Intermediate Susceptibility To Vancomycin Research Articles

Antibiotic Tolerance and Treatment Outcomes in Cystic Fibrosis Methicillin-Resistant Staphylococcus aureus Infections.

Methicillin-resistant Staphylococcus aureus (MRSA) is highly prevalent in U.S. cystic fibrosis (CF) patients and is associated with worse clinical outcomes in CF. These infections often become chronic despite repeated antibiotic therapy. Here, we assessed whether bacterial phenotypes, including antibiotic tolerance, can predict the clinical outcomes of MRSA infections. MRSA isolates (n = 90) collected at the incident (i.e., acute) and early infection states from 57 patients were characterized for growth rates, biofilm formation, hemolysis, pigmentation, and vancomycin tolerance. The resistance profiles were consistent with those in prior studies. Isolates from the early stage of infection were found to produce biofilms, and 70% of the isolates exhibited delta-hemolysis, an indicator of agr activity. Strong vancomycin tolerance was present in 24% of the isolates but was not associated with intermediate vancomycin susceptibility. There were no associations between these phenotypic measures, antibiotic tolerance, and MRSA clearance. Our research suggests that additional factors may be relevant for predicting the clearance of MRSA. IMPORTANCE Chronic MRSA infections remain challenging to treat in patients with cystic fibrosis (CF). The ability of the bacterial population to survive high concentrations of bactericidal antibiotics, including vancomycin, despite lacking resistance is considered one of the main reasons for treatment failures. The connection between antibiotic tolerance and treatment outcomes remains unexplored and can be crucial for prognosis and regimen design toward eradication. In this study, we measured the capacity of 90 MRSA isolates from CF patients to form vancomycin-tolerant persister cells and evaluated their correlation with the clinical outcomes. Additionally, various traits that could reflect the metabolism and/or virulence of those MRSA isolates were systematically phenotyped and included for their predictive power. Our research highlights that despite the importance of antibiotic tolerance, additional factors need to be considered for predicting the clearance of MRSA.

Vancomycin Resistance in Staphylococcus aureus and Enterococcus Species isolated at the University Teaching Hospitals, Lusaka, Zambia: Should We Be Worried?

Background: Staphylococcus aureus and Enterococcus species cause invasive infections such as bacteremia and infective endocarditis. Despite vancomycin being the drug of choice for drug-resistant infections caused by these species, few studies have been conducted to ascertain vancomycin resistance in the African setting. This is crucial given the rising resistance in these organisms. This study aimed to isolate S. aureus and Enterococcus species and determine their susceptibility to vancomycin and other antibiotics at the University Teaching Hospitals in Lusaka, Zambia. Methods: This was a cross-sectional study in which S. aureus and Enterococcus spp isolates from the skin, soft tissue and bloodstream infections were included. Standard microbiological and Kirby-Baur (disc diffusion and E-strips) methods were used to identify and determine the susceptibility of the organisms, respectively. Results: From 59 S. aureus isolates, 37 were from the skin and soft tissue and 22 from blood culture. Twenty-six (44.1%) of these were Methicillin-resistant S. aureus. Thirty-nine Enterococcus were isolated from blood cultures only. Of the S. aureus (16) and Enterococcus (14) isolates tested with vancomycin E-strips, none were vancomycin-resistant. However, 12.5% S. aureus and 14.3% Enterococcus showed intermediate vancomycin susceptibility. S. aureus were resistant to penicillin (93.2%), erythromycin (52.5%) and tetracycline (50.8%). Enterococcus showed resistance to penicillin (83%) and tetracycline (84.6%). Conclusions: There was no vancomycin resistance among S. aureus and Enterococcus, implying vancomycin is still a viable treatment option for invasive infections. Given the intermediate vancomycin susceptibility, treatment guided by minimum inhibitory concentration results, continued surveillance and prudent use are key.

Draft Genome Sequences of Three Northern German Epidemic Staphylococcus aureus (ST247) Strains Containing Multiple Copies of IS256.

