In vitro activity of tedizolid against the Mycobacterium abscessus complex

Infections due to Mycobacterium abscessus carry a poor prognosis since this rapidly growing mycobacterium is intrinsically resistant to most antibiotics. Here, we evaluate the in vitro activity of the new oxazolidinone tedizolid against a collection of 44M. abscessus clinical isolates. The MIC₅₀s and MIC₉₀s of tedizolid (2 and 8μg/mL, respectively) were 2- to 16-fold lower than those of linezolid. There was no difference between the 3M. abscessus subspecies. Time-kill assays did not show any bactericidal activity at 4- and 8-fold the MIC. Combination of tedizolid with clarithromycin was synergistic against 1 out of 6 isolates, while indifferent interactions were observed for tedizolid combined with tigecycline, ciprofloxacin, and amikacin.

Inhibition by Avibactam and Clavulanate of the β-Lactamases KPC-2 and CTX-M-15 Harboring the Substitution N132G in the Conserved SDN Motif

The substitution N132G in the SDN motif of class A β-lactamases from rapidly growing mycobacteria was previously shown to impair their inhibition by avibactam but to improve the stability of acyl-enzymes formed with clavulanate. The same substitution was introduced in KPC-2 and CTX-M-15 to assess its impact on β-lactamases from Enterobacteriaceae and evaluate whether it may lead to resistance to the ceftazidime-avibactam combination. Kinetic parameters for the inhibition of the β-lactamases by avibactam and clavulanate were determined by spectrophotometry using nitrocefin as the substrate. The substitution N132G impaired (>1,000-fold) the efficacy of carbamylation of KPC-2 and CTX-M-15 by avibactam. The substitution improved the inhibition of KPC-2 by clavulanate due to reduced deacylation, whereas the presence or absence of N132G resulted in the inhibition of CTX-M-15 by clavulanate. The hydrolysis of amoxicillin and nitrocefin by KPC-2 and CTX-M-15 was moderately affected by the substitution N132G, but that of ceftazidime, ceftaroline, and aztreonam was drastically reduced. Isogenic strains producing KPC-2 and CTX-M-15 were constructed to assess the impact of the substitution N132G on the antibacterial activities of β-lactam-inhibitor combinations. For amoxicillin, the substitution resulted in resistance and susceptibility for avibactam and clavulanate, respectively. For ceftazidime, ceftaroline, and aztreonam, the negative impact of the substitution on β-lactamase activity prevented resistance to the β-lactam-avibactam combinations. In conclusion, the N132G substitution has profound effects on the substrate and inhibition profiles of class A β-lactamases, which are largely conserved in distantly related enzymes. Fortunately, the substitution does not lead to resistance to the ceftazidime-avibactam combination.

Impact of β-lactamase inhibition on the activity of ceftaroline against Mycobacterium tuberculosis and Mycobacterium abscessus

The production of β-lactamases Bla(Mab) and BlaC contributes to β-lactam resistance in Mycobacterium abscessus and Mycobacterium tuberculosis, respectively. Ceftaroline was efficiently hydrolyzed by these enzymes. Inhibition of M. tuberculosis BlaC by clavulanate decreased the ceftaroline MIC from ≥ 256 to 16 to 64 μg/ml, but these values are clinically irrelevant. In contrast, the ceftaroline-avibactam combination should be evaluated against M. abscessus since it inhibited growth at lower and potentially achievable drug concentrations.

Characterization of broad-spectrum Mycobacterium abscessus class A β-lactamase

OBJECTIVES

Imipenem and cefoxitin are used to treat Mycobacterium abscessus infections and have moderate activity against this fast-growing mycobacterium (MIC₅₀ of 16 and 32 mg/L, respectively). M. abscessus is highly resistant to most other β-lactams, although the underlying mechanisms have not been explored. Here, we characterized M. abscessus class A β-lactamase (Bla(Mab)) and investigated its role in β-lactam resistance.

METHODS

Hydrolysis kinetic parameters of purified Bla(Mab) were determined by spectrophotometry for various β-lactams and compared with those of related BlaC from Mycobacterium tuberculosis. MICs of β-lactams were determined for M. abscessus CIP104536 and for Escherichia coli producing Bla(Mab) and BlaC.

RESULTS

Bla(Mab) had a broad hydrolysis spectrum, similar to that of BlaC, but with overall higher catalytic efficiencies, except for cefoxitin. As expected from its in vivo efficacy, cefoxitin was very slowly hydrolysed by Bla(Mab) (k(cat)/K(m) = 6.7 M(-1) s(-1)). Bla(Mab) hydrolysed imipenem more efficiently (k(cat)/K(m) = 3.0 × 10(4) M(-1) s(-1)), indicating that the in vivo activity of this drug might be improved by combination with a β-lactamase inhibitor. β-Lactamase inhibitors clavulanate, tazobactam and sulbactam did not inhibit Bla(Mab). This enzyme efficiently hydrolysed clavulanate, in contrast to BlaC, which is irreversibly acylated by this inhibitor. Bla(Mab) and BlaC were functional in E. coli and the resistance profiles mediated by these enzymes were in agreement with the kinetic parameters.

CONCLUSIONS

M. abscessus produces a clavulanate-insensitive broad-spectrum β-lactamase that limits the in vivo efficacy of β-lactams.

Perineal pad test in evaluating outcome of treatments for female incontinence: a systematic review

Our objective was to systematically review clinical studies of incontinence treatments for women that used pad tests to assess outcome, to determine how closely the ICS guidelines had been followed. Our review (Medline 1988-2000, plus referenced studies) identified 75 relevant papers, carrying out pad tests in clinics ( n = 53) or patients' homes ( n = 28). Clinic pad tests lasted between 60 seconds and 2 hours, with inconsistent starting bladder volumes, activities carried out, other test details and presentation of results. Home pad tests lasted between 1.5 and 48 hours: the conduct and reporting of these tests were also variable. Only 25 studies used pad tests that were apparently consistent with ICS guidelines. Pad tests are important in identifying urine loss in clinical evaluations; however, we found wide variations in their conduct and reporting. We recommend that the ICS should review the guidelines, and that further research should develop clinically valid pad tests. Authors and journal editors should ensure that pad test details are fully reported.