Comparative MALDI-TOF Analysis of Staphylococcus spp. from the Environment including Antibiotic Resistant Strains Rory Cave (Presenter) University of East London >> POSTER (PDF) Presenter Bio: I completed my Undergraduate degree at the University of Reading with a degree in Biological Science. I did an MRes in microbiology at Nottingham Trent University where I was trying to compare the difference in virulence between Campylobacter jejuni and Campylobacter coli. Currently, I am a PhD student at the University of East London and part of my project seeks to undertake the first comparative analysis between a newly developed system such as Thinkerbell and a traditional instrument such as an established Bruker’s Autoflex MS to probe the diversity of species.

Authors: Rory cave (1), Ajit Shah(2), Vlad Serafim (2), Lyna Sellami (3), Hermine Mkrtchyan (1), Haroun Shah (2)
(1) University of East London, London, UK (2) Middlesex University, London, UK (3) Ascend Diagnostics, Manchester, UK

In this study, we did a comparative analysis of the Bruker’s Autoflex with ASTA Tinkerbell MALDI-TOF MS using samples spotted onto the same target plate. We used 10 references strains from different species to determine how accurate they identify the species. We also tested a range of environmental staphylococcal isolates that were resistant to antibiotics. From the result, we were able to determine that both excellent congruences between data analysed using ASTA’s Tinkerbell and Bruker’s Biotyper at the species and subspecies levels.

Introduction

MALDI-TOF MS is increasingly used to rapidly identify clinical isolates and in some instances subtype strains. While identification of most taxa to species level is robust and continues to gain credibility, typing of strains remains circumspect. MALDI consistently reveals diversity among wild type strains with variants revealing unique mass ions. If such mass ions are consistent for a given strain and is reproducible on different instruments, then MALDI may be established as a reliable and rapid typing tool. Previous attempts to undertake comparative MALDI analyses utilised the same cultures but spotted on different target plates prior to analysis on different instruments. Here we report comparative analysis of environmental strains of Staphylococcus spp. with varying antibiotic resistance but analysing samples from the same target plate well using two different MALDI-TOF mass spectrometers.

Methods

Cultures: references strains belonging to Pasteurella haemolityca, Corynebacterium ulcerans, Salmonella enterica, Enterococcus faecalis, Klebsiella spp., Escherichia coli, Micrococcus roseus, Proteus morganii, Pseudomonas aeruginosa and Staphylococcus aureus were used for a preliminary study to compare interspecies reproducibility while a range of fresh staphylococcal isolates were used to study intraspecies compatibility.

A minute amount of cells was smeared in triplicate on an ASTA plate (384 wells) using a toothpick and 2 µL of 70% formic acid was added. To the dried cells, 2 µL of CHCA matrix (5 mg/mL) in a mixture of ACN/2.5 % TFA (50:50, v/v) were added and the same plate used for acquiring data on the ASTA Tinkerbell MS and the Bruker’s autoflex MS.

Results

Interspecies identification: Apart from P. haemolityca which was absent in the ASTA database, all species were correctly identified with a high degree of confidence using both ASTA’s Tinkerbell and Bruker’s Biotyper MS.

The majority of staphylococci isolates were correctly identified using both instruments. When corresponding spectra from each instrument were superimposed, key mass ions for each species corroborated.

Conclusions & Discussion

Preliminary results indicate excellent congruence between data analysed using ASTA’s Tinkerbell and Bruker’s Biotyper at the species and subspecies levels. Further work on a larger number of samples are necessary to build on these preliminary data and expand the clinical applications of MALDI-TOF MS.