Streptococcus thermophilus which grows actively at temperatures

Transcription

1 STREPTOCOCCI WHICH GROW AT HIGH TEMPERATURES Department of Dairy Industry, Cornell University, Ithaca, New York Received for publication, "April 16, 1931 INTRODUCTION Although streptococci have been exhaustively studied, comparatively little work has been done on streptococci which grow at relatively high temperatures. Orla-Jensen (1919) has described Streptococcus thermophilus which grows actively at temperatures from 45 to 50 C. and has also called attention to the fact that certain other streptococci grow at 45 C. and above. Aside from the work of Orla-Jensen, very little has been published by other workers dealing with the streptococci which grow at higher temperatures, although a number of investigators have studied certain streptococci which survive pasteurization and other heat treatments of milk and milk products. The object of the present work was to obtain more definite information concerning streptococci from milk and other sources which are able to develop rapidly at temperatures too high for the growth of pathogenic streptococci, Streptococcus lactis and many of the other common streptococci. In all, 294 cultures of streptococci which grow actively at 45 C. have been studied. METHODS The method used in the isolation of cultures was to warm samples of raw milk and flasks of sterile milk to which samples of manure, human feces, ice cream, or cheese had been added, quickly in a waterbath to a temperature of 45 C. and then incubate at this temperature for twenty-four hours. At the end of this period the milk was plated on lactose agar and cultures isolated from the pre- 275

2 276 vailing types of colonies which developed. To ensure pure culture isolations, each colony was observed under the microscope before transferring to litmus milk to see that no other colony might be picked at the same time. The litmus milk was heated to 45 C. before incubation and only those cultures which grew at this temperature were studied further. Gram stains were made on each of the cultures to note chain formation and as a check on the purity of the culture. All of the cultures were isolated in this way with the exception of a majority of the cultures of Streptococcus fecalis and Streptococcus glyce7inaceus which were obtained from one-day-old Swiss cheese. The hemolysis of blood was determined by plating (not streaking) the cultures on meat-infusion horse-blood agar (ph 7.6) and incubating at 370C. for forty-eight hours. A study was made of litmus reduction in milk, the most essential point of which is whether the reduction takes place before or after the curdling of the milk. The final ph was determined by the colorimetric method after the cultures had been incubated in 1 per cent glucose broth at 37 C. for fourteen days. Cultures which were grown in 4 per cent peptone solution for forty-eight hours at 37 C. were tested with Nessler's reagent for the production of ammonia. The temperature growth limits were determined in litmus milk. In each instance the culture was cooled or heated, immediately after inoculation, to the temperature at which it was to be incubated. The ability of the cultures to ferment carbohydrates and related substances was tested with arabinose, glucose, maltose, lactose, sucrose, raffinose, inulin, mannitol, glycerol, and salicin. In order to safeguard against changes of the fermentation test substances in the sterilization process, each substance was sterilized separately by filtration as a 10 per cent solution in distilled water and added to sterile beef extract-peptone broth so as to obtain a 1 per cent solution of the substance to be tested. Controls were run as a check on the fermentations. In each instance the cultures were grown in a 0.1 per cent glucose beef extract-peptone broth for eighteen to twenty-four hours before inoculation into the various substances. Tests for action on starch were made by the use of

