LETTER
The mcr-1 gene, a transferable plasmid-mediated colistin resistance gene, was recently detected in Escherichia coli isolates from animals, food, and patients in China (1). This gene spread rapidly beyond China into southern Asia, Europe, South America, and Africa, mirroring the emerging NDM-1-like scenario (2–7). In Algeria, Olaitan et al. confirmed the presence of mcr-1 in poultry (8), but to the best of our knowledge, no human case has yet been reported. In response to this potential clinical problem, we retrospectively genotyped six colistin-resistant (breakpoint for resistance, >2 μg/ml) E. coli isolates collected between October 2009 and December 2011 from Sidi Belabess University Hospital for the presence of the mcr-1 gene using a previously described PCR method (1). The mcr-1 gene was detected in one isolate (SE65). This isolate was obtained from a urine sample of an 18-year-old polytrauma man hospitalized in May 2011 with no history of traveling abroad. The characteristics of SE65 are shown in Table 1. Multilocus sequence typing (MLST) indicated that SE65 belonged to sequence type 405 (ST405), which differs from the STs identified in clinical E. coli isolates harboring mcr-1 from Denmark (ST744) (2), Egypt (ST1011) (5), and Cambodia (ST354) (9). Colistin resistance was successfully transferred to the E. coli J53 (F− met pro Azir) strain via a conjugation experiment. The presence of mcr-1 in the transconjugant suggested that this gene was located on a transferable plasmid. This result confirms the finding that the mcr-1 gene is mobilized on plasmids that have spread to different Enterobacteriaceae (7, 10). We notice also a small reduction of ciprofloxacin's diameter of inhibition in the transconjugant strain, but this occurs without any change in the interpretation of susceptibility testing results.
TABLE 1.
Characteristics of mcr-1-positive E. coli strains and an E. coli transconjugant by antibiotic susceptibility testinga
| Antibiotic(s) | Diam of zone of inhibition (mm) of indicated strain (resistance gene[s]; MIC [μg/ml] of colistin) |
||
|---|---|---|---|
| E. coli SE65 (mcr-1 blaCTX-M15 blaTEM-1; 4) | Transconjugant (mcr-1; 4) | E. coli J53 (none; 0.125) | |
| Amoxicillin | 6 | 6 | 27 |
| Amoxicillin-clavulanate | 6 | 9 | 20 |
| Ticarcillin-clavulanate | 6 | 11 | 25 |
| Cefotaxime | 6 | 28 | 28 |
| Ceftriaxone | 6 | 27 | 27 |
| Cefepime | 6 | 28 | 28 |
| Aztreonam | 9 | 31 | 31 |
| Imipenem | 31 | 27 | 27 |
| Ertapenem | 22 | 30 | 30 |
| Gentamicin | 23 | 25 | 25 |
| Amikacin | 22 | 28 | 27 |
| Ciprofloxacin | 6 | 26 | 32 |
| Trimethoprim-sulfamethoxazole | 6 | 6 | 20 |
| Rifampin | 10 | 9 | 10 |
| Fosfomycin | 31 | 31 | 17 |
| Colistin | 15 | 16 | 19 |
Antibiotic susceptibility testing was performed according to CLSI recommendations.
Here, we report for the first time the presence of the mcr-1 colistin resistance gene in a clinical E. coli isolate from Algeria. The isolate was obtained in 2011, indicating that the existence of transmissible colistin resistance in Algerian hospitals is not a recent occurrence. The mcr-1 gene has been present, though not detected, for a long time (11). With the extensive use of colistin in hospitals, colistin resistance has already spread worldwide (8). However, there are also reports of colistin resistance in humans who have not previously received the drug. Colistin use in animals suggests that animals may be an important source of transmission of colistin resistance to humans (12).
Surveillance of the emergence of this new gene is warranted, and the situation may be alarming, because infections due to such multidrug-resistant bacteria are associated with increased lengths of stay in intensive care units and increased mortality. Unfortunately, colistin susceptibility testing for Enterobacteriaceae is not a routine procedure in diagnostic laboratories. Furthermore, the disc diffusion method has been reported to be highly unreliable for colistin. The recommended method remains the Etest (13), but MIC values for detecting mcr-1 colistin resistance genes are very low (≥4 μg/ml). Recently, a new SuperPolymyxin screening medium able to detect any polymyxin-resistant bacterium regardless of its level was developed. This medium may be used in human and veterinary medicine to monitor the dissemination of mcr-1 colistin resistance (14).
ACKNOWLEDGMENTS
We have no conflict of interest or financial interests to declare.
No funding was received for this work.
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