In vitro determination of the antibiotic susceptibility of biofilm-forming Pseudomonas aeruginosa and Staphylococcus aureus: possible role of proteolytic activity and membrane lipopolysaccharide

Figures & data

Table 1 Protease activity of Staphylococcus aureus cells

Samples	Proteolytic activity (units/10^6 bacteria/hour)
Planktonic	2.00 ± 0.33
Biofilm	3.34 ± 0.55*
Biofilm treated with (1/4) MIC of ciprofloxacin	2.44 ± 0.40
Biofilm treated with (1/32) MIC of cefaclor	2.88 ± 0.43
Biofilm treated with (1/8) MIC of cotrimoxazole	3.56 ± 0.65*
Biofilm treated with (1/16) MIC of amoxicillin	6.44 ± 0.57*

Notes: n = 4 experiments.

* indicates significant difference from the planktonic group at P < 0.05.

Abbreviation: MIC, minimum inhibitory concentration.

Table 2 Protease activity of Pseudomonas aeruginosa cells

Samples	Proteolytic activity (units/10^6 bacteria/hour)
Planktonic	2.89 ± 0.47
Biofilm	4.44 ± 0.38*
Biofilm treated with (1/8) MIC of ciprofloxacin	5.33 ± 0.46*
Biofilm treated with (1/8) MIC amikacin	5.78 ± 0.61*
Biofilm treated with (1/8) MIC ceftazidime	5.10 ± 0.44*

Notes: n = 4 experiments.

* indicates significant difference from the planktonic group at P < 0.05.

Abbreviation: MIC, minimum inhibitory concentration.

Figure 1 Electrophoretic profile of LPS of Pseudomonas aeruginosa.

Notes: Lane 1, LPS extracted from biofilm cells; lane 2, LPS extracted from planktonic cells; lane 3, LPS extracted from biofilm cells treated with (1/8) MIC of ceftazidime; lane 4, LPS extracted from biofilm cells treated with (1/4) MIC of ciprofloxacin; lane 5, LPS extracted from biofilm cells treated with (1/8) MIC of amikacin.

Abbreviations: LPS, lipopolysaccharide; MIC, minimum inhibitory concentration.

Table S1 Minimum inhibitory concentration values of Staphylococcus aureus planktonic and biofilm cells

Antibiotics	Planktonic cells	Biofilm cells
Ciprofloxacin	0.5 ± 0.1 μg/mL	128 ± 25 μg/mL
Amoxicillin	4 ± 0.9 μg/mL	512 ± 110 μg/mL
Cotrimoxazole	4 ± 0.0 μg/mL	256 ± 60 μg/mL
Cefaclor	8 ± 1.8 μg/mL	>1024 μg/mL

Table S2 Minimum inhibitory concentration values of Pseudomonas aeruginosa planktonic and biofilm cells

Antibiotics	Planktonic cells	Biofilm cells
Ciprofloxacin	0.125 ± 0.02 μg/mL	64 ± 13 μg/mL
Ceftazidime	2 ± 0.4 μg/mL	256 ± 80 μg/mL
Cotrimoxazole	256 ± 60 μg/mL	512 ± 100 μg/mL
Amikacin	2 ± 0.0 μg/mL	0.02 ± 0.004 μg/mL