Microbiology

Microbiology is the study of small life forms (bacteria, fungi, protozoa, algae and viruses)

  • The control and identification of microorganisms to explain and prevent disease

Pathogens: microorganisms capable of causing disease in the host

Infection: growth and survival of microorganisms on or in the body

Infection control: preventing microbial contamination and infection

Infectious disease: occurs when microorganisms in the body multiply and cause damage in the tissues

→ Diseases were recognised before their causative agents

Caries are caused by acids produced by oral bacteria following the fermentation of sugars.

Prokaryotic

Eukaryotic

Macroorganisms

None known

Animals, plants

Microorganisms

Archaea, bacteria

Algae, fungi, protozoa

Acellular: viruses and prions

A Level: compare prokaryotic and eukaryotic

  • Prokaryotic: smaller, simpler and singular

Microscopy (types)

+ Atomic force microscopy

Gram-positive - large layer of peptidoglycan e.g. Streptococcus mutans

→ PURPLE

Gram-negative - small layer of peptidoglycan e.g. Porphyromonas gingivalis

→ PINK

Acid-fast bacteria e.g. Mycobacterium tuberculosis

Pleomorphic = altering morphology

Diagnostic Mircobiology:

  • Collect specimen

  • Culture technique

    • Nutrient broth 24h + select agars

  • Aerobic/anaerobic incubation

  • Staining

  • Microscopy

  • Biochemical test

  • Molecular diagnostic analysis

Capsule: well organised and not easily washed off

Slime layer: a zone of diffuse, unorganised material that is removed easily (prevents desiccation and helps bacteria to adhere to substances)

Endospores: resting/dormant structure

Flagella: long (3-20um), thin filament. AIds bacteria mobility and is made up of helices of flagellin protein

Pili: appendages (0.5um) found in gram-negative bacteria. Aids bacteria adhesion and is made up of helices of pilin protein.

Planktonic bacteria are free-living bacteria.

In asexual production by binary fission, daughter cells are identical.

If all progeny survive then growth is exponential.

Biofilms:

A community of bacteria are attached to a substratum or interface or to each other, embedded in a matrix of extracellular polymeric substances and displays altered phenotype characteristics

  • Up to 1000x more resistant to antimicrobial treatments

  • Responsible for >65% of microbial infections in humans

Antibiotics target prokaryotic cells.

Fungi: are eukaryotic, ubiquitous and only a few are pathogenic to humans (200) e.g. Aspergillus, Candida, etc

Causes disease in immunocompromised hosts

Examples: angular stomatitis, Pseudomembranous oral candidosis, aspergillosis

Viruses: are small (20-300um) with simple chemical composition, subunit construction and strict geometric structures. Its genetic information as DNA or RNA, replication is strictly intracellular and there is no intracellular organelles or rigid cell walls. They are sensitive to interferon.

Prions: are associated with degenerative changes in the brain. They are small proteinaceous particles with no nucleic acid. They convert normal proteins to abnormal forms e.g. variant CJD → “mad cow disease”

Transmission

  1. Direct and indirect contact e.g. Herpes simplex

  2. Drpolet e.g. influenza

    • mucus membrane contact with mucus droplets of >5um travel up to 1m

  3. Airborne e.g. tuberculosis, measles

    • Small droplets <5um travel further

  4. Other

    • Contaminated food, water, devices, etc

Sources:

Nosocomial infection: acquired in hospital/medical facility

Opportunistic: resulting from organisms that are usually harmless but cause disease under certain conditions

Prevent:

  • Isolation and PPE

  • Hand hygiene

  • Vaccinations (keep up to date)

Vaccines are substances that trick the immune system into believing that it has been exposed to infection that results in enhanced immune responses which protect against the pathogen and its subsequent infection.

Sterilisation: destroys all forms of microbial life and is carried out by physical or chemical methods

Disinfection: eliminates many or all pathogenic microorganisms except bacterial spores or inanimate objects

Autoclave

  • 121 for 15 mins

  • Dry heat 140 for 2h

  • Irradiation to break down DNA/protein

  • Filter sterilise liquise (0.2um pores)

  • Harsh chemical treatments (bleach/alcohol)

Decontamination: removes pathogenic microorganisms from objects so they are safe to handle, use or discard.

Antimicrobial agents: active against a range of microorganisms including bacteria, viruses, fungi and protozoa (antiparasitic)

Antibiotic: a substance produced by microorganisms that kills (bactericidal) or inhibits (bacteriostatic) the growth of bacteria