CHARACTERISTICS OF CLOSTRIDIUM PERFRINGENS STRAINS ASSOCIATED WITH FOOD AND FOOD-BORNE DISEASE

Clostridium perfringens Type A Food Poisoning II. Response of the Rabbit Ileum as an Indication of Enteropathogenicity of Strains of Clostridium perfringens in Human Beings

The effect of feeding human beings individual strains of Clostridium perfringens or culture filtrates thereof was examined. The strains selected for challenge included both those which had previously been shown to produce fluid accumulation in the ligated ileum or overt diarrhea when injected into the nonligated ileum of the rabbit, or had produced both, and those which did not regularly produce these responses. Challenge doses prepared by allowing each strain to grow in beef stew for 3 hr at 46 C resulted in a 61% incidence of diarrhea when rabbit-positive cells were used. No diarrhea occurred among the subjects fed rabbit-negative strains prepared in a similar manner. The procedures employed in preparing the challenge dose appeared to influence the results obtained. When cell-free filtrates were fed, 4 of 15 persons consuming filtrates from rabbit-positive strains developed diarrhea. All subjects fed filtrates from rabbit-negative strains remained free from diarrhea. Serological tests were carried out to compare the identity of the strains of C. perfringens consumed by the subjects and those excreted in the feces. Heat resistance measured as D(100) values varied greatly among the rabbit-positive strains.

Examination of Feces from Food Handlers for Salmonellae, Shigellae, Enteropathogenic Escherichia coli, and Clostridium perfringens

Duplicate fecal specimens from food handlers were collected in Louisiana. One set of specimens was examined immediately for salmonellae and shigellae by the Central Laboratory of the Louisiana State Board of Health in New Orleans; the other set was shipped to the Food Microbiology Unit at the Robert A. Taft Sanitary Engineering Center in Cincinnati, Ohio, where it was examined for enteropathogenic Escherichia coli (EEC) and Clostridium perfringens. A total of 219 specimens were examined by both laboratories. None yielded salmonellae or shigellae; 171 (78.1%) yielded C. perfringens; 175 (79.9%) yielded E. coli; and 14 (6.4%) yielded EEC. The 14 isolates of EEC were distributed among eight serotypes; one specimen yielded two serotypes. Multiple isolations of C. perfringens strains (two to four) were made from 64 (37.4%) of the specimens, and a total of 244 strains were isolated and studied for identifying characteristics. Of the total, only 87 (35.5%) could be identified serologically by a battery of 67 antisera; only 4 (1.6%) possessed the characteristics of the English "food-poisoning type." The hemolytic activity on agar containing horse, ox, or sheep blood showed that 140 (57.1%) were "hemolytic," 81 (33.1%) were "nonhemolytic," and 23 (9.8%) gave varied results. Only 12 (4.9%) of the strains produced spores that resisted boiling for 30 min or more.

Factors contributing to heat resistance of Clostridium perfringens endospores

The endospores formed by strains of type A Clostridium perfringens that produce the C. perfringens enterotoxin (CPE) are known to be more resistant to heat and cold than strains that do not produce this toxin. The high heat resistance of these spores allows them to survive the cooking process, leading to a large number of food-poisoning cases each year. The relative importance of factors contributing to the establishment of heat resistance in this species is currently unknown. The present study examines the spores formed by both CPE(+) and CPE(-) strains for factors known to affect heat resistance in other species. We have found that the concentrations of DPA and metal ions, the size of the spore core, and the protoplast-to-sporoplast ratio are determining factors affecting heat resistance in these strains. While the overall thickness of the spore peptidoglycan was found to be consistent in all strains, the relative amounts of cortex and germ cell wall peptidoglycan also appear to play a role in the heat resistance of these strains.

