Table 5.

Analysis of false susceptibility (very major error) and false resistance (major error) results at various drug concentrations (phase III)

DrugInhibitory concn (μg/ml)No. of isolates tested by BACTEC 460 and Middlebrook 7H10 methodsa that were:Errors (%)
In BACTEC 460 mediumOn Middlebrook 7H10 agarS by both testsR by both testsbS by BACTEC 460 and R by Middlebrook 7H10R by BACTEC 460 and S by Middlebrook 7H10VMc (false S)Md (false R)
Capreomycin1.2510.02101541321.16.2h
2.5221118242.10.9
5.0223712063.2None 
Cycloserinee75.030.01755141573.78.6
100187217f389.51.6
2001900190100None 
Ethionamide0.6255.014956037None24.8
1.25177497912.55.1h
2.51824115426.82.2
Kanamycin2.55.02063402None1.0
5.02083400NoneNoneh
Amikacin0.54.02093201None0.5
1.02103200NoneNoneh
Clofazimine0.1250.5202323540.017.3
0.25227231060.04.4
0.523405398.71.3
0.1251.02040038 NAg18.6
0.252300012NA5.2
0.5239003NA1.3h
Ofloxacin1.01.0211214616.02.8
2.0217205020.0None 
4.0217187028.0None 
1.02.02152007None3.3
2.02222000NoneNoneh
4.0222182010.0None 
1.04.02151809None4.2
2.02221802None0.9
4.022317115.60.5
Rifabutin0.51.01588301None0.6h
1.015882111.20.6
0.52.01588103None1.9
1.01598102None1.3
  • a S, susceptible; R, resistant.

  • b Reliability of the analyses was questionable due to the very low number of resistant isolates.

  • c VM, very major disagreement (susceptible by BACTEC 460 and resistant by the proportion method).

  • d M, major disagreement (resistant by BACTEC 460 and susceptible by the proportion method).

  • e Site 6 was excluded. For cycloserine no recommendation concerning the critical concentration is being made.

  • f Fourteen of 17 isolates that were resistant by the Middlebrook 7H10 method but susceptible by the BACTEC 460 method were from a single laboratory (site 3).

  • g NA, not applicable since none of the tested organisms were resistant at the conventional concentration.

  • h Critical concentration.