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Chapter 40
Introduction to Microbiology
Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins
Microbiology
• The scientific study of microorganisms is microbiology.
• Microorganism or microbe
– Individual living animal or plant that is so small it
can be seen only with the aid of a microscope.
– Most do not cause disease under normal conditions.
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Microorganisms and Nursing
• Endemic
– Organisms that are present all or most of the time in
and on the body
• Pathogens
– Harmful or disease-producing microorganisms
• A nurse is responsible for taking steps to prevent disease
transmission through pathogens and thus prevent the
spread of infection.
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Characteristics of Microorganisms
• Metabolism: The ability to utilize nutrients
• Reproduction: The ability to group together to form
colonies or the ability of individual cells to become larger
• Irritability: Response to the environment
• Motion: The ability to move from place to place
• Protection: Such as spores, mutation, and development
of drug-resistant strains.
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Factors That Influence Microbial Growth
• Oxygen
– Most microorganisms require oxygen for growth;
these are called obligate aerobes. Obligate anaerobes
cannot survive in the presence of oxygen.
• Nutrients
– Microbial growth requires the presence of organic
nutrients and other chemical elements.
– Parasites are microorganisms that live on or within
the host. Saprophytes live off the organic remains of
dead plants and animals.
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Factors That Influence Microbial Growth
(cont’d)
• Temperature
– The optimal temperature for most pathogenic
microorganisms is normal body temperature.
– Some prefer either extremely cold or hot
environments.
• Moisture
– The matter in or on which all microorganisms grow
must contain available moisture or be a liquid.
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Factors That Influence Microbial Growth
(cont’d)
• pH
– Generally, microorganisms survive in environments
with a pH that is neither too acidic nor too alkaline.
• Light
– Some microorganisms need light for growth, whereas
others flourish in darkness.
– Many microorganisms die when exposed to the sun’s
ultraviolet rays.
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Factors That Influence Microbial Growth
(cont’d)
• Cultures of Organisms
– Microbiologists can grow microbes, called cultures,
under controlled conditions in the laboratory in order
to determine ways in which to arrest its growth.
– Cultures are usually grown in test tubes or Petri
dishes. The material in or on which the
microorganisms are placed is the culture medium.
– Solid media contain agar. Liquid media are called
nutrient broths.
– All culture media must start out sterile.
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Culture and Sensitivity (C&S) Reports
• A culture and sensitivity (C&S) test is ordered when
infection is suspected or known.
• **The C&S test serves the following purposes:
– Identifies the pathogenic microorganism
– Determines which treatment will eliminate the
microorganism
– Monitors the microorganism’s response to therapy
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Culture and Sensitivity (C&S) Reports
(cont’d)
• The culture and sensitivity report will indicate:
– The name of the test ordered, type of specimen
– Type of report (preliminary or final), colony count
– Type of microorganism, susceptibility testing
– The various antibiotics to which the organism is
sensitive
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Types of Microorganisms
• Each organism has a name consisting of two parts.
• The genus refers to a general grouping; the species
defines a biologically unique category.
• Example: Escherichia coli (E. coli) is found in the colon.
• Some microorganisms are
– Algae, fungi, protozoa, bacteria/prokaryotes
• Organisms with a true nucleus enclosed by a nuclear
membrane and containing chromosomes that divide by
mitosis are called eukaryotes.
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Fungi
• Mycosis is an infection caused by a fungus.
• Mycology is the study of fungi.
– RINGWORM**
• Yeasts
– Yeast cells reproduce by budding. Candida
albicans is a pathogenic yeast which causes
thrush.
• Molds
– Multicellular molds are common in the environment.
Infections caused by molds include histoplasmosis,
which affects the lungs.
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FUNGI
• Trichomonas vaginalis causes vaginal infection in
women and UTI’s in men
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Classification of Bacteria
• Bacteria may be classified according to their flagella,
shape, motility, Gram stain result, and relationship to
oxygen.
• A round or spherical bacterium is called a coccus
(plural: cocci).
• A rod-shaped bacterium is known as a bacillus
(plural: bacilli).
• A spiral-shaped bacterium has the name spirillum
(plural: spirilla or spirochete).
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Reproduction and Survival of Bacteria
• Conjugation: DNA crosses a sex pilus to the new cell by
cell-to-cell contact.
• Transduction: Genes are transferred by a virus.
• Transformation: DNA is acquired from the environment
after being released by another cell.
• When conditions are unfavorable to their growth, certain
bacteria develop a spore and go into a dormant phase.
The spore can survive extreme conditions.
• All pathogenic bacteria die at water’s boiling point except
the spore formers.
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Common Pathogenic Bacteria
• To be pathogenic, bacteria must possess the ability to:
– Colonize and invade the host
– Resist or endure the antibacterial defenses of the
host
– Form substances that are toxic to the host
• Some examples are:
– Bacillus anthracis causes anthrax.
