Studies on Hemolytic Streptococci: I. Methods of Classification

Some observations on the classification of enterococci

An investigation of enterococci from human and bovine sources by the method of Lancefield (1933) shows that they possess a specific antigen by which the enterococcus group can be defined.

The validity of this method as a means of differentiating the enterococcus from other groups of streptococci is confirmed by the biochemical and other properties, such as the association of mannitol fermentation with heat resistance of the starins used, which already differentiate the group in some degree. The tests for susceptibility to lysis by bacteriophages, carried out during the present investigation, are also confirmatory of the results obtained by the precipitin method.

As the specific antigen characteristic of enterococci cannot be demonstrated in strains representative of groups A, B, C, (Lancefield, 1933) andStr. lactis(Lister, 1873) it is concluded that these are unrelated to the enterococcus.

A number of other streptococci, however, includingStr. zymogenes(MacCallum & Hastings, 1899),Str. liquefaciens(Orla-Jensen, 1919), and group D haemolytic streptococcus (Lancefield, 1933) have been shown to possess an antigen in common with the enterococcus, as well as the other properties of enterococci, including susceptibility to lysis by bacteriophages; these are usually considered as distinct species, but reasons are advanced in the present communication for regarding them as varieties of enterococci.

The name group D haemolytic streptococcus of Lancefield, is unnecessary and may give rise to confusion. As an enterococcus, it possesses no characteristic antigenic, or haemolytic or other property which differentiates it from thezymogenesorhaemolyticusvarieties of enterococci referred to in this communication.

The more important growth characters and fermentation and other properties of the enterococci, classifield by the precipitin method in this investigation, may be summarized as follows; ability to grow at 10 and at 45°C., in broth containing 6·5% NaCl, in broth of pH 9·6, to produce chains in pure bile, to produce a final pH in 1% glucose broth of 4–4·2, to reduce methyleneblue, and to ferment trehalose, sorbitol and salicin; but deficiency in one or more of these properties was occasionally noted.

The differentiation ofStreptococcus cremorisandStreptococcus lactisby means of bacteriophage action

1. A series of lactic streptococci which were almost all capable of clotting milk in 24 hr. at 22°C. were divided into two groups on the basis of a few simple biochemical and morphological tests. The two groups corresponded to what some workers consider to be the speciesStr.lactisandStr.cremoris.

2. A series of phage races were tested for their action on the streptococci under various temperature and growth conditions.

3. The characteristics of phage attack on the organisms tended to confirm the division intoStr.lactisandStr.cremorisspecies. Each of the strains of the long-chainedcremoristype was attacked by only a few phages at the most, sometimes by a single phage only, whereas each of thelactis(short-chained) strains was attacked by a variety of phages. Furthermore, with two exceptions, the phage attacking thecremoristypes on the one hand and thelactistypes on the other formed quite separate and distinct groups.

4. None of the phages acted upon the several available strains ofStr.faecalisand other group D (Lancefield) streptococci.

5. The evidence obtained from the phage sensitivity tests seems to justify the division of the lactic streptococci into two species,Str. lactisandStr. cremoris.

The author is indebted to Dr H. R. Whitehead for his interest in this work, and for helpful criticism and advice.

Genomic sequence of C1, the first streptococcal phage

C(1), a lytic bacteriophage infecting group C streptococci, is one of the earliest-isolated phages, and the method of bacterial classification known as phage typing was defined by using this bacteriophage. We present for the first time a detailed analysis of this phage by use of electron microscopy, protein profiling, and complete nucleotide sequencing. This virus belongs to the Podoviridae family of phages, all of which are characterized by short, noncontractile tails. The C(1) genome consists of a linear double-stranded DNA molecule of 16,687 nucleotides with 143-bp inverted terminal repeats. We have assigned functions to 9 of 20 putative open reading frames based on experimental substantiation or bioinformatic analysis. Their products include DNA polymerase, holin, lysin, major capsid, head-tail connector, neck appendage, and major tail proteins. Additionally, we found one intron belonging to the HNH endonuclease family interrupting the apparent lysin gene, suggesting a potential splicing event yielding a functional lytic enzyme. Examination of the C(1) DNA polymerase suggests that this phage utilizes a protein-primed mechanism of replication, which is prominent in the phi29-like members of Podoviridae. Consistent with this evidence, we experimentally determined that terminal proteins are covalently attached to both 5' termini, despite the fact that no homology to known terminal proteins could be elucidated in any of our open reading frames. Likewise, comparative genomics revealed no close evolutionary matches, suggesting that the C(1) bacteriophage is a unique member of the Podoviridae.

Studies on bacteriophages of hemolytic streptococci. I. Factors influencing the interaction of phage and susceptible host cell

The host ranges of bacteriophages for group A, types 1, 6, 12, and 25 and group C streptococci have been determined. The findings indicate that the susceptibility to these phages is primarily a group-specific phenomenon, although it is modified by several factors such as the hyaluronic acid capsule, lysogeny, and possibly the presence of surface proteins. Phage antibody studies indicate that while the group A phages are antigenically related, they are distinct from the group C phage. This is in agreement with the observation that group A phages are not specific for their homologous streptococcal types. The purified group C carbohydrate inactivates group C phage but not the group A phages, thus suggesting that the carbohydrate, a component of the cell wall, may serve as the phage receptor site. It has not been possible to inactivate the group A phages with group A carbohydrate. Phage lysis of groups A and C streptococci is accompanied by fragmentation of the cell wall since the C carbohydrate has been identified serologically and chemically in the supernate of centrifuged lysates. The immediate lysis of groups A and C hemolytic streptococci and their isolated cell walls by an accesory heat-labile lytic factor in fresh group C lysates is also described.

Study of Red Halophilic Bacteria in Solar Salt and Salted Fish: II. Bacto-oxgall as a Selective Agent for Differentiation

A simple method, based on oxgall tolerance, is proposed for differentiating red halophilic bacteria commonly found in solar salt and discoloured salted codfish. Tests carried out on 18 strains isolated from various sources have shown that the rod forms are inhibited by low concentrations of Bacto-oxgall and that the coccus forms tolerate relatively high ones. Bacto-oxgall can thus be used as the basis of a simple selective medium. This test has been found useful for the isolation, purification and partial identification of unidentified strains and also for determining the relative proportions of the two main types of red halophilic bacteria present in solar salt and salted fish samples.