WCK 5222 (Cefepime-Zidebactam) Antimicrobial Activity against Clinical Isolates of Gram-Negative Bacteria Collected Worldwide in 2015

WCK 5222 consists of cefepime combined with zidebactam, a bicyclo-acyl hydrazide beta-lactam enhancer antibiotic with a dual action involving binding to Gram-negative bacterial PBP2 and beta-lactamase inhibition. We evaluated the in vitro activity of cefepime-zidebactam against 7,876 contemporary (2015) clinical isolates of Enterobacteriaceae (n = 5,946), Pseudomonas aeruginosa (n = 1,291), and Acinetobacter spp. (n = 639) from the United States (n = 2,919), Europe (n = 3,004), the Asia-Pacific (n = 1,370), and Latin America (n = 583). The isolates were tested by a reference broth microdilution method for susceptibility against cefepime-zidebactam (1: 1 and 2: 1 ratios) and comparator agents. Cefepimezidebactam was the most active compound tested against Enterobacteriaceae (MIC50/90, <= 0.03/0.12 mu g/ml [1: 1] and 0.06/0.25 mu g/ml [2: 1]; 99.9% of isolates were inhibited at <= 4 [1: 1] and <= 8 mu g/ml [2: 1]). Cefepime-zidebactam was active against individual Enterobacteriaceae species (MIC50/90, <= 0.03 to 0.06/<= 0.03 to 0.5 mu g/ml [1: 1]) and retained potent activity against carbapenem-resistant isolates (MIC50/90, 1/4 mu g/ml; 99.3% of isolates were inhibited at <= 8 mu g/ml [1: 1]). Cefepime-zidebactam activity was consistent among geographic regions, and only one isolate showed MIC values of >8 mu g/ml (1: 1). Cefepime-zidebactam was also very active against P. aeruginosa with MIC50/90 values of 1/4 mu g/ml, and 99.5% of isolates were inhibited at <= 8 mu g/ml (1: 1). The MIC values for cefepime-zidebactam at the 1: 1 ratio were generally 2-fold lower than those for cefepime-zidebactam at the 2: 1 ratio (MIC50/90, 2/8 mu g/ml) and zidebactam alone (MIC50/90, 4/8 mu g/ml). Against Acinetobacter spp., cefepime-zidebactam at 1: 1 and 2: 1 ratios (MIC50/90, 16/32 mu g/ml for both) was 4-fold more active than cefepime or ceftazidime. Zidebactam exhibited potent in vitro antimicrobial activity against some organisms. These results support the clinical development of WCK 5222 for the treatment of Gram-negative bacterial infections, including those caused by multidrug-resistant isolates.