Detection of vancomycin variable enterococci (VVE) among clinical isolates of Enterococcus faecium collected across India-first report from the subcontinent

PurposeEmergence of vancomycin variable enterococci (VVE) poses a challenge to empiric vancomycin therapy. Vancomycin-variable enterococci (VVE) are vanA-positive, yet phenotypically vancomycin-susceptible enterococci that can switch to a vancomycin-resistant phenotype when exposed to vancomycin. The aim of the present study was to determine the prevalence of VVE in India.MethodsIsolates of phenotypically vancomycin susceptible Enterococcus faecium from 20 tertiary care hospitals across India were collected and tested for the presence of vanA, vanR, vanS, vanB and vanC genes by conventional PCR using previously published primers. Isolates positive for vanA gene were considered as VVE.ResultsThe prevalence of VVE was 1.5% (5/340). Only one VVE isolate was positive for vanR and vanS, and all the isolates were negative for vanB and vanC.ConclusionsAlthough the prevalence is low, our finding emphasizes the importance of routinely screening for van genes in enterococci that are phenotypically susceptible. Silenced vanA able to escape detection and revert to resistance during vancomycin therapy represents a new challenge in clinical settings.     

Outbreak of Vancomycin-Susceptible Enterococcus faecium Containing the Wild-Type vanA Gene

Accurate detection of vancomycin-resistant enterococci (VRE) is essential in preventing transmission in health care settings. Chromogenic media are widely used for screening VRE because of fast turnaround times (TAT) and high sensitivity. We report an outbreak of Enterococcus faecium bearing vanA yet susceptible to vancomycin (vancomycin-variable Enterococcus [VVE]). Between October 2009 to March 2011, clinical and screening specimens (n = 14,747) were screened for VRE using VRE-selective medium and/or PCR. VVE isolates were genotyped to determine relatedness. Plasmids from these isolates were characterized by sequencing. Overall, 52 VVE isolates were identified, comprising 15% of all VRE isolates identified. Isolates demonstrated growth on Brilliance VRE agar (Oxoid) at 24 h of incubation but did not grow on brain heart infusion agar with 6 μg/ml vancomycin (Oxoid) or bile esculin azide agar with 6 μg/ml vancomycin (Oxoid) and were susceptible to vancomycin. Genotyping of 20 randomly selected VVE isolates revealed that 15/20 were identical, while 5 were highly related. PCR of the VVE transposon confirmed the presence of vanHAXY gene cluster; however, vanS (sensor) and vanR (regulator) genes were absent. The outbreak was controlled through routine infection control measures. We report an emergence of a fit strain of E. faecium containing vanA yet susceptible to vancomycin. Whether this new strain represents VRE has yet to be determined; however, unique testing procedures are required for reliable identification of VVE.     

Vancomycin-resistant Enterococcus faecium and the emergence of new sequence types associated with hospital infection

Enterococcus faecium is a major species in infections by vancomycin-resistant enterococci (VRE). New variants of the pathogen have emerged and become dominant in healthcare settings. Two such examples, vanB ST796 and vanA ST1421 sequence types, originally arose in Australia and proceeded to cause VRE outbreaks in other countries. Of concern is the detection in Europe of vancomycin variable enterococci (VVE) belonging to ST1421 that exhibit a vancomycin-susceptible phenotype but can revert to resistant in the presence of vancomycin. The recent application of genome sequencing for increasing our understanding of the evolution and spread of VRE is also explored here.     

Tracking changes in the vraSR and graSR two component regulatory systems during the development and loss of vancomycin non-susceptibility in a clinical isolate

We investigated changes in regulatory genes, vraS and graR, during development of vancomycin non-susceptibility in a patient with methicillin-resistant Staphylococcus aureus who failed therapy and following in-vitro vancomycin exposure and a subsequent drug-free growth period. Minimum Inhibitory Concentration (MICs) were determined and genes sequenced at each stage. After 30 days of vancomycin exposure, the strain attained maximum MIC (20 mg/L) and was resistant to all antibiotics. Reversion to vancomycin susceptibility occurred 21 days after removal. We observed mutations in vraS and graR during non-susceptibly development and novel stop codons in the reverted strain. Mutations in graR appear important for development of intermediate susceptibility to vancomycin. The results suggest that monitoring of vancomycin therapy could allow earlier change to appropriate agents.     

