Abstract
Matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) has been presented as a superior method for the detection of microorganisms in body fluid samples (e.g., blood, saliva, pus, etc.) However, the performance of MALDI-TOF MS in routine identification of caries-related Lactobacillus isolates from saliva of adult patients with caries has not been determined. In the present study, we introduced a new MALDI-TOF MS system for identification of lactobacilli. Saliva samples were collected from 120 subjects with caries. Bacteria were isolated and cultured, and each isolate was identified by both 16S rRNA sequencing and MALDI-TOF MS. The identification results obtained by MALDI-TOF MS were concordant at the genus level with those of conventional 16S rRNA-based sequencing for 88.6% of lactobacilli (62/70) and 95.5% of non-lactobacilli (21/22). Up to 96 results could be obtained in parallel on a single MALDI target, suggesting that this is a reliable high-throughput approach for routine identification of lactobacilli. However, additional reference strains are necessary to increase the sensitivity and specificity of species-level identification.
Highlights
Lactobacilli were the first microorganisms implicated in the development of dental caries [1] and have been shown to be associated with the dental carious process [2]
Granath et al [5] suggested that the saliva count of lactobacilli is a better criterion than that of Streptococcus mutans as the former count is strongly correlated with caries [6,7,8,9,10,11,12]
There is a strong association between lactobacilli and caries, little is known regarding the relationship at the species level because of difficulties in identifying Lactobacillus species by conventional methods [15]
Summary
Lactobacilli were the first microorganisms implicated in the development of dental caries [1] and have been shown to be associated with the dental carious process [2]. The Lactobacillus count represents the number of lactobacilli present in 1 mL of saliva (CFU/mL), and is used to determine the efficiency of dietetic measures or to evaluate caries risk. It can be used alone or in combination with other associated parameters [3,4]. There is a strong association between lactobacilli and caries, little is known regarding the relationship at the species level because of difficulties in identifying Lactobacillus species by conventional methods [15]. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a rapid, accurate, and costeffective method used to identify microorganisms [16,17,18]. MALDI-TOF MS was introduced into routine microbiological diagnoses with marked success in many fields [19,20,21,22], PLOS ONE | www.plosone.org
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