Fluoroquinolones have been recognized as promising and potent antibiotics which inhibit DNA gyrase and topoisomerase IV resulting in impeding the supercoiling of the DNA and causing bacterial death (Kocsis et al. 2016). The classic fluoroquinolones possess a considerable antimicrobial activity against Gram-negative bacteria, but their potency against Gram-positive bacteria has been controverted (Park et al. 2006). Therefore, research in the field of fluoroquinolones was oriented towards potentiating the antimicrobial efficacy against Gram-positive cocci, anaerobes and fluoroquinolone-resistant strains by finding substituents with better binding affinity to target enzymes (Kwon et al. 2006). Consequently, a number of new agents have been developed, among which was zabofloxacin (Kocsis et al. 2016). Zabofloxacin is a novel member in the family of fluoroquinolones (Park et al. 2006) with reported activity against methicillin-resistant coagulase-negative staphylococci,
The present study compared the
The specimens were cultured on Mannitol Salt Agar and identified by colony morphology, Gram stain, as well as, by biochemical characteristics, which were estimated by the commercial test system Dry Spot Staphytect Plus (Oxoid, UK). Methicillin resistance was confirmed by cefoxitin and oxacillin disc diffusion methods according to the Clinical and Laboratory Standards Institute guidelines (CLSI 2013).
Antimicrobial agent | MIC (μg/ml) | % Susceptible | % Intermediate | % Resistant | ||
---|---|---|---|---|---|---|
MIC range | MIC50* | MIC90* | ||||
Zabofloxacin | 0.03 – 4 | 0.25 | 2 | 61.2 | 0.9 | 37.9 |
Moxifloxacin | 0.06 – 16 | 0.5 | 8 | 50.9 | 8.6 | 40.5 |
Levofloxacin | 0.125 – 64 | 4 | 16 | 46.5 | 0.9 | 52.6 |
Ciprofloxacin | 0.125 – > 64 | 8 | 64 | 42.3 | 1.7 | 56 |
MIC50 and MIC90, MICs (μg/ml) for 50% and 90% of isolates tested, respectively.
MIC distribution of zabofloxacin, moxifloxacin, levofloxacin and ciprofloxacin determined by broth microdilution method for 116 MRSA isolates.
Antimicrobial agent | MIC (μg/ml) | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
0.03 | 0.06 | 0.125 | 0.25 | 0.5 | 1 | 2 | 4 | 8 | 16 | 32 | 64 | > 64 | |
Zabofloxacin | 10 | 17 | 25 | 12 | 7 | 1 | 12 | 0 | 0 | 0 | 0 | 0 | |
Moxifloxacin | 0 | 2 | 7 | 35 | 15 | 10 | 21 | 13 | 2 | 0 | 0 | 0 | |
Levofloxacin | 0 | 0 | 10 | 33 | 11 | 0 | 1 | 22 | 29 | 0 | 2 | 0 | |
Ciprofloxacin | 0 | 0 | 4 | 18 | 19 | 8 | 2 | 11 | 19 | 14 | 14 | 3a |
Bold figures indicate CLSI breakpoints applied for resistant isolates; zabofloxacin and moxifloxacin: 2 µg/ml, levofloxacin and ciprofloxacin: 4 μg/ml.
MIC for these isolates was greater than or equal to the indicated value.
The bactericidal activity of the fluoroquinolones tested against MRSA was compared by time-kill analysis. As illustrated in figure 1A–D, ZAB and MOX showed a comparable rapid bactericidal activity with a decrease in the viable count by ≥ 3 log10 CFU/ml after 6 h of contact when tested at the concentrations of 2 and 4 MIC against the fluoroquinolone-resistant clinical strain S13 (Fig. 1A and 1B). Against the fluoroquinolone-sensitive strain, S15, complete killing was achieved at 6 h when ZAB was used at a concentration of 2 MIC and at a concentration of 4 MIC when MOX was used (Fig. 2A and 2B). Regrowth of both isolates was completely inhibited by ZAB. Older classes fluoroquinolones, LEV and CIP, exhibited an inferior pattern of bactericidal activity (Fig. 2A–D).
MICs of zabofloxacin, moxifloxacin, levofloxacin and ciprofloxacin for selected 7 clinical MRSA isolates with detected mutations in QRDRs.
Strain No. | MIC (μg/ml) | Detected Mutation in QRDRs | |||||
---|---|---|---|---|---|---|---|
ZABa | MOX | LEV | CIP | ||||
S37 | 4 | 8 | 32 | 64 | S84Lb | S80Fc | P451Sd |
S30 | 2 | 8 | 16 | 64 | S84L | S80F | P451S |
S5 | 2 | 4 | 16 | 64 | S84L | S80F | P451S |
S3 | 2 | 8 | 32 | 64 | S84L | S80F | P451S |
S11 | 0.125 | 0.25 | 8 | 32 | S84L | None | P451S |
S38 | 0.25 | 0.25 | 8 | 16 | None | S80F | None |
S22 | 0.03 | 0.25 | 4 | 8 | None | S80F | None |
ZAB: zabofloxacin, MOX: moxifloxacin, LEV: levofloxacin and CIP: ciprofloxacin.
