Susceptibility to hydrophobic molecules and phospholipid composition in Pasteurella multocida and Actinobacillus lignieresii

Influence of outer membrane permeabilization on intrinsic resistance to the hydrophobic biocide triclosan in opportunistic Serratia species

Triclosan is a hydrophobic antimicrobial agent commonly employed in health care settings. While it exhibits broad-spectrum antibacterial properties, the gram-negative nosocomial opportunists Pseudomonas aeruginosa and Serratia marcescens are atypically refractory. Intrinsic resistance to triclosan in P. aeruginosa is largely due to its outer membrane impermeability properties for hydrophobic and bulky substances. The present study was undertaken to determine the relationship between triclosan and the outer cell envelopes of thirteen strains of ten Serratia species reported to be opportunistic pathogens in humans. General intrinsic resistance to hydrophobic and other outer membrane impermeant compounds was assessed using cultural selection, disk agar diffusion, and macrobroth dilution bioassays. Uptake of the hydrophobic fluorescent probe 1-N-phenylnapthylamine was assessed in four disparate strains of S. marcescens. Batch culture kinetics in the presence of combinations of triclosan and outer membrane permeabilizer compound 48/80 allowed analysis of outer membrane involvement in intrinsic resistance. Aggregate results revealed that individual species ranged in response to hydrophobic and bulky molecules from generally refractory to extremely susceptible. Moreover, susceptivity to triclosan sensitization by chemical disruption of outer membrane exclusionary properties differed markedly among species which exhibited intrinsic resistance to triclosan. These data suggest that disparate opportunistic pathogens within the genus Serratia differ phenotypically regarding the degree to which outer membrane exclusion contributes to intrinsic resistance for impermeant molecules in general, and triclosan specifically. Ancillary resistance mechanisms appear to contribute in some species and may involve constitutive multi-drug efflux systems. Importance A paucity of knowledge exists regarding the cellular and molecular mechanisms by which opportunistically pathogenic members of the genus Serratia are able to infect immunocompromised and otherwise susceptible individuals, and then evade chemotherapy. This is especially true for species other than Serratia marcescens and Serratia liquefaciens, although much remains to be learned with regard to the nature of key virulence factors and infection mechanisms which allow for the typically nosocomial acquisition of even these species. The research described in the present study will provide a better understanding of the contribution of outer cell envelope permeability properties to the pathogenicity of these opportunistic species in an ever-increasing susceptible patient population. It is our hope that greater knowledge of the basic biology of these organisms will contribute to the mitigation of suffering they cause in patients with underlying diseases.

Phospholipids and Fatty Acids Affect the Colonization of Urological Catheters by Proteus mirabilis

Proteus mirabilis-mediated CAUTIs are usually initiated by the adherence of bacteria to a urinary catheter surface. In this paper, three isolates of different origin and exhibiting different adhesion abilities were investigated in search of any changes in lipidome components which might contribute to P. mirabilis adhesion to catheters. Using GC-MS and LC-MS/MS techniques, 21 fatty acids and 27 phospholipids were identified in the examined cells. The comparison of the profiles of phospholipids and fatty acids obtained for catheter-attached cells and planktonic cells of the pathogens indicated C11:0 and PE 37:2 levels as values which could be related to P. mirabilis adhesion to a catheter, as well as cis C16:1, PE 32:0, PE 33:0, PE 38:2, PG 33:1, PG 34:0, PE 30:1, PE 32:1 and PG 30:2 levels as values which could be associated with cell hydrophobicity. Based on DiBAC₄ (3) fluorescence intensity and an affinity to p-xylene, it was found that the inner membrane depolarization, as well as strong cell-surface hydrophobicity, were important for P. mirabilis adhesion to a silicone catheter. A generalized polarization of Laurdan showed lower values for P. mirabilis cells attached to the catheter surface than for planktonic cells, suggesting lower packing density of membrane components of the adherent cells compared with tightly packed, stiffened membranes of the planktonic cells. Taken together, these data indicate that high surface hydrophobicity, fluidization and depolarization of P. mirabilis cell membranes enable colonization of a silicone urinary catheter surface.