3 STREPTOCOCCI WHICH GROW AT HIGH TEMPERATURES 277 starch agar plates. The cultures were plated with this medium in proper dilution (not streaked) and the plates were then flooded with iodine solution after three days' incubation at 30 C. The resistance of the cultures to pasteurization was tested by placing 1 cc. amounts of cultures, which had been grown in milk for two days at 37 C., into 10 cc. amounts of sterile milk, previously heated to 62.8 C., and holding the tubes at this temperature for thirty minutes. Plate counts upon lactose agar were made from the heated samples immediately before and after the pasteurization process in order to obtain an idea concerning the relative rates of destruction of the organisms at this temperature. EXPERIMENTAL The groupings which we have made in this study are based on hemolysis of blood; growth at 100, 450, and 50 C.; the production of ammonia from peptone; action on litmus milk; and the liquefaction of gelatin; supplemented by the fermentation of carbohydrates and related substances. The cultures studied are considered under four main groups: (1) Streptococcus thermophilus, Orla-Jensen, which appears to represent a homogeneous collection of organisms belonging definitely to one species; (2) the "bovis group," containing the closely related Streptococcus bovis and Streptococcus inulinaccus; (3) the "fecalis group," in which we have included Streptococcus fecalis and Streptococcus glycerinaceus, and (4) the "liquefaciens group" containing Streptococcus liquefaciens and Streptococcus zymogenes because of certain characteristics which they appear to have in common. All of the cultures isolated have been identified as belonging to previously described species. We have also been successful in bringing together the valuable works of Orla-Jensen (1919) and of Ayers and his co-workers (1922) (1923) (1924) in the cases in which these investigators apparently dealt with the same groups of organisms. Streptococcus thermophilus Seventy-six of the 294 cultures studied belong to the Streptococcus thermophilus group. This name has been applied to these

4 278 cultures because our observations conform closely to the descriptions of Streptococcus thermophilus as given by Orla-Jensen. Hucker (1928) has described cultures of Streptococcus thermophilus which were isolated from pasteurized milk. His fermentation results correspond to those given in table 1. He classes all streptococci which grow between 380 and 45 C.; ferment sucrose, but not maltose, dextrin nor salicin, and which curdle milk with slight reduction of litmus as Streptococcus thennophilus. He did not test for temperature growth limits nor production of ammonia. TABLE 1 Streptococcus thermophilus 0 an GROW'TH FERMENTATION OF: 0 0 0~~~~ SOURCE OF 0 Z CU'LTU'RES PA0.P E1 0 OR.A e '.X3 Raw milk Gamma Ft Ice cream Gamma Ft -. * Sixty-nine per cent of these cultures changed arabinose from ph 7.0 to 6.6. t Thirty-four per cent of these cultures fermented raffinose actively while 58 per cent changed the reaction of the medium from ph 7.0 to 6.6, and the other 8 per cent were negative. t Sixty-two per cent of the ice cream cultures fermented raffinose while 38 per cent did not. Some of his cultures gave a Beta hemolysis and some fermented maltose and grew on plain beef extract-peptone agar. Robertson (1927) described Streptococcus thermophilus but his cultures do not correspond to the cultures which we have reported in table 1. From work which we have done with some of the cultures which Robertson studied, it appears that his cultures belong to the Streptococcus glycerinaceus type, since they grow at 10 C.; do not grow at 50 C.; ferment salicin, nmaltose, glycerol, and mannitol; and produce a larger colony than does Streptococcus thernophilus. The outstanding characteristics of Streptococcus thermophilus

5 STREPTOCOCCI WHICH GROW AT HIGH TEMPERATURES 279 as given in table 1 are as follows: Slight reduction of litmus after coagulation of milk; active growth at 50 C.; no growth at 10 C.; only slight growth at room temperature; no fermentation of maltose, inulin, salicin, mannitol, or glycerol; fermentation of glucose, lactose and active fermentation of sucrose; and slight fermentation of raflinose and arabinose. None of the cultures grew on beef extract-peptone agar without the addition of a fermentable carbohydrate. The colonies, even when not crowded, were of "pinpoint "type on lactose agar. Long chains were formed in milk. All of the cultures in each of the groups reported in this study resisted pasteurization at 62.8 C. for thirty minutes, but cultures belonging to the Streptococcus thermophilus group showed a higher percentage survival. The bovis group Ayers and Mudge (1923) described two types of Streptococcus bovis, varieties "A" and "B" respectively. Orla-Jensen (1919) suggested that the cultures of Streptococcus bovis studied by him might be called types "A" and "X," but he classified the "X" type as Streptococcus inulinaceus, based on the fact that the type "X" fermented inulin and raffinose, frequently starch and mannitol, but not arabinose. His strain "A" differed from Strain "X" in that it fermented arabinose and hydrolyzed starch actively, but usually failed to ferment inulin. Our results, recorded in table 2, show that Streptococcus bovis does not hemolyze blood; that it does not reduce litmus before curdling the milk; and that it does not grow at 10 C. nor at 50 C., but does grow at 45 C. It ferments arabinose, glucose, maltose, lactose, sucrose, raffinose, starch, and salicin; sometimes mannitol and inulin; but fails to ferment glycerol. The cultures tested do not produce ammonia from peptone. These results are the same as those obtained by Ayers and Mudge (1923) in their study of Streptococcus bovis, except that they did not test arabinose, maltose, glycerol, and the growth at high temperatures. They also noted a weak hemolysis of blood which was not detected in our cultures. Our results also confirm the work reported by Orla-Jensen (1919). He pointed out that

