MIC values (μg/ml) for colistin and polymyxin B in P_aeruginosa and A_ baumannii strains (n = 117)Grey font numbers indicate the number of strains with equivalent MICs for colistin and polymyxin B_
| Colistin (mg/L) | >=256 | 2A | ||||||||||
| 128 | 1A | |||||||||||
| 64 | 1P+1A | |||||||||||
| 32 | 1A | |||||||||||
| 16 | 1A | 1P+1A | ||||||||||
| 8 | 1P+2A | 1P | 2P | |||||||||
| 4 | 3A | 2P+2A | 2P+1A | 5P+1A | 1A | |||||||
| 2 | 1A | 1P+5A | 10P+8A | 16P+9A | 3P | |||||||
| 1 | 1A | 4A | 12P+4A | 1P+1A | ||||||||
| 0.5 | 1P+2A | 1P+2A | ||||||||||
| 0.25 | 2P | 1P | ||||||||||
| 0.25 | 0.5 | 1 | 2 | 4 | 8 | 16 | 32 | 64 | 128 | >=256 | ||
| Polymyxin B (mg/L) | ||||||||||||
MIC values (μg/ml) for colistin and polymyxin B in E_ coli and K_ pneumoniae bacteria (n = 151)Grey font numbers indicate the number of strains with equivalent MICs for colistin and polymyxin B
| Colistin (mg/L) | >=256 | 1K | ||||||||||
| 128 | 1K | 2K | 1K | |||||||||
| 64 | 4K | 9K | 5K | |||||||||
| 32 | 3K | 12K | 8K | 1K | ||||||||
| 16 | 4K | 4K | ||||||||||
| 8 | 1K+1E | 1K | 1K | |||||||||
| 4 | 1K+3E | 1K+8E | 1K+3E | 1K | ||||||||
| 2 | 2k | 2K | 5K+9E | 2K+7E | 2E | |||||||
| 1 | 1k | 2K+2E | 2K+4E | 1K+9E | 5E | |||||||
| 0.5 | 2k | 3K+2E | 1K | 2K+2E | 1E | |||||||
| <=0.25 | 3k+1E | 2K | ||||||||||
| 0.25 | 0.5 | 1 | 2 | 4 | 8 | 16 | 32 | 64 | 128 | >=256 | ||
| Polymyxin B (mg/L) | ||||||||||||
MIC values and interpretations of colistin and polymyxin B against Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii strains
| Bac. | Col. MIC | Interp. | Poly. MIC | Int. | Bac. | Col. MIC | Interp. | Poly. MIC | Interp. | Bac. | Col. MIC | Int. | Poly. MIC | Int. | Bac. | Col. MIC | Int. | Poly. MIC | Int. | Bac. | Col. MIC | Int. | Poly. MIC | Int. |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| E1 | 1 | I | 2 | I | K1 | 1 | I | 1 | I | K64 | 64 | R | 64 | R | P1 | 2 | I | 1 | I | A1 | 4 | R | 0.5 | I |
| E2 | 1 | I | 4 | R | K2 | 1 | I | 1 | I | K65 | 64 | R | 32 | R | P2 | 4 | R | 1 | I | A2 | 4 | R | 2 | I |
| E3 | 4 | R | 1 | I | K3 | 1 | I | 2 | I | K66 | 64 | R | 32 | R | P3 | 1 | I | 1 | I | A3 | 8 | R | 1 | I |
| E4 | 2 | I | 1 | I | K4 | 1 | I | 0.5 | I | K67 | 64 | R | 32 | R | P4 | 1 | I | 1 | I | A4 | 256 | R | 128 | R |
| E5 | 1 | I | 2 | I | K5 | 1 | I | 0.25 | I | K68 | 64 | R | 16 | R | P5 | 2 | I | 1 | I | A5 | 2 | I | 0.5 | I |
| E6 | 2 | I | 2 | I | K6 | 1 | I | 0.5 | I | K69 | 64 | R | 32 | R | P6 | 4 | R | 2 | I | A6 | 4 | R | 4 | R |
| E7 | 1 | I | 4 | R | K7 | 2 | I | 1 | I | K70 | 64 | R | 16 | R | P7 | 2 | I | 4 | R | A7 | 2 | I | 1 | I |
| E8 | 1 | I | 2 | I | K8 | 2 | I | 1 | I | K71 | 64 | R | 32 | R | P8 | 1 | I | 2 | I | A8 | 0.5 | I | 0.5 | I |
| E9 | 1 | I | 2 | I | K9 | 2 | I | 1 | I | K72 | 128 | R | 64 | R | P9 | 1 | I | 1 | I | A9 | 2 | I | 0.25 | I |
