Nosocomial Infection Caused by Antibiotic-Resistant Organisms in the Intensive-Care Unit

Resistance to antimicrobial agents is an evolving process, driven by the selective pressure of heavy antibiotic use in individuals living in close proximity to others. The intensive care unit (ICU), crowded with debilitated patients who are receiving broad-spectrum antibiotics and being cared for by busy physicians, nurses, and technicians, serves as an ideal environment for the emergence of antibiotic resistance. Problem pathogens presently include multiply resistant gram-negative bacilli, methicillin-resistantStaphylococcus aureus, and the recently emerged vancomycin-resistant enterococci. The prevention of antimicrobial resistance in ICUs should focus on recognition via routine unit-based sur veillance, improved compliance with handwashing and barrier precautions, and antibiotic-use policies tailored to individual units within hospitals.

Bacterial efflux pump inhibitors from natural sources

The rapid spread of bacteria expressing multidrug resistance (MDR) has necessitated the discovery of new antibacterials and resistance-modifying agents. Since the initial discovery of bacterial efflux pumps in the 1980s, many have been characterized in community- and hospital-acquired Gram-positive and Gram-negative pathogens, such as Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and, more recently, in mycobacteria. Efflux pumps are able to extrude structurally diverse compounds, including antibiotics used in a clinical setting; the latter are rendered therapeutically ineffective. Antibiotic resistance can develop rapidly through changes in the expression of efflux pumps, including changes to some antibiotics considered to be drugs of last resort. It is therefore imperative that new antibiotics, resistance-modifying agents and, more specifically, efflux pump inhibitors (EPIs) are characterized. The use of bacterial resistance modifiers such as EPIs could facilitate the re-introduction of therapeutically ineffective antibiotics back into clinical use such as ciprofloxacin and might even suppress the emergence of MDR strains. Here we review the literature on bacterial EPIs derived from natural sources, primarily those from plants. The resistance-modifying activities of many new chemical classes of EPIs warrant further studies to assess their potential as leads for clinical development.

A review of antimicrobial peptides and their therapeutic potential as anti-infective drugs

PURPOSE

Antimicrobial peptides (AMPs) are an essential part of innate immunity that evolved in most living organisms over 2.6 billion years to combat microbial challenge. These small cationic peptides are multifunctional as effectors of innate immunity on skin and mucosal surfaces and have demonstrated direct antimicrobial activity against various bacteria, viruses, fungi, and parasites. This review summarizes their progress to date as commercial antimicrobial drugs for topical and systemic indications.

METHODS

Literature review.

RESULTS

Despite numerous clinical trials, no modified AMP has obtained Food & Drug Administration approval yet for any topical or systemic medical indications.

CONCLUSIONS

While AMPs are recognized as essential components of natural host innate immunity against microbial challenge, their usefulness as a new class of antimicrobial drugs still remains to be proven.

A laboratory evaluation of antibiotic therapy for ciprofloxacin-resistant Pseudomonas aeruginosa

PURPOSE

The emergence of ciprofloxacin-resistant Pseudomonas aeruginosa (CRPA) has created a new therapeutic challenge in ophthalmology. We evaluated ophthalmic antibiotics in vitro and in a rabbit keratitis model to determine effective therapy.

DESIGN

Experimental laboratory investigation.

METHODS

The susceptibilities of 12 CRPA isolates were determined in vitro for amikacin, ceftazidime, tobramycin, polymyxin B, gentamicin, ticarcillin, and the fluoroquinolones (that is, ciprofloxacin, ofloxacin, levofloxacin, gatifloxacin, and moxifloxacin) using E-tests and National Committee of Clinical Laboratory Standards. A rabbit keratitis model was used to determine the reduction in colony counts of CRPA and ciprofloxacin-susceptible P. aeruginosa (CSPA) isolates following topical treatment with polymyxin B/trimethoprim, tobramycin (14 mg/ml), ceftazidime (50 mg/ml), and ciprofloxacin (3 mg/ml).

