Lecture Clinical procedures for medical assisting (4/e): Chapter 15 – Booth, Whicker, Wyman

CHAPTER

15
Introduction to
Microbiology

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15­2

Learning Outcomes
15.1 Define microbiology.
15.2 Describe how microorganisms cause disease.
15.3 Describe how microorganisms are classified
and named.
15.4 Explain how viruses, bacteria, protozoans,
fungi, and parasites differ and give examples
of each.

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15­3

Learning Outcomes (cont.)
15.5 Describe the process involved in diagnosing
an infection.
15.6 List general guidelines for obtaining
specimens.
15.7 Describe how throat culture, urine, sputum,

wound, and stool specimens are obtained.
15.8 Explain how to transport specimens to outside
laboratories.

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15­4

Learning Outcomes (cont.)
15.9 Describe two techniques used in the direct
examination of culture specimens.
15.10Explain how to prepare and examine stained
specimens.
15.11Describe how to culture specimens in the
medical office.

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15­5

Learning Outcomes (cont.)
15.12Explain how cultures are interpreted.
15.13Describe how to perform an antimicrobial
sensitivity determination.
15.14Explain how to implement quality control
measures in the microbiology laboratory.

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15­6

Introduction
• Microorganisms
cause disease or
infection
– Pathogenic in
nature
– Displaced from
their natural
environment

• Medical assistant
– Identification of
microorganisms
– Proper collection
techniques
– Testing procedures
– Quality control

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Microbiology and the Role of the Medical
Assistant

15­7

• Microbiology – study of microorganisms
(simple forms of life visible only with a
microscope)
• Microorganisms
– Normal flora
– Pathogenic

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Microbiology and the Role of the Medical
Assistant (cont.)

15­8

• Medical assistant
– Assists physician
– Obtains specimens
– Prepares specimens for direct examination
– Prepares specimens for transportation to
reference laboratory
– If office has a POL, performs microbiologic
procedures

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15­9

How Microorganisms Cause Disease

• Cause disease in variety of ways
– Use nutrients needed by cells and tissues
– Damage cells directly
– Produce toxins

• May remain localized or become systemic
• Transmission
– Direct contact
– Indirect contact

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15­10

How Microorganisms Cause Disease (cont.)
• Localized symptoms
–
–
–
–

Swelling
Pain
Warmth
Redness

• Generalized
symptoms
–

–
–
–

Fever
Tiredness
Aches
Weakness

• Normal flora
– Provides a barrier
– Can cause an infection

© 2011 The McGraw-Hill Companies, Inc. All rights reserved.


15­11

Apply Your Knowledge
1. What role does the medical assistant play in

relation to microbiology?
ANSWER: The medical assistant may assist the physician in
obtaining specimens, obtain specimens herself, prepare
specimens for direct examination or transport to a reference
laboratory, and possibly perform microbiologic procedures.

2. How do microorganisms cause disease?
ANSWER: Organisms cause disease by using
nutrients needed by cells and tissues,

damaging cells directly, or producing toxins.

© 2011 The McGraw-Hill Companies, Inc. All rights reserved.


15­12

Classification and Naming of Microorganisms
• Classification by structure
– Subcellular – DNA or RNA surrounded by a protein
coat – viruses
– Prokaryotic – simple cell structure with no nucleus or
organelles – bacteria
– Eukaryotic – complex cell structure with nucleus and
specialized organelles – protozoans, fungi,
parasites

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15­13

Classification and Naming of Microorganisms
(cont.)

• Standardized naming
– Genus
• Category of biologic classification
• Example – Staphylococcus

– Species of organism
• Represents a distinct type of microorganisms
• Examples – Staphylococcus aureus and
Staphylococcus epidermidis

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15­14

Apply Your Knowledge
Describe the classifications of microorganisms and
give an example of each.
ANSWER: Microorganisms are classified as:
Subcellular organisms that have DNA or RNA surrounded by a
protein coat – viruses
Prokaryotic organisms have a simple cell structure with no
nucleus or organelles – bacteria
Eukaryotic have a complex cell structure with nucleus and
specialized organelles – protozoans, fungi, parasites

© 2011 The McGraw-Hill Companies, Inc. All rights reserved.


15­15

Viruses
• Smallest known
infectious agents
• Subcellular

microorganism
– Have only nucleic acid
surrounded by a
protein coat
– Must live and grow in
living cells of other
organisms

Hepatitis Virus

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15­16

Viruses (cont.)
• Illnesses caused by viruses
– Colds
– Influenza
– Croup
– Hepatitis
– Warts

– AIDS
– Mumps
– Rubella
– Measles
– Herpes

• Vaccines are available for many

viruses
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15­17

Bacteria
• Single-celled prokaryotic organisms
• Reproduce rapidly
• Classification
– Shape
– Ability to retain dyes
– Ability to grow
with/without air
– Biochemical reactions

Bacillus Bacterial Classification

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15­18

Bacterial Classification and Identification
• Shape
– Coccus – spherical, round, or ovoid
– Bacillus – rod-shaped
– Spirillum – spiral-shaped
– Vibrio – comma-shaped
Spirillum Bacterial

Classification

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15­19

Bacterial Classification and Identification (cont.)
• Ability to retain certain dyes
– Gram’s stain
– Acid-fast stain

• Ability to grow in presence or absence of air
– Aerobes – grow best in the presence of oxygen
– Anaerobes – grow best in the absence of oxygen

• Biochemical reactions

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Bacterial Classification and Identification

15­20

(cont.)

• Special groups
– Mycobacteria – bacilli
with a cell wall that

differs from most
bacteria
– Rickettsiae
• Very small
• Live and grow within
other living organisms
such as mites and ticks

– Chlamydiae
• Cell wall structure
differs from other
bacteria
• Live and grow within
other living cells

– Mycoplasmas –
completely lack the
rigid cell wall

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15­21

Protozoans
• Single-celled eukaryotic organisms, larger than
bacteria
• Found in soil and water
• Illnesses
– Malaria

– Amebic dysentery
– Trichomoniasis vaginitis

Protozoan Trichomonas
vaginalis

• Leading cause of death in developing countries

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15­22

Fungi
• Eukaryotic organisms
with rigid cell wall
• Yeasts
– Single-celled
– Reproduce by budding

• Molds
– Large, fuzzy,
multicelled organisms
– Produce spores

Yeasts: singlecelled fungi

• Superficial infections
– Athlete’s foot
– Ringworm

– Thrush

• Can cause systemic
infections
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15­23

Multicellular Parasites
• Organisms that live
on or in another
organism and use it
for nourishment
• Parasitic worms
– Usually due to poor
sanitation
– Roundworms
– Flatworms
– Tapeworms

• Parasitic insects
– Bite or burrow under
the skin
– Mosquitoes
– Ticks
– Lice
– Mites

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15­24

Apply Your Knowledge
Matching:
ANSWER:
D Yeast or mold
___

A. Virus

E Tapeworm/lice
___

B. Bacteria

B Classified by shape
___

C. Protozoan

Very
Good!

A Subcellular organism
___
D. Fungus
B May be aerobic or anaerobic E. Multicellular parasite
___

A Smallest known organism
___
C
___ Found in soil and water

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15­25

How Infections Are Diagnosed
• Steps to diagnosis and treatment
1. Examine the patient
• Presumptive diagnosis
• May or may not need additional tests

1. Obtain specimen(s)
• Label properly
• Include presumptive diagnosis

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