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Research Article 


An optimal method for generating stable vancomycin heteroresistance and intermediate susceptibility in methicillin-resistant Staphylococcus aureus blood isolates under in-vitro vancomycin pressure

Riad Khatib, Jinson Jose, Leonard B Johnson, Kathleen Riederer, Stephen Shemes.


Cited By:1

Abstract
Objectives: The relevance of vancomycin intermediately-susceptible (VISA) and hetero-resistant (hVISA) methicillin-resistant Staphylococcus aureus (MRSA) remains uncertain because of their low frequency. In vitro attempts to generate reduced susceptibility have been inconsistent. We describe a simple method for generating VISA/hVISA.
Materials and methods: Twenty-four SCCmec type II and IV MRSA blood isolates plus USA100 and USA300 controls were cultured (107 CFU/ml) in BHI broth with 0, 2 and 3 mg/L vancomycin for 10 days followed by 10 days vancomycin-free-passage. We monitored vancomycin minimum inhibitory concentration (MIC; Etest) and population analysis profile-area under the curve (PAP-AUC) ratios of tested isolate/Mu3 during and after vancomycin pressure (VP). PAP-AUC ratios <0.9, 0.9-1.3 and >1.3 were considered consistent with susceptible, hVISA and VISA, respectively.
Results: VP at 2 mg/L (VP-2) increased MIC to 3 mg/L in 20 (83.3%) isolates and raised PAP-AUC ratio to hVISA (n=18; 75.0%) and VISA (six; 25.0%) ranges. VP-3 increased MIC to 3 and 4 mg/L in 19 (79.2%) and three (12.5%) isolates, respectively and raised PAP-AUC ratio to hVISA (n=3; 12.5%) and VISA (n=19; 79.2%) ranges. SCCmec IV isolates had lower pre-exposure PAP-AUC ratios (0.48±0.14 vs. 0.69±0.10; p<0.001) and lower MIC (1.6±0.2 vs. 1.8±0.2 mg/L; p=0.1) but MIC rise and hVISA/VISA emergence was comparable. MIC and PAP-AUC ratio rises were stable in 20/22 isolates during drug-free passages.
Conclusions: VISA/hVISA readily emerges among MRSA SCCmec type II and IV isolates under VP. VP at the MIC level generates hVISA while pressure at slightly higher level results in the VISA phenotype. J Microbiol Infect Dis 2012; 2(4): 129-135


 
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How to Cite this Article
Pubmed Style

Khatib R, Jose J, Johnson LB, Riederer K, Shemes S. An optimal method for generating stable vancomycin heteroresistance and intermediate susceptibility in methicillin-resistant Staphylococcus aureus blood isolates under in-vitro vancomycin pressure. J Microbiol Infect Dis. 2012; 2(4): 129-134 . doi:10.5799/jmid2012.04.0059

Web Style

Khatib R, Jose J, Johnson LB, Riederer K, Shemes S. An optimal method for generating stable vancomycin heteroresistance and intermediate susceptibility in methicillin-resistant Staphylococcus aureus blood isolates under in-vitro vancomycin pressure. https://www.jmidonline.org/?mno=302657138 [Access: April 09, 2025]. doi:10.5799/jmid2012.04.0059

AMA (American Medical Association) Style

Khatib R, Jose J, Johnson LB, Riederer K, Shemes S. An optimal method for generating stable vancomycin heteroresistance and intermediate susceptibility in methicillin-resistant Staphylococcus aureus blood isolates under in-vitro vancomycin pressure. J Microbiol Infect Dis. 2012; 2(4): 129-134 . doi:10.5799/jmid2012.04.0059


Vancouver/ICMJE Style

Khatib R, Jose J, Johnson LB, Riederer K, Shemes S. An optimal method for generating stable vancomycin heteroresistance and intermediate susceptibility in methicillin-resistant Staphylococcus aureus blood isolates under in-vitro vancomycin pressure. J Microbiol Infect Dis. (2012), [cited April 09, 2025]; 2(4): 129-134 . doi:10.5799/jmid2012.04.0059


Harvard Style

Khatib, R., Jose, . J., Johnson, . L. B., Riederer, . K. & Shemes, . S. (2012) An optimal method for generating stable vancomycin heteroresistance and intermediate susceptibility in methicillin-resistant Staphylococcus aureus blood isolates under in-vitro vancomycin pressure. J Microbiol Infect Dis, 2 (4), 129-134 . doi:10.5799/jmid2012.04.0059


Turabian Style

Khatib, Riad, Jinson Jose, Leonard B Johnson, Kathleen Riederer, and Stephen Shemes. 2012. An optimal method for generating stable vancomycin heteroresistance and intermediate susceptibility in methicillin-resistant Staphylococcus aureus blood isolates under in-vitro vancomycin pressure. Journal of Microbiology and Infectious Diseases, 2 (4), 129-134 . doi:10.5799/jmid2012.04.0059


Chicago Style

Khatib, Riad, Jinson Jose, Leonard B Johnson, Kathleen Riederer, and Stephen Shemes. "An optimal method for generating stable vancomycin heteroresistance and intermediate susceptibility in methicillin-resistant Staphylococcus aureus blood isolates under in-vitro vancomycin pressure." Journal of Microbiology and Infectious Diseases 2 (2012), 129-134 . doi:10.5799/jmid2012.04.0059


MLA (The Modern Language Association) Style

Khatib, Riad, Jinson Jose, Leonard B Johnson, Kathleen Riederer, and Stephen Shemes. "An optimal method for generating stable vancomycin heteroresistance and intermediate susceptibility in methicillin-resistant Staphylococcus aureus blood isolates under in-vitro vancomycin pressure." Journal of Microbiology and Infectious Diseases 2.4 (2012), 129-134 . Print. doi:10.5799/jmid2012.04.0059


APA (American Psychological Association) Style

Khatib, R., Jose, . J., Johnson, . L. B., Riederer, . K. & Shemes, . S. (2012) An optimal method for generating stable vancomycin heteroresistance and intermediate susceptibility in methicillin-resistant Staphylococcus aureus blood isolates under in-vitro vancomycin pressure. Journal of Microbiology and Infectious Diseases, 2 (4), 129-134 . doi:10.5799/jmid2012.04.0059


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Journal of Microbiology and Infectious Diseases

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