Relevance of mutations in the TLR4 receptor in patients with gram-negative septic shock

BACKGROUND

Septic shock remains a significant health concern worldwide, and despite progress in understanding the physiological and molecular basis of septic shock, the high mortality rate of patients with septic shock remains unchanged. We recently identified a common polymorphism in toll-like receptor 4 (TLR4) that is associated with hyporesponsiveness to inhaled endotoxin or lipopolysaccharide in humans.

METHODS

Since TLR4 is a major receptor for lipopolysaccharide in mammals and gram-negative bacteria are the prevalent pathogen associated with septic shock, we investigated whether these specific TLR4 alleles are associated with a predisposition to a more severe disease outcome for patients with septic shock. We genotyped 91 patients with septic shock as well as 73 healthy blood donor controls for the presence of the TLR4 Asp299Gly and TLR4 Thr399Ile mutations.

RESULTS

We found the TLR4 Asp299Gly allele exclusively in patients with septic shock (P =.05). Furthermore, patients with septic shock with the TLR4 Asp299Gly/Thr399Ile alleles had a higher prevalence of gram-negative infections.

CONCLUSION

Mutations in the TLR4 receptor may predispose people to develop septic shock with gram-negative microorganisms.

Partners-in-infection: host proteins involved in the transformation of plant cells by Agrobacterium

Genetic modification of plant cells by Agrobacterium is the only known natural example of DNA transport between kingdoms. While the bacterial factors involved in Agrobacterium infection have been relatively well characterized, studies of their host cellular partners are just beginning. Here, we describe the plant cell factors that might participate in Agrobacterium-mediated genetic transformation and discuss their possible roles in this process. Because Agrobacterium probably adapts existing cellular processes for its life cycle, identifying the host factors participating in Agrobacterium infection might contribute to a better understanding of such basic biological processes as cell communication, intracellular transport and DNA repair and recombination as well as help expand the host range of Agrobacterium as a genetic engineering tool.

Mice lacking alpha(2)-macroglobulin show an increased host defense against Gram-negative bacterial sepsis, but are more susceptible to endotoxic shock

The onset of an acute phase response is one of the initial steps in the defense against an infectious organism. Alpha(2)-macroglobulin (alpha(2)M), an acute phase protein in most mammalian species, is known to have a broad antiprotease activity, but it can also bind a number of growth factors, cytokines, ions and lipid factors. We have shown that alpha(2)M-deficient (MAM-/-) mice are more resistant to a lethal Gram-negative infection compared to control mice. This increased resistance was reflected in significantly higher body temperatures, compared to control mice, during the infection as well as in a prolonged and increased survival. Moreover, the clearance of bacteria in MAM-/- mice was significantly more efficient than in control mice. On the other hand, MAM-/- mice were more susceptible to endotoxin. An LD(100) challenge with endotoxin in MAM-/- mice was not lethal for control mice. Our data suggest that alpha(2)M plays a dual role during an acute phase response. In the establishment of a lethal Gram-negative infection, leading to sepsis and septic shock, it has a mediating role by hampering the efficient clearance of bacteria. During endotoxic shock, however, alpha(2)M has a rather protective function.

SHV-12, SHV-5, SHV-2a and VEB-1 extended-spectrum beta-lactamases in Gram-negative bacteria isolated in a university hospital in Thailand

Sixty-one extended-spectrum beta-lactamase (ESBL)-producing isolates were collected from Srinagarind Hospital, Thailand. These included 43 Enterobacteriaceae and 18 Pseudomonadaceae. The 43 Enterobacteriaceae were found to produce the following ESBLs: 26 (60.5%) SHV-12, 13 (30.2%) SHV-5, two (4.7%) SHV-2a, one (2.3%) VEB-1 and one (2.3%) unidentified. Twenty-four isolates (55.8%) also carried bla(TEM-1B), as well as bla(SHV) or bla(VEB-1). Plasmid DNA from transconjugants carrying the bla(SHV-12) gene showed various restriction patterns, indicating the distribution of the bla(SHV-12) gene among different antibiotic resistance plasmids. In contrast, bla(SHV-5) in 13 isolates was found on a single plasmid of c. 130 kb. Pulsed-field gel electrophoresis (PFGE) analysis of genomic DNA from these isolates revealed that nine of 11 Klebsiella pneumoniae gave the same pattern, indicating clonal spread of the strain within the hospital, together with the occasional spread of the plasmid to other strains. Among the pseudomonad isolates, 16 Pseudomonas aeruginosa and one Pseudomonas putida had bla(VEB-like) and one P. aeruginosa had bla(SHV-12). Nine of the 16 isolates carrying bla(VEB-like) (56.3%) had identical PFGE patterns, suggesting the dissemination of this gene, also by clonal spread. At least six different bla(VEB-like-)containing integrons were found among the 18 isolates. This is the first report of bacteria producing SHV-12 and SHV-2a in Thailand and the first report of SHV-12 in P. aeruginosa, of VEB-1 in Citrobacter freundii and a VEB-1-like beta-lactamase in P. putida. These findings indicate that ESBL genes in the Far East are part of a gene pool capable of broad horizontal gene transfer, in that these genes can transfer between different families of Gram-negative bacilli.