We report the draft genome sequences of three multiresistant Staphylococcus aureus strains of sequence type 247 (ST247). The methicillin-resistant S. aureus (MRSA) SA1450/94 is vancomycin susceptible, while the clinical MRSA isolate S. aureus SA137/93A and its spontaneous laboratory mutant SA137/93G are characterized by intermediate vancomycin susceptibility.

Activity of Linezolid against Multidrug-resistant Gram Positive Cocci in Eastern Nepal

Background: The emergence of resistance in gram-positive bacteria has necessitated a search for new antimicrobial agents. Linezolid, an oxazolidinone, is a new class of antibacterial agents with enhanced activity against pathogens. Method: The in-vitro activity of linezolid was assessed against 461 gram-positive cocci; 301 Staphylococcus spp., 150 Enterococcus spp., 5 Streptococcus pneumoniae and 5 Streptococcus pyogenes , with an emphesis on testing multidrug-resistant isolates. Results: Linezolid demonstrated potent activity against all the isolates tested at the susceptible breakpoint (≤4µg/ml). Against methicillin-resistant staphylococci and vancomycin-resistant enterococci, linezolid was the most active agent tested. Moreover, among 29.90% methicillin-resistant staphylococcal isolates, 20 exhibited intermediate susceptibility to vancomycin. Similarly, among the enterococcal isolates, 32% exhibited high level gentamicin-resistance whereas 7.33% were found to be vancomycin-resistant. None of the streptococcal isolates exhibited resistance to any of the antimicrobials tested. Conclusions: In summary, linezolid may represent an important therapeutic option for the treatment of infections caused by gram-positive cocci in Nepal.

Using Genomics To Standardize Population Analysis Profile-Area under the Curve Ratio for Vancomycin-Intermediate Staphylococcus aureus

Detection of Staphylococcus aureus isolates with intermediate vancomycin susceptibility (VISA) and heteroresistance (hVISA) remains problematic. Population analysis profile-area under the curve ratio (PAP-AUC) is the gold standard, with the level of resistance of an isolate expressed as a ratio of

Study of Decreased Susceptibility to Vancomycin in Methicillin-Resistant Staphylococcus aureus Strains isolated from a Romanian Multidisciplinary Emergency Hospital

The clinical relevance of Staphylococcus aureus strains with heterointermediate susceptibility to vancomycin (hVISA) is still controversial, however they could be responsible for treatment failures in patients treated with vancomycin. The lack of standardization and the complexity of testing methods are the main challenge in indentifying such strains. The aim of our study was to evaluate the frequency of hVISA strains in Targu-Mures Clinical Emergency Hospital. One hundred twenty-two, non-duplicate, methicillin-resistant S. aureus (MRSA) isolates susceptible to vancomycin using standard E-test (MIC≤2 mg/L) were screened for heteroresistance with Glycopeptide Resistance Detection test (E-test GRD). Population analysis profile-area under the curve (PAP/AUC) method was used for confirmation. Twenty-four strains (19.5%) were found positive with the screening method. Two of them (1.63%) were confirmed having hVISA phenotype and no strains with intermediate vancomycin susceptibility (VISA) were detected. In conclusion, the rate of MRSA strains with reduced vancomycin susceptibility was low. However, their monitoring may be useful, taking into consideration the wide usage of glycopeptides in the treatment of serious MRSA infections.

Production of capsular polysaccharide does not influence Staphylococcus aureusvancomycin susceptibility

