chapter 18 microbiology copyright 2003, elsevier science (usa). all rights reserved. no part of this...

Chapter 18Microbiology

Chapter 18Microbiology

Copyright 2003, Elsevier Science (USA).

All rights reserved. No part of this product may be reproduced or transmitted in any form or by any means, electronic or mechanical, including input into or storage in any information system, without permission in writing from the publisher.

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Produced in the United States of America

ISBN 0-7216-9770-4

Copyright 2003, Elsevier Science (USA). All rights reserved.

IntroductionIntroduction Microbiology is the study of microorganisms.

Micro means microscopically small, and bio means living organisms.

The dental assistant must understand the nature of the pathogens (disease-producing microorganisms) and how diseases are transmitted to make important decisions regarding infection control products and procedures.

The two major oral diseases, dental caries (decay) and periodontitis are bacterial infections.

Microbiology is the study of microorganisms. Micro means microscopically small, and bio means living organisms.

The dental assistant must understand the nature of the pathogens (disease-producing microorganisms) and how diseases are transmitted to make important decisions regarding infection control products and procedures.

The two major oral diseases, dental caries (decay) and periodontitis are bacterial infections.


Pioneers in MicrobiologyPioneers in Microbiology Aristotle (384–322BC) believed that life arose from

muck, decaying food, warm rain, or even dirty shirts.

Antony van Leeuwenhoek (1632–1723) used a primitive microscope to observe stagnant water, hay infusions, and scrapings from the teeth.

John Tyndall (1820–1893) discovered that some bacteria existed in two forms: a heat stable form and a heat-sensitive form.

John Lister (1827–1912) was the first to recognize the role of airborne microorganisms in postsurgical infections.

Aristotle (384–322BC) believed that life arose from muck, decaying food, warm rain, or even dirty shirts.

Antony van Leeuwenhoek (1632–1723) used a primitive microscope to observe stagnant water, hay infusions, and scrapings from the teeth.

John Tyndall (1820–1893) discovered that some bacteria existed in two forms: a heat stable form and a heat-sensitive form.

John Lister (1827–1912) was the first to recognize the role of airborne microorganisms in postsurgical infections.


Pioneers in Microbiologycont’dPioneers in Microbiologycont’d Robert Koch (1843–1910) developed a two-part

dish for growing bacteria and a technique for isolating pure colonies of bacteria.

Julius Petri (1852–1921): Petri plates, dishes used to isolate bacterial colonies, were named after him.

Louis Pasteur (1822–1895), the Father of Microbiology, developed the process of pasteurization and discovered the first vaccine for the disease, rabies.

• The Pasteur Institute was built in France by the French government in 1888 to honor Louis Pasteur.

Robert Koch (1843–1910) developed a two-part dish for growing bacteria and a technique for isolating pure colonies of bacteria.

Julius Petri (1852–1921): Petri plates, dishes used to isolate bacterial colonies, were named after him.

Louis Pasteur (1822–1895), the Father of Microbiology, developed the process of pasteurization and discovered the first vaccine for the disease, rabies.

• The Pasteur Institute was built in France by the French government in 1888 to honor Louis Pasteur.


Major Groups of MicrorganismsMajor Groups of Microrganisms Bacteria

Algae

Protozoa

Fungi

Viruses

Bacteria

Algae

Protozoa

Fungi

Viruses


BacteriaBacteria

A large group of one-celled microorganisms that vary in shape, size, and arrangement.

Usually, pathogenic bacteria grow best at 98.6˚F (37˚C) in a moist, dark environment.

The skin, respiratory tract, and gastrointestinal tract are inhabited by a great variety of harmless bacteria called normal flora.

An infection occurs when bacteria occurring naturally in one part of the body invade another part of the body and become harmful.

A large group of one-celled microorganisms that vary in shape, size, and arrangement.

Usually, pathogenic bacteria grow best at 98.6˚F (37˚C) in a moist, dark environment.

The skin, respiratory tract, and gastrointestinal tract are inhabited by a great variety of harmless bacteria called normal flora.

An infection occurs when bacteria occurring naturally in one part of the body invade another part of the body and become harmful.


Shapes of BacteriaShapes of Bacteria Spherical (cocci)

• The cocci reproduce by dividing into two.

• The cocci that form chains as they divide are called streptococci.

• The cocci that form irregular groups or clusters are called staphylococci.

Rod-shaped (bacilli) Spiral (spirilla)

Spherical (cocci)

• The cocci reproduce by dividing into two.

• The cocci that form chains as they divide are called streptococci.

