Distinction between pore assembly by staphylococcal alpha-toxin versus leukotoxins

The staphylococcal bipartite leukotoxins and the homoheptameric α-toxin belong to the same family of β-barrel pore-forming toxins despite slight differences. In the α-toxin pore, the N-terminal extremity of each protomer interacts as a deployed latch with two consecutive protomers in the vicinity of the pore lumen. N-terminal extremities of leukotoxins as seen in their three-dimensional structures are heterogeneous in length and take part in the β-sandwich core of soluble monomers. Hence, the interaction of these N-terminal extremities within structures of adjacent monomers is questionable. We show here that modifications of their N-termini by two different processes, using fusion with glutathione S-transferase (GST) and bridging of the N-terminal extremity to the adjacent β-sheet via disulphide bridges, are not deleterious for biological activity. Therefore, bipartite leukotoxins do not need a large extension of their N-terminal extremities to form functional pores, thus illustrating a microheterogeneity of the structural organizations between bipartite leukotoxins and α-toxin.

Enhanced culture of Borrelia garinii and Borrelia afzelii strains on a solid BSK-based medium in anaerobic conditions

The growth of 29 human strains from the three main pathogenic species of Borrelia burgdorferi sensu lato on a solid BSK-based medium was compared in two culture atmospheres: 3% CO(2) air and anaerobiosis. All strains grew under anaerobic conditions, whereas only 13 strains were able to grow in aerobiosis with 3% CO(2) (P<0.001). In the latter condition, 75% of the B. burgdorferi sensu stricto strains grew versus 33% of the B. garinii and B. afzelii strains. These data suggest that, especially for B. garinii and B. afzelii species, anaerobic conditions enhance growth yield and speed of low-passage Borrelia strains.

Mimicking helical antibacterial peptides with nonpeptidic folding oligomers

Unnatural oligomeric scaffolds designed to adopt defined secondary structures (e.g., helices), while retaining the chemical diversity of amino acid side chains, are of practical value to elaborate functional mimetics of bioactive alpha-polypeptides. Enantiopure N,N'-linked oligoureas as short as seven residues long have been previously shown to fold into a stable helical structure, stabilized by 12- and 14-membered H-bonded rings. We now report that eight-residue oligoureas designed to mimic globally amphiphilic alpha-helical host-defense peptides are effective against both gram-negative and gram-positive bacteria (including methicillin-resistant Staphylococcus aureus [MRSA]) and exhibit selectivity for bacterial versus mammalian cells. Circular dichroism (CD) spectroscopy studies suggest enhanced helical propensity of oligoureas in the presence of phospholipid vesicles. The utility of this new class of nonpeptidic foldamers for biological applications is highlighted by high resistance to proteolytic degradation.

Incidence and pathogenic effect of Streptococcus pseudopneumoniae

We evaluated the incidence of Streptococcus pseudopneumoniae in clinical isolates by phenotypic methods and DNA-DNA hybridization. The pathogenic role of this organism was investigated with the mouse peritonitis/sepsis model. Our results show a low incidence (1/120 pneumococcal isolates) and a potential pathogenic effect for S. pseudopneumoniae.

Engineered covalent leucotoxin heterodimers form functional pores: insights into S-F interactions

The staphylococcal alpha-toxin and bipartite leucotoxins belong to a single family of pore-forming toxins that are rich in beta-strands, although the stoichiometry and electrophysiological characteristics of their pores are different. The different known structures show a common beta-sandwich domain that plays a key role in subunit-subunit interactions, which could be targeted to inhibit oligomerization of these toxins. We used several cysteine mutants of both HlgA (gamma-haemolysin A) and HlgB (gamma-haemolysin B) to challenge 20 heterodimers linked by disulphide bridges. A new strategy was developed in order to obtain a good yield for S-S bond formation and dimer stabilization. Functions of the pores formed by 14 purified dimers were investigated on model membranes, i.e. planar lipid bilayers and large unilamellar vesicles, and on target cells, i.e. rabbit and human red blood cells and polymorphonuclear neutrophils. We observed that dimers HlgA T28C-HlgB N156C and HlgA T21C-HlgB T157C form pores with similar characteristics as the wild-type toxin, thus suggesting that the mutated residues are facing one another, allowing pore formation. Our results also confirm the octameric stoichiometry of the leucotoxin pores, as well as the parity of the two monomers in the pore. Correctly assembled heterodimers thus constitute the minimal functional unit of leucotoxins. We propose amino acids involved in interactions at one of the two interfaces for an assembled leucotoxin.

Detection of Chlamydia trachomatis DNA using MagNA Pure DNA extraction and Cobas Amplicor CT/NG amplification

The automated MagNA Pure DNA extraction method for Chlamydia trachomatis was compared with the manual Cobas Amplicor protocol using 100 microL of input sample volume from 964 specimens. Agreement between protocols was 96.1%. The automated extraction method had a sensitivity of 99% and a specificity of 100%. Amplification inhibition observed after manual preparation of samples (3.8%) was not apparent following automated extraction. Using 200 microL of sample in the automated extraction process lowered the detection limit without raising the inhibition rate. Furthermore, the automated extraction method halved the hands-on time required for the procedure.

