Abstract
Gram-positive cocci, such as Streptococcus agalactiae, Lactococcus garvieae, Streptococcus iniae, and Streptococcus dysgalactiae subsp. dysgalactiae, are found throughout the world, particularly in outbreaks in farmed fish, and are thus associated with high economic losses, especially in the cultivation of Nile Tilapia. The aim of this study was to evaluate the efficacy of matrix-assisted laser desorption ionization (MALDI)-time of flight (TOF) mass spectrometry (MS) as an alternative for the diagnosis of these pathogens. One hundred and thirty-one isolates from Brazilian outbreaks assisted by the national authority were identified using a MALDI Biotyper from Bruker Daltonics. The results showed an agreement with respect to identification (Kappa = 1) between this technique and 16S ribosomal RNA gene sequencing for S. agalactiae and L. garvieae. However, for S. iniae and S. dysgalactiae subsp. dysgalactiae, perfect agreement was only achieved after the creation of a custom main spectra profile, as well as further comparisons with 16S ribosomal RNA and multilocus sequence analysis. MALDI-TOF MS was shown to be an efficient technology for the identification of these Gram-positive pathogens, yielding a quick and precise diagnosis.
Highlights
Gram-positive cocci infections pose a great threat to farmed fish worldwide (Evans et al, 2002; Agnew and Barnes, 2007; Abdelsalam et al, 2013) and especially impact warm water systems used for the cultivation of Nile tilapia, one of the major commodities of global aquaculture (FAO, 2016)
The aim of this study was to evaluate the efficacy of matrix-assisted laser desorption ionization (MALDI)-time of flight (TOF) mass spectrometry (MS) for the identification of four Gram-positive cocci, S. agalactiae, L. garvieae, S. iniae, and SDD isolated from the kidneys, brains or abscesses of diseased fish from different geographic locations between 2003 and 2016
The contigs from each strain were used as queries for the BLAST webserver, and a percentage value of the similarities for L. garvieae was between 98 and 100, whereas S. agalactiae, S. iniae and SDD varied between 97 and 100
Summary
Gram-positive cocci infections pose a great threat to farmed fish worldwide (Evans et al, 2002; Agnew and Barnes, 2007; Abdelsalam et al, 2013) and especially impact warm water systems used for the cultivation of Nile tilapia, one of the major commodities of global aquaculture (FAO, 2016). The performance of these tests can lead to misidentification or a lack of species-level resolution (Brigante et al, 2006; Tavares et al, 2016). Alternative molecular methods, such as species-specific PCR (Poyart et al, 1998) and the amplification and sequencing of the 16S ribosomal RNA (rRNA) gene, are useful for diagnosis (Kolbert and Persing, 1999; Patel, 2001; Clarridge, 2004) but are expensive and time consuming, mostly in trials with large number of clinical samples
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