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. 2015 Jul 24:15:142.
doi: 10.1186/s12866-015-0480-y.

Evaluation of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) for identification and clustering of Neisseria gonorrhoeae

Anna Carannante  1 , Elena De Carolis  2 , Paola Vacca  3 , Antonietta Vella  4 , Caterina Vocale  5 , Maria Antonia De Francesco  6 , Marco Cusini  7 , Simonetta Del Re  8 , Ivano Dal Conte  9 , Antonio Cristaudo  10 , Patrizia Ober  11 , Maurizio Sanguinetti  12 , Paola Stefanelli  13
Affiliations

Evaluation of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) for identification and clustering of Neisseria gonorrhoeae

Anna Carannante et al. BMC Microbiol. .

Abstract

Background: The sexually transmitted infection gonorrhea remains a public health concern for becoming resistant to drug treatments available. The purpose of this study was to evaluate the usefulness of the matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) to identify and cluster Neisseria gonorrhoeae. From a current monitoring in Italy, as part of the European Gonococcal Antimicrobial Surveillance Programme (EURO-GASP), 93 gonococci collected from 2007 to 2012 susceptible (44 isolates) and resistant (49 isolates) to cefixime were selected. Minimum Inhibitory Concentration (MIC) values for cefixime was assessed by Etest carried out in agreement with the manufacturer's instructions and interpreted referring to European Committee on Antimicrobial Susceptibility testing (EUCAST) clinical breakpoints criteria. Data obtained by N. gonorrhoeae multiantigen sequence typing (NG-MAST) and the dendrogram based on the concatenation of porB and tbpB genes were evaluated. MALDI-TOF MS, to reconfirm gonorrhea identification, analyzed single colonies from freshly grown isolates and applied directly on a ground-steel MALDI target plate. For the MALDI-TOF dendrogram cluster analysis, MSPs (Main Spectrum Profile) from each isolate were created acquiring 5000 shots from 10 technical replicates obtained from bacteria extraction.

Results: Molecular typing by NG-MAST showed 28 sequence types (STs); G1407 was the predominant accounting for 75 gonococci. All the 93 gonococci, except one, were correctly identified at species level by MALDI-TOF MS and G1407 isolates were divided into two clusters.

Conclusion: MALDI-TOF MS for a real-time detection and cluster analysis of gonorrhea is a promising tool for surveillance purposes. Moreover, additional studies are required to collect more data on the performance of MALDI-TOF MS for gonococci.

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Figures

Fig. 1
Fig. 1
Neisseria gonorrhoeae multiantigen sequence typing (NG-MAST) of 93 gonococci isolated from 2007 to 2012 in Italy
Fig. 2
Fig. 2
Phylogenetic tree obtained with Unweighted Pair Group Mean Average (UPGMA) clustering method using MEGA software [version 5.2; http://www.megasoftware.net] showing the relatedness of both porB and tbpB alleles (NG-MAST analysis) for 93 N. gonorrhoeae isolates. Circles indicate Sequence Types (STs) belonging to genogroup (G)1407
Fig. 3
Fig. 3
Cluster analysis of MALDI-TOF MS spectra obtained for 93 N. gonorrhoeae isolates. In the MSP dendrogram, relative distance between isolates is displayed as arbitrary units. Zero indicates complete similarity and 1000 indicates complete dissimilarity. The arbitrary distance level of 600 was chosen for isolates clustering evaluation. The STs listed in the Figure are different from the genogroup (G) 1407
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References

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