Disparate outer membrane exclusionary properties underlie intrinsic resistance to hydrophobic substances in Pseudomonas spp. isolated from surface waters under triclosan selection

Representative members of surface water microbiota were obtained from three unrelated municipal sites in Oklahoma by direct plating under selection by the hydrophobic biocide triclosan. Multiple methods were employed to determine if intrinsic triclosan resistance reflected resistance to hydrophobic molecules by virtue of outer membrane impermeability. While all but one organism isolated in the absence of triclosan were able to initiate growth on MacConkey agar, only one was able to initiate significant growth with triclosan present. In contrast, all bacteria selected with triclosan were identified as Pseudomonas spp. using 16S RNA gene sequencing and exhibited growth comparable to Pseudomonas aeruginosa controls in the presence of hydrophobic antibacterial agents to include triclosan. Two representative bacteria isolated in the absence of triclosan allowed for greater outer membrane association with the fluorescent hydrophobic probe 1-N-phenylnapthylamine than did two triclosan-resistant isolates. Compound 48/80 disruption of outer membrane impermeability properties for hydrophobic substances either partially or fully sensitized nine of twelve intrinsically resistant isolates to triclosan. These data suggest that outer membrane exclusion underlies intrinsic resistance to triclosan in some, but not all Pseudomonas spp. isolated by selection from municipal surface waters and implicates the involvement of concomitant triclosan resistance mechanisms.

Capsular Polysaccharide Interferes with Biofilm Formation by Pasteurella multocida Serogroup A

Pasteurella multocida is an important multihost animal and zoonotic pathogen that is capable of causing respiratory and multisystemic diseases, bacteremia, and bite wound infections. The glycosaminoglycan capsule of P. multocida is an essential virulence factor that protects the bacterium from host defenses. However, chronic infections (such as swine atrophic rhinitis and the carrier state in birds and other animals) may be associated with biofilm formation, which has not been characterized in P. multocida. Biofilm formation by clinical isolates was inversely related to capsule production and was confirmed with capsule-deficient mutants of highly encapsulated strains. Capsule-deficient mutants formed biofilms with a larger biomass that was thicker and smoother than the biofilm of encapsulated strains. Passage of a highly encapsulated, poor-biofilm-forming strain under conditions that favored biofilm formation resulted in the production of less capsular polysaccharide and a more robust biofilm, as did addition of hyaluronidase to the growth medium of all of the strains tested. The matrix material of the biofilm was composed predominately of a glycogen exopolysaccharide (EPS), as determined by gas chromatography-mass spectrometry, nuclear magnetic resonance, and enzymatic digestion. However, a putative glycogen synthesis locus was not differentially regulated when the bacteria were grown as a biofilm or planktonically, as determined by quantitative reverse transcriptase PCR. Therefore, the negatively charged capsule may interfere with biofilm formation by blocking adherence to a surface or by preventing the EPS matrix from encasing large numbers of bacterial cells. This is the first detailed description of biofilm formation and a glycogen EPS by P. multocida.

Pasteurella multocida is an important pathogen responsible for severe infections in food animals, domestic and wild birds, pet animals, and humans. P. multocida was first isolated by Louis Pasteur in 1880 and has been studied for over 130 years. However, aspects of its lifecycle have remained unknown. Although formation of a biofilm by P. multocida has been proposed, this report is the first to characterize biofilm formation by P. multocida. Of particular interest is that the biofilm matrix material contained a newly reported amylose-like glycogen as the exopolysaccharide component and that production of capsular polysaccharide (CPS) was inversely related to biofilm formation. However, even highly mucoid, poor-biofilm-forming strains could form abundant biofilms by loss of CPS or following in vitro passage under biofilm growth conditions. Therefore, the carrier state or subclinical chronic infections with P. multocida may result from CPS downregulation with concomitant enhanced biofilm formation.

Cell surface physiology and outer cell envelope impermeability for hydrophobic substances in Burkholderia multivorans

PURPOSE

The purpose of the present study was to obtain a better understanding of the relationship between cell surface physiology and outer cellular envelope permeability for hydrophobic substances in mucoid and non-mucoid B. multivorans strains, as well as in two capsule-deficient derivatives of a mucoid parental strain.

