M15: Diagnosis of Infectious Disease Flashcards
When does the colonisation by microorganisms on the body begin?
Human are usually germ-free in utero and microorganisms colonisation of the body begins at birth
Give some locations of normal microbiota on and in the human body (7)
- Nose
- Mouth
- Lungs
- Skin
- Stomach
- Gut
- Vagina/Uretra
“Normal microbiota and the host exist in symbiosis”
Define symbiosis
Long-term interaction between two or more different biological species
What are opportunistic pathogens?
- Only cause disease in compromised host
- Sometimes part of Normal Flora
Define pathogenicity
The ability of the microbe to cause disease (qualitative)
Define virulence
The quantitative ability of a microbe to cause disease
Name the 4 basic microorganisms that can cause infections in humans
- Bacteria
- Viruses
- Fungi
- Protozoans (parasites)
What is the role of the capsule in a bacteria?
Help to evade the immune response
What is the role of spores in bacteria?
Give resistance to physical and chemical agents
Comment on the cell wall of gram positive bacteria and what colour do they stain?
- Thick peptidoglycan with no outer membrane
- Purple
Comment on the cell wall of gram negative bacteria and what colour do they stain?
- Thinner peptidoglycan with outer membrane
- Pink
What are the 3 main shapes of bacteria?
- Cocci (round)
- Rod
- Curved
How are cocci arranged?
Cocci are spherical chains arranged in a cluster
How do you carry out a gram stain?
- Put colonies on a slide
- Apply crystal violet (purple dye)
- Apply iodine
- Alcohol wash for decolorisation
- Apply safarin (pink dye)
- Observe
How do you distinguish between streptococci and staphylococci?
- Catalase test
- Streptococci are catalase negative
- Staphylococci are catalase positive
[e in strep e in negative]
What can staphylococci be divide into? (2)
- Coagulase positive
- Coagulase negative
What can streptococci be divide into? (3)
- alpha-haemolytic
- beta-haemolytic
- Non-haemolytic
How are staphylococcal disease caused?
- By invasiveness of agent either local or general
- By enterotoxins
What is toxic shock syndrome an example of?
What are the symptoms of these?
- Staphylococcal disease
- High fever
- Rash
- Low blood pressure
- Malaise
- Confusion
How would you differentiate between alpha, beta and non haemolytic streptococci?
- Put on a blood agar
- beta would show complete lysis around bacteria on agar
- α would show partial lysis
- non would show no lysis at all
What is beta-haemolytic streptococci further divided into?
- Groups A to G
- Depending on which Lancefield antigen is detected on surface
What are multitest identification systems?
- Strips that combine dozens of organic / inorganic substrates
- Ability to utilise or breakdown detected by colour changes
Give some structural features of mycobacterium (4)
- Aerobic
- Non-motile
- Straight or slightly curved rods
- Distinctive waxy cell wall
Give some characteristics of mycobacterium (6)
- Resistance to drying
- Hydrophobic
- Resistance to antibiotics and disinfectants
- Resistance to acids and alkalis
- Impermeable to standard stains
- Survives in macrophages
Define parasite
Any living form which is dependent on other living forms for survival, and causing some damage to the host
Protozoa can be classified by their means of locomotion what are these 3 means?
- Pseudopodia
- Flagella
- Cilia
What are helminths?
- Helminths are multicellular eukaryotic organisms lacking backbones, notochords, or exoskeletons
- Widespread intestinal parasites
What are the 3 subdivisions of helminths?
- Trematodes (flat non-segmented)
- Cestodes (flat segments)
- Nematodes (round)
How may immunological tests help diagnose infections? (3)
- ELISA tests for antigens
- Look for at least a four-fold rise in antibody titre in acute infection
- Look for presence of IgM.
