CLSI lists only susceptible disk diffusion interpretive criteria in mm for vancomycin and Staphylococcus spp. There has not been a sufficient number of non-susceptible isolates to develop resistant and intermediate breakpoints. Performance Standards for Antimicrobial Susceptibility Testing. Sixteenth informational supplement. CLSI is a global, interdisciplinary, nonprofit, standards-developing and educational organization that promotes the development and use of voluntary consensus standards and guidelines within the healthcare community.
Go to: CLSI external icon. The term glycopeptide refers to a group of antimicrobial agents that includes vancomycin and teicoplanin. Vancomycin continues to be an important antimicrobial agent for treating infections caused by S. The reduced susceptibility of VISA and VRSA strains to vancomycin leaves clinicians with relatively few therapeutic options for treating these infections.
Three out of six confirmed VRSA isolates were not reliably detected by automated testing systems in a recent report. VISA isolates are not detected by disk diffusion.
Laboratories that use automated methods that are not validated for VRSA detection should also include a vancomycin screen agar plate for enhanced detection of VRSA.
If possible, laboratories should incorporate the vancomycin agar screen plate for testing all S. Laboratories using disk diffusion to determine vancomycin susceptibility should consider adding a second method for VISA detection. However, it is clear that the organism is virulent, causes disease that necessitates treatment e. It is of note that the most recent report from Nevada involves a patient treated with surgery plus linezolid, TMP-SMZ, and doxycycline therapy with apparent success.
Furthermore, reports to the CDC regarding patients who have S. These patients' failure to respond may have been due to decreased susceptibility to vancomycin or other factors, and it is unclear just how different the strains of S. Most of these isolates demonstrated heteroresistance to vancomycin. To ascertain the relevance of hetero-VISA in patients with clinical failure, further studies are needed.
There are some prospects for advancing the therapy of VISA on the basis of laboratory studies. In vitro studies suggest that VISA isolates may be inhibited at lower vancomycin concentrations when exposed to nafcillin or cefazolin [ 9 , 23 ]. Climo et al. They further demonstrated, in a rabbit endocarditis model, that therapy with either vancomycin or nafcillin as a single agent was ineffective, but combination therapy was associated with lower bacterial burden in the rabbits.
However, another study did not document a decrease in the MIC of methicillin, because the MIC of vancomycin increased after serial passage of VISA isolates in the absence of vancomycin [ 25 ].
There have been no confirmed reports of clinical infections with VRSA. Because of the difficulties with laboratory detection outlined above, and because of the rarity of VISA infections, the incidence of disease i. However, by reviewing several data sources, some assessments can be made.
A CDC study used several different screening agars to test clinical isolates of S. However, there are some data to suggest that VISA infections may become more common in the near future. First, the number of reports to the CDC of S. Second, if heteroresistance is a precursor to VISA, then such precursors may already be a condition of many clinical strains of S.
The frequency of heteroresistance has been generally low 0. Although the clinical relevance of these isolates is unknown, their occurrence may foretell more frequent infections with VISA, especially in populations of patients receiving recurrent courses of glycopeptide therapy, such as the patient population undergoing hemodialysis. Therefore, the CDC is asking for any clinical S. Prevention is a primary infection control issue. Although infection control experience with VISA is limited, infection control recommendations have been proposed by experts in the field [ 12 , 29 ].
For any patient suspected of having an infection with VISA or VRSA, contact precautions should be followed, and the infection control and local health departments should be notified immediately. Approximately culture specimens obtained from persons who had contact with the VISA-infected patients both health care workers and family members failed to identify any additional persons colonized or infected with VISA [ 4 , 15 , 17 ].
Contact precautions were already followed for most of the patients with MRSA infection or colonization. Because MRSA is known to be highly transmissible in health care settings, it is reasonable to assume that VISA isolates will likewise be highly transmissible. Because of the costs involved with the VISA precautions and epidemiologic and laboratory investigations, consultation with the hospital epidemiologist, local health department, and the CDC should be sought until more experience is obtained regarding patient management and infection control issues.
Hospital Infection Control Practices Advisory Committee interim recommendations for prevention of the spread of staphylococci with reduced susceptibility to vancomycin. Several studies have shown that vancomycin is frequently used for inappropriate reasons [ 30 ].
Improved use of vancomycin, use of proper diagnostic techniques to minimize prolonged empiric therapy, minimal use of temporary venous catheters, removal of prosthetic materials involving S.
Coagulase-negative staphylococci. Low-level vancomycin resistance has been reported in clinical isolates of coagulase-negative staphylococci [ 31 ]. The clinical relevance of decreased susceptibility in these species is even less clear than that for S. Infection control standards for patients with infections associated with these organisms should be determined in consultation with infection control and public health authorities.
To date, several clinical infections with VISA have been reported. Intermediate resistance appears to develop from preexisting MRSA strains in the presence of vancomycin in patients with a considerable underlying illness— in particular, chronic renal failure. VISA detection is problematic in the laboratory, and special susceptibility testing procedures or algorithms may be needed. Although all of the VISA-infected patients who died had serious underlying illnesses that may have contributed to their deaths, the infections did not appear to respond to vancomycin.
Newly developed agents, including linezolid and quinupristin-dalfopristin, appear to be effective in vitro. Further strategies are needed to evaluate the best therapeutic options for patients infected with VISA. The clinical relevance of heteroresistance is not known. Any screening for heteroresistance for the purpose of clinical decision-making is not warranted at this time.
Without continued vigilance in the enforcement of infection control measures, improved use of antimicrobials, and coordination of efforts among public health authorities, increasing levels of vancomycin resistance in S.
I thank Fred C. Tenover, PhD, for his assistance in the preparation and review of this article. Google Scholar. Google Preview. Oxford University Press is a department of the University of Oxford.
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Download PDF. Subjects Bacterial infection Epidemiology. Abstract The aim of the present study was to describe the characteristics of infections with Staphylococcus aureus with reduced vancomycin susceptibility SARVS including vancomycin-intermediate S. Introduction Antimicrobial resistance AMR is an emerging global crisis and a present threat to public health 1.
Laboratory procedures At the laboratory of the NIH, confirmatory testing was performed for vancomycin MIC using agar dilution, broth microdilution, and E-test for all S. Classification of S. Results A total of 66 patients infected or colonized with SA-RVS were reported using the sentinel surveillance system 11 in , 28 in , and 27 in Fig. Figure 1. Full size image. Figure 2. Full size table. Table 2 Clinical description of patients who died within 30 days owing to S.
Table 3 Microbiological characteristics of vancomycin-intermediate S. Table 4 Comparison of antimicrobial susceptibility of S. References 1. Article Google Scholar 2. Article Google Scholar 3. Article Google Scholar 5. Article Google Scholar 6. Article Google Scholar 9. Article Google Scholar Article Google Scholar Download references. Acknowledgements The authors thank all medical staff in sentinel medical institutions for their cooperation in collecting data. View author publications.
Ethics declarations Competing Interests The authors declare no competing interests. Supplementary information. About this article. Cite this article Park, J. Copy to clipboard. Comments By submitting a comment you agree to abide by our Terms and Community Guidelines.
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