Study Notes for NUR 209: Microbiology and Infection Prevention

COURSE CODE: NUR 209 - Microbiology and Infection Prevention

Instructor: Roselyn Assor Appau (BSc, MPhil)

COURSE OBJECTIVES

By the end of this course, students will be able to:

  • Understand the general characteristics of bacterial cells and the transmission of bacterial infections.
  • State methods for the prevention of bacterial and nosocomial infections.
  • Describe medically important fungi.
  • Describe medically important protozoa.
  • Discuss vehicles and routes of parasitic infections.
  • Describe the general characteristics of viruses and their modes of transmission.
  • Explain methods of sterilization and disinfection of hospital equipment.

ASSESSMENT REQUIREMENTS

Assessment will include:

  • Punctuality and attendance
  • Group presentations
  • Individual and group assignments
  • Unannounced short quizzes
  • Mid-semester examination
  • End-of-semester examination
    • Continuous Assessment: 60%
    • Final Examination: 40%

CLASS EXPECTATIONS

Students are expected to:

  • Attend all lectures on time and not enter the lecture room once the lecture begins.
  • Answer questions related to course content during lectures.
  • Revise previous lecture notes before each new lecture.
  • Avoid using cell phones in class; they should be placed on silent or turned off.

RECOMMENDED TEXTS FOR FURTHER READING

  • Introduction to Microbiology by Ingraham and Ingraham
  • Microbiology by Prescott, Harley, and Klein
  • Any good Microbiology textbook
  • Microbiology with Diseases by Body System by Bauman, R. W., & Primm, T. P. (2018)
  • Clinical Microbiology Made Ridiculously Simple by Gladwin, M., Trattler, W., & Mahan, C. S. (2019)
  • Medical Microbiology E-book by Murray, P. R., Rosenthal, K. S., & Pfaller, M. A. (2022)
  • Paniker's Textbook of Medical Parasitology (2017) by Paniker, C. J.
  • Microbiology: An Introduction by Tortora, G. J., Funke, B. R., & Case, C. L. (2018)

INTRODUCTION TO MICROBIOLOGY

  • Definition: Microbiology is the study of microorganisms, which are minute living creatures not visible to the naked eye.
  • Types of microorganisms:
    • Bacteria
    • Fungi
    • Protozoa
    • Viruses

MICROORGANISMS IN THE ENVIRONMENT

  • Microorganisms are ubiquitous, found in:
    • Air
    • Soil
    • Water
  • Majority of microbes do not cause disease; rather, they contribute to human well-being, which highlights the various branches of microbiology.

SPECIALIZATIONS IN MICROBIOLOGY

  • Epidemiology and Public Health Microbiology: Focuses on the distribution, spread, control, and prevention of diseases.
  • Food Microbiology: Studies the use of microbes in food production.
  • Agricultural and Veterinary Microbiology: Explores the use of microbes to enhance yields and control diseases in crops and livestock.
  • Environmental Microbiology: Investigates the beneficial and harmful effects of microbes on ecosystems.

HISTORICAL CONTEXT

  • Louis Pasteur: His experiments with grape juice fermentation led to the discovery that microbial contamination causes spoilage, resulting in the development of pasteurization.
  • Contributions by Notable Figures:
    • Semmelweis: Advocated handwashing to prevent infection.
    • John Snow: Pioneered infection control and epidemiology.
    • Jenner: Developed vaccines, marking the beginning of immunology.
    • Nightingale: Founded the principles of nursing care.

UNIT 1: COURSE CONTENT

  • Theory topics include:
    • Different types of bacteria: Bacilli, Cocci, Vibrio, and Spirochaete.
    • General characteristics of bacterial cells.
    • Transmission of bacterial infections.
    • Host responses to bacterial infections.
    • Prevention strategies for bacterial and nosocomial infections.

