Squeezing the antibiotic balloon: the impact of antimicrobial classes on emerging resistance

Antibiotic stewardship programmes in intensive care units: Why, how, and where are they leading us

Antibiotic usage and increasing antimicrobial resistance (AMR) mount significant challenges to patient safety and management of the critically ill on intensive care units (ICU). Antibiotic stewardship programmes (ASPs) aim to optimise appropriate antibiotic treatment whilst minimising antibiotic resistance. Different models of ASP in intensive care setting, include “standard” control of antibiotic prescribing such as “de-escalation strategies”through to interventional approaches utilising biomarker-guided antibiotic prescribing. A systematic review of outcomes related studies for ASPs in an ICU setting was conducted. Forty three studies were identified from MEDLINE between 1996 and 2014. Of 34 non-protocolised studies, [1 randomised control trial (RCT), 22 observational and 11 case series], 29 (85%) were positive with respect to one or more outcome: These were the key outcome of reduced antibiotic use, or ICU length of stay, antibiotic resistance, or prescribing cost burden. Limitations of non-standard antibiotic initiation triggers, patient and antibiotic selection bias or baseline demographic variance were identified. All 9 protocolised studies were RCTs, of which 8 were procalcitonin (PCT) guided antibiotic stop/start interventions. Five studies addressed antibiotic escalation, 3 de-escalation and 1 addressed both. Six studies reported positive outcomes for reduced antibiotic use, ICU length of stay or antibiotic resistance. PCT based ASPs are effective as antibiotic-stop (de-escalation) triggers, but not as an escalation trigger alone. PCT has also been effective in reducing antibiotic usage without worsening morbidity or mortality in ventilator associated pulmonary infection. No study has demonstrated survival benefit of ASP. Ongoing challenges to infectious disease management, reported by the World Health Organisation global report 2014, are high AMR to newer antibiotics, and regional knowledge gaps in AMR surveillance. Improved AMR surveillance data, identifying core aspects of successful ASPs that are transferable, and further well-conducted trials will be necessary if ASPs are to be an effective platform for delivering desired patient outcomes and safety through best antibiotic policy.

Absence of Association between Use of Ertapenem and Change in Antipseudomonal Carbapenem Susceptibility Rates in 25 Hospitals

Objective.

Ertapenem exposure has been reported to select for cross-resistance to other carbapenems in Pseudomonas aeruginosa in vitro. Single-center investigations report conflicting results. We evaluated ertapenem use and antipseudomonal carbapenem susceptibility for 6 years spanning the time of ertapenem adoption at each of 25 US hospitals.

Design.

Retrospective primary and secondary data analysis.

Methods.

Use density ratios for imipenem and meropenem (collectively, “other carbapenems”) and ertapenem were derived from data in a commercial database on the total number of grams used in the 3 years before and the 3 years after adoption of ertapenem at each hospital. A general linear model using repeated measures analysis of variance was used to explore associations between the 6-year change in antipseudomonal carbapenem susceptibility rates (determined from hospital antibiograms) and ertapenem use in each year, while controlling for other carbapenem use.

Results.

Ertapenem use increased once adopted. With regard to the postadoption period, the median use density ratio for year 4 was 4.1 (interquartile range [IQR], 1.7-5.2), for year 5 was 6.0 (IQR, 2.7-8.5), and for year 6 was 6.5 (IQR, 4.0-11.6). The median use density ratio for other carbapenem use for year 1 was 8.7 (IQR, 5.7-13.5), and by year 6 it had increased to 19.3 (IQR, 9.6-26.2). Change in mean antipseudomonal carbapenem susceptibility across time (85% in year 1 to 82% in year 6) was not significant (P = .22). Change in 6-year antipseudomonal carbapenem susceptibility was not associated with ertapenem use in any year while controlling for other carbapenem use (P > .20 for all years of ertapenem use).

Conclusion.

Although significant change in P. aeruginosa susceptibility to antipseudomonal carbapenems was not detected during this multicenter study, which to our knowledge is the most extensive assessment to date of this important drug use-susceptibility relationship, continued evaluation of the relationship is prudent.

Evaluation of new antimicrobials for the hospital formulary. Policies restricting antibiotic use in hospitals

In Spain, the inclusion of new antibiotics in hospital formularies is performed by the Infection Policy Committee or the Pharmacy and Therapeutic Committee, although now the decision is moving to a regional level. Criteria for the evaluation of new drugs include efficacy, safety and cost. For antimicrobial drugs evaluation it is necessary to consider local sensibility and impact in bacterial resistance to determinate the therapeutic positioning. There is compelling evidence that the use of antibiotics is associated with increasing bacterial resistance, and a great number of antibiotics are used incorrectly. In order to decrease the inappropriate use of antibiotics, several approaches have been proposed. Limiting the use of antimicrobials through formulary restrictions, often aimed at drugs with a specific resistance profile, shows benefits in improving antimicrobial susceptibilities and decreasing colonization by drug-resistant organisms. However, the restriction of one agent may result in the increased utilization of other agents. By using antibiotic cycling, the amount of antibiotics is maintained below the threshold where bacterial resistance develops, thus preserving highly efficient antibiotics. Unfortunately, cumulative evidence to date suggests that antibiotic cycling has limited efficacy in preventing antibiotic resistance. Finally, although there is still little clinical evidence available on antibiotic heterogeneity, the use of most of the existing antimicrobial classes could limit the emergence of resistance. This review summarizes information regarding antibiotic evaluation and available restrictive strategies to limit the use of antibiotics at hospitals with the aim of curtailing increasing antibiotic resistance.

