SEROLOGICAL RELATIONSHIPS BETWEEN SHIGELLA ANDCOLIFORM CULTURES

W. H. EWINGCommunicable Disease Center, Public Health Service, Federal Security Agency, Atlanta,

GeorgiaReceived for publication March 9, 1953

Definitive studies of the serological relation-ships between members of the E&chericki coligroup and other groups within the family Enter-obacteriaceae were made possible by the differen-tiation of the thermolabile and thermostablesomatic antigens of E. coli cultures (Kuffmann,1943, 1944a) and the subsequent introductionand establishment of the Kauiffmann-Knipschild-Vahlne antigenic schema. As introduced by Kauff-mann (1944b, 1947), the diagnostic schema con-sisted of the 25 0 antigen groups that occurredmost frequently, 55 thermolabile envelope or Kantigens, and 20 agellar or H antigens. The E.coli schema now consists of 124 0 antigen groups,60 K antigens, and 33 H antigens. E. coli cul-tures now may be typed accurately by determina-tion of their 0, K, and H antigens. For furtherdiscussion of the E. coli group and of typingmethods, the reader is referred to the publica-tions of Kuffmann (1947, 1951a, b), Kauffmannand Dupont (1950), and 0rskov (1952).

Wheeler and Stuart (1946) reported that thesomatic antigens of two coliform microorganiwere identical with those of Shigella dysenteriae3 and called attention to a relationship betweenthe antigens of Shigella dywnteriae 1 and thoseof Alkalescens-Dispar 0 group 1 (ShigeUa alka-lescens). These investigators tested 14 alkalescens-Dispar 0 group 1 cultures in eight S. dywnteriae1 antiserums and obtained agglutinative titerswhich varied from 1:160 to 1:5, 120. When S.dysen&eriae 1 cultures were tested in Alkalescens-Dispar 0 group 1 antiserums and in antiserumsprepared with certain other coliform bacteria,positive but weaker reactions were obtained.This relationship also was noted by Wheeleret al. (1946) and was confirmed by the writer.

In 1947, Ferguson and Henderson described acoliform bacterium, culture C27, that possessedsomatic antigens identical with those of form I(smooth) Shigella sonnei. The writer confirmedthis relationship and also found that the 0antigens of C27 and of S. sonnei cultures were

not related to any of the 124 E. coli 0 antigengroups. Early in 1952 a culture (602-52) similarto C27 was received from Dr. Vandepitte whoisolated it in Belgian Congo from a patient withdysentery, from whom S. 8onnei also was iso-lated. Ferguson (1952) stated that cultures similarto C27 have been isolated in Michigan since 1947and that they occurred in association with S.8onnei in some cases. Another culture of thistype was received recently from Dr. E. Schmid,Colombo, Ceylon.

Veazie (1950) reported that close antigenic re-lationships existed between cultures of Shigellaboydii 4 and E. coli 0 group 53 and betweenS. boydii 5 and E. coli 0 group 79. The writerconfirmed this report and found that the 0antigens of S. boydii 4 and S. boydii 5 were iden-tical with those of E. coli 0 group 53 and 79, re-spectively, as demonstrated by reciprocal ag-glutinin adsorption tests. These results were con-firmed by Kauffmann (1950) and by Odden(1951), who also reported that the 0 antigens ofS. dywenriae 5 cultures were identical withthose of E. coli 0 group 58 and that those ofS. boydii 2 and E. ccli 0 group 87 were relatedclosely but were not identical. Odden's resultswere confirmed in this laboratory in connectionwith studies on the thermolabile somatic antigenof S. boydii 2 cultures (Ewing et al., 1951a).Ewing et al. (1951b, c) reported that the 0

antigens of provisional S. boydii 9 and E. coli 0group 102 bore a strong reciprocal relationshipand that the 0 antigens of provisional S. boydii10 and E. coli 0 group 105 cultures were relatedsimilarly. They also reported that the 0 antigensof provisional S. boydii 11 were identical withthose of E. coli 0 group 105. Ewing, Hucks, andTaylor (1952) reported that the 0 antigens ofS. dysentriae 2 and Shigella serotype 703 wereidentical with those of E. coli 0 groups 112a,112c, and 112a, 112b, respectively. The relation-ships of the 0 antigens of Shigella serotypes 3873-50, 425, 123, and 2770-51 to E. coli 0 antigen

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groups (table 1) were reported by Ewing andHucks (1952).

