| dc.description.abstract | The presence of antibiotic residues in foods represents
a potential health hazard to man which at the present time
is difficult to assess. Nevertheless, some problems have
already been defined and legislature has been enacted to
prevent or reduce the occurrence of antibiotic substances
in food intended for human consumption. In addition,
antibiotics in milk intended for the production of cheese
or for the production of milk products requiring the use of
bacterial (or yeast) cultures may result in the killing
of these cultures with subsequent substantial losses to the
dairy industry.
Only limited information on the incidence of antibiotic
residues in milk in Kenya is available. A survr.; was
therefore carried out on pooled milk samples obtained from
various sources associated with the Kenya Cooperative
Creameries. The agar diffusion method using Micrococcus
luteus as the test organism was used for screening milk
samples for inhibitory action on growth. Whenever inhibition
of growth was observed, the milk sample was heated at
820C for 5 minutes to inactivate heat-labile inhibitory
substances of a non-antibiotic nature occasionally found in
milk. Furthermore, attempts were made to identify the
antibiotic present by using penicillinase.
A total of 1,725 samples of raw milk were examined for
the presence of heat-stable inhibitory substances to M. luteus.
89 samples (5.1%) were inhibitory, and 29 of these were shown
to contain penicillin, i.e. 1.7% of the total number of
samples, or 33% of all inhibitory samples. The inhibitory
substances in 67% of positive tests could not be identified.
Quantitation of the penicillin concentration revealed a
range from 0.02 to 0.03 iu per rnl., milk.
Minimum inhibitory concentrations of penicillin and
oxytetracycline on streptococcus lactis and Lactobacillus
bulgaricus were deteDTIined.
The results were as follows:
strept.lactis 0.26 unit/ml (Penicillin)
0.60 ~g/ml (Oxytetracyline)
0.39 unit/ml (Penicillin)
0.70 ~g/ml (Oxytetracycline)
The above results ~how that low concentrations of anti-
Lact. bulgaricus
biotics in milk can inhibit dairy "starter" cultures and cause
economic losses to cheese and fermented milk industries.
Taking into account that milk from treated cows when added
to the central milk supply is diluted, the amounts of antibiotic
residues detected in the milk samples of the present investigation,
however, were not likely to result in inhibition of
starter cultures since they were far below the values demonstrated
to have such effects.
Excretion of penicillin in milk of treated cows was also
measured. Two routes of administration were used: the
intramuscular and intramammary .. A total of 12 milking cows
were used (i.e. 6 cows per group) and the withholding
periods for penicillin turned out as follows:
Route of administration Withholding period
1. Intramuscular 2 days
2. Intrami3rrmary 4 days (infused quarters)
1 day (non-infused quarters)
The results of this study emphasize the importance of
preventing antibiotics from entering milk supplies by strictly
adhering to the appropriate withholding periods specified for
the antibiotics used. | en |
