Mutational change of CTX-M-15 to CTX-M-127 resulting in mecillinam resistant Escherichia coli during pivmecillinam treatment of a patient.
ABSTRACT: Pivmecillinam (amdinocillin pivoxil) is the recommended first-choice antibiotic used to treat urinary tract infections (UTIs) in Denmark. The frequency of mutation to mecillinam (MEC) resistance is described as high in vitro; however, treatment of UTI has a good clinical response and prevalence of mecillinam resistance in Escherichia coli remains low despite many years of use. We describe occurrence of in vivo mecillinam resistance in a clinical isolate of ESBL-producing E. coli following pivmecillinam treatment. The identified phenotypic differences in the mecillinam resistant isolate compared with the original mecillinam susceptible isolate were a full-length LPS with O-antigen (O25), mecillinam resistance and a lower MIC for ceftazidime. Regarding genotype, the resistant isolate differed with a mutation in blaCTX-M-15 to blaCTX-M-127 , loss of a part of a plasmid and a genomic island, respectively, and insertion of a transposase in wbbL, causing the rough phenotype. The observed mecillinam resistance is expected to be caused by the mutation in blaCTX-M-15 with additional contribute from the serotype shift. We continue to recommend the use of pivmecillinam as first-line treatment for UTI.
Project description:Objectives: To investigate pivmecillinam´s efficacy in uncomplicated lower urinary tract infection (UTI) caused by Staphylococcus saprophyticus-considered non-susceptible to mecillinam. Methods: Participants with confirmed UTIs caused by S. saprophyticus from four randomized controlled trials, where pivmecillinam was empirically given to females with symptoms of UTIs. The primary outcome was defined as a cumulative clinical effect-symptom resolution during the first eight days of therapy, without a recurrence of UTI symptoms in the long-term follow-up (approximately four weeks). Secondary outcomes included the bacteriological effect-elimination of the causative agent, with or without new uropathogenic bacteria present in the first control urine sample. Significant bacteriuria was defined as ≥103 bacteria/mL. The antibiotic susceptibility testing was done by disc diffusion methodology, according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST). Results: Seventy-four females (18-55 years) were empirically treated with pivmecillinam for UTIs caused by S. saphrophyticus (mean age 25 years; standard deviation (SD) 5.8). The cumulative clinical effect was 53/74 (72%), and the bacteriological effect was 51/59 (86%). Conclusion: Pivmecillinam showed a high clinical and bacteriological effect in UTIs caused by S. saprophyticus in these four clinical trials. The characterization of non-susceptibility for mecillinam regarding the treatment of UTIs caused by this common pathogen may need to be revised.
Project description:A population-based study was performed to investigate the efficacy of mecillinam treatment of community-acquired urinary tract infections (CA-UTI) caused by extended-spectrum β-lactamase (ESBL) producing Escherichia coli. The study was conducted in South-Eastern Norway. Data from patients with CA-UTI caused by ESBL-producing and non-producing (random controls) E. coli were collected through interviews, questionnaires, medical records and the Norwegian Prescription Database. Treatment failure was defined as a new antibiotic prescription appropriate for UTI prescribed within two weeks after the initial antimicrobial therapy. Multivariable logistic regression analysis was performed to identify treatment agents and patient- or bacterial traits associated with treatment failure. A total of 343 patients (mean age 59) were included, of which 158 (46%) were treated with mecillinam. Eighty-one patients (24%, mean age 54) had infections caused by ESBL producing E. coli, and 41 of these patients (51%) received mecillinam as the primary treatment. Mecillinam treatment failure was observed in 18 (44%) of patients infected by ESBL-producing strains and in 16 (14%) of patients with a CA-UTI caused by ESBL non-producing strains. Multivariable analysis showed that ESBL status (odds ratio (OR) 3.2, 95% confidence interval (CI) 1.3-7.8, p = 0.009) and increased MIC of mecillinam (OR 2.0 for each doubling value of MIC, CI 1.4-3.0, p<0.001) were independently associated with mecillinam treatment failure. This study showed a high rate of mecillinam treatment failure in CA-UTIs caused by ESBL producing E. coli. The high failure rate could not be explained by the increased MIC of mecillinam alone. Further studies addressing the use of mecillinam against ESBL-producing E. coli, with emphasis on optimal dosing and combination therapy with β-lactamase inhibitors, are warranted.
