CHAPTER
15
Introduction to
Microbiology
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15-2
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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15-3
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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15-4
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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15-5
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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15-6
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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15-7
Microbiology and the Role of the Medical
Assistant
• Microbiology – study of microorganisms
(simple forms of life visible only with a
microscope)
• Microorganisms
– Normal flora
– Pathogenic
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15-8
Microbiology and the Role of the Medical
Assistant (cont.)
• 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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15-9
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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15-10
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
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15-11
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.
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15-12
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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15-13
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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15-14
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
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15-15
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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15-16
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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15-17
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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15-18
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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15-19
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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15-20
Bacterial Classification and Identification
(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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15-21
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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15-22
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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15-23
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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15-24
Apply Your Knowledge
Matching:
ANSWER:
D Yeast or mold
___
A. Virus
E Tapeworm/lice
___
B. Bacteria
B Classified by shape
___
C. Protozoan
A Subcellular organism
___
D. Fungus
Very
Good!
B May be aerobic or anaerobic E. Multicellular parasite
___
A Smallest known organism
___
C Found in soil and water
___
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15-25
How Infections Are Diagnosed
• Steps to diagnosis and treatment
1. Examine the patient
• Presumptive diagnosis
• May or may not need additional tests
2. Obtain specimen(s)
• Label properly
• Include presumptive diagnosis
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15-26
How Infections Are Diagnosed (cont.)
3. Examine specimen directly
• Wet mount
• Smear
4. Culture specimen
Culture medium – contains nutrients
Examine culture visually and
microscopically
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15-27
How Infections Are Diagnosed (cont.)
5. Determine sensitivity to antibiotics
6. Treat the patient as ordered
• Antimicrobial – to kill pathogen or
suppress its growth
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15-28
Apply Your Knowledge
What is the process for diagnosing an infection?
ANSWER: There are six steps for diagnosis and treatment
of an infection:
1. Examine the patient
4. Culture the specimen
2. Obtain specimen(s)
5. Determine sensitivity
3. Examine specimen directly
6. Treat patient/appropriate
antimicrobial
Super!
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15-29
Specimen Collection
• Must be collected correctly
– If not, may not grow in culture
– Contaminants may be mistakenly identified
– Patient may receive
incorrect or harmful therapy
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15-30
Specimen Collection (cont.)
• Devices
– Use appropriate collection
device or specimen container
– Sterile swabs – absorbent
material on the tip
• Collection and transporting systems
– Sterile, self-contained
– Transport medium
– Aerobic or anaerobic
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15-31
Guidelines for Specimen Collection
• Avoid causing harm,
discomfort, or undue
embarrassment
• Collect from
appropriate site
• Obtain specimen at
correct time
• Obtain sufficient
quantity of specimen
• Obtain specimen prior
to the start of
antimicrobial therapy
• Label correctly
• Use appropriate
devices
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15-32
Specimen Collection (cont.)
• Throat culture specimens
– Swab back of throat in the area of the
tonsils
– Avoid touching any structures in the
mouth
– Prepare culture plate or prepare
correctly for transport
to laboratory
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15-33
Specimen Collection (cont.)
• Urine specimen
– Clean-catch
midstream to
minimize
contaminants
– Process within 60
minutes or
refrigerate
• Sputum specimen
– Specimen from
lungs
– Avoid
contaminating
specimen with
saliva
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15-34
Specimen Collection (cont.)
• Wound specimen
– Swab wound or
lesion
– Do not touch
outside of wound
• Stool specimens
– Technique varies
• Bacterial infection
• Protozoal or
parasitic infection
– Instruct patient in
correct collection
procedure
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15-35
Apply Your Knowledge
What are the general guidelines for specimen
collection?
ANSWER: They are to avoid causing harm, discomfort, or
undue embarrassment; collect from appropriate site; obtain
specimen at correct time; use appropriate collection
devices; obtain sufficient quantity of specimen; obtain
specimen prior to the start of antimicrobial therapy; and
label specimen correctly.