METHODOLOGY

Cell surface hydrophobicity properties were determined using the hydrocarbon adherence method, while outer cell envelope accessibility and permeability for non-polar compounds were measured using hydrophobic antimicrobial agent susceptibility and fluorescent probe assays. Extracellular polysaccharide (EPS) production was assessed by cultivating strains of disparate origin on yeast extract agar (YEA) containing different sugars, while the resultant colonial and cellular morphological parameters were assessed macro- and microscopically, respectively.Results/Key findings. The cell surfaces of all the strains were hydrophilic, impermeable to mechanistically disparate hydrophobic antibacterial agents and inaccessible to the hydrophobic probe N-phenyl-1-napthylamine, regardless of EPS phenotype. Supplementation of basal YEA with eight different sugars enhanced macroscopic EPS expression for all but one non-mucoid strain, with mannose potentiating the greatest effect. Despite acquisition of the mucoid phenotype, non-mucoid strains remained non-capsulated and capsulation of a hyper-mucoid strain and its two non-mucoid derivative strains was unaffected, as judged by microscopic observation.

CONCLUSION

These data support the conclusion that EPS expression and the consistent mucoid phenotype are not necessarily associated with the ability of the outer cell surface to associate with non-polar substances or cellular capsulation.

Florfenicol As a Modulator Enhancing Antimicrobial Activity: Example Using Combination with Thiamphenicol against Pasteurella multocida

Synergistic effects between the same class of antibiotics are rarely reported. Our previous study found synergistic-like interaction between florfenicol (FFC) and thiamphenicol (TAP) against Staphylococcus aureus. Here, the enhanced antimicrobial activity was evaluated in 97 clinical isolates of both Gram-negative and Gram-positive bacteria. Susceptible strains were initially identified by checkerboard microdilution assay (fractional inhibitory concentration index [FICI] ≤ 0.625), followed by confirmation of synergism using the time-kill methodology (≥2 log₁₀ CFU/ml reduction). In all, 43% of Pasteurella multocida tested were susceptible to the enhanced bactericidal effect. In chicken fowl cholera models, FFC and TAP combination at much lower dosage that is correspondent to their MIC deduction provided maximum protection in vivo. Furthermore, synergistic combination of FFC with oxytetracycline (OTC) against Pseudomonas aeruginosa in vitro was also demonstrated. Based on the enhanced uptake of TAP and OTC, FFC presumably elicits enhanced antimicrobial activity in an orderly manner through alteration of bacterial membrane permeability or efflux systems and subsequent increase of intracellular concentration of the antibiotics used in combination. Results of ethidium bromide accumulation assay and RNA-seq showed little evidence for the involvement of efflux pumps in the synergy but further investigation is required. This study suggests the potentiality of a novel combination regimen involving FFC as an initiating modulator effective against both Gram-positive and Gram-negative bacteria depending on the antibiotics that are combined. The observed improvement of bacteriostatic effect to bactericidal, and the extended effectiveness against FFC-resistant bacterial strains warrant further studies.

Cell envelope phospholipid composition of Burkholderia multivorans

Burkholderia multivorans causes opportunistic pulmonary infections in cystic fibrosis and immunocompromised patients. The purpose of the present study was to determine the nature of the phospholipids and their fatty acid constituents comprising the cell envelope membranes of strains isolated from three disparate sources. A conventional method for obtaining the readily extractable lipids fraction from bacteria was employed to obtain membrane lipids for thin-layer chromatographic and gas chromatography-mass spectrophotometric analyses. Major fatty acid components of the B. multivorans readily extractable lipid fractions included C(16:0) (palmitic acid), C(16:1) (palmitoleic acid), and C(18:1) (oleic acid), while C(14:0) (myristic acid), ΔC(17:0) (methylene hexadecanoic acid), C(18:0) (stearic acid), and ΔC(19:0) (methylene octadecanoic acid) were present in lesser amounts. Fatty acid composition differed quantitatively among strains with regard to C(16:0), C(16:1), ΔC(17:0), C(18:1), and ΔC(19:0) with the unsaturated:saturated fatty acid ratios being significantly less in a cystic fibrosis type strain than either environmental or chronic granulomatous disease strains. Phospholipids identified in all B. multivorans strains included lyso-phosphatidylethanolamine, phosphatidylglycerol, phosphatidylethanolamine, and diphosphatidylglycerol in similar ratios. These data support the conclusion that the cell envelope phospholipid profiles of disparate B. multivorans strains are similar, while their respective fatty acyl substituent profiles differ quantitatively under identical cultivation conditions.

