Non-phthalate plasticizer DEHT preserves adequate blood component quality during storage in PVC blood bags

BACKGROUND AND OBJECTIVES

Commercial blood bags are predominantly made of polyvinyl chloride (PVC) plasticized with di(2-ethylhexyl) phthalate (DEHP). DEHP is favourable for storage of red blood cells (RBC). Historically, removal of DEHP from blood bags has been linked to unacceptable haemolysis levels. Oncoming regulatory restrictions for DEHP due to toxicity concerns increase the urgency to replace DEHP without compromising RBC quality. Di(2-ethylhexyl) terephthalate (DEHT) is one suggested substitute. The aim of this study was to compare PVC-DEHT to PVC-DEHP blood bags using additive solutions saline-adenine-glucose-mannitol (SAGM) and phosphate-adenine-glucose-guanosine-saline-mannitol (PAGGSM), to determine whether DEHT can maintain acceptable component quality.

MATERIALS AND METHODS

RBC concentrates (N = 64), platelet concentrates (N = 16) and fresh frozen plasma (N = 32) were produced from whole blood collected into either DEHT or DEHP plasticized systems. Using a pool-and-split study design, pairs of identical RBC content were created within each plasticizer arm and assigned either SAGM or PAGGSM. Storage effects were assessed weekly for 49 days (RBC), 7 days (platelets) and before/after freezing (plasma).

RESULTS

Though haemolysis was slightly higher in DEHT, all study arms remained below half of the European limit 0·8%. K⁺ was lower in DEHT than in DEHP independent of additive solution. The metabolic parameters were not influenced by choice of plasticizer. Platelet activation/metabolism and plasma content were similarly preserved.

CONCLUSION

Our study demonstrates that the plasticizer DEHT provides adequate blood component quality. We propose DEHT as a strong future candidate for replacement of DEHP in blood bags.

Fosfomycin and Staphylococcus aureus: transcriptomic approach to assess effect on biofilm, and fate of unattached cells

Interest has been rekindled in the old antibiotic fosfomycin, partly because of its ability to penetrate biofilm. Using a transcriptomic approach, we investigated the modifications induced by fosfomycin in sessile cells of a clinical Staphylococcus aureus isolated from a device-associated infection. Cells still able to form biofilm after 4 h of incubation in the presence of subinhibitory concentrations of fosfomycin and cells from 24-h-old biofilm later submitted to fosfomycin had 6.77% and 9.41%, respectively, of differentially expressed genes compared with their antibiotic-free control. Fosfomycin induced mostly downregulation of genes assigned to nucleotide, amino acid and carbohydrate transport, and metabolism. Adhesins and capsular biosynthesis proteins encoding genes were downregulated in fosfomycin-grown biofilm, whereas the murein hydrolase regulator lgrA and a D-lactate dehydrogenase-encoding gene were upregulated. In fosfomycin-treated biofilm, the expression of genes encoding adhesins, the cell wall biosynthesis protein ScdA, and to a lesser extent the fosfomycin target MurA was also decreased. Unattached cells surrounding fosfomycin-grown biofilm showed greater ability to form aggregates than their counterparts obtained without fosfomycin. Reducing their global metabolism and lowering cell wall turnover would allow some S. aureus cells to grow in biofilm despite fosfomycin stress while promoting hyperadherent phenotype in the vicinity of the fosfomycin-treated biofilm.

Discrimination of Escherichia coli and Shigella spp. by Nuclear Magnetic Resonance Based Metabolomic Characterization of Culture Media

Dysentery is a major health threat that dramatically impacts childhood morbidity and mortality in developing countries. Various pathogenic agents cause dysentery, such as Shigella spp. and Escherichia coli, which are very closely related if not identical species. Sensitive and precise detection and identification of the infectious agent is important to target the best therapeutic strategy, but the differential diagnosis of these two groups remains a challenge using conventional methods. Here, we present a nuclear magnetic resonance (NMR) based multivariate classification model employing bacterial metabolic footprints in postculture growth media with remarkable segregation capability, including the discrimination of lactose negative E. coli and Shigella spp. Our results confirm the potential of metabolomic markers in the field of bacterial identification for the distinction of even very closely related species.

Phenotypic and Genomic Characterization of AmpC-Producing Klebsiella pneumoniae From Korea

The prevalence of multidrug-resistant gram-negative bacteria has continuously increased over the past few years; bacterial strains producing AmpC β-lactamases and/or extended-spectrum β-lactamases (ESBLs) are of particular concern. We combined high-resolution whole genome sequencing and phenotypic data to elucidate the mechanisms of resistance to cephamycin and β-lactamase in Korean Klebsiella pneumoniae strains, in which no AmpC-encoding genes were detected by PCR. We identified several genes that alone or in combination can potentially explain the resistance phenotype. We showed that different mechanisms could explain the resistance phenotype, emphasizing the limitations of the PCR and the importance of distinguishing closely-related gene variants.

