Sequence specificity defines the effectiveness of PPMOs targeting Pseudomonas aeruginosa.

Development of new therapeutics against antibiotic resistant pathogenic bacteria is recognized as a priority across the globe. We have reported using peptide-conjugated phosphorodiamidate morpholino oligomers (PPMOs) as species-specific antibiotics. The oligo sequences, 11 bases are designed to be complementary to specific essential genes near the Shine-Dalgarno site and inhibit translation. Here, we analyzed target specificity and the impact of genetic mutations on lead PPMOs targeting the rpsJ or acpP gene of Pseudomonas aeruginosa. Mutants in P. aeruginosa PAO1 were generated with four, two, or one base-pair mutations within the 11-base target sequence of the rpsJ gene. All mutants exhibited increased MICs compared to wild-type PAO1 when treated with the RpsJ PPMO, and the increase in the MICs was proportional to the number of base-pair mutations. Among single base-pair mutants, mutations in the middle of the sequence were more impactful than mutations in 5' or 3' end of the sequence. The increased MICs shown by the rpsJ mutants could be reversed by PPMOs designed to target the mutated rpsJ sequence. BALB/c mice infected intratracheally with mutants demonstrated increased lung burden when treated with RpsJ PPMO compared to wild-type PAO1-infected mice treated with RpsJ PPMO. Treating mice with a PPMOs designed to specifically target the mutant sequence was more effective against these mutant strains. These experiments confirm target specificity of two lead P. aeruginosa PPMOs and illustrate one potential mechanism of resistance that could emerge from an antisense approach.

Prevalence of antibiotic resistance among Egyptian Salmonella typhi strains.

This report describes the resistance of 537 Salmonella typhi isolates identified in Egypt between 1990-1994. Results indicated a high isolation rate for multiple resistant S. typhi (> 71% of isolates collected in 1992-93), particularly to the three standard drug regimens of the clinically relevant antibiotics; ampicillin, chloramphenicol and trimethoprim-sulfamethoxazole. This adds to the complexity and difficulty of treating infections caused by these organisms. Resistance of S. typhi was associated with a transferable 120 MD plasmid. The organism was sensitive to amikacin, aztreonam, cephalothin, ceftriaxone, gentamicin and nalidixic acid, suggesting the use of aztreonam and ceftriaxone as alternative therapeutic drugs for the treatment of multidrug-resistant S. typhi. These results may provide a clinically useful evaluation of the spread and acquisition of resistance among S. typhi strains in Egypt.