Chapter 5: Microbiology Basics

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. Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 2

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. Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 3

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 Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 4

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 Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 5

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 Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 6

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 Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 7

Copyright © 2007 by Saunders, an imprint of Elsevier Inc. Types of Pathogens Bacteria Viruses Fungi Protozoa Worms Arthropods Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 8

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 Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 9

Microorganisms (Microbes) (cont’d.) Three shape groups of bacteria: Cocci (round): diplococci, streptococci, staphylococci Bacilli (rod-shaped) Curved rods: vibrios, spirilla, spirochetes Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 10

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 Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 11

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 Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 12

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 Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 13

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 Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 14

The Spread of Infection Portals of entry: where pathogens enter Respiratory tract Gastrointestinal tract Genitourinary tract Eyes Skin Parenteral route Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 15

The Spread of Infection (cont’d.) Portals of exit: how pathogens leave Respiratory tract Gastrointestinal tract Genitourinary tract Eyes Skin Breasts Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 16

The Spread of Infection (cont’d.) Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 17

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) Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 18

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 Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 19

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 Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 20

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 Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 21

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 Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 22

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) Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 23

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 Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 24