Introduction to Medical Microbiology Flashcards
What disease can the fungus candida cause?
Thrush
What kind of organism causes malaria?
Protozoa
Describe prokaryotes.
No nucleus, no membrane bound organelles. Genome: a single circular DNA, haploid (a single version of each gene), non-genomic DNA sometimes. 70s ribosomes (50s 30s subunits). Peptidoglycan cell wall.
Describe eukaryotes.
Membrane bound nucleus and organelles. Genome: chromosomes in nucleus, diploid (two versions of each gene). 80s ribosomes (60s 40s subunits), no cell walls except plants and fungi
Coccus/cocci
Round Bacteria
Bacillus/bacilli
Long, rod bacteria
Coccobacillus
Elongated round bacteria (like an omega 3 pill)
Vibrio
Comma-shaped bacteria
Spirochete/ spirochetes
s
Spiral bacteria(longer and more flexible than spirilla)
Spirillum/ spirilla
Spiral bacteria(shorter and stiffer than spirochetes)
Briefly outline Gram stain procedure
Heat fix sample onto plate. Add crystal violet followed by iodine and add decolourising agent (alcohol). Add counterstain safranin
Explain what colours Gram positive and Gram negative bacteria are and what structural feature of the bacteria determines whether they are positive or negative.
Gram +ve is purple and Gram -ve is pink. Thick peptidoglycans layer leads to purple and thin peptidoglycans layer leads to pink.
Down the microscope, bacteria form/grow in……..
Chains or clusters
On solid culture mediums, bacteria grow in/ form……
Colonies
When growing on solid culture mediums, bacteria excrete enzymes and waste products into……
The environment
Studying patterns of bacterial growth can be used to……..
Diagnose Infections
List all potential growth requirements of bacteria
Atmosphere, nutrients, temperature, pH, salt content
List the 3 different types of bacteria which have different atmospheric requirements
Aerobes, obligate anaerobes, facultative anaerobes
Aerobes
Bacteria that need O2 in atmosphere to carry out aerobic respiration. Use O2 as final electron acceptor
Obligate anaerobes
Bacteria that must have anaerobic conditions. O2 is toxic, they die. Fermentation (Anaerobic respiration). Final electron acceptor is an organic molecule. Thrive when substrate is plentiful.
Facultative anaerobes
Depending on conditions, can switch between anaerobic and aerobic respiration
List GENERAL nutritional requirements of bacteria
Everything that they cannot make, they must bring in. Purines, pyrimidines, amino acids, vitamins.
List nutritional requirements of E.coli
Glucose and inorganic salts ONLY so very easy to grow in lab.
List nutritional requirements of Treponema Pallidum and state what disease it causes.
Causes syphilis. Needs a specialised enriched medium and is very hard to grow.
Fastidious
Complex nutritional requirements
List 5 genera of bacteria that are strict anaerobes (obligate)
Peptococcus, Peptostreptococcus, Clostridium, Propionibacterium, Bacteroides
Name two important exceptions to general bacteria features and tests for bacteria
Some bacteria lack cell wall and so aren’t free-living (Mycoplasma and Chlamydia genera). Some bacteria have cell wall that doesn’t stain well by Gram (mycobacteria, which cause TB)
Give the bacterial envelope structure of Gram positive bacteria
Thick peptidoglycans layer. Lipoteichoic and teichoic acid in envelope. Has a plasma membrane
What is the function of teichoic acid?
Plays a role in cell shape determination, regulation of cell division and other aspects of Gram +ve bacterial physiology
Give bacterial envelope structure of Gram -ve bacteria.
Has an outer membrane (unlike +ve) which contains proteins and pores and lipopolysaccharides (which have polysaccharide chains drifting out from bacterial surface). Thin peptidoglycans layer. Has an inner membrane (plasma membrane).
What does bacterial envelope structure determine?
Gram staining, susceptibility to antibiotics. Pathogenicity : Lipopolysaccharides (endotoxin) in Gram negative only whereas exotoxins are in both positive and negative.
