High MICs for Vancomycin and Daptomycin and Complicated Catheter-Related Bloodstream Infections with Methicillin-Sensitive Staphylococcus aureus

Daptomycin Dose Optimization in Pediatric Staphylococcus aureus Bacteremia: A Pharmacokinetic/Pharmacodynamic Investigation

Daptomycin is an antibiotic with Gram-positive activity, including methicillin-resistant Staphylococcus aureus, for which optimal pediatric dosing is unknown. This study aimed to evaluate daptomycin exposures achieved with package label dosing and to identify dosing regimens necessary to enhance efficacy and minimize toxicity in children with S. aureus bacteremia. Monte Carlo simulations were performed to determine probability of target attainment (PTA) for six pediatric age cohorts. Area under the curve to minimum inhibitory concentration ratio (AUC0-24 :MIC) ≥666 was used to determine the PTA for efficacy (PTAE ). Minimum concentration (Cmin ) ≥24.3 mg/L determined the PTA for toxicity (PTAT ). Acceptable dosing regimens were those which achieved the combined target of ≥90% PTAE and ≤5% PTAT . Package label dosing of daptomycin yielded insufficient efficacy with only 26.3% PTAE in children 13-24 months, 39.5% PTAE in children 2-6 years, 30.1% PTAE in children 7-11 years, and 50.1% PTAE in adolescents ≥12 years. To achieve the combined efficacy and safety target, doses of 18-24 mg/kg in children 3-12 months, 20-24 mg/kg in children 13-24 months, 19-24 mg/kg in children 2-6 years, 17-19 mg/kg in children 7-11 years, and 10-14 mg/kg in adolescents ≥12 years are necessary. Package label dosing resulted in suboptimal exposure for the majority of pediatric patients in all age groups evaluated. If targeting validated efficacy and safety endpoints, daily daptomycin doses of at least 20 mg/kg in children ≤6 years, 17 mg/kg in children 7-11 years, and 10 mg/kg in adolescents ≥12 years are necessary. Clinical studies evaluating these higher doses are needed.

Profiling daptomycin resistance among diverse methicillin-resistant Staphylococcus aureus lineages in China

Daptomycin (DAP) is effective against methicillin-resistant Staphylococcus aureus (MRSA). However, reduced susceptibility to DAP in MRSA may lead to treatment failures. We aim to determine the distribution of DAP minimum inhibitory concentrations (MICs) and DAP heteroresistance (hDAP) among MRSA lineages in China. A total of 472 clinical MRSA isolates collected from 2015 to 2017 in China were examined for DAP susceptibility. All isolates (n = 472) were found to be DAP susceptible, but 35.17% (166/472) of them exhibited a high DAP MIC (MIC >0.5 µg/mL). The high DAP MIC group contained a larger proportion of isolates with a higher vancomycin or teicoplanin MIC (>1.5 µg/mL) than the low DAP MIC group (19.3% vs 7.8%, P < 0.001; 22.3% vs 8.2%, P < 0.001). We compared the clonal complex (CC) distributions and clinical characteristics in MRSA isolates stratified by DAP MIC. CC5 isolates were less susceptible to DAP (MIC50 = 1 µg/mL) than CC59 isolates (MIC50 = 0.5 µg/mL, P < 0.001). Population analysis profiling revealed that 5 of 10 ST5 and ST59 DAP-susceptible MRSA isolates investigated exhibited hDAP. The results also showed that CC5 MRSA with an agrA mutation (I238K) had a higher DAP MIC than those with a wild-type agrA (P < 0.001). The agrA-I238K mutation was found to be associated with agr dysfunction as indicated by the loss of δ-hemolysin production. In addition, agr/psmα defectiveness was associated with hDAP in MRSA. Whole-genome sequencing analysis revealed mutations in mprF and walR/walK in DAP-resistant subpopulations, and most DAP-resistant subpopulations (6/8, 75%) were stable. Our study suggests that the increased DAP resistance and hDAP in MRSA may threaten the effectiveness against MRSA infections.