Influence of methylation on the antibacterial properties of triclosan in Pasteurella multocida and Pseudomonas aeruginosa variant strains

The opportunistic bacterium Pasteurella multocida is extremely susceptible to the hydrophobic biocide triclosan by virtue of its markedly permeable outer membrane, while the nosocomial pathogen Pseudomonas aeruginosa is intrinsically resistant to levels far exceeding the triclosan aqueous solubility limit. Widespread incorporation of triclosan in health and personal care products has resulted in its concomitant accumulation with metabolites such as methyl triclosan in environmental and biological systems. The present study was undertaken to investigate the possibility that methylation of triclosan may mitigate its antiseptic efficacy in healthcare settings, as well as represent a potential resistance mechanism. Comparative standardised disc agar diffusion and batch cultural turbidimetric bioassays were employed to assess the relationship between triclosan-susceptible or -resistant bacteria and methyl triclosan. A wild-type P. aeruginosa parental strain and a mutant exhibiting a permeable outer cell envelope phenotype were examined in concert with a refractory wild-type strain sensitised to triclosan susceptibility using outer membrane permeabiliser compound 48/80. All organisms examined were resistant to methyl triclosan, and all organisms excluding P. aeruginosa were susceptible to triclosan over a wide concentration range. The permeable outer membrane phenotype in both mutant and chemically sensitised wild-type strains rendered P. aeruginosa susceptible to triclosan, but not to methyl triclosan. These data support the notion that methylation of triclosan renders the compound unable to inhibit the growth of disparate bacterial pathogens in a manner independent of an intact outer membrane. It can also be concluded that biocide modification may contribute to the intrinsic resistance of P. aeruginosa to triclosan.

Effects of subminimum inhibitory concentrations of antibiotics on the Pasteurella multocida proteome: a systems approach

To identify key regulators of subminimum inhibitory concentration (sub-MIC) antibiotic response in the Pasteurella multocida proteome, we applied systems approaches. Using 2D-LC-ESI-MS², we achieved 53% proteome coverage. To study the differential protein expression in response to sub-MIC antibiotics in the context of protein interaction networks, we inferred P. multocida Pm70 protein interaction network from orthologous proteins. We then overlaid the differential protein expression data onto the P. multocida protein interaction network to study the bacterial response. We identified proteins that could enhance antimicrobial activity. Overall compensatory response to antibiotics was characterized by altered expression of proteins involved in purine metabolism, stress response, and cell envelope permeability.

Outer membrane permeability for nonpolar antimicrobial agents underlies extreme susceptibility of Pasteurella multocida to the hydrophobic biocide triclosan

Pasteurella multocida exhibits nonspecific susceptibility to nonpolar antimicrobial agents such as triclosan, despite possessing an ultrastructurally typical gram-negative cell envelope. Capsulated and noncapsulated cell surface variants were examined to investigate the role outer membrane permeability plays in triclosan susceptibility. Test strains were unable to initiate growth in the presence of bile salts and were susceptible to triclosan with minimal inhibitory concentrations (MICs) ranging from 0.06 to 0.25 microg/ml. Disk agar diffusion bioassays revealed triclosan susceptibility to be dose dependent and all strains were susceptible to the hydrophobic antibiotics novobiocin, rifamycin SV, and chloramphenicol. Triclosan minimal bactericidal concentrations were greater than MICs, thereby suggesting that dose dependency reflected both bacteriostatic and bactericidal effects. Total and viable cell density growth kinetic determinations revealed a triclosan concentration of 2.0 microg/ml resulted in loss of batch culture viability within 4-24 h. Concentrations of 0.02 and 0.2 microg/ml exerted either a bacteriostatic or bactericidal effect depending on the strain. Uptake of the hydrophobic probe 1-N-phenylnaphthylamine was greater in P. multocida strains than refractory control organisms Pseudomonas aeruginosa and Escherichia coli thereby suggesting the presence of phospholipid bilayer regions in the outer membrane. Because triclosan inhibits a conserved enoyl-ACP reductase necessary for bacterial fatty acid biosynthesis, these data support the notion that extreme susceptibility in P. multocida is due to the general inability of the outer membrane to exclude nonpolar compounds. Moreover, susceptibility is independent of the presence of capsular material and the biocide is bactericidal in a concentration dependent manner.

