Table 1.

In vitro susceptibilities to various antimicrobial agents of E. coli DH5α carrying pPAM-101 or subclones containing some of the resistance determinants of In31a

AgentMIC (μg/ml) for strain:
DH5αDH5α(pPAM-101)DH5α(pBCAM-52R)bDH5α(pKAM-36BE)cDH5α(pKAM-11H)dDH5α(pBCAM-76SX)e
Imipenem<0.25f 24 —g
Ceftazidime<0.25f >100>100
Streptomycin4f 44
Kanamycin<0.5f 88
Gentamycin0.5f 0.50.5
Tobramycin<0.5f 88
Amikacin1f 24
Netilmicin<0.5f 44
Chloramphenicol4h 864
Cetylpyridinium chloride10h 25
Benzalkonium chloride15h 20
Ethidium bromide75h 200
Sulfonamide16f >1,000>1,000
  • a The susceptibility of DH5α alone or DH5α carrying the corresponding empty vectors is also shown for comparison.

  • b pBCAM-52R is a pBC-SK derivative that contains the 5.2-kb EcoRI fragment of pPAM-101 that spans the 5′-CS of In31 together with the bla IMP,aacA4, and catB6 cassettes (Fig. 2). A 1.6-kb region of pPAM-101 flanking the 5′-CS of In31 is also present in this fragment, but no additional resistance genes are contained within this region (27). In this clone the insert orientation is such that the polarity of the gene cassettes is opposite that of thelac promoter flanking the vector polylinker.

  • c pKAM-36BE is a pK19 derivative that contains a 3.6-kb BamHI-EcoRI fragment spanning most of the 5′-CS of In31 together with the bla IMP,aacA4, and catB6 cassettes (Fig. 2).

  • d pKAM-11H is a pK19 derivative that contains a 1.1-kb HindIII fragment that spans the entireqacG cassette (Fig. 2). The MICs of quaternary ammonium compounds and ethidium bromide were the same for strains with both orientations of the insert.

  • e pBCAM-76SX is a pBC-SK derivative that contains the 7.6-kb SmaI-XbaI fragment of pPAM-101 that spans the 3′-CS of In31 together with part of the cassette array and the incomplete tni module (Fig. 2).

  • f The MIC for DH5α(pBC-SK) was identical.

  • g —, not assayed.

  • h The MIC for DH5α(pK19) was identical.