Pivmecillinam with Amoxicillin/Clavulanic acid as step down oral therapy in febrile Urinary Tract Infections caused by ESBL-producing Enterobacterales (PACUTI)

BACKGROUND

Oral treatment alternatives for febrile urinary tract infections are limited in the era of increasing antimicrobial resistance. We aim to evaluate if the combination of pivmecillinam and amoxicillin/clavulanic acid is non-inferior to current alternatives for step-down therapy in adult patients with febrile urinary tract infection.

METHODS

We plan to perform an investigator-initiated non-inferiority trial. Adult hospitalised patients treated with 1-5 days of intravenous antibiotics for acute febrile urinary tract infection caused by extended spectrum beta-lactamase (ESBL) producing Enterobacterales will be randomised 1:1 to either control (7-10 days of either oral ciprofloxacin 500 mg twice daily or oral trimethoprim-sulfamethoxazole 800 mg/160 mg twice daily or intravenous ertapenem 1 g once daily, depending on sex, drug allergy, glomerular filtration rate and susceptibility testing) or intervention (10 days of pivmecillinam 400 mg three times daily and amoxicillin/clavulanic acid 500/125 mg three times daily). The primary outcome will be clinical cure 10 days (+/- 2 days) after antibiotic treatment completion. Clinical cure is defined as being alive with absence of fever and return to non-infected baseline of urinary tract symptoms without additional antibiotic treatment or re-hospitalisation (for urinary tract infection) based on a centralised allocation-blinded structured telephone interview. We plan to recruit 330 patients to achieve 90% power based on a sample size simulation analysis using a two-group comparison, one-sided alpha of 2.5%, an absolute non-inferiority margin of 10% and expecting 93% clinical cure rate and 10% loss to follow-up. The primary endpoint will be analysed using generalised estimated equations and reported as risk difference for both intention-to-treat and per protocol populations. Patients are planned to be recruited from at least 10 centres in Sweden from 2023 to 2026.

DISCUSSION

If the combination of pivmecillinam and amoxicillin/clavulanic acid is found to be non-inferior to the control drugs there are potential benefits in terms of tolerability, frequency of interactions, outpatient treatment, side effects, nosocomial infections and drive for further antimicrobial resistance compared to existing drugs.

TRIAL REGISTRATION

NCT05224401. Registered on February 4, 2022.

Pharmacokinetic/Pharmacodynamic Determination of Systemic MIC Breakpoints for Intermittent, Extended, and Continuous Infusion Dosage Regimens of Mecillinam

Intravenous mecillinam has been used for the treatment of urosepsis at several dosing regimens, including a dose of 1,000 mg three times a day (TID). In the current pharmacokinetic/pharmacodynamic (PK/PD) study, we analyzed intermittent, extended, and continuous infusion regimens of mecillinam to provide dosage recommendations to treat infections caused by Enterobacterales exhibiting relatively higher mecillinam MICs than the wild-type strains. Monte Carlo simulation studies indicated that regimens of 1,000 mg TID and 1,000 to 1,200 mg four times a day (QID) are efficacious against wild-type and extended-spectrum β-lactamase-producing Enterobacterales, respectively. Prolonged infusion regimens (extended and continuous) could cover carbapenemase producers with a higher range of MICs (2 to 8 mg/L). IMPORTANCE Previous studies have shown that intravenous mecillinam might be suitable for treatment of urosepsis. Since multidrug-resistant Enterobacterales are common pathogens in such infections, an effort was made to delineate intermittent, extended, and continuous infusion regimens that could cover pathogens exhibiting relatively higher mecillinam MICs than the wild-type strains. Our PK/PD analysis has shown that mecillinam might be considered a valuable therapeutic option for the treatment of systemic infections caused by extended-spectrum β-lactamase- and carbapenemase-producing Enterobacterales exhibiting mecillinam MICs up to 8 mg/L.