| E10 | 4 | R | 2 | I | K10 | 2 | I | 0.5 | I | K73 | 128 | R | 64 | R | P10 | 1 | I | 1 | I | A10 | 2 | I | 2 | I |
| E11 | 1 | I | 1 | I | K11 | 2 | I | 1 | I | K74 | 128 | R | 32 | R | P11 | 1 | I | 1 | I | A11 | 2 | I | 1 | I |
| E12 | 1 | I | 2 | I | K12 | 2 | I | 0.25 | I | K75 | 128 | R | 128 | R | P12 | 2 | I | 1 | I | A12 | 16 | R | 4 | R |
| E13 | 2 | I | 2 | I | K13 | 2 | I | 0.25 | I | K76 | 32 | R | 16 | R | P13 | 2 | I | 1 | I | A13 | 2 | I | 2 | I |
| E14 | 1 | I | 2 | I | K14 | 2 | I | 0.5 | I | K77 | 0.25 | I | 0.5 | I | P14 | 1 | I | 1 | I | A14 | 0.5 | I | 0.5 | I |
| E15 | 0.5 | I | 2 | I | K15 | 2 | I | 1 | I | K78 | 0.25 | I | 0.5 | I | P15 | 4 | R | 1 | I | A15 | 2 | I | 1 | I |
| E16 | 0.5 | I | 2 | I | K16 | 2 | I | 2 | I | K79 | 0.25 | I | 0.25 | I | P16 | 2 | I | 1 | I | A16 | 2 | I | 1 | I |
| E17 | 1 | I | 1 | I | K17 | 2 | I | 2 | I | K80 | 0.25 | I | 0.25 | I | P17 | 16 | R | 16 | R | A17 | 1 | I | 0.5 | I |
| E18 | 1 | I | 0.5 | I | K18 | 4 | R | 8 | R | K81 | 0.25 | I | 0.25 | I | P18 | 2 | I | 1 | I | A18 | 2 | I | 2 | I |
| E19 | 2 | I | 1 | I | K19 | 4 | R | 1 | I | K82 | 0.5 | I | 0.25 | I | P19 | 2 | I | 2 | I | A19 | 1 | I | 2 | I |
| E20 | 4 | R | 2 | I | K20 | 4 | R | 4 | R | K83 | 0.5 | I | 0.5 | I | P20 | 1 | I | 1 | I | A20 | 2 | I | 2 | I |
| E21 | 2 | I | 2 | I | K21 | 4 | R | 2 | I | K84 | 0.5 | I | 0.5 | I | P21 | 1 | I | 1 | I | A21 | 0.5 | I | 0.25 | I |
| E22 | 2 | I | 1 | I | K22 | 8 | R | 2 | I | K85 | 0.5 | I | 1 | I | P22 | 1 | I | 1 | I | A22 | 2 | I | 2 | I |
| E23 | 1 | I | 2 | I | K23 | 8 | R | 8 | R | K86 | 0.5 | I | 0.5 | I | P23 | 1 | I | 1 | I | A23 | 2 | I | 1 | I |
| E24 | 1 | I | 4 | R | K24 | 8 | R | 4 | R | K87 | 0.5 | I | 0.25 | I | P24 | 8 | R | 2 | I | A24 | 1 | I | 1 | I |
| E25 | 4 | R | 2 | I | K25 | 16 | R | 8 | R | K88 | 0.5 | I | 2 | I | P25 | 8 | R | 4 | R | A25 | 1 | I | 1 | I |
| E26 | 2 | I | 4 | R | K26 | 16 | R | 16 | R | K89 | 0.5 | I | 2 | I | P26 | 8 | R | 4 | R | A26 | 2 | I | 2 | I |
| E27 | 1 | I | 4 | R | K27 | 16 | R | 16 | R | K90 | 32 | R | 32 | R | P27 | 2 | I | 0.5 | I | A27 | 4 | R | 1 | I |
| E28 | 2 | I | 1 | I | K28 | 16 | R | 16 | R | K91 | 256 | R | 128 | R | P28 | 2 | I | 2 | I | A28 | 256 | R | 128 | R |
| E29 | 8 | R | 2 | I | K29 | 16 | R | 8 | R | K92 | 16 | R | 8 | R | P29 | 8 | R | 1 | I | A29 | 16 | R | 16 | R |
| E30 | 4 | R | 2 | I | K30 | 16 | R | 16 | R | P30 | 2 | I | 1 | I | A30 | 2 | I | 1 | I | |||||
| E31 | 1 | I | 4 | R | K31 | 16 | R | 8 | R | P31 | 2 | I | 1 | I | A31 | 1 | I | 1 | I | |||||
| E32 | 1 | I | 2 | I | K32 | 32 | R | 8 | R | P32 | 1 | I | 1 | I | A32 | 128 | R | 64 | R | |||||
| E33 | 2 | I | 2 | I | K33 | 32 | R | 16 | R | P33 | 64 | R | 64 | R | A33 | 1 | I | 0.5 | I | |||||
