Chapter 40 Introduction to Microbiology

1. Chapter 40Introduction to Microbiology

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. 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

10. 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

11. 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.

12. 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.

13. FUNGI • Trichomonas vaginalis causes vaginal infection in women and UTI’s in men

14. 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).

15. 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.

16. 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 causesanthrax. • Klebsiella pneumoniae causespneumonia. • Neisseria gonorrhoeae causesgonorrhea.

17. 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.

18. 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.

19. 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!!

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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.

27. 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.

28. 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.

29. **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 • Convalescencestage: The acute symptoms of the infection subside and the person recovers

30. Factors That Influence the Development of Infection • Several factors other than the strength of the body’s natural defenses help determine whether or not disease-causing microorganisms will ultimately cause an infection. • Specific portal of entry • Number of microorganisms • Virulence • Host resistance