Clostridium difficile isolates with high linezolid MICs harbor the multiresistance gene cfr.
We studied the molecular mechanisms of linezolid resistance in 9 isolates of toxigenic Clostridium difficile with high linezolid MICs. The activity of linezolid was determined against 891 clinical isolates of toxigenic C. difficile. The MIC50 and MIC90 of linezolid were 0.75 μg/ml and 1.5 μg/ml, respectively. Nine strains (1%) showed high linezolid MICs (6 μg/ml to 16 μg/ml) and also were resistant to clindamycin, erythromycin, and chloramphenicol. These strains were selected for molecular studies: sequencing of domain V of the 23 rRNA gene, detection of the cfr methyltransferase gene, and sequencing of the ribosomal protein genes rplC and rplD. Molecular relatedness between strains was assessed using PCR ribotyping and MLVA (multilocus variable-number tandem-repeat analysis) typing. The strains belonged to ribotypes 001 (2/9), 017 (6/9), and 078 (1/9). MLVA showed that strains of ribotype 001 and 017 belonged to the same clonal complex in each ribotype. We did not detect mutations in the 23S rRNA gene. The cfr gene was detected in 7 of 9 strains. Sequencing of cfr amplicons revealed a similarity of 100% to a fragment of transposon Tn6218 of C. difficile, which was annotated as a putative chloramphenicol/florfenicol resistance protein. We were unable to detect mechanisms of resistance to linezolid in the 2 strains belonging to ribotype 001. While the relevance of our results lies in the detection of the cfr gene as a possible mechanism of resistance to linezolid in C. difficile, our findings should be assessed by further investigations to characterize these possible cfr genes and their contribution to linezolid resistance.
Department of Clinical Microbiology and Infectious Diseases, Hospital General Universitario Gregorio Marañón, Madrid, Spain Department of Medicine, Universidad Complutense de Madrid, Madrid, Spain CIBER de Enfermedades Respiratorias (CIBERES), Palma de Mallorca, Spain Instituto de Investigación Sanitaria Gregorio Marañón, Madrid, Spain mercedes.marinar@salud.madrid.org.
Mercedes
M
Marín
Department of Clinical Microbiology and Infectious Diseases, Hospital General Universitario Gregorio Marañón, Madrid, Spain Instituto de Investigación Sanitaria Gregorio Marañón, Madrid, Spain.
Adoración
A
Martín
Department of Clinical Microbiology and Infectious Diseases, Hospital General Universitario Gregorio Marañón, Madrid, Spain CIBER de Enfermedades Respiratorias (CIBERES), Palma de Mallorca, Spain Instituto de Investigación Sanitaria Gregorio Marañón, Madrid, Spain.
Luis
L
Alcalá
Department of Clinical Microbiology and Infectious Diseases, Hospital General Universitario Gregorio Marañón, Madrid, Spain Department of Medicine, Universidad Complutense de Madrid, Madrid, Spain CIBER de Enfermedades Respiratorias (CIBERES), Palma de Mallorca, Spain Instituto de Investigación Sanitaria Gregorio Marañón, Madrid, Spain.
Emilia
E
Cercenado
Department of Clinical Microbiology and Infectious Diseases, Hospital General Universitario Gregorio Marañón, Madrid, Spain CIBER de Enfermedades Respiratorias (CIBERES), Palma de Mallorca, Spain Instituto de Investigación Sanitaria Gregorio Marañón, Madrid, Spain.
Cristina
C
Iglesias
Department of Clinical Microbiology and Infectious Diseases, Hospital General Universitario Gregorio Marañón, Madrid, Spain Instituto de Investigación Sanitaria Gregorio Marañón, Madrid, Spain.
Elena
E
Reigadas
Department of Clinical Microbiology and Infectious Diseases, Hospital General Universitario Gregorio Marañón, Madrid, Spain Department of Medicine, Universidad Complutense de Madrid, Madrid, Spain CIBER de Enfermedades Respiratorias (CIBERES), Palma de Mallorca, Spain Instituto de Investigación Sanitaria Gregorio Marañón, Madrid, Spain.
Emilio
E
Bouza
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics*; D002701:Chloramphenicol / Q000494:pharmacology; D002981:Clindamycin / Q000494:pharmacology; D016360:Clostridioides difficile / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D004251:DNA Transposable Elements; D024901:Drug Resistance, Multiple, Bacterial / Q000187:drug effects / Q000235:genetics*; D004917:Erythromycin / Q000494:pharmacology; D006801:Humans; D000069349:Linezolid / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D012338:RNA, Ribosomal, 23S; D021521:Ribotyping; D013030:Spain
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D012338:RNA, Ribosomal, 23S; D002981:Clindamycin; D004917:Erythromycin; D002701:Chloramphenicol; D000069349:Linezolid