Effect of the vancomycin minimum inhibitory concentration on clinical outcomes in patients with methicillin-susceptible Staphylococcus aureus bacteraemia: a systematic review and meta-analysis

OBJECTIVE

The use of the vancomycin minimum inhibitory concentration (MIC) as a prognostic predictor in patients with methicillin-susceptible Staphylococcus aureus (MSSA) has been debated in the last decade. We performed a systematic review and meta-analysis to investigate whether an elevated vancomycin MIC is associated with a worse prognosis for patients with MSSA bacteraemia.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

PubMed, Embase and the Cochrane Library were searched from inception to December 2019.

ELIGIBILITY CRITERIA

Randomised controlled trials or observational studies were considered eligible if they provided clinical outcomes of patients with MSSA bacteraemia, stratified by vancomycin MIC.

DATA SYNTHESIS

Primary outcome was mortality. Secondary outcomes included septic thrombophlebitis, persistent bacteraemia and complicated bacteraemia. Pooled ORs and 95% CIs were calculated. Subgroup analyses included the susceptibility testing method.

RESULTS

Fifteen observational studies were included. Bacteraemia due to MSSA isolates with high vancomycin MICs was associated with higher mortality than isolates with low MICs (OR 1.44; 95% CI 1.12 to 1.84; I²=40.3%). Additionally, significantly greater septic thrombophlebitis (OR 3.16; 95% CI 1.11 to 9.00; I²=58.6%) and a trend towards more persistent bacteraemia (OR 1.79; 95% CI 0.97 to 3.31; I²=0%) were observed in patients with high vancomycin MICs than in patients with low MICs. Differences in complicated bacteraemia were not significant. Similar findings were obtained in subgroup analyses using Etest. However, significant differences in outcomes were not observed between the high and low vancomycin MICs detected using broth microdilution.

CONCLUSION

The available data suggest an association between elevated vancomycin MICs detected using Etest and adverse clinical outcomes for patients with MSSA bacteraemia. Future studies should validate these findings and explore the potential mechanisms.

PROSPERO REGISTRATION NUMBER

CRD42018090547.

Influence of the minimum inhibitory concentration of daptomycin on the outcomes of Staphylococcus aureus bacteraemia

OBJECTIVES

Recent studies have shown that methicillin-resistantStaphylococcus aureus (MRSA) bacteraemia with vancomycin minimum inhibitory concentration (MIC) >1 μg/mL is associated with a higher rate of treatment failure and a higher mortality rate. Daptomycin is an alternative to vancomycin but has not been as well studied. The aim of this literature review was to evaluate the effect of daptomycin MIC on the outcomes of S. aureus bacteraemia.

METHODS

We conducted a literature search for the period January 2010 to January 2019 using the MEDLINE and Embase databases.

RESULTS

Four studies were included in the review. The outcomes were clinical cure and 30- or 60-day mortality. In two retrospective studies, 60-70% ofS. aureus isolates had a low daptomycin MIC (≤0.5 μg/mL) and patients with MRSA bacteraemia who were treated with daptomycin had a lower mortality rate. In another study, patients with methicillin-susceptible S. aureus bacteraemia with low daptomycin MICs had a lower risk of developing septic thrombophlebitis. One study showed that patients with MRSA bacteraemia had a higher mortality rate if the daptomycin MIC was >0.5 μg/mL.

CONCLUSION

The included studies in this review suggest a possible association between high daptomycin MIC and unfavourable clinical outcomes ofS. aureus bacteraemia. Further prospective studies are required to evaluate the impact of the daptomycin MIC on the clinical outcomes of S. aureus bacteraemia.

