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Inactivation kinetics of a new target of beta-lactam antibiotics.

ABSTRACT: Peptidoglycan is predominantly cross-linked by serine DD-transpeptidases in most bacterial species. The enzymes are the essential targets of ?-lactam antibiotics. However, unrelated cysteine LD-transpeptidases have been recently recognized as a predominant mode of peptidoglycan cross-linking in Mycobacterium tuberculosis and as a bypass mechanism conferring resistance to all ?-lactams, except carbapenems such as imipenem, in Enterococcus faecium. Investigation of the mechanism of inhibition of this new ?-lactam target showed that acylation of the E. faecium enzyme (Ldt(fm)) by imipenem is irreversible. Using fluorescence kinetics, an original approach was developed to independently determine the catalytic constants for imipenem binding (k(1) = 0.061 ?M(-1) min(-1)) and acylation (k(inact) = 4.5 min(-1)). The binding step was limiting at the minimal drug concentration required for bacterial growth inhibition. The Michaelis complex was committed to acylation because its dissociation was negligible. The emergence of imipenem resistance involved substitutions in Ldt(fm) that reduced the rate of formation of the non-covalent complex but only marginally affected the efficiency of the acylation step. The methods described in this study will facilitate development of new carbapenems active on extensively resistant M. tuberculosis.

SUBMITTER: Triboulet S

PROVIDER: S-EPMC3123045 | biostudies-literature | 2011 Jul

REPOSITORIES: biostudies-literature

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Inactivation kinetics of a new target of beta-lactam antibiotics.

Triboulet Sébastien S Arthur Michel M Mainardi Jean-Luc JL Veckerlé Carole C Dubée Vincent V Nguekam-Moumi Angèle A Gutmann Laurent L Rice Louis B LB Hugonnet Jean-Emmanuel JE

The Journal of biological chemistry 20110504 26

Peptidoglycan is predominantly cross-linked by serine DD-transpeptidases in most bacterial species. The enzymes are the essential targets of β-lactam antibiotics. However, unrelated cysteine LD-transpeptidases have been recently recognized as a predominant mode of peptidoglycan cross-linking in Mycobacterium tuberculosis and as a bypass mechanism conferring resistance to all β-lactams, except carbapenems such as imipenem, in Enterococcus faecium. Investigation of the mechanism of inhibition of t ...[more]

PMID: 21543331

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Project description:Mycobacterium tuberculosis (M. tuberculosis) is considered innately resistant to β-lactam antibiotics. However, there is evidence that susceptibility to β-lactam antibiotics in combination with β-lactamase inhibitors is variable among clinical isolates, and these may present therapeutic options for drug-resistant cases. Here we report our investigation of susceptibility to β-lactam/β-lactamase inhibitor combinations among clinical isolates of M. tuberculosis, and the use of comparative genomics to understand the observed heterogeneity in susceptibility. Eighty-nine South African clinical isolates of varying first and second-line drug susceptibility patterns and two reference strains of M. tuberculosis underwent minimum inhibitory concentration (MIC) determination to two β-lactams: amoxicillin and meropenem, both alone and in combination with clavulanate, a β-lactamase inhibitor. 41/91 (45%) of tested isolates were found to be hypersusceptible to amoxicillin/clavulanate relative to reference strains, including 14/24 (58%) of multiple drug-resistant (MDR) and 22/38 (58%) of extensively drug-resistant (XDR) isolates. Genome-wide polymorphisms identified using whole-genome sequencing were used in a phylogenetically-aware linear mixed model to identify polymorphisms associated with amoxicillin/clavulanate susceptibility. Susceptibility to amoxicillin/clavulanate was over-represented among isolates within a specific clade (LAM4), in particular among XDR strains. Twelve sets of polymorphisms were identified as putative markers of amoxicillin/clavulanate susceptibility, five of which were confined solely to LAM4. Within the LAM4 clade, 'paradoxical hypersusceptibility' to amoxicillin/clavulanate has evolved in parallel to first and second-line drug resistance. Given the high prevalence of LAM4 among XDR TB in South Africa, our data support an expanded role for β-lactam/β-lactamase inhibitor combinations for treatment of drug-resistant M. tuberculosis.