Homologous versus heterologous interactions in the bicomponent staphylococcal gamma-haemolysin pore

Staphylococcal gamma-haemolysin HlgA-HlgB forms a beta-barrel transmembrane pore in cells and in model membranes. The pore is formed by the oligomerization of two different proteins and a still debated number of monomers. To clarify the topology of the pore, we have mutated single residues - placed near the right and left interfaces of each monomer into cysteine. The mutants were labelled with fluorescent probes, forming a donor-acceptor pair for FRET (fluorescence resonance energy transfer). Heterologous couples (labelled on complementary left and right interfaces) displayed a marked FRET, suggesting extensive HlgA-HlgB or HlgB-HlgA contacts. Heterologous control couples (with both components labelled on the same side) showed absent or low FRET. We found the same result for the homologous couple formed by HlgA [i.e. HlgA-HlgA in the presence of wt (wild-type) HlgB]. The homologous HlgB couple (HlgB-HlgB labelled on left and right interfaces and in the presence of wt HlgA) displayed a transient, declining FRET, which may indicate fast formation of an intermediate that is consumed during pore formation. We conclude that bicomponent pores are assembled by alternating heterologous monomers.

Site-directed mutagenesis to assess the binding capacity of class s protein of Staphylococcus aureus leucotoxins to the surface of polymorphonuclear cells

Staphylococcal leucotoxins result from the association of class S components and class F component inducing the activation and the permeabilization of the target cells. Like alpha-toxin, the leucotoxins are pore-forming toxins with more than 70% beta-sheet. This was confirmed by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. In addition, threonine 28 of a predicted and conserved beta-sheet at the N-terminal extremity of class S proteins composing leucotoxins aligns with histidine 35 of alpha-toxin, which has a key role in oligomerization of the final pore. Flow cytometry was used to study different aminoacid substitutions of the threonine 28 in order to evaluate its role in the biological activity of these class S proteins. Finally, results show that threonine 28 of the leucotoxin probably plays a role similar to that of histidine 35 of alpha-toxin. Mutations on this threonin largely influenced the secondary interaction of the class F component and led to inactive toxin.

Sensitive and specific detection of staphylococcal epidermolysins A and B in broth cultures by flow cytometry-assisted multiplex immunoassay

Two of the most common bacterial skin infections of young infants and children are bullous impetigo due to Staphylococcus aureus and its more acute form, staphylococcal scalded skin syndrome. Epidermolysin A (ETA), ETB and, possibly, ETD are responsible for these diseases, which may appear as epidemics in pediatric patients. We tested the reliability of a flow cytometry-assisted multiplex immunoassay (Bio-Plex system) for the detection of ETA and ETB. The Bio-Plex system was found to be highly specific and highly sensitive for toxin concentrations of between 2 and 80,000 pg/ml. The results of this assay were 100% identical to the results of a PCR-based method. We demonstrated that this test did not generate any cross-reactions with ETD-producing isolates. The level of detection of ETB by this test differed according to culture conditions and from isolate to isolate; these results must be taken into account for diagnostic purposes.

Peripartum bacteremias due to Leptotrichia amnionii and Sneathia sanguinegens, rare causes of fever during and after delivery

We report three cases of delivery and postpartum bacteremia due to unusual anaerobic bacteria in healthy young women. Leptotrichia amnionii bacteremia occurred during delivery in two mothers and was associated with fetal distress during labor. Conversely, Sneathia sanguinegens bacteremia occurred postpartum, 2 days after delivery, without consequence for the neonate.

Isolations of Corynebacterium kroppenstedtii from a breast abscess

The recently described species Corynebacterium kroppenstedtii was isolated from a breast abscess in a 38-year-old woman on two occasions. We discuss the pathogenic role of this bacteria and the methods used for its isolation.

Correlation of wbiI genotype, serotype, and isolate source within species of the Burkholderia cepacia complex

Gram-negative bacteria of the Burkholderia cepacia complex (Bcc) are opportunistic pathogens that can infect the lungs of cystic fibrosis (CF) patients and can be transmitted among these patients, causing epidemics in the CF community. Lipopolysaccharide (LPS) is an important virulence factor of many gram-negative bacteria, with the O antigen component of LPS being responsible for serotype specificity. The goal of this work was to develop a genetic method of determining the serotype of Bcc isolates based on the conserved gene wbiI. Homologues of wbiI are found in polysaccharide biosynthesis gene clusters in other bacteria. Primers to a conserved region of the Bcc wbiI gene were able to amplify by PCR a single product in 67 of 80 Bcc isolates tested. Sequencing and restriction enzyme digestion of this wbiI PCR product revealed sufficient DNA polymorphisms to distinguish and group various isolates. In five of nine instances, Bcc isolates of a single serotype had a single wbiI restriction fragment length polymorphism (RFLP) pattern, while isolates of the other four serotypes could have multiple wbiI RFLP types. Species determination of the Bcc isolates revealed no obvious correlation between wbiI RFLP type and species. There was also no apparent correlation between wbiI RFLP type and the ability of a single Bcc isolate to infect an individual with CF. However three of five Bcc outbreaks involved isolates with the same wbiI RFLP type, indicating that wbiI RFLP typing may be a useful tool to help track Bcc outbreaks.

