Bacteriology Lab Flashcards
What are the common diagnostic techniques in bacteriology?
- Culture
1a) sterile sites (blood, CSF)
1b) non-sterile sites (i.e. stool)
2) Serology
3) molecular techniques
4) antimicrobial susceptibility testing
What are sterile sites?
Sites where there should be no bacteria growing.
Where is clinical history exceptionally important?
In samples from non-sterile sites as you grow multiple things on these so you have to know what to look for
What are cultures still commonly used in bacteriology?
you can also test for antibiotic resistance
Why are people made more susceptible to infections in the hospital?
- canulas, catheters, medications
What are the different types of bacterial culture bottles?
- aerobic
- anaerobic
- paediatrics (as they take a smaller sample; also some things are more common?)
Why should you send a sample to the lab BEFORE starting the patient on antibiotics?
- unless it is VERY urgent send a sample to the lab first
if antibiotics are in the sample they prevent bacterial growth and make growing a culture much more difficult.
What is the difference between g+ and g- cells?
g+ have a thick peptidoglycan layer on the outside
g-ve have a cell wall and a thin peptidoglycan layer underneath.
-> knowing if the bacteria are g+ or g- helps with choosing the antibiotic
What is the coagulase test
Coagulase test is used to differentiate Staphylococcus aureus (positive) from Coagulase Negative Staphylococcus (CONS).
-> if it clumps the test is positive
Staphylococci
Staphylococcus aureus (including Methicillin Resistant Staphylococcus aureus, MRSA)
Severe infections eg: skin/soft tissue, endocarditis, osteomyelitis
Coagulase Negative Staphylococci
Skin commensals of low pathogenic potential. Can infect prosthetic material causing line, pacemaker infections
What pathogens cause diarrhoea?
- Bacteria: Salmonella (incl. S. type), Shigella, Campylobacter, E Coli O157, C difficile, Cholera
- Parasites: Amoeba, Giardia, Cryptosporidum
- Viruses
What are the stool sample investigations that are available?
Bacteria
Culture on agar plates.
Only Salmonella, Shigella and Campylobacter
looked for routinely.
Different pathogens have different culture
requirements.
Clostridium difficile – toxin detection or PCR for
toxin gene
Parasites
Concentration, special stains -> parasites don’t grow so you look at the concentration in faeces
Are all bacteria cultured in the same way?
- no
- some have different special agars (e.g. salmonella XLD agar, Campylobacter, Cholera on TCBS agar)
- some different high temperatures
MIC
= Minimum Inhibitory Concentration
- minimum amount of AB to inhibit growth of pathogen
What is special about C Dif investigations?
- you don’t culture it
- you report c dif cases
- the lower the prevalence, the higher the risk of false positives
