Lipids and lipoteichoic acid of autolysis-defective Streptococcus faecium strains

Autolytic Activity and an Autolysis-Deficient Mutant of Clostridium acetobutylicum

The optimum conditions for autolysis and autoplast formation in Clostridium acetobutylicum P262 have been defined. Autolysis was optimal at pH 6.3 in 0.04 M sodium phosphate buffer, and the bacterium produced latent and active forms of an autolytic enzyme. The ability of cells to autolyze decreased sharply when cultures entered the stationary phase. Autoplasts were induced by 0.25 to 0.5 M sucrose and were stable in media containing sucrose, CaCl(2), and MgCl(2). A pleiotropic autolysis-deficient mutant (lyt-1) was isolated. The mutant produced less autolysin than did the parent P262 strain, and it had an altered cell wall which was more resistant to both its own and P262 autolysins. The mutant formed long chains of cells, and lysozyme was required for the production of autoplasts. Growth of the P262 strain or the lyt-1 mutant was inhibited by the same concentrations of penicillin, ampicillin, and vancomycin. The lyt-1 mutant strain treated with the minimum growth-inhibitory concentration of penicillin autolyzed upon the addition of wild-type autolysin to the autolysis buffer at the same rate as did the untreated P262 strain. Chloramphenicol did not protect the penicillin-treated lyt-1 cells against autolysis enhanced by exogenous wild-type autolysin.

Lipoteichoic acid as a target for antimicrobial action

Daptomycin, a lipopeptide antibiotic active against gram-positive bacteria, has been found to inhibit lipoteichoic acid (LTA) synthesis as a consequence of membrane binding in the presence of Ca2+. The present study shows that among the bacterial-membrane components, daptomycin binds the protein fraction with a noncovalent bond, as suggested by the instability of the bond in the presence of an ionic detergent such as sodium dodecyl sulfate. Analysis of membrane proteins by isoelectric focusing electrophoresis reveals that 5 bands with isoelectric points ranging from 5.9 to 6.2 bind radioactive daptomycin. These proteins are therefore called daptomycin-binding proteins. In an attempt to correlate these proteins with the main inhibition observed in LTA synthesis, two-dimensional thin-layer chromatography of lipids synthesized during daptomycin treatment was performed. A 3-fold increase in diglucosyl diacylglycerol is demonstrated, while the compounds phosphatidyl-alpha-kojibiosyldiacylglycerol, glycerophosphophosphatidyl-alpha-kojibiosyldiacyl glycerol, and glycerophosphokojibiosyldiacylglycerol, which follow diglucosyl diacylglycerol in LTA synthesis, decrease progressively with time during the course of daptomycin treatment.

Correlation of penicillin-induced lysis of Enterococcus faecium with saturation of essential penicillin-binding proteins and release of lipoteichoic acid

Clinical isolates of Enterococcus faecium that had a range of susceptibilities to penicillin were found to differ significantly in their responses to the antibiotic. In the penicillin-susceptible group (MIC, less than or equal to 4 micrograms/ml), the cessation of growth (bacteriostasis) at 10 x the MIC of penicillin appeared to correlate with the inhibition of penicillin-binding protein (PBP) 5*, whereas the onset of lysis (bactericidal effect) at higher antibiotic concentrations (100 x the MIC) was concomitant with the inhibition of the lower-affinity PBP 5. In contrast, in the resistant (MIC, greater than or equal to 8 micrograms/ml) group (in which most of the strains did not contain PBP 5*), the degree of saturation of PBP 5 seemed to determine the physiological response to the antibiotic: low levels of saturation caused growth inhibition, whereas almost complete saturation correlated with lysis. The penicillin-induced cell lysis of both penicillin-susceptible and -resistant strains was attributed, at least in part, to the extensive loss of acylated lipoteichoic acid into the growth medium.

Penicillin tolerance in Streptococcus faecium ATCC 9790

Tolerant strains of Streptococcus faecium had higher levels of muramidase 2 and lower levels of trypsinactivable muramidase 1 than did susceptible strains. Susceptible strains lysed faster than did tolerant strains in buffer and at some antibiotic concentrations. The addition of Triton X-100 produced equal lysis rates for susceptible and tolerant cultures.

The effect of penicillin on fatty acid synthesis and excretion in Streptococcus mutans BHT

Treatment of exponentially growing cultures of Streptococcus mutans BHT with growth-inhibitory concentrations (0.2 microgram/ml) of benzylpenicillin stimulates the incorporation of [2-14C] acetate into lipids excreted by the cells by as much as 69-fold, but does not change the amount of 14C incorporated into intracellular lipids. At this concentration of penicillin cellular lysis does not occur. The radioactive label is incorporated exclusively into the fatty acid moieties of the glycerolipids. The increase in the radioactive content of the extracellular lipids reflects an actual net increase in the total fatty acid content as determined by a chemical assay. During a 4-hr incubation in the presence of penicillin, the extracellular fatty acid ester concentration (per mg cell dry weight) increases 1.5 fold, even though there is no growth or cellular lysis. No change is observed in the intracellular fatty acid ester content. An indication of the relative rate of fatty acid synthesis was most readily obtained by placing S. mutans BHT in a buffer containing 14C-acetate. Under these nongrowing conditions free fatty acids are the only lipids labeled, a factor which simplifies the assay. The addition of glycerol to the buffer causes all of the nonesterified fatty acids to be incorporated into glycerolipid. The cells excrete much of the lipid whether glycerol is present or not. Addition of penicillin to the nongrowth supporting buffer system does not stimulate the incorporation of [14C]-acetate into fatty acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of penicillin on synthesis and excretion of lipid and lipoteichoic acid from Streptococcus mutans BHT

Cultures of Streptococcus mutans BHT grown for at least eight generations in a chemically defined medium containing [1(3)-14C]glycerol, when treated with growth-inhibitory concentrations (0.2 micrograms/ml) of benzylpenicillin (Pen G), produced and excreted increased amounts of lipid and lipoteichoic acid per unit of cells. Cellular lysis was not observed. Compared with untreated controls, lipid excretion increased 15-fold, and lipoteichoic acid excretion increased 6-fold, 4 h after the addition of Pen G. All lipid species showed increased synthesis and excretion after exposure to Pen G. Although the same lipid types were found in both the Pen G-treated and the untreated cultures, the percent composition was altered after treatment with Pen G. The most dramatic example of this was the percentage of intracellular diphosphatidylglycerol found in the Pen G-treated cultures, 22.6%, in contrast to 5.3% found in the untreated cultures.