Reduced Vancomycin Susceptibility Research Articles

Unravelling the complex interplay between antibiotic consumption and adaptive changes in methicillin-resistant Staphylococcus aureus.

This study aims to elucidate the genomic dynamics driving the emergence of antimicrobial resistance (AMR), with a specific focus on the interplay between AMR and antimicrobial usage. We conducted a comprehensive analysis using a ST239 methicillin-resistant Staphylococcus aureus (MRSA) dataset over a continuous 12-year period from a single hospital. Genomic analyses were performed tracking the changes in MRSA populations, particularly the emergence of reduced vancomycin susceptibility, and assessing the impact of glycopeptide use on these emergence events. Our findings reveal a significant correlation between hospital glycopeptide usage and the selection of MRSA strains with reduced vancomycin susceptibility. Genomic analyses provided insights into the molecular mechanisms driving resistance emergence, including the slowing of the molecular clock rate in response to heightened antimicrobial consumption. In conclusion, this study the highlights the complex dynamics between AMR and antimicrobial use at the hospital level. The observed correlation between antimicrobial consumption and the development of less susceptible MRSA strains underscores the importance of antimicrobial stewardship programmes and the establishment of optimal consumption thresholds for mitigating AMR effectively.

Reduced Vancomycin Susceptibility in Clostridioides difficile is Associated with Lower Rates of Initial Cure and Sustained Clinical Response.

Epidemiologic studies have shown decreasing vancomycin susceptibility among clinical Clostridioides difficile isolates, but the impact on patient outcomes is unknown. We hypothesized that reduced vancomycin susceptibility would be associated with decreased rates of sustained clinical response (SCR). This multicenter cohort study included adults with C. difficile infection (CDI) treated with oral vancomycin between 2016-2021. C. difficile isolates underwent agar dilution vancomycin susceptibility testing, ribotyping, and Sanger sequencing of the vancomycin resistance vanR gene. Reduced susceptibility was defined as vancomycin minimum inhibitory concentration (MIC) >2 μg/mL. The primary outcome was 30-day SCR; secondary outcomes were 14-day initial cure, 30-day recurrence, and 30-day mortality. Exploratory analysis assessed the association between the VanR Thr115Ala polymorphism, susceptibility, and outcomes. A high proportion (34%, 102/300) of C. difficile isolates exhibited reduced vancomycin susceptibility (range: 0.5-16 μg/mL, MIC50/90 = 2/4 μg/mL). Ribotype (RT) 027 accounted for the highest proportion (77.4%, 41/53) of isolates with reduced vancomycin susceptibility. Overall, 83% (249) of patients achieved 30-day SCR. Reduced vancomycin susceptibility was associated with lower rates of 30-day SCR (76%, 78/102) than vancomycin susceptible strains (86%, 171/198; P=0.031). A significantly lower rate of 14-day initial cure was also observed among individuals infected with strains with reduced vancomycin susceptibility (89% vs. 96%; P=0.04). Reduced susceptibility remained an independent predictor of 30-day SCR in multivariable modeling (odds ratio, 0.52, 95% confidence interval 0.28-0.97; P=0.04). Reduced vancomycin susceptibility in C. difficile was associated with decreased odds of 30-day SCR and lower 14-day initial cure rates in the studied patient cohort.

AgrA directly binds to the promoter of vraSR and downregulates its expression in Staphylococcus aureus.

Staphylococcus aureus is an important human pathogen and vancomycin is widely used for the treatment of S. aureus infections. The global regulator agr is known as a well-described virulence regulator. Previous studies have found that agr-dysfunction strains are more likely to develop into vancomycin-resistant strains, but the mechanism for this phenomenon remains unknown. VraSR is a two-component regulatory system related to vancomycin resistance. In this study, we found that the expression levels of vraR were higher in agr-dysfunction clinical strains than in the agr-functional strains. We knocked out agr in a clinical strain, and quantitative reverse transcription PCR and β-galactosidase activity assays revealed that agr repressed transcription of vraR. After vancomycin exposures, population analysis revealed larger subpopulations displaying reduced susceptibility in agr knockout strain compared with wild-type strain, and this pattern was also observed in agr-dysfunction clinical strains compared with the agr-functional strains. Electrophoretic mobility experiment demonstrated binding of purified AgrA to the promoter region of vraR. In conclusion, our results indicated that the loss of agr function in S. aureus may contribute to the evolution of reduced vancomycin susceptibility through the downregulation of vraSR.

