Contribution of β-Lactamases to β-Lactam Susceptibilities of Susceptible and Multidrug-Resistant Mycobacterium tuberculosis Clinical Isolates

The β-lactamases in 154 clinical Mycobacterium tuberculosis strains were studied. Susceptibilities to β-lactam antibiotics, their combination with clavulanate (2:1), and two fluoroquinolones were determined in 24 M. tuberculosis strains susceptible to antimycobacterial drugs and in nine multiresistant strains. All 154 M. tuberculosis isolates showed a single chromosomal β-lactamase pattern (pI 4.9 and 5.1). M. tuberculosis β-lactamase hydrolyzes cefotaxime with a maximum rate of 22.5 ± 2.19 IU/liter (strain 1382). Neither amoxicillin, carbenicillin, cefotaxime, ceftriaxone, nor aztreonam was active alone. Except for aztreonam, β-lactam combinations with clavulanate produced better antimycobacterial activity.