Verificação da inflluência do Streptococcus Agalactiae sôbre a contagem bacteriana de leite em placas de gelose.
Resumo

O objetivo do presente trabalho foi verificar em que proporção a contagem bacteriana de leite de conjunto, bem como de leite individual, quando determinada pelo método de placa de gels e padrão, é atingida pela incidência do Sireptococcus agalactiae no rebanho. 54 amostras de leite de conjunto e 71 de leite individual, procedentes de rebanhos afetados com essa espécie de estreptococo, foram semeadas em gelose-padrão (ágar-extrato-peptona) e em meio de Edwards (cristal violeta-esculina-ágar sangue), para estudo de confronto. Com referência ao leite de conjunto, as contagens totais obtidas em gelos e padrão, variaram de 1.150 a 14.000.000 por ml., com a média aritmética de 1 . 442 . 657. Das 54 amostras examinadas, 49 deram contagens de Str. agalactiae beta-hemolíticas no meio de Edwards, que oscilaram entre 7 e 215 . 000 p01’ ml., com a média aritmética de 7 .228 para as 54 amostras; ao passo que em 5 destas, tais microorganismos estiveram ausentes nas placas que receberam 1 ml. da diluição

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Abstract

Thë purpose of the present investigation was to determine to what extent the total bacterial count of herd milk and individual miik, as determined by the agar plate method, is affected by the incidence of Str. agalactiae infection in the herd.
54 samples of herd milk and 71 sampies of individual milk, were platec in the standard nutrient agar (peptone — extract — agar) and in Edwards’ medium (crytal vioiet aesculin aes — culin — blod agar).
What concerns the herd milk, the total counts obtained with the standard nutrie•nt agar, ranged from 1.150 to 14. 000 . 000 per ml., with an arithmetic mean of 1.442.657. Forty nine of the 54 samples gave beta — hemolytic Str. agalactiae counts in Edwards’ medium, which ranged froni 7 to 215 . 000 per ml., with an arithmetic mean of 7.228, while in 5 of the samples none of these organisms were present in 0,1 mi. portion. The mean percentage contribuition of Str. agalactiae to the total count ali 54 samples, was only 0,50 percent.
These calculations were made correcting for the difference in the growth
— supporting abiiity of Edwards’ medium over tre standard agar (28,4%).
For the individual miik, the total counts ranged from 30 to 200 . 000 per ml., with an mean of 13.446. Thirty — one of the 71 sampies, gave beta — hemolytic Str. agalactiae counts in Edwards’ medium, wich ranged from 7 to 22.900 per ml., with an mean of 1.760, while i.n 40 of the samples fone of these organisms were present in 0,1 mi. portions. The mean percentage contribuition of Str, agalactiae to the total count for ali 71 samples, was 13,08 percent.
The results presente indicate that Str. agaiactiae may be responsibie for a large proportion of the standard plate count on 10w — count milk; but usually contributes for only a sinali percentage of the total number numbem of bacteria present in highcount milk.

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