Jpn. J. Infect. Dis., 56, 210-212, 2003
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Short Communication
Ofloxacin Minimum Inhibitory Concentration versus Disk Diffusion Zone Diameter for Salmonella enterica Serovar Typhi Isolates: Problems in the Detection of Ofloxacin Resistance
Shyamapada Mandal*, Manisha Deb Mandal and Nishith Kumar Pal
Department of Bacteriology and Serology, Calcutta School of Tropical Medicine, Kolkata 700 073, India
(Received August 25, 2003. Accepted October 22, 2003)
*Corresponding author: Mailing address: Department of Bacteriology and Serology, Calcutta School of Tropical Medicine, C. R. Avenue, Kolkata-700 073, India. E-mail: samtropmed@rediffmail.com
SUMMARY: Using the guidelines of the National Committee
for Clinical Laboratory Standards (NCCLS), a total of 421 blood
culture isolates of Salmonella enterica serovar Typhi obtained
during 1991 - 2001 were tested for susceptibility to ofloxacin
(OFX) by the disc diffusion method, and for the determination
of minimum inhibitory concentration (MIC) values of OFX by the
agar dilution method. Among 421 isolates, 248 were fully OFX-sensitive
showing MICs of 0.0125 - 0.075 mg/ml
and inhibitory zone diameters of 24 mm. The remaining 173 isolates
(MICs of 0.5 - 1.5 mg/ml) that were
treated with OFX did not respond to the therapy. However, 169
(97.69%) of the 173 isolates were determined to be susceptible
(zone diameter 16 mm) by the disc diffusion method, whereas only
3 were intermediately susceptible (zone diameter 13 - 15 mm) and
the final isolate showed OFX-resistance (zone diameter 12 mm).
Thus, following the NCCLS guidelines, OFX-resistance in S.
enterica serovar Typhi was not detected by the disc
diffusion test. The present data suggest a revision of the NCCLS
breakpoints in selecting OFX as the preferred treatment regimen
for S. enterica serovar Typhi.
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