RESULTS

For 12 CRPA isolates, the susceptibilities and median minimum inhibitory concentrations ([MIC]microg/ml) were as follows: amikacin (92%, 14.0), ceftazidime (75%, 4.0), tobramycin (67%, 1.75), polymyxin B (42%, 7.0), gentamicin (17%, 7.0), ticarcillin (0%, >32.0), and all fluoroquinolones (0%, >32.0). While no antibiotic regimen reduced colony counts in the time frame of the animal model for CRPA, ciprofloxacin alone demonstrated a significant decrease in colony counts for CSPA. Comparing CRPA with CSPA, both tobramycin and ciprofloxacin demonstrated a significant decrease in colony counts for CSPA.

CONCLUSION

Our laboratory studies suggest that current antibiotics may be suboptimal in treating CRPA keratitis. Until new antibiotics are available, combination therapy such as fortified tobramycin and ticarcillin, and others may prove effective in aggressive topical long-term therapy.

Fluoroquinolone resistance among Gram-positive cocci

Resistance to fluoroquinolones among Gram-positive cocci has emerged as these antimicrobial agents have become extensively used in clinical medicine. Resistance is effected by changes in the bacterial target enzymes DNA gyrase and topoisomerase IV, which reduce drug binding, and by action of native bacterial membrane pumps that remove drug from the cell. In both cases, quinolone exposure selects for spontaneous mutants that are present in large bacterial populations, and which contain chromosomal mutations that alter the target protein or increase the level of pump expression. Resistance among clinical isolates has been greatest in Staphylococcus aureus and particularly among meticillin-resistant strains, in which both selection by quinolone exposure and transmission of clonal strains in health-care settings have contributed to high prevalence. Resistance in Streptococcus pneumoniae has also emerged in the community. Fluoroquinolone resistance has arisen in multidrug-resistant clones and its prevalence has been especially high in Hong Kong and Spain. Further spread and selection of such resistance could compromise the utility of a valuable class of antimicrobial agents, a point that emphasises the importance of the careful use of these agents in appropriate patients and doses, as well as careful infection-control practices.

Antimicrobial management strategies for Gram-positive bacterial resistance in the intensive care unit

This article summarizes the current situation with Gram-positive infections, including the two primary consequences-failure to cure and resistance-relevant to the intensive care unit. The past few years have seen Enterococcus faecium resistance to vancomycin increase from 10% of strains to approaching 60% of strains in some centers. Failure is now so frequent that vancomycin can no longer be safely used. This has lead to use of two new antibiotics, quinupristin/dalfopristin (Synercid), first marketed in the United States in September 1999, and linezolid (Zyvox), which reached the U.S. market in May 2000. Both of these agents are being used to treat culture-proven vancomycin-resistant E. faecium. The calculated areas under the inhibitory curve (AUIC) values of vancomycin, even when its minimal inhibitory concentration (MIC) is 4.0 microg/mL, show almost all vancomycin-resistant E. faecium have AUICs <125. This explains failure, as well as the further selection of this bacteria into subpopulations with progressively higher MICs. Less well defined, but potentially an even greater problem, is the poor efficacy of vancomycin against multiresistant Staphylococcus aureus. Here, there is evidence of clinical failure in lower respiratory tract infection patients, but in most cases the MIC values of the organism have not risen to the point where AUICs are <125. However, the minimum bactericidal concentration of this organism may be considerably higher than its MIC, and in other cases there may be a high inoculum effect or a protein-binding effect to explain the failure of vancomycin to kill multiresistant S. aureus. Besides the increasing use of the new agents, strategies to manage these two increasingly resistant Gram-positive infections include cephalosporin restriction, switch and streamlining when cultures come back from the lab, combination regimens, and cycling in selected intensive care units.

Hospital-acquired pneumonia: risk factors, microbiology, and treatment

Pneumonia complicates hospitalization in 0.5 to 2.0% of patients and is associated with considerable morbidity and mortality. Risk factors for hospital-acquired pneumonia (HAP) include mechanical ventilation for > 48 h, residence in an ICU, duration of ICU or hospital stay, severity of underlying illness, and presence of comorbidities. Pseudomonas aeruginosa, Staphylococcus aureus, and Enterobacter are the most common causes of HAP. Nearly half of HAP cases are polymicrobial. In patients receiving mechanical ventilation, P aeruginosa, Acinetobacter, methicillin-resistant S aureus, and other antibiotic-resistant bacteria assume increasing importance. Optimal therapy for HAP should take into account severity of illness, demographics, specific pathogens involved, and risk factors for antimicrobial resistance. When P aeruginosa is implicated, monotherapy, even with broad-spectrum antibiotics, is associated with rapid evolution of resistance and a high rate of clinical failures. For pseudomonal HAP, we advise combination therapy with an antipseudomonal beta-lactam plus an aminoglycoside or a fluoroquinolone (eg, ciprofloxacin).