Dysfunctional accessory gene regulator (agr) as a prognostic factor in invasive Staphylococcus aureus infection: a systematic review and meta-analysis

The accessory gene regulator (agr) locus of Staphylococcus aureus is a quorum-sensing virulence regulator. Although there are many studies concerning the effect of dysfunctional agr on the outcomes of S. aureus infection, there is no systematic review to date. We systematically searched for clinical studies reporting outcomes of invasive S. aureus infections and the proportion of dysfunctional agr among their causative strains, and we performed a meta-analysis to obtain estimates of the odds of outcomes of invasive S. aureus infection with dysfunctional versus functional agr. Of 289 articles identified by our research strategy, 20 studies were meta-analysed for crude analysis of the impact of dysfunctional agr on outcomes of invasive S. aureus infection. Dysfunctional agr was generally associated with unfavourable outcomes (OR 1.32, 95% CI 1.05–1.66), and the impact of dysfunctional agr on outcome was more prominent in invasive methicillin-resistant S. aureus (MRSA) infections (OR 1.54, CI 1.20–1.97). Nine studies were meta-analysed for the impact of dysfunctional agr on the 30-day mortality of invasive S. aureus infection. Invasive MRSA infection with dysfunctional agr exhibited higher 30-day mortality (OR 1.40, CI 1.03–1.90) than that with functional agr. On the other hand, invasive MSSA infection with dysfunctional agr exhibited lower 30-day mortality (OR 0.51, CI 0.27–0.95). In the post hoc subgroup analysis by the site of MRSA infection, dysfunctional agr was associated with higher 30-day mortality in MRSA pneumonia (OR 2.48, CI 1.17–5.25). The effect of dysfunctional agr on the outcome of invasive S. aureus infection may vary depending on various conditions, such as oxacillin susceptibility and the site of infection. Dysfunctional agr was generally associated with unfavourable clinical outcomes and its effect was prominent in MRSA and pneumonia. Dysfunctional agr may be applicable for outcome prediction in cases of invasive MRSA infection with hardly eradicable foci such as pneumonia.

Can vancomycin lock therapy extend the retention time of infected long-term catheters?

We assessed the success rate of vancomycin catheter lock therapy (VLT) in combination with systemic antimicrobials in patients with staphylococcal catheter-related bloodstream infection (C-RBSI). Over a 6-year period, we retrospectively collected clinical and microbiological data from patients with long-term central venous catheters and staphylococcal C-RBSI who were treated with systemic antimicrobials and VLT. We then assessed the success rate of VLT based on two criteria: 1) catheter retention time> 3 months and 2) catheter in place until end of use. We found 217 staphylococcal C-RBSI episodes, 115 (53.0%) of which were managed with conservative therapy. Of these, 76 (66.1%) were treated with VLT (85.5% coagulase-negative staphylococci and 14.5% Staphylococcus aureus). The success rate of VLT was 42.1% with criterion 1 and 71.1% with criterion 2. We did not find statistically significant differences between success and failure in the majority of the clinical data recorded. We only found differences for crude mortality in criterion 1 and for parenteral nutrition in criterion 2. The success of catheter retention using VLT was moderate, reaching slightly more than 70% when the catheter was kept in place until the end of use.

Clinical and prognostic differences between methicillin-resistant and methicillin-susceptible Staphylococcus aureus infective endocarditis

Background

S. aureus (SA) infective endocarditis (IE) has a very high mortality, attributed to the age and comorbidities of patients, inadequate or delayed antibiotic treatment, and methicillin resistance, among other causes. The main study objective was to analyze epidemiological and clinical differences between IE by methicillin-resistant versus methicillin-susceptible SA (MRSA vs. MSSA) and to examine prognostic factors for SA endocarditis, including methicillin resistance and vancomycin minimum inhibitory concentration (MIC) values > 1 μg/mL to MRSA.

Methods

Patients with SA endocarditis were consecutively and prospectively recruited from the Andalusia endocarditis cohort between 1984 and January 2017.

Results

We studied 437 patients with SA endocarditis, which was MRSA in 13.5% of cases. A greater likelihood of history of COPD (OR 3.19; 95% CI 1.41–7.23), invasive procedures, or recognized infection focus in the 3 months before IE onset (OR 2.9; 95% CI 1.14–7.65) and of diagnostic delay (OR 3.94; 95% CI 1.64–9.5) was observed in patients with MRSA versus MSSA endocarditis.