Evaluation of Mycotube, a modified version of Lowenstein-Jensen (LJ) medium, for efficient recovery of Mycobacterium tuberculosis (MTB)

Timely diagnosis of tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB), is only achieved for ~58% cases. An improved, accurate, time- and cost-effective method for bacteriological confirmation of MTB is necessary. We evaluated Mycotube, a new variant of Lowenstein-Jensen (LJ) culture medium, by comparing it with Mycobacterium Growth Indicator Tube (MGIT) 960 (gold standard), local LJ, and bioMérieux LJ-T in terms of isolation rate and time-to-growth. Pulmonary and extra-pulmonary samples from treatment-naïve suspects (n = 207) were decontaminated by the N-acetyl-L-cysteine-sodium hydroxide method and used to inoculate the four media. Subjective and objective parameters were used for evaluation. Mycotube yielded 140 positive results, compared to 162, 69, and 141 from MGIT, local LJ, and LJ-T, respectively. Of these, 139 (67%) were true-positive results and 1 (0.5%) was false-positive. The mean time-to-growth detection was 17.4 days for Mycotube, compared to 14.5, 28.1, and 16.5 days for MGIT, local LJ, and LJ-T, respectively. The mean time-to-growth for local LJ significantly differed from that for MGIT, but not those for LJ-T and Mycotube. No contamination was observed. Mycotube had a sensitivity of 85.8% and a specificity of 97.8% as compared to MGIT. Mycotube offers good results, comparable with those observed for conventional LJ. It requires only basic laboratory infrastructure. The overall cost of the test should be nearly three times lower than that of MGIT. Mycotube helps with TB diagnosis and generates pure isolates for drug susceptibility testing.

Identification of mycobacterium spp. and nocardia spp. from solid and liquid cultures by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS)

Identification of microorganisms by MALDI-TOF MS has been widely accepted in clinical microbiology. However, for Mycobacterium spp. and Nocardia spp. such identification has not yet reached the optimal level of routine testing. Here we describe the development of an identification tool for 49 and 15 species of Mycobacterium spp. and Nocardia spp., respectively. During database construction, a number of ambiguous reference identifications were revealed and corrected via molecular analyses. Eventually, more than 2000 individual mass spectra acquired from 494 strains were included in a reference database and subjected to bio-statistical analyses. This led to correct species identification and correct combination of species into several complexes or groups, such as the Mycobacterium tuberculosis complex. With the Advanced Spectrum Classifier algorithm, class-specific bin weights were determined and tested by cross-validation experiments with good results. When challenged with independent isolates, overall identification performance was 90% for identification of Mycobacterium spp. and 88% for Nocardia spp. However, for a number of Mycobacterium sp. isolates, no identification could be achieved and in most cases, this could be attributed to the production of polymers that masked the species-specific protein peak patterns. For the species where >20 isolates were tested, correct identification reached 95% or higher. With the current spectral database, the identification of Mycobacterium spp. and Nocardia spp. by MALDI-TOF MS can be performed in routine clinical diagnostics although in some complicated cases verification by sequencing remains mandatory.

Identification of bacterial species by untargeted NMR spectroscopy of the exo-metabolome

Identification of bacterial species is a crucial bottleneck for clinical diagnosis of infectious diseases. Quick and reliable identification is a key factor to provide suitable antibiotherapies and avoid the development of multiple-drug resistance. We propose a novel nuclear magnetic resonance (NMR)-based metabolomics strategy for rapid discrimination and identification of several bacterial species that relies on untargeted metabolic profiling of supernatants from bacterial culture media. We show that six bacterial species (Gram negative: Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis; Gram positive: Enterococcus faecalis, Staphylococcus aureus, and Staphylococcus saprophyticus) can be well discriminated from multivariate statistical analysis, opening new prospects for NMR applications to microbial clinical diagnosis.