Crystal Structure of Leucotoxin S Component

Staphylococcal leucocidins and gamma-hemolysins (leucotoxins) are bi-component toxins that form lytic transmembrane pores. Their cytotoxic activities require the synergistic association of a class S component and a class F component, produced as water-soluble monomers that form hetero-oligomeric membrane-associated complexes. Strains that produce the Panton-Valentine leucocidin are clinically associated with cutaneous lesions and community-acquired pneumonia. In a previous study, we determined the crystal structure of the F monomer from the Panton-Valentine leucocidin. To derive information on the second component of the leucotoxins, the x-ray structure of the S protein from the Panton-Valentine leucocidin was solved to 2.0 angstrom resolution using a tetragonal crystal form that contains eight molecules in the asymmetric unit. The structure demonstrates the different conformation of the domain involved in membrane contacts and illustrates sequence and tertiary structure variabilities of the pore-forming leucotoxins. Mutagenesis studies at a key surface residue (Thr-28) further support the important role played by these microheterogeneities for the assembly of the bipartite leucotoxins.

Aeromonas simiae sp. nov., isolated from monkey faeces

Two Aeromonas strains, IBS S6874(T) and IBS S6652, were isolated from the faeces of two healthy monkeys (Macaca fascicularis) from Mauritius that were kept in quarantine in the Centre for Primatology, Strasbourg, France. Phylogenetic analysis based on 16S rRNA gene sequences showed that the two isolates formed an unknown genetic lineage within the genus Aeromonas. The two isolates had nearly identical sequences (0.1 % nucleotide substitution) that were related closely to those of recognized Aeromonas species (1.7-3.5 % nucleotide substitution). DNA-DNA hybridization showed that strains IBS S6874(T) and IBS S6652 had high DNA-DNA similarity (89 %) to each other and a low level of DNA-DNA similarity to closely related taxa (18 % relatedness to Aeromonas trota and 16 % relatedness to Aeromonas schubertii). Phenotypically, the two monkey isolates differed from most previously described mesophilic Aeromonas species by their lack of haemolysis on sheep-blood agar and inability to produce indole, gas from glucose or acid from mannitol. They differed from the most closely related species, A. schubertii, by their ability to produce acid from D-cellobiose and D-sucrose and by their pyrazinamidase activity. The name Aeromonas simiae sp. nov. is proposed for these isolates; strain IBS S6874(T) (=CIP 107798(T)=CCUG 47378(T)) is the type strain.

Determination of fosmidomycin in human serum and urine by capillary electrophoresis

A capillary electrophoresis method with direct UV detection was developed for the determination of fosmidomycin, a promising new anti-malarial drug, in human serum and urine. Optimization of the separation parameters resulted in a buffer system adjusted to pH 10.8 containing a cationic reagent and an organic modifier. Under these conditions, the migration time of fosmidomycin was 5.2 min with serum and 7.4 min with urine samples. Validation of the method revealed good recoveries, precision and accuracy. The limit of quantification was 0.5 microg/ml in serum and 10 microg/ml in urine. The determination of fosmidomycin in serum was linear over a range of 0.1-150 microg/ml. Short and long-term stability tests resulted in no significant loss of fosmidomycin. The described technique will provide a fast and accurate analytical method for future pharmacokinetic studies.

Regulation of virulence determinants inStaphylococcus aureus: complexity and applications

The virulence of Staphylococcus aureus is essentially determined by cell wall associated proteins and secreted toxins that are regulated and expressed according to growth phases and/or growth conditions. Gene expression is regulated by specific and sensitive mechanisms, most of which act at the transcriptional level. Regulatory factors constitute numerous complex networks, driving specific interactions with target gene promoters. These factors are largely regulated by two-component regulatory systems, such as the agr, saeRS, srrAB, arlSR and lytRS systems. These systems are sensitive to environmental signals and consist of a sensor histidine kinase and a response regulator protein. DNA-binding proteins, such as SarA and the recently identified SarA homologues (SarR, Rot, SarS, SarT, SarU), also regulate virulence factor expression. These homologues might be intermediates in the regulatory networks. The multiple pathways generated by these factors allow the bacterium to adapt to environmental conditions rapidly and specifically, and to develop infection. Precise knowledge of these regulatory mechanisms and how they control virulence factor expression would open up new perspectives for antimicrobial chemotherapy using key inhibitors of these systems.

Positive surveillance blood culture is a predictive factor for secondary metastatic infection in patients with Staphylococcus aureus bacteraemia

PURPOSE

Staphylococcus aureus bacteraemia (SAB) may be complicated by secondary metastatic infection such as endocarditis, osteomyelitis or septic arthritis. This cohort study aimed to assess the prognostic value of sustained bacteraemia for outcomes related to Staphylococcus aureus bacteraemia.

