Cell-wall deficiencies in L-forms of Staphylococcus aureus

Cell Wall-Deficient Bacteria as a Cause of Infections: A Review of the Clinical Significance

Cell wall-deficient bacteria (CWDB) are pleomorphic bacterial forms. These atypical organisms may occur naturally or they can be induced in the laboratory. Their presence has been known about for over a century, but a definite link to clinical disease outcomes has not been demonstrated. A number of case reports and laboratory studies suggest some disease associations, however. Considerable controversy surrounds the true relevance of CWDB to disease; there is a widespread belief that they may represent a response by the walled organism to adverse extracellular conditions like antibiotic pressure. This review looks at studies published between 1934 and 2003, which were identified by Dialog DataStar using the key words ‘cell wall deficient bacteria and clinical significance and infections’ and by further scanning the reference list at the end of the papers retrieved. We conclude that the evidence for the clinical significance of CWDB in disease is not compelling.

Persistence of Staphylococcus aureus L-form during experimental lung infection in rats

The course of pulmonary infection in rats infected by intranasal inoculation with a Staphylococcus aureus stable protoplast L-form was studied. Blood and bronchoalveolar samples were taken on days 3, 7, 14 and 30 after challenge and were investigated by microbiological, electron-microscopic, cytochemical and cytometric methods. The electron microscopic data and isolation of L-form cultures from bronchoalveolar samples at all experimental times demonstrated the ability of S. aureus L-form cells to internalize, replicate and persist in the lungs of infected rats to the end of the observation period, in contrast to the S. aureus parental form. It was found that persisting L-form evoked ineffectual phagocytose by alveolar macrophages and low but long-lasting inflammatory reaction in rats. The experimental model of pulmonary infection with S. aureus L-form suggests that the cell-wall-deficient bacterial forms may be involved in the pathogenesis of chronic and latent lung infections.

Induction of macrophage-mediated production of tumor necrosis factor alpha by an L-form derived from Staphylococcus aureus

We investigated the capability of an L-form derived from Staphylococcus aureus to induce tumor necrosis factor alpha (TNF-alpha) production in murine peritoneal macrophages. The activity for TNF-alpha induction was found in the membrane fraction of the L-form but not in the cytoplasmal fraction purified by the sucrose step gradient centrifugation. TNF-alpha mRNA was also detected in macrophages stimulated with L-form membranes. L-form induced TNF-alpha production in macrophages from both lipopolysaccharide-responsive and -unresponsive mouse strains. Regardless of the presence of polymyxin B, the activity of TNF-alpha induction of L-form was mostly found in the phenol layer, but not in the aqueous layer, both of which were prepared by phenol extraction method. Fractions of L-form membranes representing molecular masses of approximately between 29 and 36 kDa were primarily responsible for inducing the production of TNF-alpha consistently. Moreover, this stimulatory effect was abolished by digestion with Streptomyces griseus protease. In Western blot (immunoblot) analysis with anti-lipoteichoic acid antibody, two bands (65 and 45 kDa) were observed in the sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the phenol layer, whereas one band (14 kDa) was observed in either the aqueous layer or lipoteichoic acid of S. aureus. These results suggest that the component in the membrane of the L-form, distinct from cell wall components such as teichoic acid or lipopolysaccharide, possesses the capability to stimulate TNF-alpha production by macrophages.

Lipid composition of Staphylococcus aureus and its derived L-forms

Two strains of Staphylococcus aureus (Newman and Tazaki) and their derived L-forms were cultured in serum-containing broth and the differences in their lipid compositions were analyzed. Cardiolipin accounted for more than 50% of the total phospholipid phosphorus in L-forms, but for less than 25% in parent bacteria. The cardiolipin content of L-forms was very high through all growth phases, although it increased gradually as growth proceeded. Significant amounts of cholesterol and its esters were present in parent strains and L-forms, all of which incorporated serum cholesterol into the cell membrane. On the other hand, they could be detected in the L-forms but not in the parent strains when they were cultured in serum-free broth. To examine the ability of L-forms to synthesize cholesterol, the cholesterol content of L-forms cultured in serum-free broth was compared with that of the medium. The results indicated that staphylococcal L-forms could synthesize cholesterol and its esters. These differences in lipid composition suggested that modification of membrane lipids may occur as an adaptational change in response to the disappearance of the cell wall.

Use of polyvinylpyrrolidone in the testing of staphylococci for sensitivity to methicillin and cephradine

The use of polyvinylpyrrolidone, an inert polymer resembling plasma proteins in its colligative effects, in the testing of micrococcaceae for sensitivity to methicillin and cephradine is described. Generally results are quite comparable with those of conventional methods. The absence of any inhibitory effect of the polymer compared to sodium chloride, and its physiological inertia compared to sucrose, along with its suitability for sterilisation by autoclaving are seen as advantages. It is suggested that the use of this substance may give results which are more applicable to the in vivo situation. This may apply particularly in the case of cephradine.

Teichoic acid of a stabilized L-form of Streptococcus pyogenes

A stabilized L-form of Streptococcus pyogenes continues to synthesize glycerol teichoic acid. This polymer was obtained from S. pyogenes and its L-form, treated in identical fashion, and compared. Highly purified glycerol teichoic acid from only the L-form was found to be devoid of d-alanine and to have a shorter chain length. Otherwise, the glycerol teichoic acid from these two organisms was found to be a 1,3-phosphodiester-linked glycerophosphate polymer substituted with d-glucose. Evidence is presented that most, if not all, of the glycerol teichoic acid in this streptococcus lies between the wall and membrane. A possible need for the continued synthesis of a minute amount of glycerol teichoic acid by this L-form for survival is discussed in terms of the known function of teichoic acids in bacteria.

The chemical composition of the membranes of protoplasts and L-forms of Staphylococcus aureus

Membrane fractions were prepared from Staphylococcus aureus H and 100 after dissolution of the cell walls by a lytic enzyme from Streptomyces griseus. Membranes were also prepared from the L-forms derived from the same strains. The membranes were analysed for protein, lipid, carbohydrate and RNA contents, and the fatty acid composition of the lipids was determined. A branched-chain saturated C(15) acid was the major component in all samples, and the correspondence between L-forms and parent bacteria was fairly close. The lipids were separated into non-polar-lipid, glycolipid and phospholipid fractions; the L-forms contained a little more neutral lipid and much more glycolipid than the parent bacteria. In all membranes the glycolipid, which accounted for all the carbohydrate present, was a diglucosyl diglyceride. The major phospholipids of the protoplast membranes were phosphatidylglycerol and some lipoamino acids (lysine and a little alanine). On the other hand, diphosphatidylglycerol was the chief phospholipid found in L-form membranes.