Hypothesis: a motor neuron toxin produced by a clostridial species residing in gut causes ALS

We hypothesize that a yet-to-be-identified motor neuron toxin produced by a clostridial species causes sporadic amyotrophic lateral sclerosis (ALS) in susceptible individuals. This clostridial species would reside undetected in the gut and chronically produce a toxin that targets the motor system, like the tetanus and botulinum toxins. After gaining access to the lower motor neuron, the toxin would be transported back to the cell body, as occurs with the tetanus toxin, and destroy the lower motor neuron - the essential feature of ALS. Again like the tetanus toxin, some of the toxin would cross to neighboring cells and to the upper motor neuron and similarly destroy these motor neurons. Weakness would relentlessly progress until not enough motor neurons remained to sustain life. If this hypothesis were correct, treatment with appropriate antibiotics or antitoxins might slow or halt progression of disease, and immunization might prevent disease.

Global differential gene expression in response to growth temperature alteration in group A Streptococcus

Pathogens are exposed to different temperatures during an infection cycle and must regulate gene expression accordingly. However, the extent to which virulent bacteria alter gene expression in response to temperatures encountered in the host is unknown. Group A Streptococcus (GAS) is a human-specific pathogen that is responsible for illnesses ranging from superficial skin infections and pharyngitis to severe invasive infections such as necrotizing fasciitis and streptococcal toxic shock syndrome. GAS survives and multiplies at different temperatures during human infection. DNA microarray analysis was used to investigate the influence of temperature on global gene expression in a serotype M1 strain grown to exponential phase at 29 degrees C and 37 degrees C. Approximately 9% of genes were differentially expressed by at least 1.5-fold at 29 degrees C relative to 37 degrees C, including genes encoding transporter proteins, proteins involved in iron homeostasis, transcriptional regulators, phage-associated proteins, and proteins with no known homologue. Relatively few known virulence genes were differentially expressed at this threshold. However, transcription of 28 genes encoding proteins with predicted secretion signal sequences was altered, indicating that growth temperature substantially influences the extracellular proteome. TaqMan real-time reverse transcription-PCR assays confirmed the microarray data. We also discovered that transcription of genes encoding hemolysins, and proteins with inferred roles in iron regulation, transport, and homeostasis, was influenced by growth at 40 degrees C. Thus, GAS profoundly alters gene expression in response to temperature. The data delineate the spectrum of temperature-regulated gene expression in an important human pathogen and provide many unforeseen lines of pathogenesis investigation.

Toward a genome-scale understanding of group A Streptococcus pathogenesis

Recent significant contributions have been made to the understanding of Group A Streptococcus (GAS) pathogenesis. New regulatory pathways have been discovered, insight into the molecular basis of epidemics of serotype M1 disease has been obtained, the crystal structures of four toxins have been reported and a genome sequence of one GAS strain has been determined. Genome-scale approaches to the study of GAS pathogenesis are now rapidly emerging and will advance our fundamental understanding of the molecular basis of host-pathogen interactions.

Fur and iron transport proteins in the Brazilian purpuric fever clone of Haemophilus influenzae biogroup aegyptius

The Brazilian purpuric fever (BPF) clone of Haemophilus influenzae biogroup aegyptius causes a fatal septicaemic disease, resembling fulminant meningococcal sepsis, in children. When isolate F3031 was grown under iron-limiting conditions, the presence of several iron-regulated proteins of 38-110 kDa was revealed by electrophoretic analysis and a Fur homologue was shown by immunoblotting. Dot-blot assays and immunoblotting indicated that BPF cells bound human transferrin and contained transferrin-binding proteins in the outer membrane. However, the binding activity and the biosynthesis of these proteins were detected even under iron-rich conditions. Immunoblot analysis demonstrated the presence of a periplasmic protein related to the ferric iron-binding protein A (FbpA), the major iron-binding protein described in Neisseria spp. However, the FbpA homologue in strain F3031 was constitutively expressed and was smaller than the periplasmic protein detected in H. influenzae type b strain Eagan. The periplasm of strain F3031 also contained a protein related to the Streptococcus parasanguis FimA protein which recently has been shown to be involved in iron acquisition in Yersinia pestis. Although the Eagan and F3031 FimA homologues had a similar mol. wt, of 31 kDa, the expression of the BPF fimA-like gene was not regulated by the iron concentration of the culture medium.

