Thomas H. Rude

Potential Associations between Hematogenous Complications and Bacterial Genotype in Staphylococcus aureus Infection

BACKGROUND The impact of bacterial clonality on infections caused by Staphylococcus aureus is unclear. METHODS Three hundred seventy-nine S. aureus isolates (125 methicillin-resistant S. aureus [MRSA] and 254 methicillin-susceptible S. aureus [MSSA]) were genotyped by spa typing and multilocus sequence typing. For MRSA isolates, the staphylococcal chromosomal cassette mec (SCCmec) element was also typed. Three clinical categories were identified: nasal carriage only (n=118), uncomplicated infection (n=104), and bacteremia with hematogenous complications (n=157). RESULTS By use of eBURST, 18 clonal complexes (CCs) were found in 371 isolates. Eight CCs accounted for 89% of isolates and occurred in all clinical categories. CC5 (P=.0025) and CC30 (P=.0308) exhibited a significant trend toward more frequent hematogenous complications. Isolates within spa types 2 and 16 showed the same significant trend and grouped within CC5 and CC30, respectively. SCCmec II isolates also showed the same significant trend compared with SCCmec IV; 96% were CC5 or CC30. CONCLUSIONS Although most S. aureus genotypes exhibited the capacity to cause invasive disease, strains within CC5 and CC30 exhibited a significant trend toward increasing levels of hematogenous complications. Isolates within these CCs were also implicated by use of spa and SCCmec typing. The genetic determinants underlying these findings remain to be demonstrated.

Genotypic Characteristics of Staphylococcus aureus Isolates from a Multinational Trial of Complicated Skin and Skin Structure Infections

ABSTRACT The impact of bacterial genetic characteristics on the outcome of patients with Staphylococcus aureus infections is uncertain. This investigation evaluated potential associations between bacterial genotype and clinical outcome using isolates collected as part of an international phase 2 clinical trial (FAST II) evaluating telavancin for the treatment of complicated skin and skin structure infections (cSSSI). Ninety S. aureus isolates from microbiologically evaluable patients with cSSSI enrolled in the FAST II trial from 11 sites in the United States (56 isolates, or 62%) and 7 sites in South Africa (34 isolates, or 38%) were examined for staphylococcal cassette chromosome mec, agr, and the presence of 31 virulence genes and subjected to pulsed-field gel electrophoresis (PFGE). South African methicillin-susceptible S. aureus (MSSA) isolates were more likely to carry certain virulence genes, including sdrD (P = 0.01), sea (P < 0.01), and pvl (P = 0.01). All 44 (49%) methicillin-resistant S. aureus (MRSA) isolates were from the United States; 37 (84%) were strain USA 300 by PFGE. In the United States, MRSA isolates were more likely than MSSA isolates to carry genes for sdrC (P = 0.03), map/eap (P = 0.05), fnbB (P = 0.11), tst (P = 0.02), sea (P = 0.04), sed (P = 0.04), seg (P = 0.11), sej (P = 0.11), agr (P = 0.09), V8 (P = 0.06), sdrD, sdrE, eta, etb, and see (P < 0.01 for all). MRSA isolates were more often clonal than MSSA isolates by PFGE. Isolates from patients who were cured were significantly more likely to contain the pvl gene than isolates from patients that failed or had indeterminate outcomes (79/84 [94%] versus 3/6 [50%]; P = 0.01). S. aureus strains from different geographic regions have different distributions of virulence genes.

Characterization and regulation of the trehalose synthesis pathway and its importance in the pathogenicity of Cryptococcus neoformans.