Inorganic phosphate induces spore morphogenesis and enterotoxin production in the intestinal pathogen Clostridium perfringens

Clostridium perfringens enterotoxin (CPE) is an important virulence factor for food poisoning and non-food borne gastrointestinal (GI) diseases. Although CPE production is strongly regulated by sporulation, the nature of the signal(s) triggering sporulation remains unknown. Here, we demonstrated that inorganic phosphate (Pi), and not pH, constitutes an environmental signal inducing sporulation and CPE synthesis. In the absence of Pi-supplementation, C. perfringens displayed a spo0A phenotype, i.e., absence of polar septation and DNA partitioning in cells that reached the stationary phase of growth. These results received support from our Northern blot analyses which demonstrated that Pi was able to counteract the inhibitory effect of glucose at the onset of sporulation and induced spo0A expression, indicating that Pi acts as a key signal triggering spore morphogenesis. In addition to being the first study reporting the nature of a physiological signal triggering sporulation in clostridia, these findings have relevance for the development of antisporulation drugs to prevent or treat CPE-mediated GI diseases in humans.

PCR identification of the plasmid-borne enterotoxin gene (cpe) in Clostridium perfringens strains isolated from food poisoning outbreaks

It is generally accepted that Clostridium perfringens strains associated with food poisoning carry their enterotoxin gene, cpe, on the chromosome, while C. perfringens strains isolated from non-food-borne diseases, such as antibiotic-associated diarrhea and sporadic diarrhea, carry cpe on the plasmid. However, we recently encountered a food poisoning outbreak caused by C. perfringens bearing a plasmid cpe. We therefore investigated a total of 31 clinical and non-clinical C. perfringens strains to locate the cpe gene by PCR. The cpe of nine heat-sensitive (100 degrees C for 10min) strains isolated from three outbreaks of food poisoning were located on the plasmid, while those of six heat-resistant strains from other food poisoning outbreaks were located on the chromosome. Moreover, the cpe of 5 heat-sensitive strains isolated from healthy human feces and those of 11 heat-sensitive soil strains were also located on the plasmid. These findings indicate that heat-sensitive, cpe-plasmid-borne C. perfringens strains should not be disregarded as causative agents of food poisoning.

Effects of chilling rate on outgrowth of Clostridium perfringens spores in vacuum-packaged cooked beef and pork

Cooked, chilled beef and cooked, chilled pork were inoculated with three strains of Clostridium perfringens (NCTC 8238 [Hobbs serotype 2], NCTC 8239 [Hobbs serotype 3], and NCTC 10240). Inoculated products were heated to 75 degrees C, held for 10 min in a circulating water bath to heat activate the spores, and then chilled by circulating chilled brine through the water bath. Samples were chilled from 54.4 to 26.6 degrees C in 2 h and from 26.6 to 4.4 degrees C in 5 h. Differences in initial C. perfringens log counts and log counts after chilling were determined and compared with the U.S. Department of Agriculture (USDA) stabilization guidelines requiring that the chilling process allow no more than 1 log total growth of C. perfringens in the finished product. This chilling method resulted in average C. perfringens increases of 0.52 and 0.68 log units in cooked beef and cooked pork, respectively. These log increases were well within the maximum 1-log increase permitted by the USDA, thus meeting the USDA compliance guidelines for the cooling of heat-treated meat and poultry products.

RESPONSE OF CLOSTRIDIUM PERFRINGENS SPORES AND VEGETATIVE CELLS TO TEMPERATURE VARIATION

The vegetative cells and spores of four strains of Clostridium perfringens were examined to determine the effect of lowered and elevated temperatures. Spores were produced by following the method of Ellner, and vegetative cells were obtained from thioglycolate cultures. After exposure to freezing or refrigeration temperatures (-17.7 and 7.1 C, respectively), only small numbers of the vegetative cells were recovered. After similar treatment, 16 to 58% of the spores were recovered. Essentially no vegetative cells and few spores survived holding at 80 C for 10 min. Although all strains were isolated from food, only one strain of the four studied had its origin in a food-poisoning outbreak, and it had been carried on laboratory media for approximately 10 years.