Clinical and economic outcomes of a prospective antimicrobial stewardship program

PURPOSE

A pre-post analysis of an antimicrobial stewardship program (ASP) involving the use of data-mining software to prospectively identify cases for ASP intervention was conducted.

METHODS

The investigators evaluated clinical outcomes and cost metrics before and after implementation of the ASP, which entailed daily physician review of summary reports on all adult inpatients receiving antimicrobial therapy. The primary outcome measures were annual antimicrobial expenditures and rates of infections due to common nosocomial pathogens; secondary outcome measures included patient survival and length of stay (LOS) in cases involving the indicator diagnoses of pneumonia and abdominal sepsis.

RESULTS

Antimicrobial expenditures, which had increased by an average of 14.4% annually in the years preceding ASP implementation, decreased by 9.75% in the first year of the program and remained relatively stable in subsequent years, with overall cumulative cost savings estimated at $1.7 million. Rates of nosocomial infections involving Clostridium difficile, methicillin-resistant Staphylococcus aureus, and vancomycin-resistant enterococci all decreased after ASP implementation. A pre-post comparison of survival and LOS in patients with pneumonia (n = 2186) or abdominal sepsis (n = 225) showed no significant differences in those outcomes in either patient group, possibly due to the hospital's initiation of other, concurrent infection-control programs during the study period.

CONCLUSION

A prospective collaborative ASP employed automated reports to efficiently identify key data for ASP review. After ASP implementation, antimicrobial expenditures and rates of nosocomial infections caused by resistant pathogens dropped without significant changes in patient survival, LOS, and readmissions for the two studied illness categories.

Patented drug extension strategies on healthcare spending: a cost-evaluation analysis

BACKGROUND

Drug manufacturers have developed "evergreening" strategies to compete with generic medication after patent termination. These include marketing of slightly modified follow-on drugs. We aimed to estimate the financial impact of these drugs on overall healthcare costs and also to examine the impact of listing these drugs in hospital restrictive drug formularies (RDFs) on the healthcare system as a whole ("spillover effect").

METHODS AND FINDINGS

We used hospital and community pharmacy invoice office data in the Swiss canton of Geneva to calculate utilisation of eight follow-on drugs in defined daily doses between 2000 and 2008. "Extra costs" were calculated for three different scenarios assuming replacement with the corresponding generic equivalent for prescriptions of (1) all brand (i.e., initially patented) drugs, (2) all follow-on drugs, or (3) brand and follow-on drugs. To examine the financial spillover effect we calculated a monthly follow-on drug market share in defined daily doses for medications prescribed by hospital physicians but dispensed in community pharmacies, in comparison to drugs prescribed by non-hospital physicians in the community. Estimated "extra costs" over the study period were €15.9 (95% CI 15.5; 16.2) million for scenario 1, €14.4 (95% CI 14.1; 14.7) million for scenario 2, and €30.3 (95% CI 29.8; 30.8) million for scenario 3. The impact of strictly switching all patients using proton-pump inhibitors to esomeprazole at admission resulted in a spillover "extra cost" of €330,300 (95% CI 276,100; 383,800), whereas strictly switching to generic cetirizine resulted in savings of €7,700 (95% CI 4,100; 11,100). Overall we estimated that the RDF resulted in "extra costs" of €503,600 (95% CI 444,500; 563,100).

CONCLUSIONS

Evergreening strategies have been successful in maintaining market share in Geneva, offsetting competition by generics and cost containment policies. Hospitals may be contributing to increased overall healthcare costs by listing follow-on drugs in their RDF. Therefore, healthcare providers and policy makers should be aware of the impact of evergreening strategies.

Correlation between carbapenem consumption and resistance to carbapenems among Enterobacteriaceae isolates collected from patients with intra-abdominal infections at five medical centers in Taiwan, 2006-2010

We investigated the trend in resistance to carbapenems among isolates of Enterobacteriaceae that had been collected from patients with intra-abdominal infections at five medical centers in Taiwan from 2006 to 2010 and evaluated the correlation between resistance to carbapenems and consumption of said agents as part of the Study for Monitoring Antimicrobial Resistance Trends (SMART). During the study period, the usage of ertapenem and that of total carbapenems (ertapenem, imipenem, and meropenem) increased significantly from 6.13 to 13.38 defined daily doses per 1000 patient-days for ertapenem and from 20.43 to 34.25 defined daily doses per 1000 patient-days for total carbapenems. The most common species were Escherichia coli (n = 1095), Klebsiella spp. (n = 663), and Enterobacter spp. (n = 202). The susceptibility of all isolates to ertapenem and to imipenem varied during the study period. For ertapenem, the rates of nonsusceptibility ranged from 3.5% to 10.3% and those for imipenem ranged from 3.5% to 10.7%. Although the use of carbapenems increased during the study period, there was no marked increase in resistance to carbapenems. Continuous monitoring of resistance trends is necessary so that antimicrobial prescription policies can be adjusted and infection control intervention programs can be implemented.

