Degradative effect of phenol on endotoxin and lipopolysaccharide preparations from Serratia marcescens

A Simple and Rapid Microscale Method for Isolating Bacterial Lipopolysaccharides

Bacterial endotoxins (lipopolysaccharides (LPSs)) are important mediators of inflammatory processes induced by Gram-negative microorganisms. LPSs are the key inducers of septic shock due to a Gram-negative bacterial infection; thus, the structure and functions of LPSs are of specific interest. Often, highly purified bacterial endotoxins must be isolated from small amounts of biological material. Each of the currently available methods for LPS extraction has certain limitations. Herein, we describe a rapid and simple microscale method for extracting LPSs. The method consists of the following steps: ultrasonic destruction of the bacterial material, LPS extraction via heating, LPS purification with organic solvents, and treatment with proteinase K. LPSs that were extracted by using this method contained less than 2-3% protein and 1% total nucleic acid. We also demonstrated the structural integrity of the O-antigen and lipid A via the sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) methods, respectively. We demonstrated the ability of the extracted LPSs to induce typical secretion of cytokines and chemokines by primary macrophages. Overall, this method may be used to isolate purified LPSs with preserved structures of both the O-antigen and lipid A and unchanged functional activity from small amounts of bacterial biomass.

Purification and characterization of lipopolysaccharides

Lipopolysaccharides are the major components on the surface of most Gram-negative bacteria, and recognized by immune cells as a pathogen-associated molecule. They can cause severe diseases like sepsis and therefore known as endotoxins. Lipopolysaccharide consists of lipid A, core oligosaccharide and O-antigen repeats. Lipid A is responsible for the major bioactivity of endotoxin. Because of their specific structure and amphipathic property, purification and analysis of lipopolysaccharides are difficult. In this chapter, we summarize the available approaches for extraction, purification and analysis of lipopolysaccharides.

Electrophoretic analysis of the lipopolysaccharides of Bacteroides spp

Lipopolysaccharide (LPS) extracts of reference strains and isolates of Bacteroides spp. prepared by the proteinase K method were resolved by tricine-sodium-dodecyl-sulphate-polyacrylamide gel electrophoresis and located by silver staining. A considerable diversity of LPS profiles was evident within the Bacteroides genus although profiles were essentially species-specific, with some minor interstrain variations apparent among isolates of B. uniformis, B. ovatus, B. eggerthii and B. thetaiotaomicron. The LPS of most species consisted of a major rough LPS component of 2-5 kDa and a series of higher molecular weight bands which varied with species. B. vulgatus LPS was distinctive in showing an extensive ladder of multiple repeating oligosaccharide units with molecular weights ranging from 4 to > 17 kDa B. stercoris LPS included a high molecular weight (> 17 kDa) ladder of repeating oligosaccharide units. B. fragilis and B. thetaiotaomicron differed from most other species in producing a short ladder of repeating oligosaccharide units interspersing the rough LPS and a 5.6 kDa (B. fragilis) or 9 kDa (B. thetaiotaomicron) yellow-staining component. The heterogeneity of LPS profiles within the Bacteroides genus may reflect the differences in pathogenicity among the species and prove useful for typing.

Production of a monoclonal antibody that recognizes the lipopolysaccharide of a Campylobacter-like organism

A monoclonal antibody was produced to a Campylobacter-like organism (RMIT 32A) which was isolated from the terminal ileum of a pig with proliferative enteritis. Isotyping of the antibody revealed that it was an IgG2a with kappa light chains. Immunoblots using the antibody against proteinase-K-treated whole cell lysates of RMIT 32A, a selection of Campylobacter species and other enteric bacteria showed that the antibody was specific for RMIT 32A and was directed against the lipopolysaccharide. This antibody can be used for the specific detection of RMIT 32A.

Stimulation of human monocytes by endotoxin-associated protein: inhibition of programmed cell death (apoptosis) and potential significance in adjuvanticity

Mononuclear phagocytes are essential for adjuvant activity and polyclonal immunoglobulin synthesis induced by endotoxin-associated protein (EP) from Salmonella spp. To define the mechanisms of EP-mediated immunostimulation, we evaluated monocyte functions central to adjuvanticity following exposure to Salmonella typhimurium EP. In this study, we show that EP promotes the survival of monocytes by blocking programmed cell death (apoptosis), enhancing the production of the immunostimulatory cytokine interleukin-1 (IL-1) and stimulating the increased expression of HLA-DR and IL-2 receptors, which are cell membrane proteins that facilitate antigen presentation and IL-2 regulation, respectively. These results indicate that, like lipopolysaccharide, EP is a potent activator of human monocytes and suggest that EP-induced immunostimulation may be mediated, in part, by enhanced monocyte survival, cytokine release, and receptor expression.