CLOSTRIDIUM PERFRINGENS IN MEAT AND MEAT PRODUCTS

A total of 262 specimens of meat and meat dishes were examined for the presence of Clostridium perfringens. Of this total, 161 were raw, unprocessed beef, veal, lamb, pork, or chicken; 101 were processed meats and meat dishes. C. perfringens was isolated from 113 (43.1%) of these specimens. The highest percentage of contamination (82%) was found in veal cuts, and the lowest (4.7%) in sliced sandwich meats and spreads. Only 2 of the 113 isolates were shown to produce heat-resistant spores, which indicates a very low incidence (0.8%) of contamination. These findings indicate that outbreaks of C. perfringens food-borne disease in the Cincinnati area are caused principally by the contamination of the food with vegetative cells or spores of the organism after cooking. Studies of the effects of various holding temperatures on the growth of C. perfringens indicated that, in the range of 5 to 15 C, no multiplication would occur, but that viable cells would still be present at the end of a 5-day holding period. Extremely rapid growth occurred at temperatures around 45 C, and complete inhibition of growth was accomplished between 49 and 52 C.

RAPID TECHNIQUE FOR THE ENUMERATION OF CLOSTRIDIUM PERFINGENS

A new medium, Tryptone-sulfite-neomycin (TSN) agar, and an incubation procedure for the enumeration of Clostridium perfringens are described. Tolerance to neomycin, optimal growth at 46 C, and sulfite-reducing properties of C. perfringens were used as a basis for development of the medium. Comparisons were made between sulfite-polymyxin-sulfadiazine (SPS) agar and TSN agar at 37 and 46 C with C. perfringens and other organisms. These studies indicate the quantitative and selective superiority of TSN agar, incubated at 46 C, over SPS agar.

RESISTANCE OF CLOSTRIDIUM PERFRINGENS TYPE A SPORES TO GAMMA-RADIATION

The radiation resistance of the spores of a classical strain and of an atypical, heat-resistant strain of Clostridium perfringens was determined. Spores were produced in Ellner's and in a Trypticase broth medium. Approximately 10(6) viable spores per milliliter were suspended in 0.06 m phosphate buffer and irradiated with gamma rays from cobalt-60; the survivors were counted in Tryptone-yeast extract-agar by the Prickett-tube technique. Radiation D values for spores of the atypical strain in phosphate buffer and in cooked-meat broth were 0.23 and 0.30 Mrad, respectively, and the D value of the classical strain was 0.25 Mrad in phosphate buffer. Spores of the classical and atypical strains of C. perfringens type A are characterized by differences in heat resistance; yet, all strains tested demonstrated similar radiation resistance. Also, the spores were more resistant to ionizing radiation in cooked-meat broth than in phosphate buffer.

Clostridium perfringens food poisoning: use of serotyping in an outbreak setting

An outbreak of Clostridium perfringens food poisoning occurred among attendees of a firehouse luncheon. The predominant symptoms of diarrhea (100%) and abdominal pain (81%) among case-patients, the mean incubation period (13.4 h), and the mean duration of illness (21.2 h) were all characteristic of C. perfringens enteritis. Roast beef, although not epidemiologically implicated, was the most likely vehicle of transmission. Fecal specimens from case-patients contained a median C. perfringens spore count of greater than 10(6) and yielded isolates that were heat sensitive and predominantly nonhemolytic, produced C. perfringens enterotoxin A, and, in the majority of specimens (four of five), were identical in serotype. Food samples were negative. This outbreak demonstrates that following enumeration of C. perfringens from a suitable number of fecal specimens from case-patients, serotyping of the isolates may be helpful in implicating C. perfringens as the cause of foodborne illness. This is especially true when implicated food items test negative or are no longer available for testing.

Faecal carriage of Clostridium perfringens

The numbers and serotypes of Clostridium perfringens present in the faeces of three groups of hospital patients and young healthy laboratory workers were examined in studies lasting between 10 and 13 weeks. In one hospital some long-stay geriatric patients carried relatively high numbers of C. perfringens (greater than 10(7)/g) most of the time and it was not unusual in any one week for the majority of these patients to carry the same serotype(s). However, the numbers of C. perfringens in the faeces of young long-stay patients in the same hospital were in the range of 10(3)-10(4)/g and carriage of common serotypes was not observed. These results were similar to the findings with the young laboratory workers. This investigation indicates that two of the laboratory criteria often used in the investigation of C. perfringens food poisoning, i.e. faecal counts of greater than or equal to 10(5) C. perfringens/g and patients carrying the same serological type need to be interpreted with caution with suspected outbreaks involving some groups of geriatric long-stay hospital patients.