SUBJECTS AND METHODS

The study took place in three tertiary-care, university-affiliated hospitals. Patients were prospectively included if they agreed to participate and if the following data were available: (a). surveillance blood culture taken between 24 and 48 h after commencement of effective antibiotic therapy; (b). appropriate investigations (at least a TTE) performed as suggested by the infectious diseases consult service. Patients with sustained bacteraemia defined as persistent positive blood cultures more than 24 h after commencement of effective antibiotic therapy were compared to patients for whom the surveillance blood culture was negative.

RESULTS

One hundred and four patients were enrolled, including 51 patients diagnosed with sustained bacteraemia. Sustained bacteraemia was significantly associated with a higher frequency of secondary metastatic infection (p<0.001) and with a higher frequency of CRP>100 mg/l. Frequency of acute complications due to infection, septic shock and death due to bacteraemia was higher for patients with sustained bacteraemia but this difference was not statistically significant. Using a Cox model, the risk for death associated with sustained SAB, controlling for Index of comorbidity and age (categorised as<or>or=70 years), was 1.2 (95% CI: (0.5, 3); p>0.05).

CONCLUSION

In conclusion, surveillance blood cultures, especially performed on effective antibiotic therapy, may be a simple and cost-effective way to select a population at risk for secondary metastatic infection from SAB.

Facteurs de virulence d’Aeromonas caviae isolés de cas cliniques

Aeromonas caviae, an ubiquitous aquatic organism, has long been considered to be of low pathogenicity, and its virulence mechanisms are still not clearly understood. Twenty-eight A. caviae isolates of clinical origin, most often monomicrobic, were identified in our university hospital over a four year period. Patients, mostly immunocompromised, were: eight diarrhoeal infants, 13 diarrhoeal adults, seven bacteraemic adults. Adults were frequently suffering from underlying intestinal malignancy, hepatobiliary disease, gastrectomy. Virulence factors were investigated. Adherence, studied by use of tissue culture HEp-2 cells, and staining of characteristic lateral flagella, were observed in diarrhoeal strains. Extracellular hemolytic activity was tested on rabbit erythrocytes suspensions at 25 and 37 degrees C. One blood culture isolate showed an important hemolytic activity at 25 degrees C, but none at 37 degrees C. Treatment with furin activated the aerolysin precursor and resulted in significant hemolysis at 37 degrees C, and fluid accumulation in rabbit ileal loops similar to that of A. hydrophila as control. The presence of the hemolysin gene was confirmed in this strain by PCR. In conclusion, A. caviae was shown to be a pathogen isolated from diarrhoea and bacteraemia in immunocompromised patients with malignancies and low gastric acidity as favouring factors. Virulence including the ability to adhere to cells and the production of lateral flagella was observed in diarrhoeal strains. The expression and the production of extracellular hemolytic activity and enterotoxicity at 37 degrees C depended on the activation of the pore forming toxin aerolysin precursor by furin. In vivo the protoxin is probably processed to its mature form by host proteases.

Ion channels and bacterial infection: the case of beta-barrel pore-forming protein toxins of Staphylococcus aureus

Staphylococcus aureus strains causing human pathologies produce several toxins, including a pore-forming protein family formed by the single-component alpha-hemolysin and the bicomponent leukocidins and gamma-hemolysins. The last comprise two protein elements, S and F, that co-operatively form the active toxin. alpha-Hemolysin is always expressed by S. aureus strains, whereas bicomponent leukotoxins are more specifically involved in a few diseases. X-ray crystallography of the alpha-hemolysin pore has shown it is a mushroom-shaped, hollow heptamer, almost entirely consisting of beta-structure. Monomeric F subunits have a very similar core structure, except for the transmembrane stem domain which has to refold during pore formation. Large deletions in this domain abolished activity, whereas shorter deletions sometimes improved it, possibly by removing some of the interactions stabilizing the folded structure. Even before stem extension is completed, the formation of an oligomeric pre-pore can trigger Ca(2+)-mediated activation of some white cells, initiating an inflammatory response. Within the bicomponent toxins, gamma-hemolysins define three proteins (HlgA, HlgB, HlgC) that can generate two toxins: HlgA+HlgB and HlgC+HlgB. Like alpha-hemolysin they form pores in planar bilayers with similar conductance, but opposite selectivity (cation instead of anion) for the presence of negative charges in the ion pathway. gamma-Hemolysin pores seem to be organized as alpha-hemolysin, but should contain an even number of each component, alternating in a 1:1 stoichiometry.

Control of the oxidative burst of human neutrophils by staphylococcal leukotoxins

The ability of staphylococcal two-component leukotoxins to induce an oxidative burst and/or to prime human polymorphonuclear cells (PMNs) was studied by using spectrofluorometry or flow cytometry. At sublytic concentrations, the HlgA-HlgB, HlgA-LukF-PV, LukS-PV-LukF-PV, and HlgC-LukF-PV combinations of leukotoxins, but not the LukS-PV-HlgB and HlgC-HlgB combinations, were able to induce H(2)O(2) production similar to the H(2)O(2) production induced by 1 micro M N-formyl-Met-Leu-Phe (fMLP). In addition, when added at sublytic concentrations, all of the leukotoxin combinations primed PMNs for H(2)O(2) production induced by fMLP. Leukotoxin activation was dependent on the presence of Ca(2+) and was inhibited by wortmannin, an inhibitor of phosphatidylinositol 3-kinase, but not by N-methyl-L-arginine, an inhibitor of NO generation, which eliminates the possibility that NO plays a role in the action of leukotoxins. At higher concentrations, all leukotoxins inhibited H(2)O(2) production by PMNs activated by fMLP, phorbol 12-myristate 13-acetate (PMA), or the leukotoxins themselves. This inhibition was not related to the pore formation induced by leukotoxins. Intracellular release of H(2)O(2) induced by fMLP and PMA was not primed by leukotoxins but was inhibited. It seems that leukotoxin inhibition of H(2)O(2) release is independent of pore formation but secondary to an intracellular event, as yet unknown, triggered by leukotoxins.