A Chlorhexidine- Agar Plate Culture Medium Protocol to Complement Standard Broth Culture of Mycobacterium tuberculosis

The culture of Mycobacterium tuberculosis using parallel inoculation of a solid culture medium and a liquid broth provides the gold standard for the diagnosis of tuberculosis. Here, we evaluated a chlorhexidine decontamination-MOD9 solid medium protocol versus the standard NALC-NaOH-Bactec 960 MGIT protocol for the diagnosis of pulmonary tuberculosis by culture. Three-hundred clinical specimens comprising 193 sputa, 30 bronchial aspirates, 10 broncho-alveolar lavages, 47 stools, and 20 urines were prospectively submitted for the routine diagnosis of tuberculosis. The contamination rates were 5/300 (1.7%) using the MOD9 protocol and 17/300 (5.7%) with the Bactec protocol, respectively (P < 0.05, Fisher exact test). Of a total of 50 Mycobacterium isolates (48 M. tuberculosis and two Mycobacterium abscessus) were cultured. Out of these 50, 48 (96%) isolates were found using the MOD9 protocol versus 35 (70%) when using the Bactec protocol (P < 0.05, Fisher exact test). The time to positivity was 10.1 ± 3.9 days versus 14.7 ± 7.3 days, respectively, (P < 0.05, Student’s t-test). These data confirmed the usefulness of parallel inoculation of a solid culture medium with broth for the recovery of M. tuberculosis in agreement with current recommendations. More specifically, chlorhexidine decontamination and inoculation of the MOD9 solid medium could be proposed to complement the standard Bactec 960 MGIT broth protocol.

Effects of antibiotics on biofilm and unattached cells of a clinical Staphylococcus aureus isolate from bone and joint infection

Treatment of orthopaedic infections remains challenging owing to the inability of antibiotics to eradicate biofilms and prevent their regrowth. The present study characterized the effects of 12 antibiotics on in vitro biofilm formed by a representative strain of meticillin-susceptible Staphylococcus aureus (MSSA) isolated from a bone infection. Determination of the minimum biofilm eradication concentrations indicated that in vitro eradication of 24 h-old biofilms required concentrations up to 51,200 times higher than MICs. The influence of the same panel of antibiotics was also investigated on biofilm formation at concentrations including the breakpoints, by numbering viable cells in the suspensions (individual cells) and the biofilm biomass. Except for fusidic acid, the presence of antibiotics during the initial steps of biofilm formation resulted in significant decreases in the number of sessile viable bacteria at the highest concentrations tested. Ceftarolin, daptomycin, fosfomycin, gentamicin, ofloxacin, rifampicin and vancomycin were the most effective drugs. Confocal microscopy analysis indicated that daptomycin was more efficient at bacteria lysis than gentamicin and vancomycin. However, viable individual cells were still detectable in the assays performed with ceftarolin, fosfomycin, ofloxacin, rifampicin and vancomycin at concentrations for which no sessile cells were detected. Although none of the molecules tested was effective at classical therapeutic concentrations against 24 h-old MSSA biofilms, all except fusidic acid were able to impair biofilm formation at concentrations near the breakpoints. However, presence of viable individual unattached cells could imply a significant risk of microbial dissemination and increased risk of infections.

Label-free SRM-based relative quantification of antibiotic resistance mechanisms in Pseudomonas aeruginosa clinical isolates

Both acquired and intrinsic mechanisms play a crucial role in Pseudomonas aeruginosa antibiotic resistance. Many clinically relevant resistance mechanisms result from changes in gene expression, namely multidrug efflux pump overproduction, AmpC β-lactamase induction or derepression, and inactivation or repression of the carbapenem-specific porin OprD. Changes in gene expression are usually assessed using reverse-transcription quantitative real-time PCR (RT-qPCR) assays. Here, we evaluated label-free Selected Reaction Monitoring (SRM)-based mass spectrometry to directly quantify proteins involved in antibiotic resistance. We evaluated the label-free SRM using a defined set of P. aeruginosa isolates with known resistance mechanisms and compared it with RT-qPCR. Referring to efflux systems, we found a more robust relative quantification of antibiotic resistance mechanisms by SRM than RT-qPCR. The SRM-based approach was applied to a set of clinical P. aeruginosa isolates to detect antibiotic resistance proteins. This multiplexed SRM-based approach is a rapid and reliable method for the simultaneous detection and quantification of resistance mechanisms and we demonstrate its relevance for antibiotic resistance prediction.

The ongoing revolution of MALDI-TOF mass spectrometry for microbiology reaches tropical Africa

Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) represents a revolution in routine pathogen identification in clinical microbiology laboratories. A MALDI-TOF MS was introduced to tropical Africa in the clinical microbiology laboratory of the Hôpital Principal de Dakar (Senegal) and used for routine pathogen identification. Using MS, 2,429 bacteria and fungi isolated from patients were directly assayed, leading to the identification of 2,082 bacteria (85.7%) and 206 fungi (8.5%) at the species level, 109 bacteria (4.5%) at the genus level, and 16 bacteria (0.75%) at the family level. Sixteen isolates remained unidentified (0.75%). Escherichia coli was the most prevalent species (25.8%) followed by Klebsiella pneumoniae (14.8%), Streptococcus agalactiae (6.2%), Acinetobacter baumannii (6.1%), Pseudomonas aeruginosa (5.9%), and Staphylococcus aureus (5.9%). MALDI-TOF MS has also enabled the detection of rare bacteria and fungi. MALDI-TOF MS is a powerful tool for the identification of bacterial and fungal species involved in infectious diseases in tropical Africa.

