Table 2.
MIC determination for clinical P. aeruginosa isolates mexZ mutations. MIC determined with E-tests (Liofilchem®, Roseto degli Abruzzi, Italy) on Müller-Hinton agar; Amikacin (AMK), Tobramycin (TOB), Gentamicin (GEN), Ceftazidime (CEF), Meropenem (MER), Aztreonam (AZT), Ciprofloxacin (CIP), and Colistin (COL).
| Tobramycin | Sensitive [4≤] | Resistance [>4] | |||
|---|---|---|---|---|---|
| Res phenotype | INDEL in mexZ | n = 104 | 101 (97%) | 3 (3%) | |
| SNP in mexZ | n = 80 | 71 (89%) | 9 (11%) | ||
| TOTAL | n = 184 | 172 (93%) | 12 (7%) | ||
| Fraction of TOB resistance strains with a mexZ mutation: | 12/30 (40%) | ||||
| Ciprofloxacin | Sensitive [0.5≤] | Intermediate [0.75–1] | Resistance [>1] | ||
| Res phenotype | INDEL in mexZ | n = 104 | 40 (38%) | 33 (32%) | 31 (30%) |
| SNP in mexZ | n = 80 | 47 (59%) | 12 (15%) | 21 (26%) | |
| TOTAL | n = 184 | 87 (47%) | 45 (25%) | 52 (28%) | |
| Fraction of CIP resistance strains with a mexZ mutation: | 45/75 (60%) | 52/107 (49%) | |||
| Gentamicin | Sensitive [4≤] | Resistance [>4] | |||
| Res phenotype | INDEL in mexZ | n = 104 | 83 (80%) | 21 (20%) | |
| SNP in mexZ | n = 80 | 56 (70%) | 24 (30%) | ||
| TOTAL | n = 184 | 139 (76%) | 45 (24%) | ||
| Fraction of GEN resistance strains with a mexZ mutation: | 45/87 (52%) | ||||
| Colistin | Sensitive [4≤] | Resistance [>4] | |||
| Res phenotype | INDEL in mexZ | n = 104 | 104 (100%) | 0 (0%) | |
| SNP in mexZ | n = 80 | 80 (100%) | 0 (0%) | ||
| TOTAL | n = 184 | 184 (100%) | 0 (0%) | ||
| Fraction of COL resistance strains with a mexZ mutation: | 0/0 (0%) | ||||
| Piperacillin | Sensitive [16≤] | Resistance [>16] | |||
| Res phenotype | INDEL in mexZ | n = 104 | 90 (87%) | 14 (13%) | |
| SNP in mexZ | n = 80 | 50 (62%) | 30 (38%) | ||
| TOTAL | n = 184 | 140 (76%) | 44 (24%) | ||
| Fraction of PIP resistance strains with a mexZ mutation: | 44/90 (49%) | ||||
| Aztreonam | Sensitive [1≤] | Intermediate [1.5–16] | Resistance [>16] | ||
| Res phenotype | INDEL in mexZ | n = 104 | 32 (30%) | 64 (62%) | 8 (8%) |
| SNP in mexZ | n = 80 | 18 (23%) | 44 (54%) | 18 (23%) | |
| TOTAL | n = 184 | 50 (27%) | 108 (59%) | 26 (14%) | |
| Fraction of AZT resistance strains with a mexZ mutation: | 108/363 (30%) | 26/46 (57%) | |||
| Ceftazidime | Sensitive [8≤] | Resistance [>8] | |||
| Res phenotype | INDEL in mexZ | n = 104 | 95 (91%) | 9 (9%) | |
| SNP in mexZ | n = 80 | 64 (80%) | 16 (20%) | ||
| TOTAL | n = 184 | 159 (86%) | 25 (14%) | ||
| Fraction of CEF resistance strains with a mexZ mutation: | 25/65 (38%) | ||||
| Meropenem | Sensitive [2≤] | Intermediate [2.5–8] | Resistance [>8] | ||
| Res phenotype | INDEL in mexZ | n = 104 | 84 (80%) | 11 (11%) | 9 (9%) |
| SNP in mexZ | n = 80 | 61 (76%) | 10 (13%) | 9 (11%) | |
| TOTAL | n = 184 | 146 (79%) | 21 (12%) | 18 (9%) | |
| Fraction of MER resistance strains with a mexZ mutation: | 21/44 (47%) | 18/51 (35%) | |||
MIC determinations for each antibiotic are given for the total population of mexZ mutants as well as the fraction of mexZ mutants with either an insertions/deletions (INDEL) or a Single-Nucleotide Polymorphism (SNP). In addition, the fraction of resistant strains with a mexZ mutation is given for each tested antibiotic. MIC values were compared to the clinical EUCAST breakoff points21.