Susceptibility of compound 48/80-sensitized Pseudomonas aeruginosa to the hydrophobic biocide triclosan

Pseudomonas aeruginosa is intrinsically resistant to the hydrophobic biocide triclosan, and yet it can be sensitized to low concentrations by permeabilization of the outer membrane using compound 48/80. A selective plating assay revealed that compound 48/80-permeabilized YM64, a triclosan-recognizing efflux pump-deficient variant, was unable to initiate growth on a medium containing triclosan. Macrobroth dilution assay data revealed that treatment with compound 48/80 synergistically decreased minimal inhibitory concentrations of the hydrophobic antibacterial agents rifamycin SV and chloramphenicol for all cell envelope variant strains examined. A low concentration of triclosan exerted a transient bactericidal effect on permeabilized wild-type strain PAO1, after which exponential growth resumed within 4 h. Permeabilized strain YM64 was unable to overcome the inhibition; yet, both strains remained susceptible to chloramphenicol for as long as 6 h, thereby suggesting that the outer membrane remained permeable to nonpolar compounds. These data support the notion that the transitory nature of compound 48/80 sensitization to triclosan in P. aeruginosa does not involve obviation of the hydrophobic diffusion pathway through the outer membrane. The inability of strain YM64 to overcome the synergistic effect of compound 48/80 and triclosan strongly suggests that triclosan-recognizing efflux pumps are involved in maintaining viability in wild-type cells whose outer membranes are otherwise compromised.

Effect of outer membrane permeabilisation on intrinsic resistance to low triclosan levels in Pseudomonas aeruginosa

The present study was undertaken to investigate the possibility that outer cell envelope impermeability might be involved in the intrinsic resistance of Pseudomonas aeruginosa to low levels of the hydrophobic biocide triclosan. Macrobroth dilution and batch cultural turbidimetric assays were employed to assess the ability of compounds that render the Gram-negative outer membrane permeable to non-polar molecules to sensitise cell envelope variants to triclosan. Pseudomonas aeruginosa strains possessing highly refractory (PAO1) and atypically permeable (Z61) outer cell envelopes as well as a PAO1 derivative lacking four multidrug efflux pumps (YM64) were examined. Whilst the triclosan minimal inhibitory concentrations (MICs) differed dramatically for both PAO1 and Z61, significant decreases were seen for both strains in the presence of the outer membrane permeabiliser polymyxin B-nonapeptide. Strain YM64 was as resistant to triclosan as strain PAO1. Turbidimetric assessments of batch cultural growth kinetics revealed that the three chemically unrelated outer membrane permeabilisers polymyxin B-nonapeptide, compound 48/80 and ethylenediaminetetraacetate (EDTA) sensitised all strains to a sub-MIC concentration of triclosan (2.0 microg/mL). These data support the notion that the outer membrane exclusionary properties of P. aeruginosa for non-polar molecules confer intrinsic resistance to low concentrations of triclosan such as might be expected to occur in environmental residues. Moreover, a role for outer cell envelope impermeability is suggested for resistance to high triclosan concentrations in vitro.

Status of methods for assessing bacterial cell surface charge properties based on zeta potential measurements

Surface interfacial physiology is particularly important to unicellular organisms with regard to maintenance of optimal cell function. Bacterial cell surfaces possess net negative electrostatic charge by virtue of ionized phosphoryl and carboxylate substituents on outer cell envelope macromolecules which are exposed to the extracellular environment. The degree of peripheral electronegativity influences overall cell surface polarity and can be assessed on the basis of zeta potential which is most often determined by estimating the electrophoretic mobility of cells in an electric field. The purpose of this review is to provide bacteriologists with assistance as they seek to better understand available instrumentation and fundamental principles concerning the estimation of zeta potential as it relates to bacterial surface physiology.

