Screening Test Method for the Determination of the in vitro Activity of Topical Antimycotics

ABSTRACT We investigated the in vitro activity of micafungin against clinical Aspergillus isolates (n = 37) (Aspergillusfumigatus [n = 21], Aspergillusflavus [n = 14], and Aspergillus niger [n = 2]) by using NCCLS M38A microdilution and an investigational disk diffusion assay. Microdilution assay results were evaluated by using the end points of a MIC-2 (measured in micrograms per milliliter) and minimum effective concentration (MEC, measured in micrograms per milliliter; the lowest concentration of micafungin that produces short and aberrant hyphal branchings microscopically). Disk diffusion results were interpreted by measuring the zone(s) of inhibition (ZOI, measured in millimeters). Micafungin proved to be similarly active against all Aspergillus species tested. At 24 h, MIC-2s and MECs were identical. At 48 h, however, MIC-2s increased unpredictably, leading to the loss of a consistent correlation between the two end points. MECs and ZOI remained consistent and correlated at both reading times, suggesting their use as relevant end points in susceptibility testing of micafungin against Aspergillus. All Aspergillus isolates yielded intrazonal growth on disk diffusion agar plates. The intrazonal colonies contained short, aberrant hyphal branchings microscopically. The in vivo significance of these findings remains to be further investigated.

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Determination of a Tentative Epidemiological Cut-Off Value (ECOFF) for Dalbavancin and Enterococcus faecium

Antibiotics ◽

10.3390/antibiotics10080915 ◽

2021 ◽

Vol 10 (8) ◽

pp. 915

Author(s):

Robert E. Weber ◽

Carola Fleige ◽

Franziska Layer ◽

Bernd Neumann ◽

Michael Kresken ◽

...

Keyword(s):

Central Europe ◽

Enterococcus Faecium ◽

Resistance Mechanisms ◽

Vitro Activity ◽

In Vitro Activity ◽

Glycopeptide Resistance ◽

Gram Positive ◽

Gram Positive Bacteria

Dalbavancin is a lipoglycopeptide antibiotic that shows potent activity against Gram-positive bacteria. It circumvents vanB-type glycopeptide resistance mechanisms; however, data on the in vitro activity of dalbavancin for Enterococcus faecium (E. faecium) are scarce, and thus, no breakpoints are provided. In recent years, there has been a continuing shift from vanA-type to vanB-type vancomycin-resistance in enterococci in Central Europe. Therefore, we aimed to investigate the in vitro activity of dalbavancin against different van-genotypes, with particular focus on vanB-type E. faecium. Dalbavancin susceptibility was determined for 25 van-negative, 50 vanA-positive, and 101 vanB-positive clinical E. faecium isolates (typed by cgMLST). Epidemiological Cut-Off Values (ECOFFs) were determined using ECOFFinder. For vanB-type E. faecium isolates, dalbavancin MICs were similar to those of vancomycin-susceptible isolates reaching values no higher than 0.125 mg/L. ECOFFs for van-negative and vanB-positive isolates were 0.5 mg/l and 0.25 mg/L respectively. In contrast, E. faecium possessing vanA predominantly showed dalbavancin MICs >8 mg/L, therefore preventing the determination of an ECOFF. We demonstrated the potent in vitro activity of dalbavancin against vancomycin-susceptible and vanB-type E. faecium. On the basis of the observed wildtype distribution, a dalbavancin MIC of 0.25 mg/L can be suggested as a tentative ECOFF for E. faecium.

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In Vitro Activities of Fluoroquinolones against the Spirochete Borrelia burgdorferi

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.45.9.2486-2494.2001 ◽

2001 ◽

Vol 45 (9) ◽

pp. 2486-2494 ◽

Cited By ~ 19

Author(s):

Peter Kraiczy ◽

Judith Weigand ◽

Thomas A. Wichelhaus ◽

Peter Heisig ◽

Herbert Backes ◽

...

Keyword(s):

Borrelia Burgdorferi ◽

Rank Order ◽

Dark Field ◽

Vitro Activity ◽

In Vitro Activity ◽

Conventional Culture ◽

Microdilution Method ◽

Time Kill

ABSTRACT Little is known to date about the in vitro activity of fluoroquinolones against Borrelia species. Our study aimed at determining the in vitro activities of 15 quinolones against nine isolates of the Borrelia burgdorferi sensu lato complex in addition to one Borrelia valaisiana and oneBorrelia bissettii tick isolate. For the determination of MICs, a standardized colorimetric microdilution method was applied. Determination of minimal borreliacidal concentrations providing 100% killing of the final inoculum (MBCs) after 72 h and time-kill experiments were performed by conventional culture in Barbour-Stoenner-Kelly medium in combination with dark-field microscopy. The rank order of potency on a microgram-per-milliliter basis for the substances with in vitro activity against B. burgdorferi was gemifloxacin (MIC at which 90% of the isolates tested are inhibited [MIC90], 0.12 μg/ml) > sitafloxacin (MIC90, 0.5 μg/ml), grepafloxacin (MIC90, 0.5 μg/ml) > gatifloxacin (MIC90, 1 μg/ml), sparfloxacin (MIC90, 1 μg/ml), trovafloxacin (MIC90, 1 μg/ml) > moxifloxacin (MIC90, 2 μg/ml), ciprofloxacin (MIC90, 2 μg/ml) > levofloxacin (MIC90, 4 μg/ml) > ofloxacin (MIC90, 8 μg/ml), norfloxacin (MIC90, 8 μg/ml) > fleroxacin (MIC90, >16 μg/ml), and pefloxacin (MIC90, 32 μg/ml) > nalidixic acid (MIC90, 256 μg/ml). After 72 h of exposure, gemifloxacin was borreliacidal (100% killing) against the isolates investigated at a median MBC of 4 μg/ml. In the other compounds tested, median MBCs were higher (≥8 μg/ml). Results of electron microscopy and time-kill studies clearly support an in vitro activity of some fluoroquinolones against borreliae. Our study demonstrates for the first time the enhanced in vitro effectiveness of some of the recently introduced 4-quinolones against B. burgdorferi.

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