Identification and Characterization of Clostridium difficile Sequence Type 37 Genotype by Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry

DOI: 10.1128/JCM.01990-17

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FIG 1
Exemplary whole-cell mass spectra of C. difficile strains and isolates of ST37 (ATCC 43598, CD013, CD015, CD017, CD026, and CD126; red lines) and non-ST37 (ATCC BAA-1382, ATCC BAA-1804, ATCC BAA-1870, ATCC BAA-1812, CD105 (ST3), and CD151 (ST2); blue lines). The lower panel (b) shows an enlarged section of the full upper spectra (a).
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FIG 2
Cluster analysis of spectra of 49 ST37 isolates of different geographic origins. The dendrogram was computed in SARAMIS with a single-linkage agglomerative algorithm-based relative spectrum similarity (percentage of matching peaks within a tolerance of 0.08%). The dotted purple line indicates 65% similarity, which is generally the threshold for intraspecies similarity. Yellow, Hebei; green, Hangzhou; blue, New York; black, ATCC 43598.

TABLE 1

Sources and sequence types of clinical isolates recruited in this study

TABLE 2

Experimental variability of peak height values in spectra of ST37 and non-ST37 isolates^a

Expt	m/z	Mean peak ht value (integrated in thousands) ± SD for following isolate of ST37 genotype:			Mean ± SD	CV (%)	Mean peak ht value (integrated in thousands) ± SD for following isolate of non-ST37 genotype:			Mean ± SD	CV (%)	ST37/non-ST37 ratio	Mann-Whitney U	P
Expt	m/z	CD001	CD038	CD090	Mean ± SD	CV (%)	CD003	CD045	CD086	Mean ± SD	CV (%)	ST37/non-ST37 ratio	Mann-Whitney U	P
1	3,242	1,219 ± 1,035	5,881 ± 5,483	1,516 ± 1,722	2,871 ± 3,899	136	25 ± 49	15 ± 26	8 ± 14	16 ± 32	200	179	51	<0.001
	3,286	6,325 ± 6,151	19,169 ± 16,845	5,854 ± 6,131	10,449 ± 12,249	117	452 ± 861	0	0	151 ± 525	348	69	17	<0.001
	3,370	14 ± 36	142 ± 203	280 ± 293	145 ± 227	157	5 ± 9	70 ± 99	41 ± 64	31 ± 56	181	5	296	0.193
2	3,242	941 ± 1,177	1,370 ± 3,142	832 ± 800	1,048 ± 1,928	184	11 ± 10	5 ± 7	7 ± 14	8 ± 11	138	131	16	<0.001
	3,286	4,076 ± 5,084	5,082 ± 10,544	3,548 ± 3,215	4,236 ± 6,765	160	0	0	0	0	NA	NA	<0.001	<0.001
	3,370	54 ± 86	10 ± 19	20 ± 31	31 ± 56	181	9 ± 12	4 ± 7	29 ± 28	13 ± 20	154	2	287	0.305
3	3,242	659 ± 693	9,448 ± 1,076	204 ± 144	3,437 ± 7,173	209	39 ± 50	26 ± 20	18 ± 28	28 ± 33	118	123	1	<0.001
	3,286	1,266 ± 2,111	17,937 ± 15,370	459 ± 288	6,554 ± 11,682	178	0	0	0	0	NA	NA	<0.001	<0.001
	3,370	197 ± 105	63 ± 127	17 ± 23	93 ± 118	127	24 ± 29	6 ± 7	17 ± 25	16 ± 22	138	6	50	0.182

↵a For experimental conditions and the no. of replicates, see the text. NA, not applicable; SD, standard deviation; CV, coefficient of variation.

TABLE 3

Molecular characteristics of ST37 and non-ST37 C. difficile isolates

Genotype	Geographic origin	No. of isolates tested	MS^a peak (no. present [%]) at m/z:			tcdA or tcdB phenotype^b
Genotype	Geographic origin	No. of isolates tested	3,242	3,286	3,370	A⁺B⁺	A⁻B⁺	A⁻B⁻
ST37	Hebei, China	31	31 (100)	30 (96.8)	30 (96.8)	0 (0)	31 (100)	0 (0)
	Hangzhou, China	5	5 (100)	4 (80.0)	5 (100)	0 (0)	5 (100)	0 (0)
	Asia Pacific region	5	5 (100)	5 (100)	5 (100)	0 (0)	5 (100)	0 (0)
	New York, USA	8	8 (100)	8 (100)	1 (12.5)	ND	ND	ND
	All ST37 origins	49	49 (100)	47 (95.9)	41 (83.7)
Non-ST37	Hebei, China	147	62 (42.2)	1 (0.7)	135 (91.8)	116 (78.9)	1 (0.7)	30 (20.4)
	Asia Pacific region	2	0 (0)	0 (0)	2 (100)	2 (100)	0 (0)	0 (0)
	New York, USA	6	2 (33.3)	1 (16.7)	0 (0)	ND	ND	ND
	All non-ST37 origins	155	64 (41.3)	2 (1.3)	137 (88.4)