Peptides with higher therapeutic indexes (7a, 12a, 7b, 15c, 16c, and 20c) were selected for broad-spectrum antimicrobial activity. The extended-spectrum screening experiments were conducted by JMI Laboratories (North Liberty, IA) and subcontracted by the National Institute of Health. The activity results are illustrated in Table . Except 16c, all selected peptides showed good activity against methicillin-susceptible (MSSA) (ATCC 29213), methicillinresistant (MRSA) (1193193), and multi-drug resistant (MDR) S. aureus (1195201) with MICs of 4 µg/mL. Noticeably, while all peptides displayed a comparable activity to classical antibiotic meropenem, they demonstrated 4-to 8-fold higher activity against MRSA and MDR S. aureus compared to cefepime (Table ). Except for 7b against A. baumannii (1188767), all selected cyclic peptides showed moderate activity (MIC = 8-32 µg/mL) against all the tested strains of E. coli and A. baumannii. Consistent with the activity data mentioned above (Figure ), the peptides showed lower potency against all tested strains of P. aeruginosa and K. pneumoniae compared to E. coli and A. baumannii. Overall, these activity results closely align with the activity data obtained in our in-house conducted activity.