Impact of a region wide antimicrobial stewardship guideline on urinary tract infection prescription patterns

BACKGROUND

Fluoroquinolones are frequently prescribed for non complicated urinary tract infection treatments and have a negative ecological impact. We aimed to substitute them by antibiotics with narrower activity spectrum in order to preserve fluoroquinolone activity in complicated hospital infections.

OBJECTIVE

To assess the impact of a multi-modal approach that combines the dispatching of antibiotic prescription guidelines and voluntary attendance at educational sessions on general practitioners' (GP) antibiotic prescription habits.

SETTING

This study was led in Franche-Comté, a French eastern region, where GPs were given a guideline recommending a restricted use of fluoroquinolones for urinary tract infections.

METHOD

Segmented regression analysis of interrupted time series was used to assess changes in antibiotic prescription.

MAIN OUTCOME MEASURE

The antibiotic prescription data of nitrofurantoin, fosfomycin-trometamol and fluoroquinolones for women aged 15-65 years were obtained from the regional agency of health insurance.

RESULTS

Twenty months after intervention, the number of nitrofurantoin and fosfomycintrometamol prescriptions increased by 36.8% (95% CI: 30.6-42.2) and 28.5% (95% CI: 22.9-35.4), respectively, while that of norfloxacin decreased by 9.1% (95% CI: -15.3 to -3.5).

CONCLUSION

This study suggests that the dispatch of the guideline on urinary tract infection had a moderate impact on antibiotic prescriptions.

Occurrence of Plasmid-Mediated AmpC β-Lactamases Among Escherichia coli and Klebsiella pneumoniae Clinical Isolates in a Tertiary Care Hospital in Bangalore

Therapeutic options for infections caused by gram-negative organisms expressing plasmid-mediated AmpC β-lactamases are limited because these organisms are usually resistant to all the β-lactam antibiotics, except for cefepime, cefpirome and the carbapenems. These organisms are a major concern in nosocomial infections and should therefore be monitored in surveillance studies. Hence, this study was aimed out to determine the prevalence of plasmid-mediated AmpC β-lactamases in E. coli and K. pneumoniae from a tertiary care in Bangalore. A total of 63 E. coli and 27 K. pneumoniae were collected from a tertiary care hospital in Bangalore from February 2008 to July 2008. The isolates with decreased susceptibility to cefoxitin were subjected to confirmation test with three dimensional extract tests. Minimum inhibitory concentrations (MICs) were determined by agar dilution method. Conjugation experiments, plasmid profiling and susceptibility testing were carried out to investigate the underlying mechanism of resistance. In our study, 52 (57.7%) isolates showed resistance to cefoxitin, the occurrence of AmpC was found to be 7.7% of the total isolates. Plasmid analysis of the selected isolates showed the presence of a single plasmid of 26 kb in E. coli and 2 Kb in K. pneumoniae. Plasmid-mediated AmpC β-lactamases were found in 11.1% of K. pneumoniae and in 6.3% of E. coli. Curing and conjugation experiments showed that resistance to cephamycins and cephalosporins was plasmid-mediated. Our study has demonstrated the occurrence of plasmid-mediated AmpC in E. coli and K. pneumoniae which illustrates the importance of molecular surveillance in tracking AmpC-producing strains at general hospitals and emphasizes the need for epidemiological monitoring.

A national cross-sectional study on socio-behavioural factors that influence physicians' decisions to begin antimicrobial therapy

PURPOSE

Current efforts to prevent antimicrobial resistance include limiting antimicrobial use, providing education about appropriate use, and developing better point-of-care tests, but what do physicians actually think of rational prescribing and potential interventions? We tried to ascertain which factors can influence a physician's decision to start antimicrobial therapy on a patient, and their opinions on measures to promote rational prescribing.

METHODS

We conducted a nationwide, cross-sectional survey of 10,600 physicians from medical registries of all known board-certified physicians in Germany.

RESULTS

Among respondents (n = 3,492; 33%; detailed non-response bias analysis included), 90% indicated that they decide to start antimicrobial therapy on a patient at least weekly, and 66% reported that they decide daily. We identified correlates for deciding to start antimicrobial therapy on a patient. Predictors were status as a hospital physician (odds ratio (OR) 1.29 (95% confidence interval (CI) 1.00-1.68)), male physician (OR 1.81 (95% CI 1.42-2.31)), being age 50-59 (OR 1.56 (95% CI 1.10-2.21)), and practising in states in the former East Germany (OR 1.60 (95% CI 1.15-2.21)). Each specialist was significantly less likely to decide to start a course of antimicrobial therapy than ENTs and urologists. Other predictors were agreeing to prescribe to be on the safe side (OR 1.34 (95% CI 1.03-1.76)), believing that the quality of prescribing practice improves after receiving continuing education from pharmaceutical companies (OR 1.43 (95% CI 1.11-1.84)), and having experience with failed therapy for resistant pathogens (OR 2.42 (95% CI 1.83-3.19)).

