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

Group B Streptococcus, phospholipids and pulmonary hypertension

OBJECTIVE

Group B Streptococcus is the most common cause of bacterial infection in the newborn. Our aim was to purify and identify molecules produced by the bacterium, which cause pulmonary hypertension.

STUDY DESIGN

Guided by bioassays performed in neonatal lambs, we utilized standard biochemical techniques for the purification of these bioactive compounds. The compounds were identified by mass spectrometry. Fully synthetic compounds were then tested using the bioassay to confirm their ability to induce pulmonary hypertension.

RESULT

The purified bacterial components causing pulmonary hypertension were the phospholipids cardiolipin and phosphatidylglycerol. Synthetic cardiolipin or phosphatidylglycerol also induced pulmonary hypertension in lambs.

CONCLUSION

Bacterial phospholipids are capable of causing pulmonary hypertension. This finding opens new avenues for therapeutic intervention in persistent pulmonary hypertension of the newborn and generates hypotheses regarding the etiology of respiratory distress in the newborn and the possible effect of antibiotic therapy.

Hypothesis: Neonatal respiratory distress may be related to asymptomatic colonization with group B streptococci

BACKGROUND

Phospholipids from the group B streptococcal (GBS) cell wall cause pulmonary hypertension in experimental animals. When exposed to penicillin, Streptococcus mutans releases phospholipids immediately. We hypothesize that newborns colonized with GBS receive bacterial phospholipids leading to pulmonary hypertension and respiratory distress, especially in the situation of newborns of penicillin-treated mothers. We examined clinical and epidemiologic data on these relations.

METHODS

We used data from a prospective multicenter GBS study conducted from 1995 to 1999 in which 1674 of 17,690 newborns cultured at 4 sites were colonized with GBS. Our analyses included 1610 colonized newborns > or =32 weeks gestation without early-onset disease. Clinical features were compared between 1003 lightly colonized (GBS positive at < or =2 sites) and 607 heavily colonized (positive at 3 or 4 sites) newborns. The rates of respiratory distress were compared between colonized newborns of penicillin-treated mothers and those of untreated mothers.

RESULTS

Of the 1610 colonized newborns, 8.8% had signs of respiratory distress within 48 hours after birth (cases). Oxygen supplementation was used in 60% of the cases, mechanical ventilation was required in 5% and persistent pulmonary hypertension was diagnosed in 2%. Compared with light colonization, heavy colonization increased the rate of respiratory distress 1.73-fold (95% CI, 1.26-2.38), a discharge diagnosis of respiratory disorder 2.02-fold (95% CI, 1.16-3.52), a blood/cerebrospinal fluid obtained for culture 1.54-fold (95% CI, 1.24-1.93) and antibiotic administration after birth 1.87-fold (95% CI, 1.34-2.61). Penicillin use during labor was associated with a 2.62-fold (95% CI, 1.79-3.83) increase in respiratory distress in the colonized newborn.

CONCLUSIONS

Our findings support the association of neonatal respiratory distress with asymptomatic GBS colonization and with penicillin use during labor. These data require confirmation.

A continuum of anionic charge: structures and functions of D-alanyl-teichoic acids in gram-positive bacteria

Teichoic acids (TAs) are major wall and membrane components of most gram-positive bacteria. With few exceptions, they are polymers of glycerol-phosphate or ribitol-phosphate to which are attached glycosyl and D-alanyl ester residues. Wall TA is attached to peptidoglycan via a linkage unit, whereas lipoteichoic acid is attached to glycolipid intercalated in the membrane. Together with peptidoglycan, these polymers make up a polyanionic matrix that functions in (i) cation homeostasis; (ii) trafficking of ions, nutrients, proteins, and antibiotics; (iii) regulation of autolysins; and (iv) presentation of envelope proteins. The esterification of TAs with D-alanyl esters provides a means of modulating the net anionic charge, determining the cationic binding capacity, and displaying cations in the wall. This review addresses the structures and functions of D-alanyl-TAs, the D-alanylation system encoded by the dlt operon, and the roles of TAs in cell growth. The importance of dlt in the physiology of many organisms is illustrated by the variety of mutant phenotypes. In addition, advances in our understanding of D-alanyl ester function in virulence and host-mediated responses have been made possible through targeted mutagenesis of dlt. Studies of the mechanism of D-alanylation have identified two potential targets of antibacterial action and provided possible screening reactions for designing novel agents targeted to D-alanyl-TA synthesis.

