Enhanced In Vivo Activity of Cefditoren in Pre-Immunized Mice against Penicillin-Resistant S. pneumoniae (Serotypes 6B, 19F and 23F) in a Sepsis Model

Abstract

BackgroundSpecific antibodies are likely to be present before S. pneumoniae infection. We explored cefditoren (CDN) total and free values of serum concentrations exceeding the MIC (t>MIC) related to efficacy in a mice sepsis model, and the effect of specific gammaglobulins on in-vitro phagocytosis and in-vivo efficacy.Methodology/Principal FindingsWe used three pneumococcal isolates (serotype, MIC of CDN): Strain 1 (6B, 1 µg/ml), Strain 2 (19F, 2 µg/ml) and Strain 3 (23F, 4 µg/ml). Hyperimmune serum (HS) was obtained from mice immunized with heat-inactivated strains. In-vitro, phagocytosis by HS diluted 1/10 in presence/absence of sub-inhibitory concentrations was measured by flow cytometry including fluorescent bacteria and a neutrophil cell line. In-vivo dose-ranging experiments with HS (dilutions 1/2–1/16) and CDN (6.25 mg/kg–100 mg/kg tid for 48 h) were performed to determine the minimal protective dilution/dose (highest survival) and the non-protective highest dilution/dose (highest mortality: HS-np dilution and CDN-np dose) over 7 days. Efficacy of CDN-np in animals pre-immunized with HS-np (combined strategy) was explored and blood bacterial clearance determined. The CDN measured protein binding was 86.9%. In-vitro, CDN significantly increased phagocytosis (vs. HS 1/10). In non pre-immunized animals, t>MIC values for CDN of ≈35% (total) and ≈19% (free) were associated with 100% survival. Significant differences in survival were found between HS-np alone (≤20%) or CDN-np alone (≤20%) vs. the combined strategy (90%, 60% and 60% for Stains 1, 2 and 3), with t>MIC (total/free) of 22.8%/14.3%, 26.8%/16.0%, and 22.4%/12.7% for Strains 1, 2 and 3, respectively. Prior to the second dose (8 h), median bacterial counts were significantly lower in animals surviving vs. dead at day 7.Conclusions/SignificanceIn mice (CDN protein binding similar to humans) total t>MIC values of ≈35% (≈19% free) were efficacious, with a decrease in the required values in pre-immunized animals. This reinforces that immunoprotection to overcome resistance may provide lifesaving strategies.

Macrolides and β-Lactam Antibiotics Enhance C3b Deposition on the Surface of Multidrug-Resistant Streptococcus pneumoniae Strains by a LytA Autolysin-Dependent Mechanism

“…The results of the present study confirm that C3b deposition on the bacterial surface was enhanced in the presence of specific antibodies and subinhibitory concentrations of either ␤-lactams, such as AMX, CDN, and CTX, or macrolides, such as ERY, AZM, and MDM. These results support previous findings using AMX, CTX, or CDN, demonstrating that immunization against S. pneumoniae increases the efficacy of the antibiotic treatment with ␤-lactams by enhancing the ability of the host immune system to efficiently recognize and destroy pneumococcal resistant strains (4,5,26,27). However, sub-MIC levels of LVX did not affect opsonization by C3b in any of the investigated strains, explaining why the treatment with subtherapeutic doses of LVX in mice previously immunized against a highly encapsulated serotype 6B S. pneumoniae strain did not increase survival rates (20).…”

“…Sera containing specific antibodies against S. pneumoniae were obtained by immunizing groups of 5 BALB/c mice (up to 5 weeks old) with a heat-inactivated suspension of the different strains, as previously described (4,5). The titers of specific IgG antibodies against strains 48, 69, and 1515/97 were 251 mg ml Ϫ1 , 371 mg ml Ϫ1 , and 1,056 mg ml Ϫ1 , respectively (4).…”

“…Using mice infected with a pneumococcal resistant strain and treated with subtherapeutic doses of ␤-lactam antibiotics, we previously found that bacterial clearance and survival were increased in mice immunized against S. pneumoniae, suggesting a synergistic effect between antimicrobial chemotherapy and the acquired immune response (5,28). Moreover, we have recently demonstrated that the efficiency of either human or mouse neutrophils in phagocytosing resistant strains of S. pneumoniae is markedly improved in the presence of serum containing specific antibodies and subinhibitory concentrations of cephalosporins, demonstrating cooperative roles of the immune system and antibiotics (4). However, whether this synergistic effect is partially due to increased recognition of S. pneumoniae by the complement system and whether it might be extended to other groups of antibiotics are unknown.…”

Cefditoren and Ceftriaxone Enhance Complement-Mediated Immunity in the Presence of Specific Antibodies against Antibiotic-Resistant Pneumococcal Strains

“…The impaired released of this cell wall component in resistant strains might be involved in the reduced immunogenicity of capsular serotypes usually associated with PEN-resistance [24], [25]. In this sense, HS against the serotype 6B strain (that had the lowest MIC to CDN and CRO among the three strains used) contained the higher antibody titer compared to HS against the 19F and 23F strains [15].…”

Cefditoren in upper and lower community-acquired respiratory tract infections

“…Considering that protein binding rates in humans and mice are equal for cefditoren, the extrapolation to humans of pharmacodynamic data obtained in animal models acquires special interest. A pneumococcal sepsis model in mice infected by strains with exceptionally high cefditoren MIC (1–2 μg/mL) showed that cefditoren t > MIC of ≈35% (free t > MIC of ≈20%) produced 100% survival in contrast to placebo (0% survival) 48. Free t > MIC of ≈20% was also related to >99.9% reduction in bacterial load (of 2 isolates serotypes 6B and 15A with MIC = 0.25 μg/mL) in an in vitro pharmacodynamic simulation with physiological albumin concentrations and 86% protein binding rate in the device 49.…”