If bacteria doesn’t have a cell wall, what can you not do to them
Stain or culture
Describe peptidoglycans
3D polymer. Backbone made of N-acetylated sugars:
N-acetylglucosamine and N-acetylmuramic acid alternate to make glycan chains which are linked by branches of 4 amino acids. These AAs are resistant to enzymatic destruction. Amino acids in different amino-sugar chains are cross-linked by transpeptidase enzyme which forms peptide bridges.
Give three steps of peptidoglycan synthesis targeted by antibiotics.
Polymerisation of sugars in backbone of peptidoglycans. Elongation of AA side-chains to add peptide bridges. Transpeptidase to cross-link.
M. leprae (Mycobacterium leprae)
Causes leprosy
Name 4 bacteria that can cause TB in humans
M. tuberculosis, M.bovis, M. africanum, M. microt
Unique features of Mycobacteria
A Gram +ve cell wall that doesn’t stain Gram positive because of very thick lipid membrane (mycolic acid mycomembrane) anchored to peptidoglycan layer on top of cell wall
Virulence
Relates to the fundamental properties of a microorganism which determine its ability to cause disease and/or the nature of the disease which it causes
(a factor which) Confers Virulence
This means that a microorganism is able to cause disease in a way it would not be able to do without that factor e.g. a lipid coat. Allows microorganism to cause disease in a way that it could not if it did not have the factor.
Pathogenicity
The probability that an organism is causing disease in patient
In mycobacteria, what are the two main functions of the mycolic acid mycomembrane?
It is anti-phagocytic and confers virulence
Describe structure and function of bacterial capsule as well as any downsides to it.
Polysaccharide coat. Hides immunogenic cell wall so immunity to the bacteria requires antibodies to the capsule. Confers virulence. However it is a metabolic burden on the bacterium.
Immunogenic
Containing receptors that can be recognised by the immune system
Name 2 mobile genetic elements
Plasmids, Transposons.
Plasmids in bacteria
Circular ‘extra-chromosomal’ DNA. Independently replicates. Present in many (not all) bacteria. Code for dozens of genes. Passed down to progeny. Some are transmitted between bacteria.
What do mobile genetic elements in bacteria code for?
Toxins and antibiotic resistance genes.
Transposons in bacteria
DNA sequences that are able to move location in the genome (including in non-genomic DNA). Encode transposase and other genes. Mobile between genomic and plasmid DNA and vice versa and between plasmids.
Mobile Genetic Elements
DNA sequences that can move around the genome, changing their number of copies or simply changing their location, affecting the activity of nearby genes (includes plasmids even though they are considered non-genomic)
Progeny
Descendants
Disinfection vs Sterilisation
Disinfection is the reduction or removal of any harmful organisms whereas sterilisation is the killing of all microorganisms present
Bacterial spores
Some bacteria make spores. These are the non-replicating dormant form of the bacterium. They are resistant to drying, temperature, disinfection and digestion. Reactivate when conditions are favourable.
How to do infection control when dealing with spores
Prolonged high temperatures, sterilisation instead of disinfection
Give the phases of growth of bacteria
Lag, Exponential/log, stationary, death
What controls bacterial growth? Explain what this controlling factor is
Gene regulation. Genes are switched on and off to do different functions and thus influence growth.
Explain what is happening in terms of gene regulation in lag and death phases?
Lag- genes are switched on in preparation for growing as presence of CO2 or sugar detected. Death- death phase genes are switched on as resources are exhausted.
Describe each stage of bacterial growth. Give examples of what you would see in clinical cases at appropriate stages.
Lag- Bacteria is responding to new environment it is on and has detected presence of nutrients. Preparing for growth. Log- Lots of nutrients so rapid cell doubling. This is when infection would be seen. For example bacteraemia. Stationary- nutrients start running out because so many bacteria and thus also a build up of metabolite. Cell division stops. For example, an abscess. Death- resources exhausted and due to metabolite and lack of resources, environment is now toxic to bacteria.
In response to changing environments, how can bacteria use gene regulation?
Genes enable different functions so bacteria switch on and off genes to alter growth rate or change metabolic pathways e.g. facultative anaerobes. Genes that will help them to stick to things in environment (adhesion molecules) like bone or skin. Switch genes on to activate enzymes to digest proteins in host or to inactivate immune system (by degrading immune mediators) or lyse host cells.
Immune mediators
Responsible for generating immune responses and for cell signalling
