Antibiotic residues in milk : the farmer's responsibility

Journal of the Department of Agriculture, Journal of the Department of Agriculture, Western Australia, Series 4 Western Australia, Series 4

Volume 2

Number 11 November, 1961 Article 13

1-1-1961

Antibiotic residues in milk : the farmer's responsibility Antibiotic residues in milk : the farmer's responsibility

N Ingleton

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Recommended Citation Recommended Citation

Ingleton, N (1961) "Antibiotic residues in milk : the farmer's responsibility," Journal of the Department of Agriculture, Western Australia, Series 4: Vol. 2: No. 11, Article 13.

Available at: https://library.dpird.wa.gov.au/journal_agriculture4/vol2/iss11/13

This article is brought to you for free and open access by the Agriculture at Digital Library. It has been accepted for inclusion in Journal of the Department of Agriculture, Western Australia, Series 4 by an authorized administrator of Digital Library. For more information, please contact library@dpird.wa.gov.au.

Antibiotic residues in milk : the farmer's responsibility Antibiotic residues in milk : the farmer's responsibility

Cover Page Footnote Cover Page Footnote

The help of Mr. J. Craig and Mr. G. Robinson for material supplied and to Mr. K. Needham for encouragement and helpful suggestions is gratefully acknowledged.

This article is available in Journal of the Department of Agriculture, Western Australia, Series 4:

https://library.dpird.wa.gov.au/journal_agriculture4/vol2/iss11/13

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COLOUR TEST FOR ANTIBIOTICS IN MILK

Readily detectable colour variations result from acid production by Streptococcus thermophilus when this organism Is added to milk containing the dye brom cresol purple. Where antibiotics are present little growth occurs, acid production is limited accordingly, and the colour remains blue. The change in colour gives a

measure of the amount of antibiotic present.

Journal of Agriculture, Vol 2 No 11, 1961

ANTIBIOTIC RESIDUES IN MILK

—The Farmers Responsibility

By N. INGLETON, M.D.D. (Hons.), Dairy Laboratory

T

HE LEVEL of antibiotic residues in commercial milk supplies has been steadily increasing over t h e past few years. These residues find their way into t h e bulk milk as a result of milk from cows under antibiotic t r e a t m e n t for mastitis or other infections being included in t h e bulk milk for sale.

As t h e use of antibiotics for t r e a t m e n t of diseases—particularly mastitis—in dairy h e r d s h a s increased, so t h e level of residues in commercial milk h a s risen. I t h a s now become a t h r e a t to t h e welfare of t h e dairy industry.

The responsibility for inclusion of these undesirable residues falls squarely on t h e farmer. It is well known t h a t no milk from antibiotic-treated cows should be in- cluded for sale until t h r e e days after t h e last t r e a t m e n t .

Those affected by antibiotic residues in dairy products a r e : —

• T h e consumer, because antibiotic residues in milk a n d milk products can cause allergies a n d sensitisa- tion, or can affect people already sensitive to antibiotics as a result of previous medical t r e a t m e n t . Serious illness or d e a t h is possible in e i t h e r case.

• T h e m a n u f a c t u r e r , because resi- dues affect his m a n u f a c t u r i n g processes. T h e results are higher costs, lower quality products, and dwindling m a r k e t s .

• T h e farmer, because h e a n d his family fall into t h e first group, and because his economic interests are t h r e a t e n e d in t h e same way as those of t h e m a n u f a c t u r e r .

PUBLIC HEALTH

T h e presence of antibiotic residues in milk and its products continues to cause concern to public h e a l t h authorities t h r o u g h o u t t h e world.

Consumers have begun to t a k e an active interest, a s m a n y cases of allergy condi- tions a n d sensitisation t h r o u g h t h e con- sumption of contaminated milk or its products have been recorded.

It h a s been estimated (1) t h a t in t h e United States of America, about five per cent, of all individuals are sensitive to some form of penicillin, and there is a mortality rate of 10 per cent, among the 3,000 to 4,000 cases of anaphylactoid shock

(allergy reaction) reported each year.

This h a s created a greater recognition of the importance of penicillin a n d other antibiotic residues in milk utilised for h u m a n consumption.

Another factor which is causing concern is the appearance of antibiotic-resistant staphylococcal organisms in milk and dairy products. This introduces a risk of food poisoning.

MANUFACTURED PRODUCTS Antibiotic residues in milk can easily reach t h e level where they kill or inhibit bacteria added to t h e milk for cheese manufacture. The immediate result is a n extension of t h e m a n u f a c t u r i n g time be- cause t h e bacteria take longer to develop and do their work. This in t u r n causes a rise in costs.

A lower quality product also results, because without the necessary production of acid by lactic acid bacteria the cheddar cheese characteristics do not develop.

