High level of persister frequency in clinical staphylococcal isolates

BMC Microbiology

Table 3 Minimum inhibitory concentration (MIC) values of biofilm forming and non-forming isolates as detected by possession of icaAD genes

Antibiotics	icaAD			Antibiotics	icaAD
Antibiotics	Positive (n = 86)	Negative (n = 289)	P value	Antibiotics	Positive (n = 86)	Negative (n = 289)	P value
Oxacillin				Tetracycline
Range	0.125- > 32	0.125- > 32		Range	0.125- > 4	0.125- > 4
MIC₅₀	2	1		MIC₅₀	0.5	0.5
MIC₉₀	> 32	32		MIC₉₀	1	2
% resistance	44.6%	37.2%	⃰	% resistance	-	-	0.217
Vancomycin				Clindamycin
Range	0.125- > 4	0.125- > 4		Range	0.125- > 512	0.125- > 512
MIC₅₀	1	2		MIC₅₀	0.125	0.125
MIC₉₀	2	4		MIC₉₀	8	128
% resistance	-	-	⃰	% resistance	10.5%	14.5%	0.069
Cotrimoxazole				Penicillin
Range	0.5/9.5- > 16/304	0.5/9.5- > 16/304		Range	0.125- > 8	0.125- > 8
MIC₅₀	0.5/9.5	16		MIC₅₀	0.25	0.5
MIC₉₀	16/304	> 16/304		MIC₉₀	2	2
% resistance	32.6%	42.9%	0.045	% resistance	-	-	0.023
Erythromycin				Ciprofloxacin
Range	0.125- > 512	0.125- > 512		Range	0.125–520	0.125–520
MIC₅₀	32	32		MIC₅₀	8	4
MIC₉₀	512	> 512		MIC₉₀	64	128
% resistance	59.3%	63.3%	0.003	% resistance	46.5%	24.9%	0.015
Chloramphenicol				Gentamicin
Range	0.125- > 16	1- > 16		Range	0.125- > 64	0.125- > 64
MIC₅₀	4	4		MIC₅₀	1	1
MIC₉₀	8	8		MIC₉₀	64	64
% resistance	3.8%	2.3%	0.516	% resistance	23.3%	26.6%	0.231

The MICs values of were determined by the agar dilution method. The sensitivity towards the antibiotics was evaluated among biofilm forming and non-forming isolates based on icaAD genes. The Chi-square test was performed to see the association between MIC value and biofilm formation ability taking P < 0.05 statistically significant.
*The resistant range of MIC values of oxacillin and vancomycin is different for S. aureus and CNS. For this reason, p value is not mentioned in the table. The sensitivity of oxacillin (n = 20, 44.4%) in biofilm producers (n = 45) vs sensitivity (n = 63, 54.3%) in biofilm non-producers S. aureus was significantly different (p = 0.006). Likewise, the sensitivity of oxacillin (n = 30, 73.2%) in biofilm producers (n = 41) vs sensitivity (n = 142, 82.1%) in biofilm non-producers (n = 173) CNS were significantly different (p = 0.012). Irrespective of whether biofilm producers or not, all the isolates were sensitive towards vancomycin (Supplementary Table 2).

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