Cellular fatty acid composition of Lautropia mirabilis

Ten strains of Lautropia mirabilis (ATCC 51599(T) and nine phenotypically similar clinical isolates) were examined for cellular fatty acid (CFA) composition to evaluate their chemical relatedness to known bacterial species and groups. The CFAs were liberated from whole cells by base hydrolysis, methylated, and analyzed by gas-liquid chromatography. CFA profiles were generated by using a commericial software package (MIDI, Newark, Del.). All strains tested had an identical CFA profile characterized by major amounts of 16:1omega7c (41%) and 16:0 (44%); smaller amounts (1 to 4%) of 3-OH-10:0, 12:0, 14:0, 15:0, and 18:1 omega7c; trace amounts (<1%) of 10:0, 18:2 and 18:0; and no cyclopropane acids. This profile was similar to the CFA profiles of Acidovorax delafieldii, Comamonas terrigena, and strains of an unclassified Centers for Disease Control group designated weak oxidizer group 1. CFA analysis, when supplemented by phenotypic characterization, is useful for the identification of L. mirabilis isolates.

Multiplex polymerase chain reaction for distinguishing Taylorella equigenitalis from Taylorella equigenitalis-like organisms

It is difficult to distinguish isolates of Taylorella equigenitalis, the cause of contagious equine metritis, from a T. equigenitalis-like organism isolated from asymptomatic donkeys and horses. Although T. equigenitalis is responsible for a severe, contagious disease of the reproductive tract of equids, the T. equigenitalis-like organism, although contagious, does not appear to produce disease. Because of the economic consequences of correctly distinguishing isolates of these 2 microorganisms, a polymerase chain reaction (PCR)-based assay was developed that will distinguish isolates of T. equigenitalis from the T. equigenitalis-like microorganism. The primers used in the PCR assay were designed to amplify unique regions of the gene encoding the 16S ribosomal RNA.

Gene variants of the bactericidal/permeability increasing protein and lipopolysaccharide binding protein in sepsis patients

OBJECTIVES

To determine whether the genotype frequencies of the five bi-allelic polymorphisms in the bactericidal/permeability increasing protein (BPI) (Lys216 --> Glu; PstI polymorphism in intron 5; silent mutation G545 --> C) and the lipopolysaccharide binding protein (LBP) (Cys98 --> Gly; Pro436 --> Leu) are associated with the incidence and lethality of sepsis.

DESIGN

Case control study of patients with sepsis.

SETTING

Intensive care units within university hospitals.

PATIENTS

A total of 204 patients diagnosed with sepsis and 250 healthy blood donors.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Short DNA fragments containing the polymorphic sites of the LBP and BPI locus were amplified by the polymerase chain reaction or mismatched polymerase chain reaction. The individual polymorphisms were determined with the appropriate restriction enzyme digestions and subsequent agarose gel electrophoresis. The presence of LBP genotypes with the less frequent Gly98 allele was found to be associated with sepsis (p < .02) in male patients, but not in females. Patients which were homozygote for either of the rare Gly98 (n = 6) and/or Leu436 (n = 5) LBP alleles, furthermore, exclusively were nonsurvivors of sepsis. The genotype frequencies in the BPI gene did not differ between patients and control individuals.

CONCLUSIONS

Our findings suggest that common polymorphisms in the gene for LBP in combination with male gender are associated with an increased risk for the development of sepsis and, furthermore, may be linked to an unfavorable outcome. These data support the important immunomodulatory role of LBP in Gram-negative sepsis and suggest that genetic testing may be helpful for the identification of patients with an unfavorable response to Gram-negative infection.