In the present study, the 0 antigens of 331known Shigella serotypes were compared withthose of 124 E. coli groups and those of certainstrains of intermediate coliform bacteria. A num-ber of relationships in addition to those reportedearlier were found. The methods used in thisstudy were the same as those employed previouslyby the writer and co-workers (1951a, b, 1952)and were based upon the recommendations ofKauffmann (1947, 1951a, b).Four distinct classes of major relationships

were noted in the study. The first was 0 antigenidentity, as demonstrated by reciprocal agglutininadsorption tests. There were 10 instances inwhich the 0 antigens of Shigella serotypes werefound to be identical with those of coliform cul-tures (table 1). In eight of these instances the re-lationships involved established E. coli 0 antigengroups, and in two instances intermediate oraberrant coliform cultures were concerned. Theresults of reciprocal agglutinin adsorption testsperformed with 0 antigens and 0 antiserums pre-pared with cultures of S. dysenteriae 3 and E.coli 0 group 124 are given in table 2 as an exampleof this class of reciprocal relationship. The cul-tures were cross agglutinated to the titer of theO antiserums, and all agglutinin was removedfrom the antiserums in reciprocal agglutinin ad-sorption tests (table 2).The first six cultures of the bacterial type re-

ferred to as E. coli 0 antigen group 124 wereisolated in Italy by the author during 1944 and1945. Their relationship to S. dysenteriae 3 wasnoted at the time of isolation. Three of the strainswere studied by Wheeler and Stuart (1946) whoreported that the cultures contained a Vi-likeantigen. Six additional cultures were collectedfrom England, Brazil, and the United Statesso that 12 strains were available for this study.The biochemical reactions given by these 12cultures were like those given by typical E. colicultures except that one strain (336) was posi-

1 In this enumeration of known Shigella sero-types, it is considered that there are only six Shi-gellaflexneri serotypes. Sub-serotypes, such as S.flexneri la and lb are not counted individually.If sub-serotypes were considered individually,there would be at least 11 S. flexneri types and atotal of 38 Shigella serotypes.

tive in Simmons' citrate agar after two days andseveral cultures did not utilize lactose until afterseveral days' incubation. Two of the cultureswere anaerogenic. The results of reciprocal ag-glutinin adsorption tests indicated that the 0antigens of the 12 strains were identical. The Hantigens of three of the cultures, including thetype culture no. 227, were found to be E. coliH antigen 32. Three cultures contained unidenti-fied H antigens, and six of the cultures werenonmotile. That 0 group 124 cultures contain Kantigen was evidenced by the inagglutinabilityof living suspensions of most of them in 0 anti-serum. However, the K antigens of these cul-tures were not studied in detail. The 0 antigensof the 12 cultures were not related to those ofany of the 123 E. coli 0 antigen groups and hencewere given the designation 0 antigen group 124.It should be noted that the bacterium describedby Hobbs, Thomas, and Taylor (1949) under thedesignation paracolon 411 belonged to E. coliO group 124. These investigators isolated cul-tures of this bacterial type in outbreaks andsporadic cases of gastroenteritis and cited evi-dence that the microorganisms were the probablecause of the disease in these cases. Further,Sanders (1952) reported that cultures of this 0group were isolated from outbreaks and sporadiccases of acute diarrhea in Japan during the pe-riod 1948 to 1951.

Further examples of 0 antigen identity werethe relationships of coliform culture C27 to S.sonnei, mentioned above, and that which wasdemonstrated between S. dyseneriae 4 and ananaerogenic coliform bacterium, culture no. 3588-51. The 0 antigens of culture no. 3588-51 werenot related to those of any of the 124 E. coli 0groups. Seeliger (1952) isolated cultures of inter-mediate coliform bacteria that were related sero-logically to S. dysenteriae 4. The writer examinedSeeliger's cultures and found that heated antigensprepared from them were agglutinated by S.dysentriae 4 antiserum in a dilution of 1:2,560(homologous titer 1:10,240) but were not re-lated to 0 antigens 1 to 124 of the E. coli group.