BackgroundDiverse mechanisms (increased cell wall thickness, low cross linking, decreased autolysis, etc.) have been reported for Staphylococcus aureus strains with intermediate vancomycin susceptibility (VISA). This study was conducted to identify common mechanisms responsible for decreased vancomycin susceptibility in a VISA strain pair.ResultsTranscriptional profiling of the clinical heterogeneous VISA isolate SA137/93A and its spontaneous homogeneous mutant strain SA137/93G pointed to an increased capsule production in the strain pair compared to a susceptible control. Furthermore, transcript quantification of the gene cap5E, which is essential for capsule biosynthesis, revealed elevated levels in the VISA strains SA137/93A, SA137/93G and Mu50 in comparison with susceptible strains Reynolds, Newman and SA1450/94. The increased expression was observed in bacteria from exponential as well as stationary growth phase. However, suppression of type 5 capsule formation by expression of antisense RNA did not increase vancomycin susceptibility in the VISA strain SA137/93G. Likewise, construction of inducible mutants of S. aureus Newman or repair of capsule biosynthesis of S. aureus HG001 and S. aureus 1450/94 did not influence resistance to vancomycin. Furthermore, purified type 5 polysaccharide did not protect indicator strains from the action of vancomycin.ConclusionsThe VISA strain tested in this study displayed an increased production of type 5 capsular polysaccharide. However, the production of capsule material did not protect strain SA137/93G and three vancomycin sensitive strains in the presence of vancomycin and thus is not part of the resistance mechanism; however it may represent a by-product of VISA life style that is often characterized by a high sigma factor B activity.

Reduced Susceptibility to Vancomycin in Staphylococcus aureus

To the Editor: I read with interest the article by Aguado et al. (1). I congratulate the authors for their high-quality research and would like to make 2 brief comments. My first point regards the mechanism by which methicillin-susceptible Staphylococcus aureus (MSSA) with reduced susceptibility to vancomycin would also acquire decreased susceptibility to β-lactams. The authors “hypothesize that certain structural modifications might also occur in the cell wall of strains with high vancomycin MIC, including a thicker cell wall as it has been described in MRSA [methicillin-resistant S. aureus].” In addition to cell wall thickening, possible mechanisms could include reduction in autolysis (2,3) and in the cell wall content of penicillin binding protein 4 (PBP4) (3). A study of MSSA isolates has shown a reduction in autolysis and in the bactericidal activity of oxacillin after development of intermediate vancomycin susceptibility (2). Lower content of PBP4 and decreased autolysis were reported in MRSA isolates after reduced susceptibility to vancomycin developed after exposure to this antimicrobial drug (3). Decreased PBP4 has been associated with reduced methicillin susceptibility in S. aureus (4). Second, knowing whether the authors had the exact vancomycin MIC of the isolates by broth microdilution to compare with the Etest results would be interesting. In the article, they only state that “all 99 MSSA strains were susceptible to vancomycin (MIC <2 μg/mL) by the broth microdilution method.” Although difficult to compare (because Etest dilution progression is arithmetic and broth microdilution is performed with a geometric dilution), some authors have found substantial differences between the vancomycin MIC results given by these 2 methods (5). These differences could have major laboratory and clinical implications.

Detection of Intermediately Vancomycin-Susceptible and Heterogeneous Staphylococcus aureus Isolates: Comparison of Etest and Agar Screening Methods

Detection of Staphylococcus aureus isolates with intermediate vancomycin susceptibility (VISA) and heteroresistance (hVISA) remains problematic. The population analysis profile/area under the curve (PAP/AUC) is the gold standard but is cumbersome. We compared the performance of two Etest screening methods (macromethod [MAC] and glycopeptide resistance detection [GRD]) plus brain heart infusion (BHI) agars supplemented with 3 (BHI-V3) or 4 (BHI-V4) mg/liter vancomycin in detecting hVISA and/or VISA phenotypes. Etest hVISA screenings were done in parallel for 485 saved methicillin-resistant S. aureus (MRSA) blood isolates according to the manufacturer's instructions. The PAP/AUC was measured for all isolates according to the modified method. PAP/AUC test isolate/Mu3 ratios of <0.9, 0.9 to 1.3, and >1.3 were considered positive for susceptible MRSA (S-MRSA), hVISA, and VISA, respectively. PAP/AUC revealed seven VISA and 33 hVISA phenotypes. MAC screening was positive for 30 (75.0%) hVISA/VISA and 49 (11.0%) S-MRSA isolates. GRD screening was positive for 28 (70.0%) hVISA/VISA and 63 (14.2%) S-MRSA isolates. Growth on BHI-V3 was noted in all hVISA/VISA and 24 (5.4%) S-MRSA isolates. Growth on BHI-V4 was noted in all VISA and four (12.1%) hVISA isolates. None of the S-MRSA isolates grew on BHI-V4 agar. The sensitivity, specificity, and positive (PPV) and negative (NPV) predictive values were 75.0%, 89.0%, 38.0%, and 97.5% for MAC; 70.0%, 85.8%, 30.8%, and 97.0% for GRD; 100%, 94.6%, 62.5%, and 100% for BHI-V3; and 100, 99.2%, 63.6%, and 100% for BHI-V4 (for detecting VISA). These findings suggest that both Etest screening methods have excellent NPV, but positive results require confirmation. BHI-V3 and BHI-V4 agars provide more precise identification of hVISA and VISA, respectively; they may be reasonable alternatives to PAP/AUC.

