2.8. Scanning electron microscopy for studying egg shell translucency
For studying the ultrastructure of translucent egg shells, eggs were
candled and areas of severe translucency on egg shells were selected
and marked with a pencil. The egg shell pieces of approximately 1 cm2
were cut from two non translucent and four severely translucent eggs.
After soaking the eggs shells in water, the egg shell membranes were
manually removed. The outer membrane was removed from the dry
shell by plasma etching, using Bio Rad RF plasma Barrel Etcher PT
7150, as described by Brackpool (1995). The etchant gas was mixture
of Tetrafluoromethane and oxygen adjusted to a total pressure of
0.3 mbar. Etching was conducted at 100 W for up to 15 min.
The mammillary region of the egg shell was examined for ultra
structural characteristics as described by Brackpool (1995). Egg shell
pieces from non translucent areas were also cut and processed for
comparative observations. The samples were mounted on aluminium
stub and gold-coated (Polaron E5100). The samples were observed
under a scanning electron microscope (Neoscope, Coherent scientific,
Australia).
Observation regarding changes in mammilary cap arrangements,
size, early fusion, late fusion depression, erosions, types A and B
bodies were made and recorded (Solomon, 1991).
3. Results
Out of 500 eggs tested in the present experiment, 35 E. coli spp.
were isolated from the egg shell surface. Ten E. coli strains were also
isolated from the shell crush. Salmonella spp. was not detected either
in internal egg contents or egg shell surface. Salmonella spp. was not
detected in egg shell crush.
Bacteria were not isolated from any of the egg internal contents.
All 45 strains of E. coli were tested for heat stable enterotoxin A and B
(STa & STb) and colicin V plasmid (cvaC) gene. Out of 35 E. coli strains
obtained from the egg shell surface, four strains were positive for heat
stable enterotoxin A (STa) gene. The ten E. coli isolates isolated from
egg shell crush were negative for enterotoxin A (STa) gene. Heat
stable enterotoxin B (STb) or Colicin V (cvaC) gene could not be
detected in any of the E. coli strains.