Intro to Medical Microbiology Flashcards
basic differences between viruses, bacteria and fungi
Bacteria are free-living prokaryotic cells that can live inside or outside a body, while viruses are a non-living collection of molecules that need a host to survive. Fungi can be unicellular or multicellular and are eukaryotes.
3 domains of life
- Bacteria (prokaryote)
- Archaea (prokaryote)
- Eucarya (Eukaryote)
differences between prokaryotes and eukaryotes
- Membrane boud organelles absent in prokaryotes
- Prokaryotes unicellular, eukaryotes mostly multicellular
- Eukaryotes larger
- Porkaryotes simpler (no nucleus, just single chromosome and plasmids)
What is microbiology
Study of microorganisms (when applied => medical microbiology)
5 causes of microbial infection
(go from most to least common)
- Bacteria
- Viruses
- Fungi
- Parasites
- Prions (proteins)
What can the 5 microbial causes of incetion be classified as
- Bacteria - prokaryotes
- Viruses - unclassified
- Fungi - eukaryotic
- Parasites - eukaryotic (usually)
- Prions (proteins) - unclassified
Define bacterium
“Chiefly round, spiral or rod shaped single celled prokaryotic organism that typically lives in soil, water, organic matter or the bodies of plants and animals”
Define virus
“A unique, acellular, metabolically inert organism that only replicate within living cells”.
Define fungus
“Any of a kingdom of saprophytic and parasitic spore-producing eukaryotic typically filamentous organisms including moulds, yeasts, mushrooms and yeasts”
Define parasite
“An organism living in, with or on another organism”.
Define prion
“Protein of unknown function that resides on the surface of brain cells. An abnormal form of
prion protein that in mammals includes pathogenic forms that arise spontaneously (e.g. genetic
mutation) or transmission (e.g. via infected tissue) and upon accumulation in the brain cause a prion
disease e.g. BSE or CJD.”
(Relative) sizes of microorganisms
- Parasites - microscopic to over 30 m
- Fungi - 2 to 10 µm
- Bacteria - 0.2 to 0.5 µm
- Viruses - 20 to 400 nm
- Prions - 10 nm (often measured in Angstrom [1 A = 0.1 nm)
speciman types
2
- Sterile sites (shouldn’t contain bacterial flaura)
- Non-sterile sites
Give some sterile sites
brain, heart, liver, kidney
Give some non-sterile sites
mouth, oesophagus, stomach, lungs, intestine
Common specimen types for bacterial culture
Not sure if need to memorise all
- Mid stream specimen of urine (MSSU) - urinary tract infection
- Sputum - lower respiratory tract infection
- Throat swab - tonsillitis / pharyngitis
- Swabs - wound infection, genital tract infection
- Faeces - infectious diarrhea
- Blood culture - septicaemia (sepsis)
- Cerebrospinal fluid CSF) - meningitis
- Aspirate of pus - abscess
- Bone - osteomyelitis.
Sterile site
definition
an area where microorganisms are not typically found
Non-sterile site
definition
areas where microbes are often found and are usually more accessible from the environment
Explain microscopy
- Light microscopy (x1000 magnification)
- Unstained - to see white blood cells (e.g. urine, CSF), to see parasites (faeces)
- Gram stain - to visualise bacteria and yeasts/fungi
- Special stains= Ziehl Neelsen stain or auramine stain for mycobacteria
- Viruses not visible in light microscope!!!
What WBC are increased in viral infaction
Lymphocytes
What WBC are increased in bacterial infaction
neutrophils
Importance of microscopy in clinical setting
Is rapid - urgent info relayed to clinicians. Is not specific but assists provisional diagnosis and empiric antimicrobial therapy
Empiric antimicrobial therapy
And definitive therapy
Antibiotics that are administered during the period prior to the receipt of blood culture and antibiotic susceptibility test results
Term “definitive therapy” refers to the antibiotic therapy given subsequent to receipt of these results.
What is microscopy followed by
Bacterial culture and susceptibility testing
healthcare associated infection
- Prevention is key: onset typically following 48h admission
- S.aureus bacteraemia and C.difficile infection both common hospital infections
- Multi-drug resistant organisms e.g. MRSA, VRE, ESBL, CPE
- Norovirus
Infection control measures
- Hand sanitation
- Foam hand sanitizers inside and outside each patient’s room to use on entry and exit
- Disposable paper gowns and latex gloves worn when entering the rooms of immunocompromised patients or patients with dangerous infectious diseases, such as MRSA.
- Aseptic technique when procedures are performed (such as inserting a catheter).
Detecting viruses from clinical samples
not sure if need to know everything
- Molecular methods= real time / multiplex PCR
- Antigen detection
- Serology to determine immunity
- Virtually obsolete methods e.g. electron microscopy, cell or tissue culture - inoculate a “cell line”
When do we see IgM and IgG antibodies
- IgM - start of infection
- IgG - later on in infection
Diagnostic principles in parasitology
- Microscopy of different life cycle stages e.g. parasites, cysts and ova in faeces, blood films for malaria
- Culture rarely possible
- Serology sometimes useful
- Importance of reference laboratories