Synergy between Mecillinam and Ceftazidime/Avibactam or Avibactam against Multi-Drug-Resistant Carbapenemase-Producing Escherichia coli and Klebsiella pneumoniae

Background: Carbapenemase-producing Klebsiella pneumoniae and Escherichia coli have become a significant global health challenge. This has created an urgent need for new treatment modalities. We evaluated the efficacy of mecillinam in combination with either avibactam or ceftazidime/avibactam against carbapenemase-producing clinical isolates. Materials and methods: Nineteen MDR clinical isolates of K. pneumoniae and E. coli were selected for the presence of blaKPC, blaNDM, blaOXA or blaIMP based on whole-genome sequencing and phenotypic susceptibility testing. We tested the synergy between mecillinam and avibactam or ceftazidime/avibactam. We used time−kill studies in vitro and a mouse peritonitis/sepsis model to confirm the synergistic effect. We investigated avibactam’s impact on mecillinam´s affinity for penicillin-binding proteins with a Bocillin assay, and cell changes with phase-contrast and confocal laser scanning microscopy. Results: Mecillinam combined with ceftazidime/avibactam or avibactam substantially reduced MICs (from up to >256 µg/mL to <0.0016 µg/mL) for 17/18 strains. Significant log-CFU reductions were confirmed in time−kill and in vivo experiments. The Bocillin assay did not reveal changes. Conclusion: Mecillinam in combination with avibactam or ceftazidime/avibactam has a notable effect on most types of CPEs, both in vitro and in vivo. The mecillinam/avibactam combination treatment could be a new efficient antibiotic treatment against multi-drug-resistant carbapenemase-producing Gram-negative pathogens.

Clavulanate combinations with mecillinam, cefixime or cefpodoxime against ESBL-producing Enterobacterales frequently associated with blaOXA-1 in a paediatric population with febrile urinary tract infections

OBJECTIVES

Oral treatment of febrile urinary tract infections (FUTIs) can be impaired by MDR Enterobacterales often combining ESBL and inhibitor-resistant genes. We studied the impact of β-lactamases and Enterobacterales' genotypes on the cefixime, cefpodoxime and mecillinam ± amoxicillin/clavulanate MICs.

MATERIALS AND METHODS

In this multicentric study, we included 251 previously whole-genome-sequenced ESBL-producing Enterobacterales, isolated in French children with FUTIs. The MICs of cefixime, cefpodoxime, mecillinam alone and combined with amoxicillin/clavulanate were determined and analysed with respect to genomic data. We focused especially on the isolates' ST and their type of β-lactamases. Clinical outcomes of patients who received cefixime + amoxicillin/clavulanate were also analysed.

RESULTS

All isolates were cefixime and cefpodoxime resistant. Disparities depending on blaCTX-M variants were observed for cefixime. The addition of amoxicillin/clavulanate restored susceptibility for cefixime and cefpodoxime in 97.2% (MIC50/90 of 0.38/0.75 mg/L) and 55.4% (MIC50/90 of 1/2 mg/L) of isolates, respectively, whatever the ST, the blaCTX-M variants or the association with inhibitor-resistant β-lactamases (34.2%). All isolates were susceptible to mecillinam + amoxicillin/clavulanate with MIC50/90 of 0.19/0.25 mg/L, respectively. Neither therapeutic failure nor any subsequent positive control urine culture were reported for patients who received cefixime + amoxicillin/clavulanate as an oral relay therapy (n = 54).

CONCLUSIONS

Despite the frequent association of ESBL genes with inhibitor-resistant β-lactamases, the cefixime + amoxicillin/clavulanate MICs remain low. The in vivo efficacy of this combination was satisfying even when first-line treatment was ineffective. Considering the MIC distributions and pharmacokinetic parameters, mecillinam + amoxicillin/clavulanate should also be an alternative to consider when treating FUTIs in children.

Inoculum effect of β-lactam antibiotics

The phenomenon of attenuated antibacterial activity at inocula above those utilized for susceptibility testing is referred to as the inoculum effect. Although the inoculum effect has been reported for several decades, it is currently debatable whether the inoculum effect is clinically significant. The aim of the present review was to consolidate currently available evidence to summarize which β-lactam drug classes demonstrate an inoculum effect against specific bacterial pathogens. Review of the literature showed that the majority of studies that evaluated the inoculum effect of β-lactams were in vitro investigations of Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Haemophilus influenzae and Staphylococcus aureus. Across all five pathogens, cephalosporins consistently displayed observable inoculum effects in vitro, whereas carbapenems were less susceptible to an inoculum effect. A handful of animal studies were available that validated that the in vitro inoculum effect translates into attenuated pharmacodynamics of β-lactams in vivo. Only a few clinical investigations were available and suggested that an in vitro inoculum effect of cefazolin against MSSA may correspond to an increased likeliness of adverse clinical outcomes in patients receiving cefazolin for bacteraemia. The presence of β-lactamase enzymes was the primary mechanism responsible for an inoculum effect, but the observation of an inoculum effect in multiple pathogens lacking β-lactamase enzymes indicates that there are likely multiple mechanisms that may result in an inoculum effect. Further clinical studies are needed to better define whether interventions made in the clinic in response to organisms displaying an in vitro inoculum effect will optimize clinical outcomes.

