In vitro susceptibility of ceftolozane/tazobactam against typhoidal, non-typhoidal and extended spectrum β-lactamase-producing Salmonella.

Both typhoidal and non-typhoidal salmonellae are included in the top 15 drug-resistant threats described by the Center for Disease Control and Prevention of the United States. There is an urgent need to look for alternative antibiotics for the treatment of Salmonella infections. We examined the in vitro susceptibilities of ceftolozane/tazobactam and six other antibiotics on typhoidal and non-typhoidal salmonellae, including isolates that are extended-spectrum β-lactamase (ESBL)-positive, using the broth microdilution test. Of the 313 (52 typhoidal and 261 non-typhoidal) Salmonella isolates tested, 98.7% were susceptible to ceftolozane/tazobactam. Based on the overall MIC50/90 values, Salmonella isolates were more susceptible to ceftolozane/tazobactam (0.25/0.5 mg/L) compared to all other comparator agents: ampicillin (≥64/≥64 mg/L), levofloxacin (0.25/1 mg/L), azithromycin (4/16 mg/L), ceftriaxone (≤0.25/4 mg/L), chloramphenicol (8/≥64 mg/L) and trimethoprim/sulfamethoxazole (1/≥8 mg/L). When comparing the activity of the antimicrobial agents against non-typhoidal Salmonella isolates according to their serogroup, ceftolozane/tazobactam had the highest activity (100%) against Salmonella serogroups D, G, I and Q isolates, whereas the lowest activity (85.7%) was observed against serogroup E isolates. All the 10 ESBL-producing Salmonella (all non-typhoidal) isolates, of which 8 were CTX-M-55-producers and 2 were CTX-M-65-producers, were sensitive to ceftolozane/tazobactam albeit with a higher MIC50/90 value (1/2 mg/L) than non-ESBL-producers (0.25/0.5 mg/L). In summary, our data indicate that ceftolozane/tazobactam is active against most strains of both typhoidal and non-typhoidal salmonellae and also active against ESBL-producing salmonellae.