Effects of Aggregate and Individual Antibiotic Exposure on Vancomycin MICs for Staphylococcus aureus Isolates Recovered from Pediatric Patients

We evaluated the evolution of vancomycin MICs for Staphylococcus aureus and their relationship with vancomycin use among hospitalized children. S. aureus isolates recovered from sterile sites were prospectively tested for vancomycin susceptibility using the Etest between 1 April 2000 and 31 March 2008. Vancomycin MICs were grouped into three categories: ≤1, 1.5, and 2 μg/ml. The association between vancomycin MICs and aggregate vancomycin use and individual patient vancomycin exposure 6 months prior to the documented infection was assessed. The geometric mean values for vancomycin MICs for S. aureus fluctuated over time without a significant trend (P = 0.146). Of the 436 patients included in the study, 363 (83%) had methicillin-susceptible S. aureus (MSSA) and 73 (17%) had methicillin-resistant S. aureus (MRSA) infections. The rate of isolates with a vancomycin MIC of 2 μg/ml increased from 4% (2 of 46) in 2000 to 2001 to 24% (11 of 46) in 2007 to 2008, despite a decrease in vancomycin use (r = −0.11; P = 0.825). The percentage of isolates with a vancomycin MIC of 2 μg/ml was higher for MRSA (15%; 11 of 73) than for MSSA strains (5.2%; 19 of 363) (χ² = 9.2; P = 0.01). Individual patient vancomycin exposure was not associated with a higher vancomycin MIC. In the unadjusted model, in which we compared patients with S. aureus infections with MICs of ≤1 μg/ml, the odds ratios of exposure rates for patients with isolates with MICs of 1.5 μg/ml and 2 μg/ml were 1.02 (P = 0.929) and 1.13 (P = 0.767), respectively. In our experience, the geometric means of vancomycin MICs from S. aureus isolates recovered from hospitalized children oscillated over time and were not associated with previous individual patient vancomycin exposure or aggregate vancomycin use.     

Vancomycin MIC creep in methicillin-resistant Staphylococcus aureus (MRSA) isolates from 2006 to 2010 in a hospital in China

Purpose: To assess whether vancomycin minimum inhibitory concentration (MIC) creeps among clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) in a regional hospital in China. Furthermore, to analyze the causes of vancomycin MIC creeps and the relationship between vancomycin MICs and the outcome among patients with MRSA infection. Materials and Methods: All clinical isolates of MRSA from 2006-2010 were retrieved and tested by the broth microdilution procedure to determine their vancomycin MIC. Meanwhile, related patient records were analyzed. Results: While all isolates were susceptive to vancomycin, the percentage of isolates with a vancomycin MIC = 1 mg/L increased significantly from 2006 (37.0%) to 2010 (75.7%). Meanwhile, vancomycin usage density (DDDs/1000 bed-days) had increased significantly from 2006-2010. Mean linear correlation analysis showed a statistically significant positive correlation (r = 0.905, P < 0.05) between the consumption of vancomycin and the percentage of MRSA isolates with a vancomycin MIC = 1 mg/L. Clinical records revealed high vancomycin MIC was associated with a higher microbiologic failure rate in MRSA bloodstream infections. Conclusions: The data demonstrated vancomycin MIC creep among clinical isolates in our hospital, and the MIC creep may be caused by the increasing usage of vancomycin. Furthermore, the analysis strongly suggested this shift of vancomycin MIC within the susceptible range may be associated with an increasing probability of treatment failure.     

Genetic and Molecular Predictors of High Vancomycin MIC in Staphylococcus aureus Bacteremia Isolates

An elevated vancomycin MIC is associated with poor outcomes in Staphylococcus aureus bacteremia (SAB) and is reported in patients with methicillin-susceptible S. aureus (MSSA) bacteremia in the absence of vancomycin treatment. Here, using DNA microarray and phenotype analysis, we investigated the genetic predictors and accessory gene regulator (agr) function and their relationship with elevated vancomycin MIC using blood culture isolates from a multicenter binational cohort of patients with SAB. Specific clonal complexes were associated with elevated (clonal complex 8 [CC8] [P < 0.001]) or low (CC22 [P < 0.001], CC88 [P < 0.001], and CC188 [P = 0.002]) vancomycin MIC. agr dysfunction (P = 0.014) or agr genotype II (P = 0.043) were also associated with an elevated vancomycin MIC. Specific resistance and virulence genes were also linked to an elevated vancomycin MIC, including blaZ (P = 0.002), sea (P < 0.001), clfA (P < 0.001), splA (P = 0.001), and the arginine catabolic mobile element (ACME) locus (P = 0.02). These data suggest that inherent organism characteristics may explain the link between elevated vancomycin MICs and poor outcomes in patients with SAB, regardless of the antibiotic treatment received. A consideration of clonal specificity should be included in future research when attempting to ascertain treatment effects or clinical outcomes.     

