TABLE 3.

Bacterial load (log CFU/ml) of three carbapenem-resistant Acinetobacter baumannii strains in biofilms after 24 h and 48 h of exposure to five antimicrobials used alone or in combination at susceptibility breakpoint concentrations^a

Antimicrobial(s)	Bacterial load (log CFU/ml) in biofilms by strain after:
	24 h			48 h
	Ab15151(pOXA-82-2)	Ab1987	Ab2147	Ab15151(pOXA-82-2)	Ab1987	Ab2147
No antimicrobial	8.20 ± 0.61	6.93 ± 0.04	7.15 ± 0.09	9.35 ± 0.19	7.48 ± 0.22	7.76 ± 0.19
MEM	6.95 ± 0.42	7.09 ± 0.39	7.16 ± 0.26	7.94 ± 0.18	7.08 ± 0.18	7.07 ± 0.19
IPM	8.01 ± 0.34	7.06 ± 0.09	7.20 ± 0.11	9.33 ± 0.43	7.81 ± 0.16	8.06 ± 0.10
SUL	8.21 ± 1.23	7.45 ± 0.30	7.48 ± 0.21	6.59 ± 0.23	7.11 ± 0.21	6.65 ± 0.25
CST	8.56 ± 0.52	7.62 ± 0.04	7.89 ± 0.16	7.40 ± 0.54	9.06 ± 0.11	9.07 ± 0.36
TGC	6.77 ± 0.29	7.70 ± 0.21	7.85 ± 0.52	5.00 ± 1.03b	8.87 ± 0.11	9.41 ± 0.20
MEM + SUL	6.56 ± 0.14	6.10 ± 0.09	6.33 ± 0.12	4.78 ± 0.40	4.57 ± 0.49c	4.11 ± 0.37c
MEM + CST	7.20 ± 0.20	6.59 ± 0.28	6.99 ± 0.70	7.93 ± 0.13	7.79 ± 0.39	6.09 ± 0.64
MEM +TGC	5.72 ± 0.48	6.01 ± 0.17	6.37 ± 0.34	4.37 ± 0.31	7.27 ± 0.24	6.33 ± 0.53
IPM + SUL	7.25 ± 0.10	6.40 ± 0.07	6.48 ± 0.11	6.87 ± 0.69	5.57 ± 0.61	5.21 ± 0.26
IPM + CST	7.89 ± 0.38	7.47 ± 0.06	7.52 ± 0.07	9.27 ± 0.54	8.20 ± 0.29	8.60 ± 0.17
IPM + TGC	7.51 ± 0.74	6.32 ± 0.20	6.72 ± 0.18	5.71 ± 1.15	7.95 ± 0.08	8.28 ± 0.23
SUL + CST	7.34 ± 0.23	7.65 ± 0.52	7.61 ± 0.38	6.62 ± 0.53	6.42 ± 0.13	6.01 ± 0.41
SUL + TGC	6.10 ± 0.32	7.68 ± 0.31	7.64 ± 0.50	4.06 ± 0.38	4.92 ± 0.37c	3.94 ± 0.30c
CST + TGC	6.54 ± 0.35	7.69 ± 0.08	7.99 ± 0.30	4.92 ± 0.08	8.50 ± 0.16	9.40 ± 0.20

^aSusceptibility breakpoint concentrations of antimicrobials: meropenem (MEM), 2 mg/liter; imipenem (IPM), 2 mg/liter; sulbactam (SUL), 4 mg/liter; colistin (CST), 2 mg/liter; and tigecycline (TGC), 2 mg/liter. Values are means ± standard deviations.

^bIndicates bactericidal effect (>3-log reduction in bacterial load compared to that without antibiotic treatment).

^cIndicates synergism.