Characterisation of protein co-extracted together with LPS in Escherichia coli, Salmonella minnesota and Yersinia enterocolitica

The porin proteins of Escherichia coli, Yersinia enterocolitica, and Salmonella minnesota were found to co-extract by the phenol-chloroform-petroleum ether method together with the R lipopolysaccharide of these strains. Lipopolysaccharide free protein recovered from the phenolic residue of the phenol-chloroform-petroleum ether extract migrated as a Mr 36-37,000 protein. We could demonstrate that the protein was extracted from bacteria as a high molecular weight protein-lipopolysaccharide complex. Once exposed to phenolic conditions, the protein was no longer soluble in the phenol-chloroform-petroleum ether extraction mixture, indicating a highly specific lipopolysaccharide-protein association.

Naturally occurring pasteurellosis in laboratory rabbits: chemical and serological studies of whole cells and lipopolysaccharides of Pasteurella multocida

Whole cells and lipopolysaccharides (LPS) of 10 isolates of Pasteurella multocida from laboratory rabbits were subjected to chemical and serological analysis. LPS of most of these isolates possessed pyrogenic potency comparable to LPS from Salmonella minnesota 9700, although their average ketodeoxyoctonate content was only 18% of that of salmonella. A gel diffusion precipitin test for somatic antigens extracted in a formal-saline solution demonstrated several isolates with three to four somatic antigens, with some variation in the major somatic type from one test to another. Conversely, the use of LPS as antigen in the gel diffusion precipitin test (i) eliminated cross-reactivity with reference antisera and (ii) often resulted in the organism being typed as serotype 12 even when the type 12 antigen was a minor antigen in the formal-saline extracts. Antisera from specific pathogen-free rabbits immunized with either whole cells or LPS of two isolates were tested against whole cells of LPS of the 10 isolates by enzyme immunoassay and indirect hemagglutination. Both whole cells and LPS of one of the isolates (isolate 2) were serologically specific, whereas those of the other isolate (isolate 1) were moderately to strongly cross-reactive with other isolates. The data indicate that although LPS is the major antigen responsible for typing based on the gel diffusion precipitin test, substances other than LPS (probably capsular polysaccharide) are responsible for the type specificity that forms the basis for the A, B, D, or E classification of this organism.

Procedure for isolation of bacterial lipopolysaccharides from both smooth and rough Pseudomonas aeruginosa and Salmonella typhimurium strains

Lipopolysaccharide (LPS) is a major component of the outer membrane of gram-negative bacteria. It is now well established that within a single organism, size heterogeneity of this molecule can exist. We have developed a LPS isolation procedure which is effective in extracting both smooth and rough LPS in high yields (51 to 81% of the LPS present in whole cells as quantitated by using hydroxy fatty acid, heptose, and 2-keto-3-deoxyoctonate yields) and with a high degree of purity. The contamination by protein (0.1% by weight of LPS), nucleic acids (1%), lipids (2 to 5%), and other bacterial products was low. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the LPS demonstrated the presence of a high degree of size heterogeneity in the isolated smooth LPS as well as the presence of significant amounts of rough-type LPS. The Pseudomonas aeruginosa LPS interacted well with a monoclonal antibody in a variety of immunochemical analyses. The usefulness of the procedure was demonstrated by comparing LPS preparations obtained from wild-type and mutant strains of P. aeruginosa and Salmonella typhimurium. For example, it was shown that the LPS of an antibiotic supersusceptible mutant Z61 of P. aeruginosa, which was previously characterized as identical to wild type with respect to the ratio of smooth to rough LPS molecules isolated by the phenol-water procedure, actually contained only a small proportion of O-antigenic side chains.