Genetic characterization of tetracycline-resistant Staphylococcus aureus with reduced vancomycin susceptibility using whole-genome sequencing.

This study aimed to analyze the genetic characteristics of Staphylococcus aureus with reduced vancomycin susceptibility (RVS-SA). Whole-genome sequencing was performed on 27 RVS-SA clinical isolates, and comparative genomic analysis was performed using S. aureus reference strains. Pan-genome orthologous groups (POGs) were identified that were present in RVS-SA but absent in the reference strains, but further analysis showed that the presence of these POGs was influenced by tetracycline resistance rather than vancomycin resistance. Therefore, we restricted our analysis to tetracycline-resistant (tetR) RVS-SA and tetR vancomycin-susceptible S. aureus (VSSA). Phylogenomic analysis showed them to be closely related, and further analysis revealed the presence of an uncharacterized protein SAB0394 and the absence of lytA in tetR RVS-SA, which are involved in cell wall thickening. In summary, using whole-genome sequencing we identified gain or loss of genes in tetR RVS-SA strains. These findings provide insights into the investigation of mechanisms associated with reduced vancomycin susceptibility and have the potential to contribute to the development of molecular biomarkers for the rapid and efficient detection of RVS-SA.

Genetic alterations in methicillin-susceptible Staphylococcus aureus associated with high vancomycin minimum inhibitory concentration

There are many reports on gene mutations observed in methicillin-resistant Staphylococcus aureus (MRSA) showing reduced susceptibility to vancomycin. However, there are limited studies on the genetic alterations that contribute to high vancomycin minimum inhibitory concentrations (MICs) in methicillin-susceptible S. aureus (MSSA). This study aimed to compare MSSA strains with high vancomycin MICs with those with low MICs, and to identify specific genetic alterations associated with increased vancomycin MICs. In total, 124 MSSA strains were analysed, with 62 having vancomycin MICs of 1-2 mg/L (MS-HV) and the remaining 62 having MICs <1 mg/L (MS-LV) as control. Polymerase chain reaction amplification and sequencing were conducted to identify point mutations and amino acid changes in the vraSR, graRS and walRK operons and rpoB gene. The number of single nucleotide polymorphisms (SNPs) and specific mutations in the indicated gene were compared between the two groups. The MS-HV strains had a significantly higher median number of SNPs in studied genes than the MS-LV strains (5 vs 3; P < 0.0001), with higher frequency of SNPs in the graR and walK genes. The MS-HV strains also displayed a significantly higher prevalence of specific mutations in the graR gene (V135I, I136V and V136I) compared with the MS-LV strains. The odds of having a high vancomycin MIC was 5.54 times higher in strains with a mutation in the graR gene, and 5.32 times higher in strains with a mutation in the walK gene, compared with those without these mutations. Mutations in the graR and walK genes may contribute to reduced vancomycin susceptibility in MSSA. This study gives key insights into the mechanisms underlying this phenomenon.