6 280 the typical Streptococcus bovis ferments arabinose, has capsules in milk, and hydrolyzes starch, while Streptococcus inulinaceus does not ferment arabinose, readily ferments inulin, hydrolyzes starch only weakly, and does not form capsules in milk. With the cultures studied by us, this was found to be true. In other respects the two strains are found to be practically identical, so far as revealed by the tests applied in this study. TABLE 2 Bovis group O 5 go GROWTH FERMENTATION OF: oik 1 04 SOURCE OF 0 noa CULTURES p ~~~~~ S 5 ~~~~~~~0 Streptococcus bovlinaes milk...12 Gamma Milk... o Gamma - 4L _ _*_F Mouth of cow.. 36 Gamma *=t Human feces Gamma 4.2-_ * Starch was faintly hydrolyzed in some instances. t Thirty-six per cent of these cultures fermented mannitol while the other 64 per cent were negative or showed a very slight change in reaction. t Eighty-six per cent of those from the mouths of cows fermented mannitol while 14 per cent did not. While it perhaps would be more logical for the present to designate the arabinose negative, inulin positive type as only a variety of Streptococcus bovis, we have followed Orla-Jen4en in calling it Streptococcus inulinaceus. Of particular interest in this connection is the observation of Ayers and Mudge (1923) that the inulin fermenting type is characteristic of the mouth of cows, while the type isolated from cow feces is characteristically inulin negative. Our results confirm this finding. All of the cultures isolated by us

7 STREPTOCOCCI WHICH GROW AT HIGH TEMPERATURES 281 from the mouths of cows were of the inulinaceus type, while the bovis type was obtained from cow feces. The fecalis group As may be seen from table 3, the cultures of this group are divided into two types: (1) Streptococcus fecalis, Andrewes and Horder, and (2) Streptococcus glyce7inaceus, Orla-Jensen. The SOURCE OF O C z CULTURES 0 S TABLE 3 Fecalis group _ 'GROWTH FERMENTATION OF: I PO 0 Streptococcus fecalis Swiss cheese 10 Gamma Swiss cheese processed Gamma, T*+ Streptococcus glycerinaceus Milk Gamma t Swisscheese Gamma Ice cream Gamma Tt Bovine feces Gamma * Seventy-five per cent of the processed cheese cultures actively fermented mannitol. t Eighty-four per cent of the milk cultures fermented raffinose while 16 per cent were negative. t Thirty-one per cent of the ice cream cultures fermented raffinose while 69 per cent were negative. cultures of this group were isolated from one-day-old Swiss cheese, processed Swiss cheese, raw market milk which had been held at 450C. for twenty-four hours, fresh ice cream which had been incubated at 450C. for twenty-four hours, and bovine feces which were placed in sterile milk and some samples held at 500C. for twentyfour hours and other samples held at 100C. for four days.

