Within-population distribution of trimethoprim resistance in Escherichia coli before and after a community-wide intervention on trimethoprim use

Costs of antibiotic resistance genes depend on host strain and environment and can influence community composition

Antibiotic resistance genes (ARGs) benefit host bacteria in environments containing corresponding antibiotics, but it is less clear how they are maintained in environments where antibiotic selection is weak or sporadic. In particular, few studies have measured if the direct effect of ARGs on host fitness is fixed or if it depends on the host strain, perhaps marking some ARG-host combinations as selective refuges that can maintain ARGs in the absence of antibiotic selection. We quantified the fitness effects of six ARGs in 11 diverse Escherichia spp. strains. Three ARGs (blaTEM-116, cat and dfrA5, encoding resistance to β-lactams, chloramphenicol, and trimethoprim, respectively) imposed an overall cost, but all ARGs had an effect in at least one host strain, reflecting a significant strain interaction effect. A simulation predicts these interactions can cause the success of ARGs to depend on available host strains, and, to a lesser extent, can cause host strain success to depend on the ARGs present in a community. These results indicate the importance of considering ARG effects across different host strains, and especially the potential of refuge strains to allow resistance to persist in the absence of direct selection, in efforts to understand resistance dynamics.

Pivmecillinam, the paradigm of an antibiotic with low resistance rates in Escherichia coli urine isolates despite high consumption

OBJECTIVES

Pivmecillinam, the oral version of mecillinam, represents one of the major recommended and used antibiotics for empiric and targeted treatment of urinary tract infections in primary care in Denmark, Norway and Sweden. Mecillinam resistant mutants in Escherichia coli develop easily in vitro, but their fitness cost has been shown to be high.

METHODS

We revisited the resistance and consumption data from the monitoring programmes in the three countries and compared pivmecillinam with ciprofloxacin from 2010 to 2020.

RESULTS

Mecillinam resistance rates in Escherichia coli remained around 6% in Denmark and Norway relative to a constant consumption in Norway of 1.6-1.8 DID (defined daily doses per 1000 inhabitants per day), and even increasing in Denmark from 1.6 to 2.3 DID. In Sweden resistance was significantly lower at 4% related to the lower consumption of 0.5 DID. For ciprofloxacin, resistance rates fluctuated around 6%-12%, highest in Sweden with the highest consumption (0.8-0.6 DID) and lowest in Denmark (0.55-0.35 DID) and Norway (0.7-0.3 DID), although consumption declined significantly in all three countries.

CONCLUSIONS

Pivmecillinam is an example of an antibiotic, which easily develops resistance in vitro, but apparently can be used broadly in primary care without increase in resistance rates.

Antibiotic resistance in urinary tract infections: A re-visit after five years and experience over two sites

OBJECTIVE

The aim of this study was to repeat a previous audit, performed from 2009 to 2013, for the cohort of 2018 to determine how the resistance rates in urinary pathogens in women over 18 years of age have changed. A secondary aim of the study was to use resistance data from a different UK hospital in the same year to compare differences in resistance rates across different geographic locations.

STUDY DESIGN

This was a retrospective study of all positive urine cultures grown from female patients attending two different hospitals in the year 2018. Resistance patterns were analysed.

RESULTS

The resistance rate to co-amoxiclav continues to increase with amoxicillin retaining high resistance patterns. There are some significant differences in resistance patterns between the different locations.

CONCLUSION

Antimicrobial resistance is a significant problem in the UK particularly in antibiotics used to treat UTI. These patterns can vary across different geographical locations and over time; therefore, up-to-date knowledge of local anti-biotic resistance is essential when making an appropriate prescription choice.

Low Cassette Variability in Class 2 and Class 1 Integrons of Aeromonas spp. Isolated from Environmental Samples

Integrons are prokaryotic genetic elements known to carry and exchange antibiotic resistance gene cassettes through a site-specific recombinase called integrase. In this work, 107 Aeromonas isolates from environmental origin, including fish, water, and sediments, were investigated for the presence of integrons. Using specific primers for Class 1, 2 and 3 integrases, only Class 1 and Class 2 integrons were detected. Detection of Class 2 integrases and their associated variable regions required two rounds of polymerase chain reaction (PCR). Sequencing of the intI2 amplicons confirmed them as integrase-derived products. Class 1 integrons were detected in 26 out of 107 isolates. PCR amplification of the variable regions associated to these integrons revealed an outstanding homogeneity, 25 of them having variable regions with an identical dfrA12-orfF-aadA2 cassette array and one integron carrying only the dfrA16 cassette. To assess clone diversity, chromosomal DNA from isolates was subjected to enterobacterial repetitive intergenic consensus-PCR (ERIC-PCR), which discarded clonality in all instances. Class 2 integrons were surprisingly more prevalent than Class1 integrons, being detected in 60 out of 107 isolates. Forty-six of them showed a unique ERIC profile, while the remaining 14 strains displayed profiles that could be grouped in five different patterns. Cassette arrangements of all Class 2 variable regions were those described as the most prevalent (dfrA1-sat2-aadA1). A rather startling result of this work is the sensitivity to trimethoprim, streptomycin, and streptothricin of most strains, despite the presence of the cognate resistance genes. To know the integron distribution in environmental Aeromonas species, a phylogenetic reconstruction was done using rpoD/gyrB or rpoD/gyrA gene sequences. Isolates bearing these elements corresponded to Aeromonas hydrophila, Aeromonas veronii, Aeromonas salmonicida, Aeromonas dhakensis, Aeromonas sanarellii, Aeromonas taiwanensis, Aeromonas media, Aeromonas caviae, Aeromonas jandaei, and Aeromonas sp. This work revealed an unusual high incidence of Class 2 integrons and a low variability of cassette arrangements in environmental Aeromonas species.

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.