380. A molecular epidemiological exploration of reduced vancomycin susceptibility in Clostridioides difficile

Abstract Background Use of vancomycin to treat Clostridioides difficile infection (CDI) has increased following recent IDSA/SHEA treatment guideline updates, applying a selection pressure for resistance development. We previously demonstrated acquired mutations in VanSR two-component system led to constitutive vanG expression and improved in vitro C. difficile survival in physiologic vancomycin concentrations. We aim to describe the molecular epidemiology of reduced vancomycin susceptibility in clinical isolates during a period of high vancomycin use. Methods A cohort study was performed including adult patients hospitalized with CDI in two health systems (14 hospitals) in the Houston Area between 2017-2021. (Stool transport) C. difficile were ribotyped by fluorescent PCR and susceptibility tested by agar dilution in accordance with CLSI standards. Reduced vancomycin susceptibility was defined by minimum inhibitory concentrations (MICs) &amp;gt;2 mg/L. Sanger sequencing was conducted on a subgroup of isolates to identify VanSR mutations. Analysis using Chi square was performed using IBM SPSS Statistics (v 28.0.1.0). Results A total of 36% (165/465) of isolates exhibited reduced vancomycin susceptibility (MIC50 = 2 mg/L, MIC90 = 4 mg/L, range 0.5-16 mg/L), of which 348 were ribotyped. A significantly higher proportion of ribotype (RT) 027 isolates demonstrated reduced vancomycin susceptibility (83%) compared to other common ribotypes (30%); p&amp;lt; 0.001). No differences based on collection year (p=0.3) or healthcare system (p=0.08) were observed. Overall, 11% (7/56) of isolates exhibiting mutations in VanS (n=1), VanR (n=5), or both (n=1). VanSR mutations were present in 47% (7/15) of those with MICs &amp;gt;2mg/L vs 0% (0/41) of those with MICs ≤2 mg/L (p&amp;lt; 0.001). Conclusion A high proportion of clinical C. difficile isolates exhibited elevated MICs to vancomycin, which was most common in RT027 isolates. Mutations in the vanG regulator, VanSR, correlated with elevated MICs in a subgroup of isolates. Future research is needed to expand upon molecular mechanisms and clinical implications of reduced vancomycin susceptibility. Disclosures Kevin W. Garey, PharmD, MS, Acurx Pharmaceuticals: Grant/Research Support|Paratek Pharmaceuticals: Grant/Research Support|Seres Therapeutics: Grant/Research Support|Summit Pharmaceuticals: Grant/Research Support.

Impact of vancomycin use trend change due to the availability of alternative antibiotics on the prevalence of Staphylococcus aureus with reduced vancomycin susceptibility: a 14-year retrospective study

BackgroundWe investigated the trend change in vancomycin-intermediate Staphylococcus aureus (VISA)/heterogeneous VISA (hVISA) prevalence among methicillin-resistant S. aureus (MRSA) bacteremia strains and antistaphylococcal antibiotic use together with mutation studies of vancomycin resistance-related gene loci to evaluate the impact of changes in antibiotic use after new antistaphylococcal antibiotics became available.MethodsAmong 850 healthcare-associated MRSA isolates from 2006 to 2019 at a tertiary hospital in South Korea, hVISA/VISA was determined by modified PAP/AUC analysis, and the identified hVISA/VISA strains were genotyped. Gene mutations at vraSR, graSR, walKR, and rpoB were studied by full-length sequencing. Antistaphylococcal antibiotic use in 2005–2018 was analyzed.ResultsTwo VISA and 23 hVISA strains were identified. The prevalence rate ratio of hVISA/VISA carrying mutations at the two-component regulatory systems among MRSA was 0.668 (95% CI 0.531–0.841; P = 0.001), and the prevalence rate ratio of hVISA/VISA carrying rpoB gene mutations was 1.293 (95% CI 0.981–1.702; 174 P = 0.068). Annual vancomycin use density analyzed by days of therapy (DOT) per 1,000 patient-days did not decrease significantly, however the annual average length of time analyzed by the number of days vancomycin was administered for each case showed a significantly decreasing trend.ConclusionsDuring the 14-year period when the average length of vancomycin therapy decreased every year with the availability of alternative antibiotics, the prevalence of hVISA/VISA did not decrease significantly. This seems to be because the resistant strains carrying the rpoB mutations increased despite the decrease in the strains carrying the mutations at the two-component regulatory systems.

Antibiotic Exposure Leads to Reduced Phage Susceptibility in Vancomycin Intermediate Staphylococcus aureus (VISA).