The one-year mortality rate due to SA endocarditis was 44.3% and associated with decade of endocarditis onset (1985–1999) (OR 8.391; 95% CI (2.82–24.9); 2000–2009 (OR 6.4; 95% CI 2.92–14.06); active neoplasm (OR 6.63; 95% CI 1.7–25.5) and sepsis (OR 2.28; 95% CI 1.053–4.9). Methicillin resistance was not associated with higher IE-related mortality (49.7 vs. 43.1%; p = 0.32).

Conclusion

MRSA IE is associated with COPD, previous invasive procedure or recognized infection focus, and nosocomial or healthcare-related origin. Methicillin resistance does not appear to be a decisive prognostic factor for SA IE.

Recent pattern of antibiotic resistance in Staphylococcus aureus clinical isolates in Eastern India and the emergence of reduced susceptibility to vancomycin

PURPOSE:

We aimed to determine the recent pattern of antibiotic resistance and assess the vancomycin susceptibility profile of clinical Staphylococcus aureus in view of emerging reports of vancomycin creep, reduced vancomycin susceptibility (RVS), including heterogeneous vancomycin-intermediate S. aureus (hVISA) and vancomycin-intermediate S. aureus, and vancomycin resistance in S. aureus isolates.

MATERIALS AND METHODS:

Consecutive, nonduplicate isolates of S. aureus between July 2015 and June 2016 were subjected to antimicrobial susceptibility testing using standard disk diffusion test or Etest as per the Clinical and Laboratory Standards Institute 2015. Detection of hVISA was done by glycopeptide resistance detection Etest according to the manufacturer's instructions in strains with vancomycin minimum inhibitory concentration of 1–2 μg/ml.

RESULTS:

A total of 284 S. aureus were obtained from pus (175, 61.6%), respiratory tract (31, 10.9%), urine (27, 9.5%), blood (25, 8.8%), body fluids (18, 6.3%), and catheter tips (8, 2.8%). 127 (44.7%) isolates were methicillin resistant, and 158 (55.6%) were multidrug resistant. High resistance was observed to penicillin (81.7%), erythromycin (62.3%), and ciprofloxacin (52.1%), whereas the resistance was low to gentamicin (5.3%), rifampicin (8.1%), and doxycycline (9.5%). Two hundred and fifty-one (88.3%) isolates were fully susceptible to vancomycin, whereas 33 (11.6%) demonstrated RVS. All were uniformly susceptible to linezolid, tigecycline, and daptomycin.

CONCLUSIONS:

A moderately high percentage of S. aureus isolates demonstrated RVS, which may limit its usefulness in methicillin-resistant isolates and may be associated with increased complications in methicillin-susceptible infections. In view of increasing glycopeptide resistance, the susceptibility status of vancomycin along with other antibiotics among clinical S. aureus isolates should be investigated periodically.

The Cefazolin Inoculum Effect and the Presence of type A blaZ Gene according to agr Genotype in Methicillin-Susceptible Staphylococcus aureus Bacteremia

BACKGROUND

Recent data suggests the inoculum effect of methicillin-susceptible Staphylococcus aureus (MSSA) against beta-lactam antibiotics and their association with functionality or genotypic variation of agr locus.

METHODS

MSSA blood isolates were collected at a tertiary care hospital in Korea from June 2014 to December 2017. The functionality of the agr operon was measured by δ-hemolysin assays. Multiplex PCR was performed to determine the agr genotype. The cefazolin minimum inhibitory concentrations (MICs) at a high inoculum concentration (~5 × 10⁷ CFU/ml) were compared to the MICs at a standard inoculum concentration (~5 × 10⁵ CFU/ml) to identify strains with the cefazolin inoculum effect (CIE). The DNA sequencing of blaZ gene was performed to classify the blaZ genotype.

RESULTS

Among the 195 MSSA blood isolates, agr genotype I was most common (68.2%), followed by type III (16.4%), type IV (9.2%), and type II (6.2%). Sixty-seven (34.3%) MSSA isolates had dysfunctional agr, but neither CIE nor blaZ genotype was associated with dysfunctional agr. The MSSA with agr type III genotype exhibited significantly higher CIE positivity (agr III 43.8% vs. non-agr III 5.5%, P <0.01) and erythromycin/clindamycin resistance. In the subgroup analysis of type A blaZ possessing MSSA, almost all of the agr III MSSA isolates exhibited CIE, while only 20% of non-agr III isolates had CIE (P <0.01).

