Molecular Characterization of Cefoxitin-Resistant Escherichia coli from Canadian Hospitals

DOI: 10.1128/AAC.49.1.358-365.2005

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FIG. 1.
Number of cefoxitin-resistant strains isolated by month and by site over the length of the study. Colors represent the total number of strains at a specific site.
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FIG. 2.
Dendrogram depicting DNA macrorestriction patterns of cefoxitin-resistant E. coli strains generated with XbaI. The shaded region highlights the largest outbreak cluster described in the text.
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FIG. 3.
Schematic diagram showing the insertion of the IS10 (two strains) and IS911-like (one strain) elements in the ampC promoter region, as found in this study.

TABLE 1.

Site of isolation of cefoxitin-resistant strains

↵ a A total of 209 cefoxitin-resistant E. coli isolates recovered from 232 reported sites of isolation.

TABLE 2.

Antimicrobial resistance patterns of study strains^a

Antimicrobial agent	% (no.) of resistant strains^b
Antimicrobial agent	AmpC producers (n = 232)	Non-AmpC producers (n = 183)
Amoxicillin-clavulanate	66 (152)	43 (79)
Ampicillin	96 (223)	82 (150)
Cefazolin	55 (127)	36 (65)
Ceftazidime	1.3 (3)	1.1 (2)
Ceftriaxone	2.1 (5)	11 (21)
Piperacillin-tazobactam	4.7 (11)	2.2 (4)
Cefotetan	0 (0)	0 (0)
Imipenem	0 (0)	0 (0)
Ciprofloxacin	45 (105)	19 (35)
Levofloxacin	44 (102)	19 (34)
Nitrofurantoin	7.3 (17)	1.6 (3)
Gentamicin	27 (63)	25 (45)
Amikacin	1.3 (3)	2.2 (4)
Tobramycin	26 (60)	18 (33)
Trimethoprim-sulfamethoxazole	51 (118)	33 (60)

↵ a As determined with Vitek GNS 121 cards.
↵ b Cefoxitin MICs were ≥32 μg/ml for AmpC producers and <32 μg/ml for non-AmpC producers, as determined by broth microdilution.

TABLE 3.
Mutations at given positions in ampC promoter region for specific promoter types^a

↵ a Position numbering as defined by Jaurin et al. (13). Type numbers were assigned arbitrarily. WT, wild-type promoter from E. coli K-12; DEL, deletion at the indicated position.
b Positions −42, −18, and −15 are involved in the alternate promoter; positions −32 and −11 are part of the wild-type promoter; positions −13.1 and −13.2 are part of the spacer region of the wild-type promoter; nucleotides between positions +17 and +37 are located in the attenuator; and positions +63, +70, and +81 are located in the coding region.
TABLE 4.
Promoter sequence types of strains containing CMY-2 gene
Promoter sequence type No. of strains No. of strains with CMY-2
Wild type 14 7
03 36 1
04 19 1
07 8 5
11 10 2
17 1 1
18 12 5
22 1 1
48 1 1
52 1 1