Enzyme-linked immunosorbent assay for detection of Pseudomonas aeruginosa Lipopolysaccharides

A double-antibody sandwich method of enzyme-linked immunosorbent assay was developed to detect lipopolysaccharides (LPS) from the eight most prevalent Pseudomonas aeruginosa serotypes (O1, O2,5,16, O3, O4, O6, O9, O10, and O11). Immunoglobulin M fractions from rabbit antisera were used as the coating antibody and as the antibody to be conjugated to an enzyme. When two fractions of LPS (I and II) obtained by Sepharose 2B column chromatography were assayed, LPS II showed 10 to 100 times more activity than LPS I; the detection level of LPS II was 0.1 ng/ml. When LPS in purified preparations or in culture filtrates was examined with both homologous and heterologous antibody systems, the same specificity pattern was demonstrated, suggesting that, in crude filtrates, antigens other than LPS do not interfere in the assay. The method described can be used to detect LPS in biological fluids.

Structural studies of the O-specific polysaccharide from Serratia marcescens N.C.T.C. 1377

The putative O-specific polysaccharide of Serratia marcescens N.C.T.C. 1377 is a partially acetylated glucorhamnan. By means of 1H- and 12C-n.m.r. spectroscopy, methylation analysis, and periodate oxidation, it was shown that the polymer has a disaccharide repeating-unit for which the following structure is proposed: leads to 4)-alpha-D-Glcp-(1 leads to 3)-beta-L-Rhap-(1-leads. O-Acetyl groups are probably located at C-2 of the rhamnopyranosyl residues. Except for the extent of O-acetylation, the polysaccharide is identical with the corresponding product from S. marcescens Bizio (A.T.C.C. 264), for which a different structure has previously been proposed.

Isolation of two protein-free and chemically different lipopolysaccharides from Bordetella pertussis phenol-extracted endotoxin

Endotoxin prepared from several Bordetella pertussis strains in both immunological phases I and IV gave two lipopolysaccharide peaks (LPS-I and LPS-II) when analyzed on hydroxylapatite columns in a phosphate buffer containing 0.1% sodium dodecyl sulfate; these lipopolysaccharides, present in the ratio of 2:3, are true endotoxins by both chemical and biological criteria. Endotoxins isolated from Escherichia coli, Salmonella typhimurium, and Shigella flexneri gave single lipopolysaccharide peaks when analyzed by the same procedure. Upon hydrolysis with acetic acid (pH 3.4) at 100 degrees C for 1 h, LPS-I released a polysaccharide (PS-I); the linkage broken was that of the glycosidic bond of a non-phosphorylated 3-deoxy-oct-2-ulosonic acid. Treatment with 0.25 M mineral acid at 100 degrees C for 30 min was required to free the polysaccharide moiety (PS-II) of LPS-II, the linkage broken being the glycosidic bond of a phosphorylated 3-deoxy-oct-2-ulosonic acid. Chemical and physical differences of the polysaccharide moieties PS-I and PS-II present in LPS-I and LPS-II have been described previously (25). By using the technique of 125I labeling, it was shown that the totality of labeled proteins present in the endotoxin extracted from Bordetella pertussis by the phenol-water procedure could be separated from the lipopolysaccharide by column chromatography on hydroxylapatite; it follows that these proteins are not linked by covalent bonds to the lipopolysaccharide.

Characterization of the chemical and physical properties of a novel B-lymphocyte activator, endotoxin protein

Endotoxin protein, a novel mouse B-lymphocyte mitogen, is a hydrophobic acidic compound composed of approximately 85% protein and 2.2% glucosamine, but no 2-keto-3-deoxyoctonate. Endotoxin protein also contains lipid, and analysis of the fatty acids in this material demonstrated the presence of beta-hydroxymyristate, a marker for lipid A. In addition, analysis of endotoxin protein by polyacrylamide gel electrophoresis showed that it is heterogeneous, containing four or five major polypeptides, depending upon the bacterial species from which it was isolated. The mitogenicity of endotoxin protein was diminished by alkaline hydrolysis, but not by treatment with hydrochloric or acetic acid. Furthermore, its activity was resistant to digestion with trypsin, chymotrypsin, and pronase and was only partially degraded by papain.