Serum trough level as a postmarketing quality measure of generic vancomycin products

BackgroundThe vancomycin trough level (VTL) is the most widely used pharmacokinetic parameter for monitoring its clinical efficacy. Whether the VTL is affected in patients receiving different vancomycin products has not previously been determined.MethodsFrom 2005 to 2015, five vancomycin products, including the innovator (designated as VAN-Lilly) and four generic versions (designated as VAN-A, VAN-B, VAN-C and VAN-D), were sequentially used in a teaching hospital. The initial VTLs were compared between patients who received different vancomycin products after propensity score (PS) weighting and matching for clinical covariates.ResultsAmong 8735 patients with initial VTL levels available for analysis, a significant association was identified between the VTL and different vancomycin products in children aged 1 month to 12 years (P < 0.0001). The PS weighting analysis in the paediatric group disclosed children on VAN-C had higher VTL compared to those on other four products (P = 0.0008). PS matching analysis revealed that children who received VAN-C had significantly higher VTLs than those who received VAN-Lily (P = 0.0001), VAN-A (P = 0.0008), VAN-B (P = 0.0002) or VAN-D (P = 0.0015). Furthermore, the coefficient of variation of the VTL was much greater in patients who received VAN-C than in those who received the other four versions, suggesting an unstable quality of this product.ConclusionA generic version of vancomycin generated significantly higher concentrations and greater variation of VTLs than the innovator and other generic vancomycin products in children. The VTL can serve as an indicator to monitor the quality of vancomycin products after marketing.     

Acute Kidney Injury in Hematopoietic Cell Transplantation Patients Receiving Vancomycin and Piperacillin/Tazobactam Versus Vancomycin and Cefepime

Empiric antimicrobials are frequently utilized in the pre-engraftment phase after hematopoietic cell transplantation (HCT). Recent evidence suggests an increased risk of acute kidney injury (AKI) from combination of vancomycin with piperacillin/tazobactam; however, this has not specifically been evaluated in the HCT population. A single-center, retrospective review was conducted from 2011 to 2017 on 110 autologous and 60 allogeneic HCT patients with the primary objective of comparing incidence of AKI for those who received vancomycin with piperacillin/tazobactam versus vancomycin with cefepime in the pre-engraftment phase. Demographics and outcomes were compared for all patients who received vancomycin with piperacillin/tazobactam versus vancomycin with cefepime as well as within the autologous and allogeneic subgroups. The primary endpoint of incidence of AKI, defined as increase in serum creatinine by .3?mg/dL or?>50% from baseline (whichever was larger), was significantly higher for those who received vancomycin with piperacillin/tazobactam versus cefepime for the overall cohort (68% versus 27%; P?<?.001) resulting in an odds ratio (OR) of 5.16 (95% confidence interval [CI], 2.5 to 10.5) when adjusting for hypotension. Results were similar within the autologous (59% versus 22%; P?<?.001; OR, 4.63; 95% CI, 1.85 to 11.6) and allogeneic (79% versus 39%; P?=?.0021; OR, 5.41; 95% CI, 1.60 to 18.3) subgroups. Within the overall cohort between those who received vancomycin with piperacillin/tazobactam versus cefepime the time to onset of AKI was more commonly within 48 hours of concomitant antimicrobial use (53% versus 26%; P?=?.012), whereas resolution of AKI by discharge date was not different (39% versus 26%; P?=?.23). No difference in percentage of patients requiring at least 1 session of dialysis, duration of hospital stay, or 30-day mortality was found between overall cohorts. Further studies of HCT patients are warranted to fully elucidate the risk of various combination antimicrobial regimens on renal outcomes.     

