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STAPHYLOCOCCAL FOOD P O I SON I NG*

DOROTHY H. STROHQ

I n considering the question of staphylococcus food poisoning i n re la t ion t o meat there may be some temptation t o feel tha t because the pro- blem has been recognized f o r sometime somehow it must have been solved and therefore i s no longer of much significance. the s i tuat ion. In a report i n 1964 by an ad hoc Food Protection CoPPPittee it was stated that "poultry and meat products have been the sources of about half of the food-borne outbreaks reported since 1956". breaks of foodborne i l l n e s s recorded as caused by staphylococci i n the United States between 195701962, 61 (approximately 30$) involving 2386 cases were a t t r ibu ted t o meat and i s here rei terated, that any t rue assessment of the microbiological hazards of meat, or any other food, based upon s t a t i s t i c s concerning out- breaks and cases are grossly inaccurate because the reporting of incidents is known t o be very incomplete. number of outbreaks of staphylococcus food poisoning incriminating meat is underestimated, perhaps i n the magnitude of one-tenth the actual number of such incidents, the number of such incidents a t t r ibu tab le t o meat i s s t i l l cause f o r concern.

Unfortunately, t h i s i s not

OP the 206 out-

(Dack, 1963) It has long been recognized,

Recognizing tha t the above f igures for the

As t o the organism i t se l f - - the staphylococci considered t o be of public health significance when found In food are those c lass i f ied as pathogenic. physiologically complex organism, and cer ta in s t r a ins produce toxins called enterotoxins, one o r more of which cause emesis i n man. i s t i c s of the organism which would appear t o be of especial i n t e re s t t o persons interested i n meat science include the high salt tolerance mani- fested by cer ta in of the enterotoxin-producing s t r a ins aad the a b i l i t y under aerobic conditions of these bacter ia t o withstand a fairly high degree of acidi ty . The organism wlll grow i n media containing a large percentage of sodium chloride and is not suppressed t o t a l l y by the presence of n i t r i t e s ; thus, survival and even multiplication is possible i n curing solutions.

The species is designated as Staphylococcus aureus. It i s a

Other character-

The pat tern of cause and ef fec t f o r staphylococcus food poison- ing i s well-established. terotoxin-producing s t r a i n of staphylococci becomes infected, frequently through the carelessness of a food handler, responsible for some phase of the food preparation or processing. when the food handler allows secretions from nose, throat or suppurating

A food sui table f o r the development of an en-

Often conteslination i s the result

* Published with the permission of the Director of the Agricultural Ekperiment Station, Madison, Wisconsin.

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wounds or burns t o get i n t o the food. unclean equipment such as grinders and slicers, and contamination by insec ts . Once the enterotoxin-producing s t r a i n of staphylococci i s i n the food, mult ipl icat ion of c e l l s may occur within the temperature range of 40°-1200F. 70°-1000F, and under t h i s condition of holding enterotoxin may be produced i n su f f i c i en t quant i ty t o cause human i l l n e s s i n approximately 4-6 hours. Gne cha rac t e r i s t i c of t h e enterotoxin which i s of especial significance i s i t s apparent heat s t a b i l i t y i n food. It has been shown t o withstand boi l ing f o r one hour or more i n a food substrate .

Other sources of in fec t ion include

Growth i s most rap id when t h e food i s held i n t h e range of

When the e f f ec t of low temperature has been studied, it has been noted t h a t t he lowest temperature a t which Staphylococcus aureus appears t o grow i s 40-44'F and t h a t toxin production does not occur below 64OF. The staphylococci have been observed t o survive frozen storage a t O°F f o r many months. Upon thawing food containing staphylococci, growth of the organ- i s m with attendant toxin formation may occur i f conditions of handling o r storage a re inproper.

Once ingested, t he physiological act ion of t he staphylococcus tox in i s t o produce i n susceptible people, i n about 2-3 hours' time, nausea, vomiting, abdominal cramps, diarrhea, sweating and prostrat ion. Usually no fever i s present. The i l l n e s s i s almost never f a t a l and the vict im e f f e c t s an uneventful recovery i n a short t i m e .

More recent ly it has been shown t h a t there i s not one but th ree or more enterotoxins produced by the staphylococci. A l l are believed t o be protein i n nature but whether they a l l induce the same physiological re- act ion i n man i s s t i l l debated. There seems t o be some agreement t h a t the enterotoxin indicated a s A i s one which does induce the commonly accepted syndrome.

