TABLE 4.

Phenotype and molecular analysis of the mechanism(s) responsible for LZD resistance in LRSA isolatesa

Isolate, yr of collection (patient no.)ASTcLZD MIC (μg/ml)Result of molecular analysis of genes conferring LZD resistance
Domain V 23S rRNA copiescfrPeptidyltransferase center
rrn1rrn2rrn3rrn4rrn5rrn6L3 (rplC gene)L4 (rplD gene)L22 (rplV gene)
M36, 2004 (patient 2)AZI (R), CLIN (R), VAN (S), TET (S), TMP-SXT (R), RIF (NT)>256G2576TG2576Te+G2576TGly139Arg++
I32, 2004 (patient 3)AZI (R), CLIN (I), VAN (S), TET (S), TMP-SXT (S), RIF (S)>256G2576TG2576TG2576TG2576T++++
M41, 2005 (patient 5d)AZI (R), CLIN (R), VAN (S), TET (S), TMP-SXT (R), RIF (S)16++G2576T+++++
M94, 2005 (patient 6d)AZI (R), CLIN (I), VAN (S), TET (S), TMP-SXT (R), RIF (S)64G2576TG2576T++G2576T+++
M86, 2006 (patient 7)AZI (R), CLIN (R), VAN (S), TET (R), TMP-SXT (S), RIF (S)64G2576T+G2576TG2576T C2461T++++
M92, 2009bAZI (R), CLIN (R), VAN (S), TET (S), TMP-SXT (S), RIF (S)32+G2576TG2576TG2576TG2576T+++
M32, 2009bAZI (R), CLIN (R), VAN (S), TET (S), TMP-SXT (S), RIF (S)8+++++Gly152Asp++
M71, 2009bAZI (R), CLIN (R), VAN (S), TET (S), TMP-SXT (S), RIF (S)32+G2576TG2576TG2576T++++
  • a R, resistant; S, susceptible; +, complete gene or protein without mutations; −, gene not amplified by PCR analysis; AZI, azithromycin; CLIN, clindamycin; VAN, vancomycin; TET, tetracycline; TMP-SXT, trimethoprim-sulfamethoxazole; RIF, rifampin.

  • b These isolates were recently collected from CF patients who were not included in the clinical statistical analysis covering the 7-year period (2000 to 2006).

  • c All isolates were resistant to methicillin (MRSA) and were mecA positive according to PCR/ESI-MS analysis. Results were interpreted according to CLSI guidelines (7).

  • d Patients 5 and 6 are siblings.

  • e —, the 23S rRNA gene was not amplified by PCR but was possibly present on the basis of the results of Southern blotting (Fig. 1).