In vitro synthesis of the delta-lysin of Staphylococcus aureus

Association between mortality and serum uric acid levels in non-diabetes-related chronic kidney disease: An analysis of the National Health and Nutrition Examination Survey, USA, 1999-2010

The relationship between serum uric acid (SUA) and cardiovascular (CV) mortality in patients with chronic kidney disease (CKD) has been described as either a J- or U-shaped function. However, its effect in non-diabetic CKD (and varying severities of CKD) remains unclear. We analyzed the database of the National Health and Nutrition Examination Survey, USA, from the years 1999 to 2010. We then grouped the subjects into 4 categories according to their SUA levels: (a) < 5 mg/dl, (b) 5-7 mg/dl, (c) 7-9 mg/dl and (d) ≥ 9 mg/dl. For mortality comparison purposes (CV related, cancer related and all-cause mortality), we set the SUA group of 5-7 mg/dl as the reference. We also separated this population into moderate (stage 3) and severe (stages 4 and 5) CKD. A total of 1860 participants were included in this study. Results showed that the group with the lowest SUA levels (< 5 mg/dl), were the least male gender (19.25%), had the lowest body mass index (26.41(95% CI = 25.66-27.16) kg/m2), highest systolic blood pressure (139.02 (95% CI 135.72-142.32) mmHg), highest high-density cholesterol (59.55 (95% CI 57.37-61.74) mg/dl), lowest blood glucose (95.46 (95% CI 93.16-97.76) mg/dl), highest total cholesterol (210.31 (95% CI 203.36-217.25) mg/dl), lowest serum albumin (4.09 (95% CI 4.04-4.14) g/dl), highest estimated glomerular filtration rate (eGFR) (47.91 (95% CI 45.45-50.49) ml/min/1.732m2), least history of hypertension (54.4%), and least total energy intake (1643.7 (95% CI 1536.13-1751.27) kcal/day). In the group with SUA ≥ 9 mg/dl, patients had higher all-cause mortality (HR = 2.15) whatever their baseline CVD status. In non-DM CKD patients with a CVD history, the group with SUA ≥ 9 mg/dl had the highest all-cause mortality (HR = 5.39), CVD mortality (HR = 8.18) and CVD or cancer (HR = 8.25) related mortality. In non-DM patients with severe CKD (eGFR < 30 ml/min/1.732m2), the group with SUA < 5 had a significantly increased all-cause mortality. On the contrary, in non-DM patients with moderate CKD (eGFR = 30-60 ml/min/1.832m2), the group with SUA ≥ 9 had a significantly increased all-cause mortality. In moderate non-DM CKD, SUA ≥ 9 mg/dl is associated with higher all-cause mortality. However, once progressing to severe non-DM CKD, SUA < 5 mg/dl is associated with higher all-cause mortality (even though it has the least risk factors for metabolic syndrome).

Vancomycin modifies the expression of the agr system in multidrug-resistant Staphylococcus aureus clinical isolates

Staphylococcus aureus is an opportunistic pathogen that colonizes human hosts and causes a wide variety of diseases. Two interacting regulatory systems called agr (accessory gene regulator) and sar (staphylococcal accessory regulator) are involved in the regulation of virulence factors. The aim of this study was to evaluate the effect of vancomycin on hld and spa gene expression during the exponential and post-exponential growth phases in multidrug-resistant (MDR) S. aureus.

Methods: Antibiotic susceptibility was evaluated by the standard microdilution method. The phylogenetic profile was obtained by pulsed-field gel electrophoresis (PFGE). Polymorphisms of agr and SCCmec (staphylococcal cassette chromosome mec) were analyzed by multiplex polymerase chain reaction (PCR). The expression levels of hld and spa were analyzed by reverse transcription-PCR. An enzyme-linked immunosorbent assay (ELISA) was performed to detect protein A, and biofilm formation was analyzed via crystal violet staining.