Treatment of infections caused by multidrug-resistant Gram-negative bacteria: report of the British Society for Antimicrobial Chemotherapy/Healthcare Infection Society/British Infection Association Joint Working Party

The Working Party makes more than 100 tabulated recommendations in antimicrobial prescribing for the treatment of infections caused by multidrug-resistant (MDR) Gram-negative bacteria (GNB) and suggest further research, and algorithms for hospital and community antimicrobial usage in urinary infection. The international definition of MDR is complex, unsatisfactory and hinders the setting and monitoring of improvement programmes. We give a new definition of multiresistance. The background information on the mechanisms, global spread and UK prevalence of antibiotic prescribing and resistance has been systematically reviewed. The treatment options available in hospitals using intravenous antibiotics and in primary care using oral agents have been reviewed, ending with a consideration of antibiotic stewardship and recommendations. The guidance has been derived from current peer-reviewed publications and expert opinion with open consultation. Methods for systematic review were NICE compliant and in accordance with the SIGN 50 Handbook; critical appraisal was applied using AGREE II. Published guidelines were used as part of the evidence base and to support expert consensus. The guidance includes recommendations for stakeholders (including prescribers) and antibiotic-specific recommendations. The clinical efficacy of different agents is critically reviewed. We found there are very few good-quality comparative randomized clinical trials to support treatment regimens, particularly for licensed older agents. Susceptibility testing of MDR GNB causing infection to guide treatment needs critical enhancements. Meropenem- or imipenem-resistant Enterobacteriaceae should have their carbapenem MICs tested urgently, and any carbapenemase class should be identified: mandatory reporting of these isolates from all anatomical sites and specimens would improve risk assessments. Broth microdilution methods should be adopted for colistin susceptibility testing. Antimicrobial stewardship programmes should be instituted in all care settings, based on resistance rates and audit of compliance with guidelines, but should be augmented by improved surveillance of outcome in Gram-negative bacteraemia, and feedback to prescribers. Local and national surveillance of antibiotic use, resistance and outcomes should be supported and antibiotic prescribing guidelines should be informed by these data. The diagnosis and treatment of both presumptive and confirmed cases of infection by GNB should be improved. This guidance, with infection control to arrest increases in MDR, should be used to improve the outcome of infections with such strains. Anticipated users include medical, scientific, nursing, antimicrobial pharmacy and paramedical staff where they can be adapted for local use.

In vitro activity of imipenem-relebactam against non-MBL carbapenemase-producing Klebsiella pneumoniae isolated in Greek hospitals in 2015-2016

Relebactam is a β-lactamase inhibitor of class A and class C β-lactamases, including carbapenemases. We evaluated the ability of relebactam to restore imipenem susceptibility against a collection of Klebsiella pneumoniae isolates from Greek hospitals. We tested 314 non-MBL carbapenemase-producing K. pneumoniae consecutive clinical strains isolated from unique patients at 18 hospitals in Greece, between November 2014 and December 2016. Susceptibility testing of imipenem, imipenem-relebactam, meropenem, doripenem, gentamicin, and colistin was performed using broth microdilution. Additionally, MICs of ceftazidime-avibactam, fosfomycin, and tigecycline were determined by MIC Test Strips. MICs were interpreted per EUCAST breakpoints. Imipenem-relebactam MICs were interpreted using the breakpoints proposed for imipenem. Carbapenemase genes were detected using PCR. Whole genome sequencing was performed for selected isolates. Imipenem-relebactam inhibited 98.0% of the KPC-producing isolates at ≤ 2 mg/L (MIC₅₀/₉₀, 0.25/1 mg/L) and was considerably more active than imipenem (MIC₅₀/₉₀, 32/> 64 mg/L). Reduced activity of imipenem-relebactam was rarely detected (2%) and was associated with chromosomal factors (ompK35 disruption and/or mutated ompK36). Only ceftazidime-avibactam showed in vitro activity comparable to imipenem-relebactam (99.6% susceptible). Relebactam provided only weak potentiation of imipenem activity against K. pneumoniae with class D OXA-48-like enzymes. Relebactam exhibited strong potential for restoring the in vitro activity of imipenem against KPC-producing K. pneumoniae, lowering the imipenem MIC₅₀ and MIC₉₀ from 32 to 0.25 mg/L, and from > 64 to 1 mg/L, respectively. Production of KPC carbapenemase represents the main cause of carbapenem resistance among K. pneumoniae in Greek hospitals (66.5%), and this carbapenemase appears to be very well inhibited by relebactam.