MORPHOLOGY OF BACTERIAL CELLS

  • Bacterial cells are prokaryotic, lacking a defined nucleus and complex organelles.
  • Structural components include:
    • Cell membrane and cell wall composed of peptidoglycan.
    • Bacteria shape classifications:
    • Cocci: Spherical bacteria arranged in various formations, e.g.,
      • Staphylococcus (clusters)
      • Streptococcus (chains)
    • Bacilli: Rod-shaped bacteria which may be curved, e.g.,
      • Bacillus anthracis
      • Vibrio cholerae (curved bacillus)
    • Spirilli: Spiral-shaped bacteria, which may be tightly coiled (spirochaetes).
      • Treponema pallidum
      • Borrelia burgdorferi

BACTERIAL ARRANGEMENTS

  • Cocci Arrangements:
    • Diplococci: Divide in pairs (e.g., Neisseria gonorrhoeae).
    • Streptococci: Form chains (e.g., Streptococcus pyogenes).
    • Tetrads: Divide in two planes and group in fours (e.g., Micrococcus species).
    • Staphylococci: Divide in multiple planes forming clusters (e.g., Staphylococcus aureus).

BACILLI ARRANGEMENTS

  • Bacilli can only divide across their short axis, resulting in isolated cells or pairs:
    • Diplobacilli: Pairs of rods.
    • Vibrios: Curved rod shapes, like a comma (e.g., Vibrio cholerae).
    • Spirochaetes: Have a helical form and are flagellated (e.g., Treponema pallidum).

BACTERIAL RESPIRATION

  • Types of respiration in bacteria:
    • Obligate Aerobes: Require oxygen for growth (e.g., Mycobacterium tuberculosis).
    • Obligate Anaerobes: Cannot exist in the presence of oxygen; perform fermentation.
    • Facultative Anaerobes: Can grow with or without oxygen, switching between respiration and fermentation based on oxygen availability.

CELL STRUCTURE AND COMPONENTS

  • Bacterial Cell Features:
    • Appendages: Flagella, pili, fimbriae
    • Forms: Capsule, cell wall, cell membrane
  • Cytoplasm:
    • Contains water, enzymes, and cell structures (ribosomes) without membrane-bound organelles.
    • Responsible for growth, metabolism, and replication.

PLASMA MEMBRANE

  • A thin, semi-permeable membrane that separates the cell interior from the environment and houses critical functions, including ATP generation.
  • Composed of phospholipid molecules oriented with hydrophilic heads facing outward and hydrophobic tails inward.

CELL WALL

  • Composed of peptidoglycan, providing structural integrity and support while allowing free passage of solutes.
  • The cell wall's composition includes differences between Gram-positive and Gram-negative bacteria.

BACTERIAL INCLUSIONS

  • Granules or Inclusions: Used for nutrient storage and can aid in bacterial identification through staining.
  • Nucleoid: Contains chromosomal DNA and plasmids.
  • Spores: Enable bacteria to survive adverse conditions.

GLYCOCALYX

  • Includes polysaccharide and polypeptide substances, with forms being either a capsule or a slime layer.
  • Importance of Capsule: Serves as a virulence factor, protecting bacteria from phagocytosis (e.g., Streptococcus pneumoniae).

BACTERIAL PATHOGENICITY

  • Pathogenicity Definition: The ability of bacteria to cause disease.
  • Virulence: Refers to the degree of pathogenicity or severity of disease produced by different microbial strains.

FACTORS OF VIRULENCE

  • Adhesion: Initial attachment through adhesins.
  • Colonization: Ability to establish and persist in host tissues (e.g., Helicobacter species counter stomach acidity by producing urease).
  • Invasiveness: Ability to spread within host tissue (e.g., highly invasive organisms lead to septicemia).
  • Toxigenicity: Includes the production of exotoxins and endotoxins.
    • Exotoxins: Secreted protein toxins mainly produced by Gram-positive bacteria.
    • Endotoxins: Part of the outer membrane of Gram-negative bacteria, released upon bacterial cell lysis.

TRANSMISSION OF BACTERIAL INFECTIONS

  • Direct Contact:

    • Transmission occurs through physical interaction, e.g., skin-to-skin contact with Staphylococcus aureus or sexual contact with Neisseria gonorrhoeae.

  • Airborne/Droplet Transmission:

    • Spread via respiratory droplets during coughing or sneezing (e.g., Mycobacterium tuberculosis, Streptococcus pyogenes).

  • Vector-Borne Transmission:

    • Transmitted through living organisms like ticks (e.g., Borrelia burgdorferi causing Lyme disease).