Vancomycin-Variable Enterococcus faecium: In Vivo Emergence of Vancomycin Resistance in a Vancomycin-Susceptible Isolate

We report the emergence of vancomycin resistance in a patient colonized with a vanA-containing, vanRS-negative isolate of Enterococcus faecium which was initially vancomycin susceptible. This is a previously undescribed mechanism of drug resistance with diagnostic and therapeutic implications.     

Liofilchem? Chromatic VRE and vancomycin MIC Test Strip detected glycopeptide resistance in a vanB neonatal Enterococcus faecium isolate showing alternate vancomycin susceptibility and resistance with bioMérieux Vitek2

A 1-month old neonate urine sample yielded vanB Enterococcus faecium; nevertheless, the isolate alternatively showed susceptibility and resistance to vancomycin with bioMérieux Vitek2 (cards AST592, AST632, AST586), while glycopeptide resistance was detected by Liofilchem^® vancomycin MIC Test Strip and disc along with the Chromatic VRE chromogenic medium. This communication emphasizes that, as vanB gene may be heterogeneously expressed within a given Enterococcus population, glycopeptide resistance may be missed when using automated systems for antibiotic susceptibility testing. We suggest therefore that vancomycin in vitro activity be studied on all clinical isolates through agar methods, including use of chromogenic media.     

Low-Level Vancomycin Resistance in Clostridium innocuum

Low-level vancomycin resistance was observed for 28 clinical Clostridium innocuum isolates and C. innocuum NCIB 10674, whereas teicoplanin was active. DNA from three clinical isolates and the type strain could not be amplified by PCR with primers specific for the genes vanA, vanB, and vanC, suggesting that C. innocuum is intrinsically resistant to vancomycin.     

Effects of intra-articular D-amino acids combined with systemic vancomycin on an experimental Staphylococcus aureus-induced periprosthetic joint infection

BackgroundThe D-isoforms of amino acids (D-AAs) exhibit anti-biofilm potential against a diverse range of bacterial species in vitro, while its role in vivo remains unclear. The aim of this study was to investigate the effects of a combination of D-AAs and vancomycin on a PJI rat model.MethodsEight-week-old male SD rats were randomized to the control group, sham group, vancomycin group, D-AAs–vancomycin group. After treatment for 6 weeks, we analysed the levels of inflammatory factors in serum, behavioural change, imaging manifestations. The anti-biofilm ability of D-AAs was detected by crystal violet staining and scanning electron microscope observation, and its ability to assist antibiotics in killing bacteria was assessed by culture of bacteria. Additionally, micro-CT and histological analysis were used to evaluate the impact of D-AAs combined with vancomycin on the bone remodelling around the prosthesis.ResultsThe group treated with a D-AAs–vancomycin combination sustained normal weight gain and exhibited reduced the serum levels of α2M, IL-1β, IL-6, IL-10, TNF-α and PGE2. Moreover, treated with D-AAs in combination with vancomycin improved the weight-bearing activity performance, increased the sizes and widths of distal femurs, and improved Rissing scale scoring. In particular, treatment using D-AAs enhanced the ability of vancomycin to eradicate Staphylococcus aureus, as demonstrated by the dispersion of existing biofilms and the inhibition of biofilm formation that occurred in a concentration-dependent manner. This treatment combination also resulted in a reduction in bacterial burden with in the soft tissues, bones, and implants. Furthermore, D-AAs–vancomycin combination treatment attenuated abnormal bone remodelling around the implant, as evidenced by an observed increase in BMD, BV/TV, and Tb.Th and the presence of reduced Trap⁺ osteoclasts and elevated osterix⁺ osteo-progenitors.ConclusionsCombining D-AAs with vancomycin provides an effective therapeutic strategy for the treatment of PJI by promoting biofilm dispersion to enhance antimicrobial activity.     

