Novel physico-chemical diagnostic tools for high throughput identification of bovine mastitis associated gram-positive, catalase-negative cocci

Table 4 Accuracy of MALDI-TOF mass spectrometry for the identification of Streptococcus spp. and related species

Species	No of strains	Correct species identification log(score) value ≥ 2.3	Probable species identification log(score) value 2.0-2.299 0.15 distance between single species	Correct genus identification log(score) value 2.0-2.299 < 0.15 distance between single species	Mis-identification^#
A. viridans	6	4	2 (33.3%)
E. faecalis	35	35
E. faecium	6	6
L. garvieae	6	5	1 (16.6%)
L. lactis	11	11
S. agalactiae	11	11
S. gallolyticus/bovis*	6	5			1 (16.6%)
S. canis	6	5		1 (16.6%)
S. dysgalactiae	36	33		2 (5.5%)	1 (2.8%)
S. parauberis	6	4	2 (33.3%)
S. pyogenes	11	11
S. uberis	70	70
Total	210	200	5 (2.4%)	3 (1.4%)	2 (1%)

^#Misidentification only at species level, all isolates were correctly identified by genus level. *S. bovis is indicated as S. gallolyticus in the MALDI-TOF reference database. One strain was misidentified as Streptococcus lutetiensis.
A subset of 231 strains derived from the strain panel, generated for this study (see Table 1), was used for this validation approach. Results were analyzed following the score value system according to Bruker Daltonik GmbH (Bremen, Germany). Log(score) values from 3.00 to 2.30 indicate reliable species identification. Log(score) values from 2.29 to 2.00 indicate reliable genus and probable species identification, if a score value distance of at least 0.15 between the two best-scored species is given (Huber et al., unpublished).

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