  • Faecal-Oral Route:

    • Occurs via contaminated food or water (e.g., Salmonella spp., Vibrio cholerae).

  • Vertical Transmission:

    • From mother to child during pregnancy, childbirth, or breastfeeding (e.g., Treponema pallidum causing congenital syphilis, Listeria monocytogenes).

  • Fomite Transmission:

    • Through contaminated inanimate objects, e.g., MRSA from shared gym equipment.

INFECTIOUS DISEASE TYPES

  • Endemic Diseases: Constantly present in a region (e.g., Typhoid fever in India).
  • Epidemic Diseases: Rapidly spread in a region at the same time.
  • Pandemic Diseases: Global spread affecting large populations (e.g., COVID-19).

STAGES OF INFECTIOUS DISEASE

  1. Incubation Period: No symptoms.
  2. Prodromal Period: Mild, nonspecific symptoms (fever, weakness).
  3. Invasive Stage: Symptoms specific to the disease.
  4. Decline Stage: Symptoms begin to subside.
  5. Convalescence: Recovery to normal health.

LATENCY IN BACTERIA

  • Latent Tuberculosis: Mycobacterium tuberculosis can remain dormant in the host without causing disease for years, reactivating under certain conditions such as immunosuppression or age.

PREVENTION OF BACTERIAL INFECTIONS

  • Vaccination: Protects against many bacterial diseases (e.g., tetanus, whooping cough).
  • Hygiene Practices: Importance of hand washing, cleanliness of clothing, and avoidance of sharing personal items.
  • Wound Care: Keeping wounds clean and covered.
  • Safe Food Handling: Proper storage and preparation to limit bacterial growth.
  • Safe Sexual Practices: Use of condoms during sexual activity.
  • Outdoor Safety: Use protective clothing and bug spray to prevent infections.

HOST DEFENSE MECHANISMS

  • Immune System Components:
    • Innate or nonspecific immune system.
    • Adaptive or specific immune system.

INNATE IMMUNITY

  • Characteristics:
    • Primary defense mechanism, active from birth.
    • Includes cells such as macrophages and neutrophils which identify and destroy microorganisms.
    • Phagocytosis Steps:
    1. Contact
    2. Engulfment
    3. Phagosome formation
    4. Fusion with lysosome
    5. Killing and digestion

ADAPTIVE IMMUNE RESPONSE

  • Specialized Response: Develops after microbial exposure or vaccination.
  • Involves B- and T-lymphocytes producing antibodies against specific pathogens.
Antibody Function
  • Neutralization of toxins
  • Enhanced phagocytosis via opsonization
  • Prevention of pathogen adherence (e.g., IgA on mucosal surfaces).

NOSOCOMIAL INFECTIONS

  • Defined as infections acquired in the hospital setting, where the patient did not have the infection at the time of admission.
  • Sources of Infection:
    • Endogenous (patient's flora).
    • Exogenous (other patients, staff, environment).

COMMON NOSOCOMIAL INFECTIONS

  • UTIs: Most common healthcare-associated infections, often related to catheterization (e.g., E. coli).
  • Pneumonia: Leading cause of mortality within healthcare-associated infections (e.g., Staphylococcus aureus).
  • Wound Infections: Occur post-surgery from introduction of pathogens (e.g., Staphylococcus aureus).
  • Bacteremia and Septicemia: Bloodstream infections (e.g., caused by infected IV lines).
  • Tetanus: Improper aseptic techniques during surgeries.

PREVENTION OF NOSOCOMIAL INFECTIONS

  • Importance of hand hygiene: The single most effective measure to reduce the risk of transmission.
  • Adherence to safety protocols and regular equipment disinfection are crucial in preventing infections in healthcare settings.

HAND HYGIENE PRACTICES

  • Must be bacteriologically effective in all clinical settings:
    • Wash hands before any procedure requiring gloves.
    • After contact with infected individuals or materials.
    • Utilize soap and water or antibacterial soap.
    • Follow a comprehensive handwashing routine to ensure complete cleaning of hands.

SAFETY MEASURES IN HEALTHCARE

  • Assume all patients are potential sources of infections.
  • Proper transportation of specimens and use of personal protective equipment (PPE) to safeguard against exposure.