ABSTRACTIn the time of antimicrobial resistance, phage therapy is frequently suggested as a possible solution for such difficult-to-treat infections. Vancomycin-intermediate Staphylococcus aureus (VISA) remains a relatively rare yet increasing occurrence in the clinic for which phage therapy may be an option. However, the data presented herein suggest a potential cross-resistance mechanism to phage following vancomycin exposure in VISA strains. When comparing genetically similar strains differing in their susceptibility to vancomycin, those with intermediate levels of vancomycin resistance displayed decreased sensitivity to phage in solid and liquid assays. Serial passaging with vancomycin induced both reduced vancomycin susceptibility and phage sensitivity. As a consequence, the process of phage infection was shown to be interrupted after DNA ejection from adsorbed phage but prior to phage DNA replication, as demonstrated through adsorption assays, lysostaphin sensitivity assays, electron microscopy, and quantitative PCR (qPCR). At a time when phage products are being used for experimental treatments and tested in clinical trials, it is important to understand possible interference between mechanisms underlying antibiotic and phage resistance in order to design effective therapeutic regimens.

Houston, We Have a Problem: Reports of Clostridioides difficile Isolates With Reduced Vancomycin Susceptibility.

During the past 4 decades, oral vancomycin has been a mainstay of Clostridioides difficile infection (CDI) therapy with no reports of treatment failure due to emergence of vancomycin resistance. However, C. difficile isolates with high-level phenotypic resistance to vancomycin have recently been reported in 3 distinct geographic regions. There is an urgent need for surveillance to determine if strains with reduced vancomycin susceptibility are circulating in other areas. In a Cleveland-area hospital, screening of 176 CDI stool specimens yielded no C. difficile isolates with reduced vancomycin susceptibility and highlighted the potential for false-positive results due to contamination with vancomycin-resistant enterococci. Additional studies are needed to clarify whether reduced vancomycin susceptibility is an emerging problem that will alter clinical practice. Clinicians should alert their health department if they observe a substantial increase in the frequency of vancomycin treatment failure in patients diagnosed with CDI with no alternative explanation for diarrhea.

Different Antimicrobial Susceptibility Testing Methods to Determine Vancomycin Susceptibility and MIC for Staphylococcus aureus with Reduced Vancomycin Susceptibility.

The methods and results obtained using commercialized automation systems used for antimicrobial susceptibility testing are not entirely consistent. Therefore, we evaluated different antimicrobial susceptibility testing methods to determine vancomycin susceptibility and minimum inhibitory concentration (MIC) for Staphylococcus aureus with reduced vancomycin susceptibility (SA-RVS). A total of 128 clinical isolates of S. aureus were tested, including 99 isolates showing an MIC of ≥2 µg/mL using the VITEK2 system (VITEK2). Antimicrobial susceptibility tests were performed using the Sensititre system (Sensititre), Phoenix M50 system (Phoenix), and MicroScan WalkAway 96 Plus system (MicroScan). Vancomycin MICs were determined using the broth microdilution method (BMD) and Etest. Essential agreement and category agreement for each method were compared with BMD results as the reference method. The BMD and Etest showed complete essential agreement (100%). VITEK2, Sensititre, and Phoenix showed high essential agreement (>99%), while MicroScan showed the lowest essential agreement (92.2%). The MIC MICs determined via Etest, VITEK2, and MicroScan tended to be higher than that determined via BMD. When comparing BMD with Etest, the category agreement was 93.8% and minor errors were observed for eight isolates. VITEK2, Sensititre, and Phoenix showed category agreements of 96.1%, 96.1%, and 99.2%, respectively, while MicroScan showed the lowest category agreement of 85.2%. The determination of vancomycin susceptibility and MIC for S. aureus varied among the methods. Caution should be taken when interpreting RVS and intermediate results for S. aureus. For confirmation of SA-RVS results, it would be appropriate to test with BMD or a more reliable testing method.

Antibiotic Resistance and Biofilm Production Capacity in Clostridioides difficile.