| E34 | 0.5 | I | 4 | R | K34 | 32 | R | 16 | R | P34 | 1 | I | 1 | I | A34 | 32 | R | 32 | R | |||||
| E35 | 4 | R | 4 | R | K35 | 32 | R | 64 | R | P35 | 0.25 | I | 1 | I | A35 | 2 | I | 1 | I | |||||
| E36 | 1 | I | 1 | I | K36 | 32 | R | 32 | R | P36 | 2 | I | 1 | I | A36 | 64 | R | 64 | R | |||||
| E37 | 4 | R | 2 | I | K37 | 32 | R | 32 | R | P37 | 2 | I | 2 | I | A37 | 1 | I | 1 | I | |||||
| E38 | 2 | I | 1 | I | K38 | 32 | R | 16 | R | P38 | 2 | I | 1 | I | A38 | 0.5 | I | 0.25 | I | |||||
| E39 | 1 | I | 2 | I | K39 | 32 | R | 32 | R | P39 | 0.5 | I | 0.5 | I | A39 | 1 | I | 0.5 | I | |||||
| E40 | 4 | R | 2 | I | K40 | 32 | R | 16 | R | P40 | 2 | I | 2 | I | A40 | 1 | I | 0.25 | I | |||||
| E41 | 4 | R | 2 | I | K41 | 32 | R | 32 | R | P41 | 0.25 | I | 0.25 | I | A41 | 4 | R | 8 | R | |||||
| E42 | 2 | I | 2 | I | K42 | 32 | R | 8 | R | P42 | 0.25 | I | 0.25 | I | A42 | 2 | I | 0.5 | I | |||||
| E43 | 4 | R | 4 | R | K43 | 32 | R | 16 | R | P43 | 0.5 | I | 0.25 | I | A43 | 2 | I | 0.5 | I | |||||
| E44 | 2 | I | 2 | I | K44 | 32 | R | 8 | R | P44 | 4 | R | 2 | I | A44 | 4 | R | 1 | I | |||||
| E45 | 4 | R | 4 | R | K45 | 32 | R | 16 | R | P45 | 4 | R | 4 | R | A45 | 4 | R | 0.5 | I | |||||
| E46 | 2 | I | 4 | R | K46 | 32 | R | 32 | R | P46 | 2 | I | 4 | R | A46 | 2 | I | 0.5 | I | |||||
| E47 | 1 | I | 0.5 | I | K47 | 32 | R | 16 | R | P47 | 2 | I | 2 | I | A47 | 4 | R | 0.5 | S | |||||
| E48 | 2 | I | 1 | I | K48 | 32 | R | 16 | R | P48 | 2 | I | 2 | I | A48 | 2 | I | 0.5 | I | |||||
| E49 | 1 | I | 1 | I | K49 | 32 | R | 16 | R | P49 | 2 | I | 2 | I | A49 | 8 | R | 1 | I | |||||
| E50 | 4 | R | 2 | I | K50 | 32 | R | 16 | R | P50 | 2 | I | 2 | I | A50 | 2 | I | 2 | I | |||||
| E51 | 0.25 | I | 0.25 | I | K51 | 32 | R | 32 | R | P51 | 2 | I | 2 | I | A51 | 2 | I | 2 | I | |||||
| E52 | 0.5 | I | 0.5 | I | K52 | 32 | R | 32 | R | P52 | 4 | R | 4 | R | A52 | 1 | I | 0.5 | I | |||||
| E53 | 2 | I | 2 | I | K53 | 32 | R | 16 | R | P53 | 4 | R | 4 | R | A53 | 2 | I | 2 | I | |||||
| E54 | 4 | R | 1 | I | K54 | 64 | R | 32 | R | P54 | 2 | I | 2 | I | A54 | 2 | I | 1 | I | |||||
| E55 | 0.5 | I | 0.5 | I | K55 | 64 | R | 32 | R | P55 | 4 | R | 4 | R | ||||||||||
| E56 | 2 | I | 1 | I | K56 | 64 | R | 16 | R | P56 | 2 | I | 2 | I | ||||||||||
| E57 | 2 | I | 1 | I | K57 | 64 | R | 32 | R | P57 | 2 | I | 2 | I | ||||||||||
| E58 | 2 | I | 1 | I | K58 | 64 | R | 16 | R | P58 | 2 | I | 2 | I | ||||||||||
| E59 | 4 | R | 1 | I | K59 | 64 | R | 64 | R | P59 | 2 | I | 2 | I | ||||||||||
| K60 | 64 | R | 64 | R | P60 | 2 | I | 2 | I | |||||||||||||||
| K61 | 64 | R | 64 | R | P61 | 2 | I | 2 | I | |||||||||||||||
| K62 | 64 | R | 32 | R | P62 | 2 | I | 4 | R | |||||||||||||||
| K63 | 64 | R | 64 | R | P63 | 4 | R | 4 | R |
