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Table 2 Minimum inhibitory concentration (MIC) values of biofilm forming and non-forming isolates as detected by TCP method

From: High level of persister frequency in clinical staphylococcal isolates

Antibiotics Biofilm Antibiotics Biofilm
Positive
(n = 86)
Negative
(n = 289)
P value Positive
(n = 86)
Negative
(n = 289)
P value
Oxacillin Tetracycline
 Range 0.125–64 0.125–64    Range 0.125–8 0.125–8  
 MIC50 1 1    MIC50 0.5 0.5  
 MIC90 64 64    MIC90 2 8  
 % resistance 65 (37.4%) 93 (46.3%) *  % resistance 8 (4.6%) 22 (10.9%) 0.076
Vancomycin Clindamycin
 Range 0.125–8 0.125–8    Range 0.125–1024 0.125–1024  
 MIC50 2 2    MIC50 0.125 0.125  
 MIC90 4 4    MIC90 256 128  
 % resistance - - *  % resistance 32 (18.4%) 36 (17.9%) 0.479
Cotrimoxazole Penicillin
 Range 0.5/9.5–16/304 0.5/9.5–16/304    Range 0.125–8 0.125–8  
 MIC50 2/38 16    MIC50 0.25 0.5  
 MIC90 16/304 512    MIC90 8 4  
 % resistance 78 (44.8%) 76 (37.8%) 0.265  % resistance 132 (75.9%) 163 (81.1%) 0.017
Erythromycin Ciprofloxacin
 Range 0.125–1024 0.125–1024    Range 0.125–256 0.125–256  
 MIC50 16 64    MIC50 8 8  
 MIC90 1024 1024    MIC90 128 128  
 % resistance 102 (58.6%) 139 (69.2%) 0.375  % resistance 104 (59.8%) 115 (57.2%) 0.985
Chloramphenicol Gentamicin
 Range 0.125–32 1–32    Range 0.125–128 0.125–128  
 MIC50 4 4    MIC50 1 2  
 MIC90 8 8    MIC90 64 64  
 % resistance 7 (4.0%) 12 (6.0%) 0.028  % resistance 81 (46.6%) 98 (48.8%) 0.225
  1. The MICs values of the isolates were determined by the agar dilution method. The sensitivity towards each antibiotic was compared between biofilm forming and non-forming isolates. The Chi-square test was used to evaluate the statistical significance of differences in the results. The p value of < 0.05 was considered statistically significant.
  2. *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 = 45, 58.4%) in biofilm producers (n = 77) vs sensitivity (n = 38, 45.2%) in biofilm non-producers S. aureus was not significantly different (p = 0.542). Whereas the sensitivity of oxacillin (n = 76, 84.4%) in biofilm producers vs. sensitivity (n = 96, 77.4%) in biofilm non-producers CNS were significantly different (p = 0.086). Irrespective of whether biofilm producers or not, all the isolates were vancomycin susceptible (Supplementary Table 1).