Abstract:
Two hundred and twenty five gram negative bacilli were isolated from urinary specimens
sent to mic biology laboratory, General Hospital Kandy within a 3 month period. All these
isolates were test against antibiotics-ceftriaxone, ciprofloxacin and netilmicin by three
susceptibility testing meth stocks' method, break - point method and minimum inhibitory
concentration. Escherichia coli NC 10418 was taken as the control strain for all the three
methods. A correct result of sensitive or resist was assigned to each strain/antibiotic
combination according to the following recommended MIC val for urinary isolatesceftriaxone 2 . .Iml, ciprofloxacin 4 . .Im\. There was a statistically significant differed
between stokes' method and M1C for ciprofloxacin and netilmicin (ciprofloxacin x2 4.076
and P val 0.05,netilmicin x2 10.64 and P value 0.001). Discrepancies of sensitivity results at
species va' among different species for different antibiotics. The data illustrate that the
susceptibility testing by stokes' method showed one error for every 4 strains tested.MIC
was done by two methods (a novel methods) to check the practicability of the novel method
for MIC determination on differ antibiotics for different organisms. The novel method was a
broth method carried out on Microtel trays. The broth consisted of 1 per cent glucose, 1 per
cent peptone water, 0.5 per cent sodium chlo' and 1 per cent andrades indicator. With
growth, fermentation of the sugar resulted in colour change frcolourless to pink.
Comparison of the two methods were studied on 225 urinary isolates for the antibiotics used
for the study. Only netilmicin showed acceptable difference of more than I dilute which was
statistically significant (x2 20.906, p O.OO 1)
