Rapid identification and source-tracking of Listeria monocytogenes using MALDI-TOF mass spectrometry.
Listeria monocytogenes is an important foodborne pathogen responsible for the sometimes fatal disease listeriosis. Public health concerns and stringent regulations associated with the presence of this pathogen in food and food processing environments underline the need for rapid and reliable detection and subtyping techniques. In the current study, the application of matrix assisted laser desorption/ionisation-time-of-flight mass spectrometry (MALDI-TOF MS) as a single identification and source-tracking tool for a collection of L. monocytogenes isolates, obtained predominantly from dairy sources within Australia, was explored. The isolates were cultured on different growth media and analysed using MALDI-TOF MS at two incubation times (24 and 48 h). Whilst reliable genus-level identification was achieved from most media, identification at the species level was found to be dependent on culture conditions. Successful speciation was highest for isolates cultured on the chromogenic Agar Listeria Ottaviani Agosti agar (ALOA, 91% of isolates) and non-selective horse blood agar (HBA, 89%) for 24h. Chemometric statistical analysis of the MALDI-TOF MS data enabled source-tracking of L. monocytogenes isolates obtained from four different dairy sources. Strain-level discrimination was also observed to be influenced by culture conditions. In addition, t-test/analysis of variance (ANOVA) was used to identify potential biomarker peaks that differentiated the isolates according to their source of isolation. Source-tracking using MALDI-TOF MS was compared and correlated with the gold standard pulsed-field gel electrophoresis (PFGE) technique. The discriminatory index and the congruence between both techniques were compared using the Simpsons Diversity Index and adjusted Rand and Wallace coefficients. Overall, MALDI-TOF MS based source-tracking (using data obtained by culturing the isolates on HBA) and PFGE demonstrated good congruence with a Wallace coefficient of 0.71 and comparable discriminatory indices of 0.89 and 0.86, respectively. MALDI-TOF MS thus represents a rapid and cost-effective source-tracking technique for L. monocytogenes.
Department of Chemistry and Biotechnology, Faculty of Science, Engineering and Technology, Swinburne University of Technology, P.O. Box 218, Hawthorn 3122, Victoria, Australia.
Snehal
S
Jadhav
Department of Chemistry and Biotechnology, Faculty of Science, Engineering and Technology, Swinburne University of Technology, P.O. Box 218, Hawthorn 3122, Victoria, Australia.
Vandana
V
Gulati
Food and Nutrition, Commonwealth Scientific and Industrial Research Organisation (CSIRO), 671 Sneydes Road, Werribee, Victoria 3030, Australia.
Edward M
EM
Fox
Department of Chemistry and Biotechnology, Faculty of Science, Engineering and Technology, Swinburne University of Technology, P.O. Box 218, Hawthorn 3122, Victoria, Australia; Land and Water Flagship, Commonwealth Scientific and Industrial Research Organisation (CSIRO), P.O. Box 56, Highett, Victoria 3190, Australia.
Avinash
A
Karpe
Land and Water Flagship, Commonwealth Scientific and Industrial Research Organisation (CSIRO), P.O. Box 56, Highett, Victoria 3190, Australia.
David J
DJ
Beale
bioMérieux Australia Pty Ltd, Unit 25 Parkview Business Centre, 1 Maitland Place, Baulkham Hills, NSW 2153, Australia.
Danielle
D
Sevior
Department of Chemistry and Biotechnology, Faculty of Science, Engineering and Technology, Swinburne University of Technology, P.O. Box 218, Hawthorn 3122, Victoria, Australia.
Mrinal
M
Bhave
Department of Chemistry and Biotechnology, Faculty of Science, Engineering and Technology, Swinburne University of Technology, P.O. Box 218, Hawthorn 3122, Victoria, Australia. Electronic address: epalombo@swin.edu.au.
Enzo A
EA
Palombo
D001315:Australia; D003611:Dairy Products / Q000382:microbiology; D016521:Electrophoresis, Gel, Pulsed-Field; D005516:Food Microbiology / Q000379:methods*; D008089:Listeria monocytogenes / Q000502:physiology*; D008088:Listeriosis / Q000382:microbiology / Q000517:prevention & control; D013045:Species Specificity; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
Chemometrics; Food safety; Mass spectrometry; PFGE; Source-tracking