Microbiology Flashcards
Describe the four main groups of human pathogens
- Protozoa- single celled animals (eukaryotes)
- Fungi- higher plant like organisms (eukaryotes)
- Bacteria- generally small, single celled (prokaryotes)
- Viruses- very small obligate parasites (non-living)
Describe the nucleoid in prokaryotes
An irregularly shaped region within the cell of a prokaryote that contains DNA and proteins. There is no nuclear membrane. Genetic information contained in a single circular molecule.
Describe the cytoplasmic membrane in prokaryotes
- Bacteria are sensitive to disruption of the plasma membrane by physical or chemical methods.
- Therefore, if the membrane is disturbed the cell cannot function.
Describe the difference in cell walls between gram negative and gram positive bacteria
o Gram-negative- single layer of peptidoglycan, lipopolysaccharide structure (LPS)
o Gram-positive- thick multi-layer of peptidoglycan
Describe the flagellin in prokaryotes
Protein unit making up a multi stranded filament core, they allow for bacterial movement.
Describe the fimbriae (attachment pilus) in prokaryotes
Thinner and shorter than a flagellum and allows prokaryote to attach to target tissues of host.
Describe prokaryotic protein synthesis in comparison to eukaryotes
- Transcription is carried out on a singular chromosome that is not compartmentalised.
- There is co-transcriptional translation (transcription and translation occur simultaneously).
- This is impossible in eukaryotes as transcription happens in the membrane bound nucleus and translation in the cytoplasm.
- No process of splicing out introns as these are very rare.
Describe five common shapes of microorganism
- Cocci (spheres)- division in one plane to produce chains or division in three planes to produce clumps,
- Bacilli (rods)- may be regular rods associated in pairs or long chains of rods
- Curved rods- gram negative
- Spiral-shaped- can be rigid spiral or flexible spiral
- Fusiform- very extended shapes
What colours will gram negative and positive bacteria stain
Gram negative- stain pink
Gram positive- stain purple
Explain the idea of selective media
Presence of specific substances permits the growth of one organism over another e.g. mannitol salt agar
Explain the idea of differential media
Incorporation of chemicals produces visible changes in colonies that facilitate identification.
What can haemolysis be used to identify?
Streptococci species
What biochemical tests can be done to identify bacteria?
Find out if they are coagulase - or + or catalase - or +
What do serological tests look for?
Antibodies
Define Microbiome
The collective genomes of the microbes (composed of bacteria, bacteriophage, fungi, protozoa and viruses) that live inside and on the human body.
Define pathogenesis
The development of a disease and the chain of events leading to that disease.
Define parasitic relationship
The parasite benefits from taking nutrients or energy from the host and the host is harmed.
Define virulence
The capacity of a microbe to cause damage to the host
Define pathogen
A harmful organism that produces a pathology
Define commensal
An organism that is part of the normal flora, often a mutualistic relationship and they are endogenous.
Define opportunistic pathogen
An organism that causes infection when opportunity change in natural immunity arises e.g. immunocompromised individual.
Define contaminant
An organism that is growing in a culture by accident.
What are six types of infectious agent?
- Bacteria: Prokaryotic, single celled organisms
- Viruses: Non-living, obligate parasites
- Fungi: Eukaryotic single to multi-cellular infectious agents e.g. candida
- Protozoa: Eukaryotic e.g. Amoeba, Plasmodium, Toxoplasma
- Parasites
- Prions: Infectious proteins e.g. mad cow disease
Describe Gram Negative Cocci
They appear in pairs. 2/10 species are pathogenic. Neisseria Meningitidis (common cause of meningitis) and Neisseria gonorrhoeae (causes gonorrhoea)
Describe Gut commensal coliforms
Gram Negative
Normal gut flora.
Includes most strains of E.coli.
They grow best aerobically but can be grown anaerobically.
Any coliform that gets into a normally sterile site can cause serious infection.
Describe Group A Streptococci
Gram Positive
They cause diseases such as pneumonia, necrotising fasciitis and scarlet fever.
Describe Enterococci
Gram Positive
They are non-Haemolytic Streptococci and cause enteric infections
Describe Staphylococci
Gram Positive
Two main pathogenic species are S. Aureus and S. Epidermis
S. Epidermis is found in the skin and will affect those who are immunocompromised.
S. Aureus is a significant problem especially due to the MRSA strain.
Describe Clostridium
Gram Positive
Produces spores that can survive outside the body for many months.
Clostridium difficile causes antibiotic associated diarrhoea as the antibiotics kill everything in the gut but the spores allowing them to fully colonise the gut.
What triggers fever and sepsis?
Endotoxins are part of the outer membrane of the cell wall of Gram-negative bacteria.
Endotoxin/LPS will be released from Gram negative cell walls when the bacteria die.
These toxins will bind to receptors on macrophages, B cells and other cells triggering acute release of cytokines resulting in inflammation.
Gram positive bacteria can also cause sepsis and fever through release of different toxins (only gram negative bacteria have endotoxins).
Explain what happens during fever and sepsis
- Fever occurs when the body’s set temperature is raised.
