Microbiology Flashcards
The Human Microbiome
- The microbiome is the genetic material of all the microbes- bacteria, fungi, Protozoa, and viruses- that live on and inside the human body.
- The number of genes in all the microbes in one person’s microbiome is 200 times the number of genes in the human genome.
Key features of microbes
• Boundary -Barrier from the environment. -Cell wall (in some), membrane • Cytoplasm -Aqueous mixture of macromolecules -Proteins, lipids, nucleic acids polysaccharides, other organic and inorganic molecules. -Organelles (in some) • Transport requirements -Nutrients in, products out. -Membrane permeability and mechanisms of transport.
Fungi
- Eukaryotes
- Candida: a yeast- unicellular, reproduce by budding
- Aspergillus: mould- multicellular, reproduce by spores
Protozoa
Huge family of single-celled eukaryotic parasites. Major tropical and zoonotic diseases.
Helminths
- Huge family of single celled eukaryotic parasites.
- Major tropical and zoonotic diseases
Bacterial morphology
-Shape: Round (coccus, cocci), Long (bacillus/bacilli), A few are spiral/branched (filamentous), comma shaped
Gram positive and Gram negative
Based on the ability to take up the stain based on the thickness and accessbility of cell wall peptidoglycans.
Gram-pog: cell wall with peptidoglycan so turns out purple
Gram neg: thin peptidoglycan layer and an outer membrane. turns out pink
Bacterial growth requirements-physical:
• Temperature
• PH
• Salt content
All used for selection of bacteria in the lab.
Peptidoglycan structure and synthesis
A 3D polymer
• N-acetylated sugars
-glucosamine (NAG) and muramic acid (NAM)
And
• 3-5 amino acid peptides
-AA s peculiar to peptidoglycans- resistant to enzymatic destruction
• Cross-linked by transpeptidase enzymes
Synthetic pathways- unique to bacteria. • Polymerisation of sugars -To make the back bone • Elongation of aa side-chains -To add the peptides • Transpeptidase -To cross link
Mycobacteria
- Basically a Gram positive cell wall
- Dont stain Gram positive
- Very thick lipid membrane (mycolic acid mycomembrane) anchored to peptidoglycan layer- intracellular survival
Other important features of bacteria
• Capsule
-Polysaccharide coat
-‘hides’ immunogenic cell wall
-immunity requires antibodies to the capsule
-metabolic burden on the bacterium
-confers virulence e.g., haemophilia influenzae
• Ribosomes
-engines of protein synthesis
-70S (sedimentation rate): smaller than in eukaryotes 80S
-Subunits 50S and 30S
-Each contains RNA and proteins
-Bacterial RNA: target antibiotics and diagnostic tests
• Mobile genetic elements
• Spores
• Gene regulation
Mobile genetic elements: Plasmids vs Transposons
Plasmids: -circular ‘extra-chromosal’ DNA -independently replicating -present in many bacteria -can code for dozens of genes -like viruses: passes down to progeny, some transmitted between bacteria.
Transposons
-DNA sequences that are able to move location in the genome. -Encode transposase -Plus other genes -Mobile between: genomic and plasmid DNA, plsmids, plasmids and genomic DNA.
Code for toxins and antibiotics resistance genes.
Glycopeptides
Vancomycin, Teicoplanin, Telavancin- only active in G+
Used (intravenous) for serious gram pos organisms which produce beta-lactamases or are not responding to other treatments
Oral: not absorbed but used to treat Clostridium difficile anaerobic) associated with diarrhoea (vancomycin)
Important: Nephrotoxicity (renal toxicity)
Metronidazole
- Prodrug: only anaerobic organisms can metabolite to its active form
- Metabolites produced are toxic to DNA-bactericidal
- Considered potentially mutagenic, carcinogenic and teratogenic.
Rifampicin
-Bactericidal-Mycobateria (M.tuberculosis, M.leprae)
-Binds to RNA polymerase- inhibits mRNA synthesis
Metabolic interactions: strong induction of CP450, Orange colour: saliva, tears, and sweat
Resistance Mechanisms
- Inactivation or modification of the antibiotic
- Alteration of the microbial enzymes that transform pro-drugs to the effective moieties
- Alteration of the target
- Reduced uptake of the antibiotics
- Enhanced export of the antibiotic (efflux pumps)
- Development of alternative pathways
Ribosomes of bacteria
- engines of protein synthesis.
- 70S (sedimentation rate): smaller than in eukaryotes.
- subunits 50S and 30S
- each contains RNA and proteins.
- bacteria RNA: target for antibiotics and diagnostics.
Bacteria that produce spores?
Clotridia and Bacillus.
- Non replicating dormant form.
- Resistant to drying, temperature, disinfection, digestion.
- Important in clinical disease pattern, infection control.
Gene regulation-bacterial growth
- The lag phase: no increase in cell numbers, adjustment to new environment, gene regulation
- The exponential phase: cell doubling, slope of the curve= growth rate environment.
- The stationary phase: nutrients become depleted, metabolites build up, division stops, gene regulation
- The death phase: -exhaustion of resourced, toxicity of environment.
Virus latency
Virus lies dormant (latent) within a cell
Viral pathogenesis
a process by which viral infection results in disease
two components of viral disease
- effects of virus replication on the host
- effects of host reponse on the virus and host.
three requirements for a successful infection
- Enough virus
- Cells accessible, susceptible, permissive
- Local antiviral defence absent or overcome
horizontal transmission
between members of the same species (zoonotic different species)
Latrogenic transmission
activity of health care worker leads to infection of patient
nosocomial transmission
when an indiivdual is infected whilst in hospital or healthcare facility
vertical transmission
transfer of infection between parent and offspring.
Germ line transmission
agent is transmission as part of the genome, e.g., proviral DNA
Respiratory tract affected by virus
- most common route of viral entry
- barriers to infection: swallowing, ciliary acion from lower tract, macrophages in alveoli (no cilia or mucous)
- can enter by aeorosolised droplets from cough or sneeze or contact with saliva
- large droplets lodge in nose; smaller in airways or alveoli
Ailmentary tract affected by virus
- eating, drinking, social activities introduce viruses into the ailmentary tract
- designed to mix, digest, absorb food, so content are always in motion, good opportunities for virus-cell interactions.
- extremely hostile environment: stomach is acidic, intestine is alkaline, presence of digestive enzymes, bile detergents, mucous, antibodies, phagocytic cells.
- viruses have evolved to infect are resistant, e.g., enteroviruses, reoviruses