Transcript 1133693644_460426

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CHAPTER 1
The Background of Microbiology
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Introduction
• Microbiology: study of organisms that
cannot be seen by gross examination
• Microscope is needed
• Three types of microscopes
– Basic compound microscope
– Scanning electron microscope
– Confocal laser microscope
(Continues)
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Introduction
• Microorganisms
– Abundant in/on the body
– Many are beneficial (normal flora)
– Few cause disease (pathogenic)
– Increased ability to produce an infection
(virulence)
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Classifications of Microorganisms
• According to cell type
– Protists (one-celled organisms)
• Two groups
Prokaryotes (e.g., bacteria, mycoplasmas)
Eukaryotes (e.g., animals, plants)
(Continues)
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Classifications of Microorganisms
• Unclassified microorganisms include
– Viruses
• Incapable of reproducing on their own
• Require a host cell
• For example, measles, HIV, common cold
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Infectious Proteins
• Prions
– Do not fit any cellular category
– Anucleate
– Cause CNS infections
– Lack nucleic acid
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Eukaryotes
• Cell membrane
– Outer layer; selectively permeable
– Protects; provides passage for nutrient/waste
• Nucleus
– Control center
– Contains DNA
(Continues)
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Eukaryotes
• Cytoplasm
– Maintains cell shape
• Nucleolus
– Within the nucleus
– Needed for protein manufacture
• Ribosomes
– Site of protein synthesis
– Contain RNA
(Continues)
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Eukaryotes
• Mitochondria
– Powerhouses
– Store energy in the form of ATP
• Golgi apparatus
– Combines CHO with proteins
• Lysosomes
– Synthesized in ER
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Prokaryotes
• Contain
– Cell membrane, cell wall
– No nucleus (anucleate)
– Nucleoid for storing DNA
– Capsule of slime layer to increase resistance
to antibacterial agents
(Continues)
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Prokaryotes
• Cilia (short, fine filaments that move fluid
over a surface)
• Flagella (long filaments that provide
motility for the cell)
• Spores (hard outer wall produced by
inactive bacterial cells)
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Normal Flora versus Pathogens
• Normal flora
– Exist on, in, or around us; may become
pathogenic if they do not remain in intended
location of the body
– Most prevalent in areas open to the outside
– Not found in blood or CSF
• Pathogen
– Capable of causing disease
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Immune System
• Three lines of defense
– Protective barriers
– Circulatory or bloodstream response
– Innate, adaptive response
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Protective Barriers
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Intact skin and its secretions
Respiratory tract (e.g., mucus, sneezing)
GI tract (e.g., saliva, acidic pH of stomach)
GU tract (e.g., expulsion of urine)
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Circulatory and Bloodstream Response
• Phagocytes (phag/o = to eat)
– Neutrophils, monocytes, macrophages,
dendritic cells
• Lysosomes
– May be in fixed locations (e.g., bone marrow,
liver) or may roam to location of foreign
substance
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Innate Immune Response
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Exists at birth
Is not pathogen specific
Does not require previous exposure
Kills invading microbes
Begins inflammatory response (redness,
swelling, and pain)
• Alerts adaptive immune response
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Innate/Adaptive Immune Response
• Antigen presenting cells (APCs)
– Macrophages and dendritic cells kill microbes
– Present intruding microorganisms to T cells
• Antigen
– Marker recognized as foreign
– Phagocytic cells engulf pathogen, presenting
fragments on its surface, notifying the
adaptive immune system of invader
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Adaptive Immune Response
• Cellular mediated
– Recognizes pathogen
– Activates T cells (which secrete cytokines)
• Humoral response
– T cells interact with B cells that produce
antibodies (immunoglobulins)
– Antibodies destroy antigen
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Infection
• Caused by invasion by microbe
• Localized or generalized
• Virulence determined by
– Cell structure
– Production of endotoxin (contained within the
microbe) or exotoxin (produced by and
secreted by the microbe)
(Continues)
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Infection
• Most common disease-causing
microorganisms in humans
– Bacteria
– Viruses
– Fungi
– Parasites
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Direct and Indirect Disease
Transmission
• Contact transmission
– Direct contact (with the person)
– Indirect contact (with fomite, vector, common
vehicle, or airborne droplets)
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Fever and the Inflammatory Response
• Infection accompanied by
– Fever
• Assists in clearing infections
• Important defense mechanism
– Inflammation
• Part of the innate immune response
• Caused by dilatation of blood vessels
• Infiltration of infected site by antibodies and WBCs
results in death of the microbe
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Summary
• Classification of microorganisms
– Prokaryotic
– Eukaryotic
• Normal flora
– Live on/in body
• Pathogens
– Cause disease
(Continues)
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Summary
• Immune system response
– Innate
– Adaptive
• Cellular
• Humoral
• Pathogenicity
– Ability of microbes to cause disease
• Virulence
– Strength of disease-causing microbe
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