Bacteriology lab Flashcards
Line cocci vs clumped cocci (gram +ve)
Lines= strep
Clumped=Staph
For staph. What type of test
Coagulase….. +ve= staph aureus, -ve=low pathological potential (apart from prosthetic material)
Gram -ve bacilli
E. Coli, klebsiella
How is brucellosis caught
Animals (think bruce)
Poorly cooked meat
Unpasteurised milk or cheese
How is melliodosis caught
Soil
Which diagnositc techniques can be used in bacteriology lab
CULTURE (sterile=blood/CSF, non sterile)
SEROLOGY
MOLECULAR TECHNIQUE
ANTIMICROBIAL SUSCEPTIBILITY TESTING
Differentiate gram pos and gram neg
Pos means thick cell wall (cos this absorbs the dye)….. so cell membrane then thick cell wall
Neg means think cell wall, so 2 cell membranes. HAS LPS
What are bacterial cell walls composed of
NAM and NAG alternating units
After positive blood culture then what
Then smear onto agar plates
After smearing onto agar plates then what
Look under microscope
What are the 3 bacteria morphology
Cocci (round)
Bacillus (rod)
Spiral
If there are gram positive cocci, what is indicated if these cocci are in clumps
Clumps of gram +ve cocci is staphylococci
If there are gram positive cocci, what is indicated if these cocci are in chains
Chains of gram +ve is streptococci
What is indicated by gram +ve bacillus
Clostridium or listeria
What would be the next test if you had gram +ve clumps of cocci
Coagulase test
What is indicated by coagulase +ve and coagulase -ve
COAGULASE DONE ON STAPHYLOCOCCUS
COAG +VE= Staph Aureus (severe infections….. skin/soft tissue, endocarditis and osteomyelitis)
COAG -VE= skin commensals of low pathogenic potential
Is coag -ve bacteria ever harmful?
Normally skin commensals, BUT can infect prosthetic material causing line, pacemaker infections and endocarditis
Other than looking at clumps and chains, how can you confirm whether a gram pos is strep or staph
Catalase
Cat positive is staph
Cat neg is strep
What tests can be done on catalase negatives to determine the bacteria type
So it’s strep….
then do haemolysis….
How is does haemolysis work, including the colour of each
Strep induce haemolysis to underlying erthrocytes when placed on a blood agar
Alpha –> green… PARTIAL haemolysis
Beta –> yellow… COMPLETE haemolysis
Gamma –> no haemolysis so stays red
Examples of alpha and each type of beta haemolytic strep
Alpha= Strep pneumonia or strep viridans (–> subacute endocarditis SBE
Beta split into group A, group B and group C
A: strep pyogenes
B: S. agalactiae, or group B Streptococcus causes pneumonia and meningitis in newborn and elderly
C: not important in humans
Goes up to F
Gram negative bacilli example
Enterobacteriae including E. Coli, shigella, salmonella
Bacterial and parasitic and viral cause of diarrohea
Bacteria:
Salmonella (inc S. typhi ), Shigella, Campylobacter,
E coli O157, C difficile, Cholera
Parasites:
Amoeba, Giardia, Cryptosporidium
Viruses:
Norwalk virus, cytomegalovirus and viral hepatitis. Rotavirus is a common cause of acute childhood diarrhea.
In stool sample what bacteria are routinely tested for
Culture, then
Only Salmonella, Shigella and Campylobacter
looked for routinely.
How is clostridium difficile tested for as it is not tested routinely
toxin detection or PCR for
toxin gene
How do you test AB suitability
Gradient minimum inhibotry concentration strips
T/f IgM will rise in the secondary and primary response to infection
T… but second exposure causes much greater IgG than IgM response
Why are samples taken prior to AB
So that the AB doesn’t kill the organism before being able to work out what it was!
Why do we look for NITRITES in the urine
Nitrites strongly suggest bacteriuria as many species of gramnegative bacteria convert nitrates to nitrites.
What might we look for in urine as evidence of infection
nitrites, leucocytes, blood, protein, bilirubin, ketones
How can we possibly culture stool samples when there are so many pathogens there
Give examples of the agar used
Culture on inhibitory media – e.g. deoxycholatecitrate agar (DCA), selenite (Faeces contains 1012-14 bacteria per gram, so selective media are used to suppress background ‘flora’ organisms)
What substances can be used for microscopy
Gram stain of CSF, joint fluid, purulent exudates
ZN/auramine stain of e.g. sputum, for TB
When is FTA used
To check for antibodies to T. pallidum
What is the ZN/auramine stain sed for
e.g. sputum, for TB
Examples of direct antigen detection
Meningococcal antigen in CSF
C. difficile toxin in faeces
Legionella and Pneumococcal antigen in urine
Examples of PCR
Chlamydia in genital specimens
Rapid PCR for MRSA
