Reduced Vancomycin Susceptibility of Methicillin-Susceptible Staphylococcus aureus Has No Significant Impact on Mortality but Results in an Increase in Complicated Infection

Abstract

Methicillin-susceptible Staphylococcus aureus (MSSA) bloodstream infections (BSIs) often lead to severe complications despite the availability of effective antibiotics. It remains unclear whether elevated vancomycin MICs are associated with worse outcomes. We conducted a 2-year retrospective cohort study (n ϭ 252) of patients with MSSA BSIs at a tertiary care hospital. We defined reduced vancomycin susceptibility (RVS) as a Microscan MIC of 2 mg/liter. All strains were genotyped (spa) and assessed for agr functionality. Multivariable logistic regression models were used to examine the impact of RVS phenotype and strain genotype on 30-day allcause mortality and complicated bacteremia (metastatic spread, endovascular infection, or duration Ն3 days). One-third of patients (84/252) were infected with RVS isolates. RVS Infections were more frequently associated with metastatic or embolic sites of infection (36% versus 17%, P Ͻ 0.001), and endovascular infection (26% versus 12%, P ϭ 0.004). These infections occurred more often in patients with fewer underlying comorbidities (Charlson comorbidity index of Ն3 [73% versus 88%, P ϭ 0.002]). Genotyping identified 127 spa-types and 14 Spa-clonal complexes (Spa-CCs). Spa-CC002 and Spa-CC008 were more likely to exhibit the RVS phenotype versus other Spa-CCs (OR ϭ 2.2, P Ͻ 0.01). The RVS phenotype was not significantly associated with 30-day mortality; however, it was associated with complicated bacteremia (adjusted odds ratio of 2.35 [range, 1.26 to 4.37]; P ϭ 0.007) in adjusted analyses. The association of RVS strains with complicated infection and fewer underlying comorbidities suggests the phenotype as a potential marker of strain virulence in MSSA BSIs. The RVS phenotype itself was not a significant predictor of mortality in this patient cohort. Further studies are necessary to explore this host-pathogen relationship.KEYWORDS MSSA bacteremia, reduced vancomycin susceptibility S taphylococcus aureus is a dynamic pathogen causing a broad range of clinical syndromes, from localized skin-and-soft tissue infections to invasive disease (1). S. aureus bloodstream infections (SAB) often result in endovascular seeding and are frequently associated with poor outcomes, including 30-day mortality estimated at 20 to 40% (2-6). While bloodstream infections (BSIs) caused by methicillin-resistant S. aureus (MRSA) have historically attracted the most attention, methicillin-sensitive S. aureus (MSSA) is responsible for the majority of S. aureus BSIs (7,8).Morbidity and mortality in patients with S. aureus BSI are due to a complex interplay between timely and effective treatment, host-pathogen interactions, underlying pa-

Association of Vancomycin MIC and Molecular Characteristics with Clinical Outcomes in Methicillin-Susceptible Staphylococcus aureus Acute Hematogenous Osteoarticular Infections in Children

“…Holmes et al described higher mortality in adults with infection due to MSSA isolates with a vancomycin MIC of Ն2 g/ml, regardless of initial antibiotic choice (15). Other investigators have noted an increased rate of bacteremia-related complications in MSSA infections with a vancomycin MIC of Ն2 g/ml in adults (30). We observed a higher incidence of negative clinical outcomes in MSSA AHOAI isolates with elevated vancomycin MICs.…”

Promising anti-microbial effect of apple vinegar as a natural decolonizing agent in healthcare workers

“…MRSA express resistance to many families of antibiotics which limit the treatment possibilities [33]. Some studies [34,35] reported high rates of resistance against erythromycin among MRSA from HCWs and which were similar to our findings.…”

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

“…Therefore, it is possible that weakened virulence due to agr dysfunction nullifies the effect of persistent infections, and these effects may be more prominent in MSSA than in MRSA. A previous study demonstrated a relationship between isolates with reduced vancomycin susceptibility (RVS) and dysfunctional agr in MSSA bacteraemia 26 , and several studies demonstrated that infection caused by the RVS phenotype in MSSA isolates was associated with poor clinical outcomes regardless of antibiotics 37,[58][59][60][61] . However, we observed that dysfunctional agr was significantly associated with lower mortality in invasive MSSA infections.…”