Markets are no longer available for low quality products; in fact, newer m a r k e t s are d e m a n d i n g t h a t products be of high 897

quality and contain no antibiotic, weedi- cide or pesticide residues, oestrogenic sub- stances, organisms of the E. coli group, or staphylococcal organisms.

TRENDS IN MASTITIS

Antibiotic therapy has resulted in a shift from streptococci to staphylococci as the major cause of mastitis. Other organisms capable of causing mastitis are: S. penu- moniae, E. coli, Ps. pyocyanea, P. cereus and some fungal agents, but these are comparatively rare.

Streptococcus agalactiae still causes some mastitis, but this has been greatly reduced by antibiotic therapy. One American survey showed that the incidence of this form of mastitis dropped from 34 per cent, to 10.5 per cent, of the total of all forms during 1949-50. The incidence of pencillin-resistant Staphylococcus aureus in herd milk increased from 9.7 per cent, in 1954 to 37 per cent, in 1956.

A limited survey involving 1,300 cows in Western Australia indicated that 16.8 per cent, had mastitis of one form or another.

Of the 1,300 cows 1.4 per cent, had strepto- coccal mastitis and 15.4 per cent, had staphylococcal mastitis; 20.6 per cent, of all mastitis cases failed to respond to penicillin.

The emergence of antibiotic resistant staphylococci (3) gives rise to increasing numbers of this type of organism being shed in the milk. This predisposes to food poisoning outbreaks if the milk is im- properly handled.

It is believed (2) that recent American cases of food poisoning involving dried milk and Cheddar cheese could have re- sulted from such contamination. Similar forms of Staphylococcus aureus were isolated from the cheese, and from the milk from two out of eight herds which supplied the factory where the toxic cheese was made.

TREATMENT OF MASTITIS

In Western Australia, antibiotics for animal treatment appear to be readily available to the farmer from most phar- macists, and sometimes from other retail outlets. The dosage rate of many products for intra-mammary infusion is 100,000 units of penicillin, but recent dosages of up to 500,000 units have been noted.

For other infections, such as foot rot, intra-muscular injection rates of 4,500,000 units of penicillin are common.

Antibiotic residues are found in the milk from cows treated either by intra-mam- mary infusion or intra-muscular injection, and in both cases the levels take some time to fall to zero, as shown by the graphs in Figs. 1 and 2.

33-

S at

£ 20 z u

0

3

0 12 24 36 48 60 72 HOURS AFTER INJECTION

Fig. 1.—Penclllln levels In milk following intra-mam- mary Infusion. Dose: 100,000 units aqueous solution

0 3 . '

S

Q£

£ 0 2- z

l

z 05.

02. / ^ ^ > . 0 16 24 4 0 48 60 72

HOURS AFTER INJECTION

Pig. 2.—Penicillin levels in milk following intra-mus- cular injection. Dose: 4,300,000 units aqueous solution

When penicillin is injected (one dose of 4,500,000 units) it takes 48 hours before the level of antibiotic in the milk falls to zero. Where dosage is by intra-mammary infusion (one dose of 100,000 units) this takes between 48 and 72 hours.

898 Journal of Agriculture, Vol 2 No 11, 1961

All milk from a cow t r e a t e d by i n t r a - m a m m a r y infusion m u s t be withheld for 72 hours. This applies also when only one quarter is treated, as t h e other quarters receive t h e antibiotic t h r o u g h t h e blood stream.

The g r a p h s in Figs. 1 a n d 2 relate to penicillin in aqueous solutions. When oil base suspensions are used, t h e antibiotic levels in milk may be detectable for longer periods.

METHODS OF DETECTION Detection of milk containing antibiotics by a test which would yield almost immediate results would be extremely desirable wherever milk is received. Such a test would probably be chemical r a t h e r t h a n biological, but a s yet t h i s type of test has not been devised.

However, we do have two tests which when used either singly or together, detect low levels of antibiotics in milk, although t h e results are only available some time after t h e milk h a s been received a n d processed.

These two methods a r e : — 1.—Colour Test

To 10 ml. of a sample which h a s been heated for five minutes, is added a fast growing acid producing sensitive culture of Streptococcus thermophilus, a n d brom cresol purple dye. The test tubes are in- cubated for 2i hours, together with a series of known concentrations and blanks, t h e colour change being matched with the known concentrations. This is a quick and satisfactory test. It was first suggested by Berridge (4) and h a s since been modi- fied by Keogh (6). With this test, levels down to 0.01 units of penicillin or its equivalent are readily detectable, as shown by the colour plate.

