Activity of ceftolozane-tazobactam and comparators against gram-negative bacilli: Results from the study for monitoring antimicrobial resistance trends (SMART – Brazil; 2016–2017)

Multi-drug resistant Gram-negative bacilli (GNB) have been reported as cause of serious hospital-acquired infections worldwide. The aim of this study was to investigate the in vitro activity of ceftolozane-tazobactam compared to other agents against GNB isolated from patients admitted to Brazilian medical centers between the years 2016 and 2017. Presence of β-lactamase encoding genes was also evaluated. METHODS: Antimicrobial susceptibility testing of GNB isolated from intra-abdominal (IAI), respiratory (RTI), and urinary tract infections (UTI) was performed according to ISO 227-1 guidelines and interpreted following CLSI and BrCAST/EUCAST guidelines. Qualifying Enterobacteriaceae isolates were screened for the presence of β-lactamase genes by PCR followed by DNA sequencing. RESULTS: 1748 GNB collected from UTI (45.2%), IAI (25.7%) and RTI (29.1%) were evaluated. Ceftolozane-tazobactam remained highly active (94.7%) against E. coli isolates. Among K. pneumoniae, susceptibility rates were 85.9% and 85.4% for amikacin and colistin, whereas ceftolozane-tazobactam (44.1% susceptible) and carbapenems (55.2-62.2% susceptible) showed poor activity due to bla(KPC-2). Against E. cloacae amikacin, imipenem, and meropenem retained good activity (>90%). Ceftolozane-tazobactam was the most potent β-lactam agent tested against P. aeruginosa (90.9% susceptible), including ceftazidime and imipenem resistant isolates. β-lactamase encoding genes testing was carried out in 433 isolates. bla(CTX-M) variants were predominant in E. coli, P. mirabilis and E. cloacae. Among the K. pneumoniae molecularly tested, most carried bla(KPC) (68.5%), with all harboring bla(KPC-2,) except two isolates carrying bla(KPC-3) or bla(KPC-30). ESBL encoding genes, mainly CTX-M family, were frequently detected in K. pneumoniae, plasmid-mediated AmpC were rare. A variety of PDC encoding genes were detected in P. aeruginosa isolates with five isolates harboring MBL and one KPC encoding genes. CONCLUSION: Ceftolozane-tazobactam was very active against E. coli, P. mirabilis and P. aeruginosa isolates and could constitute an excellent therapeutic option including for those isolates resistant to extended-spectrum cephalosporins and carbapenems but not producers of carbapenemases.