- Sepsis occurs because inflammation causes the blood vessels to become leaky and lose fluid into the tissues.
- Lower blood volume requires the heart to work harder to maintain oxygenation of tissues.
- Poor tissue oxygen perfusion means the blood supply to less essential organs is shut down.
- The blood clotting system is activated causing blood clotting in tiny vessels, this uses up clotting factors and results in an increased risk of haemorrhage.
Describe the Viral Cycle
1) Attachment- this is a specific interaction, the virus can only attach to certain cell types.
2) Entry- Internalisation of both the receptor and the virus is triggered.
3) Uncoating- viral nucleic acid is released from the capsid.
4) Nucleic acid and protein synthesis- Nucleic acid is used as instructions to produce new viral proteins - host ribosomes are used and host polymerases may be used. Viral nucleic acid is replicated into progeny genomes.
5) Assembly- Nucleic acid and proteins packaged together.
6) Release- release can be through a process that is almost the reverse of entry phagocytosis or lysis.
How do viruses cause disease?
- Cell death due to lysis or hijacking of cell machinery.
- Cell death due to immune system (especially by cytotoxic T cells).
- Cell proliferation (increasing number of cells).
- Viruses can infect a person and that person can be infectious but without symptoms.
- A lot of symptoms are actually caused by the immune response to the foreign body and not the virus itself e.g. fever.
Explain viral persistence
- The virus may become dormant with no active replication
- Such viruses may reactivate (e.g. herpes simplex virus)
- Alternatively, the virus may remain continually active for years.
- These patients may remain asymptomatic but infectious for decades before getting life threatening complications
How can viral infection be confirmed in the laboratory?
- PCR (polymerase chain reaction)
- Antigen detection (by various methods)
- Detection of viral antibodies can also be used to differentiate recent from past infections.
Define Antimicrobials
A drug used to treat or prevent infection caused by micro-organisms.
Define Antibiotics
Antimicrobial substance that’s active against bacteria
Define Bacteriostatic
Inhibits the growth of bacteria.
Define Bacteriocidal
Kills Bacteria
List five antibiotic targets
- Cell Wall
- Ribosomes
- DNA Replication
- DNA Gyrases
- Metabolic Pathways
What are three groups of antibiotics that target the cell wall?
Penicillins, Cephalosporins and Glycopeptides
How do the penicillins work?
Works by inhibiting the synthesis of the peptidoglycan layer of bacterial cell walls resulting in the cell wall becoming compromised.
Describe four commonly used penicillins
- Amoxicillin: Safe, well tolerated antibiotic.
- Temocillin: This antibiotic has been reintroduced due to increasing bacterial resistance.
- Coamoxiclav: Broad spectrum antibiotic
- Flucloxacillin: very narrow spectrum and only used for staph and strep only. It replaced methicillin however MRSA is now also resistant to flucloxacillin.
Why do the cephalosporins have a restricted use in many places?
They kill off normal gut bacteria and allow the overgrowth of C. difficile which causes nasty gastroenteritis.
How do the glycopeptides differ from the penicillins and cephalosporins?
They aren’t Beta-lactam antibiotics
Name 3 groups of antibiotic that target protein synthesis
Aminoglycosides, tetracyclines and macroclides
Name 2 groups of antibiotic that affect nucleic acids
Metronidazole and Fluoroquinolones
Which main groups of antibiotic target folic acid synthesis and why does this work?
Folic acid is a vitamin required for synthesis of key cellular components.
Two main groups are Trimethoprim and Sulphonamides.
Why may bacteria have natural resistance to an antibiotic?
- The target is not present e.g. there may not be a cell wall
- The target is not accessible
- It is in a developmental structure/state e.g. a spore
- Metabolism e.g. uptake of the antibiotic may require anaerobic conditions
How do biofilms allow resistance?
The organisms are resistant to antimicrobial agents and host defenses as they exist as part of a community in a three-dimensional structure.
Describe persistor cells
- They are tolerant not resistant
- They are metabolically inert with very slow growth, targets may not be active resulting in the antibiotic having no effect
- They have subpopulations of cells and may be enriched in biofilms
Describe acquired resistance
- Mutation and genetic variation results in the drug no longer being active against the entire population of cells.
- As bacteria have rapid growth and multiplication this increases the chance of genetic mutations occurring.
- If these mutations are advantageous then through selection they will increase in the population resulting in resistant strains growing in numbers.
- Genes for resistance can be passed to bacteria of the same generation through horizontal gene transfer
Describe four mechanisms that allow bacteria resistance to a drug
1) Altered permeability- the drug cannot reach its target
2) Inactivation- the drug reaches its target but is inactivated
3) Altered Target Site- the binding site changes
4) Replacement of a Sensitive Pathway- e.g. Folic Acid Synthesis
Name the ten SICPs
- Hand Hygiene
- Sharps Management
- Clinical Waste
- PPE
- Patient Placement
- Body Fluid Spillages
- Environmental Cleanliness
- Clean Equipment
- Laundry
- Respiratory Etiquette
5 ways any infection can spread?
- Inhalation
- Ingestion
- Inoculation
- Infant (from mother)
- Intercourse