In addition to 0 antigen identity, two othertypes of strong reciprocal relationships were notedbetween Shigella serotypes and E. coli or coli-form 0 antigens. The first of these, illustrated bythe 0 antigens of S. boydii 3 and E. coli 0 group85 (table 3), was referred to, arbitrarily, as an

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TABLE 1

Relationship of the heat stable antigens of Shigella serotypes and provisional Shigella serotypes to those ofcoliforrm cultures

SEIGELLA OLDR DESIGNATIONS RLATE TO RSCERICHA COLI 0 GROup(S)OR TO COLIPORM CULTURES

Subgroup AShigella dysenteriae 1 Shiga's bacillus 1, reciprocal, a,b - a,c; 120, unilateral

2 S. schmitzii, S. ambigua 112 a,c, identical3 Q771 124, identical4 Q1167 88, unilateral; coliform 3588-51, iden-

tical5 Q1030 58, identical6 Q454 No relationship, 1-124; related coli-

form*7 Q902 121, reciprocal, a - a,b

(Provisional) 8 Serotype 599-52 38, reciprocal, a,b,c - a,b; 23, a,dSerotype 58 No relationship, 1-124Serotype 3873-50 29, reciprocal, a - a,bSerotype 2050-52 No relationship, 1-124

Subgroup BShigella flexneri la V 1, 19a, 62, 69, 73

lb VZ 1, 16, 19a, 62, 69, 732a W 13, a,b - a,c2b WX 13, a,b-a,c; 733 (III:6,7,8) Z 13,163 (111:3,4,6,7,8) 13, 163 (III:6) 13, 164a 103 1,134b 103Z 134 Rabaul 1, 17, 19a, 735 P119 13, 166 88 3438-51, a,b - a,c; 19a

X variant 1, 13, 19, 50Y variant 1, 13, 19, 50

Subgroup CShigella boydii 1 170 50, reciprocal, a,b - a,c

2 P288 87, reciprocal, a,b - a,c; 96, reciprocal,a,b - a,c

3 DI 85, reciprocal, a,b - a,c4 P274 53, identical5 P143 79, identical6 D19 76, reciprocal, a,b - a,c7 Lavington, Etousa No relationship, 1-124

(Provisional) 8 112 114, minor(Provisional) 9 102, reciprocal, a,b - a,c(Provisional) 10 105, reciprocal, a,b - a,c(Provisional) 11 105, identicalSerotype 425 98, reciprocal, a,b-a,cSerotype 703 112, a,b, identicalSerotype 2770-51 32, identical; 83, reciprocal, a,b - a,cSerotype 123 (and "M") 7, reciprocal, a,b,c - a,d (M - a,b)

Subgroup DShigella sonnei No relationship, 1-124, identical 0

antigen of coliform C27

* Two intermediate coliform cultures were received from Dr. Seeliger (1952), who stated that theywere related to S. dysenteriae 6. The writer confirmed the fact that the coliform cultures were aggluti-nated strongly by S. dysenteriae 6 antiserum but did not pursue the investigation since it was assumedthat Dr. Seeliger would made a detailed investigation.

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a,b - a,c2 relationship. The two cultures shareda common antigen, labeled a, and each culturecontained a specific factor, labeled b and c, re-spectively. There were at least 14 instances(table 1) in which the 0 antigens of Shigellaserotypes were found to be related to those ofE. coli or other coliform bacteria in this manner.

6 cultures and those of E. coli 0 group cultures;these relationships will be discussed later.The other variety of strong reciprocal rela-

tionship, called the a - a,b type, was illustratedby the relationship noted between the 0 antigensof Shigella serotype 3873-50 and E. coli 0 group29 cultures (table 4). Again, the cultures con-

TABLE 20 antigen identity

The relationship of Shigella dysenteriae 8 and Escherichia coli 0 group 124

0 ANTISERUMS

0 ANTIGEN SUSPENSIONS (100 C, IEHRt) ShigeJla dysenteriae 3 Esclsericlsia coli 0 Group 124

Adsorbed AdsorbedUnadsorbed by Escherickia Unadsorbed by ShigeUa

coli 0124 dysers#i 3

Shigella dysenteriae 3.............................. 5,120 0 5,120 0Escherichia coli 0 group 124.................... 5,120 0 5,120 0

TABLE 3A reciprocal relationship

The 0 antigenic relationship of Shigella boydii 3 and Escherichia coli 0 group 85