BackgroundClostridioides difficile (C. difficile) is one of the primary pathogens responsible for infectious diarrhea. Antibiotic treatment failure, occurring in about 30% of patients, and elevated rates of antibiotic resistance pose a major challenge for therapy. Reinfection often occurs by isolates that produce biofilm, a protective barrier impermeable to antibiotics. We explored the association between antibiotic resistance (in planktonic form) and biofilm-production in 123 C. difficile clinical isolates.ResultsOverall, 66 (53.6%) out of 123 isolates produced a biofilm, with most of them being either a strong (44%) or moderate (34.8%) biofilm producers. When compared to susceptible isolates, a statistically higher percentage of isolates with reduced susceptibility to metronidazole or vancomycin were biofilm producers (p < 0.0001, for both antibiotics). Biofilm production intensity was higher among tolerant isolates; 53.1% of the metronidazole-susceptible isolates were not able to produce biofilms, and only 12.5% were strong biofilm-producers. In contrast, 63% of the isolates with reduced susceptibility had a strong biofilm-production capability, while 22.2% were non-producers. Among the vancomycin-susceptible isolates, 51% were unable to produce biofilms, while all the isolates with reduced vancomycin susceptibility were biofilm-producers. Additionally, strong biofilm production capacity was more common among the isolates with reduced vancomycin susceptibility, compared to susceptible isolates (72.7% vs. 18.8%, respectively). The distribution of biofilm capacity groups was statistically different between different Sequence-types (ST) strains (p =0.001). For example, while most of ST2 (66.7%), ST13 (60%), ST42 (80%) isolates were non-producers, most (75%) ST6 isolates were moderate producers and most of ST104 (57.1%) were strong producers.ConclusionsOur results suggest an association between reduced antibiotic susceptibility and biofilm production capacity. This finding reinforces the importance of antibiotic susceptibility testing, mainly in recurrence infections that may be induced by a strain that is both antibiotic tolerant and biofilm producer. Better adjustment of treatment in such cases may reduce recurrences rates and complications. The link of biofilm production and ST should be further validated; if ST can indicate on isolate virulence, then in the future, when strain typing methods will be more available to laboratories, ST determination may aid in indecision between supportive vs. aggressive treatment.

Challenges in replicating secondary analysis of electronic health records data with multiple computable phenotypes: A case study on methicillin-resistant Staphylococcus aureus bacteremia infections

BackgroundReplication of prediction modeling using electronic health records (EHR) is challenging because of the necessity to compute phenotypes including study cohort, outcomes, and covariates. However, some phenotypes may not be easily replicated across EHR data sources due to a variety of reasons such as the lack of gold standard definitions and documentation variations across systems, which may lead to measurement error and potential bias. Methicillin-resistant Staphylococcus aureus (MRSA) infections are responsible for high mortality worldwide. With limited treatment options for the infection, the ability to predict MRSA outcome is of interest. However, replicating these MRSA outcome prediction models using EHR data is problematic due to the lack of well-defined computable phenotypes for many of the predictors as well as study inclusion and outcome criteria. ObjectiveIn this study, we aimed to evaluate a prediction model for 30-day mortality after MRSA bacteremia infection diagnosis with reduced vancomycin susceptibility (MRSA-RVS) considering multiple computable phenotypes using EHR data. MethodsWe used EHR data from a large academic health center in the United States to replicate the original study conducted in Taiwan. We derived multiple computable phenotypes of risk factors and predictors used in the original study, reported stratified descriptive statistics, and assessed the performance of the prediction model. ResultsIn our replication study, it was possible to (re)compute most of the original variables. Nevertheless, for certain variables, their computable phenotypes can only be approximated by proxy with structured EHR data items, especially the composite clinical indices such as the Pitt bacteremia score. Even computable phenotype for the outcome variable was subject to variation on the basis of the admission/discharge windows. The replicated prediction model exhibited only a mild discriminatory ability. ConclusionDespite the rich information in EHR data, replication of prediction models involving complex predictors is still challenging, often due to the limited availability of validated computable phenotypes. On the other hand, it is often possible to derive proxy computable phenotypes that can be further validated and calibrated.

