Growth of Streptococcus pyogenes in milk stored at atmospheric temperatures

Experiments on infection of cows with typhoid bacilli

1. A cow given by the mouth very large doses of virulent typhoid bacilli (275 and 125 thousand millions) on two occasions at an interval of 29 days failed to show signs of infection or to pass the bacilli in faeces or milk.

2. Of two-month-old calves, dosed with about 100 ml. ascites broth culture of typhoid mixed with milk, one became infected and typhoid bacilli were grown from the intestine and ileocaecal gland. Both, however, passed typhoid bacilli in the faeces on the first or second day after dosing.

3. When large numbers of typhoid bacilli (say, 1–3 thousand millions) were instilled into the udder through the teat canal, excretion of the bacilli in the milk usually ceased within 10 days (fourteen quarters of four cows). In two quarters of one of these cows excretion continued for 25 and 27 days, and in two quarters of another cow for at least 85 days. The procedure usually caused an acute mastitis lasting for a few days, and the ‘H’ and ‘O’ agglutinin titre of the blood rose.

4. When large numbers of typhoid bacilli were applied to the teat orifice, even when this had been grossly injured beforehand by slitting the sphincter, there was as a rule only a very transient infection. In eleven cases out of twelve, either the organism could not be found in the milk or was found for 1 day only; in the remaining case there was intermittent excretion for 7 days.

5. The strain of typhoid used for most of the above experiments was of high Vi content and was isolated from the carrier involved in the Bournemouth-Poole epidemic of 1936.

6. These experiments do not support the view that milk-borne typhoid outbreaks are brought about by an active infection of the cow and suggest that the main object of the epidemiologist must still be the location of the human carrier.

7. The chances of typhoid bacilli growing in the milk after its withdrawal from the cow are stressed.

This work was rendered possible by financial assistance from the Ministry of Health and from United Dairies Limited. Thanks are due to Dr A. Felix for providing a Vi-rich culture of typhoid, and to Dr V. D. Allison for valuable help in checking the draft paper and making suggestions.

499. The inhibition of micro-organisms by raw milk: I. The occurrence of inhibitory and stimulatory phenomena. Methods of estimation

1. A diffusion cup technique using Micrococcus lysodeikticus has been found suitable for lysozyme estimation. By this method raw milk gave only small zones of inhibition. The inhibitory substance of milk was shown not to be lysozyme.

2. Dose-response curves (dilution v. pH) were obtained with Streptococcus pyogenes as the test organism. They indicated that the effect of milk on this organism was the result of the interaction of one stimulatory and at least two inhibitory substances.

3. The existence of two inhibitory substances was confirmed by dilution assays, one, L1, occurring mainly in colostrum, the other, L2, occurring mainly in milk. The inhibition is greatest when L1 and L2 act simultaneously.

4. The pH and heat stabilities of the two substances are slightly different. L1 is most stable at pH 6−6·5, 90% being destroyed at 68° C. L2 is most stable at pH 7 and 95% is destroyed at 74°C.

559. The inhibition of micro-organisms by raw milk: III. Distribution and properties of two inhibitory substances, lactenin 1 and lactenin 2

1. The L1 and L2 contents of a number of samples of bulk milk and milk from separate quarters of cows with and without infection have been determined. The milk of cows sensitive to mastitis has about the same content as the milk from resistant ones.

2. The effect of heat on L1 and L2 has been observed for various combinations of time and temperature. Heat treatment corresponding to the legal standards of pasteurization destroyed 50% L1, but did not affect L2.

3. The inhibitory action of L1 and L2 has been observed on several micro-organisms. All the organisms tested were sensitive to lactenin in sterilized milk. Stimulatory substances have been shown to interfere with the inhibition by lactenin.

4. The action of lactenin on the growth of Str. pyogenes has been studied. The effect of hydrogen peroxide on lactenin has been compared with that of cysteine.

Growth of Salmonella typhi and certain other members of the Salmonella group in milk and butter stored at atmospheric temperatures

1. A technique for studying the behaviour of Salmonella in milk is described.

2. S. typhi, paratyphi B, dublin, cholerae-suis, typhi-murium, enteritidis and bovis-morbificans all multiplied readily even in absolutely fresh raw milk stored at 15°C., and in commercial grades of raw and of heat-treated milk rapid multiplication also occurred.

3. Strains of S. typhi recently isolated from man showed more rapid multiplication in milk than did stock laboratory cultures.

4. These Salmonella all survived at least 2 months when incorporated in various grades of salted and unsalted butter.

Excretion of Streptococcus pyogenes in the milk of naturally infected cows

An account is given of two cows which were concerned in milk-borne Streptococcus outbreaks at Mørkøv (Denmark) and Doncaster (England) respectively, and. which were afterwards kept under close observation. The Danish cow excreted Str. pyogenes from the affected quarter for at least 13 months, including a dry period of about 3 months; the other animal excreted similar streptococci for about 6 weeks. In both cases there were stages when symptoms of mastitis were either not evident or not pronounced, although the milk was known to be infective.