0 ANTISERUMS

0 ANTIGEN SUSPENSIONS (100 C, 1 ]RR) SkilcUa boydii 3 Esckerichia coli 0 group 85

Adsorbed AdsorbedUnadsorbed by Esckerichia Unadsorbed by Skidlia

coli 085 boydis 3

Shigella boydii................................... 5,120 2,560 5,120 0Escherichia coli 0 group 85....................|. 2,56 0 10,240 2,560

TABLE 4A reciprocal relationship

The 0 antigenic relationship of Shigella serotype 3873-50 and Escherichia coli 0 group 29

0 ANTISERUMS

0 ANTIGEN SUSPENSIONS (100 C, 1 Ext) Skig.laserotype 3873-50 Rsckeckia coli 0 grup 29

Adsorbed AsreUnadsorbd by Esckerickia Unadorbed by 3873-50.~~~~~cl 029

Shigella serotype 3873-50.......................... 5,120 640 20,480 0Escherichia coli 0 group 29....................... 5,120 0 20,480 0

In two of the instances the relationship concernedthe 0 antigens of Shigella flexneri 2 and S. flezneri

2 These arbitrary formulas were used merely asan aid to make the relationships clearer and shouldnot be interpreted as permanent designations forthe antigens involved.

tained a common factor, designated a, but onlyone of the cultures contained a special factor.In the example (table 4), the Shigella serotypecontained an additional factor (b) that remainedin its antiserum after adsorption with the E.coli 0 group 29 culture. The E. coli 0 group 29culture did not contain any 0 antigenic factor

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SEROLOGICAL RELATIONSHIPS BETWEEN SHIGELLA AND COLIFORM

that was not present in the Shigella serotypesince all agglutinin was removed from the E.eoli 0 group 29 antiserum when it was adsorbedwith the Shigella culture. Two other examples ofthe a -a,b relationship were noted between the0 antigens of cultures of S. dysenteriae 7 and E.coli 0 group 121 and between E. coli 0 group 38and provisional S. dysenteriae 8 (Ewing et al.,1952). The 0 antigens of provisional S. dysen-triae 8 strains also were related to those of E.coli 0 group 23. These 0 antigenic relationshipswere expressed in an arbitrary formula as follows:

Provisional S. dysenriae 8 a,b,cE. coli 0 group 23 a,dE. coli 0 group 38 a,b

The fourth class of 0 antigenic relationship wasthe unilateral variety in which a ShigeUa sero-

(1952). Except for a slight relationship to S.dysenriae 2, serotype 2050-52 was found to beunrelated to known ShigeUa serotypes. It didnot utilize mannitol nor produce indole.Members of the S. Jlexneri subgroup were

found to be related to E. coli 0 group cultures inseveral ways. Some of the relationships wereminor and a few were unilateral but several werequite strong and extensive. It was established thatwhile 0 antigen suspensions prepared with S.flexneri serotypes usually were not agglutinatedstrongly by E. coli 0 group antiserums, severalE. coli 0 group cultures reacted to high titers incertain of the S. flexneri antiserums. Except forthose which existed between E. coli 0 groups andS. flexneri serotypes 2 and 6, the relationshipslisted in table 1 were not investigated beyond thedetermination of their reciprocal nature. How-

BLE 5A nonreciprocal relationship

The relationship of the 0 antigens of Shigella dysenteriae 4 and Escherichia coli 0 group 88

0 ANVSZISEEt

0 ANTIGEN SUSPENSIONS (100 C, 1 M) Skigella dysenteiae 4 Esclwickia coli 0 group 88Adsorbed Adsorbed

Unadsorbed by Eschericsia Unadsorbed by Suige4lacoli 088 dysenteriae 4

Shigella dysenteriae 4............................. 5,120 5,120 10,240 0Escherichia coli 0 group88.0 0 10,240 10,240

type was found to be agglutinated by an E. coli0 antiserum, but the E. coli 0 group culture didnot react in antiserum prepared with the Shigellaserotype. Such unilateral relationships were foundbetween the 0 antigens of S. dysenreiae 4 andE. coli 0 group 88 (table 5) and between the 0antigens of S. dyeentriae 1 and E. coli 0 group120.Of the 33 known Shigella serotypes, only four