Meropenem/colistin synergy testing for multidrug-resistant Acinetobacter baumannii strains by a two-dimensional gradient technique applicable in routine microbiology

OBJECTIVES

Precise assessment of potential therapeutic synergy, antagonism or indifference between antimicrobial agents currently depends on time-consuming and hard-to-standardize in vitro chequerboard titration methods. We here present a method based on a novel two-dimensional antibiotic gradient technique named Xact™.

METHODS

We used a test comprising a combination of perpendicular gradients of meropenem and colistin in a single quadrant. We compared test outcomes with those obtained with classical chequerboard microbroth dilution testing in a study involving 27 unique strains of multidrug-resistant Acinetobacter baumannii from diverse origins.

RESULTS

We were able to demonstrate 92% concordance between the new technology and classical chequerboard titration using the A. baumannii collection. Two strains could not be analysed by Xact™ due to their out-of-range MIC of meropenem (>128 mg/L).

CONCLUSIONS

The new test was shown to be diagnostically useful, easy to implement and less labour intensive than the classical method.

Comparison of two approaches for the classification of 16S rRNA gene sequences

The use of 16S rRNA gene sequences for microbial identification in clinical microbiology is accepted widely, and requires databases and algorithms. We compared a new research database containing curated 16S rRNA gene sequences in combination with the lca (lowest common ancestor) algorithm (RDB-LCA) to a commercially available 16S rDNA Centroid approach. We used 1025 bacterial isolates characterized by biochemistry, matrix-assisted laser desorption/ionization time-of-flight MS and 16S rDNA sequencing. Nearly 80 % of isolates were identified unambiguously at the species level by both classification platforms used. The remaining isolates were mostly identified correctly at the genus level due to the limited resolution of 16S rDNA sequencing. Discrepancies between both 16S rDNA platforms were due to differences in database content and the algorithm used, and could amount to up to 10.5 %. Up to 1.4 % of the analyses were found to be inconclusive. It is important to realize that despite the overall good performance of the pipelines for analysis, some inconclusive results remain that require additional in-depth analysis performed using supplementary methods.

Challenges in the culture-independent analysis of oral and respiratory samples from intubated patients

The spread of microorganisms in hospitals is an important public health threat, and yet few studies have assessed how human microbial communities (microbiota) evolve in the hospital setting. Studies conducted so far have mainly focused on a limited number of bacterial species, mostly pathogenic ones and primarily during outbreaks. We explored the bacterial community diversity of the microbiota from oral and respiratory samples of intubated patients hospitalized in the intensive care unit and we discuss the technical challenges that may arise while using culture-independent approaches to study these types of samples.

Automatic identification of mixed bacterial species fingerprints in a MALDI-TOF mass-spectrum

MOTIVATION

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry has been broadly adopted by routine clinical microbiology laboratories for bacterial species identification. An isolated colony of the targeted microorganism is the single prerequisite. Currently, MS-based microbial identification directly from clinical specimens can not be routinely performed, as it raises two main challenges: (i) the nature of the sample itself may increase the level of technical variability and bring heterogeneity with respect to the reference database and (ii) the possibility of encountering polymicrobial samples that will yield a 'mixed' MS fingerprint. In this article, we introduce a new method to infer the composition of polymicrobial samples on the basis of a single mass spectrum. Our approach relies on a penalized non-negative linear regression framework making use of species-specific prototypes, which can be derived directly from the routine reference database of pure spectra.

RESULTS

A large spectral dataset obtained from in vitro mono- and bi-microbial samples allowed us to evaluate the performance of the method in a comprehensive way. Provided that the reference matrix-assisted laser desorption/ionization time-of-flight mass spectrometry fingerprints were sufficiently distinct for the individual species, the method automatically predicted which bacterial species were present in the sample. Only few samples (5.3%) were misidentified, and bi-microbial samples were correctly identified in up to 61.2% of the cases. This method could be used in routine clinical microbiology practice.

