Acquisition of mcr-1 Plasmid-Mediated Colistin Resistance in Escherichia coli and Klebsiella pneumoniae during Hajj 2013 and 2014.

Aplasmid-mediated transferable colistin resistance gene, mcr-1, was recently described in China (1) and was rapidly reported in several other countries (2). The spread of the mcr-1 gene was not only reported in Escherichia coli but also associated with other Enterobacteriaceae species isolated from human clinical samples, farm animals, and travelers (2, 3). However, whether or not the mcr-1 gene is acquired during the Hajj (the Muslim pilgrimage to Mecca) remains unknown. We conducted two cohort studies of pilgrims traveling to Mecca in 2013 (22 September to 23 October) (4, 5) and in 2014 (19 September to 12 October) (6). A total of 440 rectal swab samples were collected from pilgrims (in 2013, 129 pilgrims [before and after their pilgrimage]; in 2014, 92 pilgrims before and 90 pilgrims after their pilgrimage) and were then screened for the presence of the mcr-1 gene by real-time PCR and results confirmed by standard PCR and sequencing as described previously (7). All PCR-positive samples were then tested in an attempt to isolate mcr-1-resistant strains by culture on Cepacia agar (bioMérieux, Marcy-l’Étoile, France). Different colonies were tested by matrixassisted laser desorption ionization–time of flight (MALDI-TOF), antibiotic susceptibility testing (EUCAST), Etest (MIC susceptibility, 2 mg/liter), PCR, sequencing of the mcr-1 and extendedspectrum-beta-lactamase (ESBL) genes (blaCTX-M, blaTEM, and blaSHV) (5), and multilocus sequence typing (MLST) analysis (http://mlst.warwick.ac.uk/mlst/dbs/Ecoli/ and http://bigsdb.web .pasteur.fr/klebsiella/klebsiella.html). All mcr-1 and ESBL gene sequencing results were then analyzed with NCBI database. The prevalences of mcr-1-positive isolates determined by PCR in rectal swabs of pilgrims were similar in 2013 and 2014, and the prevalence was significantly higher upon return (in 2013, 1.55% [2/129] before the pilgrimage versus 8.53% [11/129] after the pilgrimage [P 0.0104]; in 2014, 1.02% [1/92] before the pilgrimage versus 9.18% [9/90] after the pilgrimage [P 0.0091]). Ten E. coli isolates and 1 K. pneumoniae isolate from 23 pilgrims who were mcr-1 positive by PCR were successfully identified by culture (Table 1). The sequence of the detected mcr-1 gene showed 100% identity with the published sequence (1). Our colistin-resistant isolates were not resistant to all antibiotics (Table 1). MICs of colistin ranged from 3 to 4 mg/liter. Two unrelated pilgrims (no. 95 and 96) carried the common sequence type of E. coli, ST10, likely suggesting that the isolates from those two pilgrims represented the same clone. Also, two other unrelated pilgrims (no. 6 and 117) carried the same sequence type of E. coli, ST648. Conversely, two Moroccan pilgrims (no. 134 and 143) who formed a