The effect of rifampin on the pharmacokinetics of vinorelbine in the micropig

BACKGROUND

Vinorelbine has been shown to be metabolised by CYP3A4 in vitro. To evaluate the impact of CYP3A in the disposition of vinorelbine in vivo, we compared the kinetics of the alkaloid given intravenously alone and combined with rifampin, a potent CYP3A inducer, in the micropig.

ANIMALS AND METHODS

Four healthy Yucatan micropigs, about 20 kg, received a first infusion of vinorelbine (0.5 mg/kg). During the next week they were injected rifampin (600 mg daily) and a second vinorelbine infusion (0.5 mg/kg) on the 7th day of rifampin dosing. Serum concentrations of vinorelbine and rifampin were measured by high performance liquid chromatography.

RESULTS

The mean peak concentrations of vinorelbine were 274.2 ng/ml (Standard Deviation or SD: 90) and 458 ng/ml (SD: 448), the mean areas under the serum concentration-time curve were 8,344 ng.min.ml-1 (SD: 2,604) and 14,093 ng/ml.min-1 (SD: 10,000) and the total clearances were 1.146 l/min (SD: 0.333) and 1.003 l/min (SD: 0.714) when the Catharanthus alkaloid was given alone or was combined with rifampin, respectively.

CONCLUSION

We did not observe an increase in vinorelbine elimination by rifampin related to a CYP3A induction in an animal model physiologically close to humans. Although the number of animals was small, these results suggest that CYP3A metabolism constitutes a minor pathway of elimination of intravenous vinorelbine in the micropig.

Moxifloxacin efficacy and vitreous penetration in a rabbit model of Staphylococcus aureus endophthalmitis and effect on gene expression of leucotoxins and virulence regulator factors

Bacterial endophthalmitis is a serious complication of ocular surgery and of eye trauma; the leading causative organisms are Staphylococcus aureus strains. Tissue damage is due both to the host inflammatory response and to toxin synthesis by bacteria. Systemic treatment remains difficult because most antibiotics show poor ocular penetration. Moxifloxacin (MXF), a novel fluoroquinolone, was evaluated for its penetration into the vitreous of normal rabbit eyes and of eyes of rabbits infected for 24 h with methicillin-susceptible and methicillin-resistant S. aureus (MSSA and MRSA) following a single intravenous administration of 5 or 20 mg/kg. MXF penetration was rapid and efficient regardless of the dose, ranging from 28 to 52%. An inflammatory state of the vitreous significantly increased penetration after the 20-mg/kg dose, with penetration reaching 52%. Concentrations determined in the vitreous cavity following a 20-mg/kg administration showed a 3.5-fold decrease of the bacterial density within 5 h for MSSA (MIC, 0.125 micro g/ml) and a 1.6-fold decrease for MRSA (MIC, 4 micro g/ml) strains, respectively. By using a semiquantitative reverse transcription-PCR method, the expression of luk-PV and hlgCB, but not hlgA, encoding staphylococcal leukotoxins, was detected in the vitreous without MXF treatment. A slight decrease in the expression of leucotoxins and sarA, agr, and sigB virulence regulatory factors was observed 1 h following the administration of 5 mg of MXF per kg.

Staphylococcal epidermolysins

PURPOSE OF REVIEW

Staphylococcal epidermolysins are the major causative toxins of bullous impetigo and staphylococcal scalded skin syndrome. This disease is characterized by the splitting of the epidermis between two cell layers resulting in exfoliation. It predominantly affects newborn babies and exposes them to secondary infections. This leads to the risk of epidemics, especially in nurseries. With only an experimental model which consists of skin injections in newborn mice and the recent determination of three-dimensional structures, the essential function of these toxins remained controversial, split between that of specific proteases and that of superantigens.

RECENT FINDINGS

Staphylococcal epidermolysins now constitute a family of toxins, with the recent characterizations of two new serotypes: ETC and ETD. They may be secreted by sensitive or methicillin-resistant strains. Four molecules were also identified in Staphylococcus hyicus responsible for exudative epidermitis in swine. While different observations suggested a proteolytic action to these toxins, the histological parallel made with pemphigus foliaceus greatly helped in the characterization of the targets for epidermolysins ETA, ETB, ETD: desmoglein-1, a desmosome-constitutive protein, and incidentally melanocyte-stimulating hormones, which accounts for the blisters observed clinically.

