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S M Harmon

Publications and source records attributed to S M Harmon.

26 records · Page 2Linked to original sources
PubMed1976

Collaborative study of an improved method for the enumeration and confirmation of Clostridium perfringens in foods.

A collaborative study was conducted in 10 laboratories to evaluate the performance of a new method for the enumeration of vegetative cells of Clostridium perfringens in foods. Results obtained by the new method were compared with results from the official first action method, 46.049-46.053. Per cent recoveries of 4 C. perfringens strains from inoculated roast beef samples were higher and more consistent in tryptose-sulfite-cycloserine (TSC) agar with or without added egg yolk than in sulfite-polymyxin-sulfadiazine (SPS) agar, specified in the official first action method. The confirmatory technique utilized in the new method was also found to be more reliable than the technique described in the official first action method. Based on the collaborative results, the new method with TSC agar for enumeration and a modified motility-nitrate medium together with a lactose-gelatin medium for confirmation of C. perfringens has been adopted as official first action to replace 46.049-46.053.

Agar↗
PubMed1971

Comparison of media for the enumeration of Clostridium perfringens.

For the enumeration of viable vegetative cells and spores of Clostridium perfringens, noncommercial (laboratory prepared) sulfite-polymyxin-sulfadiazine (SPS) agar, tryptone-sulfite-neomycin (TSN) agar, and Shahidi-Ferguson-perfringens (SFP) agar were statistically compared to SPS agar without antibiotics. The selectivities of these four media were also evaluated on the basis of their ability to inhibit the growth of pure cultures of a variety of other organisms. The average recovery of vegetative cells of 10 strains of C. perfringens with SFP agar was not significantly higher than with SPS agar with 10(4) organisms per g, but with 10(6) organisms per g it yielded significantly higher recoveries than SPS agar. TSN agar yielded significantly lower recoveries at both inoculum levels. SFP agar gave significantly higher recoveries of spores than SPS and TSN agars. Average plate counts of spores in SFP agar were 75% as high as in SPS agar without antibiotics, but only 45% of the spores grew in SPS agar and 25% in TSN agar. TSN agar was the most selective of the three media, but the selectivity of SPS agar approached that of TSN agar under the test conditions. SFP agar, which was the least selective of the media, allowed growth to some extent of nearly all of the facultative anaerobes tested.

Bacteria↗
PubMed1971

Improved medium for enumeration of Clostridium perfringens.

An improved selective medium, Tryptose-sulfite-cycloserine (TSC) agar, for the enumeration of Clostridium perfringens is described. It consists of the same basal medium as Shahidi-Ferguson-perfringens (SFP) agar, but with 400 mug of D-cycloserine per ml substituted for the kanamycin and polymyxin. Tolerance of C. perfringens for D-cycloserine, its production of lecithinase, and its ability to reduce sulfite were used as the basis for development of this medium. Comparisons were made between TSC and SFP agars for the recovery of vegetative cells of C. perfringens by using statistical methods. The results showed that TSC allowed virtually complete recovery of most of the C. perfringens strains while inhibiting practically all facultative anaerobes tested. SFP agar allowed a slightly higher rate of recovery of C. perfringens but was found to be much less selective.

Agar↗
PubMed1970

Method for estimating the presence of Clostridium perfringens in food.

The methods currently used for the enumeration of Clostridium perfringens in food are often inadequate because of the rapid loss of viability of this organism when the sample is frozen or refrigerated. A method for estimating the presence of C. perfringens in food which utilizes the hemolytic and lecithinase activities of alpha toxin was developed. The hemolytic activity was measured in hemolysin indicator plates. Lecithinase activity of the extract was determined by the lecithovitellin test. Of 34 strains of C. perfringens associated with foodborne disease outbreaks, 32 produced sufficient alpha toxin in roast beef with gravy and in chicken broth to permit a reliable estimate of growth in these foods. Alpha toxin was extracted from food with 0.4 m saline buffered (at pH 8.0) with 0.05 mN-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid and concentrated by dialysis against 30% polyethylene glycol. A detectable quantity of alpha toxin was produced by approximately 10(6)C. perfringens cells per g of substrate, and the amount increased in proportion to the cell population. Results obtained with food samples responsible for gastroenteritis in humans indicate that a correlation can be made between the amount of alpha toxin present and previous growth of C. perfringens in food regardless of whether the organisms are viable when the examination is performed.

Animals↗
PubMed1966

Antagonistic effect on Clostridium botulinum type E by organisms resembling it.

A bacteriocin-like substance, active against strains of Clostridium botulinum type E, is produced by certain nontoxic organisms whose biochemical properties and morphological characteristics are similar to type E. The substance, for which the name "boticin E" is proposed, is bacteriolytic for vegetative cells and bacteriostatic for spores of type E. Its spectrum of activity is somewhat strain-specific. Of the clostridial species tested, only C. botulinum type E and, to a lesser extent, C. perfringens and C. acetobutylicum, but not C. botulinum types A, B, or F, are sensitive. Irreversibly resistant variants originating from both vegetative cells and spores of certain strains were obtained. The active substance is heat-stable and dialyzable, and is not inactivated by chloroform but is digested by trypsin. Ethyl alcohol and acetone precipitates are fully active, whereas trichloroacetic acid precipitates are only partially active. Other nontoxic organisms producing similar antagonistic substances are discussed.

Acetone↗
PubMedDate not supplied

Lipid globule staining to aid in differentiating Bacillus species.

The use of the lipid globule stain to aid in differentiating the Bacillus cereus group (i.e., B. cereus, B. cereus var. mycoides, and B. thuringiensis) from other Bacillus species was investigated. Smears from colonies grown on suitable agar were made on precleaned slides, stained, and examined microscopically for characteristic deep blue lipid globules. The study included a total of 649 cultures of Bacillus species plus 143 incompletely characterized Bacillus isolates from food. Only B. cereus, B. cereus var. mycoides, B. thuringiensis, B. megaterium, and B. sphaericus were consistently positive for lipid globules, although at times, a few cells of B. aneurinolyticus and B. thiaminolyticus were also positive. The lipid globule stain procedure is of value in differentiating Bacillus species, especially when performed by an experienced analyst and used in conjunction with tests for cell and spore morphology.

Bacillus↗
PubMedDate not supplied

Enumeration of Clostridium perfringens spores in human feces: comparison of four culture media.

Enumeration of Clostridium perfringens spores was compared using 4 culture media. Duplicate 1 g portions of 35 stools (25 from C. perfringens food poisoning outbreaks and 10 from normal stools) were heat treated 20 min at 75 degrees C and tested on tryptose-sulfite-cycloserine (TSC) agar, trypticase-soy-blood (TSB) agar, lactose-sulfite (LS) medium, and iron milk (IM) medium. Dilutions were plated directly onto TSB and TSC, and a 3-tube most probable number determination was made with each specimen in LS and IM incubated at 45 degrees C. TSB was easiest to use and nonhemolytic food poisoning strains were readily differentiated from the normal hemolytic biotype on this medium. Confirmed counts on TSC and TSB were similar for all specimens, but counts of 8 of 25 outbreak specimens were 2-4 log units lower in LS and IM than on plating media; spores in specimens associated with 2 of 5 outbreaks were intolerant of the elevated temperatures. Results showed that elevated temperature MPN methods in LS and IM are inappropriate for the examination of outbreak stools.

Clostridium perfringens↗