• The cocci that form irregular groups or clusters are called staphylococci.

Rod-shaped (bacilli) Spiral (spirilla)


Fig. 18-4 The three basic shapes of bacteria. Fig. 18-4 The three basic shapes of bacteria.

Fig. 18-4Fig. 18-4


Fig. 18-5 Colonies of streptococci growing on the agar medium are diagnostic for strep throat. Fig. 18-5 Colonies of streptococci growing on the agar medium are diagnostic for strep throat.

Fig. 18-5Fig. 18-5


Fig. 18-6 Golden-yellow colonies of Staphylococcus bacteria.Fig. 18-6 Golden-yellow colonies of Staphylococcus bacteria.

Fig. 18.6Fig. 18.6


Gram-Positive and Gram-Negative Bacteria Gram-Positive and Gram-Negative Bacteria Hans Christian Gram (1853-1938) developed a

four-step staining process for separating bacteria into two groups.

Gram staining requires the sequential use of a crystal violet dye, iodine solution, alcohol solution, and a safranin dye.

The bacteria that are stained by the dye are classified as gram-positive. (They appear dark purple under the microscope.)

The bacteria that are not consistently stained are classified as gram-variable (Mycobacterium tuberculosis).

Hans Christian Gram (1853-1938) developed a four-step staining process for separating bacteria into two groups.

Gram staining requires the sequential use of a crystal violet dye, iodine solution, alcohol solution, and a safranin dye.

The bacteria that are stained by the dye are classified as gram-positive. (They appear dark purple under the microscope.)

The bacteria that are not consistently stained are classified as gram-variable (Mycobacterium tuberculosis).


Bacteria’s Need For Oxygen Bacteria’s Need For Oxygen

Aerobes are a variety of bacteria that require oxygen to grow.

Anaerobes are bacteria that grow in the absence of oxygen and are destroyed by oxygen.

Facultative anaerobes are organisms that can grow in either the presence or the absence of oxygen.

Aerobes are a variety of bacteria that require oxygen to grow.

Anaerobes are bacteria that grow in the absence of oxygen and are destroyed by oxygen.

Facultative anaerobes are organisms that can grow in either the presence or the absence of oxygen.


Capsules Capsules Some types of bacteria form a capsule that

forms a protective layer covering the cell wall (Streptococcus mutans).

This type of bacteria are generally virulent (capable of causing serious disease).

The capsule increases their ability to resist the defense mechanisms of the body.

The capsule may also prevent antibiotic agents from having an effect on the bacteria.

Some types of bacteria form a capsule that forms a protective layer covering the cell wall (Streptococcus mutans).

This type of bacteria are generally virulent (capable of causing serious disease).

The capsule increases their ability to resist the defense mechanisms of the body.

The capsule may also prevent antibiotic agents from having an effect on the bacteria.


SporesSpores Some bacteria change into a highly resistant form

called spores. The disease tetanus is an example of a spore-forming bacillus.

Bacteria remain alive in the spore form but are inactive.

Spores represent the most resistant form of life known.

They can survive extremes of heat and dryness and even the presence of disinfectants and radiation.

Harmless spores are used to test the effectiveness of the techniques used to sterilize dental instruments.

Some bacteria change into a highly resistant form called spores. The disease tetanus is an example of a spore-forming bacillus.

Bacteria remain alive in the spore form but are inactive.

Spores represent the most resistant form of life known.

They can survive extremes of heat and dryness and even the presence of disinfectants and radiation.

Harmless spores are used to test the effectiveness of the techniques used to sterilize dental instruments.


Rickettsias Rickettsias

The rickettsias are short, nonmovable rods that normally live in the intestinal tract of insects such as lice, fleas, ticks, and mosquitoes.

They are very small and require host cells in order to reproduce.

The diseases caused by rickettsia are typhus and Rocky Mountain spotted fever.

These diseases are transmitted to humans via the bite of an infected insect.

The rickettsias are short, nonmovable rods that normally live in the intestinal tract of insects such as lice, fleas, ticks, and mosquitoes.

They are very small and require host cells in order to reproduce.

The diseases caused by rickettsia are typhus and Rocky Mountain spotted fever.

These diseases are transmitted to humans via the bite of an infected insect.


Chlamydias Chlamydias

The chlamydias are the smallest of all bacteria.

They are important because of their role in sexually transmitted diseases.

Chlamydias are also responsible for the human disease known as trachoma, a leading cause of blindness in the world.

They also cause disease in some birds and mammals.

The chlamydias are the smallest of all bacteria.