SUMMARY

The growing complexity in staphylococcal toxins has to be taken into account both for their association with diseases and for diagnosis purposes. Even though cases of staphylococcal scalded skin syndrome in adults are rare, they raise further questions about the pathogenic features of the disease such as individual sensitivity and distribution of the toxins into the body.

Isolation of sulfate-reducing bacteria from human thoracoabdominal pus

To evaluate the prevalence of sulfate-reducing bacteria in septic processes, we searched for these bacteria by culture in 100 consecutive abdominal and pleural pus specimens. Twelve isolates were obtained from abdominal samples and were identified by a multiplex PCR as Desulfovibrio piger (formerly Desulfomonas pigra) (seven strains), Desulfovibrio fairfieldensis (four strains), and Desulfovibrio desulfuricans (one strain).

Ex vivo pharmacodynamics of amoxicillin-clavulanate against beta-lactamase-producing Escherichia coli in a yucatan miniature pig model that mimics human pharmacokinetics

The objective of the present study was to investigate the potential bactericidal activity of amoxicillin-clavulanate against beta-lactamase-producing Escherichia coli strains and to elucidate the extent to which enzyme production affects the activity. Six adult Yucatan miniature pigs received a single intravenous dose of 1.1 g of amoxicillin-clavulanate as an intravenous infusion over 30 min. The pharmacokinetic parameters were determined for the serum samples and compared to the published data for humans (2.2-g intravenous dose). The parameters were comparable for the two species, and therefore, the miniature pig constitutes a good model for pharmacodynamic study of amoxicillin-clavulanate. Therefore, the model was used in an ex vivo pharmacodynamic study of amoxicillin-clavulanate against four strains of Escherichia coli producing beta-lactamases at different levels. The E. coli strains were cultured with serial dilutions (1:2 to 1:256) of the serum samples from the pharmacokinetic study, and the number of surviving bacteria was determined after 1, 3, and 6 h of exposure. Amoxicillin-clavulanate at concentrations less than the MIC and the minimal bactericidal concentration had marked bactericidal potency against the strain that produced low levels of penicillinase. For high-level or intermediate-level beta-lactamase-producing strains, the existence of a clavulanate concentration threshold of 1.5 to 2 micro g/ml, below which there was no bactericidal activity, was demonstrated. The index of surviving bacteria showed the existence of mixed concentration- and time-dependent actions of amoxicillin (in the presence of clavulanate) which varied as a function of the magnitude of beta-lactamase production by the test strains. This study shows the effectiveness of amoxicillin-clavulanate against low- and intermediate-level penicillinase-producing strains of E. coli. These findings are to be confirmed in a miniature pig experimental infection model.

Dialister pneumosintes associated with human brain abscesses

In this report, we review two cases of brain infection due to Dialister pneumosintes in previously healthy patients. The bacterium was isolated from the first patient by blood culture and directly from a brain abscess in the second patient. In both cases, the infection was suspected to be of nasopharyngeal or dental origin. The patients had favorable outcomes following surgical debridement and antibiotic treatment. After in vitro amplification and partial sequencing of the 16S rRNA gene, two strains were classified as D. pneumosintes. However, traditional biochemical tests were not sufficient to identify the bacteria. In addition to causing periodontal and opportunistic infections, D. pneumosintes, contained in mixed flora, may behave as a clinically important pathogen, especially in the brain. In addition to phenotypic characterization, 16S rRNA partial sequencing was used to identify D. pneumosintes definitively.

Protein engineering modulates the transport properties and ion selectivity of the pores formed by staphylococcal gamma-haemolysins in lipid membranes

Staphylococcal gamma-haemolysins are bicomponent toxins in a family including other leucocidins and alpha-toxin. Two active toxins are formed combining HlgA or HlgC with HlgB. Both open pores in lipid membranes with conductance, current voltage characteristics and stability similar to alpha-toxin, but different selectivity (cation instead of anion). Structural analogies between gamma-haemolysins and alpha-toxin indicate the presence, at the pore entry, of a conserved region containing four positive charges in alpha-toxin, but either positive or negative in gamma-haemolysins. Four mutants were produced (HlgA D44K, HlgB D47K, HlgB D49K and HlgB D47K/D49K) converting those negative charges to positive in HlgA and HlgB. When all charges were positive, the pores had the same selectivity and conductance as alpha-toxin, suggesting that the cluster may form an entrance electrostatic filter. As mutated HlgC-HlgB pores were less affected, additional charges in the lumen of the pore were changed (HlgB E107Q, HlgB D121N, HlgB T136D and HlgA K108T). Removing a negative charge from the lumen made the selectivity of both HlgA-HlgB D121N and HlgC-HlgB D121N more anionic. Residue D121 of HlgB is compensated by a positive residue (HlgA K108) in the HlgA-HlgB pore, but isolated in the more cation-selective HlgC-HlgB pore. Interestingly, the pore formed by HlgA K108T-HlgB, in which the positive charge of HlgA was removed, was as cation selective as HlgC-HlgB. Meanwhile, the pore formed by HlgA K108T-HlgB D121N, in which the two charge changes compensated, retrieved the properties of wild-type HlgA-HlgB. We conclude that the conductance and selectivity of the gamma-haemolysin pores depend substantially on the presence and location of charged residues in the channel.