contained 0 antigens unrelated to described E.coli 0 antigen groups or to the 0 antigens of thecoliform bacteria that were investigated (table1). These were Shigella serotype 58 (Cox andWallace, 1948), Shigella serotype 2050-52, S.boydii 7, and provisional S. boydii 8. A minor 0antigen relationship was noted between pro-visional S. boydii 8 and E. coli 0 group 114 cul-tures, but it was regarded as unimportant.Shigella serotype 2050-52 was isolated from adysenteric stool in Belgian Congo by Vandepitte

ever, preliminary results indicated that in somecases the group antigens of the S. flexneri sero-types were involved in the relationships whilein other instances portions of the type antigenappeared to be involved. Since the relationshipsof S. flexneri serotypes to E. coli 0 groups arecomplicated and since it is thought that a thor-ough study of them might lead to a clearer under-standing of intragroup relationships within theS. flexneri subgroup itself, it is planned to makethese relationships the subject of another studyand of a separate paper.The 0 antigens of S. flexneri 6 cultures proved

to be related to those of E. coli 0 group 19 in amanner similar to that described above as thea,b - a,c type and illustrated in table 3. Funda-mentally, the relationship of S. flexneri 2 cul-tures to E. coli culture 537-52 (E. coli 0 group 13)also was of the a,b - a,c variety and involved thetype antigen of S. flexneri 2 cultures (table 6).

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E. coli culture 537-52 was found to belong toE. coli 0 group 13, but its 0 antigens were notidentical with those of the type culture of 0group 13. The following arbitrary formulas maybe used to explain these relationships: E. coli 0group 13 - 013a, 013b; culture 537-52 - 013a,013c. Heated suspensions of culture 537-52, S.flexneri 2a, and S. Jlexneri 2b were cross agglu-tinated strongly by both S. flexneri 2 antiserumsand by an 0 antiserum prepared with E. coliculture 537-52 (table 6). Further, 0 antigen sus-pensions of culture 537-52 were agglutinated byan adsorbed S. Jlexneri 2 antiserum which wasprepared for typing cultures of that serotype.Adsorption of S. flexneri 2a antiserum by culture537-52 resulted in removal of agglutinin for S.flexneri 2b, for the adsorbing culture, and in re-

glutinin for both S. flexneri 2a and culture 537-52remained while agglutinin for the adsorbing strainwas removed. These results were explained by theuse of arbitrary formulas as follows:

S. flexneri 2a a,b,dS. flexneri 2b a,cE. coli no. 537-52 a,d

All of these cultures contained a factor in com-mon, labeled a, which was interpreted as repre-senting the type antigen of S. flexneri 2 serotypes.Cultures of S. flexneri 2a contained a component(b) that was not present in cultures of S. flexneri2b or in culture 537-52; this factor was a portionof the group antigen complex of S. flexneri 2astrains. S. flexneri 2b cultures contained a similarfactor which was labeled c in the formulas given

TABLE 6Relationship of the 0 antigens of Shigella flexneri 2 and culture 637-62 (Escherichia coli 0

group 13)0 ANTISERUMS

Shigela Jiexueri 2a Shigella flexueri 2b Escherclsia coli no. 537-520 ANTIGEN SUSPENSIONS (100 C, 1 XI)

|Un- | Adsorbed Adsorbed Adsorbed byadsoirbed by no. adsr-e by no- Un-dsorbed__adsorbed S37-52 adobd S,igua Shigeiaf|lexnei 2a fJexuei 2b

Escherichia coli no. 537-52 (E. coli 0group 13)............................. 20,480 0 20,480 0 20,480 0 2,560

Shigella flexneri 2a...................... 20,480 1,280 20,480 0 5,120 0 640Shigellaflexneri 2b...................... 20,480 0 20,480 1,280 5,120 0 0

duction of the titer for the homologous S. flexneri2a culture from 1:20,480 to 1,280 (table 6).Similar results were obtained when S. flexneri2b antiserum was adsorbed with a suspension ofE. coli culture 537-52 except that, in this in-stance, agglutinin for S. flexneri 2b remained inthe adsorbed antiserum. It was clear that onlygroup factor agglutinin remained in thesetwo antiserums following adsorption withculture 537-51 since S. flexneri 2b cultures didnot react in the former adsorbed antiserum andS. flexneri 2a cultures were not agglutinated bythe latter. In the reciprocal agglutinin adsorp-tion tests, adsorption of 0 antiserum preparedwith culture 537-52 by S. flexneri 2a resulted inthe removal of all agglutinin from the antiserum(table 6). When antiserum for culture 537-52 wasadsorbed with a culture of S. flexneri 2b, ag-