IL-10, but not IL-4, suppresses infection-stimulated bone resorption in vivo

Periapical bone resorption occurs following infection of the dental pulp and is mediated mainly by IL-1alpha in the murine model. The production and activity of IL-1alpha is modulated by a network of regulatory cytokines, including those produced by Th1 (pro-inflammatory) and Th2 (anti-inflammatory) subset T cells. This study was designed to assess the functional role of the Th2-type cytokines IL-4 and IL-10 in infection-stimulated bone resorption in vivo. The dental pulps of the first molars were exposed and infected with a mixture of four common endodontic pathogens, and bone destruction was determined by micro-computed tomography at sacrifice on day 21. The results demonstrate that IL-10(-/-) mice had significantly greater infection-stimulated bone resorption in vivo compared with wild-type mice (p < 0.001), whereas IL-4(-/-) exhibited no increased resorption. IL-10(-/-) had markedly elevated IL-1alpha production within periapical inflammatory tissues (>10-fold) compared with wild type (p < 0.01), whereas IL-4(-/-) exhibited decreased IL-1alpha production (p < 0.05). IL-10 also suppressed IL-1alpha production by macrophages in a dose-dependent fashion in vitro, whereas IL-4 had weak and variable effects. We conclude that IL-10, but not IL-4, is an important endogenous suppressor of infection-stimulated bone resorption in vivo, likely acting via inhibition of IL-1alpha expression.

Virulence properties of motile aeromonads isolated from farmed frogs Rana tigerina and R. rugulosa

Virulence factors were compared in Aeromonas species isolated from clinically normal and septicaemic farmed frogs from Thailand. Haemolysin activities against frog erythrocytes were significantly different within the collection of aeromonads. Groups of high haemolytic activity (unspeciated Aeromonas, Au), moderate haemolytic activity (A. hydrophila), and low haemolytic activity (A. veronii biovar sobria, A. veronii biovar veronii, A. caviae, A. schubertii) were noted. DNA colony hybridisation studies revealed that Au isolates possessed a haemolysin gene (ASH1) which was not present in any of the other Thai aeromonads or type strains tested. Elastinolytic activity was demonstrated in 90% of the Au isolates, 60% of the A. hydrophila isolates and in none of the other motile aeromonads. The cytotoxic activity of the Aeromonas isolates varied according to the source of cells used in the assays. Cells from rainbow trout were extremely sensitive to Au toxins but less so to toxins produced by other species. In contrast mammalian cells showed very little sensitivity to Au toxins but were more sensitive to toxins produced by A. hydrophila. Selection of suitable assay substrates is therefore important.

Two consecutive outbreaks of Stenotrophomonas maltophilia (Xanthomonas maltophilia) in an intensive-care unit defined by restriction fragment-length polymorphism typing

OBJECTIVE

To investigate and control consecutive outbreaks of Stenotrophomonas maltophilia infections in intensive-care-unit (ICU) patients.

DESIGN

Epidemiological investigation; restriction fragment-length polymorphism typing by pulsed-field gel electrophoresis (PFGE) of genomic DNA of outbreak strains; institution of infection control measures to limit spread.

SETTING

The medical-surgical ICU in an 800-bed tertiary-care center in Calgary, Alberta, Canada.

RESULTS

S. maltophilia was recovered from 14 ICU patients (12 infected, 2 colonized) between February 1993 and February 1994. Ten of the 14 patient isolates and 1 environmental isolate were available for PFGE typing. Patient isolates from 6 of the first 10 patients were identical. Isolates from the next 3 of 4 patients and an isolate recovered from a ventilator being used by a patient not infected with S. maltophilia also were identical, but different from the first 6. The ventilator isolate was temporally associated with the latter 4 patients.

CONCLUSION

Molecular typing allowed us to determine that there were two separate consecutive S maltophilia outbreaks rather than a single protracted outbreak. Recovery of S. maltophilia from patient ventilators and an in-line suction catheter suggests that the organism may have been spread by cross-contamination from contaminated equipment or from an environmental source.