Retrospective evaluation of nitrofurantoin and pivmecillinam for the treatment of lower urinary tract infections in men

OBJECTIVES

This study aimed to retrospectively assess the clinical outcome with nitrofurantoin and pivmecillinam for lower urinary tract infections (UTI) in men. Patients treated with trimethoprim were also included for comparison.

METHODS

All prescriptions of the study antibiotics to adult men in Uppsala County, Sweden, during 2012 were extracted. Data on patient characteristics, therapy, clinical outcome and microbiological results were obtained from the electronic medical records. The relative impact of antibiotic therapy, patient factors and pathogens on clinical outcome was assessed with univariate logistic regression using a 95% confidence interval (CI).

RESULTS

832 prescriptions were identified, and 171 patients treated with nitrofurantoin (n = 69), pivmecillinam (n = 57) and trimethoprim (n = 45) met the inclusion criteria. Treatment failure occurred in one patient treated with nitrofurantoin and in four patients treated with pivmecillinam. New prescriptions of UTI antibiotics and relapse within 3 months after completion of therapy were more frequent with nitrofurantoin (34% and 15%) and pivmecillinam (30% and 17%) than trimethoprim (22 and 7%). However, these differences were not statistically significant and substantial heterogeneity was noted between the treatment groups. Urinary tract catheterization was associated with a higher risk for new antibiotic prescriptions (OR 2.34, 95% CI 1.14-4.80; P = 0.022) and prostate cancer was associated with a higher incidence of relapse (OR 3.01, 95% CI 1.09-8.29; P = 0.042).

CONCLUSIONS

The clinical outcome with nitrofurantoin and pivmecillinam was acceptable in comparison with the results of previous studies. These antibiotics are suitable for empirical treatment of lower UTI in men considering their high activity against Escherichia coli and limited impact on the intestinal microbiota.

Synergistic and bactericidal activities of mecillinam, amoxicillin and clavulanic acid combinations against extended-spectrum β-lactamase (ESBL)-producing Escherichia coli in 24-h time-kill experiments

This study aimed to evaluate the potential synergistic and bactericidal effects of mecillinam in combination with amoxicillin and clavulanic acid against extended-spectrum β-lactamase (ESBL)-producing Escherichia coli. Eight clinical E. coli isolates with varying susceptibility to mecillinam [minimum inhibitory concentrations (MICs) of 0.125 mg/L to >256 mg/L] and high-level resistance to amoxicillin (MICs > 256 mg/L) were used. Whole-genome sequencing was performed to determine the presence of β-lactamase genes and mutations in the cysB gene. The activities of single drugs and the combinations of two or three drugs were tested in 24-h time-kill experiments. Population analysis was performed for two strains before and after experiments. Only one strain had a mutation in the cysB gene resulting in an amino acid substitution. With the two-drug combinations, initial killing was observed both with mecillinam and amoxicillin when combined with clavulanic acid. Synergy was observed with mecillinam and clavulanic acid against one strain and with amoxicillin and clavulanic acid against three strains. However, following significant re-growth, a bactericidal effect was found only with amoxicillin and clavulanic acid against two strains. Pre-existing subpopulations with elevated mecillinam MICs were detected before experiments and were selected with mecillinam alone or in two-drug combinations. In contrast, the three-drug combination showed enhanced activity with synergy against six strains, a bactericidal effect against all eight strains, and suppression of resistance during 24-h antibiotic exposure. This combination may be of clinical interest in the treatment of urinary tract infections caused by ESBL-producing E. coli.

