Which organisms are microbes? What are the types of microbes? Structure of the bacterial cell and the virus. Taxonomy and nomenclature of bacteria. Bacterial features.
Introduction to medical microbiology
Microbes fall into one of the following groups:
Viruses
Fungi and other microscopic eukaryotes
Bacteria
Microbes can only be seen by microscopy- light or electron microscope
electron microscope – 1Å– 100µm (small molecule, viruses, bacterium)
light microscope – 1µm- 1cm (bacterium, animal cell, plant cell)
Fungi, other microscopic eukaryotes and bacteria are cellular and have complex genomes
Viruses are not cellular, relatively simple genomes
Viruses:
- they need to grow in cells (classed as infectious agents)
- many different viral pathogens (all have small genomes this reduces the number of potential
antiviral targets
Human infection
Common complaints – rhinovirus
more clinical concern – influenza, herpes virus
dangerous pathogens – ebola virus
Certain viruses infect bacterial cells – bacteriophage
Concerns about viruses – potential for rapid spread –
e.g. influenza virus spread in 2 months; potential for high
fatality rate/ lack of treatment options – e.g. nipah virus
– causes illness and inflammation of the brain and/or
respiratory disease – has fatality rate of 40-75% ( no
drugs or vaccines available to treat it)
General features of an enveloped virus:
Nucleic acid – SS/DS (single stranded/double stranded)
RNA/DNA typically contained in a capsid
Capsid – protein ‘NA container’
Nucleocapsid is NA + Capsid – symmetry formed
diagnostic use
Glycoprotein- interacts with external environment
Matrix protein- structural/ assembly roles
Not all viruses are enveloped:
- Envelope free viruses tend to last longer in environments
- enveloped viruses – host cell entry / immune evasion
, Fungi and other microscopic eukaryotes
All eukaryotes cells have a nuclear membrane which makes them harder to treat by antibiotics;
Some can form resting stages or spores which are more difficult to deal with
Fungi:
- Grow as single cells (yeast) or long branches (hyphae)
- Some fungi are dimorphic – can grow as either yeast or hyphae
- Most clinical concern – Candida albicans. Aspergilus fumigatus ( invasive infections/ and
immunocompromised; number of invasive infections
Other (non-fungal) microscopic eukaryotes- parasites:
Primarily protozoa
e.g. Plasmodium falciparum which causes the most dangerous form of malaria
Bacteria:
- Biggest clinical problem
- Bacterial and archaeal cells are prokaryotes ( Differ from eukaryotes as they lack a nuclear
membrane; Grow typically as single cell outside human cells)
- May bacterial species- 35,000 to 2,000,000 species estimated (hundreds can be human
pathogens)
- Divided into Gram positive and Gram negative cell types (reflects different cell wall
structures; detected by chemical staining
Staphylococcus aureus – blue cocci
Escherichia coli – pink bacilli
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