Heat resistance, spore germination, and enterotoxigenicity of Clostridium perfringens

Heat resistance at 95 C, heat activation at 75 C, and germination response were determined for spores of 10 serotype strains of Clostridium perfringens type A, including five heat-resistant and five heat-sensitive strains. The D95-values ranged from 17.6 to 63.0 and from 1.3 to 2.8 for the heat-resistant and the heat-sensitive strains, respectively. The heat-activation values, the ratios between the heated and unheated viable counts of spore suspensions, ranged from 0.0035 to 0.65 and from 6.5 to 60.0 for the heat-sensitive and the heat-resistant strains, respectively. Spores of these strains were divided into two distinct germination types on the basis of their germination response; spores of the heat-resistant strains germinated in KC1 medium after heat activation (K-type), and spores of the heat-sensitive strains germinated in a mixture of L-alanine, inosine, and CaCl2 in the presence of CO2 without heat activation (A-type). The strains were tested for enterotoxigenicity by a reversed passive latex-agglutination (RPLA) test. All the heat-resistant strains were RPLA-positive, whereas the heat-sensitive strains were all RPLA-negative. A total of 37 strains of the organism isolated from food-poisoning outbreaks were tested for spore germination and enterotoxin formation. All of the 20 heat-resistant strains showed K-type spore germination and, except for three strains, were RPLA-positive, whereas all of the 17 heat-sensitive strains showed A-type spore germination and, except for only one strain, were RPLA-negative.

Clostridium perfringens and other anaerobes isolated from bile

Clostridium perfringens was isolated from bile in 13 cases of 150 patients examined. The serotypes of C perfringens strains isolated from bile and faeces were investigated using antisera to Hobbs' type 1-17. Two or more serological types were often found in a single specimen, but in the same patient the serotypes of C perfringens strains isolated from the bile were identical with those from the faeces. Beta-glucuronidase production in these C perfringens serotypes was tested with the API-Strep system. Strains agglutinated with Hobbs' antisera produced beta-glucuronidase, but non-agglutinated strains did not.

Thermal inactivation of ileal loop-reactive Clostridium perfringens type A strains in phosphate buffer and beef gravy

The thermal resistance of spore crops produced from each of two ileal loop-reactive strains of Clostridium perfringens type A was determined in two suspending vehicles consisting of 0.067 M (pH 7.0) phosphate buffer and a commercial beef gravy. D115.6 values obtained in buffer and enumerated after pretreatment with sodium ethylenediaminetetraacetate and recovery in plating medium containing lysozyme were two- to threefold greater than those obtained without this treatment. D115.6 values obtained with beef gravy were less than those obtained in buffer with or without lysozyme; however, the D98.9 and D104.4 values were 1.3 to 2 times greater than those obtained in buffer with lysozyme. The z values were within the ranges reported by previous investigators.

Effect of lysozyme on ionic forms of spores of Clostridium perfringens type A

H spores of Clostridium perfringens type A (two strains) were more sensitive to germination by lysozyme than native spores. Resistance to lysozyme of H spores was restored by calcium loading.

Clostridium welchii and Bacillus cereus infection and intoxication

Clostridium welchii type A is a common agent of food poisoning when allowed to proliferate to large numbers in cooked foods, usually meat and poultry. The main factors of importance are survival of the spores, frequently found on raw products, through the cooking process, and possible contamination of cooked meats transferred to unclean containers; subsequent germination of spores and rapid multiplication of the vegetative cells during long slow cooling and non-refrigerated storage lead to heavy contamination. The toxin responsible is different from the soluble antigens, and its formation in the intestine is associated with sporulation.

Large numbers of Cl. welchii of the same serological types in food and faeces is the main diagnostic factor. Important preventive measures are rapid cooling and cold storage to prevent growth.

