SUMMARY: Probiotics are defined as live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. There is now mounting evidence that selected probiotic strains can provide health benefits to their human hosts. Numerous clinical trials show that certain strains can improve the outcome of intestinal infections by reducing the duration of diarrhea. Further investigations have shown benefits in reducing the recurrence of urogenital infections in women, while promising studies in cancer and allergies require research into the mechanisms of activity for particular strains and better-designed trials. At present, only a small percentage of physicians either know of probiotics or understand their potential applicability to patient care. Thus, probiotics are not yet part of the clinical arsenal for prevention and treatment of disease or maintenance of health. The establishment of accepted standards and guidelines, proposed by the Food and Agriculture Organization of the United Nations and the World Health Organization, represents a key step in ensuring that reliable products with suitable, informative health claims become available. Based upon the evidence to date, future advances with single- and multiple-strain therapies are on the horizon for the management of a number of debilitating and even fatal conditions.

▪ Abstract Toxic shock syndrome (TSS) is an acute onset illness characterized by fever, rash formation, and hypotension that can lead to multiple organ failure and lethal shock, as well as desquamation in patients that recover. The disease is caused by bacterial superantigens (SAGs) secreted from Staphylococcus aureus and group A streptococci. SAGs bypass normal antigen presentation by binding to class II major histocompatibility complex molecules on antigen-presenting cells and to specific variable regions on the β-chain of the T-cell antigen receptor. Through this interaction, SAGs activate T cells at orders of magnitude above antigen-specific activation, resulting in massive cytokine release that is believed to be responsible for the most severe features of TSS. This review focuses on clinical and epidemiological aspects of TSS, as well as important developments in the genetics, biochemistry, immunology, and structural biology of SAGs. From the evolutionary relationships between these important toxins, we propose that there are five distinct groups of SAGs.

The lack of a reliable scoring system that predicts the development of septic shock and death precludes comparison of disease and/or treatment outcomes in animal models of sepsis. We developed a murine sepsis score (MSS) that evaluates seven clinical variables, and sought to assess its validity and reliability in an experimental mouse model of polymicrobial sepsis.

Genome sequences are available for many bacterial strains, but there has been little progress in using these data to understand the molecular basis of pathogen emergence and differences in strain virulence. Serotype M3 strains of group AStreptococcus(GAS) are a common cause of severe invasive infections with unusually high rates of morbidity and mortality. To gain insight into the molecular basis of this high-virulence phenotype, we sequenced the genome of strain MGAS315, an organism isolated from a patient with streptococcal toxic shock syndrome. The genome is composed of 1,900,521 bp, and it shares ≈1.7 Mb of related genetic material with genomes of serotype M1 and M18 strains. Phage-like elements account for the great majority of variation in gene content relative to the sequenced M1 and M18 strains. Recombination produces chimeric phages and strains with previously uncharacterized arrays of virulence factor genes. Strain MGAS315 has phage genes that encode proteins likely to contribute to pathogenesis, such as streptococcal pyrogenic exotoxin A (SpeA) and SpeK, streptococcal superantigen (SSA), and a previously uncharacterized phospholipase A₂(designated Sla). Infected humans had anti-SpeK, -SSA, and -Sla antibodies, indicating that these GAS proteins are madein vivo. SpeK and SSA were pyrogenic and toxic for rabbits. Serotype M3 strains with the phage-encodedspeKandslagenes increased dramatically in frequency late in the 20th century, commensurate with the rise in invasive disease caused by M3 organisms. Taken together, the results show that phage-mediated recombination has played a critical role in the emergence of a new, unusually virulent clone of serotype M3 GAS.

We have previously demonstrated that the presence of oxygen is necessary for the production of toxic shock syndrome toxin 1 (TSST-1) byStaphylococcus aureusin vitro. To investigate the mechanism by which oxygen might regulate toxin production, we identified homologs inS. aureusof theBacillus subtilis resDEgenes. The two-component regulatory system encoded byresDE, ResD-ResE, has been implicated in the global regulation of aerobic and anaerobic respiratory metabolism inB. subtilis. We have designated theS. aureushomologssrrAB(staphylococcal respiratory response). The effects ofsrrABexpression on expression of RNAIII (the effector molecule of theagrlocus) and on production of TSST-1 (an exotoxin) and protein A (a surface-associated virulence factor) were investigated. Expression of RNAIII was inversely related to expression ofsrrAB. Disruption ofsrrBresulted in increased levels of RNAIII, while expression ofsrrABintranson a multicopy plasmid resulted in repression of RNAIII transcription, particularly in microaerobic conditions. Disruption ofsrrBresulted in decreased production of TSST-1 under microaerobic conditions and, to a lesser extent, under aerobic conditions as well. Overexpression ofsrrABresulted in nearly complete repression of TSST-1 production in both microaerobic and aerobic conditions. Protein A production by thesrrBmutant was upregulated in microaerobic conditions and decreased in aerobic conditions. Protein A production was restored to nearly wild-type levels by complementation ofsrrABinto the null mutant. These results indicate that the putative two-component system encoded bysrrAB, SrrA-SrrB, acts in the global regulation of staphylococcal virulence factors, and may repress virulence factors under low-oxygen conditions. Furthermore,srrABmay provide a mechanistic link between respiratory metabolism, environmental signals, and regulation of virulence factors inS. aureus.

The production of the staphylococcal exotoxin toxic shock syndrome toxin-1 (TSST-1) by Staphylococcus aureus has been associated with essentially all cases of menstruation-associated toxic shock syndrome (TSS). In this work, we show that the human vaginal isolate Lactobacillus reuteri RC-14 produces small signaling molecules that are able to interfere with the staphylococcal quorum-sensing system agr , a key regulator of virulence genes, and repress the expression of TSST-1 in S. aureus MN8, a prototype of menstrual TSS S. aureus strains. Quantitative real-time PCR data showed that transcription from the P tst promoter, as well as the P2 and P3 promoters of the agr system from all four agr subgroups of S. aureus , was strongly inhibited in response to growth with L. reuteri RC-14 cultural supernatant. Alterations in the transcriptional levels of two other virulence-associated regulators sarA and saeRS were also observed, indicating a potential overall influence of L. reuteri RC-14 signals on the production of virulence factors in S. aureus . S. aureus promoter- lux reporter strains were used to screen biochemically fractionated L. reuteri RC-14 supernatant, and the cyclic dipeptides cyclo( l -Phe- l -Pro) and cyclo( l -Tyr- l -Pro) were identified as the signaling molecules. The results from this work contribute to a better understanding of interspecies cell-to-cell communication between Lactobacillus and Staphylococcus , and provide a unique mechanism by which endogenous or probiotic strains may attenuate virulence factor production by bacterial pathogens.