Table 3.

Gram-negative species with antibiotic resistance after various types of low level exposure (<MIC value) to chlorhexidine digluconate (CHG).

Species	Strain(s)	MIC Increase (CHG)	Antibiotic(s)	Pre-Value	Post-Value	Category	Reference
Bacteroides fragilis	ATCC 25285	-	Ampicillin Cefoxitin Cefoperazone Chloramphenicol Metronidazole Norfloxacin Tetracycline	46 1 7 1 52 1 2 1 0.6 1 0.6 1 0.6 1	77 1 13 1 126 1 2 1 0.9 1 0.9 1 2 1	- - - - - - -	[30]
Burkholderia cepacia complex	B. lata strain 383	-	Imipenem Meropenem Ciprofloxacin Ceftazidime Tobramycin	24 2 40.7 2 30 2 40.3 2 7.3 2	15–21 (2) 2 33 (1) 2 11–20 (2) 2 30–33 (2) 2 -	- - - - -	[6]
Chrysobacterium spp.	2 biocide-sensitive strains from organic foods	5-fold–6-fold	Ampicillin Cefotaxime Ceftazidime Sulfamethoxazol Tetracycline	- - - - -	64 (1) 2 128 (2) 2 64 (2) 2 1024 (1) 2 16 (1) 2	R R R R R	[31]
Enterobacter cloacae	2 biocide-sensitive strains from organic foods	10-fold–16-fold	Cefotaxime Ceftazidime Imipenem Sulfamethoxazol Tetracycline	- - - - -	64 (1) 2 64 (2) 2 16 (2) 2 1024 (2) 2 32 (1) 2	R R R R R	[31]
Enterobacter ludwigii	2 biocide-sensitive strains from organic foods	6-fold–8-fold	Ceftazidime Imipenem Sulfamethoxazol	- - -	64 (2) 2 16 (2) 2 1024 (2) 2	R R R	[31]
Enterobacter spp.	6 biocide-sensitive strains from organic foods	4-fold–10-fold	Cefotaxime Ceftazidime Imipenem Sulfamethoxazol	- - - - -	64 (1) 2 128 (1) 2 64 (3) 2 16 (3) 2 1024 (2) 2	R R R R R	[31]
Escherichia coli	NCIMB 8545	≤6-fold	Tobramycin	-	- 2	R 3	[32]
Escherichia coli	NCTC 12900 strain O157	Approx. 50-fold	Various antibiotics	No cross-resistance 4		n.a.	[10]
Klebsiella oxytoca	2 biocide-sensitive strains from organic foods	2-fold–8-fold	Various antibiotics	No cross-resistance 2		n.a.	[31]
Klebsiella pneumoniae	6 clinical strains with a variety of antibiotic resistance markers	4-fold–16-fold	Azithromycin Cefepime Colistin Teicoplanin	8–64 (6) 0.06–0.125 (1) ≥64 (5) 2–4 (6) >64 (6)	8–64 (6) 2 0.06–0.5 (2) 2 ≥64 (4) 2 >64 (5) 2 >64 (6) 2	n.a. n.a. n.a. R n.a.	[33]
Klebsiella spp.	Biocide-sensitive strain from organic foods	2-fold	Ceftazidime Imipenem	- -	64 2 16 2	R R	[31]
Pantoea agglomerans	5 biocide-sensitive strains from organic foods	5-fold–10-fold	Cefotaxime Ceftazidime Imipenem Sulfamethoxazol Tetracycline	- - - - -	64–128 (3) 2 64 (3) 2 16 (1) 2 1024 (2) 2 16–32 (2) 2	R R R R R	[31]
Pantoea ananatis	2 biocide-sensitive strains from organic foods	10-fold–50-fold	Cefotaxime Ceftazidime Imipenem Sulfamethoxazol Tetracycline	- - - - -	64–128 (2) 2 64 (1) 2 16 (1) 2 1024 (1) 2 16 (1) 2	R R R R R	[31]
Pantoea spp.	3 biocide-sensitive strains from organic foods	5-fold–16-fold	Ampicillin Cefotaxime Ceftazidime Imipenem Sulfamethoxazol Tetracycline	- - - - - -	32 (1) 2 128 (1) 2 64 (1) 2 16 (1) 2 1024 (1) 2 16–32 (2) 2	R R R R R R	[31]
Salmonella Virchow	Food isolate	Approx. 10-fold	Various antibiotics	No cross-resistance 4		n.a.	[10]
Salmonella spp.	3 biocide-sensitive strains from organic foods	5-fold–10-fold	Cefotaxime Imipenem Nalidixic acid Sulfamethoxazol Tetracycline	- - - -	128 (2) 2 16 (2) 2 64 (2) 2 1024 (1) 2 32 (1) 2	R R R R R	[31]
Salmonella spp.	6 strains with higher MICs to biocidal products	50-fold–200-fold (2 strains)	Tetracycline Chloramphenicol Nalidixic acid	<1 4 4 4 4 4	>16 (1) 5 8 (1) 5 16 (1) 5	R I I	[16]

¹ spiral gradient endpoint method (mg/L); ² microdilution method (mg/L); ³ unstable; ⁴ disc diffusion test (mm); ⁵ NARMS plates (mg/L); - no information; R = resistant; I = intermediate susceptible; S = susceptible; () number of strains or isolates.