Project description:BACKGROUND:Although uncomplicated urinary tract infections (UTIs) are often self-limiting, most patients will be prescribed antibiotic treatment. We assessed whether treatment with ibuprofen was non-inferior to pivmecillinam in achieving symptomatic resolution by day 4, with a non-inferiority margin of 10%. METHODS AND FINDINGS:This was a randomized, controlled, double-blind non-inferiority trial. We recruited patients from 16 sites in a general practice setting in Norway, Sweden, and Denmark. Non-pregnant women aged 18-60 years presenting with symptoms of uncomplicated UTI were screened for eligibility from 11 April 2013 to 22 April 2016. Patients with informed consent were randomized (1:1 ratio) to treatment with either 600 mg ibuprofen or 200 mg pivmecillinam 3 times a day for 3 days. The patient, treating physician, and study personnel were blinded to treatment allocation. The primary outcome was the proportion of patients who felt cured by day 4, as assessed from a patient diary. Secondary outcomes included the proportion of patients in need of secondary treatment with antibiotics and cases of pyelonephritis. A total of 383 women were randomly assigned to treatment with either ibuprofen (n = 194, 181 analyzed) or pivmecillinam (n = 189, 178 analyzed). By day 4, 38.7% of the patients in the ibuprofen group felt cured versus 73.6% in the pivmecillinam group. The adjusted risk difference with 90% confidence interval was 35% (27% to 43%) in favor of pivmecillinam, which crossed the prespecified non-inferiority margin. Secondary endpoints were generally in favor of pivmecillinam. After 4 weeks' follow-up, 53% of patients in the ibuprofen group recovered without antibiotic treatment. Seven cases of pyelonephritis occurred, all in the ibuprofen group, giving a number needed to harm of 26 (95% CI 13 to 103). Five of these patients were hospitalized and classified as having serious adverse events; 2 recovered as outpatients. A limitation of the study was the extensive list of exclusion criteria, eliminating almost half of the patients screened. We did not register symptoms in the screening process; hence, we do not know the symptom burden for those who declined to participate. This might make our results less generalizable. CONCLUSIONS:Ibuprofen was inferior to pivmecillinam for treating uncomplicated UTIs. More than half of the women in the ibuprofen group recovered without antibiotics. However, pyelonephritis occurred in 7 out of 181 women using ibuprofen. Until we can identify those women who will develop complications, we cannot recommend ibuprofen alone as initial treatment to women with uncomplicated UTIs. TRIAL REGISTRATION:ClinicalTrials.gov NCT01849926 EU Clinical Trials Register (EU-CTR), EudraCT Number 2012-002776-14.
Project description:Mecillinam (amdinocillin) is a ?-lactam antibiotic used to treat uncomplicated urinary tract infections (UTIs). We have previously shown that inactivation of the Escherichia coli cysB gene is the major cause of mecillinam resistance (MecR) in clinical isolates. In this study, we used different E. coli strains (laboratory and clinical isolates) that were MecR due to cysB mutations to determine how mecillinam susceptibility was affected during growth in urine compared to growth in the commonly used growth medium Mueller Hinton (MHB). We also examined mecillinam susceptibility when bacteria were grown in urine obtained from 48 different healthy volunteers. Metabolome analysis was done on the urine samples and the association between the mecillinam susceptibility patterns of the bacteria and urine metabolite levels was studied. Two major findings with clinical significance are reported. First, MecRE. coli cysB mutant strains (both laboratory and clinical isolates) were always more susceptible to mecillinam when grown in urine as compared to laboratory medium, with many strains showing complete phenotypic susceptibility in urine. Second, the degree of reversion to susceptibility varied between urine samples obtained from different individuals. This difference was correlated with osmolality such that in urine with low osmolality the MecR mutants were more susceptible to mecillinam than in urine with high osmolality. This is the first example describing conditional resistance where a genetically stable antibiotic resistance can be phenotypically reverted to susceptibility by metabolites present in urine. These findings have several important clinical implications regarding the use of mecillinam to treat UTIs. First, they suggest that mecillinam can be used to treat also those clinical strains that are identified as MecR in standard laboratory tests. Second, the results suggest that testing of mecillinam susceptibility in the laboratory ought to be performed in media that mimics urine to obtain clinically relevant susceptibility testing results. Third, these findings imply that changes in patient behavior, such as increased water intake or use of diuretics to reduce urine osmolality and increased intake of cysteine, might induce antibiotic susceptibility in an infecting MecRE. coli strain and thereby increase treatment efficiency.
