Elevated cell wall serine in pleiotropic staphylococcal mutants

Preparation of Cell Wall Antigens of Staphylococcus aureus

Cell walls were prepared from Staphylococcus aureus strains Copenhagen and 263 by high-speed mixing in the presence of glass beads followed by differential centrifugation. Insoluble peptidoglycan complexes were derived from cell walls by extraction of teichoic acid with 10% trichloroacetic acid. Intact teichoic acid was prepared from each strain by digestion of cell walls with lysostaphin and isolated by column chromatography. Soluble glycopeptide (peptidoglycan in which only the glycan has been fragmented) and the stable complex of teichoic acid with glycopeptide were prepared by digestion of cell walls with Chalaropsis B endo-N-acetylmuramidase and were separated by column chromatography. Amino acid and amino sugar contents of walls and subunits of walls were comparable to those reported by others.

The lysostaphin endopeptidase resistance gene (epr) specifies modification of peptidoglycan cross bridges in Staphylococcus simulans and Staphylococcus aureus

Staphylococcus simulans biovar staphylolyticus produces an extracellular glycylglycine endopeptidase (lysostaphin) that lyses other staphylococci by hydrolyzing the cross bridges in their cell wall peptidoglycans. The genes for endopeptidase (end) and endopeptidase resistance (epr) reside on plasmid pACK1. An 8.4-kb fragment containing end was cloned into shuttle vector pL150 and was then introduced into Staphylococcus aureus RN4220. The recombinant S. aureus cells produced endopeptidase and were resistant to lysis by the enzyme, which indicated that the cloned fragment also contained epr. Treatments to remove accessory wall polymers (proteins, teichoic acids, and lipoteichoic acids) did not change the endopeptidase sensitivity of walls from strains of S. simulans biovar staphylolyticus or of S. aureus with and without epr. Immunological analyses of various wall fractions showed that there were epitopes associated with endopeptidase resistance and that these epitopes were found only on the peptidoglycans of epr+ strains of both species. Treatment of purified peptidoglycans with endopeptidase confirmed that resistance or susceptibility of both species was a property of the peptidoglycan itself. A comparison of the chemical compositions of these peptidoglycans revealed that cross bridges in the epr+ cells contained more serine and fewer glycine residues than those of cells without epr. The presence of the 8.4-kb fragment from pACK1 also increased the susceptibility of both species to methicillin.

Relationship between lysostaphin endopeptidase production and cell wall composition in Staphylococcus staphylolyticus

Mutants of Staphylococcus staphylolyticus incapable of producing an extracellular staphylolytic glycylglycine endopeptidase were isolated and found to have cells in the population susceptible to lysis by this enzyme, as did the wild-type organism under conditions in which the endopeptidase was not produced. These results suggest that cultures of this organism normally contain a heterogeneous population of cells with regard to cell wall composition and susceptibility to the enzyme. Production of the endopeptidase appears to act as a selective pressure which removes the susceptible cells in the population as the enzyme appears in the medium. A comparison of the peptidoglycan of the wild-type organism grown under conditions in which the endopeptidase was produced with that of this organism grown under nonproducing conditions and with those of endopeptidase-less mutants showed that in the presence of the endopeptidase the cell population had peptidoglycan with shorter peptide cross bridges and a greater percentage of serine in these cross bridges than was found in cells grown in the absence of the enzyme. The inability of the endopeptidase to hydrolyze glycylserine and serylglycine peptide bonds suggests that at least part of the resistance this organism has to the endopeptidase is due to relative amounts of serine found in the peptide cross bridges of some cells in the population.

Lysogenic conversion for multiple characters in a strain of Staphylococcus aureus