Bacillus cereus is an aerobic sporulating organism commonly found in cereals. Outbreaks described from Europe have a different aetiology with regard to food vehicles, incubation period and symptoms from those that have been reported recently in the U.K. from fried and boiled rice. The spores survive through cooking procedures and grow out to cells which sporulate readily in the cooked food and which are assumed to produce toxin in the food. Large numbers of B. cereus are found in foods causing illness and, as with Cl. welchii, the main preventive measure is inhibition of growth by quick cooling and cold storage of foods cooked ahead of requirements. A comparative table of the characteristics and clinical symptoms of Cl. welchii and B. cereus is given.

Enumeration of food-borne Clostridium perfringens in egg yolk-free tryptose-sulfite-cycloserine agar

The SFP (Shahidi-Ferguson perfringens), TSC (tryptose-sulfite-cycloserine), EY (egg yolk)-free TSC, and OPSP (oleandomycin-polymyxin-sulfadiazine perfringens) agars have been tested for their suitability to enumerate Clostridium perfringens in naturally contaminated foods. Complete recoveries of C. perfringens were obtained in each of the four media, but only the TSC and EY-free TSC agars were sufficiently selective to ensure subsequent confirmatory tests without interference from facultative anaerobes. Because of some disadvantages associated with the use of egg yolk, EY-free TSC agar is recommended for enumeration of C. perfringens in foods. Several conditions for convenient shipment of foods and C. perfringens isolates with minimum loss of viability have been tested. The highest viable counts were preserved when foods were mixed 1:1 (wt/vol) with 20% glycerol and kept in a container with dry ice. Isolated C. perfringens strains remained viable for at least 2 weeks at ambient temperatures on blood agar slopes with a 2% agar overlay in screw-cap culture tubes.

The effect of two methods of cooking and cooling on Clostridium welchii and other bacteria in meat

A comparison was made of beef cooked in conventional and moist air (Rapidaire) ovens. In both large (ca. 4.5 kg.) and small (ca. 2.7 kg.) joints, spores of Clostridium welchii survived after cooking but vegetative cells, Escherichia coli, and Staphylococcus aureus, did not, regardless of the type of oven used.Cooling at room temperature after cooking permitted growth of Cl. welchii. Although some multiplication also occurred in the centre of large roasts cooled under refrigeration, the viable counts were considered too low to constitute a potential health risk.

Analysis of Clostridium botulinum toxigenic types A, B, and E for fatty and carbohydrate content

Lyophilized, 48-hr log-phase vegetative cells were extracted with chloroform-methanol (2:1, v/v) and ethanol-ether (3:1, v/v) and then saponified with methanolic KOH. Gas-liquid chromatography of the methyl esters of extractable fatty acids revealed distinctive "pattern profiles" of Clostridium botulinum toxigenic types "A," "B," and "E." C. perfringens type "A" and Escherichia coli strain "B" were also studied in a similar manner and were found to give pattern profiles which were distinct even from those obtained for the C. botulinum microorganisms. Amino sugar content of the five microorganisms was determined by using a Beckman amino acid analyzer. The molar ratio of glucosamine to that of galactosamine was found to be of further assistance in distinguishing the individual microorganisms.

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.

Immunochemistry of a formamide-extracted antigen from Clostridium perfringens cell walls

The type-specific antigen of a strain of Clostridium perfringens involved in food poisoning was isolated from the cell wall by the use of hot formamide. The antigen appears to consist of polysaccharide or mucopeptide. The formamide extract was shown to be heterogeneous by gel filtration on Sephadex G-200. The serologically active fraction contained about 25% of the amount of protein present in the original formamide extract. Hexosamine, acetyl groups, and carbohydrate also were detected. The formamide extract showed a high degree of serological activity. The serological activity was increased twofold on Sephadex gel filtration.

Haemolytic activity of the alpha and theta toxins of Clostridium welchii

The lecithinase and haemolytic activity of thirty strains ofCl. welchiiisolated from food, faeces, and soil, was studied. The strains from foods produced smaller amounts of lecithinase and were, in general, less haemolytic than the strains isolated from soil and faeces.