ABSTRACT The disaccharide trehalose has been found to play diverse roles, from energy source to stress protectant, and this sugar is found in organisms as diverse as bacteria, fungi, plants, and invertebrates but not in mammals. Recent studies in the pathobiology of Cryptococcus neoformans identified the presence of a functioning trehalose pathway during infection and suggested its importance for C. neoformans survival in the host. Therefore, in C. neoformans we created null mutants of the trehalose-6-phosphate (T6P) synthase (TPS1), trehalose-6-phophate phosphatase (TPS2), and neutral trehalase (NTH1) genes. We found that both TPS1 and TPS2 are required for high-temperature (37°C) growth and glycolysis but that the block at TPS2 results in the apparent toxic accumulation of T6P, which makes this enzyme a fungicidal target. Sorbitol suppresses the growth defect in the tps1 and tps2 mutants at 37°C, which supports the hypothesis that these sugars (trehalose and sorbitol) act primarily as stress protectants for proteins and membranes during exposure to high temperatures in C. neoformans. The essential nature of this pathway for disease was confirmed when a tps1 mutant strain was found to be avirulent in both rabbits and mice. Furthermore, in the system of the invertebrate C. elegans, in which high in vivo temperature is no longer an environmental factor, attenuation in virulence was still noted with the tps1 mutant, and this supports the hypothesis that the trehalose pathway in C. neoformans is involved in more host survival mechanisms than simply high-temperature stresses and glycolysis. These studies in C. neoformans and previous studies in other pathogenic fungi support the view of the trehalose pathway as a selective fungicidal target for use in antifungal development.

Heterogeneous Vancomycin-Intermediate Susceptibility Phenotype in Bloodstream Methicillin-Resistant Staphylococcus aureus Isolates from an International Cohort of Patients with Infective Endocarditis: Prevalence, Genotype, and Clinical Significance

BACKGROUND The significance of heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) is unknown. Using a multinational collection of isolates from methicillin-resistant S. aureus (MRSA) infective endocarditis (IE), we characterized patients with IE with and without hVISA, and we genotyped the infecting strains. METHODS MRSA bloodstream isolates from 65 patients with definite IE from 8 countries underwent polymerase chain reaction (PCR) for 31 virulence genes, pulsed-field gel electrophoresis, and multilocus sequence typing. hVISA was defined using population analysis profiling. RESULTS Nineteen (29.2%) of 65 MRSA IE isolates exhibited the hVISA phenotype by population analysis profiling. Isolates from Oceania and Europe were more likely to exhibit the hVISA phenotype than isolates from the United States (77.8% and 35.0% vs 13.9%; P < .001). The prevalence of hVISA was higher among isolates with a vancomycin minimum inhibitory concentration of 2 mg/L (P = .026). hVISA-infected patients were more likely to have persistent bacteremia (68.4% vs 37.0%; P = .029) and heart failure (47.4% vs 19.6%; P = .033). Mortality did not differ between hVISA- and non-hVISA-infected patients (42.1% vs 34.8%, P = .586). hVISA and non-hVISA isolates were genotypically similar. CONCLUSIONS In these analyses, the hVISA phenotype occurred in more than one-quarter of MRSA IE isolates, was associated with certain IE complications, and varied in frequency by geographic region.

Relationship of the Glyoxylate Pathway to the Pathogenesis of Cryptococcus neoformans

ABSTRACT Functional genomics has become a major focus in the study of microbial pathogenesis. This study used a functional genomic tool, differential display reverse transcription-PCR, to identify a transcriptional profile of Cryptococcus neoformans cells as they produced meningitis in an immunosuppressed host. This serial global gene expression during infection allowed for the identification of up- and down-regulated genes during infection. During this profiling, a single gene for the enzyme isocitrate lyase (ICL1) was found to be up regulated at 1 week of infection in a rabbit meningitis model and during a time of maximum host cellular response. The finding suggested that this enzyme and the glyoxylate shunt pathway are important to this yeasts energy production during infection. However, site-directed icl1 mutants had no apparent virulence defect in two animal models and no growth defect within macrophages. These observations suggest that although the yeast responded to a certain environmental cue(s) by an increase in ICL1 expression during infection, this gene was not necessary for progression of a C. neoformans infection. Compounds that specifically target only ICL1 are unlikely to cripple C. neoformans growth in vivo.

