Medical microbiology

Question 1

What are the basic differences between viruses, bacteria and fungi

Answer 1

Structure
Viruses: Composed of genetic material (DNA or RNA) encased in a protein coat; may have an outer lipid envelope. Non-cellular and unable to reproduce independently.
Bacteria: Single-celled prokaryotes with a simple structure, including a cell wall and nucleoid region containing DNA. Can reproduce independently via binary fission.
Fungi: Eukaryotic organisms that can be unicellular (yeasts) or multicellular (molds, mushrooms). They have a complex structure, including a chitin cell wall, and reproduce through spores.
Reproduction
Viruses: Depend on a host cell for replication, using the host’s machinery to create new viruses.
Bacteria: Reproduce asexually through binary fission and can exchange genetic material via conjugation, transformation, or transduction.
Fungi: Reproduce both sexually and asexually, primarily through spores, budding, or fragmentation.
Metabolism
Viruses: Lack metabolic processes and rely entirely on host cells for energy and replication.
Bacteria: Possess diverse metabolic pathways; can be aerobic or anaerobic, and autotrophic or heterotrophic.
Fungi: Mostly heterotrophic, absorbing nutrients through external digestion, and play a vital role in decomposition.
Living Status
Viruses: Often considered non-living due to their inability to carry out metabolic processes or reproduce without a host.
Bacteria: Classified as living organisms because they can reproduce and perform metabolic activities.
Fungi: Also regarded as living organisms, featuring complex life cycles and cellular structures.
Diseases
Viruses: Responsible for diseases ranging from the common cold to severe illnesses like HIV/AIDS and COVID-19.
Bacteria: Can cause infections such as strep throat and tuberculosis, but many are harmless or beneficial.
Fungi: Can lead to infections (e.g., athlete’s foot, candidiasis) and diseases in plants.

Question 2

Lists the categories of micro-organism that cause infection.

Answer 2

Bacteria: Single-celled prokaryotes that can lead to various infections, such as strep throat, pneumonia, and urinary tract infections.

Viruses: Tiny infectious agents that require a host to replicate, causing diseases like influenza, HIV/AIDS, and COVID-19.

Fungi: Eukaryotic organisms, including yeasts and molds, that can cause infections such as candidiasis and athlete’s foot.

Parasites: Organisms that live on or in a host, including protozoa (like malaria) and helminths (like worms), which can lead to infections and diseases.

Prions: Misfolded proteins that can cause infectious neurodegenerative diseases, such as Creutzfeldt-Jakob disease.

Question 3

List the common specimen types collected for culture.

Answer 3

• Mid stream specimen of urine (MSSU) – urinary tract infection.
• Sputum – lower respiratory tract infection.
• Throat swab – tonsillitis / pharyngitis.
• Swabs – wound infection, genital tract infection.
• Faeces – infectious diarrhea.
• Blood culture – septicaemia (sepsis).
• Cerebrospinal fluid CSF) – meningitis.
• Aspirate of pus – abscess.
• Bone – osteomyelitis.

Question 4

Outline the role of microscopy and culture in the diagnosis of bacterial infection.

Answer 4

• Still highly relevant today despite modern advances!
• Microscopy is rapid - urgent information relayed to clinicians.
• Microscopy is not specific but assists provisional diagnosis
  and empiric antimicrobial therapy.
• Followed by bacterial culture and susceptibility testing.

Question 5

Explain the difference between sterile and non sterile sites.

Answer 5

Areas of the body that are normally free of microorganisms. Should remain free of pathogens to prevent infections.
Medical procedures involving these sites (e.g., surgeries) require strict aseptic techniques to maintain sterility.
Sterile sites include:
Brain
Heart
Liver
Kidney

Areas of the body that naturally harbor microorganisms, including both harmless and potentially harmful ones. Home to normal flora (beneficial microorganisms) that can help protect against infection.
Infections can occur when pathogens from these sites enter sterile sites or when the balance of microorganisms is disrupted.
Non-sterile sites include:
Mouth
Oesophagus
Lungs
Stomach
Intestine

Question 6

Outline the methods of detecting viruses.

Answer 6

• Molecular methods
• real time / multiplex PCR
• Antigen detection
• Serology to determine immunity
• Virtually obsolete methods e.g.
• Electron microscopy
• Cell or tissue culture - inoculate a “cell line”