Rapid clinical bacteriology and its future impact

Clinical microbiology has always been a slowly evolving and conservative science. The sub-field of bacteriology has been and still is dominated for over a century by culture-based technologies. The integration of serological and molecular methodologies during the seventies and eighties of the previous century took place relatively slowly and in a cumbersome fashion. When nucleic acid amplification technologies became available in the early nineties, the predicted "revolution" was again slow but in the end a real paradigm shift did take place. Several of the culture-based technologies were successfully replaced by tests aimed at nucleic acid detection. More recently a second revolution occurred. Mass spectrometry was introduced and broadly accepted as a new diagnostic gold standard for microbial species identification. Apparently, the diagnostic landscape is changing, albeit slowly, and the combination of newly identified infectious etiologies and the availability of innovative technologies has now opened new avenues for modernizing clinical microbiology. However, the improvement of microbial antibiotic susceptibility testing is still lagging behind. In this review we aim to sketch the most recent developments in laboratory-based clinical bacteriology and to provide an overview of emerging novel diagnostic approaches.

Equivalence of quality control strains of microorganisms used in the compendial microbiological tests: are national culture collection strains identical?

The pharmacopoeias list a number of microorganisms to be used in the compendial microbiological tests for confirming the growth-promoting, indicative, and inhibitory properties of the media and demonstrating the suitability of the test for a specific test article. Major national culture collections are specified as the sources for these test strains based on their history of deposition and maintenance and use in the compendial tests. Using these microorganisms, it has long been assumed that these strains are interchangeable and that sourcing the strains from different culture collections has no impact on the result of the media quality control and method qualification tests. In order to evaluate whether this assumption is correct and to add more certainty to the procedures, we investigated whether there are detectable differences among isolates of the same strain sourced from different culture collections. Using various phenotypic and genotypic identification and strain typing methods, nine major pharmacopoeial species were analyzed. As expected, most of the species showed very uniform patterns across the isolates, indicating that the strains were indeed identical. Surprisingly, the strains of Salmonella enterica subsp. enterica serotype abony showed distinct differences at both the genotypic and the phenotypic level, suggesting that the strains sourced from the different culture collections were not identical strains, or that they have undergone detectable genetic shift from the time they were derived from the original depositor. Irrespective of the level of genotypic or phenotypic homology identified here, there are no practical consequences on their performance in compendial assays. It is concluded that the compendial strains investigated in this study are indeed equivalent and will perform identically in compendial tests, making it safe to base pharmaceutical quality control procedures on the strains sourced from any of the recognized national culture collections.

Evaluation of an automated repetitive sequence-based PCR system for subtyping Enterobacter sakazakii

Enterobacter sakazakii is regarded as a ubiquitous organism that can be isolated from a wide range of foods and environments. Infection in at-risk infants has been epidemiologically linked to the consumption of contaminated powdered infant formula. Preventing the dissemination of this pathogen in a powdered infant formula manufacturing facility is an important step in ensuring consumer confidence in a given brand together with the protection of the health status of a vulnerable population. In this study we report the application of a repetitive sequence-based PCR typing method to subtype a previously well-characterized collection of E. sakazakii isolates of diverse origin. While both methods successfully discriminated between the collection of isolates, repetitive sequence-based PCR identified 65 types, whereas pulsed-field gel electrophoresis identified 110 types showing > or =95% similarity. The method was quick and easy to perform, and our data demonstrated the utility and value of this approach to monitor in-process contamination, which could potentially contribute to a reduction in the transmission of E. sakazakii.

Yeast identification--past, present, and future methods

The focus of this review is the evolution of biochemical phenotypic yeast identification methods with emphasis on conventional approaches, rapid screening tests, chromogenic agars, comprehensive commercial methods, and the eventual migration to genotypic methods. As systemic yeast infections can be devastating and resistance is common in certain species, accurate identification to the species level is paramount for successful therapy and appropriate patient care.

Evaluation of a novel chromogenic agar medium for isolation and differentiation of vancomycin-resistant Enterococcus faecium and Enterococcus faecalis isolates

