In vitro evaluation of β-lactams and non-β-lactams against β-lactamase producing Gram-negative clinical isolates

Abstract

Background: Antimicrobial resistance mechanisms including the beta-lactamases (βLs) such as extended-spectrum beta-lactamases (ESBLs), AmpC βLs, metallo-beta-lactamases (MBLs) and inhibitor-resistant TEM βLs (IRTs) are continuously developing, and infections due to such resistance bacteria are left with limited treatment options. Aims: This study was conducted to evaluate the activity of different beta-lactams and non-beta-lactam antibiotics against βL producing Gram-negative clinical isolates. Materials and Methods: Isolation, identification of different βLs and antibiotic susceptibility testing in 350 non-repeat, consecutive, Gram-negative clinical isolates were performed using the automated Vitek 2 system (bioMe΄rieux, Marcy l'Etoile, France). Eighteen antimicrobials were included in the AST N-280 panel of Vitek 2. Phenotypic disk diffusion methods were also employed for the detection of various βLs. Result: Both the automated and phenotypic methods identified 34% (119/350) βLs of which 18.29%, 6%, 1.14%, 2.86%, 3.42%, and 1.43% were ESBLs, AmpC βLs, MBLs, ESBL with AmpC, ESBL with MBL and AmpC with MBL, respectively. IRTS were detected in 3 (0.86%) isolates. Among the β-lactams and β-lactams with βL inhibitors, the least resistant antimicrobials against βLs were respectively cefepime (73%) and pipercillin/tazobactam (45.5%). Regarding the non-beta-lactams, maximum sensitivity was observed with colistin (96.4%), followed by tigecycline (94%), meropenem (87.4%), amikacin (86.6%) and ertapenem or imipenem (82.4%). The activity of nitrofurantoin was relatively good with a sensitivity of 61.4%. Conclusion: In our setting, colistin, tigecycline and meropenem turned out to be the best available antimicrobials to tackle the infections caused by βLs. Nitrofurantoin could be used in the management of urinary tract infection caused by multidrug-resistant isolates if its activity is high enough.