CONCLUSIONS

Physicians in our sample decide to start antimicrobial therapy on a patient, and they value intervention to support prudent use, for example continuing education, practice guidelines and implementation of surveillance measures. Socio-behavioural factors, regional variation, gender, and age merit further research to promote rational antimicrobial prescribing and explore related influencing factors.

Fluoroquinolone use is not associated with the change in imipenem susceptibility of Pseudomonas aeruginosa in 25 hospitals

INTRODUCTION

Evidence suggests use of fluoroquinolones is associated with carbapenem resistance in Pseudomonas aeruginosa, and fluoroquinolone use has been identified as a risk factor for clinical acquisition of imipenem-resistant P. aeruginosa in single-center studies. Imipenem susceptibility and fluoroquinolone use was evaluated within 25 hospitals over 9 years.

METHODS

Use density ratios (UDR) for fluoroquinolones: ciprofloxacin, gatifloxacin, levofloxacin, and moxifloxacin, and for three other antibiotic classes (carbapenems: ertapenem, doripenem, imipenem, and meropenem; other antipseudomonal beta-lactams: cefepime, ceftazidime, and piperacillin/tazobactam; and aminoglycosides: gentamicin and tobramycin) were derived from drug purchase data for up to 9 years, ending in 2008. Susceptibility data were obtained from hospital antibiograms in corresponding years. A mixed model repeated measures ANOVA (Analysis of Variance) explored associations between 9-year repeated imipenem susceptibility and fluoroquinolone UDR in each year while controlling for other drug classes, teaching status, and number of beds.

RESULTS

All sites had 7 years of data; n=22 had 8 years; n=18 had 9 years. Teaching hospitals were 36% of the cohort; median number of beds was 714 for teaching hospitals and 381 for nonteaching hospitals. Fluoroquinolone use declined from year (Y) 1-5; such use then rose over Y6-9, which was heavily influenced by ciprofloxacin/moxifloxacin: mean fluoroquinolone UDR from Y1-9 was: 303.8, 186.5, 156.8, 174.4, 169.1, 275.0, 504.2, 477.0, and 423.3. Mean imipenem susceptibility was (Y1-9 %) 85.2, 82.8, 82.7, 82.2, 82.8, 82.4, 82.3, 81.7, and 80.6; this change across time was not significant (P=0.46). Change in 9-year imipenem susceptibility was not associated with fluoroquinolone UDR (P=0.17), nor with any other drug class (P>0.40 for each). Results were not different when considering only sites with top 25% fluoroquinolone UDR during Y7-9.

CONCLUSION

Single-center studies of fluoroquinolone use have reported changes in P. aeruginosa susceptibility to carbapenems. Our study finds no such association while controlling for other drug classes. As such, resistance development in individual patients versus institutions warrants further research.

Correlation between antibiotic consumption and resistance of Gram-negative bacteria causing healthcare-associated infections at a university hospital in Taiwan from 2000 to 2009

OBJECTIVES

This study investigated the correlation between antibiotic consumption and antimicrobial resistance in Gram-negative bacteria causing healthcare-associated infections at a university hospital in Taiwan from 2000 to 2009.

METHODS

Disc susceptibility data of Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Serratia marcescens, Proteus spp., Pseudomonas aeruginosa, Acinetobacter spp., Stenotrophomonas maltophilia and other non-fermentative Gram-negative bacilli causing healthcare-associated infections were evaluated. Data on annual patient-days and annual consumption (defined daily doses per 1000 patient-days) of extended-spectrum cephalosporins, β-lactam/β-lactamase inhibitor combinations, carbapenems, aminoglycosides and fluoroquinolones were analysed.

RESULTS

The trend of total consumption of extended-spectrum cephalosporins, β-lactam/β-lactamase inhibitor combinations, carbapenems, aminoglycosides and fluoroquinolones significantly increased between 2000 and 2003 and remained stable between 2004 and 2009. The decreasing use of gentamicin and amikacin in recent years was associated with increasing susceptibility of E. coli, E. cloacae, S. marcescens and P. aeruginosa to gentamicin, as well as increasing susceptibility of P. aeruginosa to amikacin. The use of piperacillin/tazobactam was positively correlated with the prevalence of piperacillin/tazobactam-resistant E. coli and S. maltophilia. In contrast, the use of cefotaxime and piperacillin/tazobactam was negatively correlated with the prevalence of cefotaxime-resistant E. coli and piperacillin/tazobactam-resistant S. maltophilia, respectively. The consumption of fluoroquinolones was positively correlated with the rates of ciprofloxacin-resistant E. coli, piperacillin/tazobactam-resistant P. aeruginosa and ceftazidime-resistant S. maltophilia.

CONCLUSIONS

The relationship between antibiotic prescription and the rates of resistance for Gram-negative bacteria is complicated; every type of antimicrobial agent or even individual agent can have distinct associations with different pathogens.