The development of reliable and rapid methods for the identification of patients colonized with vancomycin-resistant enterococci (VRE) is central to the containment of this agent within a hospital environment. To this end, we evaluated a prototype chromogenic agar medium (VRE-BMX; bioMérieux, Marcy l'Etoile, France) used to recover VRE from clinical specimens. This medium can also identify isolated colonies as either vancomycin-resistant Enterococcus faecium or Enterococcus faecalis, based on distinct colony colors. We compared the performance of VRE-BMX with bile esculin azide agar supplemented with vancomycin (BEAV). For this study, 147 stool samples were plated on each test medium and examined after 24 and 48 h of incubation. At 24 h, the sensitivity and specificity of each medium were as follows: BEAV, 90.9% and 89.9%, respectively; VRE-BMX, 96.4% and 96.6%, respectively. The positive predictive values (PPV) of VRE-BMX and BEAV at 24 h were 89.8% and 80.7%, respectively. VRE-BMX provided the identification of 10 isolates of vancomycin-resistant E. faecalis and 4 isolates of vancomycin-resistant E. faecium that were not recovered by BEAV. Further, VRE-BMX was capable of identifying patients colonized with both E. faecium and E. faecalis, a feature useful for infection control purposes that is not a function of BEAV. In terms of the recovery of vancomycin-resistant E. faecium and E. faecalis, the sensitivity and PPV were as follows: BEAV, 75.7% and 74.6%, respectively; VRE-BMX, 95.5% and 91.3%, respectively. In this initial evaluation, we found that VRE-BMX provided improved recovery of VRE from stool specimens, with the added advantage of being able to differentiate between vancomycin-resistant E. faecalis and E. faecium. Extending the incubation period beyond 24 h did not significantly improve the recovery of VRE and resulted in decreased specificity.

tRNA gene clusters at the 3' end of rRNA operons are specific to virulent subgroups of Streptococcus agalactiae strains, as demonstrated by molecular differential analysis at the population level

The aim of this work was to characterize a 2.4 kb randomly amplified polymorphic DNA (RAPD) fragment described as a marker for a phylogenetic group of Streptococcus agalactiae strains significantly associated with neonatal meningitis. This fragment was analysed by cloning and sequencing, and showed that two types of tRNA gene cluster flank the 3' end of the rRNA operons in S. agalactiae strains. Both types of tRNA gene cluster act as markers for phylogenetic subgroups of strains within the species. One type could be used to distinguish two of the three virulent intraspecies subgroups to which most of the S. agalactiae strains able to invade the central nervous system of neonates belong. This raises the possibility that there is a link between these tRNA genes and the virulence of the bacterium. Based on this analysis, PCR primers were designed to determine whether S. agalactiae strains are likely to belong to lineages of organisms in which most of the highly virulent strains isolated from cerebrospinal fluid cluster. In addition, this work demonstrated that RAPD can be used to detect novel particularities within intraspecies variants of pathogens.

Host variation in cytokine responses to superantigens determine the severity of invasive group A streptococcal infection

Cytokines elicited by superantigens have been suggested to play a central role in severe systemic clinical manifestations of gram-positive sepsis. Here we provide evidence for a potent inflammatory cytokine response in acute invasive group A streptococcal infections, and show a direct correlation between the magnitude of this response and the severity of systemic manifestations of the disease. Severe invasive cases suffering from toxic shock and/or necrotizing fasciitis had significantly higher frequencies of IL-2-, IL-6-, and TNF-alpha-producing cells in their circulation as compared to non-severe invasive cases (p=0.05-0.01). This difference was even more accentuated when severe and non-severe cases infected with a clonal M1T1 strain were compared (p=0.03-0. 004). To determine whether host factors were responsible for this difference in magnitude of cytokine responses, paired age- and gender-matched severe and non-severe M1T1 cases (n=8) were tested in vitro during their convalescent phase for immune response to superantigens produced by their infecting isolate. The results showed persistent and inherent differences in the magnitude of proliferative and cytokine responses of severe and non-severe patients to the streptococcal superantigens to which they had been exposed during infection. Thus, the study provides evidence that patients with a propensity to produce higher levels of inflammatory cytokines in response to streptococcal superantigens develop significantly more severe systemic manifestations than patients who have a propensity to produce lower levels of inflammatory cytokines to the same superantigens. We therefore conclude that host factors influence the magnitude of cytokine responses to superantigens and consequently the clinical outcome of the infection.

Genetic relatedness and superantigen expression in group A streptococcus serotype M1 isolates from patients with severe and nonsevere invasive diseases

The relatedness of group A streptococcal (GAS) strains isolated from 35 Canadian patients with invasive disease of different severity was investigated by a variety of molecular methods. All patients were infected with M1T1 strains and, based on clinical criteria, were classified as severe (n = 21) and nonsevere (n = 14) invasive GAS infection cases. All the M1 strains studied had the emm1.0 allele and the same streptococcal pyrogenic exotoxin (Spe) genotype, speA(+) speB(+) speC speF(+) speG(+) speH smeZ(+) ssa. All isolates had the same speA allotype, speA2. The randomly amplified polymorphic DNA banding pattern with two different primers was identical for all strains, and pulsed field gel electrophoresis analysis showed that 33 and 30 isolates had identical banding patterns after DNA digestion with SfiI or SmaI, respectively; the nonidentical isolates differed from the main pattern by only one band. A relatively high degree of polymorphism in specific regions of the sic gene was observed among isolates; however, this polymorphism was not associated with disease severity. Likewise, although the phenotypic expression of SpeA, SpeB, and SpeF proteins varied among the M1T1 isolates, there was no correlation between the amount of Spe expressed and disease severity. Importantly, mitogenic and cytokine responses induced by partially purified bacterial culture supernatants containing a mixture of expressed superantigens were very similar for isolates from severe and nonsevere cases (P > 0.1). Together, the data indicate that highly related invasive M1T1 isolates, some indistinguishable, can cause disease of varying severity in different individuals. These findings underscore the contribution of host factors to the outcome of invasive GAS infections.

