Efficacy of Aminomethyl Spectinomycins against Complex Upper Respiratory Tract Bacterial Infections

Abstract

The most frequent ailment for which antibiotics are prescribed is otitis media (ear infections), which is most commonly caused by Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae Treatment of otitis media is complicated by the fact that the bacteria in the middle ear typically form biofilms, which can be recalcitrant to antibiotic treatment. Furthermore, bacterial respiratory infections can be greatly exacerbated by viral coinfection, which is particularly evidenced by the synergy between influenza and S. pneumoniae In this study, we sought to ascertain the in vivo efficacy of aminomethyl spectinomycin lead 1950, an effective antibacterial agent both in vitro and in vivo against Streptococcus pneumoniae in the context of complex respiratory infections and acute otitis media. A single dose of 1950 significantly reduced bacterial burden in the respiratory tract for all three pathogens, even when species were present in a coinfection model. Additionally, a single dose of 1950 effectively reduced pneumococcal acute otitis media from the middle ear. The agent 1950 also proved efficacious in the context of influenza-pneumococcal super infection. These data further support the development of this family of compounds as potential therapeutic agents against the common causes of complex upper respiratory tract infections and acute otitis media.

Keywords: Haemophilus influenzae; Streptococcus pneumoniae; otitis media.

FIG 1

Aminomethyl spectinomycin effective for treatment of acute otitis media. Mice infected with S. pneumoniae (A) or H. influenzae (B) and subsequently treated with a single dose of vehicle, ampicillin, or 1950. Bacterial burden in the ears was measured by CFU enumeration at 24 h postchallenge. Groups were compared by Mann-Whitney U testing. *, indicates P < 0.05 compared with vehicle control group for (A) and (B). Each data point represents an individual ear. Dotted line indicates the limit of detection. (C) Structure of aminomethyl spectinomycin analog 1950. (D) The zone of inhibition was compared for each species between spectinomycin and 1950 by Mann-Whitney U testing, with the asterisk (*) indicating P < 0.05.

FIG 2

Bioluminescent images of pneumococcal acute otitis media. Representative images from vehicle control, ampicillin-treated, and 1950-treated groups demonstrate a marked reduction in luminescent signal detected from the ears. Images were taken at 24 h postchallenge immediately prior to tissue harvest. Scale bar indicates luminescent intensity.

FIG 3

Efficacy of 1950 against etiological agents of community-acquired pneumonia. Bacterial burden in the lungs following treatment with vehicle, ampicillin, or 1950 in mice infected with S. pneumoniae (A), H. influenzae (B), or M. catarrhalis (C). Bacterial burden in the lungs was measured by CFU enumeration. The strains of H. influenzae and M. catarrhalis used in these challenges are resistant to ampicillin. Groups were compared by Mann-Whitney U testing. *, indicates P < 0.05 compared with vehicle control group. Each data point represents titers from one animal. Dotted line indicates the limit of detection.

FIG 4

The 1950 treatment reduces the extent of alveolar involvement during pneumococcal pneumonia. Representative lung sections subjected hematoxylin and eosin staining of vehicle (A, B), ampicillin (C, D), and 1950 (E, F) at 24 h postchallenge. Scale bar for ×4 magnification in (A, C, and E) is 1 mm and indicated in (A). Scale bar for ×10 magnification in (B, D, and F) is 200 μm and indicated in (A). Pathologist scores for (G) indicated 1950 significantly reduced the extent of alveolar involvement in lung inflammation in a manner indistinguishable from ampicillin treatment. No differences were observed at this time point in terms of severity of perivascular inflammation and edema (H). Groups were compared by Mann-Whitney U testing. *, indicates P < 0.05 compared with vehicle control group. Each data point represents scores from one animal.

FIG 5

Efficacy of 1950 in mixed bacterial infections. Bacterial burden from S. pneumoniae/H. influenzae coinfected lungs (A, B) and S. pneumoniae/M. catarrhalis coinfected infected lungs (C, D) following treatment with vehicle, ampicillin, or 1950. Bacterial burden in the lungs was measured by CFU enumeration. Groups were compared by Mann-Whitney U testing. *, indicates P < 0.05 compared with vehicle control group. Each data point represents 1 animal. Dotted line indicates the limit of detection.

FIG 6

Efficacy of 1950 in an influenza-pneumococcal superinfection model. Murine survival following previous infection with influenza and subsequent S. pneumoniae challenge (A). Mice were treated starting 6 h post-bacterial challenge and twice daily thereafter, with data representing overall survival time. Bacterial burden in bloodstream 24 h postchallenge (B). Pathology scores of levels of consolidation and alveolar neutrophil infiltrate in lung tissue 24 h postchallenge (C). Representative histopathology images of vehicle (D), ampicillin treated (E), and 1950 treated (F) at 24 h following bacterial challenge. Scale bar represents 200 μm and indicated in (D). *, indicates P < 0.05 by Mantel log-rank test compared with vehicle; **, indicates P < 0.05 by Mantel log-rank test compared with ampicillin.