Apt (Adenine Phosphoribosyltransferase) Mutation in Laboratory-Selected Vancomycin-Intermediate Staphylococcus aureus.

Comparative genomic sequencing of laboratory-derived vancomycin-intermediate Staphylococcus aureus (VISA) (MM66-3 and MM66-4) revealed unique mutations in both MM66-3 (in apt and ssaA6), and MM66-4 (in apt and walK), compared to hetero-VISA parent strain MM66. Transcriptional profiling revealed that both MM66 VISA shared 79 upregulated genes and eight downregulated genes. Of these, 30.4% of the upregulated genes were associated with the cell envelope, whereas 75% of the downregulated genes were associated with virulence. In concordance with mutations and transcriptome alterations, both VISA strains demonstrated reduced autolysis, reduced growth in the presence of salt and reduced virulence factor activity. In addition to mutations in genes linked to cell wall metabolism (ssaA6 and walK), the same mutation in apt which encodes adenine phosphoribosyltransferase, was confirmed in both MM66 VISA. Apt plays a role in both adenine metabolism and accumulation and both MM66 VISA grew better than MM66 in the presence of adenine or 2-fluoroadenine indicating a reduction in the accumulation of these growth inhibiting compounds in the VISA strains. MM66 apt mutants isolated via 2-fluoroadenine selection also demonstrated reduced susceptibility to the cell wall lytic dye Congo red and vancomycin. Finding that apt mutations contribute to reduced vancomycin susceptibility once again suggests a role for altered purine metabolism in a VISA mechanism.

Letter to the Editor Regarding “Safety of Deep Brain Stimulation Lead Placement on Patients Requiring Anticlotting Therapies”

Telavancin was the first marketed lipoglycopeptide. Although licensed in Europe in 2011 for the treatment of nosocomial pneumonia caused by meticillin-resistant Staphylococcus aureus (MRSA), it did not become clinically available until March 2014. Given the limited clinical experience with telavancin in Europe, this review provides an overview of its antimicrobial and clinical activity as well as its position among today's antimicrobials, with particular focus on the implications of its licensing requirements. Telavancin has potent in vitro activity against isolates of Gram-positive pathogens, including MRSA and glycopeptide-intermediate S. aureus strains. In addition, at clinically attainable doses telavancin inhibits Gram-positive isolates of antibiotic-resistant strains from biofilm models. The in vitro potency of telavancin has been corroborated in the clinical setting. Comparative clinical studies of telavancin demonstrate non-inferiority compared with vancomycin in the treatment of hospital-acquired Gram-positive pneumonia, with high cure rates for telavancin-treated patients with monomicrobial S. aureus infection, including isolates with reduced vancomycin susceptibility. These studies also demonstrate an overall similar safety profile for telavancin and vancomycin, although importantly, patients with moderate-to-severe renal impairment at baseline are at greater risk for mortality with telavancin and this feature must be taken into account when selecting patients for its usage. In Europe, telavancin is a useful alternative for patients with difficult-to-treat, hospital-acquired MRSA pneumonia when there are very few alternatives. For example, it should be considered in such patients when vancomycin and linezolid are not suitable and where renal function permits.

Genomic Analysis of Heterogeneous Vancomycin-Intermediate Staphylococcus aureus Strains from Different Clonal Lineages in South Korea.

Recent genomic studies of methicillin-resistant Staphylococcus aureus (MRSA) have revealed genetic diversity in the various clonal lineages. Along with clinical concerns of MRSA infection, infection with heterogeneous vancomycin-intermediate S. aureus (hVISA) is closely associated with treatment failure. In this study, we investigated the magnitude of genetic variation and features at the genomic level of hVISA strains isolated in South Korea. Four hVISA strains were analyzed by molecular epidemiology, antimicrobial susceptibility, and whole-genome sequencing methods, and they were compared with the reference VISA and vancomycin-susceptible S. aureus strains in the same clonal lineage. The epidemiologic features of hVISA strains were closely related to the ST5 and ST239 clones. Comparative analysis of the whole genome showed genetic mutations, particularly in two-component systems (TCSs) and transcriptional regulators. Genetic mutations in walK were commonly found in both ST5- (F545L, E378K, T500K) and ST239-related (E424D, T492R) hVISA strains. hVISA strains in the ST5 clonal lineage contained mutations in TCS genes, including the walK, vraR, and agr loci, whereas ST239-related strains harbored different genetic variations in walK, lytR, and saeR. This study suggests that the diverse genetic variation of TCSs and transcriptional regulators are involved in reduced vancomycin susceptibility through different mechanisms in each clonal lineage.

