Impact of unit-wide chlorhexidine bathing in intensive care on bloodstream infection and drug-resistant organism acquisition.

BACKGROUND: Chlorhexidine gluconate (CHG) bathing has been reported to decrease bloodstream infections and colonisation of multidrug-resistant organisms (MROs) in intensive care units (ICUs). However, its effectiveness in an Australian setting has not been assessed. OBJECTIVE: To test whether the introduction of ICU-wide CHG bathing in place of triclosan would affect rates of the primary outcome of central line-associated bloodstream infections (CLABSI), or the secondary outcomes of ICU-acquired positive blood cultures or other clinical specimens, and MRO colonisation including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE). METHODS: We conducted a single-centre, sequential, before-and-after observational study. Patient microbiological and clinical data were compared in the 12 months before and after the introduction of CHG bathing in the ICU. RESULTS: A total of 4262 ICU admissions were studied, 2117 before and 2145 during the CHG-bathing period. There were no significant changes in the rates of CLABSI (from 1.69/1000 central venous catheter-days [95% CI, 0.68-3.48] to 1.33 [95% CI, 0.49-2.90]; P = 0.68), or ICU-acquired positive blood cultures (from 5.14/1000 patientdays [95% CI, 3.45-7.39] to 4.45 [95% CI, 3.00-6.36]; P = 0.58). However, we observed a lower incidence of MRSA acquisition during the CHG-bathing period (mean difference, -2.13 [95% CI, -3.65 to -0.60] per 1000 patient-days; P = 0.007). There was no difference in the rate of isolates involving other pathogens including VRE. CONCLUSIONS: In a tertiary Australian ICU, routine CHG bathing compared with triclosan did not affect the rates of ICU-acquired CLABSI or positive blood cultures. However, it significantly decreased the incidence of MRSA acquisition.

Cutaneous protothecosis in a patient with hypogammaglobulinemia.

Prototheca wickerhamii has been predominantly recognised as a pathogen in immunocompromised hosts with deficits in innate or cellular immunity. The role of specific immunoglobulin against Prototheca in host immunity is uncertain. We describe a case of persistent cutaneous protothecosis in a patient with hypogammaglobulinemia most likely due to common variable immunodeficiency, with clinical response to voriconazole.

Daptomycin non-susceptibility in vancomycin-intermediate Staphylococcus aureus (VISA) and heterogeneous-VISA (hVISA): implications for therapy after vancomycin treatment failure.

OBJECTIVES: The aim of this study was to establish the relationship between reduced vancomycin and daptomycin susceptibility among Australasian vancomycin-intermediate Staphylococcus aureus (VISA) and heterogeneous-VISA (hVISA) isolates from patients never exposed to daptomycin. METHODS: Forty-seven stored clinical isolates of hVISA/VISA collected before November 2008 from around Australia and New Zealand were selected. Daptomycin and vancomycin MIC testing was performed using broth microdilution (BMD) and Etest methods. Daptomycin population analysis was performed on a subset of isolates. RESULTS: The percentage of daptomycin non-susceptible isolates was 0% for vancomycin-susceptible S. aureus (VSSA) (Etest and BMD), for hVISA it was 26% by Etest and 15% by BMD, and for VISA 62% by Etest and 38% by BMD. Population analysis profile testing demonstrated daptomycin heteroresistance among the hVISA and VISA strains tested. CONCLUSIONS: This is the highest rate of daptomycin non-susceptibility reported among hVISA isolates to date. Clinicians should exhibit caution when using daptomycin in situations where serious hVISA or VISA infection is a possibility.

Genomic analysis reveals a point mutation in the two-component sensor gene graS that leads to intermediate vancomycin resistance in clinical Staphylococcus aureus.

Methicillin-resistant Staphylococcus aureus (MRSA), once restricted to hospitals, is spreading rapidly through the wider community. Resistance to vancomycin, the principal drug used to treat MRSA infections, has only recently emerged, is mainly low level, and characteristically appears during vancomycin therapy (vancomycin-intermediate S. aureus [VISA] and hetero-resistant VISA). This phenomenon suggests the adaptation of MRSA through mutation, although defining the mutations leading to resistance in clinical isolates has been difficult. We studied a vancomycin-susceptible clinical MRSA isolate (MIC of 1 microg/ml) and compared it with an isogenic blood culture isolate from the same patient, despite 42 days of vancomycin treatment (MIC of 4 microg/ml). A whole-genome sequencing approach allowed the nearly complete assembly of the genome sequences of the two isolates and revealed only six nucleotide substitutions in the VISA strain compared with the parent strain. One mutation occurred in graS, encoding a putative two-component regulatory sensor, leading to a change from a polar to a nonpolar amino acid (T136I) in the conserved histidine region of the predicted protein. Replacing the graS allele of the vancomycin-susceptible parent strain with the graS allele from the VISA derivative resulted in increased vancomycin resistance at a level between those of the vancomycin-susceptible S. aureus and VISA clinical isolates, confirming a role for graRS in VISA. Our study suggests that MRSA is able to develop clinically significant vancomycin resistance via a single point mutation, and the two-component regulatory system graRS is a key mediator of this resistance. However, additional mutations are likely required to express the full VISA phenotype.

Different bacterial gene expression patterns and attenuated host immune responses are associated with the evolution of low-level vancomycin resistance during persistent methicillin-resistant Staphylococcus aureus bacteraemia.