Preferential stimulation of human lymphocytes by oligodeoxynucleotides that copy DNA CpG motifs present in virulent genes of group A streptococci

Immunostimulatory oligodeoxynucleotides (ODN) containing CpG dinucleotides have been shown to stimulate murine and human lymphocytes. We investigated the presence of stimulatory DNA motifs in specific group A streptococcal (GAS) genes to elucidate the potential role of DNA in the immunopathogenesis of GAS infections. Despite low GC content in GAS DNA, the emm1 gene encoding the streptococcal M1 protein contained a relatively high frequency of TTCG(T/C), TCGTCG and (G/A)TCGT motifs that preferentially stimulated human lymphocytes. Interestingly, these motifs were also found in genes encoding M-like proteins of group C and G streptococci. ODN copying the emm1 gene sequences harboring these motifs induced the proliferation of human B cells and up-regulated the expression of CD25 on their surface. T cells were not required for the response to the ODN, indicating a direct effect of these motifs on B lymphocytes. Inter-individual variations in responsiveness to ODN were observed, suggesting that host factors potentiate these responses. The finding that GAS DNA contains stimulatory motifs that induce activation of human B cells in a T cell-independent manner suggests that this may be an important mechanism by which the bacteria can target the innate arm of the immune system in the early stages of invasive infections.

Genomic relatedness among Actinobacillus pleuropneumoniae field strains of sterotypes 1 and 5 isolated from healthy and diseased pigs

Forty-four Actinobacillus pleuropneumoniae isolates recovered from both healthy and diseased pigs were characterized by random amplified polymorphic DNA analysis (RAPD), pulsed field gel electrophoresis (PFGE) and apx toxin gene typing. Nine RAPD types and 14 PFGE patterns were identified. No common RAPD or PFGE patterns were found between strains of serotype 1 and those of serotype 5. The RAPD analysis indicated that the 15 serotype 1 strains isolated from diseased pigs were assigned to 4 RAPD types, with 66% of strains characterized by the same RAPD type. By contrast, the 5 strains of serotype 1 isolated from healthy carriers were dispersed in 4 RAPD types. These data suggest that the diversity of strains isolated from healthy pigs could be higher than that of strains recovered from diseased pigs. In addition, all serotype 5 strains exhibited a unique RAPD type. Unlike RAPD, PFGE analysis allowed discrimination among isolates of serotype 1 and among those of serotype 5. All but 3 isolates showed the same apx genotype as their respective serotype reference strain. These data indicate that RAPD analysis is a valuable rapid tool for routine subtyping of strains of serotype 1. For strains of serotype 5, a combination of several typing methods, such as PFGE and apx gene typing, is needed to provide useful information on the molecular epidemiology of swine pleuropneumonia.

Relatedness of Streptococcus suis serotype 2 isolates from different geographic origins as evaluated by molecular fingerprinting and phenotyping

The genetic diversity of 88 Streptococcus suis serotype 2 isolates which were recovered from various countries was examined by randomly amplified polymorphic DNA (RAPD) analysis with three primers. This bacterial collection included 80 isolates of porcine origin and 8 of human origin. This investigation allowed the identification of 23 RAPD types containing 1 to 30 isolates originating from one to six countries. Common RAPD patterns were found between human and pig isolates. The isolates were also tested for the production of virulent factors such as hemolysin, muramidase-released protein (MRP), and extracellular factor (EF). All isolates exhibiting the virulent phenotype hemolysin+ MRP+ EF+ clearly clustered on the basis of fingerprinting by RAPD analysis. In a similar way, most of isolates with the hemolysin- MRP- EF- phenotype were assigned to one RAPD cluster. Therefore, RAPD clusters are more related to the phenotype defined with hemolysin, MRP, and EF than to the geographic origin of the isolates. These data indicate that RAPD analysis used in conjunction with phenotypic methods provides a reliable method for the assessment of the clonal relationship between S. suis isolates responsible for infections in pigs or humans, especially for those exhibiting the classic "virulent" phenotype hemolysin+ MRP+ EF+.