Results: In total, 60.60% (20/33) of S. aureus clinical isolates were MDR. Half (10/20) of the MDR S. aureus isolates were distributed in subcluster 10, with >90% similarity among them. In the isolates of this subcluster, a high prevalence (100%) for the agrII and the cassette SCCmec II polymorphisms was found. Our data showed significant increases in hld expression during the post-exponential phase in the presence and absence of vancomycin. Significant increases in spa expression, protein A production and biofilm formation were observed during the post-exponential phase when the MDR S. aureus isolates were challenged with vancomycin.

Conclusion: The polymorphism agrII, which is associated with nosocomial isolates, was the most prevalent polymorphism in MDR S. aureus. Additionally, under our study conditions, vancomycin modified hld and spa expression in these clinical isolates. Therefore, vancomycin may regulate alternative systems that jointly participate in the regulation of these virulence factors.

Type I signal peptidase and protein secretion in Staphylococcus aureus

Staphylococcus aureus is an important human pathogen whose virulence relies on the secretion of many different proteins. In general, the secretion of most proteins in S. aureus, as well as other bacteria, is dependent on the type I signal peptidase (SPase)-mediated cleavage of the N-terminal signal peptide that targets a protein to the general secretory pathway. The arylomycins are a class of natural product antibiotics that inhibit SPase, suggesting that they may be useful chemical biology tools for characterizing the secretome. While wild-type S. aureus (NCTC 8325) is naturally resistant to the arylomycins, sensitivity is conferred via a point mutation in its SPase. Here, we use a synthetic arylomycin along with a sensitized strain of S. aureus and multidimensional protein identification technology (MudPIT) mass spectrometry to identify 46 proteins whose extracellular accumulation requires SPase activity. Forty-four possess identifiable Sec-type signal peptides and thus are likely canonically secreted proteins, while four also appear to possess cell wall retention signals. We also identified the soluble C-terminal domains of two transmembrane proteins, lipoteichoic acid synthase, LtaS, and O-acyteltransferase, OatA, both of which appear to have noncanonical, internal SPase cleavage sites. Lastly, we identified three proteins, HtrA, PrsA, and SAOUHSC_01761, whose secretion is induced by arylomycin treatment. In addition to elucidating fundamental aspects of the physiology and pathology of S. aureus, the data suggest that an arylomycin-based therapeutic would reduce virulence while simultaneously eradicating an infection.

Purification and characterization of a novel delta-lysin variant that inhibits Staphylococcus aureus and has limited hemolytic activity

Delta-lysins (DL) that are produced by various species of staphylococci are not widely known for their antimicrobial activity. We have purified and characterized a novel DL variant, E229DL and examined its spectrum of inhibitory activity. The biological activity of E229DL, produced by Staphylococcus epidermidis strain E229, shows relatively broad-spectrum activity against Gram-positive pathogens, including representatives of MRSA and epidemic MRSA type 15. E229DL was purified to homogeneity from 95% acidified-methanol extracts of cell cultures by using a series of reversed-phase chromatographic separations. The fully processed form of E229DL is a 25-amino-acid peptide with a predicted mass of 2841.4 Da, but the purified biologically active molecule appears to be N-formylated (mass 2867.33 Da). The DL gene (hld) resembles that of other types of DL, but differs in five codons with hld in Staphylococcus aureus (26 residues) and one codon with the closest homolog, the hld-II in S. warneri (25 residues). The characterization of E229DL showed that its activity is stable in agar exposed to high temperatures (80 degrees C/45 min). In addition, biological testing of the native and synthetic peptides against a range of human and animal erythrocytes and Vero cells indicated that E229DL is an antibacterial agent with no detectable cytopathic effects at concentrations equivalent to the minimum inhibitory concentration for EMRSA15-A208. Initial investigation of the mode of action of E229DL indicated that it is rapidly lytic for target cells. This is the first description of a native form of DL having only limited cytotoxic activity for eukaryotic cells at concentrations that are inhibitory to staphylococci.