CONCLUSION

In MSSA blood isolates, CIE might be associated with agr genotype rather than with dysfunctional agr.

Molecular Epidemiology of Staphylococcus aureus Bacteremia: Association of Molecular Factors With the Source of Infection

Staphylococcus aureus bacteremia (SAB) is associated with high morbidity and mortality, which varies depending on the source of infection. Nevertheless, the global molecular epidemiology of SAB and its possible association with specific virulence factors remains unclear. Using DNA microarrays, a total of 833 S. aureus strains (785 SAB and 48 colonizing strains) collected in Spain over a period of 15 years (2002–2017) were characterized to determine clonal complex (CC), agr type and repertoire of resistance and virulence genes in order to provide an epidemiological overview of CCs causing bloodstream infection, and to analyze possible associations between virulence genes and the most common sources of bacteremia. The results were also analyzed by acquisition (healthcare-associated [HA] and community-acquired [CA]), methicillin-resistant (MRSA) and methicillin-susceptible (MSSA) strains, and patient age (adults vs. children). Our results revealed high clonal diversity among SAB strains with up to 28 different CCs. The most prevalent CCs were CC5 (30.8%), CC30 (20.3%), CC45 (8.3%), CC8 (8.4%), CC15 (7.5%), and CC22 (5.9%), which together accounted for 80% of all cases. A higher proportion of CC5 was found among HA strains than CA strains (35.6 vs. 20.2%, p < 0.001). CC5 was associated with methicillin resistance (14.7 vs. 79.4%, p < 0.001), whereas CC30, CC45, and CC15 were correlated with MSSA strains (p < 0.001). Pathogen-related molecular markers significantly associated with a specific source of bacteremia included the presence of sea, undisrupted hlb and isaB genes with catheter-related bacteremia; sed, splE, and fib genes with endocarditis; undisrupted hlb with skin and soft tissue infections; and finally, CC5, msrA resistance gene and hla gene with osteoarticular source. Our study suggests an association between S. aureus genotype and place of acquisition, methicillin resistance and sources of bloodstream infection, and provides a valuable starting point for further research insights into intrinsic pathogenic mechanisms involved in the development of SAB.

Sub-inhibitory concentrations of oxacillin modify the expression of agr locus in Staphylococcus aureus clinical strains belonging to different clonal complexes

Background

The ability of Staphylococcus aureus to invade tissues and cause an infectious disease is the result of a multi-factorial process supported by the huge number of virulence factors inherent to this microorganism tightly regulated by the accessory gene regulator (agr). During antimicrobial therapy bacteria may be exposed to sub-inhibitory concentrations (subMICs) of antibiotics that may trigger transcriptional changes that may have an impact on the pathogenesis of infection. The objective of this study was to investigate the effect of oxacillin sub-MICs on agr system expression as the key component in the regulation of virulence in methicillin-susceptible (MSSA) and -resistant S. aureus (MRSA) strains. Furthermore, we studied the genetic basis of the agr locus and their potential association with the expression levels.

Methods

We have examined the expression of RNAIII and agrA mRNA as biomarkers for agr expression in the presence and absence of oxacillin subMICs in 10 MSSA and 4 MRSA clinical strains belonging to 5 clonal complexes (CC45-agrI, CC8-agrI, CC5-agrII, CC15-agrII and CC30-agrIII) causing endovascular complications. The DNA sequences of agr locus were obtained by whole genome sequencing.

Results

Our results revealed that exposure to subMICs of oxacillin had an impact on agr locus expression modifying the relative levels of expression with increases in 11 strains and with decreases in 3 strains. Thereby, the exposure to subMICs of oxacillin resulted in higher levels of expression of agr in CC15 and CC45 and lower levels in CC30. We also observed the presence of mutations in agrC and agrA in 13/14 strains with similar mutation profiles among strains within individual CCs except for strains of CC5. Although, agr expression levels differed among strains within CCs, the presence of these mutations was associated with differences in agr expression levels in most cases.

