Salmonella in Commercially Produced Dried Dog Food: Possible Relationship to a Human Infection Caused by Salmonella enteritidis Serotype Havana.

Identification of Salmonella enteritidis serotype Havana, isolated from a 2½-month old female, engendered efforts to trace the source of infection. The inquiry led to examination of commercially prepared dehydrated dog foods. Twenty-five samples, representing four different manufacturers plus two retail store brands, were examined. Each of 11 samples, produced by one manufacturer, contained one or more Salmonella serotypes. Eight of them contained S. enteritidis serotype Havana. Isolates of serotype Havana from the index case and her mother had antibiotic susceptibility patterns essentially identical to those of nine of 10 serotype Havana isolates recovered from one sample of dog food. The possibility that the human isolates were related to the dog food isolates could not be eliminated.

Practical application of diagnostic virus serology.

A number of virologists have suggested that current methods of virus serology are impractical and should be discontinued. An evaluation of the results in our laboratory showed positive confirmation in 1,571 of 6,599 suspected clinical cases or 23.6% including hundreds of cases which were still in the hospital or under the care of the physician. Further analysis of these 1,571 cases revealed that 75.9% had antibody titers in the acute specimen. These results suggest that optimal utilization is not being made of information currently available and that a practical service can be provided locally in most cases with existing techniques simply by more frequent sampling and testing of the patients' sera.

Interrelationship of heat and relative humidity in the destruction of Clostridium botulinum type E spores on whitefish chubs.

Heat destruction of types B and E Clostridium botulinum spores on whitefish chubs was observed to be dependent upon the relative humidity (RH) in the chamber in which fish were heated. Experimental conditions were designed to simulate those attainable in commercial fish-smoking plants. Low numbers of type E spores were destroyed with regularity, within 30 min, on fish which were held at an internal temperature of 77 C (170.6 F) in an atmosphere of at least 70% RH. However, an internal temperature of 82 C (179.6 F) and a minimum RH of 70% were required to destroy several hundred thousand type E spores. Quantitative estimates of spore destruction were arrived at with a modified most probable number procedure. Type E spore populations were reduced by 2 to 4 logarithms at 77 C (170.6 F), by 5 to 6 logarithms at 82 C (179.6 F), and by more than 6 logarithms at 88 C (190.4 F) when fish were heated in an atmosphere of 70% RH. A 5 to 6 logarithm reduction of spores was also observed when fish inoculated with type B spores were processed at 82 C (179.6 F) in an atmosphere of 70% RH.

Sensitivity of an enrichment culture procedure for detection of Clostridium botulinum type E in raw and smoked whitefish chubs.

The sensitivity of an enrichment culture procedure for detecting Clostridium botulinum type E in whitefish chubs (Leucichthys sp.) was assayed. Data demonstrated that fish inoculated with 10 or more viable C. botulinum spores regularly develop specifically neutralizable enrichment cultures. Mild heat treatment (60 C, 15 min) substantially reduced the sensitivity of enrichment culturing. This effect was particularly noticeable in the culturing of fish which harbored fewer than 10 spores each. Evidence is presented which indicates that sensitivity of enrichment, without heat, approaches the level of one spore per fish. Smoked whitefish chubs, containing from one to several hundred spores each, were examined for toxin content after storage at 5, 10, 15, and 28 C for as long as 32 days. The lowest temperature at which detectable toxin was produced was 15 C. This occurred in 1 of 10 fish incubated for 14 days. C. botulinum was regularly recovered, by enrichment culture, from fish inoculated with small numbers of spores, even though toxin was not detected by direct extraction of incubated fish. Persistence of C. botulinum type E spores was observed to decline with an increase in the temperature and time at which inoculated fish were stored.

Demonstration and isolation of Clostridium botulinum types from whitefish chubs collected at fish smoking plants of the Milwaukee area.

A total of 1,071 whitefish chub samples were examined at eight stages of processing, including sampling aboard ship, various processing steps in the smoking plant, and display in retail cases. The frequency of Clostridium botulinum contamination of freshly caught and eviscerated chubs was approximately 13 to 14%. The highest percentage of contamination (20%) was noted among chubs sampled at the brining step of processing. The prevalence of contamination among chubs sampled at other processing stages prior to the smoking operation ranged from 6 to 14%. Of 858 freshly smoked chubs that had been processed at 180 F for 30 min (internal temperature of loin muscle), 10 were contaminated with C. botulinum (1 Type B and 9 Type E). The use of heat-shocked (60 C for 15 min) and nonheat-shocked enrichment cultures in combination yielded a greater number of positive samples than either method yielded when used alone. Each toxic enrichment culture obtained was subcultured to obtain isolation of the toxigenic organism. Toxigenic pure cultures of C. botulinum were obtained from 80% of the fish samples observed to produce toxic enrichment cultures.