Relative quantitative comparisons of the extracellular protein profiles of Staphylococcus aureus UAMS-1 and its sarA, agr, and sarA agr regulatory mutants using one-dimensional polyacrylamide gel electrophoresis and nanocapillary liquid chromatography coupled with tandem mass spectrometry

One-dimensional polyacrylamide gel electrophoresis followed by nanocapillary liquid chromatography coupled with mass spectrometry was used to analyze proteins isolated from Staphylococcus aureus UAMS-1 after 3, 6, 12, and 24 h of in vitro growth. Protein abundance was determined using a quantitative value termed normalized peptide number, and overall, proteins known to be associated with the cell wall were more abundant early on in growth, while proteins known to be secreted into the surrounding milieu were more abundant late in growth. In addition, proteins from spent media and cell lysates of strain UAMS-1 and its isogenic sarA, agr, and sarA agr regulatory mutant strains during exponential growth were identified, and their relative abundances were compared. Extracellular proteins known to be regulated by the global regulators sarA and agr displayed protein levels in accordance with what is known regarding the effects of these regulators. For example, cysteine protease (SspB), endopeptidase (SspA), staphopain (ScpA), and aureolysin (Aur) were higher in abundance in the sarA and sarA agr mutants than in strain UAMS-1. The immunoglobulin G (IgG)-binding protein (Sbi), immunodominant staphylococcal antigen A (IsaA), IgG-binding protein A (Spa), and the heme-iron-binding protein (IsdA) were most abundant in the agr mutant background. Proteins whose abundance was decreased in the sarA mutant included fibrinogen-binding protein (Fib [Efb]), IsaA, lipase 1 and 2, and two proteins identified as putative leukocidin F and S subunits of the two-component leukotoxin family. Collectively, this approach identified 1,263 proteins (matches of two peptides or more) and provided a convenient and reliable way of identifying proteins and comparing their relative abundances.

Characterizing the effect of the Staphylococcus aureus virulence factor regulator, SarA, on log-phase mRNA half-lives

Bacterial pathogens regulate virulence factor expression at both the level of transcription initiation and mRNA processing/turnover. Within Staphylococcus aureus, virulence factor transcript synthesis is regulated by a number of two-component regulatory systems, the DNA binding protein SarA, and the SarA family of homologues. However, little is known about the factors that modulate mRNA stability or influence transcript degradation within the organism. As our entree to characterizing these processes, S. aureus GeneChips were used to simultaneously determine the mRNA half-lives of all transcripts produced during log-phase growth. It was found that the majority of log-phase transcripts (90%) have a short half-life (<5 min), whereas others are more stable, suggesting that cis- and/or trans-acting factors influence S. aureus mRNA stability. In support of this, it was found that two virulence factor transcripts, cna and spa, were stabilized in a sarA-dependent manner. These results were validated by complementation and real-time PCR and suggest that SarA may regulate target gene expression in a previously unrecognized manner by posttranscriptionally modulating mRNA turnover. Additionally, it was found that S. aureus produces a set of stable RNA molecules with no predicted open reading frame. Based on the importance of the S. aureus agr RNA molecule, RNAIII, and small stable RNA molecules within other pathogens, it is possible that these RNA molecules influence biological processes within the organism.

Enterocins L50A and L50B, two novel bacteriocins from Enterococcus faecium L50, are related to staphylococcal hemolysins