Group B streptococcal phospholipid causes pulmonary hypertension

Group B Streptococcus is the most common cause of bacterial infection in the newborn. Infection in many cases causes persistent pulmonary hypertension, which impairs gas exchange in the lung. We purified the bacterial components causing pulmonary hypertension and identified them as cardiolipin and phosphatidylglycerol. Synthetic cardiolipin or phosphatidylglycerol also induced pulmonary hypertension in lambs. The recognition that bacterial phospholipids may cause pulmonary hypertension in newborns with Group B streptococcal infection opens new avenues for therapeutic intervention.

Molecular analysis of lipoteichoic acid from Streptococcus agalactiae

A method for the analysis of lipoteichoic acid (LTA) by polyacrylamide gel electrophoresis (PAGE) is described. Purified LTA from Streptococcus agalactiae tended to smear in the upper two-thirds of a 30 to 40% linear polyacrylamide gel, while the chemically deacylated form (cdLTA) migrated as a ladder of discrete bands, reminiscent of lipopolysaccharides. The deacylated polymer appeared to separate in this system on the basis of size, as evident from results obtained from PAGE analysis of cdLTA subjected to limited acid hydrolysis and LTA that had been fractionated by gel filtration. A survey of cdLTA from other streptococci revealed similarities in molecular weight ranges. The polymer from Enterococcus hirae was of a higher molecular weight. This procedure was used to examine the effect of penicillin and chloramphenicol on the synthesis, turnover, and heterogeneity of LTA in S. agalactiae. Penicillin appeared to enhance LTA synthesis while causing the release of this polymer into the supernatant fluid. In contrast, chloramphenicol inhibited the synthesis of this molecule and resulted in its depletion from the cell surface. Penicillin did not alter the heterogeneity of this polymer, but chloramphenicol caused an apparent shift to a lower-molecular-weight from of the LTA, as determined by PAGE. This shift in the heterogeneity of LTA did not appear to be due to increased carbohydrate substitution, since chloramphenicol did not alter the electrophoretic migration profile of LTA from E. hirae. From a pulse-chase study, it was determined that LTA was released as a consequence of deacylation.

Lipid metabolism in anaerobic ecosystems

In anaerobic ecosystems, acyl lipids are initially hydrolyzed by microbial lipases with the release of free fatty acids. Glycerol, galactose, choline, and other non-fatty acid components released during hydrolysis are fermented to volatile fatty acids by the fermentative bacteria. Fatty acids are not degraded further in the rumen or other parts of the digestive tract but are subjected to extensive biohydrogenation especially in the rumen. However, in environments such as sediments and waste digestors, which have long retention times, both long and short chain fatty acids are beta-oxidized to acetate by a special group of bacteria, the H2-producing syntrophs. Long chain fatty acids can also be degraded by alpha-oxidation. Biotransformation of bile acids, cholesterol, and steroids by intestinal microorganisms is extensive. Many rumen bacteria have specific growth requirements for fatty acids such as n-valeric, iso-valeric, 2-methylbutyric, and iso-butyric acids. Some species have requirements for C13 to C18 straight-chain saturated or monoenoic fatty acids for growth.

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.

Synergism between penicillin G and the antimicrobial ether lipid, rac-1-dodecylglycerol, acting below its critical micelle concentration

rac-1-Dodecylglycerol (DDG) and penicillin G (Pen G) act synergistically to dramatically lower the minimum inhibitory concentration (MIC) of each other in four Gram-positive bacteria studied. At one-half its MIC, DDG ether lowered the MIC of Pen G 10- to 80-fold. Under the same conditions, Pen G lowered the MIC of DDG 4- to 7.5-fold. The critical micelle concentration of DDG was determined to be 7.93 mg/ml (0.0305 mM), which is approximately two-fold greater than the minimum inhibitory concentration of DDG determined in the presence of a protein-free chemically defined medium. This finding suggests that DDG is not killing bacteria through its detergent action. Pen G also did not alter the critical micelle concentration of DDG, which indicates that the synergism between these two agents is not related to micelle formation.

The ability to sensitize host cells for destruction by autologous complement is a general property of lipoteichoic acid