– Klebsiella pneumoniae causes pneumonia.
– Neisseria gonorrhoeae causes gonorrhea.
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Viruses
• Viruses are protein-covered sacs containing the genetic
material of either DNA or RNA and other organic
materials.
• When a virus enters the cell of a living organism, the
host cell becomes a culture medium for viral
reproduction.
– Poxvirus causes smallpox.
– Adenovirus causes conjunctivitis.
– Picornavirus causes the common cold and upper
respiratory infections.
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Drug-Resistant Microorganisms
• The most common method of development of
antimicrobial-resistant microorganisms occurs when
invading microorganisms survive and transfer their
resistance to future generations.
• Prevent development of drug-resistant microorganisms:
– Take antimicrobial drugs only as prescribed for
the entire period prescribed; discuss the
necessity of antibiotics for mild infections.
– Do not share antimicrobial drugs with others.
– Do not use antibiotics for viral infections.
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Nosocomial Illnesses
• HA-MRSA is today’s most prevalent nosocomial illness or
infection, one originating in a healthcare facility.
• The major route of transmission is via contaminated
hands of healthcare workers.
– WASH YOUR HANDS!!
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Nosocomial Illnesses (cont’d)
• Risk factors for clients in healthcare facilities include:
– A compromised immune system owing to
conditions such as AIDS, cancer, aplastic
anemia, chemotherapy, radiation, or
overproduction of corticosteroids
– A break in the skin following situations, such as
surgery or a burn
– The presence of a central or peripheral intravenous
catheter
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Nosocomial Illnesses (cont’d)
– Invasive medical procedures, serious underlying
disorders
– Previous exposure to antimicrobial drugs, reducing
the normal flora of the body
– Repeated hospitalizations, thus increasing exposure
– Very old age or very young age, increasing
vulnerability
– Previous infections by multidrug–resistant organisms
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Nosocomial Illnesses (cont’d)
• Organisms that commonly cause nosocomial infections
include:
– MRSA: Methicillin-resistant Staphylococcus
aureus
– VRE: Vancomycin-resistant enterococci
– ESBLs: Extended-spectrum β-lactamases (resistant
to cephalosporins and monobactams)
– PRSP: Penicillin-resistant Streptococcus
pneumoniae, which causes pneumonia, often in
older people
– EMRSA: Epidemic MRSA
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Chain of Infection
• An infection is caused when pathogens invade the body.
• The chain of infection contains the following elements:
– Pathogenic microorganism, reservoir in which it can
live and grow
– Portal of exit from which the microorganism can
leave the reservoir
– Vehicle to transmit the organism
– Portal of entry through which it can enter the host
– Susceptible host in which it can find a reservoir
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Chain of Infection (cont’d)
• Break the chain by:
– Thoroughly washing hands often
– Sterilizing instruments and dressings
– Disinfecting floors and equipment
– Placing contaminated articles in moisture-proof bags
– Never using any sterile package that has become
wet or has a broken seal
– Using personal protective equipment as needed
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Transmission of Infectious Disease
• A human carrier does not exhibit the symptoms of a
disease, but carries the pathogens and transmits them to
others.
• Modes of transmission include
– Direct or indirect
– Airborne, foodborne, waterborne
– Vectors
– Contaminated articles
• DRESSINGS FROM WOUNDS
– Bloodborne
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Prevention at the Portal of Entry
• Keep the client’s skin clean and dry.
• Be careful if clipping a client’s nails. Urge clients not to
bite their fingernails or cuticles.
• Avoid positioning clients against objects that could cause
skin breaks.
• Frequently reposition clients who have impaired mobility.
• Provide clean, dry, wrinkle-free linens.
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Prevention at the Portal of Entry (cont’d)
• Make sure urine collection bags are lower than the client.
• Disinfect tubes and ports before collecting specimens
from drainage tubes or intravenous lines.
• Keep wounds that are draining and breaks in skin
covered.
• Use sterile technique when performing invasive
procedures.
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Toxins
• Toxins cause harmful effects by traveling through the
circulatory system to damage other body cells.
• Endotoxins
– They are part of the cell walls of gram-negative
bacteria. When a microorganism dies, the cell wall
decays and releases the toxins.
• Exotoxins
– Toxins manufactured by the microorganism and
excreted into the surrounding tissue.
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**Normal Course of Infection
• Incubation period: The time from when the pathogen
enters the body to the appearance of the first symptoms
of illness
• Prodromal stage: The period from the onset of initial
symptoms to more severe symptoms
• Full stage of illness: The symptoms are acute and specific
to the type of infection
• Convalescence stage: The acute symptoms of the
infection subside and the person recovers
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Factors That Influence the Development
of Infection
• Several factors other than the strength of the body’s
natural defenses help determine whether or not diseasecausing microorganisms will ultimately cause an
infection.
– Specific portal of entry
– Number of microorganisms
– Virulence
– Host resistance
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