Antibiotic sensitivity test: In vitro antibiotic sensitivity test was done according to the guidelines of Clinical and Laboratory Standard Institute (CLSI), 2007, formerly it was known as NCCLS using disc diffusion test. Briefly the bacerial isolates were inoculated into Nutrient Agar and Selection of 3 to 5 well isolated colonies from the agar plate were selected. The top of the colony was touched with a loop and the growth was transferred into a tube containing 4 to 5 ml of saline solution. The turbidity with 0.5 McFarland Standard was adjusted and inoculated into Mueller Hinton Agar. The antibiotic disc into Mueller Hinton Agar was placed and the zone of diameter was measured according to the CLSI (2007) standard.
Inoculum preparation: To standardize the density of the inoculum for a susceptibility test, a BaSO4 turbidity standard, equivalent to a 0.5 McFarland standard or its optical equivalent was used. At least 3-5 well isolated colonies of the same morphological type were selected from an agar plate culture. The top of the colony was touched with a loop and the growth was transferred into a tube containing 4-5 ml of a suitable broth medium such as tryptic soy broth. The broth culture was incubated at 35oC until it achieves or exceeds the turbidity of the 0.5 McFarland standards. The turbidity of the actively growing broth culture is adjusted with sterile saline or broth to obtain turbidity optically comparable to that of the 0.5 McFarland standards. This results in a suspension containing approximately 1-2 x108 CFU/ ml.
Inoculation of test plates Optimally, within 15 minutes after adjusting the turbidity of the inoculums suspension, a sterile cotton swab is dipped into the adjusted suspension. The swab was rotated several times and pressed firmly on the inside wall of the tube above the fluid level. The dried surface of a Mueller- Hinton agar plate is inoculated by streaking the swab over the entire sterile agar surface. The lid was ajarred for 3 to 5 minutes, but no more than 15 minutes, to allow for any excess surface moisture to be absorbed before applying the drug impregnated disks.
Application of discs to inoculated agar plates The predetermined battery of antimicrobial discs was dispensed onto the surface of the inoculated agar plate. Each disc was pressed down to ensure complete contact with the agar surface. Whether the discs were placed down individually or with a dispensing apparatus, they were distributed evenly so that they are no closer than 24 mm from centre to centre. The plates were inverted and placed in an incubator set to 35oC within 15 minutes after the disc was applied. After 16 to18 hours of incubation each plate was examined. If the plate was satisfactorily streaked, and the inoculum was correct, the resulting zones of inhibition were uniformly circular and there was a confluent lawn of growth. The diameters of the inhibition zones were measured to the nearest whole millimeter, using sliding calipers or a ruler, which was held on the back of the inverted petri plate. The results were recorded at 16-18 hours post incubation.
Overall sensitivity pattern of E. coli Among the antibiotics Amoxicillin and Tetracycline were 100% resistant and 0% sensitive and intermediate sensitive. Ciprofloxacin was 4.48% sensitive, 20.90% intermediate and 74% resistant. Cephradin was 0% sensitive, 20.90% intermediate and 79.10% resistant. Cephalexin was 20.90% sensitive, 55.22% intermediate and 23.88% resistant. Gentamycin was 89.55%, 4.48% intermediate to 7.46% resistant. Kanamycin was 86.57% sensitive, 5.97% intermediate and 7.46 % resistant. Streptomycin was 1.49% sensitive, 0% intermediate and 80.60% resistant.
Antibiotic sensitivity and resistance pattern of E. coli isolates based on the breeds of chicken All the isolates from layer and indigenous chicken were sensitive to Gentamycin. On the other hand 100% indigenous were sensitive to Kanamycin. 92.86% broiler and 64.70% sonali were sensitive to Gentamycin. 85.72% broiler, 80% layer and 82.35% indigenous were sensitive to Kanamycin. 21.43% broiler, 29.42% and 37.5% indigenous were sensitive to Cephalexin. 12.5% indigenous and 5.88% sonali were sensitive to Ciprofloxacin and Streptomycin. No isolates of broiler, layer, sonali and indigenous were sensitive to Amoxicillin, Cephradin and Tetracycline. No isolates of layer were sensitive to Ciprofloxacin, Cephalexin and streptomycin. No isolates were of sonali and indigenous were sensitive to streptomycin. No isolates of broiler were sensitive to Ciprofloxacin.