Previous studies have demonstrated that lipoteichoic acid (LTA) from Streptococcus pneumoniae binds to erythrocytes and renders them susceptible to lysis by autologous complement. The present study was performed to determine whether LTA from two other gram-positive bacterial species had the ability to render mammalian cells susceptible to lysis by autologous complement. Human erythrocytes were sensitized with LTA from S. pneumoniae, Streptococcus pyogenes, or Lactobacillus fermentum. Under incubation in normal autologous serum, lysis was observed with each of the LTA-sensitized erythrocyte preparations. When erythrocytes from a C2-deficient patient were sensitized with the LTA preparations and then incubated in autologous, C2-deficient serum, the erythrocytes sensitized with S. pyogenes or L. fermentum LTA demonstrated relatively little lysis, whereas the erythrocytes sensitized with S. pneumoniae LTA yielded near-total lysis. After reconstitution of the C2-deficient serum with purified human C2, lysis was observed with all three LTA preparations. When erythrocytes from an agammaglobulinemic patient were sensitized with either the S. pyogenes or the L. fermentum LTA, they were not lysed in the presence of autologous agammaglobulinemic serum, whereas the erythrocytes sensitized with S. pneumoniae LTA were completely lysed. Serum obtained from the agammaglobulinemic patient after reconstitution with intravenous pooled gamma globulin was able to lyse autologous erythrocytes sensitized with each of the three LTA preparations. These results demonstrate that the ability to render host cells susceptible to lysis by autologous complement is a general property of LTA. Whether activation of the autologous complement occurs by the classical or alternative pathways and whether it is antibody dependent depends on the nature of the bacterial LTA.

Cell surface hydrophobicity of Bifidobacterium bifidum subsp. pennsylvanicum

The possible role of lipoteichoic acid with respect to cell surface properties of Bifidobacterium bifidum subsp. pennsylvanicum was studied. Standard suspensions of bacteria were mixed with octane or xylene. B. bifidum subsp. pennsylvanicum was shown to possess a strongly hydrophobic cell surface. Hydrophobicity of the bacteria could be reduced by treatment with trypsin, pepsin (at pH 4.5), HCl and penicillin. The latter treatment resulted in an increased excretion of lipoteichoic acid. Albumin was capable of inhibiting the adherence to octane when it was present in the assay buffer. The data suggest that both protein and lipoteichoic acid may be involved in cell surface hydrophobicity. A great divergence in cell surface properties was observed within the genus Bifidobacterium.

Suppression of intrinsic resistance to penicillins in Staphylococcus aureus by polidocanol, a dodecyl polyethyleneoxid ether

With polidocanol, it was possible to reduce the MIC as well as the MBC of methicillin, oxacillin, penicillin G, and ampicillin against resistant staphylococci. The strongest effects were obtained with methicillin and oxacillin. All strains tested could be resensitized to these penicillins independent of the original resistance levels. Polidocanol was not inhibitory by itself for Staphylococcus aureus. Furthermore, it did not inhibit the activity of staphylococcal beta-lactamase. This permits the conclusion that an intrinsic resistance mechanism is affected by this substance. Its action cannot be simply explained by an improved accessibility of the penicillin targets as uptake, and binding of methicillin and penicillin G in resistant cells was not changed by polidocanol. On the other hand, the lysis induced by combinations of this substance with small amounts of a penicillin was antagonized by chloramphenicol. This suggests that autolytic enzymes are involved in the polidocanol effect and possibly in the intrinsic resistance mechanism itself. Before polidocanol can trigger lysis, the penicillin must act first in some way. As could be seen with a susceptible strain, the resulting lysis did not exceed that obtained with penicillins alone. Thus, polidocanol does not exhibit an independent lytic mechanism but obviously is able to substitute penicillins in their lytic action.

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)

Products of phospholipid metabolism in Bacillus stearothermophilus

The products of phospholipid turnover in Bacillus stearothermophilus were determined in cultures labeled to equilibrium and with short pulses of [32P]phosphate and [2-3H]glycerol. Label lost from the cellular lipid pool was recovered in three fractions: low-molecular-weight extracellular products, extracellular lipid, and lipoteichoic acid (LTA). The low-molecular-weight turnover products were released from the cells during the first 10 to 20 min of a 60-min chase period and appeared to be derived primarily from phosphatidylglycerol turnover. Phosphatidylethanolamine, which appeared to be synthesized in part from the phosphatidyl group of phosphatidylglycerol, was released from the cell but was not degraded. The major product of phospholipid turnover was LTA. Essentially all of the label lost from the lipid pool during the final 40 min of the chase period was recovered as extracellular LTA. The LTA appeared to be derived primarily from the turnover of cardiolipin and the phosphatidyl group of phosphatidylglycerol. Three types of LTA were isolated; an extracellular LTA was recovered from the culture medium, and two types of LTA were extracted from membrane preparations or whole-cell lysates by the hot phenol-water procedure. Cells contained 1.5 to 2.5 mg of cellular LTA per g of cells (dry weight), over 50% of which remained associated with the membrane when cells were fractionated. Over 75% of the 3H label incorporated into the cellular LTA pool during a 90-min labeling period was released from the cells during the first cell doubling after the chase. Label lost from the lipid pool was incorporated into cellular LTA which was then modified and released into the culture medium.