Methicillin-susceptible Staphylococcus aureus endocarditis isolates are associated with clonal complex 30 genotype and a distinct repertoire of enterotoxins and adhesins.

BACKGROUND Using multinational collections of methicillin-susceptible Staphylococcus aureus (MSSA) isolates from infective endocarditis (IE) and soft tissue infections (STIs), we sought to (1) validate the finding that S. aureus in clonal complex (CC) 30 is associated with hematogenous complications and (2) test the hypothesis that specific genetic characteristics in S. aureus are associated with infection severity. METHODS IE and STI isolates from 2 cohorts were frequency matched by geographic origin. Isolates underwent spa typing to infer CC and multiplex polymerase chain reaction for presence of virulence genes. RESULTS 114 isolate pairs were genotyped. IE isolates were more likely to be CC30 (19.5% vs 6.2%; P = .005) and to contain 3 adhesins (clfB, cna, map/eap; P < .0001 for all) and 5 enterotoxins (tst, sea, sed, see, and sei; P ≤ .005 for all). CC30 isolates were more likely to contain cna, tst, sea, see, seg, and chp (P < .05 for all). CONCLUSIONS MSSA IE isolates were significantly more likely to be CC30 and to possess a distinct repertoire of virulence genes than MSSA STI isolates from the same region. The genetic basis of this association requires further study.

Presence of Genes Encoding the Panton-Valentine Leukocidin Exotoxin Is Not the Primary Determinant of Outcome in Patients with Complicated Skin and Skin Structure Infections Due to Methicillin-Resistant Staphylococcus aureus: Results of a Multinational Trial

ABSTRACT The role of Panton-Valentine leukocidin (PVL) in determining the severity and outcome of complicated skin and skin structure infections (cSSSI) caused by methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) is controversial. We evaluated potential associations between clinical outcome and PVL status by using MRSA isolates from patients enrolled in two large, multinational phase three clinical trials assessing telavancin for the treatment of cSSSI (the ATLAS program). MRSA isolates from microbiologically evaluable patients were genotyped by pulsed-field gel electrophoresis (PFGE) and PCR for pvl and 31 other putative virulence determinants. A single baseline pathogen of MRSA was isolated from 522 microbiologically evaluable patients (25.1%) among 2,079 randomized patients. Of these MRSA isolates, 83.2% (432/519) exhibited the USA300 PFGE genotype and 89.1% (465/522) were pvl positive. Patients with pvl-positive MRSA were more likely than those with pvl-negative MRSA to be young, to be North American, and to present with major abscesses (P < 0.001 for each). Patients were significantly more likely to be cured if they were infected with pvl-positive MRSA than if they were infected with pvl-negative MRSA (91.6% versus 80.7%; P = 0.015). This observation remained statistically significant after adjustment for presence of abscess, fever, or leukocytosis; infection size; diabetes; patient age; and study medication received. The fnbA, cna, sdrC, map-eap, sed, seg, sei, sej, SCCmec type IV, and agr group II genes were also associated with clinical response (P < 0.05). This contemporary, international study demonstrates that pvl was not the primary determinant of outcome in patients with MRSA cSSSI.

Associations between the Genotypes of Staphylococcus aureus Bloodstream Isolates and Clinical Characteristics and Outcomes of Bacteremic Patients