Characteristics of lipid A-protein complex from endotoxin of Shigella dysenteriae type 1 (S and R strains)

Mild acetic acid hydrolysis of endotoxin (lipopolysaccharide-protein complex) of Shigella dysenteriae type 1 (S and R forms) yielded a lipid A-protein complex that consisted of amino acids, fatty acids, and sugar and, in terms of chemical composition, displayed no marked differences between the S and R forms. Its protein portion (53 to 56%) consisted of at least 16 amino acids. In the fatty acid portion (14 to 18%), myristic, 3-hydroxymyristic, palmitic, and stearic acids accounted for 50%. The sugar portion (10 to 12%) consisted solely of glucosamine. The remainder was unidentified substances, most of which contained phosphorus. Lipid A-protein complexes derived from both S and R forms were not toxic for mice in doses up to 1,000 microgram/mouse, but their Linulus test activity had increased considerably as compared with the starting lipopolysaccharide-protein complex material: from 10(-6) to 10(-10--10(-12) mg/ml. The lipid A-protein complexes were readily soluble in a water solution of triethylamine, in dimethyl sulfoxide, and in pyridine.

Absence of glycerol teichoic acids in certain oral streptococci

Glycerol teichoic acids were not detected immunochemically or chemically in phenol-water, hot saline (Rantz and Randall), or supernatant fluids of disrupted cells of Streptococcus mitis. Thus teichoic acids do not appear to be found in most Gram-positive bacteria, as has been suggested.

Pseudomonas ribosomal vaccines: preparation, properties, and immunogenicity

The preparation, properties, and immunogenicity of ribosomal vaccines from Pseudomonas aeruginosa are described. These preparations, containing protein and RNA, were tested for immunogenicity by active immunization of mice and subsequent challenge with homologous, live bacteria. The results demonstrated that vaccines prepared from a majority of serotypes used were immunogenic, i.e., afforded 60 to 100% mouse protection against a challenge inoculum containing 8 to 50 50% lethal doses. In some cases vaccine doses as low as 1 microgram of RNA provided 100% mouse protection. Molecular sieve chromatography of a highly immunogenic ribosomal preparation on Sepharose 4B demonstrated the presence of two molecular weight fractions: (i) peak A, an excluded peak (thus having a molecular weight of at least 2 times 10(7)), and (ii) peak B, considerably retarded, with an elution position corresponding to a molecular weight of about 2.2 X 10(6), approximating that of typical 70S ribosomes. Both peaks A and B were immunogenic; however, the immunogenicity of peak A was greater (i.e., a smaller immunizing dose was required) than that of peak B. Peak A was shown to contain components of lipopolysaccharide in addition to protein and RNA (which comprised 80% of the dry weight of peak A). On the other hand, peak B was shown to be free of lipopolysaccharide, and 100% of its dry weight consisted of protein and RNA.

Involvement of Rhizobium japonicum O antigen in soybean nodulation

Non-nodulating mutant strains of Rhizobium japonicum lacked a surface antigen that was present on the wild type. This surface antigen is associated with the O antigen portion of the lipopolysaccharide. Paper chromatography of hydrolyzed lipopolysaccharide and O antigen revealed three major component differences between the non-nodulating strains and the wild type.

Bacterial lipopolysaccharides as inducers of disease resistance in tobacco

The cell wall component of Pseudomonas solanacearum that induces disease resistance in tobacco was highly heat stable at neutral or alkaline pH but highly labile at acid pH. Activity was unaffected by nucleases and proteases but destroyed by a mixture of beta-glycosidases. Washing of bacterial cell walls released a lipopolysaccharide (LPS) fraction with high inducer activity. Purified LPS, extracted by a variety of procedures from whole cells, isolated cell walls, and culture filtrates of both smooth and rough forms of P. solanacearum, induced disease resistance in tobacco at concentrations as low as 50 microgram/ml. The LPS from the non-plant pathogens Escherichia coli B, E. coli K, and Serratia marcescens was also active. Cell wall protein, free phospholipid, and nucleic acids were not necessary for activity. Moreover, since LPS from rough forms was active, the O-specific polysaccharide of the LPS was not required for activity. Hydrolysis of the remaining core-lipid A linkage or deacylation of lipid A destroyed inducer activity. When injected into tobacco leaves, purified LPS attached to tobacco mesophyll cell walls and induced ultrastructural changes in the host cell similar to those induced by attachment of whole heat-killed bacteria.