The haemolytic activity ofCl. welchiion erythrocytes from different animal species displayed considerable variation. Sheep erythrocytes were the most sensitive to the action of alpha toxin, whereas rabbit blood was most sensitive to haemolysis by theta toxin. The degree of haemolysis was also dependent upon the concentration of the enzyme, and temperature and length of incubation.

The haemolytic activity of commercial lecithinase was observed to be similar to the haemolytic activity of the alpha toxin ofCl. welchii. This finding provides further evidence that the haemolytic and lecithinase activities ofCl. welchiiare due to one substance, the alpha toxin. Exposure of commercial lecithinase to heat resulted in the destruction of its haemolytic properties.

Sporulation, heat resistance, and biological properties of Clostridium perfringens

A sporulation medium for 134 Clostridium perfringens strains, including types A, B, C, D, E, and F, was devised according to Grelet's observation that sporulation occurred when cultural environment became limited in any nutritional requirement indispensable for the growth of the organism. Sporulation took place most prominently when 10% cooked-meat broth (pH 7.2) containing 3% Proteose Peptone and 1% glucose was used for the preculture and 2% Poli Peptone medium (pH 7.8) was used for the subculture medium. Sometimes, terminal spores could be observed. A correlation between sporulation and heat resistance was examined by use of C. perfringens strains isolated from samples heated at different temperatures. Almost all strains isolated from unheated samples and from those heated at lower temperatures gave rise to spores in our sporulation medium, but the spores were weakly heat-resistant, whereas strains isolated from samples heated at 100 C for 60 min were highly heat-resistant but sporulated poorly. A majority of these heat-resistant strains were non-gelatinolytic and definitely salicin-fermenting.

Cytology of spore formation in Clostridium perfringens

The sequential morphological events in spore formation by Clostridium perfringens type D were observed in Ellner's medium where 80 to 100% of the cells formed spores. Gross structural changes were studied with the light microscope under phase-contrast, and in fixed cells by the use of both nigrosin and Giemsa preparations. Fine structure was examined with the electron microscope in both thin sections and frozen-etched preparations. During the first 3 hr of incubation, the original rod-shaped cells became ellipsoid to ovoid in shape; by 5 to 6 hr, subterminal spores had developed within these enlarged cells. The fine structural sequence was in most respects identical to that in other Bacillaceae, although some stages were illustrated with particular clarity. A unique feature was the development of a convoluted, membranous exosporium which adhered to the outer surface of the two coats and had an unusual fine structure resembling a rectangular array of subunits.

Rabbit ileal loop response to strains of Clostridium perfringens

The ligated loop of the rabbit intestine was investigated as a possible experimental model for the study of Clostridium perfringens food poisoning. The method of preparation of the challenge inoculum was important in determining whether a given strain would provoke a response. When cultures were grown for 4 hr at 37 C in Skim Milk (Difco), 14 of 29 type A strains isolated from food-poisoning outbreaks consistently produced exudation of fluid and consequent dilation of the ileal segments. In contrast, 15 of the 18 strains derived from other sources failed to elicit a response. By use of different inoculum preparations, nearly all strains could be made to give at least an occasional positive loop reaction. Diarrhea was not obtained in rabbits by intraluminal injection into the normal ileum or by per os administration of the cultures. Lecithinase, purified and in concentrated culture supernatant fractions, failed to produce a response in the isolated ileal loops.

Food poisoning caused by heat-sensitive Clostridium welchii. A report of five recent outbreaks

Details of confirmed outbreaks of food poisoning due to heat-sensitive Cl. welckii are given. In 4/5 incidents heat-sensitive Cl.welckiiwere isolated in large numbers from the majority of the faeces. In the remaining outbreak the faecal samples were not collected until 7–9 days after the illness. The causative organism was isolated from the food in 3/5 instances.

In addition four outbreaks of food poisoning in which both heat-sensitive and heat-resistant Cl.welckiiwere isolated are described.

The role of heat-sensitive Cl.welckiiin food poisoning outbreaks is discussed and a suggested method of examining faeces for Cl.welchiiis given.