Project description:Beta-lactam allergy is a common problem in everyday medical practice and is recognized as a major public health issue. Carrying this label frequently leads to the avoidance of all beta-lactam antibiotics, favoring the use of other less preferred classes of antibiotics, that are more expensive and associated with more side effects and increased antimicrobial resistance. Therefore, delabeling a beta-lactam allergy is part of antimicrobial stewardship programs. Herein, we retrospectively examined the clinical records of 576 patients who were referred to our center for a label of allergy to beta-lactam antibiotics and were systematically investigated following a standardized algorithm. Our main aim was to evaluate the frequency of confirmed immediate- and delayed-type allergy to commonly prescribed subclasses of beta-lactam antibiotics (penicillin and cephalosporin), as well as the negative predictive value (NPV) and the sensitivity of skin tests. Our secondary aims were to examine the safety of beta-lactam skin testing and drug challenge. We identified that 260 patients reported a history of immediate reactions, 131 of delayed reactions, and 114 of unknown timing or mechanism of reactions. Following assessment and testing, 86 (18.3%) patients had a confirmed allergy to any beta-lactam antibiotics; 63 (13.4%) with an immediate- and 23 (4.9%) with a delayed-type reaction. Most frequently identified confirmed allergy was to penicillins (65 patients), followed by cephalosporins (21 patients). When immediate-type reactions were examined, NPV of skin tests were 96.3% and 100% for penicillins and cephalosporins, respectively. When delayed reactions were considered, NPV were 91.9 and 87.5% for penicillins and cephalosporins, respectively. Evaluation of the safety of skin tests according to the standardized procedure showed that systemic allergic reactions occurred in only 0.7% of skin tests and in 3.1% of drug challenges. Overall, our data indicate that only 18.3% of patients with a beta-lactam allergy label have a confirmed allergy and non-allergic patients can be safely delabeled through allergic workup based on skin tests and drug challenge. This approach supports the policy of saving second-line antibiotics through a standardized allergy workup.

Project description:Study objectiveMinimizing the duration of broad-spectrum antimicrobial exposure in the critically ill is a commonly used strategy aimed at preventing resistance. Our objective was to correlate the duration of exposure to antipseudomonal β-lactam antibiotics with the development of new resistance in critically ill patients.DesignSingle-center, retrospective cohort study.SettingA large, academic, tertiary care hospital.PatientsA total of 7118 adults with a discharge diagnosis of severe sepsis or septic shock who received at least one dose of cefepime, meropenem, or piperacillin-tazobactam during their hospitalization between 2010 and 2015.Measurements and main resultsCohort entry was defined as the first day of any antipseudomonal β-lactam initiation, and exposure was defined as the cumulative days of any antipseudomonal β-lactam exposure during the 60-day follow-up period. The primary outcome was development of new resistance to any antipseudomonal β-lactam > 3 days after cohort entry. New resistance was defined as detection of resistance to any antipseudomonal β-lactam not identified within 180 days before cohort entry. Patients without an outcome (i.e., did not develop new resistance) or who died by day 60 were censored. Cox proportional hazards models were performed to assess the risk of development of new resistance to any antipseudomonal β-lactam with each additional day of exposure. Analyses of each individual antipseudomonal β-lactam were evaluated as secondary outcomes. Each additional day of exposure to any antipseudomonal β-lactam resulted in an adjusted hazard ratio (aHR) of 1.04 (95% confidence interval [CI] 1.04-1.05) for new resistance development. The risk of developing new resistance to cefepime, meropenem, and piperacillin-tazobactam for each additional day of exposure resulted in an aHR of 1.08 (95% CI 1.07-1.09), 1.02 (95% CI 1.01-1.03), and 1.08 (95% CI 1.06-1.09), respectively.ConclusionAmong critically ill patients who receive antipseudomonal β-lactam antibiotics, each additional day of exposure to cefepime, meropenem, and piperacillin-tazobactam is associated with an increased risk of new resistance development.

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Inactivation kinetics of a new target of beta-lactam antibiotics.

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Inactivation kinetics of a new target of beta-lactam antibiotics.

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