Molecular characterization of Staphylococcus aureus isolated from hospital acquired sepsis in pediatrics, relation to antibiotics, resistance and virulence genes.

The objective of this study was to determine the prevalence of antibiotic resistance genes mecA, vanA, B, C and virulence genes Panton-Valentine Leucocidin (PVL) and fibronectin-binding protein (fnBPA) among S. aureus isolates from hospital-acquired sepsis from pediatric intensive care units. The study was a retrospective cross-sectional study, including 250 unique isolates of S. aureus obtained from pediatric patients with hospital-acquired sepsis. The isolates were subjected to study of antibiotic susceptibility by disc diffusion method and molecular analysis of antibiotic resistance genes and certain virulence genes (PVL and fnBPA genes). Methicillin resistant S. aureus represented 178 (71%) of the isolated S. aureus and reduced susceptibility to vancomycin was detected by minimum inhibitory concentration in 39 (22%) isolates. It was found that there was a strong association between the MRSA strains and resistance to some antibiotics, devices association (p<0.001) and patient outcomes (p=0.003). There was a significant association between reduced vancomycin susceptibility (p=0.010), the presence of a central line catheter (p=0.000) and fnBPA gene (p<0.001) and mortality rate. The present study highlights that major S. aureus strains isolated from sepsis in pediatric patients were methicillin resistant with a substantial proportion of reduced susceptibility to vancomycin. Although none of the isolates had van genes responsible for vancomycin resistance, this finding warrants a considerable attention for study as it was a risk factor for mortality in those patients. The virulence genes fibronectin-binding protein and Panton-Valentine Leucocidin were not uncommon in S. aureus.

Reduced Vancomycin Susceptibility, MRSA and Treatment Failure in Pediatric Staphylococcus aureus Bloodstream Infections.

Clinical implications of reduced vancomycin susceptibility (RVS) among pediatric Staphylococcus aureus bloodstream infections are unknown. We identified all children at 2 children's hospitals with ≥1 blood culture positive for S. aureus. We compared patient and clinical factors for RVS and non-RVS infections using Wilcoxon rank-sum and chi-squared tests. Treatment failure and the duration of bacteremia for RVS versus non-RVS and for methicillin-resistant Staphylococcus aureus (MRSA) versus methicillin-susceptible Staphylococcus aureus (MSSA) infections were compared using multivariable logistic and Poisson regressions, respectively. For MRSA infections, the association of empiric vancomycin monotherapy with treatment failure was assessed using multivariable logistic regression. RVS was present in 72% (309/426) of cases. No patient or infection characteristics, including methicillin resistance, were associated with RVS. RVS was associated with an increased duration of bacteremia compared with non-RVS infections, aIRR = 1.15 (95% confidence interval: 1.02-1.30). The odds of treatment failure was similar for RVS and non-RVS infections, aOR = 1.04 (0.62-1.74). In contrast, MRSA infections were more likely to have treatment failure than MSSA infections, aOR = 3.03 (95% confidence interval: 1.84-5.00). For MRSA infections, empiric vancomycin monotherapy was associated with an increased odds of treatment failure compared with non-vancomycin or combination anti-MRSA antibiotics, aOR = 3.23 (1.12-9.26). RVS was common and was associated with a longer duration of bacteremia but not with treatment failure. Treatment failure was more common for MRSA than for MSSA bloodstream infections. Empiric vancomycin monotherapy increased the odds of treatment failure for MRSA infections.