Serine → Leucine,
Serine → Phenylalanine,
Proline → Serine.
Microorganism inoculum (CFU/mouse) | Antimicrobial agenta | MIC (μg/ml) | Count in dissected lungs log10 (CFU/ml)b | ED50c (mg/kg) |
---|---|---|---|---|
Methicillin-resistant | Zabofloxacin | 0.06 | 3.66 | 29.05 |
Moxifloxacin | 0.06 | 4.31 | 38.69 | |
Levofloxacin | 8 | 4.01 | > 40.00 | |
Ciprofloxacin | 16 | 4.24 | > 40.00 |
Each antimicrobial agent was administrated twice orally at 1 and 4 h post infection.
Count in control group receiving saline was log10 5.5 CFU/ml.
ED50: median effective dose needed to protect 50% of the mice.
The mice group treated with ZAB showed the lowest count in the dissected lungs (3.66 log10 CFU/ml), when compared to other tested fluoroquinolones or to the control receiving saline (Table IV). These results again agreed with the
The histopathological examination of lung tissue sections obtained from CIP-treated mice group showed obvious features of acute bronchopneumonia almost the same as those in the untreated control with marked congestion, oedema, inflammatory infiltration, necrosis with accumulation of necro-inflammatory exudate within the lumen of bronchioles (Fig. 3). The lungs of ZAB-treated mice group revealed very mild congestion and inflammation with scarce inflammatory cells in the interstitial spaces. The mice group treated with MOX and LEV displayed moderate interstitial inflammation, moderate congestion and oedema (Fig. 3). Figure 4 demonstrates a patent alveolus dissected from ZAB-treated mice group, showing clear alveolar spaces and normal vessels and bronchioles lined by a layer of pneumocytes. The degree of congestion, inflammation, oedema and necrosis was scored using a scoring system adapted from Dubin and Kolls (2007) and summarized in Table V. Mice groups infected with MRSA clinical isolate S19 and treated with ZAB at an adjusted dose of 20 mg/kg of body weight/day, displayed best scores with least detected congestion, inflammation, oedema and necrosis followed by MOX, then LEV and finally CIP, all administrated at same dose regimen.
Scoring of detected congestion, inflammation, oedema and necrosis in lung tissues of mice groups infected with MRSA clinical isolate S19 and treated with zabofloxacin, moxifloxacin, levofloxacin and ciprofloxacin at a dose of 20 mg/kg of body weight/day.
Histological observationa | (Score 0–3) | |||
---|---|---|---|---|
ZABb | MOX | LEV | CIP | |
Congestion | 0 (40%) | |||
+1 (20%) | +1 (60%) | +2 (80%) | +3 (60%) | |
+2 (40%) | +2 (40%) | +1 (20%) | +1 (40%) | |
Inflammation | 0 (40%) | |||
+1 (20%) | +1 (60%) | +2 (80%) | +3 (60%) | |
+2 (40%) | +2 (40%) | +1 (20%) | +1 (40%) | |
Edema | 0 (40%) | |||
+1 (20%) | +1 (60%) | +2 (80%) | +3 (60%) | |
+2 (40%) | +2 (40%) | +1 (20%) | +1 (40%) | |
Necrosis | 0 (40%) | |||
+1 (20%) | +1 (60%) | +2 (80%) | +3 (60%) | |
+2 (40%) | +2 (40%) | +1 (20%) | +1 (40%) |
Randomly selected sections blindly scored with a score applied to review of a whole lung section, scored at X10 magnification.
ZAB: Zabofloxacin, MOX: moxifloxacin, LEV: levofloxacin and CIP: ciprofloxacin.
Zabofloxacin is a novel fluoroquinolone recently appro ved and launched in South Korea (Kocsis and Szabo 2016) with reported potent
The MIC results showed that ZAB was 4, 8 and 32-fold more active than MOX, LEV and CIP, respectively (Tables I and II). Among the 116 tested MRSA isolates, 61.2% showed susceptibility to ZAB, the highest rate obtained among comparators. The MIC50 and MIC90 of ZAB were 0.25 and 2 µg/ml, respectively. These values were lower than that reported by Kwon et al. (2006) and Park et al. (2006) for MRSA isolates; probably due to lack of exposure of Egyptian isolates to this new antibiotic. In addition, ZAB exhibited a rapid bactericidal activity with a decrease in the viable count by ≥ 3 log10 CFU/ml after 6 h of contact when tested against a fluoroquinolone-resistant isolate and complete killing when tested against a fluoroquinolone-sensitive strain with inhibition of regrowth in both cases (Fig. 1A–D and 2A–D). Similar rapid bactericidal activity was reported by Park et al. (2016), when ZAB was tested against clinical isolates of
In
The
In conclusion, ZAB, a new fluoroquinolone not yet introduced to the Egyptian market, was proved to possess high