TABLE 2.

Phenotypic variations of the epidemic clone

StrainDate of recoveryMIC (μg/ml) ofaβ-Lactamase activitybExpression of production ofGeneration timef (min)
AMKGENTOBTICPIPFEPCAZATMIMPCIPmexAcoprMcOprMdmexXcmexYcMexYd46-kDa proteine
PAO1421163222410.5161.001.00±1.001.00+27
Epidemic clone
    97-2May 19972>5123264128881643210,4001.851.45++3.701.95++34
    97-3Aug. 1997425616641284482323,6001.853.40+++3.704.00++42.5
    97-4Dec. 1997212816>5121286416328327,4003.454.60+++4.255.95+++37
    98-1Feb. 19984256161281281683216323,0002.604.35+++2.503.95+35
    98-2June 19984256161281281683216323,0003.353.30+++3.254.40+42
    98-3July 199841281612812816163216321,9002.853.00+++2.854.40+40
    98-4Nov. 199841281664128168322322,0003.354.40+++1.302.70++36
    99-1Mar. 199941283264128168322324,4001.952.30+++1.952.75++37
    99-2May 19994256166412884164325,6001.653.50++1.651.60++39.5
    99-3July 19994256166412844162326,1001.701.85+++4.101.95++45
    99-4Oct. 19994256166412844164325,5002.909.65+++3.353.60+++36
    00-1Jan. 20004128166412888162321,8001.602.15+3.102.75++32
    00-2Apr. 2000425632<8641142165300.500.60++3.453.65++34
    00-3Aug. 200045123216322124161800.750.95±3.804.05++32.5
    00-4Nov. 20004512323225684164164,1000.500.70+0.851.00+++35
    01-1Feb. 200082561616128448481,5000.801.15+2.902.80+++25
    01-2June 200145123264128168328326,2002.153.10+4.702.45+±28
    01-3Aug. 2001225616641281681616324,0003.107.75+++3.705.00+39
Mode4256166412816816432
  • a AMK, amikacin; GEN, gentamicin; TOB, tobramycin; TIC, ticarcillin; PIP, piperacillin; FEP, cefepime; CAZ, ceftazidime; ATM, aztreonam; IMP, imipenem; CIP, ciprofloxacin.

  • b Cephalosporinase activities are expressed in nanomoles of nitrocefin hydrolyzed per minute per milligram of protein. Values are means of two determinations.

  • c mRNA quantification by reverse transcriptase PCR (see Materials and Methods). Values are means of two determinations. Numerical values are expressed relative to PAO1, which is set at 1.00.

  • d As determined by Western blot analysis with an OprM or MexY antiserum. Semiquantitative values are expressed as a range fro − (negative) or ± (weakly positive) to +++ (strongly positive).

  • e putative OprD, as determined by SDS-PAGE of outer membrane preparations stained with Coomassie blue.

  • f Values are means of four determinations calculated at the logarithmic phase by regression analysis from different cultures (see Materials and Methods).