8 282 These two types are similar in that they do not hemolyze blood; reduce litmus before curdling the milk; produce ammonia from peptone; give a final ph in glucose broth of about 4.2; grow at 100C., 450C., and 500C.; ferment arabinose, glucose, maltose, lactose, and salicin; do not ferment inulin nor hydrolyze starch. The members of this group differ in that the fecalis type does not ferment glycerol and usually does not ferment sucrose, while the glycerinaceus types ferments both these substances. The glycerinaceus type reduces litmus more rapidly, but does not curdle milk as soon as the fecalis type. Orla-Jensen (1919) described Streptococcus faecium which appears to be similar to Streptococcus fecalis as described by Andrewes and Horder (1906), and more fully by Ayers and Johnson (1924). The cultures we have designated as Streptococcus fecalis agree with the description as given by Ayers and Johnson for their cultures, and also with Orla-Jensen's description of Streptococcus faecum. We are inclined to the belief that these species are the same, and, therefore, that the name Streptococcus fecalis, Andrewes and Horder, should be used. Ayers and Johnson (1924) concluded that Streptococcus lactis and Streptococcus fecalis are similar if not identical. It is generally conceded that Streptococcus lactis does not grow at 450C., as was shown by Sherman and Albus (1918) and by Orla-Jensen (1919). Since the cultures of Streptococcus fecalis studied by Ayers and Johnson were not tested for growth at 450C., it is felt that it might be possible to use the temperature growth limits as a means of differentiating Streptococcus lactis from Streptococcus fecatis. Further work on this problem will be reported in another paper, but it may be stated now that other tests have been found which clearly differentiate these two species. The liquefacies group As has been noted by Orla-Jensen, Streptococcus glycerinaceus and Streptococcus liquefaciens are practically identical in the fermentation of test substances, but the outstanding difference is that Streptococcus liquefaciens liquefies gelatin and digests casein while Streptococcus glycerinaceus does not. Included in our study

9 STREPTOCOCCI WHICH GROW AT HIGH TEMPERATURES 283 were eight cultures of the liquefaciens type which were isolated from milk. MacCallum and Hastings (1899) described a new organism from a case of acute endocarditis as Micrococcus zymogenes. They stated that the organism had points of resemblance to the pneumococcus and Streptococcus pyogenes on the one hand and to the pyogenic staphylococci on the other. While the fermentation tests and blood agar were not in vogue at that time, the description of these workers is excellent in bringing out clearly the cultural and physiological characteristics of the organism. The proteoly- TABLE 4 Liquefaciens group GROWTH FERMENTATION OF: 0 Streptococcus liquefaciens Milk. 8j Gamma FF* Streptococcus zymogee Humanfeces.j12IBeta +j4.3j+j+j * Seventy-five per cent of these cultures did not grow at 60 C. sis of gelatin and milk was noted. The strong reducing action of the organiism in litmus milk was described, the significant point being noted that the litmus is reduced before acidulation and coagulation of the milk. MacCallulm and Hastings also noted that growth was more profuse on glycerol agar than on plain nutrient agar, which indicates that this substance was utilized. In1 a recent study of this organismn Frobisher and Denny (1928) conclude that it should be classified as a streptococcus, perhaps as a variety of Streptococcus l iquefaiens. The cultures of Streptococcus zymogenes studied by us were all isolated from the feces of one person who was suffering from a temporary but severe attack of diarrhea.

