α and β Chains of Hemoglobin Inhibit Production of Staphylococcus aureus Exotoxins

Abstract

Prior studies suggest Staphylococcus aureus exotoxins are not produced when the organism is cultured in human blood. Human blood was fractionated into plasma and water-lysed red blood cells and demonstrated that mixtures of α and β globins of hemoglobin (as low as 1 ug/ml) inhibited S. aureus exotoxin production while increasing production of protein A and not affecting bacterial growth. Pepsin but not trypsin digestion destroyed the ability of α and β globin to inhibit exotoxin production. Exotoxin production by both methicillin-resistant and susceptible organisms was inhibited. Production of streptococcal pyrogenic exotoxin A by Streptococcus pyogenes was unaffected by α and β globin chains, but was inhibited when produced in S. aureus. Use of isogenic S. aureus strains suggested the targets of α and β globin chains, leading to inhibition of staphylococcal exotoxins, included the two component system SrrA-SrrB. Delta hemolysin production was also inhibited, suggesting the two component (and quorum sensing) system AgrA-AgrC was targeted. The α and β globin chains represent promising molecules to interfere with the pathogenesis of serious staphylococcal diseases.Staphylococcus aureus causes large numbers of human diseases, primarily initiated by colonization of mucosal surfaces (1,2). At any particular time, as many as 40% of humans may be colonized by culturable S. aureus strains on either nasal or vaginal mucosal surfaces (1,3). The organism may cause relatively benign infections, such as boils, and life threatening infections such as toxic shock syndrome (TSS) (4), scalded skin syndrome (5), necrotizing pneumonia (6-8), and the recently described staphylococcal purpura fulminans (9,10). Antibiotic resistance in S. aureus strains is an ever increasing problem, with recognition of both community-and hospital-associated methicillin-resistant strains (MRSA) (1,2,11). † This work was supported by a research grant from Procter & Gamble, Cincinnati, Ohio and USPHS research grant HL36611 from the National Heart, Lung, and Blood Institute.*To whom correspondence should be addressed. Phone: 612-624-1484; Fax: 612-626-0623; E mail: schli001@umn.edu Recently, two methicillin-resistant, vancomycin-resistant strains were isolated in association with human infections (12,13).The ability of S. aureus to cause serious human diseases depends on production of both cellsurface and secreted virulence factors by the organism (1,4). The cell-surface virulence factors, often referred to as microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) (14), allow the organism to attach to host tissues and in some instances evade the host immune system (15). MSCRAMMs include staphylococcal protein A. The secreted virulence factors, including a large array of exotoxins, allow the organism to gain access to nutrients and avoid the host immune system (4,5,16). For example, the hemolysin family of exotoxins allows the organism both to resist destruction by leukocytes and at the same time gain access to host tissue ...

Staphylococcal and Streptococcal Superantigen Exotoxins

“…These conditions include growth in complex media containing animal protein with low glucose (glucose functions as a catabolite repressor of exotoxin production), neutral pH (as expected vaginally during menstruation), temperature of 37°C to 40°C, and oxygen balanced with CO 2 (84,168). As noted previously, blood components, and more specifically hemoglobin peptides, negatively affect production of TSST-1 (147). The introduction of oxygen into the human vagina, a typically anaerobic environment, by tampons is now considered the major reason for the tampon association with mTSS (84,168,169).…”

“…Investigators have shown that certain superantigens, notably SEA, TSST-1, and SEC, are overrepresented in sepsis cases compared to nonsepsis cases (253)(254)(255). However, it is unlikely that superantigens are directly produced in the bloodstream of patients, since hemoglobin peptides inhibit superantigen production (147). It is more likely that superantigens are produced in focal sites of infection protected from hemoglobin peptides and then secreted into the bloodstream.…”

Control of the Staphylococcus aureus Toxic Shock tst Promoter by the Global Regulator SarA

“…The environmental triggers and molecular mechanisms that control the production of TSST-1 are complex and not fully understood. Multiple factors, such as glucose, pH, CO 2 , O 2 , NaCl, magnesium concentration, the ␣ and ␤ chains of hemoglobin, and TSST-1 itself, have been assessed and shown to affect toxin production (4,19,46,48,56,59).…”

Staphylococcus aureus Exotoxins Are Present In Vivo in Tampons

“…S. aureus CFU/ml were determined by plate counts from each section. The amount of TSST-1 (g/section) was determined by semiquantitative Western immunoblot analysis, which allows for the detection of TSST-1 in the presence of antibodies and blood components (26). The Western immunoblots were developed with alkaline phosphatase-conjugated antibodies and substrate (3).…”

“…In vitro studies demonstrate that O 2 and CO 2 , iron, pH, glucose, and temperature are factors that can alter the concentration of TSST-1 produced by S. aureus (10,12,25,33,36). Recent in vitro studies have shown that both ␣-and ␤-globin chains of human hemoglobin can inhibit the production of TSST-1 without impacting growth of the organism (26). Given that menstrual blood is rich in hemoglobin, the study suggests that toxigenic S. aureus present on tampons might produce TSST-1 only in areas that lack menstrual blood.…”