Antibacterial mechanism of soybean isoflavone on Staphylococcus aureus

Effects of different flavonoids on various bacterial strains have been extensively reported; however, the mechanism(s) of their action on bacterial cells remain largely elusive. In this study, the antibacterial mechanism of soybean isoflavone (SI) on Staphylococcus aureus is systematically investigated using 4'6-diamidino-2-phenylindole (DAPI) staining, pBR322DNA decatenation experiment mediated by topoisomerase and agarose gel electrophoresis for direct decatenation. The results of fluorescence microscopy and fluorescence spectrophotometer indicated that DAPI was integrated in Staphylococcus aureus. Additionally, the quantity of both DNA and RNA reduced to 66.47 and 60.18%, respectively, after treated with SI for 28 h. Effects of SI on topoisomerase I and II were also investigated. SI completely inhibited the pBR322DNA unwinding mediated by topoisomerase I and topoisomerase II at the concentration of 6.4 mg/ml and could denature the plasmid DNA at the concentration of 12.8 mg/ml. These results indicate that topoisomerase I and II are the most important targets by SI to restrain bacterial cell division.

A model of drug resistance with infection by health care workers

Antibiotic resistant organisms (ARO) pose an increasing serious threat in hospitals. One of the most life threatening ARO is methicillin-resistant staphylococcus aureus (MRSA). In this paper, we introduced a new mathematical model which focuses on the evolution of two bacterial strains, drug-resistant and non-drug resistant, residing within the population of patients and health care workers in a hospital. The model predicts that as soon as drug is administered, the average load of the non-resistant bacteria will decrease and eventually (after 6 weeks of the model's simulation) reach a very low level. However, the average load of drug-resistant bacteria will initially decrease, after treatment, but will later bounce back and remain at a high level. This level can be made lower if larger amount of drug is given or if the contact between health care workers and patients is reduced.

Ambulatory antibiotic use and prescription drug coverage in older adults

BACKGROUND

Several studies have shown that use of medications to treat chronic conditions is highly sensitive to out-of-pocket price and influenced by changes in insurance coverage. Because antibiotics target infections and are used for a short period, one may expect antibiotic use to be less responsive to price. However, no studies have evaluated how antibiotic use changes with drug coverage. We evaluate changes in ambulatory oral antibiotic use after implementation of the Medicare drug benefit (Part D).

METHODS

We conducted a comparison group analysis 2 years before and after implementation of Part D using insurance claims data from a large Medicare Advantage plan (January 1, 2004, through December 31, 2007). Outcomes included the likelihood of using any oral antibiotics and major antibiotic subclasses among 35 102 older adults and rates of antibiotic use among those with pneumonia and other acute respiratory tract infections.

RESULTS

Overall antibiotic use increased most among those who did not previously have drug coverage (relative odds ratio [OR], 1.58; 95% confidence interval [CI], 1.36-1.85). Use of the broad spectrum antibiotic subclasses of quinolones (OR, 1.70; 95% CI, 1.35-2.15) and macrolides (1.59; 1.26-2.01) increased more than the use of other subclasses, especially for those with prior drug coverage. Rates of ambulatory antibiotic use associated with pneumonia increased (OR, 3.60; 95% CI, 2.35-5.53) more than those associated with other acute respiratory tract infections (2.29; 1.85-2.83).

CONCLUSIONS

Antibiotic use increased among older adults whose drug coverage improved after Part D implementation, with the largest increases for broad spectrum, newer, and more expensive antibiotics. Our study suggests reimbursement may play a role in addressing inappropriate antibiotic use.

Health Care-Associated Infection Prevention and Control: Pharmacists' Role in Meeting National Patient Safety Goal 7

Health care-associated infections and antimicrobial resistance are continually increasing, with fewer drugs available for effective treatment. Potential benefits of infection control and antimicrobial stewardship programs include improvements in antibiotic use and conversion from intravenous (IV) to oral antibiotics and reductions in resistance and infection rates and length of hospital stay. NorthShore University HealthSystem in Evanston, Illinois, was the first large hospital system in North America that adopted universal inpatient surveillance for methicillin-resistant Staphylococcus aureus (MRSA). Results showed that nasal MRSA was a powerful predictor of MRSA disease and antibiotic resistance in other organisms. MRSA infections occurring up to 30 days posthospitalization decreased by approximately 70%. At the Hospital of Saint Raphael, a community teaching hospital in New Haven, Connecticut, an antimicrobial stewardship pilot program focused on automatic conversation from IV to oral antimicrobials and appropriate antimicrobial use. The percentage of patients receiving oral fluconazole increased from 63% to 77%; the percentage of those receiving oral linezolid increased from 54% to 71%. Total antibiotic use decreased by 6%. Based on the 60-day trial, potential cost savings were estimated as $874,000 annually, less the cost of a pharmacist's salary and benefits. Infection control and antimicrobial stewardship programs offer pharmacists new opportunities for helping improve patient safety and quality of care. Pharmacy-medical staff partnership, combined with support from microbiology, infection control, information technology, and hospital administration, is key to a successful program.

