Introduction to microbiology Flashcards
(40 cards)
What are the 5 groups of microbes?
-Parasites (Protozoa and Helminths)
-Fungi
-Bacteria
-Viruses
-Prions
Give 3 examples of how microbes interact with hosts and cause disease
-Structural and molecular makeup
-Biochemical and metabolic strategies
-Reproductive processes
Comparison of microbes (table)
Macroparasites vs Microparasites
How are microbes classified?
-Microbes are divided into related groups based on similar characteristics
-All microbes (except viruses) are named according to the binomial Linnean system (genus and species)
What characteristics of bacteria are used for classification?
Morphological:
-nature of cell wall
-staining
-shape (cocci/ball, bacilli/rods, spirochetes/spirals)
-spore forming abilities
Biochemical:
-Metabolism (bacterial growth is affected by oxygen depending on their energy generating system
-Production of specific enzymes or toxins
More recently:
-DNA sequencing of their genome
What characteristics of viruses are used for classification?
-Type of nucleic acid (DNA/RNA)
-Number of strands of nucleic acid (ss/ds) & their physical construction (e.g.
segmented)
* Polarity of viral genome (e.g. positive or negative strand RNA)
* Symmetry of nucleocapsid
* Lipid envelope (presence or absence)
Which microbes are eukaryotes and prokaryotes?
Eukaryote:
-Fungi and parasites (protozoa and helminths)
Prokaryotic:
-Bacteria
What are Helminths (parasite)?
-Multicellular worms that infest many organs of the body, most commonly
the GI tract
-Many have complex life cycles that progress from egg to larva to adult
-Transmission can be:
-Direct through swallowing infective stages/larvae penetrating the skin
-Indirect via intermediate non-human hosts
-Most serious helminth infections are caused by TAPEWORMS (e.g. Taenia solium) and FLUKES (e.g. Schistosoma mansoni)
What are Protozoa (parasite)?
-Protozoa are single cell organisms
-Life cycle includes a metabolically active growth stage (trophozoite)
and a dormant stage (cyst).
-May be free-living or life cycle may require one or more hosts
-Infections acquired through ingestion of contaminated water, food or
via insect vectors
-Examples of common diseases caused by protozoa:
* Malaria (Plasmodium spp.)
* Toxoplasmosis (Toxoplasma gondii)
* Leishmaniasis (Leishmania spp.)
What are fungi
-Fungi grow as single cell (yeasts), branched filaments (hyphae) or both (dimorphic fungi). In filamentous fungi the mass of hyphae forms a mycelium
-Fungi have a thick cell wall composed primarily of chitin, as opposed to bacterial cell walls, which are composed of peptidoglycan
-Species causing disease may be acquired from the environment or occur as part of the normal flora
Common fungal diseases (familiarise nit memorise)
Essential and non-essential components of bacteria
Essential:
-Cell wall
-Plasma membrane
-Ribosome
-Nucleoid
Non-essential:
-Capsule
-Flagella
-Pili
-Plasmid
-Spore
Describe the structure of bacteria cell wall
-Cell wall is a multilayered structure mainly composed of peptidoglycan (also known as mucopeptide or murein)
-Peptidoglycan is a polymer composed of the hexose sugars N-acetylglucosamine and N-
acetylmuramic acid (glycan chain) and amino acids (tetrapeptide chain)
Why do bacteria stain differently?
-Peptidoglycan layer in gram positive bacteria is thicker
-Due to thin peptidoglycan layer, gram negative bacteria don’t retain
primary staining
-They become pink with Safranin counter stain
Summary of gram positive vs gram negative cell wall
Which bacteria can’t be seen with gram stain and why?
Acid fast bacteria
-They have an outer layer of complex waxy lipids (e.g. mycolic acid) which can’t be penetrated by dyes in gram stain
-Ziehl-Neelsen (ZN) stain used instead
What is the capsule in bacteria?
-Gelatinous layer outside cell wall
mainly composed of polysaccharide
(sugars)
-Determinant of virulence
(antiphagocytic)
-Helps bacterial adherence to human tissues
-Antigenic; can be component of
vaccine
-Used for identification and lab
diagnosis: swelling reaction
What is the flagella in bacteria?
-Organ of motility
* Flagellated bacteria have a
characteristic fixed number and
location of flagella
-Plays a role in pathogenesis
-Used for identification and lab
diagnosis
What are Pili (fimbriae) in bacteria?
-Hair-like filaments that extend from cell
surface
-Thinner and shorter than flagella
-Two main functions:
-Attachment (ordinary pili/fimbriae)
-Conjugation (sex pili)
What are plasmids in bacteria?
-Additional extra-chromosomal genetic material
-Mostly circular dsDNA
-Capable of self-replication
-Can contain antibiotic resistance genes
-Transmissible by conjugation, transduction or transformation
What are spores in bacteria?
-Only produced by some Gram-positive bacteria (Bacillus and Clostridium species)
-Highly resistant structures formed in response to adverse conditions
-Contain bacterial DNA surrounded by a thick keratin-like coat that confers resistance to
heat, chemicals and drying
What is the medical importance of spores?
What are the distinguishing characteristics of viruses?
-Viruses are intracellular parasites
-They contain either DNA or RNA genomes comprised of novel genetic material encoding structural and functional proteins needed for self
perpetuation
-New virus particles are formed by assembly of components synthesised using host cell proteins
