A Novel Selective Medium for Isolation of Bacteroides fragilis from Clinical Specimens

DOI: 10.1128/JCM.01988-16

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FIG 1
Culture on a plate of Bacteroides fragilis selective (BFS) medium after 48 h of anaerobic incubation at 35°C. B. fragilis (white arrows) appears as large yellow colonies (glucose fermentation) with blackening of the surrounding medium (esculin hydrolysis).

TABLE 1

Growth characteristics of Bacteroides fragilis and other bacteria in BFS medium

Isolate type and organism (no. of isolates)^a	Colony profile on BFS agar (no. of isolates)
	Esculin positive^f	Growth after 48 h			Yellow colonies	Blackening of the medium
	Esculin positive^f	Absent	Good	Poor^g	Yellow colonies	Blackening of the medium
Anaerobic bacteria (215)
Bacteroides caccae	4 (4)		4		4	4
Bacteroides dorei	4 (4)			4	4	4
Bacteroides eggerthii	1 (1)			1	1	1
Bacteroides fragilis (division I)	52 (52)		52		52	52
Bacteroides fragilis (division II)	52 (52)		52		52	52
Bacteroides intestinalis	2 (2)			2	2	2
Bacteroides massiliensis	1 (0)			1	1
Bacteroides nordii	4 (4)		4		4	4
Bacteroides ovatus	11 (11)		11		11	11
Bacteroides pyogenes	2 (0)			2	2
Bacteroides salyersiae	2 (2)		2		2	2
Bacteroides stercoris	2 (2)			2	2	2
Bacteroides thetaiotaomicron	10 (10)		10		10	10
Bacteroides uniformis	10 (10)			10	10	10
Bacteroides vulgatus	10 (4)			10	10	4
Clostridium species	15 (3)	15
Fusobacterium species^b	3 (0)	2	1		1
Parabacteroides distasonis	2 (2)			2	2	2
Parabacteroides faecis	2 (0)		2		2
Parabacteroides goldsteinii	2 (0)			2	2
Peptostreptococcus species	3 (0)	3
Prevotella species	16 (1)	16
Other anaerobes^c	5 (0)	5
Aerobic and facultative anaerobic bacteria (88)
Enterobacteriaceae	16 (8)	16
Enterococcus species	6 (6)	6
Lactobacillus species	5 (5)	5
Nonfermenters^d	7 (2)	7
Staphylococcus species	23 (0)	23
Streptococcus species	22 (4)	22
Vibrio species	6 (2)	6
Other bacteria^e	3 (2)	3
Total	303 (193)	129	138	36	174	160

↵a The total includes 48 reference strains and 255 clinical isolates. The designations of the reference strains and the clinical isolates are listed in Tables S1 and S2 in the supplemental material.
↵b Fusobacterium mortiferum (n = 1; good growth), F. varium (n = 1, absent), and F. nucleatum (n = 1, absent).
↵c Bifidobacterium bifidum (n = 1), Finegoldia magna (n = 1), Parvimonas micra (n = 1), Propionibacterium acnes (n = 1), and Veillonella parvula (n = 1).
↵d Acinetobacter baumannii (n = 2), Brevundimonas diminuta (n = 1), Flavobacterium meningosepticum (n = 1), Pseudomonas aeruginosa (n = 2), and Stenotrophomonas maltophilia (n = 1).
↵e Aeromonas hydrophila (n = 1), Kocuria rosea (n = 1), and Listeria monocytogenes (n = 1).
↵f Ability of the organisms to hydrolyze esculin was determined by separate testing.
↵g Poor growth is defined by pinpoint-sized colonies after 48 h of incubation.

TABLE 2

Isolation of Bacteroides species from 1,209 clinical specimens plated onto Bacteroides fragilis selective (BFS) and routine anaerobic plates

↵a In total, 65 B. fragilis isolates were detected: 41 by both methods, 5 by routine plates only, and 19 by BFS plates only. McNemar's test, P = 0.008 for comparison of results for B. fragilis detection by the two methods.