[Structure of shigella antigens. Heterogeneity of specific polysaccharides of 2 Shigella flexneri strains and 2 Sh. flexneri/Escherichia coli hybrids]

The S-specific polysaccharide from 2 Sh. flexneri wild strains (with serological var. X- and var. Y-specificity, respectively) and 2 Sh. flexneri E. coli hybrids (with the same specificities) can be separated by means of gel chromatography on Sephadex G-200 and G-50 into altogether 6 fractions per strain. Fraction G-200/1 (molecular weight greater than 10(6)D) represents a polymer consisting nearly exclusively of glucose and is present mainly in the two Y-type strains, much less in the two X-type strains. Fractions G-200/2 and G-200/3 (molecular weight approximately 10(5)D and approximately 2 - 10(4)D, respectively) seem to consist mainly of the S-specific side chains while fraction G-50/2 (molecular weight approximately 2000 D) presumably contains an SR-polysaccharide (core with one repeating unit.) Fraction G-50/3 (molecular weight approximately 100 D) contains the core polysaccharide and fraction G-50/4 splitting products (mainly KDO). No significant differences in chromatographical behaviour and quantitative composition could be found between the polysaccharides of the wild strains and the hybrid strains. Because of the well-known stability of the glucosaminyl linkages the sugar analysis was not only performed after acidic hydrolysis. In some cases the acid hydrolysate was reacted with HNO2 to cleave the glucosaminyl linkages. In most cases the values obtaines now were higher than those obtained directly.

Biological activities of endotoxins from Yersinia enterocolitica

The chemical properties and the general biological activities of lipopolysaccharide (LPS) and Boivin-type endotoxin obtained respectively by phenol-water and trichloroacetic acid extraction from Yersinia enterocolitica serotypes O3 and O9 were studied. The yield of LPS from the O9 strain was about 10% of the O3 strain possibly because of the lower solubility of O9-LPS in aqueous phase. However, the chemical composition of O9-LPS was similar to that of O3-LPS in the proportions of reducing sugar, glucosamine, heptose, KDO, and lipid A. In pyrogenicity and local Shwartzman reactivity in rabbits and lethality for mice, there was also no difference between O3 and O9-LPS. The anthrone-positive carbohydrate and lipid A contents of Boivin-type endotoxin from O3 were higher than those of the endotoxin from O9. The biological activities of Boivin-type endotoxin from O3 were also remarkably higher than those of the endotoxin from O9. It seems that endotoxin of Y. enterocolitica serotype O3 may play an important role in infection by this organism.

Lipoteichoic acid from Bacillus licheniformis 6346 MH-1. Comparative studies on the lipid portion of the lipoteichoic acid and the membrane glycolipid

A lipoteichoic acid and a membrane glycolipid were isolated from Bacillus licheniformis 6346 MH-1. The fatty acid composition of the two preparations were similar. Most of the fatty acids were of the branched chain type. The glycolipid was shown to be a diacyl derivative of O-beta-D-glucopyranosyl-(1 leads to 6)-O-beta-D-glucopyranosyl-(1 leads to 3)-glycerol. The lipoteichoic acid contained lipid, polyglycerol phosphate, and glucosamine. The lipid was released by treatment with hydrofluoric acid and by hydrolysis in dilute acid and was shown to have a structure identical with that of the membrane glycolipid.

Immunologic properties of bacterial lipopolysaccharide (LPS). II. The unresponsiveness of C3H/HeJ Mouse spleen cells to LPS-induced mitogenesis is dependent on the method used to extract LPS

