1. Chapter 5: Microbiology Basics

2. Copyright © 2007 by Saunders, an imprint of Elsevier Inc.
Lesson 5.1 Objectives
Define disease and infection.
Describe the types of bacteria by shape and staining characteristics.
List the characteristics of the different types of pathogens.
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3. Lesson 5.1 Objectives (cont’d.)
Define portals of exit and portals of entry.
List common ways in which infections are spread.
Identify the microbiological principles described in six germ-laden stories.
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4. Copyright © 2007 by Saunders, an imprint of Elsevier Inc.
What is Disease?
Disease: failure of the body to function normally
Pathogens: disease-producing microorganisms
Infection: invasion of the body by a pathogen
Localized: restricted to a small area
Systemic: more widespread; usually spread through blood
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5. Key Microbiological Terms
Definition
Antibiotics
Chemicals used to treat bacterial infections
Communicable disease
Any disease that can be spread from one host to another
Epidemic disease
Disease acquired by many people in a given area over a short period of time
Epidemiology
Study of occurrence and distribution of a disease in a population
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6. Key Microbiological Terms (cont’d.)
Definition
Incubation period
Lapsed period of time from exposure to a pathogen to the development of the symptoms of the disease
Normal flora
Group of microorganisms that colonize a host without causing disease
Nosocomial infection
Hospital-acquired infection
Reservoir of infection
Continual source of infection
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7. Key Microbiological Terms (cont’d.)
Definition
Resistance
Ability to ward off disease
Sterilization
Process that destroys all living organisms
Vector
Carrier of pathogens from host to host
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8. Copyright © 2007 by Saunders, an imprint of Elsevier Inc.
Types of Pathogens
Bacteria
Viruses
Fungi
Protozoa
Worms
Arthropods
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9. Microorganisms (Microbes)
Bacteria: single-celled organisms
Have a cell wall, not just a cell membrane like human cells
Form spores to survive in harsh environments
Normal flora: organisms that harmoniously live in body without causing disease
Pathogenic bacteria cause damage by:
Entering and growing in cells
Releasing toxins that damage cells
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10. Microorganisms (Microbes) (cont’d.)
Three shape groups of bacteria:
Cocci (round): diplococci, streptococci, staphylococci
Bacilli (rod-shaped)
Curved rods: vibrios, spirilla, spirochetes
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11. Microorganisms (Microbes) (cont’d.)
Rickettsiae and chlamydiae
Parasites classified with bacteria, but smaller than bacteria
Reproduce within living cells
Viruses
Smallest pathogens
Formed of either RNA or DNA surrounded by protein shell
Difficult to kill without damaging host’s cells
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12. Microorganisms (Microbes) (cont’d.)
Fungi
Plantlike organisms
Pathogenic fungi cause mycotic infections
Mycotic infections usually localized, but can be systemic
Protozoa
Single-cell, animal-like organisms
Types of protozoa: amebas, ciliates, flagellates, and sporozoa
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13. Multicellular Pathogens
Parasitic worms (helminths)
Includes roundworms, flatworms, and pinworms
Usually transmitted by fecal-oral route: from feces to mouth, usually carried by the hands
Arthropods
Some arthropods are ectoparasites: parasites that live on the surface of the body and mucous membranes
Other arthropods can act as vector organisms for pathogens
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14. Identifying Pathogens
Bacteria can be identified by staining with a dye:
Gram stain
Gram-positive (purple or blue)
Gram-negative (pink or red)
Acid-fast stain (retains red stain)
Culture: pathogen sample collected and grown in a medium in a laboratory
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15. The Spread of Infection
Portals of entry: where pathogens enter
Respiratory tract
Gastrointestinal tract
Genitourinary tract
Eyes
Skin
Parenteral route
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16. The Spread of Infection (cont’d.)
Portals of exit: how pathogens leave
Respiratory tract
Gastrointestinal tract
Genitourinary tract
Eyes
Skin
Breasts
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17. The Spread of Infection (cont’d.)
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18. The Spread of Infection (cont’d.)
Pathogens spread through:
Person-to-person contact, either directly or by way of a contaminated object (fomite)
Environment-to-person contact
“Tiny animal”-to-person contact, either as part of the life cycle (biological vector) or by contact (mechanical vector)
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19. Six Germ-Laden Stories
Dr. Semmelweis Screams “Wash Those Mitts!”
Puerperal fever common in clinic
Dr. Semmelweis’s observations led him to believe that the infection was transmitted by particles
Dr. Semmelweis began requiring handwashing, and infection rate dropped
Nosocomial infection: hospital-acquired infection
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20. Six Germ-Laden Stories (cont’d.)
Flora and Her Vaginal Itch
Antibiotic prescribed for sinus infection
Normal flora: microbes that inhabit an area without causing harm
Superinfection: an infection occurring during treatment for another infection; normal flora are disturbed, allowing an overgrowth of organisms
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21. Six Germ-Laden Stories (cont’d.)
Rick, Nick, and the Sick Tick
Tick carrying Rickettsia rickettsii transferred pathogen to Rick
Host: organism infected with a pathogen
Animal vector: organism that transmits a pathogen
Arthropod: class of tiny animals with jointed legs
Rick treated with an antibiotic for Rocky Mountain Spotted Fever (RMSF)
Rick’s friend Nick didn’t get sick because RMSF is communicable but not contagious
Zoonosis: animal disease transmissible to humans
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22. Six Germ-Laden Stories (cont’d.)
Why Typhoid Mary Needed to Lose Her Gallbladder
Cook infected with Salmonella typhi unknowingly caused typhoid outbreak
Carrier: person or animal that shows no symptoms of a disease but harbors the infectious agent of that disease and transmits it to others
Typhoid carriers harbor S. typhi in bile of gallbladder
Only way to end carrier status is to remove gallbladder
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23. Six Germ-Laden Stories (cont’d.)
A Pox News Alert!
Pox: disease that causes skin lesions
Pox diseases are not limited geographically or to humans
Chickenpox: disease of children caused by Varicella-Zoster (a herpes virus)
Some people believe the chickenpox vaccine is unsafe and deliberately expose children to the virus
Great Pox: a name for syphilis, which is not a pox (lesion)
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24. Six Germ-Laden Stories (cont’d.)
The Chief of Staph Reports . . .
Staphylococcus-induced skin conditions include impetigo, boils, and Scalded Skin Syndrome
Antibiotic-resistant strains of staph are on the rise
Staphylococcus aureus: gram (+) strain that causes gold-colored exudate
MRSA (methicillin-resistant S. aureus): a major cause of resistant nosocomial infection
Vancomycin-resistant strains have also appeared
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