Methicillin-resistant Staphylococcus epidermidis isolates with reduced vancomycin susceptibility from bloodstream infections in a neonatal intensive care unit.

Introduction. Vancomycin has become the first-line therapy for most infections caused by methicillin-resistant staphylococci.Aim. To evaluate the vancomycin MIC, staphylococcal cassette chromosome mec (SCCmec) types and clonality of coagulase-negative staphylococci (CoNS) isolates recovered from neonates with true primary bloodstream infections (BSI).Methodology. CoNS isolates were prospectively recovered from blood cultures of non-repetitive patients admitted to a neonatal intensive care unit (NICU) in a tertiary-care hospital during a 3-year period. BSI was defined based on established criteria. Micro-organisms were identified phenotypically and by PCR. MIC-values for vancomycin and oxacillin were determined by broth dilution method and E-test. The SCCmec type conferring methicillin resistance was determined by multiplex PCR. The heterogeneous vancomycin (hV) resistance phenotype was screened on brain heart infusion agar containing 4 µg ml-1 of vancomycin. The clonality was investigated by PFGE.Results. Seventy-four CoNS isolates were recovered from blood cultures of neonates during the study period but only 40 (54 %) were associated with true primary BSI. Nine (22.5%) babies died. Staphylococcus epidermidis was the most prevalent species (95 %; 38/40). All S. epidermidis isolates were methicillin-resistant (MR). SCCmec type IV was predominant (55.3 %; 21/38). Most (80.0 %; 32/38) isolates exhibited vancomycin MIC-values of 2-4 µg ml-1 not associated with the SCCmec type or clonality. Sixteen (42.1%) isolates displayed hV resistance. All babies who died were harbouring MR-S. epidermidis exhibiting vancomycin MICs of 2-4 µg ml-1.Conclusion. The findings of this study demonstrated that blood invasive MR-S. epidermidis isolates recovered at NICU tend to show decreased vancomycin susceptibility making therapy of those fragile patients difficult.

136. Factors Associated with Reduced Vancomycin Susceptibility in Pediatric Staphylococcus aureus Bacteremia

BackgroundVancomycin is often used empirically for treatment of pediatric Staphylococcus aureus bacteremia while susceptibility testing is being performed. Reduced vancomycin susceptibility (RVS) occurs when the minimum inhibitory concentration (MIC) for vancomycin is elevated, potentially resulting in decreased efficacy. Patient factors associated with RVS in pediatric S. aureus infections have not been well studied.MethodsChildren aged <18 years admitted from 2012 to 2016 to two tertiary care children’s hospitals with a blood culture positive for S. aureus were identified. Demographics, presence of comorbidities, hospitalizations in the year prior to the infection, surgical procedures in the 30 days prior to the infection, presence of a central venous catheter at diagnosis and methicillin-resistant (MRSA) vs. methicillin-susceptible S. aureus (MSSA) were abstracted from the electronic medical record using a structured data collection form. RVS was defined as a MIC >1 µg/mL as reported by the clinical microbiology laboratory. Wilcoxon rank-sum and Fisher’s exact test to compare continuous and categorical variables, respectively. A multivariable logistic regression model was used to evaluate the association of RVS with patient factors, MRSA vs. MSSA, admitting hospital, and year.ResultsWe identified 221 S. aureus bloodstream infections. Most (84%) had RVS though there were differences by the hospital, 74% vs. 87%, P = 0.037. Bloodstream infections in the setting of a musculoskeletal infection were most common (36%), followed by central line-associated bloodstream infections (22%). The median age was similar between RVS and non-RVS infections, 3 (25th, 75th %tiles: 0, 9) vs. 5 (0, 12) but, when adjusted for patient factors, younger children were more likely to have RVS infections than older children, aOR: 0.92 (0.85, 0.99). Black children were more likely to have RVS than white children on both univariate and adjusted analyses (table).ConclusionRVS is common among pediatric S. aureus bloodstream infections and appears to be influenced by patient age and race but not by the source of the infection or other clinical factors. Disclosures All authors: No reported disclosures.

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.