Nuch e f f o r t has gone in to attempting t o f i nd a means of ascer ta ining the presence of enterotoxin i n an incriminated food. I n t h e past feeding o r in jec t ion of animals with suspensions of viable c e l l s or with ce l l - f r ee f i l t r a t e s was frequent ly used f o r t h i s purpose but never with grea t success because some animals were re f rac tory . Vith the fu r the r e lucidat ion of t he nature of t he toxin new procedures a re now being t e s t ed . Chief among them a re antigen-antibody reactions. Casrran and Bennett (1964) have described a s l ide double-diffusion t e s t which permits i den t i f i ca t ion of two toxins, Enterotoxin A and 13. It i s based on gel-diffusion techniques. study i n which they too employed the pr inc ip le of gel-diffusion for de- t ec t ing staphylococcal enterotoxin B. The unique e f f o r t i n t h e i r work w a s t h e attempt t o de tec t the staphylococcal enterotoxin B d i r e c t l y i n t h e food. They were not successful i n so-doing f o r a l l foods but t h e i r r e s u l t s a r e suggestive. A s the chemical s t ruc ture of t he enterotoxins a re e luci- dated, t h e p o s s i b i l i t y of t he detect ion of t he enterotoxin i n foods by serological or other means becomes increasingly hopeful.

A l i t t l e e a r l i e r Ea11 e t a l . (1963) published the r e s u l t s of a

In the endeavor t o f i n d means of confirming a given food as t h e cause of a food poisoning, an a l t e rna t ive approach t o detect ing the en- terotoxin has been a search f o r cha rac t e r i s t i c s of enterotoxin-producing

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s t r a ins of staphylococci which d i f f e ren t i a t e them from other s t ra ins . e f fo r t s have not been t o t a l l y successful, e i t he r . c r i t e r ion i s the coagulase test based on the a b i l i t y of the organism t o coagulate c i t r a t e d o r oxalated blood plasma. producing staphylococci a r e coagulase-positive but not a l l coagulase-positive s t r a i r s a re enterotoxigenic. typing. s table . divided i n t o 4 groups. i f necessary. typing i n de t a i l .

These The most commonly used

Apparently, a l l enterotoxin

Another procedure i n use today i s phage The phage pa t te rn of a given s t r a i n has been found t o be qui te By the use of 2 1 basic phages many s t r a ins of the organism can be

B l a i r and Williams (1961) described the procedures f o r such Additional phages are avai lable f o r fur ther typing,

Emphasis i s given t o the general problem of microbial contamina- t i o n of food, including meat by the recent report (1964) referred t o above as published by an -- ad hoc sub-committee on food microbiology appointed by the National Academy of Sciences--National Research Council Food Protection Committee. pract ices i n production, processing, preservation, d i s t r ibu t ion and serving of foods have ra i sed new questions concerning the microbiological contamin- a t ion of products now reaching large segments of the public i n p a r t i a l l y or completely prepared form." t o include several addi t ional points: American food-buying and eating habi t s t o include many more frozen and pre- cooked foods and those foods which a re purveyed by vending machines, (2) the possible microbiological impact of the s h i f t i n preparation of food from the home t o the factory, (3) the e f fec t , i n terms of bacter iological qual i ty , of "mildly processed" foods a s contrasted with foods processed by the more t r a d i t i o n a l methods, (4) the re lat ionship of present-day procedures f o r packaging, t ransportat ion and storage of foods t o the microbial f l o r a and (5) the question of es tabl ishing reasonably uniform microbiological standards f o r foods across the country.

The committee emphasized t h a t "departure f r o m time-honored

This statement of the committee w a s elaborated (1) the e f f ec t of changes i n

Turning now t o the implications of t he preceding generalizations In a study bearing d i r ec t ly on t h e p o s s i b i l i t y of contamination f o r m e a t .

of meat by staphylococci, Casman, McCoy and Brana3-y i n 1963 reported t h a t r a w and cooked beef, raw and cooked pork and canned ham supported growth of t he one s t r a i n of staphylococci with concurrent enterotoxin A production. They concluded t h a t enterotoxin production and good growth were obtained i n a l l samples. The growth appeared t o be greater, but there w a s no s ign i f i - cant increase i n enterotoxin production, i n the samples following cooking. The data presented by t h e authors a re shown on Table I.

TABLE I. Growth and enterotoxigenicity of staphylococcal s t r a i n 234 on meat

Staph yloc oc c a l Meat count (per a ) Enterotoxin A

Raw beef Cooked beef Raw pork Cooked pork Canned ham

150 x 107 150 x 107

0.6 0.64 1.28 0.4 0.96

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A s suggested by marketing of food changed Recently a paper appeared e f f ec t of heat processing

the Food Protection Committee methods of and i n t h i s regard meat i s no exception. (Wilkinson, e t a l . , 1965) dealing with t h e on the destruct ion of pathogenic bac ter ia

i n turkey rolls. require a l t e r a t i o n i n cooking procedures as compared with the more t r a - d i t i o n a l methods applied t o whole b i rds , s ince t h e geometry of the pro- duct i s a l t e r ed . It would appear t h a t , s imilar ly , t h e now cormon prac t ice of offer ing meat for sale i n the re ta i l market which i s boned, sometimes closely trimmed, of ten ro l led and frequent ly package may suggest a need f o r reevaluation i n terms of microbiological qua l i ty of t h e time-temperature treatments such products receive during cookery. The r e s u l t s of t h e experiments with t h e turkey rolls indicated t h a t staphylococci d id not survive when the product had been heated t o an i n t e r n a l temperature of 150°F. gators recommended t h a t turkey rolls should be brought t o an i n t e r n a l temperature of 160°F i n a 2 2 5 9 oven t o insure destruct ion of Staphylococcus aureus.

