 38 ATPs from complete oxidation of 1 glucose molecule.

1. Can be either aerobic or anaerobic process:

Microbial Observation

Observation of microorganisms may be either macroscopic or microscopic, depending on total number of organisms.

Specimen Preparation and Staining

Specimens MUST be prepared and then stained to be seen under light microscope because refractive index of MOST organisms is clear. Basic dyes (e.g., crystal violet, methylene blue, safranin) are positively charged and combine with negatively charged cell constituents. Acidic dyes (e.g., eosin, nigrosin, basic fuchsin) possess negative charge and combine with positively charged cell components.

Bacterial (Prokaryotic) Structure and Function

Small bacteria possess variety of shapes and sizes and internal or external structures that aid in survival and are useful in identification of different bacteria. Survival is KEY to involvement with infectious processes.

B. Cellular ultrastructure:

4. Cell surface structures external to the cell wall:

C. Chemical differences in cell wall structure between gram-positive and gram-negative bacteria:

Bacterial Growth and Nutrition

Bacterial growth is the increase in the numbers of bacterial cells by binary fission. Growth is influenced by the physical environment and the availability of essential nutrients. This is important NOT only in pathogenesis of systemic infections but also with development of infectious oral disease (periodontal disease and caries) and its MAIN etiological factor, dental biofilm (dental plaque).

Table 8-1 Microbial interactions

Term Microorganism Host
Symbiosis Benefits Benefits
Commensalism Benefits Benign
Parasitism Benefits Benign or harmed
Pathogenesis Benefits Harmed


Microorganisms generally MUST breach host defense barriers to initiate disease-causing reactions and transfer to new hosts, whether it involves bacteria or viruses. EXCEPTION is transmission by ingestion of preformed microbial (bacterial) toxin that can cause toxemia (poison in the bloodstream) (see later discussion). There are many overlaps between the routes of transmission of infectious materials, since the overwhelming goal of the microorganism is to survive at ANY means; there are also nonspecfic and specific host defenses.

Each route of transmission is discussed here with the MOST common examples of infectious disease that have practical association with major risks for exposure in the dental setting. Risk factors for NOT achieving oral health are also listed when involved. Infection control protocol and standard precautions to prevent transmission are discussed later.

Bacterial Infections

Many infections are bacterial in origin, but many have vaccinations developed against them or are sensitive to antibiotics and other infection control procedures. However, resistant strains are now a developing problem in healthcare. See later discussion on antibiotics.

See Chapters 6, General and Oral Pathology: oral infections, infectious peptic ulcers; 9, Pharmacology: antibiotic premedication patient; 17, Community Oral Health: epidemiology.
B. Tuberculosis (TB): caused by Mycobacterium tuberculosis transmitted by respiratory route (droplets produced by coughing).


Sex image Male image Female The patient presents at a walk-in medical and dental clinic with weight loss, fever, oral sore. A sputum smear shows the presence of acid-fast bacilli. A chest radiograph shows evidence of pulmonary lesions. Two days later, a test the patient took on his skin is determined to be positive; however, he says he has never received any vaccinations since he was a baby.
Height 5′10″
Weight 140 LBS
BP 98/67
Chief Complaint “I am coughing all the time now.”
Medical History

Current Medications None Social History

Bacterial Toxins

Some bacteria may cause disease in humans because of toxic (poisonous) properties present in protein molecules (toxins), which they carry and release, producing a toxemia. Disease from toxin exposure may NOT require bacterial replication in the body, because in some cases exposure to the toxin alone is sufficient.

Jan 1, 2015 | Posted by in Dental Hygiene | Comments Off on 8: Microbiology and Immunology
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