Project description:Mecillinam (amdinocillin) is a ?-lactam antibiotic that inhibits the essential penicillin-binding protein 2 (PBP2). In clinical isolates of Escherichia coli from urinary tract infections, inactivation of the cysB gene (which encodes the main regulator of cysteine biosynthesis, CysB) is the major cause of resistance. How a nonfunctional CysB protein confers resistance is unknown, however, and in this study we wanted to examine the mechanism of resistance. Results show that cysB mutations cause a gene regulatory response that changes the expression of ?450 genes. Among the proteins that show increased levels are the PBP1B, LpoB, and FtsZ proteins, which are known to be involved in peptidoglycan biosynthesis. Artificial overexpression of either PBP1B or LpoB in a wild-type E. coli strain conferred mecillinam resistance; conversely, inactivation of either the mrcB gene (which encodes PBP1B) or the lpoB gene (which encodes the PBP1B activator LpoB) made cysB mutants susceptible. These results show that expression of the proteins PBP1B and LpoB is both necessary and sufficient to confer mecillinam resistance. The addition of reducing agents to a cysB mutant converted it to full susceptibility, with associated downregulation of PBP1B, LpoB, and FtsZ. We propose a model in which cysB mutants confer mecillinam resistance by inducing a response that causes upregulation of the PBP1B and LpoB proteins. The higher levels of these two proteins can then rescue cells with mecillinam-inhibited PBP2. Our results also show how resistance can be modulated by external conditions such as reducing agents.
Project description:Background:To investigate if a 5-day course pivmecillinam (amdinocillin pivoxil) 400?mg three times daily is superior to a 3-day course in women with uncomplicated urinary tract infection (UTI). Methods:A randomised, double-blind, placebo-controlled trial conducted at nine primary care centres in Denmark. 368 women (18-70?years) with symptoms compatible with UTI were randomised to blinded therapy of 5 days [5d] or 3 days followed by 2 days of placebo [3d] from May 2015 to November 2017. Clinical data were assessed using a validated questionnaire at inclusion (day-0), daily the following 7 days and once again within the 2nd to 6th week after intervention. Bacteriological data were collected prior to intervention and twice between day 7 and 42. Main clinical endpoints were days to symptom resolution within 7?days after inclusion and proportions with clinical success at the end of intervention. Main bacteriological endpoint was proportion of participants with significant reduction of bacteriuria (? 102 CFU/mL) in 1st control urine sample. ClinicalTrialsRegister.eu: 2014-001321-32. Findings:180 (5d) and 188 (3d) participants were included in the study (mean age: 35.4 [5d] and 34.9 [3d]). Of these, 125 (70% [5d]) and 122 (66% [3d]) had a positive baseline urine culture. Forty-four participants were lost to follow-up, leaving 161 [5d] and 163 [3d] participants for analysis, respectively. Mean time to symptom resolution was 2.91 (SD 1.46; [5d]) days and 2.94 (SD 1.42; [3d]) days (P?=?.894). Clinical success at the end of treatment occurred for 117 of 153 (76%) receiving the 5d-course and for 115 of 157 (73%) receiving the 3d course (difference 3.2% [95% CI -7.1% - 13.5%]; P?=?.601). Bacteriological success was seen in 92 of 104 (88%) participants given the 5d course and in 86 of 99 (87%) given the 3d course (difference 1.6% [95% CI -8.4%-11.6%]; P?=?.895). Interpretations:A 5-day course of pivmecillinam was not superior to a 3-day course in clinical or bacteriological outcomes for UTI. Primary funding source:The Danish Regions [no. 14/217].
Project description:Bacterial cells are typically surrounded by an net-like macromolecule called the cell wall constructed from the heteropolymer peptidoglycan (PG). Biogenesis of this matrix is the target of penicillin and related beta-lactams. These drugs inhibit the transpeptidase activity of PG synthases called penicillin-binding proteins (PBPs), preventing the crosslinking of nascent wall material into the existing network. The beta-lactam mecillinam specifically targets the PBP2 enzyme in the cell elongation machinery of Escherichia coli. Low-throughput selections for mecillinam resistance have historically been useful in defining mechanisms involved in cell wall biogenesis and the killing activity of beta-lactam antibiotics. Here, we used transposon-sequencing (Tn-Seq) as a high-throughput method to identify nearly all mecillinam resistance loci in the E. coli genome, providing a comprehensive resource for uncovering new mechanisms underlying PG assembly and drug resistance. Induction of the stringent response or the Rcs envelope stress response has been previously implicated in mecillinam resistance. We therefore also performed the Tn-Seq analysis in mutants defective for these responses in addition to wild-type cells. Thus, the utility of the dataset was greatly enhanced by determining the stress response dependence of each resistance locus in the resistome. Reasoning that stress response-independent resistance loci are those most likely to identify direct modulators of cell wall biogenesis, we focused our downstream analysis on this subset of the resistome. Characterization of one of these alleles led to the surprising discovery that the overproduction of endopeptidase enzymes that cleave crosslinks in the cell wall promotes mecillinam resistance by stimulating PG synthesis by a subset of PBPs. Our analysis of this activation mechanism suggests that, contrary to the prevailing view in the field, PG synthases and PG cleaving enzymes need not function in multi-enzyme complexes to expand the cell wall matrix.