They are important because of their role in sexually transmitted diseases.

Chlamydias are also responsible for the human disease known as trachoma, a leading cause of blindness in the world.

They also cause disease in some birds and mammals.


Algae Algae

Algae ranges from the microscopic single cell organism to the larger multiple cell organisms such as seaweed and kelp.

All algae contain chlorophyll, as well as pigments that cause them to appear yellow-green, brown, or red.

Algae are found in abundance in both freshwater and marine habitats.

Most algae do not produce human disease.

Algae ranges from the microscopic single cell organism to the larger multiple cell organisms such as seaweed and kelp.

All algae contain chlorophyll, as well as pigments that cause them to appear yellow-green, brown, or red.

Algae are found in abundance in both freshwater and marine habitats.

Most algae do not produce human disease.


Protozoa Protozoa

Protozoa consist of a large group of single cell organisms.

Some protozoa can remain viable as cysts for long periods of time outside their hosts.

The majority of protozoa do not cause disease, but some live in hosts and do cause damage.

A small number of protozoa are responsible for intestinal infections of humans; others invade the blood, lungs, liver, or brain.

Protozoa consist of a large group of single cell organisms.

Some protozoa can remain viable as cysts for long periods of time outside their hosts.

The majority of protozoa do not cause disease, but some live in hosts and do cause damage.

A small number of protozoa are responsible for intestinal infections of humans; others invade the blood, lungs, liver, or brain.


Fungi Fungi

Fungi are plants, such as mushrooms, yeasts, and molds, that lack chlorophyll.

Candida is a common yeast found in the oral cavity of about half of the population. It also is found in the gastrointestinal tract, female genital tract, and sometimes the skin.

Cross infection may occur from mother to baby, and among infant siblings.

Fungi are plants, such as mushrooms, yeasts, and molds, that lack chlorophyll.

Candida is a common yeast found in the oral cavity of about half of the population. It also is found in the gastrointestinal tract, female genital tract, and sometimes the skin.

Cross infection may occur from mother to baby, and among infant siblings.


Oral CandidiasisOral Candidiasis Caused by the yeast Candida albicans. All forms of candidiasis are considered to be

opportunistic infections, and are found in patients that are very young, very old, and very ill.

Oral candidiasis is characterized by white membranes on the surface of the oral mucosa, tongue, and elsewhere in the oral cavity.

The lesions can look like thin cottage cheese and can be wiped off to reveal a raw, red, and sometimes bleeding base.

Caused by the yeast Candida albicans. All forms of candidiasis are considered to be

opportunistic infections, and are found in patients that are very young, very old, and very ill.

Oral candidiasis is characterized by white membranes on the surface of the oral mucosa, tongue, and elsewhere in the oral cavity.

The lesions can look like thin cottage cheese and can be wiped off to reveal a raw, red, and sometimes bleeding base.


Fig. 18-9 A, Multiple white plaques of pseudomembranous candidias (thrush) in an HIV-infected individual.Fig. 18-9 A, Multiple white plaques of pseudomembranous candidias (thrush) in an HIV-infected individual.

Fig. 18-9 AFig. 18-9 A


Fig. 18-9 B, Candidas-associated denture stomatitis showing the edentulous maxillary arch.Fig. 18-9 B, Candidas-associated denture stomatitis showing the edentulous maxillary arch.

Fig. 18-9 BFig. 18-9 B


Viruses Viruses

Viruses are ultramicroscopic infectious agents that despite their minute size, cause fatal diseases.

New and increasingly destructive viruses are being discovered and have caused the creation of a special area within microbiology called virology.

Viruses can live and multiply only inside an appropriate host cell. The host cells may be human, animal, plant, or bacteria.

A virus invades a host cell, replicates (produces copies of itself), and then destroys the host cell so the viruses are released into the body.

Viruses are ultramicroscopic infectious agents that despite their minute size, cause fatal diseases.

New and increasingly destructive viruses are being discovered and have caused the creation of a special area within microbiology called virology.

Viruses can live and multiply only inside an appropriate host cell. The host cells may be human, animal, plant, or bacteria.

A virus invades a host cell, replicates (produces copies of itself), and then destroys the host cell so the viruses are released into the body.


Virus Specificity Virus Specificity

Viruses can have specificity (preference) for particular cell types to replicate.

For example, HIV infects cells known as CD4+ cells, whereas the hepatitis virus infects only liver cells.

Some other viruses are able to cause disease in more than one organ.

Unfortunately, some viruses can cross the placenta and infect the fetus.

