Antimicrobial Susceptibility Studies
Characterization of variables that may influence ozenoxacin in susceptibility testing, including MIC and MBC values,☆☆

https://doi.org/10.1016/j.diagmicrobio.2013.11.010Get rights and content

Abstract

Ozenoxacin is a new des-fluoro-(6)-quinolone active against pathogens involved in skin and skin structure infections, including Gram-positives resistant to fluoroquinolones. The in vitro bacteriostatic and bactericidal activity of ozenoxacin, ciprofloxacin, and levofloxacin was studied against 40 clinical isolates and 16 ATCC quality control strains under different test conditions, including cation supplementation, pH, inoculum size, inoculum preparation, incubation time, human serum, and CO2 incubation. The activity of ozenoxacin was unaffected by cation test medium supplementation, inoculum preparation, incubation time, and the increasing CO2 environment. On the contrary, ozenoxacin activity decreased by high inoculum (107 CFU/mL), increased presence of human serum in the medium, and increased pH. The last effect was different for ciprofloxacin and levofloxacin, which decreased activity when pH decreased. The bactericidal mode of action of ozenoxacin and control drugs was consistently maintained (MBC/MIC ratios ≤4) in spite of variations of their activity under different test conditions.

Introduction

Ozenoxacin, a novel non-fluorinated quinolone antibacterial agent (Fig. 1), is currently in late stage phase III trials for the topical treatment of impetigo. It has shown an excellent in vitro activity against relevant Gram-positive cocci, such as Staphylococcus aureus and Streptococcus pyogenes, causing skin and soft tissue infections (SSTI), including clinical isolates with resistance to levofloxacin or with mutations in gyrA and/or parC genes, which confer resistance to fluoroquinolones (Morrissey et al., 2012, López et al., 2013). A similar potency to retapamulin has also been demonstrated, and it is more potent than other commonly prescribed topical agents such as fusidic acid or mupirocin. Moreover, it is more potent than levofloxacin (Morrissey et al., 2012). Ozenoxacin could represent a first-in-class treatment option for a variety of infectious skin conditions, including those due to S. pyogenes and S. aureus, the most frequent pathological causes of impetigo (Drucker, 2012).

In this study, we compared the in vitro bacteriostatic and bactericidal activity of ozenoxacin with the activities of ciprofloxacin and levofloxacin and determined the effects of different testing parameters on their MICs and MBCs. Testing parameters were selected according to M23-A3 document guidelines (CLSI, 2003) that consider the study of procedural variations known to impact antimicrobial susceptibility testing of other structurally established antimicrobial agents. The activity of quinolones has been shown to be influenced by cation supplementation and mainly by pH, including pH changes that occur during CO2 incubation (Bolmstrom and Karlsson, 2002, Smith et al., 1988). We focused our study on the effect of these 2 parameters. Additionally, the effect of inoculum size, inoculum preparation, incubation time, human serum, and incubation with CO2 were also investigated.

Section snippets

Bacterial strains

Sixteen ATCC quality control (QC) strains and 40 non-duplicated clinical isolates from blood or SSTI collected at Ramón y Cajal University Hospital during 2010 were tested. ATCC strains included S. aureus ATCC 29213, S. aureus ATCC 33591, S. aureus ATCC 700789, Staphylococcus epidermidis ATCC 12228, Staphylococcus haemolyticus ATCC 29970, Enterococcus faecalis ATCC 29212, E. faecalis ATCC 51299, S. pyogenes ATCC 19615, Escherichia coli ATCC 25922, E. coli ATCC 35218, Klebsiella pneumoniae ATCC

Results and discussion

The ozenoxacin, ciprofloxacin, and levofloxacin MIC range, MIC50, and MIC90 values obtained by the broth microdilution method for the 40 clinical isolates under standard CLSI test conditions are summarized in Table 1. We mainly focused on the main pathogens associated with skin infection, but a representative low number of some species such as P. aeruginosa or Enterococcus spp. has also been included. Despite this limitation, we observed differences not only in the ozenoxacin activity among

References (24)

  • R. Girardello et al.

    Cation concentration variability of four distinct Mueller-Hinton agar brands influences polymyxin B susceptibility results

    J Clin Microbiol

    (2012)
  • P.G. Higgins et al.

    Activity of the investigational fluoroquinolone finafloxacin against ciprofloxacin-sensitive and -resistant Acinetobacter baumannii isolates

    Antimicrob Agents Chemother

    (2010)
  • Cited by (40)

    • Development of chloramphenicol wound dressing protein-based microparticles in chitosan hydrogel system for improved effectiveness of dermal wound therapy

      2022, Biomaterials Advances
      Citation Excerpt :

      The ratio of MBC to MIC is <4. A ratio of 4 indicates bactericidal activity, and a ratio > 4 shows bacteriostatic activity [53]. Accordingly, a higher concentration of CPL MPs was required to kill the SA.

    • Thermosensitive and mucoadhesive in situ ocular gel for effective local delivery and antifungal activity of itraconazole nanocrystal in the treatment of fungal keratitis

      2021, International Journal of Pharmaceutics
      Citation Excerpt :

      As for the MFC, all the obtained values are higher compared to the respective MIC. However, it is important to note that in all cases, the ratio between MFC and MIC was < 4, which suggests that ITZ exhibited fungicidal activity (Tato et al., 2014). Overall, these findings suggest that solubilization plays an important role in the antifungal activity of ITZ.

    • Comparative in vitro susceptibility of a novel fluoroquinolone antibiotic candidate WFQ-228, levofloxacin, and moxifloxacin against Mycobacterium tuberculosis

      2021, International Journal of Infectious Diseases
      Citation Excerpt :

      According to the ratio MBC/MIC, we appreciated antibacterial activity. The effect was considered to be bactericidal if the ratio MBC/MIC was no more than four, but the effect was defined as bacteriostatic if the ratio MBC/MIC was higher than four (Tato et al., 2014). A Kruskal–Wallis test was performed to assess whether varying resistance levels are associated with the different gyrA mutations.

    • Selective delivery of silver nanoparticles for improved treatment of biofilm skin infection using bacteria-responsive microparticles loaded into dissolving microneedles

      2021, Materials Science and Engineering C
      Citation Excerpt :

      The ratio of MBC to MIC was less than 4, indicating that the silver NPs formed in this study possessed bactericidal ability. It has been reported that a ratio of >4 indicates bacteriostatic activity and a ratio of ≤4 indicates bactericidal activity [56]. The mechanism of action of silver NPs as antibacterial agents has been proposed to be mainly due to their ability to disturb membrane permeability.

    View all citing articles on Scopus

    Funding: The study was performed with a research grant from Ferrer International S.A. (Barcelona, Spain) and partially supported by the Ministerio de Sanidad, Instituto de Salud Carlos III, Spanish Network for Research in Infectious Diseases (REIPI RD12/0015).

    ☆☆

    Conflict of interest: Fernando Garcia-Alonso and Domingo Gargallo-Viola are employed by Ferrer Laboratories. Other authors declare no conflicts of interest.

    View full text