Human-Microorganism Interactions and Infection Control

Chapter 9 This chapter discusses the relationship between humans and microorganisms, focusing on the role of microorganisms in causing infections. It explores different types of infections caused by bacteria, viruses, fungi, and parasites, as well as the challenges of antibiotic resistance. The chapter highlights the importance of vaccines and immunotherapy in protecting against infections. Structure of bacteria: Bacteria are prokaryocytes They can be aerobic or anaerobic, motile or immotile Spherical bacteria are called cocci, rod-like forms are called bacilli, and spiral forms are termed spirochetes Gram staining differentiates bacteria as gram-positive (dark purple) or gram-negative (light pink) Gram-positive bacteria have teichoic acid and peptidoglycan in their outer membranes Gram-negative bacteria have lipopolysaccharide (LPS) in their outer membranes Bacteria can survive in extracellular or intracellular environments Extracellular vs Intracellular Bacteria Extracellular bacteria proliferate in body fluids of the extracellular environment. Intracellular bacteria can enter and survive inside various cells, evading humoral antibodies. Intracellular bacteria can only be eliminated by a cellular immune response. Examples of intracellular bacteria include C. trachomatis, M. tuberculosis, and Mycobacterium leprae. Virulence Factors of Bacteria Pili (fimbria): Hair-like projections that help bacteria attach to and invade cells and tissues. Flagella: Rotary structures that provide motility and express adhesion molecules. Capsules: Outer coverings of the cell wall that prevent phagocytosis and resist host immunity. Enzymes: Proteins that promote tissue invasion, such as proteases and lipases. Toxins: Poisonous substances that cause injury, including exotoxins (direct injury) and endotoxins (indirect injury). Microbial Competition for Resources Microorganisms compete for iron and nutrients to support their metabolism and growth. Examples of Bacterial Infections Respiratory Tract Infections: Corynebacterium diphtheriae, Haemophilus influenzae, Streptococcus pyogenes, etc. Otitis Media (Middle Ear Infection): Haemophilus influenzae, Streptococcus pneumoniae, etc. Lower Respiratory Tract Infections: Bacillus anthracis, Bordetella pertussis, Chlamydia pneumoniae, etc. Gastrointestinal Infections (Inflammatory): Bacillus anthracis, Clostridium difficile, Escherichia coli O157:H7, etc. Gastrointestinal Infections (Invasive): Brucella abortus, Helicobacter pylori, Listeria monocytogenes, etc. Food Poisoning: Bacillus cereus, Clostridium botulinum, Clostridium perfringens, Staphylococcus aureus, etc. Sexually Transmitted Infections: Chlamydia trachomatis Neisseria gonorrhoeae (urethritis) Gram-negative bacteria Aerobic Facultative intracellular Treponema pallidum (spirochete; syphilis) Gram-negative bacteria Aerobic Extracellular Bacillus anthracis (cutaneous anthrax) Gram-positive bacteria Facultative anaerobic Extracellular Borrelia burgdorferi (Lyme disease; spirochete) Gram-negative bacteria Aerobic Extracellular Clostridium tetani (tetanus) Gram-positive bacteria Anaerobic Extracellular Clostridium perfringens (gas gangrene) Gram-positive bacteria Anaerobic Extracellular Mycobacterium leprae (leprosy) Gram-positive bacteria Aerobic Extracellular (weakly) Pseudomonas aeruginosa Gram-negative bacteria Aerobic Extracellular Rickettsia prowazekii (rickettsia; typhus) Gram-negative bacteria Aerobic Obligate intracellular Staphylococcus aureus Gram-positive bacteria Facultative anaerobic Extracellular Streptococcus pyogenes (group A) Gram-positive bacteria Facultative anaerobic Extracellular Chlamydia trachomatis (conjunctivitis) Not stainable Aerobic Obligate intracellular Haemophilus aegyptius (pink eye) Gram-negative bacteria Facultative anaerobic Extracellular