A male and female gametocyte functional viability assay to identify biologically relevant malaria transmission-blocking drugs.

Malaria elimination will require interventions that prevent parasite transmission from the human host to the mosquito. Experimentally, this is usually determined by the expensive and laborious Plasmodium falciparum standard membrane feeding assay (PfSMFA), which has limited utility for high-throughput drug screening. In response, we developed the P. falciparum dual gamete formation assay (PfDGFA), which faithfully simulates the initial stages of the PfSMFA in vitro. It utilizes a dual readout that individually and simultaneously reports on the functional viability of male and female mature stage V gametocytes. To validate, we screen the Medicines for Malaria Venture (MMV) Malaria Box library with the PfDGFA. Unique to this assay, we find compounds that target male gametocytes only and also compounds with reversible and irreversible activity. Most importantly, we show that compound activity in the PfDGFA accurately predicts activity in PfSMFAs, which validates and supports its adoption into the transmission-stage screening pipeline.

Comparative assessment of transmission-blocking vaccine candidates against Plasmodium falciparum.

Malaria transmission-blocking vaccines (TBVs) target the development of Plasmodium parasites within the mosquito, with the aim of preventing malaria transmission from one infected individual to another. Different vaccine platforms, mainly protein-in-adjuvant formulations delivering the leading candidate antigens, have been developed independently and have reported varied transmission-blocking activities (TBA). Here, recombinant chimpanzee adenovirus 63, ChAd63, and modified vaccinia virus Ankara, MVA, expressing AgAPN1, Pfs230-C, Pfs25, and Pfs48/45 were generated. Antibody responses primed individually against all antigens by ChAd63 immunization in BALB/c mice were boosted by the administration of MVA expressing the same antigen. These antibodies exhibited a hierarchy of inhibitory activity against the NF54 laboratory strain of P. falciparum in Anopheles stephensi mosquitoes using the standard membrane feeding assay (SMFA), with anti-Pfs230-C and anti-Pfs25 antibodies giving complete blockade. The observed rank order of inhibition was replicated against P. falciparum African field isolates in A. gambiae in direct membrane feeding assays (DMFA). TBA achieved was IgG concentration dependent. This study provides the first head-to-head comparative analysis of leading antigens using two different parasite sources in two different vector species, and can be used to guide selection of TBVs for future clinical development using the viral-vectored delivery platform.

Austrian national survey of prevalence of antimicrobial resistance among clinical isolates of Streptococcus pneumoniae 1994-96.

The antimicrobial susceptibilities of 1385 clinical isolates of Streptococcus pneumoniae obtained from 25 laboratories across Austria between December 1994 and January 1996 were tested. Minimal inhibitory concentration (MIC) values were determined in tests with penicillin, amoxycillin, amoxycillin/clavulanate, ceftriaxone, cefodizime, cefpirome, cefotaxime, cefpodoxime, cefadroxile, azithromycin, clarithromycin, josamycin and roxithromycin by the agar-dilution method. A total of 40 isolates (2.9%) demonstrated intermediate resistance (MIC 0.125-1 microg/ml) and 28 isolates (2.0%) had high-level resistance (MIC > or = 2 microg/ml) to penicillin. Excepting cefadroxil, with an MIC90 of 2 microg/ml, all other tested beta-lactams had MIC90s of 0.03-0.06 microg/ml. Penicillin-resistant strains were much more likely to be also resistant to the other beta-lactams. The macrolides proved to be very active compounds against pneumococci with MIC90s of 0.06 microg/ml (clarithromycin) and 0.25 microg/ml (all other macrolides). Regional differences within Austria with regard to antimicrobial resistance were not observed.

Comparative susceptibility to penicillin and quinolones of 1385 Streptococcus pneumoniae isolates. Austrian Bacterial Surveillance Network.

Antibiotic resistance among Streptococcus pneumoniae isolates has spread rapidly throughout the world since the first description of a strain with diminished susceptibility to penicillin in Australia in 1967. A total of 1385 strains of S. pneumoniae, collected in several centres throughout Austria, were assessed for their sensitivity to moxifloxacin, trovafloxacin, ciprofloxacin, ofloxacin, levofloxacin and lomefloxacin. The MICs were determined using the agar dilution method, according to NCCLS guidelines. Both moxlfloxacin and trovafloxacin showed good anti-pneumococcal activity in terms of MIC50 (both 0.125 mg/L) and MIC90 (both 0.25 mg/L). Less active, but with similar activity to each other, were ciprofloxacin and levofloxacin, each with an MIC50 of 1 mg/L and an MIC90 of 2 mg/L. Ofloxacin showed only moderate activity (MIC50, 1 mg/L; MIC90, 2 mg/L) and lomefloxacin was the least active compound (MIC50, 4 mg/L; MIC90, 8 mg/L). Both moxifloxacin and trovafloxacin at a concentration of < or = 0.5 mg/L inhibited all of the S. pneumoniae strains tested.