Retrieving biological activity from LukF-PV mutants combined with different S components implies compatibility between the stem domains of these staphylococcal bicomponent leucotoxins

Bicomponent leucotoxins, such as Panton-Valentine leucocidin, are composed of two classes of proteins, a class S protein such as LukS-PV, which bears the cell membrane binding function, and a class F protein such as LukF-PV, which interacts to form a bipartite hexameric pore. These leucotoxins induce cell activation, linked to a Ca(2+) influx, and pore formation as two consecutive and independently inhibitable events. Knowledge of the LukF-PV monomer structure has indicated that the stem domain is folded into three antiparallel beta-strands in the water-soluble form and has to refold into a transmembrane beta-hairpin during pore formation. To investigate the requirements for the cooperative assembly of the stems of the S and F components to produce biological activity, we introduced multiple deletions or single point mutations into the stem domains of LukF-PV and HlgB. While the binding of the mutated proteins was weakly dependent on these changes, Ca(2+) influx and pore formation were affected differently, confirming that they are independent events. Ca(2+) entry into human polymorphonuclear cells requires oligomerization and may follow the formation of a prepore. The activity of some of the LukF-PV mutants, carrying the shorter deletions, was actually improved. This demonstrated that a crucial event in the action of these toxins is the transition of the prefolded stem into the extended beta-hairpins and that this step may be facilitated by small deletions that remove some of the interactions stabilizing the folded structure.

Bartonella bovis Bermond et al. sp. nov. and Bartonella capreoli sp. nov., isolated from European ruminants

Two novel species of Bartonella isolated from European ruminants are described. Bartonella capreoli sp. nov. was isolated from the blood of roe-deer (Capreolus capreolus) captured in Chizé, France. The type strain is IBS 193T (= CIP 106691T = CCUG 43827T). It is distinct from another European ruminant isolate that originated from a cow from a French herd of 430 dairy cattle. The latter isolate belongs to a novel species named Bartonella bovis Bermond et al. sp. nov. The type strain is strain 91-4T (= CIP 106692T = CCUG 43828T). The two bacteria appeared as small, fastidious, aerobic, oxidase-negative, gram-negative rods. Their biochemical properties were similar to those of members of the genus Bartonella. The sequences of the 16S rRNA and citrate synthase genes obtained from the two type strains were highly related to sequences of the different Bartonella species. Hybridization values when testing type strains of recognized Bartonella species, obtained with the nuclease/trichloroacetic acid method, support the creation of two novel species.

Staphylococcus aureus isolated in cases of impetigo produces both epidermolysin A or B and LukE-LukD in 78% of 131 retrospective and prospective cases

Clinical symptoms of impetigo and staphylococcal scalded skin syndrome may not only be expressed as the splitting of cell layers within the epidermis but are often accompanied by some localized inflammation. Toxin patterns of Staphylococcus aureus isolates originating from patients with impetigo and also from those with other primary and secondary skin infections in a retrospective isolate collection in France and a prospective isolate collection in French Guiana revealed a significant association (75% of the cases studied) of impetigo with production of at least one of the epidermolysins A and B and the bicomponent leucotoxin LukE-LukD (P < 0.001). However, most of the isolates were able to produce one of the nonubiquitous enterotoxins. Pulsed-field gel electrophoresis (PFGE) of genomic DNA hydrolyzed with SmaI showed a polymorphism of the two groups of isolates despite the fact that endemic clones were suspected in French Guiana and France. The combination of toxin patterns with PFGE fingerprinting may provide further discrimination among isolates defined in a given cluster or a given pulsotype and account for a specific virulence. The new association of toxins with a clinical syndrome may reveal principles of the pathological process.

Evidence for a true post-beta-lactamase-inhibitor effect of clavulanic acid against Klebsiella pneumoniae and Haemophilus influenzae

OBJECTIVE

The purpose of this study was to investigate and characterize in vitro the post-beta-lactamase inhibitor effect (PLIE) of clavulanic acid against two beta-lactamase-producing species of bacteria.

METHODS

The PLIE was investigated against one strain of Klebsiella pneumoniae and one strain of Haemophilus influenzae. A stationary-phase inoculum of about 107 colony-forming units per mL of each bacterium was pre-exposed for 2 h to clavulanic acid, either alone or in combination with amoxicillin at various concentrations. After pre-exposure, the dilution required to remove the beta-lactamase inhibitor was 1:100 or 1:1000 according to the bacterial species and their susceptibilities to clavulanic acid. Bacteria were counted hourly after drug removal, on solid agar medium.

RESULTS

Control cultures exposed to amoxicillin alone after dilution, showed a delay in growth, which may be inherent to the time required to synthesize sufficient beta-lactamase after the dilution steps. Control experiments clearly distinguished the post-antibiotic effect and the growth delay from the PLIE.

CONCLUSION

The PLIE could be one of several factors explaining why beta-lactam/beta-lactamase inhibitor combinations remain effective throughout the dosing interval, even if a few hours after in vivo administration, serum concentrations of beta-lactamase inhibitor fall below levels that are active in vitro.

