CHAPTER © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 46 Introduction to...

CHAPTER

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

46Introduction to Microbiology


46-2

Learning Outcomes

46.1 Define microbiology.

46.2 Describe how microorganisms cause disease.

46.3 Describe how microorganisms are classified and named.

46.4 Explain how viruses, bacteria, protozoans, fungi, and parasites differ and give examples of each.


46-3

Learning Outcomes (cont.)

46.5 Describe the process involved in diagnosing an infection.

46.6 List general guidelines for obtaining specimens.

46.7 Describe how throat culture, urine, sputum, wound, and stool specimens are obtained.

46.8 Explain how to transport specimens to outside laboratories.


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46.9 Describe two techniques used in the direct examination of culture specimens.

46.10Explain how to prepare and examine stained specimens.

46.11Describe how to culture specimens in the medical office.


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46.12Explain how cultures are interpreted.

46.13Describe how to perform an antimicrobial sensitivity determination.

46.14Explain how to implement quality control measures in the microbiology laboratory.


46-6

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


46-7

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


46-8

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


46-9

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


46-10

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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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.


46-12

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


46-13

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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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 – virusesProkaryotic 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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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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Viruses (cont.)

• Illnesses caused by viruses– Colds

– Influenza

– Croup

– Hepatitis

– Warts

• Vaccines are available for many viruses

– AIDS– Mumps – Rubella– Measles– Herpes


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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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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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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 (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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Protozoans • Single-celled eukaryotic organisms, larger than

bacteria

• Found in soil and water

• Illnesses – Malaria– Amebic dysentery– Trichomoniasis vaginitis

• Leading cause of death in developing countries

Protozoan Trichomonas vaginalis


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Fungi• Eukaryotic organisms

with rigid cell wall• Yeasts

– Single-celled– Reproduce by budding

• Molds– Large, fuzzy,

multicelled organisms– Produce spores

• Superficial infections– Athlete’s foot– Ringworm– Thrush

• Can cause systemic infections

Yeasts: single-celled fungi


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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


46-24


Matching:

___ Yeast or mold A. Virus

___ Tapeworm/lice B. Bacteria

___ Classified by shape C. Protozoan

___ Subcellular organism D. Fungus

___ May be aerobic or anaerobic E. Multicellular parasite

___ Smallest known organism

___ Found in soil and water

E

A

B

B

C

A

Very Good!E

B

E

A

B

E

B

A

B

E

D

A

B

A

B

E

ANSWER:

D


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How Infections Are Diagnosed

• Steps to diagnosis and treatment1. 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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How Infections Are Diagnosed (cont.)

3. Examine specimen directly• Wet mount

• Smear

4. Culture specimenCulture medium – contains nutrientsExamine culture visually and

microscopically


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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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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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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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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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Guidelines for Specimen Collection

• Avoid causing harm, discomfort, or undue embarrassment

• Collect from appropriate site

• Obtain specimen at correct time

• Use appropriate devices

• Obtain sufficient quantity of specimen

• Obtain specimen prior to the start of antimicrobial therapy

• Label correctly


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• 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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• Urine specimen– Clean-catch

midstream to minimize contaminants

– Process within 60 minutes or refrigerate

• Sputum specimen– Specimen from

lungs – Avoid

contaminating specimen with saliva


46-34


• 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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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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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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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


46-38


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!


46-39

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


46-40

Preparation and Examination of Stained Specimens

• Quick, tentative diagnosis

• Differentiation between types of infections

• Gram’s stain– Moderate-

complexity test– Bacteria either

retain or lose purple color

• Gram-positive bacteria

• Gram-negative bacteria


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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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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.


46-43


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.


46-44

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


46-45


• 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


46-46


• 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


46-47

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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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.


46-49

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


46-50

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


46-51


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!


46-52

In Summary

46.1 Microbiology is the study of microorganisms, which are simple life forms that are microscopic and are commonly made up of a single cell.

46.2 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.

46.3 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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In Summary (cont.)

46.4 Viruses, bacteria, protozoans, fungi, and parasites differ in the following ways: viruses are among the smallest known infectious agents; bacteria are single-celled 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.

46.5 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.


46-54

In Summary (cont.)

46.6 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.

46.7 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.


46-55

In Summary (cont.)

46.8 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.

46.9 Direct examination of culture specimens is accomplished in two ways: wet mounts and KOH mounts.


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In Summary (cont.)

46.10 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.

46.11 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.


46-57

In Summary (cont.)

46.12 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.

46.13 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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In Summary (cont.)

46.14 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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Each organism's environment, for the most part, consists of other organisms.

~ Kevin Kelly

End of Chapter 46

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