Introduction: Tazobactam-piperacillin (TZP) is a mixture of a broad-spectrum penicillin and an irreversible β-lactamase inhibitor. TZP is effective against Gram-negative bacteria that produce extended-spectrum β-lactamases, and it is used as a first-line or second-line drug to treat serious infections.
Methods: This study identified three TZP-resistant and two TZP-intermediate strains among 514 clinical isolates of Escherichia coli.
Results: These five isolates possessed one or more β-lactamase genes, blaTEM-1, blaCTX-M-2, blaCTX-M-14, and/or blaCMY-8. The expression levels of β-lactamase genes and acrAB genes in the strains were examined by using real-time reverse transcription PCR. The total enzymatic piperacillin-degrading activity in cells was determined. Two TZP-resistance mechanisms were identified: hyperproduction of TEM-1 in the two resistant strains; and simultaneous high production of β-lactamase and efflux pump AcrAB in the two TZP-intermediate isolates. The latter are an international high-risk clone O25b:H4-ST131-H30R.
Conclusion: TZP resistance is still rare in clinical isolates of E. coli. However, resistance can develop on high production and/or combinations of known antimicrobial resistance mechanisms in different ways.
Keywords: AcrAB; Antimicrobial resistance; Extended-spectrum β-lactamase; Tazobactam-piperacillin.
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