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15-36
Transporting Specimens to an
Outside Laboratory
• Many offices send cultures to an outside
lab
• Three main objectives
– Follow proper collection
procedures and use proper
collection device
– Prevent deterioration of
specimen
– Protect anyone handling
specimen
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15-37
Transporting Specimens to an Outside
Laboratory (cont.)
•
Regularly scheduled daily pickups by the lab
•
As-needed pickup by the lab
•
Through the mail
–
–
Follow U.S. Public Health Service regulations
Etiologic Agent label
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15-38
Apply Your Knowledge
What are the objectives for transporting a
specimen to an outside laboratory?
ANSWER: They are to follow proper collection procedures
and use the proper collection device, prevent deterioration of
the specimen during transport, and protect anyone that will
handle the specimen from exposure.
Impressive!
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15-39
Direct Examination of Specimens
• Enables physician to
initiate treatment
immediately
• Wet mounts
– NaCl mixed with
specimen of glass
slide
– Presence of pathogen
and movement of
microorganism
• Potassium hydroxide
(KOH) mounts
– Used if a fungal
infection of the skin,
nails, or hair is
suspected
– KOH dissolves keratin
that can mask
presence of a fungus
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15-40
Preparation and Examination of Stained
Specimens
• Quick, tentative
diagnosis
• Differentiation
between types of
infections
• Gram’s stain
– Moderatecomplexity test
– Bacteria either
retain or lose
purple color
• Gram-positive
bacteria
• Gram-negative
bacteria
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15-41
Culturing Specimens in the Medical Office
• More common to send
specimens for culture to
outside labs
• Culturing involves placing a sample of
specimen on a culture medium
– Medium – nutrients
– Place in incubator for growth – colony
develops as microorganism multiplies
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15-42
Apply Your Knowledge
1. What are the methods for preparing a slide for
direct examination by the physician?
ANSWER: They are wet mount and KOH mount.
2. How does the examination of stained
specimens facilitate patient care?
ANSWER: Stained specimens enable the physician to provide a
quick, tentative diagnosis and differentiate between types of
infections.
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15-43
Apply Your Knowledge
3. What is the process for culturing a specimen?
ANSWER: The culture medium is inoculated with the
specimen and placed in an incubator to promote
growth of the organism on the culture medium.
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15-44
Culturing Specimens (cont.)
•
Culture media
– Liquid, semisolid, or
solid forms
– Contains agar
– Selective or nonselective
•
Special culture units
– Rapid urine culture – Uricult
– Also available for throat, vaginal, and blood
specimens
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15-45
Culturing Specimens (cont.)
• Inoculating a culture plate
– Transfer some of the specimen onto a culture
plate
– Label the plate correctly
– Qualitative analysis – determination of type
of pathogen
– Quantitative analysis – number of bacteria
present in sample
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15-46
Culturing Specimens (cont.)
• Incubating culture plates
– 35 to 37º C for 24 to 78 hours
– Agar side up
• Interpreting cultures
–
–
–
–
Requires skill and practice
Characteristics of colonies
Relative number
Changes to media around colonies
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15-47
Determining Antimicrobial Sensitivity
• An outside lab reports
– Sensitive – no growth
– Intermediate – little
growth
– Resistant – overgrown
• Procedure
– Filter paper containing
antimicrobial agents
placed on inoculated
agar plate
– Incubated for 24 hours
– Evaluate effectiveness
of agent
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15-48
Apply Your Knowledge
1. What is the difference between selective and
nonselective culture media?
ANSWER: Selective culture media allows the growth of only certain kinds
of bacteria. Unselective culture media support the growth of most
organisms.
2. The office received a culture sensitivity report
on a bacteria that said it was resistant to an
antimicrobial. What does this mean?
ANSWER: It means that the bacteria was not killed by the antimicrobial and
that there was an overgrowth of the bacteria.