Performance Validation of Selective Screening Agars for Guiding Antimicrobial Prophylaxis in Patients Undergoing Prostate Biopsy

A rectal culture-guided antimicrobial prophylaxis strategy may prevent infections after transrectal ultrasound-guided prostate biopsy (TRUSP). The use of selective culture media could assist the choice of appropriate antibiotic prophylaxis. The objective of our study was to evaluate the performance of four selective media used for guidance of oral antibiotic prophylaxis in TRUSP. In this prospective validation study, we used MacConkey media with vancomycin plus one of the following antibiotics: ciprofloxacin (McC3+CIP/V), trimethoprim (McC3+TMP/V), fosfomycin (McC3+FOF/V), and amdinocillin-amoxicillin-clavulanic acid (McC3+MEC/V). First, clinical strains of Gram-negative bacilli (GNB) (n = 33) were evaluated for growth on the selective media. Thereafter, rectal swabs (n = 97) were randomly collected from residual material of fresh stool samples and plated on a growth control and the four selective media. Levels of recovery of GNB on the growth control and selective media were compared, and the MICs of the antibiotics used in this study were determined. The sensitivity and specificity of the four selective media amounted, respectively, to 90.0% (55.5 to 99.8%) and 98.7% (93.1 to 100.0%) for McC3+CIP/V, 95.7% (85.2 to 99.5%) and 100.0% (91.6 to 100.0%) for McC3+TMP/V, 95.5% (84.5 to 99.4%) and 97.8% (88.2 to 99.9%) for McC3+FOF/V, and 100.0% (76.8 to 100.0%) and 97.6% (87.4 to 99.9%) for McC3+MEC/V. In conclusion, the four selective media were sufficiently sensitive and specific for the identification of rectal GNB resistant to ciprofloxacin, trimethoprim, fosfomycin, or amdinocillin-amoxicillin-clavulanic acid. These media can have added value in streamlining the optimal culture based antibiotic prophylaxis in TRUSP in a non-labor-intensive manner.

Mecillinam for the treatment of acute pyelonephritis and bacteremia caused by Enterobacteriaceae: a literature review

Purpose

The pharmacokinetic properties of mecillinam (MEC) for urinary tract infections are excellent, and the resistance rate in Enterobacteriaceae is low compared to other recommended antibiotics. The oral prodrug pivmecillinam (P-MEC) has been used successfully as first choice for cystitis in the Nordic countries for many years. Norwegian and Danish guidelines also recommend P-MEC for acute uncomplicated pyelonephritis (AUP) and intravenous (IV) MEC for suspected urosepsis (only in Denmark). Here, we wish to present an updated investigation on the clinical data behind these recommendations together with sparse but more current clinical data.

Methods

Prospective clinical trials evaluating MEC as monotherapy or in polytherapy with one other beta-lactam (mostly ampicillin [AMP]) for pyelonephritis or bacteremia were reviewed. Outcomes of primary interest were clinical and bacteriological success and relapse, respectively. Search databases used were PubMed, Cochrane Library, and Embase.

Results

Twelve clinical studies (1979-2015) were included in this integrated literature review. Clinical success was seen in 38/51 (75%) patients treated with MEC as monotherapy and in 152/164 (93%) patients treated with MEC and one other beta-lactam. Bacteriological success was seen in 35/47 (74%) and 117/167 (70%) patients treated with MEC alone and with one other beta-lactam, respectively. In complicated infections, bacteriological success was much lower. Clinical relapse rate was not well described. Several uropathogenic bacteremia cases were treated successfully with MEC alone (ie, 10/15 [67%] and 13/15 [87%] for clinical and bacteriological success, respectively) or with one other beta-lactam (ie, 57/65 [88%] and 53/63 [84%] for clinical and bacteriological success, respectively). However, data on bacteremia are very sparse. Adverse reactions were few and mild (73/406 [18%]) and primarily seen when AMP was co-administered (69/73 [95%]). No serious adverse reactions were reported.

Conclusion

IV MEC or oral P-MEC for 14 days may be suitable for the treatment of AUP and pediatric pyelonephritis. Randomized controlled trials using a single standardized dose of P-MEC compared to other current recommendations are warranted. Similarly, more evidence is required before MEC should be recommended for bacteremia or sepsis due to Enterobacteriaceae.

Prostate Biopsy-related Infection: A Systematic Review of Risk Factors, Prevention Strategies, and Management Approaches

A systematic review to identify risk factors for prostate biopsy-related infection, preventative strategies, and optimal management of infectious complications was conducted. Significant risk factors for postbiopsy infection include urogenital infection, antibiotic use, international travel, hospital exposure, bacteriuria, previous transrectal biopsy, and resistance of fecal flora to antibiotic prophylaxis (especially fluoroquinolones). Patients at risk may benefit from an adjusted biopsy protocol comprising transrectal biopsy under targeted prophylaxis, and/or the use of rectal disinfection techniques or using a transperineal approach. Management of biopsy-related infection should be based on individual risk and local resistance profiles with input from multiple specialties.