Characterization of an Enterococcus gallinarum Isolate Carrying a Dual vanA and vanB Cassette

The ability of vancomycin resistance determinants to be horizontally transferred within enterococci species is a concern. Identification and characterization of vancomycin-resistant enterococci (VRE) in a clinical isolate have a significant impact on infection control practices. In this study, we describe a clinical isolate of Enterococcus gallinarum exhibiting high-level resistance to vancomycin and teicoplanin. The genetic characterization of this isolate showed the presence of vanA and vanB genes in addition to the naturally carried vanC gene. vanA was identified on pA6981, a 35,608-bp circular plasmid with significant homology to plasmid pS177. The vanB operon was integrated into the bacterial chromosome and showed a high level of homology to previously reported Tn1549 and Tn5382. To the best of our knowledge, this is the first report of E. gallinarum carrying both vanA and vanB operons, indicating the importance of identifying the vancomycin resistance mechanism in non-E. faecium and non-E. faecalis enterococcal species.     

Sol–gel silica controlled release thin films for the inhibition of methicillin-resistant Staphylococcus aureus

The incidence of methicillin-resistant Staphylococcus aureus (MRSA) infection has significantly increased. Generally, the success of this bacterium as a pathogen is attributed to its ability to adhere to surfaces and remain there, under the protection of an extracellular matrix known as biofilm. To combat MRSA with regular doses of vancomycin, efforts are continuously underway to increase its effectiveness. A promising technique is to use combinational therapeutics. In vitro experiments showed that farnesol can be used as an adjuvant with conventional antibiotics. Farnesol is a natural sesquiterpenoid and quorum-sensing molecule. The biggest obstacle to using this concept is that farnesol is highly water insoluble. This compromises its bioavailability if it were to be used along with vancomycin at the site of infection when the treatment needs to be administered in vivo. Herein we designed an efficient therapeutic strategy for the simultaneous delivery of both antibiotic and adjuvant in order to treat MRSA infections. We demonstrate that sufficient quantities of both vancomycin and farnesol can be incorporated into sol–gel silica applied as thin films on an implant surface. The incorporation of the hydrophobic farnesol does not affect the stability of the thin films and neither does it affect the controlled release of vancomycin. The data demonstrate the potent adjuvant effect of farnesol on vancomycin in inhibiting MRSA infection. In vitro experiments show the complete inhibition (10⁶ fold reduction in growth compared to control) of methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) when the ratio of vancomycin to farnesol in the sol–gel silica films is optimized. The local delivery of antibiotics minimizes the need for systemic antibiotics. The incorporation of vancomycin and farnesol into thin sol–gel films represents a new treatment paradigm for the topical delivery of antibiotics with adjuvant. The potential clinical benefits are significant and include avoiding the need for revision surgery, preventing surgical site infection and controlling healthcare costs.     

Daptomycin versus vancomycin for osteoarticular infections due to methicillin-resistant Staphylococcus aureus (MRSA): a nested case–control study

Vancomycin is the standard antibiotic for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections. While daptomycin is approved for MRSA bacteremia, its effectiveness in osteoarticular infections (OAIs) has not been established. A 1:2 nested case–control study of adult patients with MRSA OAIs admitted to an academic center from 2005 to 2010 was carried out. Clinical outcomes and drug toxicity in patients treated with daptomycin versus vancomycin were compared. Twenty patients with MRSA OAIs treated with daptomycin were matched to 40 patients treated with vancomycin. The median age of the patients was 52 years (range, 25–90), and 40 (67 %) were male. Most patients had osteomyelitis (82 %), predominantly from a contiguous source (87 %). Forty percent were diabetics. Diabetic patients were more likely to receive vancomycin than daptomycin [20 (50 %) vs. 4 (20 %); p?=?0.03]. Vancomycin was more often combined with antibiotics other than daptomycin [22 (55 %) vs. 5 (25 %); p?=?0.03]. The median total antibiotic treatment duration was 48 (daptomycin) vs. 46 days (vancomycin) (p?=?0.5). Ninety percent of daptomycin-treated patients had previously received vancomycin for a median of 14.5 days (range, 2–36). Clinical success rates were similar between daptomycin and vancomycin at 3 months [15 (75 %) vs. 27 (68 %); p?=?0.8] and 6 months [14 (70 %) vs. 23 (58 %); p?=?0.5], even after propensity score-based adjustment for antibiotic assignment. The frequency of adverse events was similar between treatment groups [1 (5 %) vs. 7 (18 %); p?=?0.2]. Daptomycin and vancomycin achieved similar rates of clinical success and drug tolerability. Daptomycin is a reasonable alternative for treating MRSA OAIs, particularly in patients where therapy with vancomycin has not been well tolerated.     

