Table 1

Resistance against azithromycin of clinical and laboratory strains used in this study

StrainMutations in 23S rRNAbFraction of reads supporting the mutations (%)Start of systematic treatment with azithromycin (yr)Resistance against azithromycin (%)c
Clinical isolatesa
    CF30-1979dNone200136 (±39)
    CF333-2007dA2045G (A2058G)100200685 (±14)
    CF66-2008dC1433T, A2045G (C1446T, A2058G)21, 100200196 (±39)
    CF206-2002C2598T (C2611T)53200675 (±32)
    CF223-2002C2598T (C2611T)73200188 (±35)
    CF311-2002A93G, A2046G (A106G, A2059G)26, 70200485 (±23)
    CF180-2002C1433T (C1446T)25200114 (±27)
    CF240-2002None200635 (±32)
    CF173-2005None20060
Laboratory strains
    PAO1NoneN/AfN/A0
    PAO1-pMES-23SNoneN/AN/A1 (±1)
    PAO1-pMES-23S(A2045G)A2045GeN/AN/A96 (±22)
    PAO1-pMES-23S(C2598T)C2598TeN/AN/A92 (±14)
  • a Names of clinical isolates are given according to their patient origin and sampling year (i.e., isolate CF30-1979 was sampled from patient CF30 in 1979). All clinical isolates belong to the P. aeruginosa DK2 clone type.

  • b The corresponding E. coli 23S rRNA position is given in parentheses.

  • c Inhibition of cell growth by azithromycin was calculated as the number of CFU from cultures grown with azithromycin relative to cultures grown without azithromycin. The assay was replicated at least three times for each strain, and 95% confidence intervals are given in parentheses. No CFU appeared in cultures grown with azithromycin for strains PAO1 and CF173-2005.

  • d Whole-genome sequence of the isolate has been described previously (15).

  • e The strain carries a mutated 23S rRNA allele on the low-copy-number plasmid vector pME6031.

  • f N/A, not applicable.