Lysogenization of nonlysogenic strains of Staphylococcus aureus was performed with two different bacteriophages, LS1 and LS2, that were unable to plaque on any of the strains of S. aureus tested. Infection of recipient strains was achieved when protoplasts were inoculated with LS1 or LS2 or when bacterial cultures were simultaneously inoculated with a virulent phage together with LS1 or LS2. Lysogenization was demonstrated by changes in phenotypic characters of the host strain and by liberation of bacteriophages from the modified strains as shown by electron microscopic examination. The lysogenic strains differed from the host strains by the following characters: they were coagulase, deoxyribonuclease, and lipase negative; they were untypable by the basic set of phages; they did not ferment mannitol under anaerobic conditions; and they produced only l-(+)-lactic acid by glucose fermentation. Their cell walls contained less glycine and concomitantly more serine than those of the host strains. Furthermore, they were devoid of protein A. Conversely, some antigenic factors as well as the presence of ribitol in the cell wall teichoic acid, indicated a parental relationship between the host strains and the derived lysogenic ones. Phages LS1 and LS2 could be excluded from the lysogenic strains by invading phages, and the revertant nonlysogenic strains recovered all of the characteristics of the initial host strains. It was thus concluded that the phenomenon described was due to lysogenic conversion. The origin of phages LS1 and LS2 is discussed.

Cell wall composition of novobiocin-resistant pleiotropic mutant staphylococci

Physically purified cell walls were prepared from selected pleiotropic novobiocin-resistant staphylococcal strains. The quantitative amino acid, amino sugar, and phosphorus contents of these walls are reported. This pleiotype was culturally diagnosed by its inability to support the growth of typing phages, inability to release latent bacteriophage, failure to elaborate coagulase, altered sugar catabolic pattern, and resistance to novobiocin. The strains were divided into two groups on the basis of wall composition. The walls of both groups of strains appeared to possess at least two phosphorus-containing polymers. On group of strains contained elevated levels of phosphorus in the cell walls. The second group contained the novel amino sugar galactosamine in the cell walls. This amino sugar is probably associated with one of the phosphorus-containing wall polymers of this group. On the basis of the data presented, it is suggested that the pleiotropy of these strains is the result of genetic change in the control of the biosynthesis of teichoic acids.

Bacteriophage-typable revertants from pleiotropic staphylococcal mutants

Cell walls were physically purified from bacteriophage-typable revertants that had been isolated from modified cell wall pleiotropic strains derived from Staphylococcus aureus NCTC 8511. The quantitative amino acid, amino sugar, and phosphorus contents of these cell walls are reported. Among the revertants were some whose walls possessed elevated serine and one strain whose walls contained the novel amino sugar galactosamine. The similarities in bacteriophage typing patterns between the revertants and the original parental strain lead to the conclusion that the previously described pleiotropic strains are mutants of NCTC 8511.

Alterations in the composition and bacteriophage-binding properties of walls of Staphylococcus aureus H grown in continuous culture in simplified defined media

A nutritional mutant of Staphylococcus aureus H has been isolated and grown in media in which the only amino acids are arginine, cysteine, glutamic acid and proline. Walls of the bacteria grown in such media in continuous culture under potassium limitation differ in composition from walls of the bacteria grown in batch culture in rich nutrient broth in that they contain less glycine, the peptidoglycan component is less highly cross-linked and the teichoic acid component contains a reduced proportion of N-acetylglucosaminyl substituents. Walls of the potassium-limited bacteria retain the ability to bind bacteriophage 52a but are more susceptible to the action of lytic peptidases than are wall samples in which the peptidoglycan is more highly cross-linked. Teichoic acid was present in walls of the bacteria grown under phosphate limitation in the defined medium and these walls were also able to absorb bacteriophage 52a.

In vitro incorporation of serine into the staphylococcal cell wall

A variant of Staphylococcus aureus 44A HJD was isolated by serial growth in Trypticase soy broth to which 2 M serine had been added (wt/vol). Amino acid analysis of hydrolysates of purified mucopeptides from the variant showed that they contained 1.266 serine and 2.156 glycine residues per glutamic acid residue, compared with 0.174 serine and 3.144 glycine residues per glutamic acid residue in the mucopeptide of the parent strain. In addition to this alteration in the chemical composition of the mucopeptide, the variant lost many of the biochemical and cultural characteristics of the parent organism. The variant was not sensitive to the lytic action of lysostaphin and was non-phage-typable. Moreover, in vitro tests indicated that the organism was coagulase negative, did not produce gelatinase or deoxyribonuclease, and did not hemolyze sheep erythrocytes. Apparently due to the change in the serine content in the cell wall of the parent S. aureus strain, the organism had become "epidermidis-like" in its properties.

Peptidoglycan types of bacterial cell walls and their taxonomic implications

Images