Relationship of carbapenem restriction in 22 university teaching hospitals to carbapenem use and carbapenem-resistant Pseudomonas aeruginosa

Many hospital antimicrobial stewardship programs restrict the availability of selected drugs by requiring prior approval. Carbapenems may be among the restricted drugs, but it is unclear if hospitals that restrict availability actually use fewer carbapenems than hospitals that do not restrict use. Nor is it clear if restriction is related to resistance. We evaluated the relationship between carbapenem restriction and the volume of carbapenem use and both the incidence rate and proportion of carbapenem-resistant Pseudomonas aeruginosa isolates from 2002 through 2006 in a retrospective, longitudinal, multicenter analysis among a consortium of academic health centers. Carbapenem use was measured from billing records as days of therapy per 1,000 patient days. Hospital antibiograms were used to determine both the incidence rate and proportion of carbapenem-resistant P. aeruginosa isolates. A survey inquired about restriction policies for antibiotics, including carbapenems. General linear mixed models were used to examine study outcomes. Among 22 hospitals with sufficient data for analysis, overall carbapenem use increased significantly over the 5 years of study (P < 0.0001), although overall carbapenem resistance in P. aeruginosa did not change. Hospitals that restricted carbapenems (n = 8; 36%) used significantly fewer carbapenems (P = 0.04) and reported lower incidence rates of carbapenem-resistant P. aeruginosa (P = 0.01) for all study years. Fluoroquinolone use was a potential confounder of these relationships, but hospitals that restricted carbapenems actually used fewer fluoroquinolones than those that did not. Restriction of carbapenems is associated with both lower use and lower incidence rates of carbapenem resistance in P. aeruginosa.

Clinical review: balancing the therapeutic, safety, and economic issues underlying effective antipseudomonal carbapenem use

Antipseudomonal carbapenems have played a useful role in our antimicrobial armamentarium for 20 years. However, a review of their use during that period creates concern that their clinical effectiveness is critically dependent on attainment of an appropriate dosing range. Unfortunately, adequate carbapenem dosing is missed for many reasons, including benefit/risk misconceptions, a narrow therapeutic window for imipenem and meropenem (due to an increased rate of seizures at higher doses), increasingly resistant pathogens requiring higher doses than are typically given, and cost containment issues that may limit their use. To improve the use of carbapenems, several initiatives should be considered: increase awareness about appropriate treatment with carbapenems across hospital departments; determine optimal dosing regimens for settings where multidrug resistant organisms are more likely encountered; use of, or combination with, an alternative antimicrobial agent having more favorable pharmacokinetic, pharmacodynamic, or adverse event profile; and administer a newer carbapenem with lower propensity for resistance development (for example, reduced expression of efflux pumps or greater stability against carbapenemases).

Acinetobacter baumannii: a universal threat to public health?

Acinetobacter spp. are non-fermentative, strictly aerobic, Gram-negative microorganisms with a confusing taxonomic history. The Acinetobacter baumannii-Acinetobacter calcoaceticus complex is the species most commonly isolated from clinical specimens. It is ubiquitous in nature and has been found as part of the normal skin, throat and rectal flora as well as in food and body lice. It colonises patients in Intensive Care Units and contaminates inanimate hospital surfaces and devices as well as wounds, including war injuries. Although a frequent coloniser, Acinetobacter can be the cause of severe and sometimes lethal infections, mostly of nosocomial origin, predominantly ventilator-associated pneumonia. Bacteraemic infections are rare but may evolve to septic shock. Acinetobacter also emerges as a cause of nosocomial outbreaks and is characterised by increasing antimicrobial multiresistance. Antibiotic use, especially carbapenems and third-generation cephalosporins, is recognised as the most important risk factor for multiresistance. Described resistance mechanisms include hydrolysis by beta-lactamases, alterations in outer membrane proteins and penicillin-binding proteins, and increased activity of efflux pumps. Today, Acinetobacter resistant to carbapenems, aminoglycosides and fluoroquinolones presents a challenge to the clinician. However, sulbactam, tigecycline and colistin represent the current therapeutic approaches, which are associated with satisfactory efficacy.

Discovery and characterization of QPT-1, the progenitor of a new class of bacterial topoisomerase inhibitors

QPT-1 was discovered in a compound library by high-throughput screening and triage for substances with whole-cell antibacterial activity. This totally synthetic compound is an unusual barbituric acid derivative whose activity resides in the (-)-enantiomer. QPT-1 had activity against a broad spectrum of pathogenic, antibiotic-resistant bacteria, was nontoxic to eukaryotic cells, and showed oral efficacy in a murine infection model, all before any medicinal chemistry optimization. Biochemical and genetic characterization showed that the QPT-1 targets the beta subunit of bacterial type II topoisomerases via a mechanism of inhibition distinct from the mechanisms of fluoroquinolones and novobiocin. Given these attributes, this compound represents a promising new class of antibacterial agents. The success of this reverse genomics effort demonstrates the utility of exploring strategies that are alternatives to target-based screens in antibacterial drug discovery.

