ERP Micro December 2019

System measures the time (in the nanosecond range) between pulsed acceleration and the corresponding detector signal of the ions, and the time is converted into an exact molecular mass. The highly abundant microbial ribosomal proteins result in a mass spectrum with a characteristic mass and intensity distribution pattern. This pattern is species-specific for many bacteria, yeasts, and molds and can be used as a ‘molecular fingerprint’ to identify a test organism. The mass spectra are transformed into peak lists by the MALDI Biotyper software and are compared with the patterns in the reference library. The subtyping module starts automatically to differentiate closely related Listeria species: L. innocua , L. ivanovii , L. monocytogenes , L. seeligeri , and L. welshimeri . L. grayi does not require the use of the subtyping module. B. Apparatus and Reagents Items ( a )–( k ) are available from Bruker Daltonik GmbH (Bremen, Germany). ( a ) Microflex LT/SH MALDI-MS System (Cat. No. 8269956) or

AOAC Official Method 2017.10 Confirmation and Identification of Listeria monocytogenes , Listeria species, and Other Gram-Positive Organisms Bruker MALDI Biotyper Method First Action 2017 (Applicable to identification and confirmation of Listeria monocytogenes , Listeria species, and other Gram-positive organisms from select media types.) See Tables 2017.10A – C for a summary of results of the interlaboratory study. See additional tables in J. AOAC Int . [ J. AOAC Int . 101 , 1610(2018) DOI: https://doi.org/10.5740/jaoacint.18-0013] for detailed results of the interlaboratory study. A. Principle The Bruker MALDI Biotyper method is intended to be used for the automated confirmation and identification of bacteria isolated onto agar plates. Classification and identifications are based on proteomic fingerprinting using matrix-assisted laser desorption/ ionization time-of-flight (MALDI-TOF) mass spectrometry (MS). First, the MALDI process transforms the proteins and peptides from the isolated microorganisms into positively charged ions. This is achieved by irradiating the matrix-sample composite with a UV laser. The matrix absorbs laser energy and transfers protons to the intact proteins or peptides in the gas phase. These ions are electrostatically accelerated and arrive in the flight tube at a mass-dependent speed. Because different proteins/peptides have different masses, ions arrive at the detector at different times (TOF). The MALDI Biotyper

MALDI Biotyper Smart System (Cat. No. 1853665). ( b ) MBT Library.— Version MSP 6903 or higher . ( c ) MBT Compass software.— Cat. No. 1843241. ( d ) MBT Explorer module.— Cat. No. 1828476. ( e ) MBT Compass software.— Cat. No. 1829023. ( f ) Subtyping module software.— Cat. No. 1842250. ( g ) Barcode scanner .—Cat. No. 8268821 (optional).

( h ) Holder for barcode scanner.— Cat. No. 8276754 (optional). ( i ) MSP 96 target polished steel BC (Cat. No. 8280800) or MSP 48 target polished steel BC (Cat. No. 8281817), or MBT

Table 2017.10A. Summary of results for the confirmation and identification of Listeria monocytogenes: Inclusivity

MALDI Biotyper correctly identified to

Reference correctly identified to

Not tested

Total

Species level

Genus level

Species level

Genus level

MALDI Biotyper incorrectly identified

MALDI Biotyper

MALDI Biotyper Reference

Organism

Reference

L. monocytogenes Ad32.183 L. monocytogenes Ad285 L. monocytogenes Ad1494 L. monocytogenes Ad534 L. monocytogenes Ad273 L. monocytogenes Ad494 L. monocytogenes A00C042 L. monocytogenes Ad1781 L. monocytogenes Ad626 L. monocytogenes Ad270 L. monocytogenes Ad1498 L. monocytogenes Ad253 L. monocytogenes Ad1679 L. monocytogenes Ad816 L. monocytogenes Ad618 L. monocytogenes  Ad12407/3139

62 62 61 62 60 62 60 62 61 62 62 62 62 62 62 61

62 62 61 62 61 62 61 62 62 62 62 62 62 62 62 62

14 14 14 14 14 14 14 14 14 14 13 14 13 14 14 15

16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16

0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 1

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

2 2 3 2 2 2 3 2 2 2 2 2 2 2 2 2

62 62 61 62 62 62 61 62 62 62 62 62 62 62 62 62

16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16

 Total isolates

985

989 a

223

256

34

990 b

256 c

a  MALDI Biotyper result identified to a genus level. b  Total numbers represent isolates analyzed on the four recommended culture media: TSA/YE, O&A, OXA, and RAPID’ L. mono . c  Reference method performed from TSA/YE agar only.

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