CURRENT TEST METHODS AND FUTURE
DIRECTIONS
The antimicrobial susceptibility testing methods described in
this article provide reliable results when used according to the
procedures defined by the CLSI or by the manufacturers of the
commercial products. However, there is considerable oppor-
tunity for improvement in the area of rapid and accurate rec-
ognition of bacterial resistance to antibiotics. There is a need
for development of new automated instruments that could pro-
vide faster results and also save money by virtue of lower re-
agent costs and reduced labor requirements. To accomplish this,
it will likely be necessary to explore different methodologic
approaches for detection of bacterial growth. The direct de-
tection of resistance genes by polymerase chain reaction or
similar techniques has limited utility, because only a few resis-
tance genes are firmly associated with phenotypic resistance
(eg, mecA, vanA, and vanB) [24]. There are hundreds of b-
lactamases, and numerous mutations, acquisitions, and ex-
pression mechanisms that result in fluoroquinolone, amino-
glycoside, and macrolide resistance [25]; too many to be easily
detected by current molecular techniques. Thus, it seems likely
that phenotypic measures of the level of susceptibility of bac-
terial isolates to antimicrobial agents will continue to be clin-
ically relevant for years to come.