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In vivo emergence of subpopulations expressing teicoplanin or vancomycin resistance phenotypes in a glycopeptide-susceptible, methicillin-resistant strain of Staphylococcus aureus


Vaudaux, P; Francois, P; Berger-Bächi, B; Lew, D P (2001). In vivo emergence of subpopulations expressing teicoplanin or vancomycin resistance phenotypes in a glycopeptide-susceptible, methicillin-resistant strain of Staphylococcus aureus. Journal of Antimicrobial Chemotherapy, 47(2):163-170.

Abstract

Several reports indicate the emergence of subpopulations resistant to glycopeptides in some clinical isolates of Staphylococcus aureus. While the development of glycopeptide resistance in S. aureus is easily observed in vitro, the in vivo conditions promoting emergence of glycopeptide-resistant subpopulations are unknown. Using a rat model, subcutaneous implants were chronically infected with a methicillin-resistant strain of S. aureus, MRGR3, devoid of a significant (>10(-7)) glycopeptide-resistant subpopulation at 2 mg/L of either teicoplanin or vancomycin. After 3 weeks of infection in antibiotic-untreated animals, subpopulations emerged, growing on agar containing 10 mg/L of either glycopeptide. These subpopulations were detected in all tissue cage fluids containing >7 log cfu/mL at average frequencies of 4 x 10(-5) and 2 x 10(-5) on teicoplanin- and vancomycin-containing agar, respectively. While teicoplanin MICs increased two- to 16-fold, vancomycin MICs increased by less than two-fold. Population analysis and survival kinetic studies of three teicoplanin-selected subclones indicated that transfer from solid to liquid medium conditions decreased expression of teicoplanin resistance in the bacterial population. In Mueller-Hinton broth, >90% of cells remained fully resistant to antibiotic, but did not grow in the presence of teicoplanin for an initial period of at least 6 h. All three teicoplanin-resistant subclones expressed stable teicoplanin resistance with slight cross-resistance to vancomycin after a few transfers on teicoplanin-supplemented agar. These data suggest that some in vivo conditions may lead to selection of S. aureus subpopulations exhibiting decreased glycopeptide susceptibility and growing in the presence of otherwise inhibitory concentrations of these antimicrobial agents.

Abstract

Several reports indicate the emergence of subpopulations resistant to glycopeptides in some clinical isolates of Staphylococcus aureus. While the development of glycopeptide resistance in S. aureus is easily observed in vitro, the in vivo conditions promoting emergence of glycopeptide-resistant subpopulations are unknown. Using a rat model, subcutaneous implants were chronically infected with a methicillin-resistant strain of S. aureus, MRGR3, devoid of a significant (>10(-7)) glycopeptide-resistant subpopulation at 2 mg/L of either teicoplanin or vancomycin. After 3 weeks of infection in antibiotic-untreated animals, subpopulations emerged, growing on agar containing 10 mg/L of either glycopeptide. These subpopulations were detected in all tissue cage fluids containing >7 log cfu/mL at average frequencies of 4 x 10(-5) and 2 x 10(-5) on teicoplanin- and vancomycin-containing agar, respectively. While teicoplanin MICs increased two- to 16-fold, vancomycin MICs increased by less than two-fold. Population analysis and survival kinetic studies of three teicoplanin-selected subclones indicated that transfer from solid to liquid medium conditions decreased expression of teicoplanin resistance in the bacterial population. In Mueller-Hinton broth, >90% of cells remained fully resistant to antibiotic, but did not grow in the presence of teicoplanin for an initial period of at least 6 h. All three teicoplanin-resistant subclones expressed stable teicoplanin resistance with slight cross-resistance to vancomycin after a few transfers on teicoplanin-supplemented agar. These data suggest that some in vivo conditions may lead to selection of S. aureus subpopulations exhibiting decreased glycopeptide susceptibility and growing in the presence of otherwise inhibitory concentrations of these antimicrobial agents.

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Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > Institute of Medical Microbiology
Dewey Decimal Classification:570 Life sciences; biology
610 Medicine & health
Language:English
Date:2001
Deposited On:10 Aug 2012 13:57
Last Modified:23 Sep 2018 07:19
Publisher:Oxford University Press
ISSN:0305-7453
OA Status:Green
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1093/jac/47.2.163
PubMed ID:11157900

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