Characteristics of gram-negative urinary tract infections caused by extended spectrum beta lactamases: pivmecillinam as a treatment option within South Dublin, Ireland

Background

The prevalence of urinary tract infections (UTIs) caused by extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae is increasing and the therapeutic options are limited, especially in primary care. Recent indications have suggested pivmecillinam to be a suitable option. This pilot study aimed to assess the viability of pivmecillinam as a therapeutic option in a Dublin cohort of mixed community and healthcare origin.

Methods

A prospective measurement of mean and fractional inhibitory concentrations of antibiotic use in 95 patients diagnosed with UTI caused by ESBL-producing Enterobacteriaceae was carried out. 36 % patients were from general practice, 40 % were admitted to hospital within south Dublin, and 25 % samples arose from nursing homes. EUCAST breakpoints were used to determine if an isolate was sensitive or resistant to antibiotic agents.

Results

Sixty-nine percent of patients (N = 66) with urinary ESBL isolates were female. The mean age of females was 66 years compared with a mean age of 74 years for males. Thirty-six percent of isolates originated from primary care, hospital inpatients (26 %), and nursing homes (24 %). The vast majority of ESBL isolates were E. coli (80 %). The E tests for mecillinam and co-amoxiclav had concentration ranges from 0.16 mg/L up to 256 mg/L. The mean inhibitory concentration (MIC) of mecillinam ranged from 0.25 to 256 mg/L, while co-amoxiclav MICs ranged from 6 to 256 mg/L. The percentage of isolates resistant to mecillinam and co-amoxiclav was found to be 5.26 and 94.74 % respectively.

Conclusions

This is the first study exploring the use of pivmecillinam in an Irish cohort and has demonstrated that its use in conjunction with or without co-amoxiclav is an appropriate and useful treatment for urinary tract infections caused by ESBL-producing organisms.

Multidrug Resistant CTX-M-Producing Escherichia coli: A Growing Threat among HIV Patients in India

Extended Spectrum β-Lactamases (ESBLs) confer resistance to third-generation cephalosporins and CTX-M types have emerged as the most prominent ESBLs worldwide. This study was designed to determine the prevalence of CTX-M positive ESBL-producing urinary E. coli isolates from HIV patients and to establish the association of multidrug resistance, phylogeny, and virulence profile with CTX-M production. A total of 57 ESBL producers identified among 76 E. coli strains isolated from HIV patients from South India were screened for bla_CTX-M, AmpC production, multidrug resistance, and nine virulence associated genes (VAGs), fimH, pap, afa/dra, sfa/foc, iutA, fyuA, iroN, usp, and kpsMII. The majority (70.2%) of the ESBL producers harbored bla_CTX-M and were AmpC coproducers. Among the CTX-M producers, 47.5% were found to be UPEC, 10% harbored as many as 7 VAGs, and 45% possessed kpsMII. Multidrug resistance (CIP^RSXT^RGEN^R) was significantly more common among the CTX-M producers compared to the nonproducers (70% versus 41.2%). However, 71.4% of the multidrug resistant CTX-M producers exhibited susceptibility to nitrofurantoin thereby making it an effective alternative to cephalosporins/fluoroquinolones. The emergence of CTX-M-producing highly virulent, multidrug resistant uropathogenic E. coli is of significant public health concern in countries like India with a high burden of HIV/AIDS.

Activity of temocillin, mecillinam, ceftazidime, and ceftazidime/avibactam against carbapenem-non-susceptible Enterobacteriaceae without carbapenemase production

