| dc.description.abstract | Tetracyclines are some of the most widely used antibiotics in the
world for human and veterinary purposes. They are effective
against both gram positive and gram negative bacteria as well as
mycoplasmas, some viruses, rickettsiae, spirochaetes Chlamydia
and actinomycetes. In chicken, tetracyclines are effective against
chronic respiratory disease, infectious synovitis, infectious coryza
and fowl typhoid. They are available either as powders, injections,
capsules, boluses or infusions.
There has been an alleged misuse of the poultry soluble
antibiotics especially tetracyclines, by farmers and other users in
Kenya. The main objective of carrying out this study was to
determine whether oxytetracycline residues were present in
commercial eggs and then compare these levels with the
WHO/FAa accepted maximum limit of 0.2 ppm for oxytetracycline
residues.The other aim was to determine the concentration of
oxytetracycline residues deposited in eggs and chicken meat
following administration of 0, 400, 600, and 800 ppm of
oxytetracycline via drinking water for 7 days and thereafter
determine safe withdrawal periods in eggs and meat of chicken.
Eggs were obtained from Nairobi area (the city and its suburbs),
Mombasa and Nakuru. These areas gave a representative sample
since they are regions of intensive poultry farming. A total of 712
eggs were analysed, of which 355 were from Nairobi, 298 from
Mombasa and 59 from Nakuru areas respectively. A microbiological
method of analysis with a limit of detection of 0.1 ppm was
employed, using B. cereus var. mycoides, ATCC 11778 as the test
organism. Two assays of the yolk were run, one portion freeze-dried
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while the other one was not freeze-dried. The same procedure was
applied to the albumen. The analysis involved dispensing 200 J.lI of
each sample into wells of diameter 10 mrn, dug out on Mueller
Hinton agar and after an incubation of 18 hours at 30oC, the
diameters of the zones of inhibition were measured and compared
with standards, which were run alongside the samples. The
concentration of oxytetracycline in the samples was then
extrapolated from the standard curve.
In Nairobi, six eggs had detectable residue levels which were all
above the WHO/FAO maximum limit of 0.2 ppm. The residues
were only detected in the freeze-dried samples and the mean
concentration of the yolk samples was 0.478 ppm. The
oxytetracycline residues were only detectable in the yolk apart from
one case where both the yolk and albumen had detectable levels of
oxytetracycline (0.324 ppm of oxytetracycline in the albumen).
None of the eggs from Nakuru had detectable levels of
oxytetracycline while from Mombasa, one egg was positive for
sulfur and none for oxytetracycline.
In the feeding study, the birds were divided into four groups: the
first group (control) received antibiotic-free water, the second group
received water containing 400 ppm oxytetracycline, the third group
received water containing 600 ppm and the fourth group were
offered water containing 800 ppm. Eggs were collected during the
7-day feeding trial administration period and for another 6 days
post drug administration. Ten days after the feeding trials were
completed, the birds were sacrificed and the breast muscle
removed. The meat samples were homogenised with O.OIN
hydrochloric acid as the oxytetracycline extractant and after
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filtration. the filtrate was handled in the same way as the egg
samples. A microbiological method of analysis was used for both
the eggs and meat samples. Zones of inhibition were obtained and
their diameters were proportional to the concentration of
oxytetracycline present. For yolk. 6 out of 38 eggs were positive for
group 2. 11 out of 27 for group 3 and 29 out of 43 eggs for group 4.
The corresponding values for albumen were zero. one and
seventeen for groups 2. 3 and 4 respectively. No residues were
detected in the yolk and albumen 6 and 3 days respectively. after
medication was stopped whereas no residues were detectable in the
breast muscle samples ten days after the termination of drug
administration. There was a significant difference (p<0.05) among
the groups and also between groups 3 (600 ppm of oxytetracycline)
and 4 (800 ppm of oxytetracycline) and groups 2 (400 ppm of
oxytetracycline) and 4 for both yolk and albumen. However.
whereas there was a significant difference (p<0.05) between groups
2 and 3 for yolk! .there was no significant difference (p>0.05)
between groups 2 and 3 for albumen.
This study shows that commercial eggs obtained from the areas
of study are generally safe for human consumption. despite the
possible widespread use of antibiotic feed additives. Less than 1%
of the eggs analysed had detectable levels of oxytetracyclines even
though all were above the acceptable level of 0.2 ppm. It has also
confirmed that oxytetracycline residues in eggs reach a peak faster
in the albumen than in the yolk. The residues. however. persist
longer in the yolk than in the albumen. Higher levels of
oxytetracycline were observed in eggs from birds which received
higher dosages.
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The study confirms that oxytetracycline is eliminated to safe
levels in chicken meat within ten days even when higher dosages.
up to 800 pprn, are administered.
This study has also shown that Bacillus cereus var. my coides
ATCC 11778 is more sensitive to oxytetracycline than to sulfur | en |
