Excretion of extracellular lipids by Streptococcus mutans BHT and FA-1

Comparative Lipidomics of Oral Commensal and Opportunistic Bacteria

The oral cavity contains a vast array of microbes that contribute to the balance between oral health and disease. In addition, oral bacteria can gain access to the circulation and contribute to other diseases and chronic conditions. There are a limited number of publications available regarding the comparative lipidomics of oral bacteria and fungi involved in the construction of oral biofilms, hence our decision to study the lipidomics of representative oral bacteria and a fungus. We performed high-resolution mass spectrometric analyses (<2.0 ppm mass error) of the lipidomes from five Gram-positive commensal bacteria: Streptococcus oralis, Streptococcus intermedius, Streptococcus mitis, Streptococcus sanguinis, and Streptococcus gordonii; five Gram-positive opportunistic bacteria: Streptococcus mutans, Staphylococcus epidermis, Streptococcus acidominimus, Actinomyces viscosus, and Nanosynbacter lyticus; seven Gram-negative opportunistic bacteria: Porphyromonas gingivalis. Prevotella brevis, Proteus vulgaris, Fusobacterium nucleatum, Veillonella parvula, Treponema denticola, and Alkermansia muciniphila; and one fungus: Candida albicans. Our mass spectrometric analytical platform allowed for a detailed evaluation of the many structural modifications made by microbes for the three major lipid scaffolds: glycerol, sphingosine and fatty acyls of hydroxy fatty acids (FAHFAs).

The relative proportions of different lipid classes and their fatty acid compositions change with culture age in the cariogenic dental pathogen Streptococcus mutans UA159

The oral cariogenic bacterial pathogen Streptococcus mutans strain UA159 has become an important research organism strain since its genome was sequenced. However, there is a paucity of information on its lipidome using direct analytical biochemical approaches. We here report on comprehensive analyses of the major lipid classes and their fatty acids in cells grown in batch standing cultures. Using 2-D high-performance thin-layer chromatography lipid class composition changes were detected with culture age. More lipid components were detected in the stationary-phase compared to log-phase cells. The major lipids identified included 1,3-bis(sn-3'-phosphatidyl)-sn-glycerol (phosphatidylglycerol), 1,3-diphosphatidylglycerol (cardiolipin), aminoacyl-phosphatidylglycerol, monoglucosyldiacylglycerol, diglucosyldiacylglycerol, diglucosylmonoacylglycerol and, glycerophosphoryldiglucosyldiacylglycerol. Culture age also affected the fatty acid composition of the total polar lipid fraction. Thus, the major lipid classes detected in log-phase and stationary-phase cells were isolated and their fatty acids were analyzed by gas-liquid chromatography to determine the basis for the fatty acid compositional changes in the total polar lipid fraction. The analyses showed that the relative proportions of these acids changed with culture age within individual lipid classes. Hence fatty acid changes in the total polar lipid fraction reflected changes in both lipid class composition and fatty acid compositions within individual lipid classes.

Structural identities of four glycosylated lipids in the oral bacterium Streptococcus mutans UA159

The cariogenic bacterium Streptococcus mutans is an important dental pathogen that forms biofilms on tooth surfaces, which provide a protective niche for the bacterium where it secretes organic acids leading to the demineralization of tooth enamel. Lipids, especially glycolipids are likely to be key components of these biofilm matrices. The UA159 strain of S. mutans was among the earliest microorganisms to have its genome sequenced. While the lipids of other S. mutans strains have been identified and characterized, lipid analyses of UA159 have been limited to a few studies on its fatty acids. Here we report the structures of the four major glycolipids from stationary-phase S. mutans UA159 cells grown in standing cultures. These were shown to be monoglucosyldiacylglycerol (MGDAG), diglucosyldiacylglycerol (DGDAG), diglucosylmonoacylglycerol (DGMAG) and, glycerophosphoryldiglucosyldiacylglycerol (GPDGDAG). The structures were determined by high performance thin-layer chromatography, mass spectrometry and nuclear magnetic resonance spectroscopy. The glycolipids were identified by accurate, high resolution, and tandem mass spectrometry. The identities of the sugar units in the glycolipids were determined by a novel and highly efficient NMR method. All sugars were shown to have α-glycosidic linkages and DGMAG was shown to be acylated in the sn-1 position by NMR. This is the first observation of unsubstituted DGMAG in any organism and the first mass spectrometry data for GPDGDAG.

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.

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 basis for membrane phospholipid diversity: why are there so many lipids?

Phospholipids play multiple roles in cells by establishing the permeability barrier for cells and cell organelles, by providing the matrix for the assembly and function of a wide variety of catalytic processes, by acting as donors in the synthesis of macromolecules, and by actively influencing the functional properties of membrane-associated processes. The function, at the molecular level, of phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin in specific cellular processes is reviewed, with a focus on the results of combined molecular genetic and biochemical studies in Escherichia coli. These results are compared with primarily biochemical data supporting similar functions for these phospholipids in eukaryotic organisms. The wide range of processes in which specific involvement of phospholipids has been documented explains the need for diversity in phospholipid structure and why there are so many membrane lipids.

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.

Identification of phospholipids and neutral lipids in human gingival fluid

Gingival fluid was collected from children with a gingival index score of 2. Lipids were extracted, purified, and separated by thin-layer nanochromatography and identified. Lysophosphatidylcholines, sphingomyelins, phosphatidyl-cholines-ethanolamines-serines-inositols, polyglycerophosphatides, diphosphatidylglycerols, non-esterified fatty acids, mono- and di-glycerides, and cholesterols were observed. Serum origin of these lipids was possible, but enrichment by salivary bacterial or tissue lipids cannot be eliminated.

Glycerol incorporation in certain oral streptococci

Cells of 30 different strains of oral streptococci were grown in a chemically defined medium supplemented with [14C]glycerol to determine their ability to incorporate the labeled glycerol. Of the five species tested, only two, the rat-type strains (Streptococcus rattus) and strains isolated from wild rats (Streptococcus ferus), were able to incorporate the nonfermentable substrate, glycerol. For those strains capable of incorporating glycerol, the amount incorporated ranged from 0.15 to 0.43% of the cellular dry weight and followed simple saturation kinetics. The amount of glycerol incorporated depended solely on the concentration of glycerol in the growth medium. As a result, cultures exposed to low concentrations of glycerol ceased incorporation of the labeled glycerol before cessation of exponential growth.