In vitro activity of evernimicin and selected antibiotics against methicillin-resistant staphylococci: a 24-country study

OBJECTIVE

To collect and analyze data on susceptibility of methicillin-resistant staphylococci to evernimicin and other antimicrobial agents.

METHODS

Recent clinical isolates of methicillin-resistant staphylococci from 33 laboratories in North America, Europe and South Africa were investigated.

RESULTS

Of the antimicrobial agents tested, evernimicin had the lowest MIC90s for methicillin-resistant Staphylococcus aureus and methicillin-resistant coagulase-negative staphylococci (0.75 and 1.0 mg/L, respectively). Resistance to ciprofloxacin and erythromycin was widespread, with higher levels of resistance in North America than in other regions.

CONCLUSIONS

Susceptibility surveys help to determine the antimicrobial activity of new agents. Ciprofloxacin- and erythromycin-resistant staphylococci were prevalent throughout all regions.

Controlled clinical trial of pefloxacin versus imipenem in severe acute pancreatitis

BACKGROUND & AIMS

Antibiotic prophylaxis in severe pancreatitis has recently yielded promising clinical results, with imipenem significantly reducing the incidence of infected necrosis compared with an untreated control group. On the bases of pefloxacin's spectrum of action and pancreatic penetration, we investigated whether such drugs represent a valid alternative to imipenem.

METHODS

In a multicenter study, 60 patients with severe acute pancreatitis with necrosis affecting at least 50% of the pancreas were randomly allocated to receive intravenous treatment for 2 weeks with pefloxacin, 400 mg twice daily (30 patients), or imipenem, 500 mg three times daily (30 patients), within 120 hours of onset of symptoms. Age, sex, body weight, Ranson and Apache II scores, C-reactive protein, etiology, and time from onset of symptoms to treatment were well matched in the two groups.

RESULTS

The incidences of infected necrosis and extrapancreatic infections were 34% and 44%, respectively, in the pefloxacin group and 10% and 20% in the imipenem group. Imipenem proved significantly more effective in prevention of pancreatic infections (P </= 0.05). Mortality was not significantly different in the two groups.

CONCLUSIONS

Despite its theoretical potential, pefloxacin is inferior to imipenem in the prevention of infections associated with severe pancreatitis.

Canadian Pseudomonas aeruginosa susceptibility study from 48 medical centers: focus on ciprofloxacin

We tested 1503 clinical isolates of Pseudomonas aeruginosa, from 48 Canadian medical centers, against ciprofloxacin and 11 other antimicrobial agents to determine in vitro activity. The frequency of susceptibility was highest for carbenicillin and ticarcillin (91% each) followed by imipenem and ceftazadime (90% each). Overall susceptibility (< or = 1.0 mg/l) to ciprofloxacin was 84% while resistance (> or = 4.0 mg/l) was 12%. Ciprofloxacin resistant isolates were more common from urinary tract specimens than from specimens collected from the respiratory and/or skin and soft tissue. Isolates from cystic fibrosis patients were more resistant to all agents tested than isolates from non-cystic fibrosis patients.

Application of the ATC/DDD methodology to monitor antibiotic drug use

In order to monitor the use of antibiotics, it is essential to have comprehensive data on drug consumption. The findings of drug utilisation studies can serve to describe the pattern of drug use in a particular population, to detect areas of concern, and to evaluate the impact of interventions taken to influence the use of drugs. In the present study, the Anatomical Therapeutical Chemical Classification/Defined Daily Doses (ATC/DDD) system developed by the World Health Organisation was evaluated. The system measures the amount of drug used independent of package size and sales price, which allows comparisons not only within an institution but also within a region, a country, or even internationally. Obviously, there can be no modifications of this system. To illustrate the method, the pattern of quinolone use in the general population, in long-term care facilities, and within a single institution was analysed. These drugs were widely used in long-term care facilities in the Nijmegen region of the Netherlands, accounting for about 30% of the antibiotics used in these settings, whereas in the general population as well as in the University Hospital Nijmegen, these drugs constitute only about 6% of the total antibiotics used. These differences are large enough to warrant closer analysis of patterns of antibiotic usage in different settings to identify the reasons for the use of quinolones and to identify measures that might be taken to rationalise the prescription of these drugs.