BACKGROUND: Low-level vancomycin resistance in Staphylococcus aureus (vancomycin-intermediate S. aureus (VISA) and hetero-VISA [hVISA]) emerges during persistent infection and failed vancomycin therapy. Up-regulation of genes associated with the "cell wall stimulon" and mutations in the vraSR operon have both been implicated in the development of resistance, however the molecular mechanisms of resistance are not completely understood. To further elucidate the mechanisms leading to resistance transcriptome comparisons were performed using multiple clinical pairs of vancomycin-susceptible S. aureus (VSSA) and hVISA/VISA (n = 5), and three VSSA control pairs from hospitalized patients with persistent bacteraemia that did not develop hVISA/VISA. Based on the transcriptome results multiple genes were sequenced and innate immune system stimulation was assessed in the VSSA and hVISA/VISA pairs. RESULTS: Here we show that up-regulation of vraS and the "cell wall stimulon" is not essential for acquisition of low-level vancomycin resistance and that different transcriptional responses occur, even between closely related hVISA/VISA strains. DNA sequencing of vraSR, saeSR, mgrA, rot, and merR regulatory genes and upstream regions did not reveal any differences between VSSA and hVISA/VISA despite transcriptional changes suggesting mutations in these loci may be linked to resistance in these strains. Enhanced capsule production and reduced protein A expression in hVISA/VISA were confirmed by independent bioassays and fully supported the transcriptome data. None of these changes were observed in the three control pairs that remained vancomycin-susceptible during persistent bacteremia. In a macrophage model of infection the changes in cell surface structures in hVISA/VISA strains were associated with significantly reduced NF-kappaB activation resulting in reduced TNF-alpha and IL-1beta expression. CONCLUSION: We conclude that there are multiple pathways to low-level vancomycin resistance in S. aureus, even among closely related clinical strains, and these can result in an attenuated host immune response. The persistent infections associated with hVISA/VISA strains may be a consequence of changes in host pathogen interactions in addition to the reduced antibiotic susceptibility.

Isolates with low-level vancomycin resistance associated with persistent methicillin-resistant Staphylococcus aureus bacteremia.

Low-level vancomycin-resistant Staphylococcus aureus (vancomycin-intermediate S. aureus [VISA] and heterogenous VISA [hVISA]) is increasingly reported and leads to glycopeptide treatment failure. Various phenotypic features have been reported for these isolates, but the genetic changes leading to hVISA and VISA have yet to be clearly determined. We assessed phenotypic, antibiotic resistance, and genomic changes by using genomic DNA microarray comparison and sequencing of selected loci in five pairs of clinical hVISA/VISA strains and the initial methicillin-resistant Staphylococcus aureus (MRSA) isolates obtained prior to vancomycin therapy. The isolates were from adult patients in Australia and New Zealand who had persistent MRSA bacteremia (>7 days) while receiving vancomycin therapy. In all cases, the initial isolates were found to be fully vancomycin-susceptible Staphylococcus aureus (VSSA). The hVISA/VISA phenotype was associated with increased cell wall thickness, reduced autolytic activity in four of five hVISA/VISA strains, and a striking reduction in biofilm formation compared to the parent strains in all pairs. All five pairs appeared to be isogenic, and genomic DNA microarray comparison suggested that major genetic changes are not required for the development of the resistant phenotype in these strains. No sequence differences were found in the agr locus or the tcaRA genes for any pair, but a marked reduction in RNAIII expression was found in four pairs. In summary, hVISA/VISA arises from fully VSSA during persistent infection that fails to respond to glycopeptide therapy and is associated with significant phenotypic changes, including a marked reduction in biofilm-forming ability. These clinically derived pairs of isolates will be a useful resource to elucidate the genetic mechanism of resistance in hVISA/VISA strains.

Treatment outcomes for serious infections caused by methicillin-resistant Staphylococcus aureus with reduced vancomycin susceptibility.

Although infections caused by methicillin-resistant Staphylococcus aureus with reduced vancomycin susceptibility (SA-RVS) have been reported from a number of countries, including Australia, the optimal therapy is unknown. We reviewed the clinical features, therapy, and outcome of 25 patients with serious infections due to SA-RVS in Australia and New Zealand. Eight patients had endocarditis, 9 had bacteremia associated with deep-seated infection, 6 had osteomyelitis or septic arthritis, and 2 had empyema. All patients had received vancomycin before the isolation of SA-RVS, and glycopeptide treatment had failed for 19 patients (76%). Twenty-one patients subsequently received active treatment, which was effective for 16 patients (76%). Eighteen patients received linezolid, which was effective in 14 (78%), including 4 patients with endocarditis. Twelve patients received a combination of rifampicin and fusidic acid. Surgical intervention was required for 15 patients (60%). Antibiotic therapy, especially linezolid with or without rifampicin and fusidic acid, in conjunction with surgical debulking is effective therapy for the majority of patients with serious infections (including endocarditis) caused by SA-RVS.

Clinical features associated with bacteremia due to heterogeneous vancomycin-intermediate Staphylococcus aureus.

We assessed all episodes of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia at our hospital during a 12-month period (n=53) and compared those due to heterogeneous vancomycin-intermediate S. aureus (hVISA; n = 5, 9.4%) with those due to vancomycin-susceptible MRSA (n=48). Patients with hVISA bacteremia were more likely to have high bacterial load infections (P=.001), vancomycin treatment failure (persistent fever and bacteremia for >7 days after the start of therapy; P<.001), and initially low serum vancomycin levels (P=.006). These clinical markers of hVISA bacteremia may help focus diagnostic efforts and treatment.