Enterocin L50 (EntL50), initially referred to as pediocin L50 (L. M. Cintas, J. M. Rodríguez, M. F. Fernández, K. Sletten, I. F. Nes, P. E. Hernández, and H. Holo, Appl. Environ. Microbiol. 61:2643-2648, 1995), is a plasmid-encoded broad-spectrum bacteriocin produced by Enterococcus faecium L50. It has previously been purified from the culture supernatant and partly sequenced by Edman degradation. In the present work, the nucleotide sequence of the EntL50 locus was determined, and several putative open reading frames (ORFs) were identified. Unexpectedly, two ORFs were found to encode EntL50-like peptides. These peptides, termed enterocin L50A (EntL50A) and enterocin L50B (EntL50B), have 72% sequence identity and consist of 44 and 43 amino acids, respectively. Interestingly, a comparison of the deduced sequences of EntL50A and EntL50B with the corresponding sequences obtained by Edman degradation shows that these bacteriocins, in contrast to other peptide bacteriocins, are secreted without an N-terminal leader sequence or signal peptide. Expression in vivo and in vitro transcription/translation experiments demonstrated that entL50A and entL50B are the only genes required to obtain antimicrobial activity, strongly indicating that their bacteriocin products are not posttranslationally modified. Both bacteriocins possess antimicrobial activity on their own, with EntL50A being the most active. In addition, when the two bacteriocins were combined, a considerable synergism was observed, especially with some indicator strains. Even though the enterocins in some respects are similar to class II bacteriocins, several conserved features common to class II bacteriocins are absent from the EntL50 system. The enterocins have more in common with members of a small group of cytolytic peptides secreted by certain staphylococci. We therefore propose that the enterocins L50A and L50B and the staphylococcal cytolysins together constitute a new family of peptide toxins, unrelated to class II bacteriocins, which possess bactericidal and/or hemolytic activity.

Identification and nucleotide sequence of the delta-lysin gene, hld, adjacent to the accessory gene regulator (agr) of Staphylococcus aureus

A Tn551 insertional mutation in the accessory gene regulator (agr) locus of the Staphylococcus aureus chromosome resulted in the decreased production of at least seven extracellular toxins and enzymes and a simultaneous increase in the production of protein A and coagulase (Recsei et al. 1986). Adjacent to this locus we have now identified another gene, hld, transcribed into a 0.5 kb RNA which codes for the staphylococcal delta-lysin. The expression of hld was totally repressed in a strain carrying the agr insertional mutation. Hybridization with strand-specific probes and primer extension analysis revealed that hld and agr are transcribed in opposite directions, starting 188 nucleotides apart. The hld gene is mainly expressed during the post-exponential growth phase and is totally repressed during early exponential growth. Determination of hld mRNA half-life in different growth phases indicated that this regulation is at the level of transcription.

The amino acid sequence of a gonococcal growth inhibitor from Staphylococcus haemolyticus

A gonococcal inhibitor produced by Staphylococcus haemolyticus was separated into three components by reverse-phase h.p.l.c. The amino acid composition analysis of each of the three components indicated extensive similarities. N-Terminal sequence analysis of all three components allowed the identification of the first 27-30 residues of each. The complete primary structure of each component was determined from the sequence analysis of trypic peptides and peptides generated by mild acid hydrolysis. Each component is composed of 44 amino acid residues, with evidence suggesting the presence of an N-terminal formylmethionine residue in each. The components I, II and III have respectively 33, 29 and 33 identical amino acid residues in their sequences, which represents 75%, 65.9% and 75% homology. These components contain a high proportion of hydrophobic amino acids, and their hydrophobicity profiles are closely related. Also, each of the three components contains a positively charged residue (lysine) as the third residue, followed by a core of hydrophobic residues. These results suggest that the three components are possible signal sequences of one or more secreted or membrane-associated proteins.

Effect of phenethyl alcohol on Staphylococcus aureus alpha-lysin production

Phenethyl alcohol, at the maximum concentration which did not inhibit growth (0.3% [vol/vol]), inhibited the production of alpha-lysin and exoproteases but not that of delta-lysin in Staphylococcus aureus Wood 46. The inhibition of alpha-lysin was reversible, and transient accumulation of cell-associated alpha-lysin occurred in the presence of PEA. A precursor of alpha-lysin ca. 3,000 daltons larger than extracellular alpha-lysin was immunologically detected in the sodium dodecyl sulfate extracts of membranes and whole cells of phenethyl alcohol-treated S. aureus cultures. Also, a degraded form of alpha-lysin was detected in membranes prepared from cells lysed by lysostaphin but not in membranes from cells lysed with an X-press.