Expression, essentiality, and a microtiter plate assay for mycobacterial GlmU, the bifunctional glucosamine-1-phosphate acetyltransferase and N-acetylglucosamine-1-phosphate uridyltransferase

UDP-N-acetyl-D-glucosamine (UDP-GlcNAc) is an essential precursor of peptidoglycan and the rhamnose-GlcNAc linker region of mycobacterial cell wall. In Mycobacterium tuberculosis H37Rv genome, Rv1018c shows strong homology to the GlmU protein involved in the formation of UDP-GlcNAc from other bacteria. GlmU is a bifunctional enzyme that catalyzes two sequential steps in UDP-GlcNAc biosynthesis. Glucosamine-1-phosphate acetyl transferase catalyzes the formation of N-acetylglucosamine-1-phosphate, and N-acetylglucosamine-1-phosphate uridylyltransferase catalyzes the formation of UDP-GlcNAc. Since inhibition of peptidoglycan synthesis often results in cell lysis, M. tuberculosis GlmU is a potential anti-tuberculosis (TB) drug target. In this study we cloned M. tuberculosis Rv1018c (glmU gene) and expressed soluble GlmU protein in E. coli BL21(DE3). Enzymatic assays showed that M. tuberculosis GlmU protein exhibits both glucosamine-1-phosphate acetyltransferase and N-acetylglucosamine-1-phosphate uridylyltransferase activities. We also investigated the effect on Mycobacterium smegmatis when the activity of GlmU is fully removed or reduced via a genetic approach. The results showed that activity of GlmU is required for growth of M. smegmatis as the bacteria did not grow in the absence of active GlmU enzyme. As the amount of functional GlmU enzyme was gradually reduced in a temperature shift experiment, the M. smegmatis cells became non-viable and their morphology changed from a normal rod shape to stubby-rounded morphology and in some cases they lysed. Finally a microtiter plate based assay for GlmU activity with an OD340 read out was developed. These studies therefore support the further development of M. tuberculosis GlmU enzyme as a target for new anti-tuberculosis drugs.

The prevalence of plasmid-mediated AmpC beta-lactamases among clinical isolates of Escherichia coli and Klebsiella pneumoniae from five children's hospitals in China

The purpose of this study was to investigate the prevalence of plasmid-mediated AmpC beta-lactamases in Escherichia coli and Klebsiella pneumoniae from five children's hospitals in China. A total of 494 E. coli and 637 K. pneumoniae isolates were collected from five children's hospitals in China from 2005 to 2006. The isolates with decreased susceptibility to cefoxitin were subjected to confirmation test with 3-aminophenyl boronic acid. Polymerase chain reaction (PCR) amplification of the blaAmpC, blaTEM, blaCTXM, and blaSHV genes and their gene sequencing were performed. Transconjugants were achieved by conjugation experiments. Plasmid-mediated AmpC beta-lactamases were found in 10.1% of K. pneumoniae (64/637) and in 2.0% of E. coli (10/494) strains. The proportion of plasmid-mediated AmpC-producing strains significantly increased from 2005 (2.6%) to 2006 (9.3%) (p<0.001). The DHA-1-producing isolates were the most prevalent type (93.2%, 69/74). The sequences of blaDHA-1 genes were all identical to those from the GenBank. Strains of blaCMY-2 were isolated from five isolates (6.8%), which were all from E. coli. One sequence of blaCMY-2 differs from blaCMY-2 in the GenBank. Eighteen of the 74 (24.3%) AmpC-producing K. pneumoniae and E. coli isolates coproduced an extended-spectrum beta-lactamase (ESBL). Cefoxitin resistance was transferred to 15 of the 74 positive strains (20.3%). Our study has demonstrated the occurrence of plasmid-mediated AmpC beta-lactamases in E. coli and K. pneumoniae in Chinese pediatric patients and DHA-1 type AmpC enzymes had the highest prevalent rate. The CMY-2 AmpC beta-lactamases from the children's hospitals in China in this study are the first reported. Hence, continuous surveillance of the prevalence and evolution of AmpC beta-lactamase is important.

Role of ceftazidime dose regimen on the selection of resistant Enterobacter cloacae in the intestinal flora of rats treated for an experimental pulmonary infection

OBJECTIVES

The effect of ceftazidime dosing increments and frequency of dosing on the selection of ceftazidime-resistant Enterobacter cloacae in the intestine was studied in rats, during treatment of a pulmonary infection caused by Klebsiella pneumoniae.

METHODS

Rats with pulmonary infection (n = 10 per group) received therapy with doses of ceftazidime at 3.1 to 400 mg/kg per day at a frequency of every 6,12 or 24 h for 18 days, starting 24 h after bacterial inoculation of the lung. Emergence of resistance in intestinal E. cloacae was monitored by culturing fresh stool specimens at days 0, 8, 15, 22, 29, 36 and 43 on agar plates with (6.4 mg/L) and without ceftazidime. Pharmacodynamic indices and time within the mutant selection window (MSW) were assessed in infected rats for each regimen. Ceftazidime-resistant E. cloacae mutants were characterized by determination of the beta-lactamase activity under cefoxitin-induced and non-induced conditions.