Avoiding fluoroquinolone resistance. Strategies for primary care practice

The therapeutic usefulness of fluroquinolones for serious and difficult-to-treat infections is well documented. However, with increasing reports of organisms becoming resistant to the agents (most often the pseudomonads, staphylococci, and streptococci), the usefulness of this class of antibiotics is being threatened. Appropriate and judicious prescribing of this class of antimicrobials can greatly aid in preserving the therapeutic value of fluoroquinolones for the treatment of infections in the future.

The contribution of antibiotic use on the frequency of antibiotic resistance in hospitals

Abundant evidence suggests a relationship between antibiotic resistance and use, including animal models, consistent associations between resistance and antibiotic use in hospitals, concomitant variation in resistance as antibiotic use varies, and a dose-response relationship for many pathogen/antibiotic combinations. Much of the evidence has come from studies performed in single hospitals. Most multicentre studies on resistance have not included data on antibiotic usage. Despite this substantial body of evidence, some studies have failed to demonstrate an association between antibiotic resistance and use, suggesting other contributing factors such as cross-transmission, inter-hospital transfer of resistance, a community contribution to resistance, or a complex relationship between resistance and the use of a variety of antibiotics. A multicentre study, project ICARE (Intensive Care Antimicrobial Resistance Epidemiology), implemented in 1994 by Centers for Disease Control and Prevention and Rollins School of Public Health, Emory University, has found dramatic differences in the patterns of antibiotic usage and resistance in US hospitals. The findings suggest that antibiotic usage is the major risk factor in development of antibiotic resistance in hospitals but the relationship can be complex with additional factors involved. Understanding the problem of antibiotic resistance in a hospital cannot be achieved without knowledge of the hospital's pattern of antibiotic use.

Preventing the Emergence of Multidrug-Resistant Microorganisms Through Antimicrobial Use Controls: The Complexity of the Problem

Widespread use of antimicrobials in the inpatient and outpatient setting has been associated with the emergence of multidrug-resistant microorganisms. A variety of methods exist to improve the appropriateness of antimicrobial use in the inpatient setting, including guidelines, antimicrobial use evaluations, microbiology laboratory guidance, formulary development and antimicrobial restriction, use of antimicrobial order or automatic stop order forms, and antimicrobial audits. To decrease the selective pressure that leads to development of pathogen resistance and to reduce antimicrobial expenditures, infectious disease, infection control, pharmacy, and administrative staff need to improve clinician use of antimicrobials through development and implementation of antimicrobial use committees. Through the implementation of a comprehensive, multidisciplinary approach to antimicrobial use and development of clinician education programs, inappropriate antimicrobial use can be reduced, patient care can be improved, and substantial cost savings can be realized.

Canadian ciprofloxacin susceptibility study: comparative study from 15 medical centers. Canadian Ciprofloxacin Study Group

We tested 4,507 microorganisms, from 15 Canadian medical centers, against ciprofloxacin and several other antimicrobial agents to determine the in vitro susceptibilities. Overall, susceptibility of members of the family Enterobacteriaceae to ciprofloxacin was 97%; Moraxella and Haemophilus spp. had susceptibilities of 98 and 99%, respectively; and P. aeruginosa and S. aureus had susceptibilities of 79 and 96%, respectively.

Reasons for the emergence of antibiotic resistance

The ability of many different species of bacteria, including those that cause diseases in humans, to resist the inhibitory action of antimicrobial agents has become a global problem. Resistance continues to spread not only in nosocomial pathogens but in several key community-acquired organisms as well. Appropriate control measures for such resistant organisms depend in part on the pathways by which resistance has arisen. Unfortunately, these pathways differ greatly from organism to organism and setting to setting. In addition, although the epidemiology of resistant organisms sometimes is similar to that of susceptible organisms of the same kind, in some situations it may be quite different. In this article, the authors highlight some of the pathways leading to the development of resistance in bacteria, the importance of antimicrobial use, and the relevance of these mechanisms to measures for the control of resistant bacteria in hospital and community settings.