Ex vivo 12 h bactericidal activity of oral co-amoxiclav (1.125 g) against beta-lactamase-producing Haemophilus influenzae

The aim of the study was to evaluate the in vitro/ex vivo bactericidal activity of a new coamoxiclav single-dose sachet formulation (1 g amoxicillin + 0.125 g clavulanic acid) against a beta-lactamase-producing strain of Haemophilus influenzae. The evaluation covered the 12 h period after antibiotic administration. Serum specimens from the 12 healthy volunteers included in the pharmacokinetic study were pooled by time point and in equal volumes. Eight of 12 pharmacokinetic sampling time points were included in the study. At time points 0.5, 0.75, 1, 1.5, 2.5, 5, 8 and 12 h post-dosing, the kinetics of bactericidal activity were determined for each of the serial dilutions. Each specimen was serially diluted from 1:2 to 1:256. The index of surviving bacteria (ISB) was subsequently determined for each pharmacokinetic time point. For all the serum samples, bactericidal activity was fast (3-6 h), marked (3-6 log(10) reduction in the initial inoculum) and sustained over the 12 h between-dosing interval. The results obtained also confirmed that the potency of the amoxicillin plus clavulanic acid combination was time dependent against the species under study and that the time interval over which the concentrations were greater than the MIC (t > MIC) was 100% for the strain under study. The data thus generated constitute an interesting prerequisite with a view to using co-amoxiclav 1.125 g in a bd oral regimen.

[Chronic experimental bacteremia in Yucatan micropigs]

The Yucatan micropig has been used to develop an experimental model of chronic bacteremia. This animal exhibits clinical and biological characteristics that are close to those in humans, and the pharmacokinetic behaviours of many classes of drugs in this model are similar to those in man. Six adult female were intravenously inoculated with a mean Escherichia coli inoculum of 5.1 x 10(9) bacteria. During five days of spontaneous evolution, the medical follow-up includes biological, clinical and bacteriological parameters. A systemic inflammatory syndrome, a sepsis, an organ insufficiency and positive blood cultures mimic the human disease. In all animals there is an adynamia, a lack of motor coordination, an anorexia, a tachypnea, a fever, a leuconeutropenia followed by an hyperleucocytosis, an anemia, a thrombopenia, an acute tubulonephritis and an elevated sedimentation rate. In some cases, there is an increase of the C reactive protein, in others, an increase of IL-6 and IL-8. At day five, all animals are alive, and five micropigs have positive blood cultures. This chronic, reproducible model is thus suitable for further antibacterial treatments evaluations.

Flow cytometric determination of Panton-Valentine leucocidin S component binding

The binding of the S component (LukS-PV) from the bicomponent staphylococcal Panton-Valentine leucocidin to human polymorphonuclear neutrophils (PMNs) and monocytes was determined using flow cytometry and a single-cysteine substitution mutant of LukS-PV. The mutant was engineered by replacing a glycine at position 10 with a cysteine and was labeled with a fluorescein moiety. The biological activity of the mutant was identical to that of the native protein. It has been shown that LukS-PV has a high affinity for PMNs (Kd = 0.07 +/- 0.02 nM, n = 5) and monocytes (Kd = 0.020 +/- 0.003 nM, n = 3) with maximal binding capacities of 197,000 and 80,000 LukS-PV molecules per cell, respectively. The nonspecifically bound molecules of LukS-PV do not form pores in the presence of the F component (LukF-PV) of leucocidin. LukS-PV and HlgC share the same receptor on PMNs, but the S components of other staphylococcal leukotoxins, HlgA, LukE, and LukM, do not compete with LukS-PV for its receptor. Extracellular Ca2+ at physiological concentrations (1 to 2 nM) has only a slight influence on the LukS-PV binding, in contrast to its complete inhibition by Zn2+. The down-regulation by phorbol 12-myristate 13-acetate (PMA) of the binding of LukS-PV was blocked by staurosporine, suggesting that the regulatory effect of PMA depends on protein kinase C activation. The labeled mutant form of LukS-PV has proved very useful for detailed binding studies of circulating white cells by flow cytometry. LukS-PV possesses a high specific affinity for a unique receptor on PMNs and monocytes.

Treatment resistant Lyme arthritis caused by Borrelia garinii

Lyme arthritis is caused in Europe by three main pathogenic species of Borrelia burgdorferi sensu lato: Borrelia burgdorferi sensu stricto, Borrelia garinii, and Borrelia afzelii. Because few synovial samples have yet been analysed by species-specific DNA amplification methods, further studies are needed to define the spectra of clinical manifestations associated with these different species. Two cases of treatment resistant Lyme arthritis are reported here, in which DNA amplification of the flagellin gene followed by dot-blot hybridisation in the synovial fluid identified B garinii as the causative agent. Clinical and biological data did not differ from the usual descriptions of Lyme arthritis, but as the recently reported molecular mimicry between OspA and hLFA1 is not applicable to B garinii, the pathogenesis of the present cases remains unclear. Future studies should aim at assessing the role of B garinii in European Lyme arthritis and its possible pathogenic and therapeutic consequences.