The C3H/HeJ mouse strain, previously shown to be a nonresponder to bacterial lipopolysaccharide (LPS)-induced mitogenesis in vitro, was demonstrated by the present studies to be competent to respond mitogenically to LPS, but only to LPS preparations obtained by selected extraction methods. These preparations appear to be confined to LPS isolated by mild extraction techniques, such as TCA or butanol. In contrast, those obtained by techniques utilizing phenol were only weakly stimulatory or completely nonstimulatory for spleen cells from the C3H/HeJ. All LPS preparations tested, on the other hand, were highly stimulatory for cells from another mouse strain, namely the C3H/St. The critical importance of the method of extraction of LPS on its mitogenic activity for C3H/HeJ cells was stressed by experiments in which LPS was prepared from Escherichia coli K235 using either of two procedures. In these experiments, phenol-extracted LPS, although mitogenic in the C3H/St, was completely nonstimulatory in the C3H/HeJ; whereas, butanol-extracted LPS was highly stimulatory in both strains of mice. This striking difference was attributed to a destructive effect of phenol on LPS, as demonstrated by the fact that treatment of butanol LPS with phenol resulted in a total loss of its mitogenic activity in the C3H/HeJ, but in only a partial loss in the C3H/St. In general, the mitogenic response observed with selected LPS preparations in the C3H/HeJ was quantitatively lower and more transient than that seen with the C3H/St, although qualitatively these responses appeared to be similar. This was evidenced by the observation that in both mouse strains LPS was a specific mitogen for B cells, a property which was also attributed in both strains to the same distinct structural region of the LPS molecule, that is lipid A. A preparation of LPS that failed to stimulate B cells from the C3H/HeJ nonetheless had the capacity to block activation of these B cells by a stimulatory preparation of LPS. These results strongly suggest that mitogenic stimulation of B cells by LPS is a function of the structural integrity of both the LPS molecule and putative B-cell receptors for LPS.

Glucosamine-labelled envelope proteins of Escherichia coli K-12. I. Electrophoretic studies and partial fractionation of phenol-soluble proteins

Hydrophobic envelope proteins were extracted by phenol from a glucosamine- and leucine-requiring mutant of Escherichia coli K-12 (E-110). Three protein fractions labelled with D-[1-14C]glucosamine and L-[4,5-3H]leucine were obtained by electrophoretic separation. Envelopes were isolated from cells labelled with D-[1-14C]glucosamine--HCL and acid hydrolyzed. At least 68% of the radioactivity was recovered as glucosamine and glucose with no random distribution of label. Fingerprinting of pronase digests of glucosamine-labelled proteins showed four radioactive spots associated with peptides. The glycoproteins were pronase- and trypsin-sensitive and had apparent molecular weights of 11 000 (fast mobility), 35 000 (intermediate mobility) and 62 000 (slow mobility) as estimated by sodium dodecyl sulfate-polyacrylamide disc electrophoresis. The two heavier fractions were labelled with meso-diamino[1,7-14C2]pimelic acid, while orth[32P]phosphate was not incorporated into any fraction. The glucosamine radioactivity of the fast fraction underwent rapid changes upon a chase with non-radioactive glucosamine. Using a Sephadex LH-20 column, the radioactive proteins were separated from the phenol and subsequently fractionated on a DEAE-cellulose column. The DEAE-cellulose fractions were distinct from each other in the number and composition of protein bands, when analyzed by sodium dodecyl sulfate-polyacrylamide disc electrophoresis. Radioactive bands with intermediate and fast electrophoretic mobilities were found in separate DEAE-cellulose fractions.

Physical and chemical studies of Thiobacillus ferroxidans lipopolysaccharides

The lipopolysaccharides (LPS) of the obligate acidophile Thiobacillus ferroxidans grown on iron, sulfur, and glucose as energy sources were examined for various physical and chemical properties. Both qualitative and quantitative variation were found among the three preparations. The LPS extracted from iron-grown cells (Fe-LPS) contained less than 3% protein compared to 18 to 25% in LPS extracted from either sulfur-grown cells (S-LPS) or glucose-grown cells (G-LPS). S-LPS showed two distinct sedimentable species, 61S and 9.3S, which could be fractionated on a column of Sepharose 4B. The relative densities of both S-LPS and G-LPS were found to be significantly greater than that of Fe-LPS. Spectral differences were noted when each LPS was reacted with a carbocyanine dye. Fe-LPS showed a single absorbance maximum at 472 nm, S-LPS displayed its maximum at 650 nm, and G-LPS showed two maxima, the first at 468 nm and the other at 655 nm. Analysis of the methyl ester derivatives of the LPS fatty aicds using gas chromatography-mass spectrometry revealed the presence of a very stable species, tentatively identified as a methoxy methyl ester with a formula of CH3-3-C10H10-COOCH3, as the major component from each LPS. beta-Hydroxymyristic acid was found only in Fe-LPS.

Antibiogram and lipid analysis of a pigmented strain of Serratia marcescens and its nonpigmented variants

Antibiograms and lipid analyses of Serratia marcescens pigmented strain 08 and its nonpigmented variants are compared. The overall lack of significant differences between pigmented and nonpigmented strains suggests that the role of pigment formation may not be related to antibiotic susceptibility.