We are indeed grateful for the assistance given in collecting faecal specimens and obtaining detailed information on the food preparation, etc., by Drs G. C. Turner, J. Epsom, J. G. Wallace, P. J. Wormald, H. D. Holt, D. G. Fleck, J. M. Graham, E. Tanner and J. D. Abbott. We would also like to thank Mrs I. Batty of the Wellcome Research Laboratory for carrying out toxicological examinations for us.

One of us (R.G.A.S.) is attached to the Commonwealth Department of Health, Australia, and is at present the holder of a Public Service Board Postgraduate scholarship.

Improved medium for sporulation of Clostridium perfringens

An improved sporulation medium has been developed in which all five strains of Clostridium perfringens tested exhibited a 100- to 10,000-fold increase in numbers of spores when compared with spore yields in SEC medium under comparable conditions. In addition, three of five strains produced a 100- to 1,000-fold increase, with the remaining two strains yielding approximately the same numbers of spores, when compared with strains cultured in Ellner medium. At the 40-hr sampling time, 18 of 27 strains produced a 10- to 100-fold increase in numbers of spores in our medium, when compared to spore production obtained in a medium recently reported by Kim et al. The new medium contained yeast extract, 0.4%; proteose peptone, 1.5%; soluble starch, 0.4%; sodium thioglycolate, 0.1%; and Na(2)HPO(4). 7H(2)O, 1.0%. In some cases, the spore yield could be increased by the addition of activated carbon to the new medium. The inclusion of activated carbon in the medium resulted in spores with slightly greater heat resistance than spores produced in the new medium without added carbon or in SEC or in Ellner medium. The major differences in heat resistance of the various strains appeared to be genetically determined rather than reflections of a particular sporulation medium. A definite heat-shock requirement was shown for four of four strains, with the optimal temperature ranging from 60 C for a heat-sensitive strain to 80 C for a heat-resistant strain. Heating for 20 min at the optimal temperature resulted in a 100-fold increase over the viable count obtained after heating for 20 min at 50 C.

Heat resistance of spores of Clostridium welchii

Eight strains ofCl. welchiiwere studied for the heat-resistance of their spores. Spores ofCl. welchiiisolated from food-poisoning cases had greater heat-resistance than strains isolated from soil or faeces.D-values and trend values were calculated from the thermal death curves.

Effect of cookery and holding on hams and turkey rolls contaminated with Clostridium perfringens

Canned hams, turkey rolls, and ground-beef casseroles were inoculated with a mixture of vegetative cells and spores of selected strains of Clostridium perfringens, in approximately known numbers. After cooking and holding at different temperatures for various times, samples of the food were plated directly on sulfadiazine-polymixin-sulfite-agar. In all cases, small but measurable percentages of the organisms survived cookery. The number of cells viable after cookery of the ham or turkey was influenced by the position of the slice of meat in the roast as well as by the final temperature to which the product was heated. Plate counts for turkey or beef casserole held at temperatures in the range of 5 to 10 C for 48 hr indicated stabilization of the population or a tendency to decrease. At 24 C, the multiplication of cells was apparent in 4 hr and rapid in 6 hr. When the food was maintained at 68 C, populations remained viable for 6 hr and the counts did not change markedly. In turkey maintained at 37 C, the number of cells increased sharply within 4 hr.

Distribution of neuraminidase among food-poisoning strains of Clostridium perfringens

A survey was made to determine the distribution of the enzyme neuraminidase among 76 strains of Clostridium perfringens. Representative strains from each toxigenic type (A to F) and atypical C. perfringens type A food-poisoning strains of both American and English (Hobbs types) origin were tested. Both the American food-poisoning and nonfood-poisoning associated cultures consisted of both neuraminidase-positive and -negative strains. Furthermore, American strains which could not be differentiated from the original Hobbs cultures consisted of both neuraminidase-positive and -negative representatives. In contrast, the English (Hobbs) strains uniformly failed to produce an active intracellular or extracellular neuraminidase. No enzyme activity was detected in these strains when cultures were grown in different growth media, when grown in the presence of substrate (neuraminlactose), or upon extended incubation of enzyme preparations with substrate. With the exception of a type F strain, representative strains of the other toxigenic types (A to F) produced neuraminidase; 85% of the typical type A strains contained the enzyme.