Conclusions

Changes in agr expression induced by exposure to oxacillin subMICs should be considered because they could lead to changes in the virulence modulation and have an adverse effect on the course of infection, especially in certain clonal complexes.

Electronic supplementary material

The online version of this article (10.1186/s12879-018-3088-7) contains supplementary material, which is available to authorized users.

Morbidity from in-hospital complications is greater than treatment failure in patients with Staphylococcus aureus bacteraemia

BACKGROUND

Various studies have identified numerous factors associated with poor clinical outcomes in patients with Staphylococcus aureus bacteraemia (SAB). A new study was created to provide deeper insight into in-hospital complications and risk factors for treatment failure.

METHODS

Adult patients hospitalised with Staphylococcus aureus bacteraemia (SAB) were recruited prospectively into a multi-centre cohort. The primary outcome was treatment failure at 30 days (composite of all-cause mortality, persistent bacteraemia, or recurrent bacteraemia), and secondary measures included in-hospital complications and mortality at 6- and 12-months. Data were available for 222 patients recruited from February 2011 to December 2012.

RESULTS

Treatment failure at 30-days was recorded in 14.4% of patients (30-day mortality 9.5%). Multivariable analysis predictors of treatment failure included age > 70 years, Pitt bacteraemia score ≥ 2, CRP at onset of SAB > 250 mg/L, and persistent fevers after SAB onset; serum albumin at onset of SAB, receipt of appropriate empiric treatment, recent healthcare attendance, and performing echocardiography were protective. 6-month and 12-month mortality were 19.1% and 24.2% respectively. 45% experienced at least one in-hospital complication, including nephrotoxicity in 19.5%.

CONCLUSIONS

This study demonstrates significant improvements in 30-day outcomes in SAB in Australia. However, we have identified important areas to improve outcomes from SAB, particularly reducing renal dysfunction and in-hospital treatment-related complications.

Impact of Staphylococcus aureus phenotype and genotype on the clinical characteristics and outcome of infective endocarditis. A multicentre, longitudinal, prospective, observational study

OBJECTIVE

We aimed to evaluate the impact of Staphylococcus aureus phenotype (vancomycin MIC) and genotype (agr group, clonal complex CC) on the prognosis and clinical characteristics of infective endocarditis (IE).

METHODS

We performed a multicentre, longitudinal, prospective, observational study (June 2013 to March 2016) in 15 Spanish hospitals. Two hundred and thirteen consecutive adults (≥18 years) with a definite diagnosis of S. aureus IE were included. Primary outcome was death during hospital stay. Main secondary end points were persistent bacteraemia, sepsis/septic shock, peripheral embolism and osteoarticular involvement.

RESULTS

Overall in-hospital mortality was 37% (n = 72). Independent risk factors for death were age-adjusted Charlson co-morbidity index (OR 1.20; 95% CI 1.08-1.34), congestive heart failure (OR 3.60; 95% CI 1.72-7.50), symptomatic central nervous system complication (OR 3.17; 95% CI 1.41-7.11) and severe sepsis/septic shock (OR 4.41; 95% CI 2.18-8.96). In the subgroup of methicillin-susceptible S. aureus IE (n = 173), independent risk factors for death were the age-adjusted Charlson co-morbidity index (OR 1.17; 95% CI 1.03-1.31), congestive heart failure (OR 3.39; 95% CI 1.51-7.64), new conduction abnormality (OR 4.42; 95% CI 1.27-15.34), severe sepsis/septic shock (OR 5.76; 95% CI 2.57-12.89) and agr group III (OR 0.27; 0.10-0.75). Vancomycin MIC ≥1.5 mg/L was not independently associated with death during hospital nor was it related to secondary end points. No other genotype variables were independently associated with in-hospital death.