Viruses can have specificity (preference) for particular cell types to replicate.

For example, HIV infects cells known as CD4+ cells, whereas the hepatitis virus infects only liver cells.

Some other viruses are able to cause disease in more than one organ.

Unfortunately, some viruses can cross the placenta and infect the fetus.


Virus Latency Virus Latency Some viruses establish a latent (dormant)

state in host cells. A latent virus can be reactivated in the future

and produce more infective viral particles followed by signs and symptoms of the disease.

Stress, another viral infection, and exposure to ultraviolet light can reactivate the virus.

HIV has a latency of months to years. Hepatitis C is known to have a latency period of

15 to 25 years.

Some viruses establish a latent (dormant) state in host cells.

A latent virus can be reactivated in the future and produce more infective viral particles followed by signs and symptoms of the disease.

Stress, another viral infection, and exposure to ultraviolet light can reactivate the virus.

HIV has a latency of months to years. Hepatitis C is known to have a latency period of

15 to 25 years.


Treating Viral Diseases Treating Viral Diseases Viruses cause many clinically significant

diseases in humans. General antibiotics are ineffective in

preventing or curtailing viral infections, and even the few drugs that are effective against some specific viruses have limitations.

Viruses are also capable of mutation. It is very difficult to develop vaccines against

viruses because of the ability of viruses to change their genetic code.

Viruses cause many clinically significant diseases in humans.

General antibiotics are ineffective in preventing or curtailing viral infections, and even the few drugs that are effective against some specific viruses have limitations.

Viruses are also capable of mutation. It is very difficult to develop vaccines against

viruses because of the ability of viruses to change their genetic code.


Transmission of Viral Diseases Transmission of Viral Diseases Viral diseases are transmitted by direct

contact, insects, blood transfusions, contamination of food or water, and inhalation of droplets expelled by coughing or sneezing.

Viral diseases are transmitted by direct contact, insects, blood transfusions, contamination of food or water, and inhalation of droplets expelled by coughing or sneezing.


Viruses in the Environment Viruses in the Environment Viruses can be destroyed easily in the

external environment.

Chemicals such as chlorine (bleach), iodine, phenol, and formaldehyde easily and effectively destroy viruses on surfaces and objects.

These agents, however, are too toxic to be used internally.

Viruses can be destroyed easily in the external environment.

Chemicals such as chlorine (bleach), iodine, phenol, and formaldehyde easily and effectively destroy viruses on surfaces and objects.

These agents, however, are too toxic to be used internally.


Prions Prions Small proteinaceous infectious particles. Composed entirely of proteins that lack nucleic acids

(DNA or RNA). Until the discovery of prions, it was believed that any

agent capable of transmitting disease had to be made up of genetic material composed of nucleic acids.

Prions convert normal protein molecules into dangerous ones simply by causing the normal ones to change their shape.

Prions are a new and separate class, unlike bacteria, fungi, viruses, and all other known pathogens.

Small proteinaceous infectious particles. Composed entirely of proteins that lack nucleic acids

(DNA or RNA). Until the discovery of prions, it was believed that any

agent capable of transmitting disease had to be made up of genetic material composed of nucleic acids.

Prions convert normal protein molecules into dangerous ones simply by causing the normal ones to change their shape.

Prions are a new and separate class, unlike bacteria, fungi, viruses, and all other known pathogens.


Prion Diseases Prion Diseases Prions are responsible for “mad cow disease.” Prions are linked to human diseases such as

Creutzfeldt-Jacob disease (rare form of dementia) and possibly Alzheimer’s disease.

Prion-caused diseases have been found in humans and animals.

Prions are highly resistant to heat, chemical agents, and irradiation.

There is no treatment or vaccine against prion diseases, and the only preventive measure is not eating suspect food.

Prions are responsible for “mad cow disease.” Prions are linked to human diseases such as

Creutzfeldt-Jacob disease (rare form of dementia) and possibly Alzheimer’s disease.

Prion-caused diseases have been found in humans and animals.

Prions are highly resistant to heat, chemical agents, and irradiation.

There is no treatment or vaccine against prion diseases, and the only preventive measure is not eating suspect food.


Fig. 18-7 Gram-positive stain.Fig. 18-7 Gram-positive stain.

Fig. 18-7Fig. 18-7


Fig. 18-8 Gram-negative stain.Fig. 18-8 Gram-negative stain.

Fig. 18-8Fig. 18-8

chapter 18 microbiology copyright 2003, elsevier science (usa). all rights reserved. no part of this...

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