above. Factor c represented the group factorcomplex of S. flexneri 2b cultures. Since adsorp-tion of antiserum for culture 537-52 by a cultureof S. flexneri 2a resulted in the removal of allagglutinin from the antiserum, it was clear thatculture 537-52 contained no 0 antigen that wasnot also present in S. flexneri 2a cultures. Thatculture 537-52 contained an 0 antigenic factor inaddition to the type antigen (factor a, above)of S. flexneri 2 cultures was indicated by the factthat S. flexneri 2a cultures, as well as culture537-52, continued to react in antiserum 537-52after it was adsorbed by S. flexneri 2b (table 6).This factor was designated d and was interpretedas representing a portion of the group antigencomplex of S. Jlexneri 2a cultures. That factor ddid not represent the entire group antigen com-plex of S. J&exneri 2a cultures was shown by the

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1953] SEROLOGICAL RELATIONSHIPS BETWEEN SHIGELLA AND COLIFORM 339

adsorption test mentioned above wherein ag-glutinin (factor b) remained in S. flexneri 2aantiserum after all agglutinin for culture 537-52was removed. Further proof that this interpreta-tion of these results was correct was obtainedfrom slide agglutination tests using the abovementioned adsorbed antiserumns and suspensionsof all S. flexneri serotypes. From a knowledge ofthe group antigens of S. .texneri cultures it waspossible to predict accurately which serotypeswould react and which would not.The studies reported here afford ancillary evi-

dence in favor of the view that the family Enter-obactriaceae is a large, closely interrelated groupin which there is a community of antigenic fac-tors. The arbitrary groups or genera within thefamily are not demarcated sharply but ratherappear to be only areas of dense population in alarger community of serologically and biochemi-cally related bacteria. While a considerable vol-ume of work on the relationship of the variousgroups within the family Enterobacteriaceae hasbeen reported, it is obvious that it represents onlya beginning and that much further investigationis indicated. Although such studies are of con-siderable academic interest and importance, itshould be stressed that knowledge of relation-ships such as those reported above is of impor-tance from the practical point of view as well.In the identification of an unknown enteric bac-terium one cannot rely entirely on serology, norcan identification be made on the basis of bio-chemical reactions alone. Both methods must beemployed for accurate identification. Biochemicalreactions are used to determine the group andsubgroup to which a culture belongs, and serologyis employed to determine the serotype. Quiteoften anaerogenic and microaerogenic E. colicultures are isolated which do not utilize lactoseor sucrose promptly and hence give the appear-ance of shigellae on triple sugar iron agar andsimilar mediums. If such cultures are examinedonly by serological methods, the chance of erroris great. Culture 537-52, mentioned above, is anexcellent example. This culture was identified asa member of the S. flexneri subgroup and wassubmitted to this laboratory with a request fortype determination. Serologically, culture 537-52appeared to be S. Jlezneri 2a, but biochemicaltests indicated that it was an E. coli culture that

fermented lactose slowly and produced small gasvolumes.

ACKNOWLEDGMENT

Thanks are extended to Dr. Fritz Kauffmannof the International Salmonella and EscherichiaCenter, State Serum Institute, Copenhagen, forconfirmation of most of the relationships hereindescribed.

SUMMARY

The relationships between the 0 antigens of33 known Shigella serotypes on the one hand andof 124 Escherichia coli 0 antigen groups and ofcertain coliform cultures on the other were stud-ied and reported. The 0 antigens of 10 Shigellaserotypes were found to be identical with thoseof E. coli 0 group cultures or with those of inter-mediate coliform bacteria. Seventeen additionalShigeUa serotypes bore a strong reciprocal 0antigen relationship to E. coli 0 groups and coli-form bacteria whereas two others were related toE. coli 0 antigen groups in unilateral, nonrecipro-cal relationships. Of 33 known Shigella serotypes,the 0 antigens of only four were unrelated to E.coli 0 groups or to 0 antigens of the coliformbacteria that were investigated. An additionalE. coli 0 antigen group (124) was determinedduring the investigation.

Attention was called to the need for furtherwork on relationships within the enteric groupof bacteria, and the importance of such rela-tionships as those described to diagnostic workwas stressed.

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