Microbiology Lecture Notes - Chapter 1 Highlights
Microbes: Definition and Major Groups
- Microbe (microorganism): an organism that is too small to be seen with the naked eye and requires a microscope
- Four major microbe groups
- Bacteria
- Study of bacteria: Bacteriology
- Examples: E. coli, Salmonella
- Viruses
- Study of viruses: Virology
- Examples: coronavirus, herpes, HIV
- Fungi
- Study of fungi: Mycology
- Examples: mold (associated with cold), yeast (associated with fermentation/heat)
- Parasites
- Study of parasites: Parasitology
- Examples: protozoan parasites, worms
Important Roles of Microbes
- Roles beneficial to humans
- Key ecological roles
- Decomposers of organic wastes by bacteria and fungi
- Benefit to humans: breakdown wastes and recycle elements back into nature
- Example: wastes are broken down by microbes
- Photosynthesis
- Performed by cyanobacteria and algae (not just plants)
- Benefit to humans: production of oxygen
- Equation (photosynthesis):
CO2 + H2O
ightarrow ext{C}6 ext{H}{12} ext{O}6 + O2
- Nitrogen fixation
- By bacteria that convert atmospheric N$_2$ into usable nitrogen compounds (nitrates)
- Not directly useful to humans in its atmospheric form: N$_2$ needs to be converted
- Process: free atmospheric N$_2$ → bacteria in soil (root-associated) convert to nitrates → plants use nitrates → humans eat plants
- Bioremediation
- Artificial use of microbes for environmental cleanup; microbes metabolize pollutants
- Examples:
- Oil spills: introduced bacteria degrade oil, reducing toxicity
- Drain clogs: bacterial enzymes break down organic material in clogs
- Commercial uses in food and beverage industry
- Bacteria
- Dairy products: cheese, yogurt
- Cosmetic procedures: botulinum toxin (used in Botox) produced by bacteria
- Fungi (yeast)
- Fermentation of grape sugar to alcohol (wine)
- Alcoholic beverages: wine, beer
- Breads (leavening by yeast)
- Application in Medicine
- Microbes produce substances used as antibiotics (kill or inhibit bacteria)
- Examples: Penicillin and Neomycin
- Penicillin: produced by a fungal mold (Penicillium)
- Natural source: Penicillin mold found in mushroom gills
- Production: mold grown in deep batch fermenters with sugar and key ingredients; penicillin is then purified for medical use
Pathogenic Microbes vs Normal Microbiota
- Pathogenic Microbes = pathogens
- Definition: live agents capable of causing disease in a host
- Examples:
- Bacteria: Neisseria gonorrhoeae → gonorrhea
- Fungi: Tinea pedis → athlete’s foot
- Virus: SARS-CoV-2 → COVID-19
- Normal Microbiota (normal flora)
- Definition: resident microbes found inside and outside the human body that cause no harm; can be beneficial
- Roles: may produce substances humans cannot make (e.g., Vitamin K for blood clotting) and can prevent overgrowth of harmful microbes
- Characteristics:
- Normally found in specific body areas
- May become beneficial to the host
- Examples:
- Streptococci in the mouth
- Staphylococci on the skin
- Escherichia coli in the colon
- Note on balance: Normal microbiota will divide rapidly to occupy niches, limiting space for invading pathogens
Milestones and Major Contributions to Microbiology
1) Van Leeuwenhoek – Father of Microbiology
- Lens maker; first to observe live microorganisms through magnifying lenses
- Produced detailed drawings of microorganisms
2) Jenner – Father of Vaccines - Pioneered immunization and smallpox prevention
- Observed cowpox infection protected against smallpox in milkwomen; used cowpox material to inoculate a healthy person; established the first vaccine against smallpox
3) Pasteur - Disproved spontaneous generation (non-living → living)
- Established biogenesis: living cells arise only from pre-existing living cells; provided germ theory of disease
- Key experiment: beef broth in a long-neck flask bent into an S-shape; boiled broth; after cooling, microbes did not appear if the neck remained bent; straight-necked flasks allowed contamination; bending prevented entry
4) Lister - Pioneer of sterile surgical procedures
- Used antiseptics to treat wounds and kill microbes
- Applied germ theory to medical procedures to reduce infections and deaths
5) Koch - Established the germ theory: infectious diseases are caused by live pathogens; a specific pathogen causes a specific disease with specific symptoms
- Discovered Bacillus anthracis as the cause of anthrax in cattle and sheep
- Formulated Koch’s postulates: a sequence of experimental steps to link a specific microbe to a specific disease
6) Ehrlich - Developed chemotherapy concepts; discovered the first chemical substance against syphilis by destroying the pathogen
- Coined the term “magic bullet” for a chemical that can selectively target and destroy a pathogen without harming the host
7) Fleming - Discovered penicillin (the first antibiotic) from a fungal mold
- Observed mold contamination inhibited growth of surrounding bacteria; mold produced penicillin
8) Marshall - Demonstrated that most peptic ulcers were caused by Helicobacter pylori
- Linked H. pylori to peptic ulcers and to gastric cancer
Emerging Infectious Diseases (EIDs)
- Definition: diseases that are new or changing and are increasing in frequency or have the potential to increase in frequency in the near future
- Current prevalent EIDs in humans:
- SARS-CoV-2 → COVID-19
- Zika virus → Zika disease
- West Nile Virus → West Nile encephalitis
- Influenza virus → Influenza
Key Factors Contributing to the Emergence of EIDs
- Global travel: rapid spread of pathogens
- Rapid urbanization: crowding and altered environments increase transmission
- Natural disasters: disruption of clean water and sanitation facilities
- Contaminated water can lead to diarrheal diseases
- Frequent gene mutations: microbes can mutate to become more harmful or drug-resistant
- Climate change: shifts in habitats alter disease patterns
- Wet areas: increased mosquito-borne diseases
- Dry areas: increased airborne transmission risks
- Developing drug resistance: pathogens evolve to resist existing treatments