Pasteurization of Milk Artificially Infected with Two Strains of Brucella suis

Abstract

Undulant fever as a public health problem is unique in many ways. It has been recognized as such only recently. That the principal source of the disease is in domestic stock no well informed observer doubts. There is no uniformity of opinion concerning the relative importance of channels through which the infection may reach man from animals. No student of the subject denies that infected milk may result in spreading undulant fever among humans. A recent analysis of 155 cases of sickness that occurred during 1929 and 1930 in Illinois and which were clinically and serologically diagnosed as undulant fever cast a very strong suspicion on raw milk supplies as the agent of transmission in a significant percentage of the total incidence. Observers elsewhere have found evidence that infected milk may be an important means of transmitting the disease. Furthermore, undulant fever prevalence may be on the up curve, potentially at least. If nothing is done to control the disease a great endemic wave of this ailment among men in the not far distant future is a catastrophe which is well within the realm of the possible. On the other hand a relatively small amount of judicious energy spent now in research and control may offset that possibility. For these reasons it seems of the greatest importance to bring to light all possible knowledge about the cause of undulant fever and means of controlling the spread of it. The accompanying report is a contribution to an important phase of this knowledge. Some controversy about the efficacy of pasteurization in destroying the causative organisms of undulant fever has arisen. Doubts created by this controversy will survive until the matter is settled by indisputable scientific experimentation. This report might be accepted as closing the chapter on one phase of the necessary experimentation.-ANDY HALL, Director of Public Health, Chairman, State Undulant Fever Committee.] Results of investigations made in recent years show that (a) cattle may be spontaneously infected with Brucella strains of Assistant Bacteriologist, State Department of Agriculture.

Inactivation of VirulentBrucellaSpecies in Culture and Animal Samples

“…Our data did indicate minor differences in susceptibility to heat inactivation across Brucella species that may be consistent with other reports suggesting that porcine strains exhibit increased heat resistance. [12][13][14] However, as stated previously, these differences appear to have only minor effects on heat inactivation curves. It should also be emphasized that the current study did not use enrichment procedures after heat inactivation to try to recover viable Brucella in negative samples that might have had viable bacteria concentrations below our detection limit.…”

“…14 Differences among early reports could have been influenced by bacterial concentrations (10 7 -10 12 CFU/mL), the fluid medium (milk vs saline), isolation procedures (some inoculated inactivated cultures into guinea pigs), and incubation parameters, as some laboratories cultured Brucella under normal atmospheric conditions without the higher CO 2 concentrations as required by most B abortus strains. 1,12,13 However, the prolonged survival of Brucella after heat treatment was supported in a more recent report on preparation of heat-inactivated B abortus suspensions, where initial concentrations of 10 9 CFU/mL retained 95%, 55%, and 25% bacterial survival after heat treatment at 65°C, 75°C, or 80°C, respectively, for 120 minutes. 15 This report concluded that field strains of B abortus are more thermoduric than previously recognized, and it led to a subsequent study with milk from an infected dairy, which concluded that pasteurization procedures (63°C for 30 minutes or 72°C for 15 seconds) completely inactivated Brucella in milk.…”

“…Many studies reported complete inactivation within 5 to 10 minutes. 9,10,12,13 However, conclusions by authors in 1 report differed in that their data suggested that 40 minutes of heat treatment at 60°C was required to inactivate B suis in milk. 14 Differences among early reports could have been influenced by bacterial concentrations (10 7 -10 12 CFU/mL), the fluid medium (milk vs saline), isolation procedures (some inoculated inactivated cultures into guinea pigs), and incubation parameters, as some laboratories cultured Brucella under normal atmospheric conditions without the higher CO 2 concentrations as required by most B abortus strains.…”

“…Early work in the 1920s reported that initial concentrations of B abortus at 5 Â 10 9 CFU/mL were killed at 60 C in 15 minutes and similar populations of B suis in 20 minutes. [6][7][8][9][10][11] Data also indicated that heating at 55 C destroyed B abortus in 2 hours and temperatures of 61 C to 62 C killed all virulent B abortus strains in milk within 5 to 30 minutes. Many studies reported complete inactivation within 5 to 10 minutes.…”

Main Groups of Microorganisms of Relevance for Food Safety and Stability

“…Increasing in temperature reduces the time of thermal processing since at 61 C requires 2À6 min, whereas 67 C demands 6À17 s to reduce B. abortus counts in milk (Kronenwett, Lear, & Metzger, 1954). Similarly, B. suis could also be destroyed by pasteurization as reported for milk heated at 62 C for at least 7 min (Park, Graham, Prucha, & Brannon, 1932). The pH value can also influence the development of Brucella spp.…”