The authors pointed out t h a t compact r o l l s of meat w i l l

Allowing a safe ty f ac to r , t he inves t i -

Ekamples of newer types of processing which may need fu r the r evaluation 'based on t h e p o s s i b i l i t y t h a t the f i n a l product may support growth of enterotoxigenic staphylococci with concurrent elaboration of toxin includes i r r ad ia t ion and freeze-drying. Erdnan, Thatcher and MacQueen (1961) reported on the e f f ec t of i r r ad ia t ion on a number of organisms of significance i n food preservation and san i ta t ion . I n t h e i r experiments they included 6 coagulase-positive s t r a i n s of 2. aureus of d i f f e ren t phage pa t te rns . They determined percent survival of t h e organ- i s m s suspended i n buffer , broth or i n meat a f t e r varying doses of ir- rad ia t ion with cobalt6°. A l l s i x s t r a i n s of staphylococci showed close s imi l a r i t y i n react ion and when measured i n the range of 0 t o 400x103 R.E.P. of i r r ad ia t ion they were among t h e most r e s i s t a n t of t he organisms t e s t ed . The decreasing order of s e n s i t i v i t y w a s : M. tuberculosis , A. aerogenes, - A. cloacae, E. -- c o l i I, E. -- c o l i 11, Salmonella, Staphylococci, - S. f e c a l i s . Comparing t h e e f f ec t of the various suspending media, t h e staphylococci were least sens i t ive t o i r rad ia t ion , under conditions of t h e experiments, when placed i n chopped meat; they were l e s s sens i t ive i n broth than i n buffer . Using crude staphylococcus toxin, emetic a c t i v i t y fo r c a t s was absent after a dosage of 2.2 mil l ion R . E. P.

Published information concerning the e f f ec t of freeze-drying on staphylococci i n meat does not seem t o be avai lable although f i r m s market- ing these products have undoubtedly made such s tudies . Inferen t ia l ly , it has been indicated t h a t staphylococcus cu l tures are qui te s tab le t o freeze-drying. various types of organisms showed no s igni f icant a l t e r a t i o n a f t e r being held 10 years subsequent t o freeze-drying. O f the 10 s t r a i n s unaffected, th ree were staphylococci. It thus appears t h a t some staphylococci a re able t o survive both freeze-drying and storage.

S t ee l and Ross (1963) found t h a t 10 of 100 s t r a i n s of

The d e t a i l s of t he laboratory techniques f o r examination of food f o r t he presence of enterotoxigenic staphylococci i s without t he scope of t h i s presentat ion. For those interested, the subject i s reviewed by F. D. Cris ley (1964) i n a publication Exanxination --- of Foods f o r Enteropatho- genic and Indicator Bacteria edi ted by K. H. Lewis and R. Angelott i and --

available from the Superintendent of Documents, U.S. Government Pr int ing Office, Washington, D.C. 20402, f o r f i f t y cents.

One other face t of the problems of staphylococcus food poisoning which should be mentioned i s the observation t h a t r e s u l t s of s tudies on staphylococci made i n pure cul ture cannot necessarily be applied when the staphylococci a r e a par t of a mixed f l o r a i n a food. I n many s i tua t ions t h i s organism appeared not t o be a strong competitor when it occurs as a pa r t of a mixed f l o r a . by the na tura l microflora i n a s lur ry of poultry or beef pot-pies and on vacuumed packed bacon held at 25OC or l e s s (Dack and Lippitz, 1962; Eddy and Ingraham, 1962). t e s t ed f o r t h e i r e f f ec t on the growth of staphylococci some were inh ib i tory but others were stimulatory, (Graves and Frazier, 1963). The development of staphylococci i n a food must be judged i n terms of the t o t a l environ- ment, including the competing organisms which a r e present.

For example, growth of staphylococci w a s inhibi ted

Conversely, when pure cul tures of food bac ter ia were

This paper i s f a r from al l - inclusive; it does suggest cer ta in knowledge and some of the unanswered questions r e l a t ive t o staphylococci as they occur i n meat.