CONCLUSIONS

This is the first prospective study to assess the impact of S. aureus phenotype and genotype. Phenotype and genotype provided no additional predictive value beyond conventional clinical characteristics. No evidence was found to justify therapeutic decisions based on vancomycin MIC for either methicillin-resistant or methicillin-susceptible S. aureus.

A 5-year Survey Reveals Increased Susceptibility to Glycopeptides for Methicillin-Resistant Staphylococcus aureus Isolates from Staphylococcus aureus Bacteremia Patients in a Chinese Burn Center

Methicillin-resistant Staphylococcus aureus (MRSA) infections are prevalent in burn wards, and are especially serious in S. aureus bacteremia (SAB) patients. Glycopeptides and daptomycin are effective against MRSA infections, but MIC creeps can reduce their efficacy. Our object was to perform a molecular epidemiological investigation of S. aureus isolates in our burn center and to evaluate MICs for antimicrobials against SAB-associated MRSA isolates. A total of 259 S. aureus isolates, obtained from August 2011 to July 2016, were used in this study. Multiple molecular typing was used for molecular epidemiological analysis. E-tests were used to determine MICs of vancomycin, teicoplanin, and daptomycin for SAB-associated MRSA isolates. MIC values were stratified by collection date or source and compared. Spearman's test was used to analyze MICs correlations amongst tested antimicrobials. ST239-MRSA-III-t030-agrI clone was found to be dominant in both SAB and non-SAB patients, and significantly more in SAB patients (P < 0.0001). SAB-MRSA isolates exhibited decreased MICs for vancomycin, teicoplanin, and daptomycin during the 5-year period. Compared to those isolated from catheters or wounds, SAB-MRSA isolates from the bloodstream were less susceptible to vancomycin and daptomycin, but more susceptible to teicoplanin. MICs Correlation was found only between vancomycin and daptomycin in MRSA isolates from the bloodstream (rho = 0.250, P = 0.024). In conclusion, our results suggest that MRSA infections are still serious problems in burn centers. In contrast to most other studies, we observed increased susceptibility to glycopeptides and daptomycin against SAB-associated MRSA in our center from 2011 to 2016, suggesting the use of glycopeptides does not lead to MIC creeps. Isolates from different sites of the body may exhibit different levels of susceptibility and change trend over time for different antimicrobials, antimicrobials selection for MRSA infections should be considered comprehensively.

Intravenous Vancomycin Dosing in the Elderly: A Focus on Clinical Issues and Practical Application

The elderly population can be divided into three distinct age groups: 65-74 years (young-old), 75-84 years (middle-old), and 85+ years (old-old). Despite evidence of a shift in leading causes for mortality in the elderly from infectious diseases to chronic conditions, infections are still a serious cause of death in this population. These patients are at increased risk due to weakened immune systems, an increased prevalence of underlying comorbidities, and decreased physiologic reserves to fight infection. Additionally, elderly patients, especially adults in institutional settings, are at an increased risk of colonization and subsequent infection with methicillin-resistant Staphylococcus aureus at a rate that is five times higher than in younger individuals, causing an increase in empiric and definitive vancomycin use. Elderly patients have unique characteristics that make dosing vancomycin a challenge for clinicians, such as increased volume of distribution and decreased renal function. Using the best available evidence, it is recommended to initiate lower empiric maintenance doses and monitor vancomycin serum concentrations earlier than steady state to accurately calculate drug elimination and make appropriate dose adjustments.

High vancomycin MICs predict the development of infective endocarditis in patients with catheter-related bacteraemia due to methicillin-resistant Staphylococcus aureus

BACKGROUND

It has been suggested that there is an increased risk of treatment failure in episodes of MRSA bloodstream infection (BSI) caused by strains with high vancomycin MICs. However, it is unknown if this phenomenon may also act as a risk factor for the development of infective endocarditis (IE).

METHODS

We analysed 207 episodes of catheter-related (CR)-BSI recruited from June 2008 to December 2009 within a prospective study on MRSA BSI in 21 Spanish hospitals. Vancomycin susceptibility was centrally tested. The impact of high vancomycin MIC values (≥1.5 mg/L by Etest) on the subsequent development of IE was investigated by Cox regression.