Molecular fingerprinting of Riemerella anatipestifer by repetitive sequence PCR

Riemerella anatipestifer is a gram-negative rod-shaped bacterium associated with epizootic infections in poultry. A total of 35 R. anatipestifer isolates including the type strain ATCC11845T, reference and field strains for 18 different serotypes were characterized by repetitive sequence based-PCR (rep-PCR) with outwardly-directed primers based on the repetitive extragenic palindromic (REP) consensus sequence. This technique was applied by using either extracted genomic DNA or preparation of whole bacterial cells harvested directly from plate cultures. Rep-PCR discriminated the R. anatipestifer isolates into 19 electrophoretic types. DNA fingerprints obtained from rep-PCR of extracted genomic DNA or from preparations of whole cells yielded comparable patterns. Substantial variation was seen among the rep-PCR fingerprints of different serotypes. Moreover, different polymorphisms of the rep-PCR fingerprints were evident among epidemiologically unrelated isolates of the same serotype. These results suggest the presence of repetitive extragenic palindromic-like elements within the genome of R. anatipestifer that can be used in some isolates to discriminate between different strains belonging to the same serotype. Rep-PCR may serve as a useful molecular tool for subtyping R. anatipestifer isolates for epidemiologic investigations. The whole cell procedure offers the advantage of ease of performance requiring only small quantities of cells.

PCR-RFLP of outer membrane proteins gene of Dichelobacter nodosus: a new tool in the epidemiology of footrot

Currently only phenotypic epidemiological markers, serogrouping and virulence testing of Dichelobacter nodosus, are available for investigating footrot outbreaks in small ruminants. These methods have limitations in tracing the source of infection. In this study, a genotypic marker, PCR-RFLP of outer membrane protein gene, was used to characterize D. nodosus. The technique was evaluated in a controlled experiment involving two strains of bacteria. PCR-RFLP was found to be highly specific in differentiating isolates obtained from recipient animals infected with different strains. Subsequently, this technique was used to characterize isolates obtained from field cases of footrot in Nepal. A total of 11 patterns was recognized among 66 Nepalese D. nodosus isolates representing four different serogroups. PCR-RFLP also discriminated isolates with similar phenotypic characteristics. However, all isolates which, phenotypically, were virulent were represented by only two patterns irrespective of their serogroups. It is suggested that PCR-RFLP described here could be a useful epidemiological marker in the study of footrot.

Epidemiology of polyclonal gram-negative bacteremia

Polyclonal bacteremic episodes are caused by more than one genotype of the same species. We conducted a study to estimate the frequency and to describe the epidemiology of polyclonal Gram-negative bacteremia in our patient population. We reviewed the patients' medical records. We also did pulsed field gel electrophoresis on 66 Gram-negative isolates obtained from the 28 patients (29 episodes) who had more than one morphologically different isolate of the same Gram-negative species in a blood culture obtained between January 1, 1989 and December 31, 1993. Nine of 29 (31%) bacteremic episodes evaluated were polyclonal. The source of bacteremia was not significantly different among patients with polyclonal and monoclonal bacteremic episodes. Patients with polyclonal bacteremic episodes were younger and were more likely to have rapidly fatal diseases than were those with monoclonal bacteremic episodes; however, neither of these differences reached statistical significance. Patients with polyclonal bacteremic episodes were significantly more likely to have leukemia than were those with monoclonal bacteremic episodes (odds ratio = 18.67; 95% confidence interval, 1.92 to 255.80). Three of nine patients who had polyclonal bacteremia died compared with 2 of 19 patients who had monoclonal bacteremia (odds ratio = 4.25; 95% confidence interval, 0.41 to 50.80). Polyclonal Gram-negative bacteremia is more common than previously thought. Despite their younger age, patients with polyclonal bacteremic episodes were more likely to die than those with monoclonal bacteremic episodes. Thus, polyclonal bacteremia may be either an indicator or a risk factor for poor prognosis.

IgG receptor polymorphisms: risk factors for disease

Two groups of receptors for immunoglobulin G (FcgammaR) can be distinguished. Endothelial cells and placental syncytiotrophoblasts express an MHC class I-like FcgammaR important for regulation of IgG half-life and IgG transport, respectively. FcgammaR expressed on leukocytes constitute a heterogeneous family of membrane bound and soluble proteins. The various FcgammaR (sub) classes of this family differ in ligand affinity and specificity, which is determined by primary structure, glycosylation, association with signaling subunits, and environmental factors (such as serine proteases). The finding that polymorphisms of FcgammaRIIa, FcgammaRIIIa, and FcgammaRIIIb critically affect interaction with antibodies has prompted analysis in patients which provided tantalizing evidence for the relevance of FcgammaR polymorphisms as risk factors for a number of infectious and autoimmune diseases.