RESULTS

A reduction of intestinal ceftazidime-susceptible E. cloacae was observed and showed a significant correlation with the fAUC/MIC at days 8, 15 and 22 and with the fCmax on days 8, 15, 22, 29 and 36. More rats treated with 12-25 and 50-100 mg/kg per day every 6 h were found colonized with ceftazidime-resistant E. cloacae mutants than animals treated every 12 h or every 24 h. The proportion of rats colonized with ceftazidime-resistant E. cloacae mutants at days 15, 36 and 43 correlated with the time during which ceftazidime plasma concentrations were within the boundaries of the MSW. Only at day 15 was a correlation demonstrated between the fCmax and significantly fewer rats colonized with ceftazidime-resistant E. cloacae. Ceftazidime-resistant E. cloacae mutants (MIC >or= 128 mg/L) were characterized as stable derepressed mutants.

CONCLUSIONS

Colonization with stable derepressed ceftazidime-resistant E. cloacae mutants particularly occurred when rats were exposed to moderate doses of ceftazidime (12-25 or 50-100 mg/kg per day) administered every 6 h. Emergence of resistance was correlated with time within the MSW.

beta-Lactam resistance and beta-lactamases in bacteria of animal origin

beta-Lactams are among the most clinically important antimicrobials in both human and veterinary medicine. Bacterial resistance to beta-lactams has been increasingly observed in bacteria, including those of animal origin. The mechanisms of beta-lactam resistance include inaccessibility of the drugs to their target, target alterations and/or inactivation of the drugs by beta-lactamases. The latter contributes predominantly to beta-lactam resistance in Gram-negative bacteria. A variety of beta-lactamases have been identified in bacteria derived from food-producing and companion animals and may further serve as a reservoir for beta-lactamase-producing bacteria in humans. While this review mainly describes beta-lactamases from animal-derived Escherichia coli and Salmonella spp., beta-lactamases from animal-derived Campylobacter spp., Enterococcus spp., Staphylococcus spp. and other pathogens are also discussed. Of particular concern are the increasingly-isolated plasmid-encoded AmpC-type CMY and extended-spectrum CTX-M beta-lactamases, which mediate acquired resistance to extended-spectrum beta-lactams. The genes encoding these enzymes often coexist with other antimicrobial resistance determinants and can also be associated with transposons/integrons, increasing the potential enrichment of multidrug resistant bacteria by multiple antimicrobial agents as well as dissemination of the resistance determinants among bacterial species. Characterization of beta-lactam-resistant animal-derived bacteria warrants further investigation of the type and distribution of beta-lactamases in bacteria of animal origin and their potential impact on human medicine.

Prevention of recurrent respiratory tract infections in children using a ribosomal immunotherapeutic agent: a clinical review

Recurrent respiratory tract infections (RRTIs) in children constitute a serious problem worldwide. Some children experience considerable morbidity as a result of RRTIs and receive repeated courses of antibacterials that are not effective against viral infectious agents and can increase bacterial resistance. Furthermore, the direct and indirect costs of RRTIs to the community are substantial. In this article, we review the available clinical evidence relating to use of the bacterial immunostimulant Ribomunyl for the prevention of RRTIs in children. The product is composed of ribosomal fractions from four bacteria involved in RRTIs as well as a membrane fraction from one of these bacteria (Klebsiella pneumoniae). Ribomunyl stimulates production of specific humoral and secretory antibodies against the four bacterial strains included in the compound. The product also stimulates non-specific immunity. Thus, Ribomunyl stimulates both the innate and acquired immune systems and offers preventive efficacy against both bacterial and viral infections. To perform this review, we searched the MEDLINE database for articles on Ribomunyl and then included only those publications that described placebo-controlled studies, complied with Good Clinical Practice standards, used the product in official registered indications, and administered it at the recommended dosages. In this way, we were able to generate a comprehensive profile of use of the product and draw valid conclusions about its clinical role. In clinical trials of children, Ribomunyl reduced the number of upper or lower RRTIs, the primary outcome measures. Other favorable results relating to efficacy parameters that served as secondary outcome measures in these studies included a reduction in antibacterial treatments, shorter duration of recurrent episodes, reduced need for other medications such as expectorants, smaller number of lost school days or parent absenteeism from work, less fever, and reduced hearing loss. Studies focusing on particular conditions, such as otitis media, or those that included specific patient groups, such as very young children, reported similar findings. Adverse events occurred very rarely and were mild. Their frequency was similar to that reported in placebo groups, and consisted mostly of fever, otorhinolaryngologic symptoms, and cutaneous events. In conclusion, this review clearly demonstrated that Ribomunyl is effective in preventing upper and lower RRTIs in children. Ribomunyl provided a reduction in the number, duration, and severity of infectious episodes and, thereby, reduced antibacterial use and the likelihood of consequent development of bacterial resistance. Ribomunyl also decreased absence from work or school, which has important economic consequences.

World Wide Web resources on antimicrobial resistance

Advances of modern technology, including the development of the Internet and the World Wide Web, have given clinicians and researches the opportunity to have immediate access to continuously updated information in various scientific fields. We compiled a list of World Wide Web resources of data from surveillance studies on antimicrobial resistance that may be useful to practitioners--especially infectious diseases specialists--as well as to scientists with a research interest in the field of antimicrobial resistance.