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15-49
Quality Control in the Medical Office
• Ongoing evaluation
of the quality of
medical care being
provided
• Objective means to
define, monitor,
and correct
potential problems

Routine evaluation


All media, staining
solutions, and
reagents
Equipment
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15-50
Quality Control: Impact of CLIA ’88
• Appropriate policies and procedures
• Proper documentation
– Lab policies and procedures
– Materials
– Personnel qualifications and training
• Participation in proficiency testing program
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15-51
Apply Your Knowledge
What is the purpose of a quality control program in
the medical office?
ANSWER: To provide an ongoing evaluation of the quality of
medical care provided and to provide an objective means to
define, monitor, and correct potential problems.
Very Good!
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15-52
In Summary
15.1 Microbiology is the study of microorganisms, which
are simple life forms that are microscopic and are
commonly made up of a single cell.
15.2 Microorganisms can cause disease by using up
nutrients or other materials needed by the cells and
tissues they invade, damaging body cells, and
producing toxins.
15.3 Microorganisms are classified on the basis of their
structure and are named in a standard way, using the
genus to which the microorganism belongs and the
particular species of the organism.
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15-53
In Summary (cont.)
15.4 Viruses, bacteria, protozoans, fungi, and parasites
differ in the following ways: viruses are among the
smallest known infectious agents; bacteria are singlecelled prokaryotic organisms that reproduce very
quickly; protozoans are single-celled eukaryotic
organisms that are generally much larger than
bacteria; and fungi are eukaryotic organisms that
have a rigid cell wall.
15.5 The steps involved in diagnosing an infection are to
examine the patient, obtain specimens, examine the
specimen, culture the specimen, and determine the
culture’s antibiotic sensitivity.
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15-54
In Summary (cont.)
15.6 The general guidelines for obtaining specimens are:
obtain the specimen with care; collect the material
from a site; obtain the specimen at the proper time;
use appropriate collection devices; obtain a sufficient
quantity of the specimen; and obtain the specimen
before antimicrobial therapy begins.
15.7 Throat culture, urine, sputum, wound, and stool
specimens are obtained in very specific ways. It is
important to follow office procedures when obtaining
specimens for testing purposes.
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15-55
In Summary (cont.)
15.8 When transporting specimens to outside laboratories,
the medical assistant should follow proper collection
techniques using specific containers provided by the
laboratory, maintain the samples in a state as close to
their original as possible, and protect anyone who
handles a specimen container from exposure to
potentially infectious material.
15.9 Direct examination of culture specimens is
accomplished in two ways: wet mounts and KOH
mounts.
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15-56
In Summary (cont.)
15.10 To prepare a stained specimen, the medical
assistant must first prepare a smear, fix the sample
to the slide so that it does not wash off during the
staining process, and follow a specific staining
procedure. The sample is then observed under a
microscope for certain characteristics.
15.11 To culture a specimen, the medical assistant should
place a sample of the specimen on or in a
specialized culture medium and allow it to grow in an
incubator for 24 to 48 hours.
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15-57
In Summary (cont.)
15.12 The process of interpreting a culture involves noting
the characteristics and relative numbers of the
colonies growing on the agar as well as any changes
in the media surrounding the colonies.
15.13 Performing an antimicrobial sensitivity test involves
taking a sample of the isolated pathogen, suspending
it in a small amount of liquid medium, and streaking it
evenly on the surface of a culture plate. Small disks
of filter paper containing various antimicrobial agents
are placed on top of the inoculated agar plate and the
plate is then incubated at 37°C, and the results are
evaluated the following day.
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15-58
In Summary (cont.)
15.14 To implement a quality control program in a
microbiology laboratory, the medical assistant should
develop an up-to-date procedures manual; monitor
laboratory equipment; monitor media, supplies, and
reagents; ensure that the laboratory personnel are
qualified; and ensure adequate space.
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15-59
End of Chapter 15
Each organism's
environment, for the
most part, consists of
other organisms.
~ Kevin Kelly
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.