ABSTRACT We investigated associations between the genotypic and phenotypic features of Staphylococcus aureus bloodstream isolates and the clinical characteristics of bacteremic patients enrolled in a phase III trial of S. aureus bacteremia and endocarditis. Isolates underwent pulsed-field gel electrophoresis, PCR for 33 putative virulence genes, and screening for heteroresistant glycopeptide intermediate S. aureus (hGISA). A total of 230 isolates (141 methicillin-susceptible S. aureus and 89 methicillin-resistant S. aureus [MRSA]) were analyzed. North American and European S. aureus isolates differed in their genotypic characteristics. Overall, 26% of the MRSA bloodstream isolates were USA 300 strains. Patients with USA 300 MRSA bacteremia were more likely to be injection drug users (61% versus 15%; P < 0.001), to have right-sided endocarditis (39% versus 9%; P = 0.002), and to be cured of right-sided endocarditis (100% versus 33%; P = 0.01) than patients with non-USA 300 MRSA bacteremia. Patients with persistent bacteremia were less likely to be infected with Panton-Valentine leukocidin gene (pvl)-constitutive MRSA (19% versus 56%; P = 0.005). Although 7 of 89 MRSA isolates (8%) exhibited the hGISA phenotype, no association with persistent bacteremia, daptomycin resistance, or bacterial genotype was observed. This study suggests that the virulence gene profiles of S. aureus bloodstream isolates from North America and Europe differ significantly. In this study of bloodstream isolates collected as part of a multinational randomized clinical trial, USA 300 and pvl-constitutive MRSA strains were associated with better clinical outcomes.

Two genes on A/J chromosome 18 are associated with susceptibility to Staphylococcus aureus infection by combined microarray and QTL analyses.

Although it has recently been shown that A/J mice are highly susceptible to Staphylococcus aureus sepsis as compared to C57BL/6J, the specific genes responsible for this differential phenotype are unknown. Using chromosome substitution strains (CSS), we found that loci on chromosomes 8, 11, and 18 influence susceptibility to S. aureus sepsis in A/J mice. We then used two candidate gene selection strategies to identify genes on these three chromosomes associated with S. aureus susceptibility, and targeted genes identified by both gene selection strategies. First, we used whole genome transcription profiling to identify 191 (56 on chr. 8, 100 on chr. 11, and 35 on chr. 18) genes on our three chromosomes of interest that are differentially expressed between S. aureus-infected A/J and C57BL/6J. Second, we identified two significant quantitative trait loci (QTL) for survival post-infection on chr. 18 using N2 backcross mice (F1 [C18A]×C57BL/6J). Ten genes on chr. 18 (March3, Cep120, Chmp1b, Dcp2, Dtwd2, Isoc1, Lman1, Spire1, Tnfaip8, and Seh1l) mapped to the two significant QTL regions and were also identified by the expression array selection strategy. Using real-time PCR, 6 of these 10 genes (Chmp1b, Dtwd2, Isoc1, Lman1, Tnfaip8, and Seh1l) showed significantly different expression levels between S. aureus-infected A/J and C57BL/6J. For two (Tnfaip8 and Seh1l) of these 6 genes, siRNA-mediated knockdown of gene expression in S. aureus–challenged RAW264.7 macrophages induced significant changes in the cytokine response (IL-1 β and GM-CSF) compared to negative controls. These cytokine response changes were consistent with those seen in S. aureus-challenged peritoneal macrophages from CSS 18 mice (which contain A/J chromosome 18 but are otherwise C57BL/6J), but not C57BL/6J mice. These findings suggest that two genes, Tnfaip8 and Seh1l, may contribute to susceptibility to S. aureus in A/J mice, and represent promising candidates for human genetic susceptibility studies.

The actin gene from Cryptococcus neoformans: structure and phylogenetic analysis

Using heterologous probing of a genomic library, we have cloned and sequenced the actin gene from the pathogenic yeast Cryptococcus neoformans. The actin gene is 1371 bp in length, and exists as a single copy, as is the case for all fungi studied to date. The locations of the introns in the C. neoformans actin gene are unique among all other known actin genes, and the deduced coding sequence results in a 375 amino acid chain with very high homology to other actins. A phylogenetic tree comprising 31 actin-coding sequences from a wide variety of organisms shows that the C. neoformans actin gene is grouped on a distinct branch together with all other known fungal actin sequences. The availability of the C. neoformans actin gene will aid future phylogenetic and molecular studies of this important human pathogen.