Project description:We sequenced the genomes of 10 Salmonella enterica serovar Infantis isolates containing blaCTX-M-65 obtained from chicken, cattle, and human sources collected between 2012 and 2015 in the United States through routine National Antimicrobial Resistance Monitoring System (NARMS) surveillance and product sampling programs. We also completely assembled the plasmids from four of the isolates. All isolates had a D87Y mutation in the gyrA gene and harbored between 7 and 10 resistance genes [aph(4)-Ia, aac(3)-IVa, aph(3')-Ic, blaCTX-M-65, fosA3, floR, dfrA14, sul1, tetA, aadA1] located in two distinct sites of a megaplasmid (∼316 to 323 kb) similar to that described in a blaCTX-M-65-positive S Infantis isolate from a patient in Italy. High-quality single nucleotide polymorphism (hqSNP) analysis revealed that all U.S. isolates were closely related, separated by only 1 to 38 pairwise high-quality SNPs, indicating a high likelihood that strains from humans, chickens, and cattle recently evolved from a common ancestor. The U.S. isolates were genetically similar to the blaCTX-M-65-positive S Infantis isolate from Italy, with a separation of 34 to 47 SNPs. This is the first report of the blaCTX-M-65 gene and the pESI (plasmid for emerging S Infantis)-like megaplasmid from S Infantis in the United States, and it illustrates the importance of applying a global One Health human and animal perspective to combat antimicrobial resistance.
Project description:Antibiotic resistance is a major challenge to global public health. Discovery of new antibiotics is slow and to ensure proper treatment of bacterial infections new strategies are needed. One way to curb the development of antibiotic resistance is to design drug combinations where the development of resistance against one drug leads to collateral sensitivity to the other drug. Here we study collateral sensitivity patterns of the globally distributed extended-spectrum ?-lactamase CTX-M-15, and find three non-synonymous mutations with increased resistance against mecillinam or piperacillin-tazobactam that simultaneously confer full susceptibility to several cephalosporin drugs. We show in vitro and in mice that a combination of mecillinam and cefotaxime eliminates both wild-type and resistant CTX-M-15. Our results indicate that mecillinam and cefotaxime in combination constrain resistance evolution of CTX-M-15, and illustrate how drug combinations can be rationally designed to limit the resistance evolution of horizontally transferred genes by exploiting collateral sensitivity patterns.
Project description:Amdinocillin (mecillinam) is a β-lactam antibiotic that is used mainly for the treatment of uncomplicated urinary tract infections. The objectives of this study were to identify mutations that confer amdinocillin resistance on laboratory-isolated mutants and clinical isolates of Escherichia coli and to determine why amdinocillin resistance remains rare clinically even though resistance is easily selected in the laboratory. Under laboratory selection, frequencies of mutation to amdinocillin resistance varied from 8 × 10(-8) to 2 × 10(-5) per cell, depending on the concentration of amdinocillin used during selection. Several genes have been demonstrated to give amdinocillin resistance, but here eight novel genes previously unknown to be involved in amdinocillin resistance were identified. These genes encode functions involved in the respiratory chain, the ribosome, cysteine biosynthesis, tRNA synthesis, and pyrophosphate metabolism. The clinical isolates exhibited significantly greater fitness than the laboratory-isolated mutants and a different mutation spectrum. The cysB gene was mutated (inactivated) in all of the clinical isolates, in contrast to the laboratory-isolated mutants, where mainly other types of more costly mutations were found. Our results suggest that the frequency of mutation to amdinocillin resistance is high because of the large mutational target (at least 38 genes). However, the majority of these resistant mutants have a low growth rate, reducing the probability that they are stably maintained in the bladder. Inactivation of the cysB gene and a resulting loss of cysteine biosynthesis are the major mechanism of amdinocillin resistance in clinical isolates of E. coli.