10 284 Streptococcus zymogenes (table 4) resembles Streptococcus liquefaciens in that both reduce litmus before curdling the milk, liquefy gelatin and casein, have a final ph of about 4.2, grow at 100C. and 450C., produce ammonia from peptone, ferment glucose, maltose, lactose, sucrose, raffinose, glycerol, mannitol, and salicin, but do not ferment inulin and starch. These types differ in that zymogenes hemolizes blood and ferments arabinose while the liquefaciens type does not. SUMMARY A study was made of 294 cultures of streptococci from milk and other sources which grow actively at 450C. The most prevalent types were Streptococcus thermophilus, Streptococcus bovis, Streptococcus inulinaceus, Streptococcus fecalis, Streptococcus glycerinaceus, Streptococus liquefaciens, and Streptococcus zymogenes. Streptococcus thermophilus does not hemolyze blood; r.educes litmus milk slightly after coagulation; does not produce ammonia from peptone; grows at 500C. but not at 100C.; grows slowly at room temperature; ferments glucose, lactose, and sucrose; does not ferment maltose, inulin, mannitot, glycerol nor salicin; and may or may not ferment raffinose and arabinose. Its resistance to pasteurization is greater than that of the other types studied. When these cultures are grown in milk, long chains are formed. Streptococcus bovis does not hemolyze blood; does not reduce litmus before coagulation of milk; does not grow at 100C. nor at 500C., but does grow at 450C.; ferments arabinose, glucose, maltose, lactose, sucrose, raffinose, salicin, and hydrolyzes starch; does not ferment glycerol; but may or may not ferment inulin and mannitol. Streptococcus inulinaceus differs from Streptococcus bovi in that it always ferments inulin, but does not ferment arabinose, while starch is hydrolyzed only faintly. Streptococcus fecalis does not hemolyze blood; reduces litmus before curdling the milk; grows at 100C., 450C., and often slowly at 500C.; produces ammonia from peptone; ferments arabinose, glucose, maltose, lactose, and salicin; does not ferment raffinose, inulin, and glycerol; does not hydrolyze starch; may or may not

11 STREPTOCOCCI WHICH GROW AT HIGH TEMPERATURES 285 ferment sucrose, and mannitol; and does not digest casein nor liquefy gelatin. Streptococcus glycerinaceus differs from Streptococcus fecalis in that it ferments glycerol and always ferments sucrose. Glycerinaceus usually does not curdle milk as rapidly as fecalis. Streptococcus liquefaciens does not hemolyze blood; reduces litmus before curdling the milk; grows at 100C., 450C., and may or may not grow at 500C.; produces ammonia from peptone; ferments glucose, maltose, lactose, sucrose, raffinose, glycerol, mannitol and salicin; does not ferment arabinose and inulin; does not hydrolyze starch; but liquefies gelatin and digests casein. Streptococcus zymogenes differs from Streptococcus liquefaciens in that it is beta-hemolytic and ferments arabinose. In view of the present state of our knowledge it might be better to consider Streptococcus inulinaceus, Streptococcus glycerinaceus and Streptococcus zymogenes as only varieties of Streptococcus bovis, Streptococcus fecalis and Streptococcus liquefaciens respectively. This, however, is a matter of opinion which should be left to the specialists in taxonomy. All of the species of streptococci described in this study survive heating for thirty mmutes at 62.80C. in milk. REFERENCES ANDREWES, F. W., AND HORDER, T. J. (1906) Lancet, 171, ; ; AYERS, S. HENRY, AND MUDGE, COURTLAND S. (1922) Jour. Infect. Dis., 31, AYERS, S. HENRY, AND MUDGE, COURTLAND S. (1923) Jour. Infect. Dis., 33, AYERS, S. HENRY, AND JOHNSON, W. T., JR. (1924) Jour. Infect. Dis., 34, FROBISHER, MARTIN, JR., AND DENNY, E. R. (1928) Jour. Bact., 16, HUCKER, G. J. (1928) New York State Agr. Exp. Sta., Tech. Bul MACCALLUtM, W. G., AND HASTINGS, T. W. (1899) Jour. Exp. Med., 4,521. ORLA-JENSEN, S. (1919) Mem. Acad. Roy. Sci. et Lett. de Denmark, Copenhagen. Sect. d. Sci., 8, Ser., 5, ROBERTSON, A. H. (1927) New York State Agr. Exp. Sta., Tech. Bul SHERMAN, J. M., AND ALBUS, W. R. (1918) Jour. Bact., 3,