Rapid decrease of free vancomycin in dense staphylococcal cultures

• Published in: European journal of clinical microbiology & infectious diseases 2005-09, Vol.24 (9), p.596-602
• Main Authors: EKDAHL, C, HANBERGER, H, HÄLLGREN, A, NILSSON, M, SVENSSON, E, NILSSON, L. E
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - metabolism; Anti-Bacterial Agents - metabolism; Anti-Bacterial Agents - pharmacology; Antibacterial agents; Antibiotics. Antiinfectious agents. Antiparasitic agents; Bacteria; Bacterial diseases; Bioassays; Biological and medical sciences; Bioluminescence; Colony Count; Colony Count, Microbial; drug effects; drug therapy; Human bacterial diseases; Humans; In Vitro Techniques; Infectious diseases; Luminescence; Medical sciences; MEDICIN; MEDICINE; metabolism; Microbial; Microbiology; Microbiology in the medical area; Mikrobiologi inom det medicinska området; pharmacology; Pharmacology. Drug treatments; Staphylococcal Infections; Staphylococcal Infections - drug therapy; Staphylococcal infections, streptococcal infections, pneumococcal infections; Staphylococcus aureus; Staphylococcus aureus - drug effects; Staphylococcus aureus - metabolism; Staphylococcus epidermidis; Staphylococcus epidermidis - drug effects; Staphylococcus epidermidis - metabolism; Vancomycin; Vancomycin - metabolism; Vancomycin - pharmacology; Vancomycin Resistance
• ISSN: 0934-9723; 1435-4373; 1435-4373
• DOI: 10.1007/s10096-005-0011-0

Bacterial numbers in broth cultures were determined by bioluminescence assay of intracellular bacterial ATP. Broth MICs for strains of Staphylococcus epidermidis (ATCC 14990 and 35984) and Staphylococcus aureus (ATCC 25923, 29213 and 6538) were determined for cultures with different inocula (10(5)-10(8) bacteria/ml) after 24 h of incubation in supplemented Mueller-Hinton broth containing vancomycin. All of the tested strains except one were susceptible to methicillin, and all of the strains were susceptible to vancomycin. Free vancomycin concentrations in the broth cultures of all strains were determined with an agar well bioassay after 24 h of incubation. Free vancomycin concentrations and bacterial numbers of ATCC 35984 and ATCC 29213 were also determined after 0.5, 2, 4, and 8 h. In a low inoculum (10(5) bacteria/ml), the broth MICs were 1-4 microg/ml. In a high inoculum (approximately 10(8) bacteria/ml), the broth MICs increased two- to fourfold to 4-8 microg/ml. In dense inocula ( approximately 10(9)-10(10) bacteria/ml), the concentrations of free vancomycin in the broth were reduced, in most cases below the detection limit of the bioassay (