After overnight incubation, growths on the MCA plates suggestive of E. coli colonies
2-4mm in diameter, opaque and convex with entire edge and rose pink on account of
lactose fermentation were further streaked onto eosin methylene blue (EMB) and
incubated overnight at 37°C again. Green metallic sheen colonies indicative of E. coli
were then subjected to biochemical tests, which included indole, methyl red and
Simmons citrate tests for E. coli identification as described by Edwards and
Ewing.(23)
Susceptibility testing: The isolated E. coli were screened for anti-microbial resistance
profile using the disc diffusion method (24) according to the methods recommended
by the National Committee for Clinical Laboratory Standards Guidelines.(25) This was
done by streaking the surface of nutrient agar plates uniformly with the organisms
and thereafter exposing them to discs (Poly-Tes LabR) impregnated with known
concentrations of anti-microbial substances.
Commercial antibiotics discs used in the study were 10 and included AM, ampicillin
(25ug); CO, cotrimoxazole (50ug); NI, nitrofurantoin (100ug); GN, gentamycin (10ug);
NA, nalidixic acid (30ug); TE, tetracycline (30ug); CH, chloramphenicol (10Ug); CF,
cefuroxime (20ug); NB, norfloxacin (10ug); CP, ciprofloxacin (5ug).
Interpretations and data treatment: Susceptibility data were recorded quantitatively
by measuring the diameters to the nearest whole millimeter using a meter rule.
Following the interpretative chat of the Kirby-Bauer Sensitivity Test Method (26), the
zones were interpreted as resistant or sensitive. For the purpose of the present
study, isolates with intermediate sensitivity were categorized as sensitive.
Furthermore, proportions of isolates resistant to individual drugs and having each
anti-microbial resistance patterns were computed as averages and percentages
across the different poultry types.
OJHAS Vol 4 Issue 3, 2005-3-3: Original Article. Antimicrobial resistance profile of E.coli isolates from tropical free range chickens. www.ojhas.org/issue15/2005-3-3.htm