Clinical Microbiology Flashcards
Size range of bacteria
0.5um - 5um
Size range of viruses
20nm - 400nm
Size range of fungi
2um - 50um (for yeast and hyphae)
Size range of parasites
4um - 200um (for ova and cysts, but much larger for adult parasites)
What is pathogenesis?
How an infectious organism causes disease
What is epidemiology?
The study of the distribution and determinants of disease
What are vaccinations?
They stimulate an immune response to help protect the human body from infectious disease
What are antimicrobial agents?
A chemical that has properties which inhibit the growth of, or are lethal to bacteria, fungi, viruses and parasites
What are some common infections?
- Septicaemia
- UTIs
- Gastroenteritis
- Genital infections, including STDs
- Mucosa and soft tissue infections, wound infection
- Upper respiratory infection, sore throat, conjunctivitis, otitis media
- Meningitis
- Lower respiratory tract infection
Gram positive organisms:
- Staphylococcus aureus
- Streptococcus pyogenes
- Streptococcus pneumoniae
- Clostridium difficile
Gram negative organisms:
- Escherichia coli
- Haemophilus influenzae
- Pseudomonas aeruginosa
- Neisseria gonorrhoea
- Neisseria meningitidis
- Chlamydia trachomatis
- Campylobacter spp
Viruses organisms:
- Corona virus
- Influenza A
- HIV
- RSV
- Norovirus/Rotavirus
Fungi/Yeast organisms:
- Candida albicans
- Dermatophyte fungi
- Aspergillus fumigatus
Mycobacteria organisms:
- Mycobacterium tuberculosis
Laboratory methods for diagnosis:
- Microscopy
- Agar culture and enrichment
- Tissue culture
- Immunoassays
- Nucleic acid amplification tests
- Nucleic acid sequencing
What component of a prokaryote determines the gram stain reaction?
Bacterial cell wall
What colour is gram positive organisms?
Purple (thick layer)
What colour is gram negative organisms?
Pink (thin layer)
Process in which bacteria divides
Binary fission (20 minutes)
Elements essential for bacterial growth:
Carbon
Hydrogen
Sulphur
Oxygen
Nitrogen
Phosphorus
Potassium
What are peptones?
It is a protein digest - they contain essential components of bacterial culture media
For how long and at what temperature should the agar medium be heated at?
Autoclave for 15 mins at 121 celcius
How many types of culture media are there?
6
What is non-selective agar?
It is a solidified medium, has nutrients to grow a wide range of bacteria but there’s nothing in it that selects a particular type of organism
What is enrichment broth?
Not selective, designed to enrich small number of organisms from samples, without trying to inhibit any of the organisms that might be present
What is differential agar?
Contains nutrients to grow our target organisms, some inhibitors are present but most importantly it has a substrate that our target organism can metabolise to produce a specific colony or colony type/appearance
What is chromogenic agar?
It identifies other enzymatic pathways in the organism, and linking a substrate to a molecule which when the substrate is cleaved the molecule attached will go from a colourless to a coloured molecule, and we can colour our colonies to make it much easier to target the organism from the non-target organism
What is selective enrichment broth?
Used to grow specific microorganisms, including food borne pathogens: salmonella, staphylococcus and listeria
What is selective agar?
Selective medium contain particular ingredients that inhibit the growth of certain microbes.
What colour colonies are formed when E.coli ferments lactose on CLED agar plate?
Yellow
What method can be used to examine CSF for bacterial meningitis?
Non-selective agar (5% whole horse blood agar and chocolate agar)
What method can be used to examine blood cultures for septicaemia?
Enrichment media (brain-heart infusion broth and 5% whole horse blood agar)
What method can be used to examine urine?
Differential agar (CLED - cysteine lactose electrolyte deficient agar)
What method can be used to examine faeces?
Chromogenic agar (can also be done with selective agar)
What method is used to grow mycobacterium tuberculosis?
Lowenstein-Jensen inspissated egg yolk medium (incubated for 15 weeks, because this organism has a very slow doubling time)
Bacteria share genetic information in three ways:
- Transformation
- Conjugation
- Transduction
What is transformation?
This is were a living viable cell can take up DNA from its surroundings and incorporate it into its genome or genetic composition and create advantage for itself
Who epitomised the classic experiments in regard to transformation?
Avery and Griffiths in the 1920s
What is conjugation?
Genetic material can be shared by intimate contact through the pilli, so one cell can donate a plasmid to another cell by sending it through the pilli and making an intimate connection between the cytoplasm of both cells. Therefore a donor cell can donate, copy a plasmid to the recipient cell.
What is a negative consequence of conjugation?