Heterogeneously Vancomycin-Resistant Staphylococcus epidermidis Strain Causing Recurrent Peritonitis in a Dialysis Patient during Vancomycin Therapy

Methicillin-resistant Staphylococcus epidermidis (MRSE) was recovered over a 2-month period from the dialysis fluid of a peritoneal dialysis (PD) patient who experienced recurrent episodes of peritonitis during therapeutic and prophylactic use of vancomycin. Characterization of five consecutive MRSE isolates by molecular and microbiological methods showed that they were representatives of a single strain, had reduced susceptibility to vancomycin, did not react with DNA probes specific for the enterococcal vanA or vanB gene, and showed characteristics reminiscent of the properties of a recently described vancomycin-resistant laboratory mutant of Staphylococcus aureus. Cultures of these MRSE isolates were heterogeneous: they contained—with a frequency of 10⁻⁴ to 10⁻⁵—bacteria for which vancomycin MICs were high (25 to 50 μg/ml) which could easily be selected to “take over” the cultures by using vancomycin selection in the laboratory. In contrast, the five consecutive MRSE isolates recovered from the PD patient during virtually continuous vancomycin therapy showed no indication for a similar enrichment of more resistant subpopulations, suggesting the existence of an “occult” infection site in the patient (presumably at the catheter exit site) which was not accessible to the antibiotic.     

Post-traumatic endophthalmitis caused by Streptococcus parauberis: First human case report

A 12-year-old boy presented with trauma to left eye with a wooden stick. On examination, there was full thickness corneal laceration with cataractous lens behind the laceration. The laceration was sutured, and intravitreal injections of vancomycin, ceftazidime and clindamycin were administered. Vitreous tap grew Streptococcus parauberis. The isolate was sensitive to amoxicillin, erythromycin and vancomycin, and topical vancomycin was used to treat the infection. We present the first case of human post-traumatic infective endophthalmitis caused by the rare agent S. parauberis.     

Analysis of Vancomycin Susceptibility Testing Results for Presumptive Categorization of Telavancin

Scattergrams between vancomycin and telavancin demonstrated susceptibility agreement rates of 99.96, 99.65, and 100.00% for Staphylococcus aureus, Enterococcus faecalis, and streptococci, respectively. A single very major error was obtained against E. faecalis, while vancomycin-intermediate S. aureus (VISA) and vancomycin-resistant and teicoplanin-susceptible (VanB phenotype) E. faecalis were responsible for major and minor errors. These results support the use of vancomycin to infer telavancin susceptibility among indicated pathogens, except VISA, which should be tested for telavancin susceptibility.     

Phenotypic changes of methicillin-resistant <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> during vancomycin therapy for persistent bacteraemia and related clinical outcome

Persistent bacteraemia (PB) due to methicillin-resistant Staphylococcus aureus (MRSA) that fails to respond to glycopeptide therapy is a well-documented clinical problem. There are limited data on changes in agr functionality, vancomycin susceptibility and heteroresistance during MRSA PB. Thus, the frequency of these changes and their clinical significance remain unclear. Only patients with MRSA PB (≥7 days) from a prospective cohort of S. aureus bacteraemia were included. We collected isogenic paired strains and compared vancomycin MIC, vancomycin heteroresistance, and agr functionality between initial and final blood isolates. We also assessed the clinical outcome. A total of 49 patients had MRSA PB over 22 months. Bacteraemia persisted for a median of 13 days and most patients (98%) received glycopeptide as initial therapy. Among 49 isogenic pairs, only one pair showed a vancomycin MIC increase ≥2-fold by broth microdilution method, and only seven (14%) by E-test. Significant portions of initial isolates had vancomycin heteroresistance (49%) and agr dysfunction (76%). Development of vancomycin heteroresistance during PB occurred in four (16%) among 25 initial vancomycin-susceptible isolates, and acquisition of agr dysfunction occurred in two (16%) among 12 initial agr-functional isolates. Changes in the opposite direction occasionally occurred. These phenotypic changes during PB were not associated with mortality, whereas agr dysfunction of the initial isolates was significantly associated with mortality. During MRSA PB, phenotypic changes of MRSA isolates occurred occasionally under prolonged vancomycin exposure but were not significantly associated with clinical outcome. In contrast, initial agr dysfunction could be a predictor for mortality in MRSA PB.