Development of Reduced Vancomycin Susceptibility in Methicillin‐SusceptibleStaphylococcus aureus

Most cases of reduced vancomycin susceptibility in Staphylococcus aureus reported in the literature have been in methicillin-resistant strains. We report the development of reduced vancomycin susceptibility in a series of clonally related, methicillin-susceptible S. aureus (MSSA) clinical isolates. This isogenic series permitted us to determine whether the evolution of reduced vancomycin susceptibility in MSSA is similar to that seen in MRSA. Differences in vancomycin population analysis profiles; chemical autolysis; vancomycin, oxacillin, and daptomycin minimum inhibitory concentrations; and bactericidal activities were examined. Progressive vancomycin resistance correlated with increasing daptomycin nonsusceptibility. Chemical autolysis and the bactericidal activity of vancomycin, oxacillin, and daptomycin were reduced in the final, vancomycin-intermediate S. aureus isolate, compared with the vancomycin-susceptible MSSA progenitor. Clinicians should recognize that reduced vancomycin susceptibility can occur in S. aureus irrespective of background methicillin susceptibility and that development of intermediate vancomycin susceptibility in MSSA may result in increased tolerance to several classes of anti-staphylococcal antibiotics.

Intermediate Vancomycin Susceptibility in a Community-associated MRSA Clone

We describe a case of treatment failure caused by a strain of USA300 community-associated methicillin-resistant Staphylococcus aureus (MRSA) with intermediate susceptibility to vancomycin and reduced susceptibility to daptomycin. The strain was isolated from the bone of a 56-year-old man with lumbar osteomyelitis after a 6-week treatment course of vancomycin for catheter-associated septic thrombophlebitis.

Methicillin-resistant Staphylococcus aureus. Mechanisms of resistance and implications for treatment.

The frequency of methicillin-resistant Staphylococcus aureus (MRSA) continues to increase steadily, with nosocomial isolates approaching 50% of the total tested. Primarily isolated in hospitals, strains of MRSA have now spread into the community, complicating the management of this sometimes-fatal pathogen. Methicillin resistance in S aureus is mediated by the mecA gene, which encodes for a novel penicillin-binding protein (PBP), PBP-2a. In MRSA, exposure to methicillin inactivates the 4 high-binding-affinity PBPs normally present. PBP-2a, which displays a low affinity for methicillin, takes over the functions of these PBPs, permitting the cell to grow. Regulation of the methicillin-resistant phenotype and production of PBP-2a are influenced by the action of other genes. Two genes located upstream from mecA--mecR1 and mecI--control expression of PBP-2a. Antibiotics with high affinity for PBP-2a have displayed efficacy against MRSA in vivo, but none of these agents has made it beyond the investigational stage. Vancomycin remains the drug of choice for treatment of infections caused by MRSA, although it is intrinsically less active than the antistaphylococcal penicillins. Combinations of vancomycin with ss-lactam antibiotics may be synergistic in vivo against MRSA strains, including those with intermediate susceptibility to vancomycin. Given the increasing prevalence of MRSA in hospitals and in community settings, alternative approaches are needed for treatment of infections caused by MRSA.