Reduction of mortality in specific-pathogen-free layer chickens by a caprine serum fraction after infection with Pasteurella multocida

Caprine serum was fractionated by size, and its proteinaceous material <8,000 Da [caprine serum fraction immunomodulator 2 (CSF-I2)] was evaluated for its ability to impart immunoresistance to specific-pathogen-free (SPF) layer chickens. The SPF layers were challenged with 18 to 30 cfu of Pasteurella multocida X-73 (serotype 1) at 5 wk of age. A high degree of mortality was apparent 24 and 48 h later (62+/-14% and 88+/-7%, respectively). Mortality observed after 48 h was minimal. Noting the rapid onset of mortality, we administered CSF-I2 (material that expressed no direct antimicrobial activity but was believed to be an immunostimulant) 1 d before challenge and coincident to time of challenge. The group of birds that received CSF-I2 (either 5 or 10 mg per administration) expressed significant reduction in mortality throughout the 1-wk study period. Reduction in mortality appeared to be dose dependent. Birds that received two administrations of 10 mg CSF-I2 had significantly fewer deaths than did the group of birds that received half that amount. No deaths were recorded through 24 h, whereas, at 48 h, the percentage mortality was 13 in CSF-I2-treated birds. This study demonstrates that one or more small molecular weight compounds isolated from caprine serum were able to reduce mortality in SPF layers infected with Pasteurella multocida.

Contribution of the hydrophobic effect to microbial infection

The hydrophobic effect has been known for decades. Numerous researchers have invoked the hydrophobic effect to explain how pathogens adhere to tissues. In some cases, inhibition of adhesion can be brought about by low concentrations of aromatic compounds, such as p-nitrophenol or tryptophan. Because the hydrophobic effect has been considered to be nonspecific, the molecular biology of adhesive hydrophobins has not been studied in as much detail as lectin adhesins. The literature provides compelling evidence that a large number of bacterial and fungal pathogens depend on hydrophobic interactions for successful colonization of a host. Several laboratories are now developing effective antiadhesins, based on inhibition of hydrophobic interactions between the host and the pathogen.

Adaptive acquisition of novobiocin resistance in Pasteurella multocida strains of avian origin

Naturally occurring strains of Pasteurella multocida are atypically susceptible to hydrophobic antibiotics such as novobiocin, despite their Gram-negative cell envelope ultrastructure. Four strains adaptively resistant to 1000 micrograms/ml of novobiocin were obtained by sequentially subculturing cell surface hydrophobic variants of avian origin in the presence of increasing antibiotic concentrations. Adaptive novobiocin resistance was accompanied in all cases by the concomitant acquisition of resistance to coumermycin, a hydrophobic antibiotic possessing the same mechanism of action, but not to the functionally disparate hydrophobic antibiotic rifamycin. The acquisition of resistance was not accompanied by alterations in the lipid composition of the cell envelope. Subsequent growth of adaptively resistant strains in the absence of novobiocin did not result in the restoration of susceptibility to either novobiocin or coumermycin. Acquisition of adaptive resistance in encapsulated parental strains resulted in an inability to synthesize capsular material and enhanced cell surface hydrophobicity; however, parental encapsulation and decreased cell surface hydrophobicity were restored upon removal of novobiocin. These data suggest that acquisition of adaptive resistance to novobiocin conferred in this manner is the result of a stable genetic event affecting the mechanistic target of both novobiocin and coumermycin rather than a physiological adaptation involving outer membrane impermeability.

Biochemical characterization of lipopolysaccharides extracted from a hydrophobic strain of Pasteurella multocida

Lipopolysaccharides were extracted from freeze-dried cells of Pasteurella multocida strain P-1581 (serotype 8) by the phenol-chloroform-petroleum ether method and biochemically analysed using standard procedures. The primary neutral sugars were glucose, galactose and heptose. No deoxy sugars were detected. Amino sugars included galactosamine, glucosamine and glucosamine-6-phosphate. 3-Deoxy-D-manno-2-octulosonic acid was present at a relatively low concentration. The analyses included identification and quantification of phosphate and alanine. The primary fatty acids and their approximate relative ratios were 3-hydroxytetradecanoate and tetradecanoate 2:1. Tetradecanoic acid was bound almost exclusively by ester linkages. 3-Hydroxytetradecanoic acid was bound primarily by amide linkages, although significant numbers of ester-bound residues were noted. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis analyses indicated that the lipopolysaccharides were of low molecular weight.