Inactivation of two haemolytic toxin genes in Aeromonas hydrophila attenuates virulence in a suckling mouse model

The contribution of two unrelated Aeromonas hydrophila beta-haemolytic toxins to virulence was assessed in a suckling mouse model. The first haemolysin gene, isolated from an A. hydrophila A6 cosmid bank, encoded a potential gene product of 621 amino acids and a predicted molecular size of 69.0 kDa. The inferred amino acid sequence showed 89% identity to the AHH1 haemolysin of A. hydrophila ATCC 7966, and 51% identity to the HlyA haemolysin of Vibrio cholerae EI Tor strain O17. The second haemolysin gene (designated aerA), which encodes aerolysin, a pore-forming toxin, was partially cloned by PCR for the purpose of mutant construction. This PCR product was a 1040 bp fragment from the C-terminal region of aerA. It is proposed that the 69.0 kDa V. cholerae-HlyA-like haemolysin gene be termed hlyA to contrast with the aerA terminology for the aerolysin. A suicide vector was used to inactivate both the hlyA and aerA genes in A. hydrophila A6. When assessed in the suckling mouse model, only the hlyA aerA double mutant showed a statistically significant reduction in virulence--a 20-fold change in LD50 (Scheffe test, P < 0.05). Cytotoxicity to buffalo green monkey kidney cell monolayers and haemolysis on horse blood agar were eliminated only in the hlyA aerA double mutants. This is the first report of cloning and mutagenesis of two unrelated haemolytic toxin genes in the same strain of a mesophilic aeromonad. For A. hydrophila, a two-toxin model provides a more complete explanation of virulence.

An Aeromonas salmonicida gene required for the establishment of infection in rainbow trout (Oncorhynchus mykiss)

The asoB gene of Aeromonas salmonicida is located approximately 9 kb downstream of the structural gene (vapA) for the surface layer (A-layer). The nucleotide sequence of asoB was determined and found to encode a putative polytopic cytoplasmic membrane protein which exhibited homology to a number of bacterial transport proteins. Allele exchange mutagenesis of asoB resulted in a mutant (A449-D) which was avirulent when administered by bath immersion. However, when administered by intraperitoneal injection, A449-D is as lethal as wild type. Characterization of the phenotype of A449-D showed that there were pleiotropic effects on VapA secretion, haemolysis and outer membrane protein composition. Mobilization of cloned asoB on a broad-host-range plasmid into A449-D resulted in the complementation of VapA translocation, haemolytic activity and virulence.

Molecular mechanisms of bacterial virulence: type III secretion and pathogenicity islands

Recently, two novel but widespread themes have emerged in the field of bacterial virulence: type III secretion systems and pathogenicity islands. Type III secretion systems, which are found in various gram-negative organisms, are specialized for the export of virulence factors delivered directly to host cells. These factors subvert normal host cell functions in ways that seem beneficial to invading bacteria. The genes encoding several type III secretion systems reside on pathogenicity islands, which are inserted DNA segments within the chromosome that confer upon the host bacterium a variety of virulence traits, such as the ability to acquire iron and to adhere to or enter host cells. Many of these segments of DNA appear to have been acquired in a single step from a foreign source. The ability to obtain complex virulence traits in one genetic event, rather than by undergoing natural selection for many generations, provides a mechanism for sudden radical changes in bacterial-host interactions. Type III secretion systems and pathogenicity islands must have played critical roles in the evolution of known pathogens and are likely to lead to the emergence of novel infectious diseases in the future.

Epidemiological survey of genes encoding aminoglycoside phosphotransferases APH (3') I and APH (3') II using DNA probes

The epidemiological survey of APH (3') I and APH (3') II genes, at a time when the specific antibiotic pressure was very low, was carried out by DNA-DNA hybridization. The sample included 334 aminoglycoside resistant Gram-negative bacteria collected from patients of a General Hospital. Of these, 251 hybridized with the APH (3') I-probe and 19 with the APH (3') II-probe but only 190 strains showed high resistance levels (CIM greater than 64 micrograms/ml) for kanamycin, neomycin and paromomycin. These strains were isolated both from inpatients and outpatients with different infectious diseases. The APH (3') I-gene was dispersed among all the bacterial species and clinical specimens tested but the APH (3') II-gene was not found in Pseudomonas spp, Escherichia coli, Citrobacter freundii and Enterobacter cloacae, nor in infected catheters. Several plasmids of different sizes carrying APH (3') genes were detected among different bacteria. Plasmids along with transposable elements (the probes used in this work were developed from Tn906 and Tn5) and the high consumption of other antibiotics whose resistance is carried by these bacteria might be playing an important role in the maintenance and dispersion of APH (3') genes.