2.—Disc Assay Test

A culture of the sensitive organism S. lutea is plated in dishes with agar based media. Small filter paper discs of a diameter less t h a n 0.5 in. are saturated in the unknown milks and pressed lightly onto t h e surface of the media. The a n t i - biotic, if present, diffuses from t h e disc

A group of assay discs used to test for antibiotics In milk. The levels vary from 2.0 to 0.005 International units per ml. Discs soaked In the milk under test are placed on a culture of S. lutea growing on agar. Zones of Inhibition of the test organism are readily measured, and levels down to 0.005 i.u. per ml. can be detected

899

a n d a zone of inhibition is created which prevents t h e culture from growing. This m e t h o d detects levels of 0.005 units or lower of penicillin per ml. but it requires a n overnight incubation period. T h e m e t h o d is described by Naylor (5).

Both methods are made specific for peni- cillin by adding t h e enzyme penicillinase t o t h e second sample of t h e unknown.

Penicillinase destroys any penicillin p r e - sent in t h i s sample, so a positive reaction from t h e first sample a n d a negative r e - action from t h e second sample indicates t h e presence of penicillin in t h e milk under test.

These m e t h o d s have been in use a t t h e D e p a r t m e n t of Agriculture's Dairy Laboratory for some time, a n d have been found to be very satisfactory.

DYE PREPARATIONS

T h e inclusion of a dye preparation with t h e antibiotic for i n t r a - m a m m a r y infusion h a s h a d a good deal of success experi- mentally. With further improvement, this could be a m e a n s of detecting t h e presence of antibiotics, as both are secreted at t h e same r a t e .

LEVELS OF ANTIBIOTICS IN WEST AUSTRALIAN MILKS

Over 700 samples t a k e n at receiving platforms in Western Australia since J u n e of t h i s year h a v e revealed t h a t 10 per cent, are positive reactors. Of these, 40 per cent, are above t h e a r b i t r a r y level of 0.05 u n i t s per ml. which is considered t h e d a n g e r level for cheese milk.

From this, it is a p p a r e n t t h a t very little a t t e m p t is being m a d e to withhold milk from t r e a t e d cows.

IMPOSITION OF CONTROLS T h e question of imposing controls for t h e c o n t a m i n a t i o n of milk with antibiotics h a s been considered, a n d t h e introduction of regulations is a very real possibility so long as t h e problem continues.

F a r m e r education campaigns in t h e United S t a t e s largely failed to arrest t h e t r e n d , a n d F e d e r a l H e a l t h legislation was introduced to cover t h e situation for t h e n a t i o n . Milk found to contain residues of

antibiotic is now destroyed a n d t h e respon- sible person identified a n d penalised. I n one celebrated instance, t h e farmer h a d his licence revoked a n d finally his h e r d was sold after continued breaches.

This stage h a s not been reached in Western Australia or Australia, a n d those in t h e industry have t e n d e d to iron out their own problems. I n recent times, South Australia h a s limited i n t r a - m a m m a r y injection to 100,000 units, u n d e r its Veterinary Medicines Act, and this h a s proved helpful.

The question is being continually dis- cussed a t h i g h levels in t h e industry a n d there appears to be a commendable reluctance to t a k e recourse in legislation.

I t is possible t h a t this step m a y not have to be t a k e n .

The m a t t e r rests entirely in the h a n d s of the farmer. I t is u p to t h e farmer to prevent antibiotic loading of his product.

ACKNOWLEDGMENTS

The help of Mr. J. Craig and Mr. G.

Robinson for m a t e r i a l supplied and to Mr.

K. Needham for e n c o u r a g e m e n t and h e l p - ful suggestions is gratefully acknowledged.

REFERENCES

1. Weinstein, H. I.—The Present S t a t u s and Problems Involved in H u m a n Sensitisation to Antibiotics. Antibiotics Annual 979, 1959-60.

2. McCoy, Elizabeth.—A Shift in t h e Cause of Mastitis Poses a Difficult Problem. Am. Milk Review. 23 : 5, 1960.

3. Tee, G. H.—The Incidence of Penicillin Resistant s t r a i n s of S t a p h . Aureus in Dairy Herd Samples. Monthly Bui., Am. Med. Research Council. 16 : 141, 1957.

4. Berridge, V. J.—The Rapid Routine Assay of low c o n c e n t r a t i o n s of P e n i - cillin in Milk. J. Dairy Res. 23 : 336, 1956.

5. Naylor, J.—The Incidence of Penicillin in Australian Milk Supplies. Aust. J.

Dairy Tech. 15 : 153, 1960.

6. Keogh, Barbara.—A Simple Test for t h e Detection of Penicillin. Aust. J.

Dairy Tech. 16 : 19, 1961.

900 Journal of Agriculture, Vol 2 No 11, 1961

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