Phylogenetic diversity of Streptococcus suis strains of various serotypes as revealed by 16S rRNA gene sequence comparison

The 16S rRNA gene sequences of reference strains of Streptococcus suis serotypes 1-34 and 1/2 were determined. A comparative sequence analysis showed that the degree of sequence similarity between S. suis reference strains ranged from 93.94 to 100%. A dendrogram was constructed from the similarity matrix. Thirty-two strains representing 32 serotypes fell into a major group divided into three clusters. The other strains, S. suis serotypes 32, 33 and 34, were more distant. Biochemical characterization of the six more distant strains, including S. suis serotypes 20, 22, 26, 32, 33 and 34, revealed a profile similar to that of other S. suis serotypes. Comparison of the 16S rRNA gene sequences of S. suis reference strains with sequences of other members of the genus Streptococcus indicated that, with the exception of S. suis serotypes 32, 33 and 34, reference strains did not cluster with any other species in the genus. In conclusion, 16S rRNA gene sequence analysis defined a major group of S. suis reference strains which were very closely related and a higher divergence for S. suis serotypes 32, 33 and 34. However, to date, there is no strong evidence to reclassify strains of these serotypes in another species.

Characterization of Streptococcus agalactiae strains by randomly amplified polymorphic DNA analysis

A collection of 54 unrelated Streptococcus agalactiae strains isolated from cerebrospinal fluid samples from neonates and 60 unrelated strains isolated from carriers that had been previously studied by multilocus enzyme electrophoresis (R. Quentin, H. Huet, F.-S. Wang, P. Geslin, A. Goudeau, and R. K. Selander, J. Clin. Microbiol. 33:2576-2581, 1995) were characterized by randomly amplified polymorphic DNA (RAPD) assay. Four primers, 5'AGGGGGTTCC3', 5'AACGCGCAAC3', 5'GCATCAATCT3', and 5'AGTCGGGTGG3', named OPS16, AP42, A4, and OPS11, respectively, were selected from 29 primers tested. This investigation identified 71 RAPD types. The three families of strains defined by multilocus enzyme electrophoresis analysis, which contain most of the cerebrospinal fluid isolates, were also identified by clustering analysis of RAPD data. Each of these three groups exhibits specific RAPD patterns or fragments. The discriminatory power of the RAPD typing method was also evaluated. The simplest typing scheme was obtained by the combination of RAPD typing done with primers AP42 and OPS11 and serotyping (index of discrimination, 0.97).

Use of a DNA typing method to investigate a fatal perinatal infection due to Staphylococcus aureus

The aim of this study was to determine, by random amplified polymorphic DNA analysis, the origin of a fatal Staphylococcus aureus perinatal infection which occurred after multiple cervical examinations before induction of labor for patient convenience. This DNA typing method was able to demonstrate that this infection originated from S. aureus genital carriage and urinary tract infection of the mother, and was not acquired in the hospital. This observation argues for the systematic screening of genital flora for highly virulent strains before induction of labor for non medical reasons. In addition, the DNA typing method used demonstrates that one neonate was subsequently infected by the strain responsible for the chorioamnionitis. This shows that molecular typing methods can help determine hospital staff responsibility.

Genetic diversity of rRNA operons of unrelated Streptococcus agalactiae strains isolated from cerebrospinal fluid of neonates suffering from meningitis

The genetic diversity of a collection of 54 unrelated Streptococcus agalactiae strains isolated from the cerebrospinal fluid of neonates and of 60 unrelated carrier strains was evaluated by investigating the restriction fragment length polymorphism of the rRNA gene region. Three restriction enzymes were selected for use: PstI, HindIII, and CfoI. Clustering analysis revealed two phylogenetic groups of strains with 40% divergence. Group I contained two clusters, A and B, and group II contained three clusters, C, D, and E. Strains of serotype Ia were mostly distributed in cluster A, and strains of serotype Ib were mostly distributed in cluster E. Serotype III isolates did not cluster. Nevertheless, 37 of 39 isolates belonging to cluster B were serotype III. With HindIII, two rRNA gene banding patterns characterized 38 of the 39 strains of cluster B, which represents a high-virulence group. In addition, two rRNA gene banding patterns with each enzyme and/or a pair of CfoI fragments of 905 and 990 bp identified 81% of the invasive strains. On account of the genetic homogeneity of the cerebrospinal fluid strains, ribotyping is a powerful typing method for investigation of nosocomial or epidemic invasive infections only when all three enzymes are used or when PstI and HindIII or PstI and CfoI are combined with serotyping (index of discrimination, > 0.95).