Phenotypic and Genotypic Characteristics of Biofilm Formation in Clinical Isolates of Acinetobacter baumannii

Figures & data

Figure 1 Antimicrobial susceptibility profiles of clinical A. baumannii isolates. (A) Resistance rate of all strains to 18 antimicrobials; (B) approximately 65.4% of isolates exhibited MDR (including XDR).

Abbreviations: MDR, multiple drug resistance; XDR, extensively drug resistance.

Figure 2 Growth curves and biofilm growth curves in representative A. baumannii strains. (A) Growth curves of 17 representative A. baumannii strains at planktonic stage, and OD₅₉₀ values of each strain were measured every 2 h until 24 h; (B) growth curves for 17 representative A. baumannii strains at biofilm stage, and OD₅₇₀ values of each strain were measured every 4 h until 48 h. The data were presented as the average of three measurements. Error bars (standard deviation <10%) were omitted for simplicity.

Figure 3 Evaluation of biofilm formation capacity of strains by confocal laser scanning microscopy. (A) Biofilm Images of four representative A. baumannii strains under CLSM (B) Comparison of biofilm formation capabilities between crystal violet and CLSM. Data were expressed as mean ± SD; fluorescence intensity represents CLSM results and OD₅₇₀ indicates crystal violet results.

Table 1 Biofilm Formation Ability of Strains with Different Antimicrobial Resistance

Resistance Profile	N	OD570	rs	P
Non-MDR	36	0.98 (0.36, 1.47)	-0.212	0.03
MDR	68	0.55 (0.36, 0.85)

Notes: OD₅₇₀: The absorbance value at the wavelength of 570 nm. Data was shown in median (interquartile range, IQR).

Table 2 Correlation Between Biofilm Formation Ability and Antimicrobial Resistance to 18 Antimicrobials

Antimicrobial Category	Antimicrobial Agent	OD570		rs	P
		S	R
Aminoglycosides	Gentamicin	0.71 (0.34,1.28)	0.55 (0.38,0.84)	−0.211	0.032
	Tobramycin	0.82 (0.36,1.33)	0.53 (0.37,0.82)	−0.211	0.032
	Amikacin	0.84 (0.36,1.34)	0.53 (0.37,0.82)	−0.214	0.03
Carbapenemase	Imipenem	0.92 (0.36,1.43)	0.53 (0.37,0.85)	−0.215	0.029
	Meropenem	0.92 (0.36,1.43)	0.53 (0.37,0.85)	−0.215	0.029
Fluoroquinolones	Ciprofloxacin	0.92 (0.36,1.34)	0.55 (0.37,0.87)	−0.213	0.031
	Levofloxacin	0.92 (0.36,1.34)	0.55 (0.37,0.87)	−0.213	0.031
Penicillins + β-lactamase inhibitors	Ampicillin/sulbactam	0.98 (0.36,1.47)	0.69 (0.49,0.72)	−0.239	0.018
	Piperacillin/tazobactam	0.98 (0.36,1.47)	0.53 (0.36,0.85)	−0.235	0.016
	Ticarcillin/clavulanic acid	1.09 (0.37,1.52)	0.53 (0.36,0.84)	−0.288	0.003
Cephalosporins	Ceftazidime	0.92 (0.36,1.43)	0.53 (0.37,0.85)	−0.215	0.029
	Ceftriaxone	0.92 (0.36,1.43)	0.53 (0.37,0.85)	−0.215	0.029
	Cefotaxime	0.98 (0.37,1.38)	0.53 (0.36,0.78)	−0.263	0.007
	Cefepime	0.98 (0.36,1.47)	0.53 (0.36,0.85)	−0.235	0.016
Tetracyclines	Tetracycline	0.91 (0.38,1.25)	0.59(0.36,1.00)	−0.209	0.034
	Tigecycline	0.57 (0.36, 1.1)	0	NA	NA
Penicillins	Piperacillin	0.88 (0.36,1,30)	0.53 (0.37,0.78)	−0.204	0.037
Lipopeptides	Polymyxin B	0.57 (0.36, 1.1)	0	NA	NA

Notes: S, sensitive; R, resistance; bold indicates P < 0.05.

Table 3 Comparison of MICs and MBICs of A. baumannii Strains

Strain	Ciprofloxacin			Meropenem			Ceftazidime
	MIC for Planktonic Cells (µg/mL)	MBIC for Biofilm Cells (µg/mL)	Fold Change	MIC for Planktonic Cells (µg/mL)	MBIC for Biofilm Cells (µg/mL)	Fold Change	MIC for Planktonic Cells (µg/mL)	MBIC for Biofilm Cells (µg/mL)	Fold Change
20053^a	0.125	32	256	0.5	8	16	8	1024	128
20061^a	0.0625	32	512	0.25	16	64	4	1024	256
20068^a	0.0625	32	512	0.5	16	32	2	1024	512
20098^b	0.0625	64	1024	0.25	16	64	4	1024	256
20101^b	0.125	32	256	0.25	16	64	2	1024	512
20110^b	0.125	32	256	1	16	16	4	1024	256
20047^c	0.125	512	4096	0.5	512	1024	4	4096	1024
20180^c	0.125	64	512	0.5	16	32	8	2048	256
20250^c	0.0625	64	1024	1	16	16	8	2048	256

Notes: ^aIndicates weak biofilm producer, ^bIndicates moderate biofilm producer, ^cIndicates strong biofilm producer.

Table 4 Comparison of MBCs and MBECs of A. baumannii Strains

Strain	Ciprofloxacin			Meropenem			Ceftazidime
	MBC for Planktonic Cells (µg/mL)	MBEC for Biofilm Cells (µg/mL)	Fold Change	MBC for Planktonic Cells (µg/mL)	MBEC for Biofilm Cells (µg/mL)	Fold Change	MBC for Planktonic Cells (µg/mL)	MBEC for Biofilm Cells (µg/mL)	Fold Change
20053^a	0.25	128	512	1	128	128	16	2048	128
20061^a	0.125	64	512	0.5	32	64	8	2048	256
20068^a	0.125	64	512	1	32	32	4	2048	512
20098^b	0.125	128	1024	0.5	32	64	8	2048	256
20101^b	0.25	64	256	0.5	128	256	4	2048	512
20110^b	0.25	64	256	2	256	128	8	2048	256
20047^c	0.25	1024	4096	1	1024	1024	8	8192	1024
20180^c	0.25	128	512	1	256	256	16	4096	256
20250^c	0.125	128	1024	2	64	32	16	4096	256

Notes: ^aIndicates weak biofilm producer, ^bIndicates moderate biofilm producer, ^cIndicates strong biofilm producer.

Figure 4 Role of biofilm-associated genes in antimicrobial resistance and biofilm of clinical A. Baumannii. (A) Percentage of biofilm-associated gene in different antimicrobial-resistant strains; (B) the relative expression of abaI in eight selected A. Baumannii strains. Data were shown as fold changes between planktonic and biofilm stage, and control represented planktonic cells.

Notes: **P<0.01, ***P<0.001.