Treatment options for multidrug-resistant Gram-negative infections are scarce and therefore alternatives with a narrow spectrum or new agents are sought. Antimicrobial susceptibility to temocillin, mecillinam, ceftazidime, and ceftazidime/avibactam was determined using Etest and disk diffusion according to European Committee on Antimicrobial Susceptibility Testing (EUCAST) methodology. A total of 77 carbapenem-nonsusceptible Enterobacteriaceae were studied, including Klebsiella pneumoniae (26%), Escherichia coli (26%), Enterobacter cloacae (26%), and Enterobacter aerogenes (22%). Several phenotypic tests, PCRs followed by sequencing and a microbiological bioassay excluded carbapenemase production in all isolates. Antimicrobial susceptibility rates were low for temocillin (15.6%, minimum inhibitory concentration [MIC] range 2 to >1,024 μg/ml), moderate for mecillinam (59.7%, MIC range 0.25 to >256 μg/ml), and excellent for ceftazidime/avibactam (100%, zone diameter range 19 to 32 mm, median 25 mm). 5.2% of the isolates were susceptible to ceftazidime alone (zone diameter range 6 to 32 mm). In this study, mecillinam exhibited moderate and ceftazidime/avibactam excellent in vitro antimicrobial activity against carbapenem-nonsusceptible Enterobacteriaceae without carbapenemase production. Ceftazidime/avibactam was able to restore previously reduced susceptibility to ceftazidime in all isolates, thus potentiating its activity. Temocillin only exhibited low in vitro antimicrobial activity against the isolates. Further evaluation of mecillinam and ceftazidime/avibactam with regard to the potential clinical utility against infections caused by these pathogens has to be performed.

β-Lactam Antibiotics Renaissance

Since the 1940s β-lactam antibiotics have been used to treat bacterial infections. However, emergence and dissemination of β-lactam resistance has reached the point where many marketed β-lactams no longer are clinically effective. The increasing prevalence of multidrug-resistant bacteria and the progressive withdrawal of pharmaceutical companies from antibiotic research have evoked a strong reaction from health authorities, who have implemented initiatives to encourage the discovery of new antibacterials. Despite this gloomy scenario, several novel β-lactam antibiotics and β-lactamase inhibitors have recently progressed into clinical trials, and many more such compounds are being investigated. Here we seek to provide highlights of recent developments relating to the discovery of novel β-lactam antibiotics and β-lactamase inhibitors.

High rate of per oral mecillinam treatment failure in community-acquired urinary tract infections caused by ESBL-producing Escherichia coli

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.

β-Lactam antimicrobials: what have you done for me lately?

The "perpetual challenge of infectious diseases" is no better exemplified than by the phenomena of rapid emergence and spread of bacterial resistance. Although β-lactam antimicrobials have thus far been a mainstay of the therapeutic armamentarium for treatment of severe infections, their preeminent position has been challenged by an onslaught of resistance mechanisms in major nosocomial and community-acquired pathogens, including modification of penicillin-binding proteins, production of β-lactamases, overexpression of efflux pumps, and loss of porins. Given this formidable array of resistance mechanisms facing patients and their physicians, one can reasonably ask if there is hope for the future of β-lactams.

Extended-spectrum β-lactamase/AmpC-producing uropathogenic Escherichia coli from HIV patients: do they have a low virulence score?

Extended-spectrum β-lactamase (ESBL) production and quinolone resistance are often associated in enterobacteria. Prior exposure to 3G cephalosporins/quinolones accelerates the risk of resistance to both these groups of antibiotics. Hence, information on the antimicrobial resistance pattern of uropathogenic Escherichia coli (UPEC) isolates is important to better formulate the guidelines for the empirical therapy of urinary tract infection in the context of HIV/AIDS. The aim of this study was to determine the incidence of ESBL/AmpC and fluoroquinolone (FQ) resistance among urinary E. coli isolates and to establish the association of extraintestinal virulence and phylogenetic distribution with antibiotic resistance and host immunocompromisation. Accordingly, 118 urinary Escherichia coli isolates from HIV (n = 76) and non-HIV antenatal patients (n = 42) from Chennai, South India, were analysed for the presence of five virulence-associated genes (VAGs): pap, sfa/foc, afa/dra, iutA and kpsMII. Compared with the susceptible HIV isolates, the majority of the ESBL(+)AmpC(+)FQ(R) isolates harboured iutA (66.7%) and pap (40%). The FQ-resistant HIV isolates were significantly enriched for iutA (67.8%) and kpsMII (47.5%) and qualified as UPEC (54.2%), while a majority of the FQ-susceptible isolates from the non-HIV patients were found to harbour pap (48.4%), sfa/foc (41.9%) and kpsMII (48.4%) and were classified as UPEC (40.5%). We conclude that antibiotic-resistant (ESBL(+)AmpC(+)and/or FQ(R)) phylogroup D isolates with limited virulence are competent enough to establish infections in HIV patients, while among non-HIV patients, an array of virulence factors is essential for E. coli to overcome host defences irrespective of antibiotic resistance.