Antibiotic resistance - antibiotic markers or genes are transferred to another cell through conjugation. Therefore meaning that the cell contains antibiotic resistant material and when multiplied will be able to thrive and grow in selective environments which may contain the antibiotic
What is transduction?
This is where infection with a phage or bacteriophage can can take DNA into a new cell and that DNA can be incorporated into the genome of the recipient bacterium - which lead to a lytic cycle (replicating itself and bursting out of the cell causing infection and ultimately leading to death of the cell
Can viruses be viewed under light microscopy?
No, only electron microscopy
Types of DNA viruses:
- Herpesvirus
- Poxvirus (eg. smallpox)
- Adenovirus
- Papovavirus
- Hepadnavirus (eg. Hepatitis B)
- Parvovirus
Types of RNA viruses:
- Paramyxovirus (eg. RSV)
- Orthomyxovirus (eg. Influenza)
- Coronavirus (eg. SARS)
- Arenavirus
- Retrovirus (eg. HIV)
- Reovirus (eg. Rotavirus)
- Picornavirus
- Filovirus (eg. Ebola)
- Rhabdovirus (eg. Rabies)
- Togavirus
- Bunyavirus
Features of Influenza A
- Single stranded RNA virus
- Enveloped
- Helical capsid
- Contains two antigens = haemagglutinin (for adhesion to susceptible cells) and neuraminidase (enzyme) protein antigens on the surface of the envelope
How many segments are there of the single stranded RNA genome?
8
On an influenza virus what are the spikes on the viron envelope?
Haemagglutinin and neuraminidase proteins which are immunogenic and are the basis of the influenza vaccine
What are Haemagglutinin and neuraminidase shortened to?
HN
When was the Russian Influenza H2N2?
1889
When was the Old Hong Kong Influenza H3N8?
1900
When was the Spanish Influenza H1N1?
1918
When was the Asian Influenza H2N2?
1957
When was the Hong Kong Influenza H3N2?
1968
When was the Pandemic Influenza H1N1?
2009
Transmission route for Influenza A?
Respiratory aerosols
Transmission route for Norovirus?
Food and water (infects the gut, symptoms include vomiting and diarrhoea) or by direct contact
Transmission route for Rotavirus?
Fomites (faecal-oral), mainly an infection of under 5 year olds
Transmission route for Herpes?
Direct contact with bodily fluids (saliva, semen)
Transmission route for HIV, HPV?
Sexual contact (including birth - vertical transmission, due to secretions)
Transmission route for Hepatitis B/C?
Blood and organ transplantation (sharing needles…)
Transmission route for Rabies?
Zoonoses - bite of an infected animal
The process of viral pathogenicity:
- Acquisition
- Initiation of infection (virus is absorbing itself to the cell)
- Incubation period (once inside the virus will uncoat in which its dna/rna will be exposed and transcribed)
- Replication in the target tissue (leading to a replication of viral nucleic acid and viral proteins to make the capsid)
- Virus production and release to infect other cells/hosts (either by budding to the surface or lysing)
- Immune response (cytotoxic T cells will be sent to eradicate that cell - results in rupture of cell and release if virus particles)
- Resolution/persistence/latency (some of the particles will be collected by analysing the antigenic components and educating B/T cells to recognise…)
Steps of the infection cycle:
- Adsorption/Attachment
- Penetration
- Uncoating
- Transcription/translation (replication)
- Assembly
- Release
What are some infections that an immunodiffusion assay (LFT) can detect?
- Legionella pneumophila serotype 1 in urine
- Streptococcus pneumoniae antigen in urine
- Influenza A and B in nasopharyngeal swabs
What do LFTs contain?
Antigens which have been extracted from different types of microorganisms - specific to the infection that it is being tested for, if the patient is infected with that organism it will be present via a nasal or saliva swab
How does a LFT function?
Once the test sample is added into the sample pad on a lateral flow device, the sample flows through a filter film. If the test sample contains target analytes, it can combine with colloidal gold-labeled antigen to form a complex, which is captured by antibody coated with a colored band. The presence of colored bands indicates a positive result of the target analyte. Most of the lateral flow assays contain a control line, which works as a procedural control to inform enough samples were added into loading well. The absence of a colored control line indicates an invalid test result.
What is poliomyelitis?
- Can be prevented via vaccination
- It’s a virus that infects nervous tissue, which can result in malformation of growth of lower limbs
- Can also result in paralysis
- Iron lung was used to decrease pressure by drawing the diaphragm down and air into the lungs
What is the purpose of antiviral therapies?
To allow the body’s immune system to keep on top of viral infections so a variety of targets are used to interrupt the cycle