RESULTS

High vancomycin MIC values were observed in 46.9% of the isolates. Initial therapy consisted of vancomycin [99 episodes (44.7%)], daptomycin [25 (12.1%)], linezolid [18 (8.7%)] and other antistaphylococcal agents [16 (7.7%)]. Haematogenous complications occurred in 41 patients (19.8%), including 10 episodes complicated by IE. Early (48 h) and late (30 day) all-cause mortality were 3.4% and 25.1%, respectively. High vancomycin MIC isolates were more common among patients that developed IE compared with those free from this complication [90.9% (9/10) versus 44.7% (88/197); P  = 0.007]. This association remained significant after adjusting for multiple confounders (including initial antibiotic therapy and catheter removal) in different models (minimum hazard ratio: 9.18; 95% CI: 1.16-72.78; P  = 0.036). There were no differences in mortality according to vancomycin MIC values.

CONCLUSIONS

Decreased susceptibility to vancomycin acted as a predictor of the development of IE complicating MRSA CR-BSI.

Pathogenic Characteristics of Staphylococcus aureus Endovascular Infection Isolates from Different Clonal Complexes

Staphylococcus aureus is a major cause of bacteremia and, even with appropriate clinical management, causes high morbidity, and mortality due to its involvement in endovascular complications and metastatic infections. Through different pathogenic in vivo and in vitro models we investigated the behavior of S. aureus most relevant clonal complexes (CCs) causing endovascular complications. We analyzed 14 S. aureus strains representing CC5, CC8, CC15, CC30, and CC45 that caused endovascular complications, including methicillin susceptible and resistant isolates and strains with different functionality of the agr global regulator. Their adherence to collagen, interaction with the endothelium, resistance to immune attack, capacity to form biofilm and virulence in the Galleria mellonella model were analyzed. CC30 and CC45 showed greater adhesion to collagen and CC8 showed a trend towards higher rate of intracellular persistence in endothelial cells. All CCs exhibited similar tolerance to neutrophil antimicrobial peptide hNP-1 and were capable of forming biofilms under static conditions. The virulence assay in the G. mellonella model demonstrated that CC15 and CC30 were the most and least virulent, respectively. The analysis of the genomic sequences of the most relevant virulence genes identified some CC15 specific gene patterns (absence of enterotoxins and sak gene) and variants (mainly in leucocidins and proteases), but did not reveal any gene or variant that could be responsible for the increased virulence detected for CC15 strains. Even though all the CCs were capable of causing endovascular complications, our results showed that different CCs are likely to produce these complications through different mechanisms which, if confirmed in more sophisticated models, would indicate the need to more specific management and therapeutic approaches.

Pathogen-related factors affecting outcome of catheter-related bacteremia due to methicillin-susceptible Staphylococcus aureus in a Spanish multicenter study

Even with appropriate clinical management, complicated methicillin-susceptible Staphylococcus aureus (MSSA) catheter-related bacteremia (CRB) is frequent. We investigated the influence of molecular characteristics of MSSA strains on the risk of complicated bacteremia (CB) in MSSA-CRB. A multicenter prospective study was conducted in Spain between 2011 and 2014 on MSSA-CRB. Optimized protocol-guided clinical management was required. CB included endocarditis, septic thrombophlebitis, persistent bacteremia and/or end-organ hematogenous spread. Molecular typing, agr functionality and DNA microarray analysis of virulence factors were performed in all MSSA isolates. Out of 83 MSSA-CRB episodes included, 26 (31.3%) developed CB. MSSA isolates belonged to 16 clonal complexes (CCs), with CC30 (32.5%), CC5 (15.7%) and CC45 (13.3) being the most common. Comparison between MSSA isolates in episodes with or without CB revealed no differences regarding agr type and functionality. However, our results showed that CC15 and the presence of genes like cna, chp and cap8 were associated with the development of CB. The multivariate analysis highlighted that the presence of cna (Hazard ratio 2.9; 95% CI 1.14-7.6) was associated with the development of CB. Our results suggest that particular CCs and specific genes may influence the outcome of MSSA-CRB.