Characterization of the family Pasteurellaceae on the basis of cellular lipids and carbohydrates

Selected strains representing established and newly described taxa in the family Pasteurellaceae were investigated for their cellular lipid and carbohydrate composition to clarify the taxonomic significance of such features. Methylated cellular fatty acids and acetylated derivatives of the cellular carbohydrates were determined by capillary gas chromatography using a flame ionization detector. In part the carbohydrates were identified by mass spectrometry. Phospholipids were determined by thin layer chromatography, the lipoquinones by high pressure liquid chromatography. The cellular fatty acid patterns proved to be uniform with minor variations, but the separation from the Neisseriaceae and from Moraxella was possible. Also the distribution of the phospholipids was uniform within the family. The lipoquinone contents were useful for the discrimination of groups within the family not necessarily reflecting the degree of genomic relatedness. The analysis of the cellular carbohydrates resulted in a common sugar pattern with all members of the family and characteristic carbohydrate profiles discriminating groups, often to the species level. All of the cytochemical features considered were useful for the characterization of the family Pasteurellaceae.

Kinetics and sequence specificity of processing of prepilin by PilD, the type IV leader peptidase of Pseudomonas aeruginosa

PilD, originally isolated as an essential component for the biogenesis of the type IV pili of Pseudomonas aeruginosa, is a unique endopeptidase responsible for processing the precursors of the P. aeruginosa pilin subunits. It is also required for the cleavage of the leader peptides from the Pdd proteins, which are essential components of an extracellular secretion pathway specific for the export of a number of P. aeruginosa hydrolytic enzymes and toxins. Substrates for PilD are initially synthesized with short, i.e., 6- to 8-amino-acid-long, leader peptides with a net basic charge and share a high degree of amino acid homology through the first 16 to 30 residues at the amino terminus. In addition, they all have a phenylalanine residue at the +1 site relative to the cleavage site, which is N methylated prior to assembly into the oligomeric structures. In this study, the kinetics of leader peptide cleavage from the precursor of the P. aeruginosa pilin subunit by PilD was determined in vitro. The rates of cleavage were compared for purified enzyme and substrate as well as for enzyme and substrate contained within total membranes extracted from P. aeruginosa strains overexpressing the cloned pilD or pilA genes. Optimal conditions were obtained only when both PilD and substrate were contained within total membranes. PilD catalysis of P. aeruginosa prepilin followed normal Michaelis-Menten kinetics, with a measured apparent Km of approximately 650 microM, and a kcat of 180 min-1. The kinetics of PilD processing of another type IV pilin precursor, that from Neisseria gonorrhoeae with a 7-amino-acid-long leader peptide, were essentially the same as that measured for wild-type P. aeruginosa prepilin. Quite different results were obtained for a number of prepilin substrates containing substitutions at the conserved phenylalanine at the +1 position relative to the cleavage site, which were previously shown to be well tolerated in vivo. Substitutions of methionine, serine, and cysteine for phenylalanine show that Km values remain close to that measured for wild-type substrate, while kcat and kcat/Km values were significantly decreased. This indicates that while the affinity of enzyme for substrate is relatively unaffected by the substitutions, the maximum rate of catalysis favors a phenylalanine at this position. Interesting, PilD cleavage of one mutated pillin (asparagine) resulted in a lower Km value of 52.5 microM, which indicates a higher affinity for the enzyme, as well as a lower kcat value of 6.1 min m(-1). This suggests that it may be feasible to design peptide inhibitors of PilD.

Carbohydrate patterns, cellular lipoquinones, fatty acids and phospholipids of the genus Pasteurella sensu stricto

The carbohydrate patterns, isoprenoid quinones, fatty acids and phospholipids of the species of the genus Pasteurella sensu stricto were investigated to evaluate their taxonomic significance and their applicability for the identification of these bacteria. Forty-six representative strains of the 11 species of Pasteurella were examined. The data obtained indicated that the carbohydrate patters are species or subspecies specific and may, therefore, become an important and useful diagnostic tool. Fatty acids and phospholipids showed a feature characteristic of the members of the genus and the isoprenoid quinones exhibited a mostly genus-specific feature with remarkable quantitative differences.