2.2. Mass spectrometric analysis by protein extraction
method and intact cell method
The bacterial pellet was dissolved in 1 mL of water and
centrifuged (all centrifugation steps were performed at
13,000 g for 2 minutes) in order to wash out the residue
of BHI.
According to the protein extraction method (PEM), 1 mL
of 75% ethanol solution was added to the pellet, and after
centrifugation, the supernatant was removed by carefully
pouring it from the microtube. A second centrifugation step
was performed, and the remaining liquid was carefully
removed with a pipette. The bacterial pellets were allowed
to air-dry at room temperature for 15 minutes. A solution of
70% formic acid was added to lyse bacterial cells and to
release the inner-cell proteins, which are predominantly
ribosomal proteins that produce diagnostic ions in MALDIMS
fingerprinting. The 70% formic acid solution was added
proportionally to the size of pellet to completely dissolve it.
Subsequently, 100% acetonitrile was added to each sample
in volumes equal to the 70% formic acid solution previously
added, thus producing a bacterial extract in a (1:1) ratio of
70% formic acid and acetonitrile. A final centrifugation step
was performed to separate the bacterial cell debris from the
supernatant containing the ribosomal proteins used for the
MALDI-MS identification.
2.2. Mass spectrometric analysis by protein extractionmethod and intact cell methodThe bacterial pellet was dissolved in 1 mL of water andcentrifuged (all centrifugation steps were performed at13,000 g for 2 minutes) in order to wash out the residueof BHI.According to the protein extraction method (PEM), 1 mLof 75% ethanol solution was added to the pellet, and aftercentrifugation, the supernatant was removed by carefullypouring it from the microtube. A second centrifugation stepwas performed, and the remaining liquid was carefullyremoved with a pipette. The bacterial pellets were allowedto air-dry at room temperature for 15 minutes. A solution of70% formic acid was added to lyse bacterial cells and torelease the inner-cell proteins, which are predominantlyribosomal proteins that produce diagnostic ions in MALDIMSfingerprinting. The 70% formic acid solution was addedproportionally to the size of pellet to completely dissolve it.Subsequently, 100% acetonitrile was added to each samplein volumes equal to the 70% formic acid solution previouslyadded, thus producing a bacterial extract in a (1:1) ratio of70% formic acid and acetonitrile. A final centrifugation stepwas performed to separate the bacterial cell debris from thesupernatant containing the ribosomal proteins used for theMALDI-MS identification.
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