Differences in MIC values between colistin and polymyxin B among tested isolates
| Organisms (n) | Polymyxin B more potent by n (%) of strains | Same MIC | Colistin more potent by n (%) of strains | ||||
|---|---|---|---|---|---|---|---|
| 3 dilution | 2 dilution | 1 dilution | n (%) | 1 dilution | 2 dilution | 3 dilution | |
| E.coli (59) | 0 | 4 (6.8) | 19 (32.2) | 17 (28.8) | 11 (18.6) | 7 (11.9) | 1 (1.7) |
| K. pneumonia (92) | 2 (2.2) | 13 (14.1) | 39 (42.4) | 30 (32.6) | 6 (6.5) | 2 (2.2) | 0 |
| P. aeruginosa (63) | 1 (1.6) | 4 (6.3) | 15 (23.8) | 38 (60.3) | 4 (6.3) | 1 (1.6) | 0 |
| A. baumannii (54) | 6 (11.1) | 9 (16.7) | 18 (33.3) | 19 (35.2) | 2 (3.7) | 0 | 0 |
| Total 268 | 9 (3.4) | 30 (11.2) | 91 (34.0) | 104 (38.8) | 23 (8.6) | 10 (3.7) | 1 (0.4) |
Colistin and polymyxin B evaluation criteria for Enterobacterales, P_ aeruginosa and A_ baumannii according to CLSI and EUCAST criteria
| CLSI | Susceptible (μg/mL) | Intermediate(μg/mL) | Resistant(μg/mL) | ||
|---|---|---|---|---|---|
| Colistin | ≤2 | ≥4 | |||
| Polymyxin B | ≤2 | ≥4 | |||
| EUCAST | Susceptible (mg/L) | Intermediate (mg/L) | Resistant (mg/L) | ECOFF (mg/L) | |
| Colistin* | ≤2 | ≥4 | |||
| Colistin** | ≤4 | ≥8 | |||
| Polymyxin B* | 2 | ||||
| Polymyxin B** | 4 |
The essential agreement, categorical agreement rates of polymyxin B and resistance rates of colistin and polymyxin B in studied bacteria
| Colistin | Polymyxin B | |||||
|---|---|---|---|---|---|---|
| Bacteria | EA n (%) | CA n (%) | I n (%) | R n (%) | I n (%) | R n (%) |
| E. coli | 47 (79.7) | 39 (66.1) | 44 (74.6) | 15 (25.4) | 48 (81.4) | 11 (18.6) |
| K. pneumoniae | 75 (81.5) | 89 (96.7) | 30 (32.6) | 62 (67.4) | 33 (35.9) | 59 (64.1) |
| P. aeruginosa | 57 (90.5) | 54 (85.7) | 48 (76.2) | 15 (23.8) | 51 (81.0) | 12(19.0) |
| A. baumannii | 39 (72.2) | 46 (85.2) | 37 (68.5) | 17 (31.5) | 45 (83.3) | 9 (16.7) |
| Total | 218 (81.3) | 228 (85.1) | 159 (59.3) | 109 (40.7) | 177 (66.0) | 91 (34.0) |
Categorical agreement rates changing according to susceptibility status for colistin-polymyxin B intermediate–resistant isolates
| Strains | Colistin | Polymyxin B | % of Categorical agreement |
|---|---|---|---|
| Escherichia coli (I) | 44 | 36 | 81.8 |
| Escherichia coli(R) | 15 | 3 | 20 |
| Klebseilla pneumoniae(I) | 30 | 30 | 100 |
| Klebseilla pneumoniae(R) | 62 | 59 | 95.2 |
| Escherichia coli+ Klebseilla pneumoniae(I) | 74 | 66 | 89.2 |
| Escherichia coli+ Klebseilla pneumoniae(R) | 77 | 62 | 80.5 |
| Pseudomonas aeruginoa(I) | 48 | 45 | 93.8 |
| Pseudomonas aeruginoa(R) | 15 | 9 | 60 |
| Acinetobacter baumannii(I) | 37 | 37 | 100 |
| Acinetobacter baumannii (R) | 17 | 9 | 52.9 |
| Pseudomonas aeruginoa +Acinetobacter baumannii(I) | 85 | 82 | 96.5 |
| Pseudomonas aeruginoa +Acinetobacter baumannii(R) | 32 | 18 | 56.3 |