Influence of environmental stress on the kinetics and strength of attachment of Listeria monocytogenes Scott A to Buna-N rubber and stainless steel

Attachment and detachment of Listeria monocytogenes Scott A to Buna-N rubber and stainless steel under varying conditions of temperature and pH were investigated using model systems. Numbers of attached cells increased with increasing attachment temperature (10 to 45 degrees C) and time (up to 120 min) for both test surfaces. Compared to Buna-N rubber, the rate of attachment to stainless steel was markedly more rapid for all temperature and pH conditions studied and could not be calculated. Rate of attachment to Buna-N rubber was found to be significantly lower when cells were attached at 10 degrees C. Growth temperature did not significantly affect rates of adhesion to Buna-N rubber. Altering the medium pH during attachment between 4 and 9 demonstrated that rates of adhesion were slower under alkaline conditions. Growth pH was also found to significantly affect rates of attachment to Buna-N rubber. Detachment of cells adhered to Buna-N rubber was significantly affected by growth temperature but not growth pH. Significant differences in detachment were also found between Buna-N rubber and stainless steel, inferring stronger attachment to Buna-N rubber. Cell surface hydrophobicity was found to be affected by both growth temperature and growth pH. However, changes in hydrophobicity could not be correlated to differences in rates of attachment. Addition of 0.01% trypsin to the attachment medium during cell exposure to either test surface resulted in a 99.9% reduction in the adhered cell population when compared to controls. This would suggest that proteins play a role in the initial attachment process of L. monocytogenes.

Effect of environmental stress on the ability of Listeria monocytogenes Scott A to attach to food contact surfaces

Attachment of Listeria monocytogenes Scott A to Buna-N rubber and stainless steel under different temperature and pH conditions at the time of cell growth or at the time of attachment was investigated. All experiments were conducted using sterile phosphate buffer to avoid cell growth during exposure to the test surfaces. Numbers of attached cells increased with increasing attachment temperature (10 to 45 degrees C) and exposure time for both test surfaces. Maximum levels of attached cells were obtained when cell growth occurred at 30 degrees C. Downward, but not upward, shifts in the cell suspension holding temperature prior to attachment to Buna-N rubber resulted in reduced adhered cell populations. Maximum levels of adhered cells to Buna-N rubber were not affected by adjustments of the attachment medium pH between 4 and 9. However, after short contact times (i.e., less than 30 min), levels of attached cells were lower when attachment occurred under alkaline conditions. Growth pH was also found to affect the levels of adhered cell populations to Buna-N rubber. L. monocytogenes Scott A attached to stainless steel at higher levels for all temperature and pH parameters evaluated in this study.

Molecular and genetic analysis of iron uptake proteins in the brazilian purpuric fever clone of Haemophilus influenzae biogroup aegyptius

Haemophilus influenzae biogroup aegyptius (H. aegyptius) is the etiological agent of Brazilian purpuric fever (BPF), a recently described pediatric disease that is often fatal. The vascular destruction that occurs in this disease is a distinctive trait, and little is known about the mechanism(s) of the overwhelming purpura fulminans that causes the high mortality associated with this pediatric infection. Iron is an essential micronutrient for nearly all living cells, and the mechanisms used by bacteria to acquire and internalize iron are often associated with virulence. Therefore, the focus of our studies is the molecular characterization of the iron uptake system used by H. aegyptius. Specifically, we are investigating the high-affinity transferrin binding proteins in the bacterial outer membrane, components of ABC transporter systems, and a possible regulatory mechanism for the genes encoding these proteins. A detailed understanding of the molecular nature of the regulatory genetic components and proteins involved in the acquisition of iron will broaden the knowledge of the pathogenesis of the disease caused by H. aegyptius and will also lead to a better understanding of the nature of other infections that affect the vascular system.

Expression of iron binding proteins and hemin binding activity in the dental pathogen Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans was found to express a polypeptide immunologically related to the Neisseria gonorrhoeae FbpA iron binding protein. In addition, the expression of hitB and hitC homologs was detected by Northern blot analysis. This periodontal pathogen also expresses a polypeptide homologous to the 31-kDa Haemophilus influenzae protein, which shows amino acid sequence homology with the FimA and YfeA proteins from Streptococcus parasanguis and Yersinia pestis, respectively. Both A. actinomycetemcomitans protein homologs were located within the periplasmic space, and their synthesis was regulated by the iron and hemin concentration of the culture medium. Southern and Western blot analysis together with molecular cloning revealed the presence of a Fur-like repressor, which may control the iron regulation of gene expression in this bacterium. Cultivation in the presence of hemin or Congo red revealed the ability of this organism to bind hemin. This binding activity was further confirmed by isolating Escherichia coli DH5 alpha clones that produced red and brown colonies on agar plates containing Congo red and hemin, respectively, after transformation with an A. actinomycetemcomitans gene library.