LITERATURE CITED

B l a i r , J. E. and R. E. D. Williams, 1961. Phage typing of staphylococci. Bull. World Health Organ. - 24, 771-784.

Casman, E. P. and R. W. Bennett. 1964. Production of antiserum for staphylococcal enterotoxin. Appl. Microbiol. - 12, 363-367.

Casman, E. P., D. W. IkCoy and P. J. Brandly. 1963. Staphylococcal growth Appl. Wcrobiol. - 11, 498-500. and enterotoxin production i n meat.

Crisley, T. D. 1964. Methods of i so la t ion and enumeration of staphylococci. In Exmination of Fcods f o r Enteropathogenic and Indicator Bacteria. Edited by Lewis , K. H. and R. Angelotti U.S. Government Pr int ing Office.

Dack, G. M. 1963. Problems i n Foodborne Diseases. In Microbiological Qual i ty of Foods. Edited by Slanitz, L. W., C. 0. Chichester, A. R. Gaufin, and Z. J. Ordal. Academic Press, New York City.

Dack, G. M. and G. Lippitz. 1962. Fate of staphylococci and en ter ic micro- organisms introduced i n t o s lu r ry of frozen pot pies. Microbiol. - 10, 472-479.

Appl.

Eddy, B. P. and M. Ingram. 1962. The occurrence and growth of staphylococci on packed bacon, with special reference t o Staphylococcus aureus. J. Appl. Bacteriol . - 25, 237.

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Erdman, I. E., F. S. Thatcher and K. F. YacQueen. 1961. Studies on t h e i r r a d i a t i o n of microorganisms i n r e l a t ion t o food preservation. Canad. J. Hcrob io l . 1, 199-205.

Food Protection Coromittee. 1964. An evaluation of public hea l th hazards from microbiological contamination of foods. Board - National Academy of Sciences - National Research Council, Publication 1195. Reviewed by Walsh, J. W. i n Science - 147, 132-134 (1965).

Food and Nutrit ion

Graves, R. R. and W. C. Frazier . 1963. Food microorganisms influencing growth of Staphylococcus aureus. Appl. Microbiol. 11, 513-516.

H a l l , H. E., R. Angelotti and K. H. L e w i s . 1963. Quant i ta t ive detect ion of staphylococcal Enterotoxin B i n food by g e l diffusion methods. U.S. Pub. Health Repts. - 78, 1089-1098.

Wilkinson, R. J., W. L. Mallman, L. E. Dawson, T. F. Irmiter and J. A. Davidson. 1965. Effect of heat processing f o r t he destruct ion of pathogenic bac ter ia i n turkey rolls. Poultry Sci. - 44, 131-136.

Steel , K. J. and H. E. Ross. 1963. Survival of f reeze dr ied b a c t e r i a l cul tures . J. Appl. Eact. 26, 370-375.

DR. SULZBACHER: I th ink a f t e r those two very workmanlike presentat ions you fellows can understand why t h e University of Wisconsin enjoys such a high reputat ion i n microbiology.

Now,the two organisms t h a t w e have heard about so f a r a r e ones t h a t grow i n foods and produce tox ins and it i s t h e toxins t h a t do the damage. i s a s l i g h t l y d i f f e ren t so r t . I n t h i s case, it i s t h e organism i t s e l f t h a t invades our systems r a the r than i t s toxins. I re fer red i n my opening re- marks t o t h e typhoid outbreak i n Aberdeen, Scotland. considered t o have been caused by typhoid organisms which were present i n a can of corned beef. The causative organism of typhoid i s ca l led Salmonella typhi and it i s named f o r a former. . . . . . I mean the genus salmonella, not t h e organism of typhoid fever, i s named f o r a former Chief of t h e Bureau of Animal Industry, Dr. Salmon. These organisms axe of great importance i n animal heal th as w e l l as i n food poisoning. There are a tremendous number of these organisms. It i s a ra ther confusing f ie ld and I hes i t a t ed t o include any discussion of them i n t h i s program because of t h e f a c t t h a t they are so confusing and there are so many of them. However, Dr. Galton, who has done a good b i t of work on salmonella i n meats has been ta lk ing t o me about them. I n f a c t , she w a s hoping t o be on the program, but was unable t o come and recommended t h a t I c a l l on Dr. L. P. Williams of t h e Minnesota S ta te Health Department who got h i s D.V.14. a t Colorado and l a t e r a doctor of public heal th a t Tulane where I think he was associated with the Communicable Disease Center. come here although he i s a s t ranger t o most of us and here he i s and we a re going t o hand t h i s r e a l hard job of covering the Salmonella t o him and see what he can do with it i n twenty minutes. Dr. W i l l i a m s .

Now w e a r e going t o tu rn our a t ten t ion t o another organism, which

This outbreak w a s

D r . Williams very kindly consented t o

Thank you f o r coming ......

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