Stable Antimicrobial Susceptibility Rates for Clinical Isolates of Pseudomonas aeruginosa from the 2001–2003 Tracking Resistance in the United States Today Surveillance Studies

Pseudomonas aeruginosa: Infections, Animal Modeling, and Therapeutics

Pseudomonas aeruginosa is an important Gram-negative opportunistic pathogen which causes many severe acute and chronic infections with high morbidity, and mortality rates as high as 40%. What makes P. aeruginosa a particularly challenging pathogen is its high intrinsic and acquired resistance to many of the available antibiotics. In this review, we review the important acute and chronic infections caused by this pathogen. We next discuss various animal models which have been developed to evaluate P. aeruginosa pathogenesis and assess therapeutics against this pathogen. Next, we review current treatments (antibiotics and vaccines) and provide an overview of their efficacies and their limitations. Finally, we highlight exciting literature on novel antibiotic-free strategies to control P. aeruginosa infections.

Emergence of Multidrug- and Pandrug- Resistant Pseudomonas aeruginosa from Five Hospitals in Qatar

Background

A global rise in multidrug-resistant (MDR) nosocomial infections has led to a significant increase in morbidity and mortality. MDR Gram-negative bacteria (GNB) are recognised for rapidly developing drug resistance. Despite Pseudomonas aeruginosa being the second most common GNB isolated from healthcare associated infections, the magnitude of MDR P. aeruginosa (MDR-PA) has not been evaluated in Qatar.

Aim

To assess the prevalence and antimicrobial susceptibility patterns of MDR-PA from 5 major hospitals in Qatar.

Methods

A total of 2533 P. aeruginosa clinical isolates were collected over a one-year period. MDR-PA was defined as resistance to at least one agent of ≥ 3 antibiotic classes. Clinical and demographic data were collected prospectively.

Findings

The overall prevalence of MDR-PA isolates was 8.1% (205/2533); the majority of isolates were from patients exposed to antibiotics during 90 days prior to isolation (85.4 %, 177/205), and the infections were mainly hospital-acquired (95.1%, 195/205) with only 4.9% from the community. The majority of MDR-PA isolates were resistant to cefepime (96.6%, 198/205), ciprofloxacin, piperacillin/tazobactam (91%, 186/205), and meropenem (90%, 184/205). Patient comorbidities with MDR-PA were diabetes mellitus (47.3%, n=97), malignancy (17.1%, n=35), end-stage renal disease (13.7%, n=28) and heart failure (10.7%, n=22).

Conclusion

There was a significant prevalence of MDR-PA in Qatar, primarily from healthcare facilities and associated with prior antibiotic treatment. There was an alarming level of antimicrobial resistance to carbapenems. Our results are part of a national surveillance of MDR to establish effective containment plans.

Drug resistance profile and molecular characterization of extended spectrum beta-lactamase (ESβL)-producing Pseudomonas aeruginosa isolated from burn wound infections. Essential oils and their potential for utilization

OBJECTIVES

Pseudomonas aeruginosa producing extended spectrum β-lactamase (ESβL) enzyme had the ability for antimicrobial resistance mechanisms and its multidrug-resistant (MDR) phenotype, has been increasingly reported as a major clinical concern worldwide. The aim of this study was to (i) characterize ESβL-producing MDR P. aeruginosa isolated from burn wound infections phenotypically and molecularly, (ii) evaluate the antibacterial activity of some essential oils (EOs) against selected ESβL-producing drug resistant P. aeruginosa and (iii) characterize a promising EO.

METHODS

Identification and antibiotic susceptibility tests were performed for all isolates. ESβL production was detected phenotypically by an initial screening test (IST) and a phenotypic confirmatory test (PCT). Additionally, ESβL-producing isolates were also characterized molecularly. The antibacterial activity was detected using a disc diffusion method. Mechanisms of antibacterial action, the fatty acid profile, and functional groups characterization of the promising EO were analyzed using scanning and transmission electron microscopy (SEM & TEM), gas chromatography-mass spectrometry (GC-MS), and Fourier transform infrared (FTIR) spectroscopy, respectively.

RESULTS

A total of 50 non duplicated P. aeruginosa isolates from the wound samples of burn patients were identified. Of these, MDR and pan-drug resistance (PDR) showed a high prevalence in 38 (76%) isolates obtained from 10 clusters, while 21 (42%) were identified as ESβL-producing MDR or PDR P. aeruginosa isolates. Phenotypic detection of ESβL production showed that 20% were considered positive ESβL-producing P. aeruginosa using the IST, and were increased to 56% by the PCT. The most prevalent ESβL-encoding gene was blaOXA-2 (60.7%), followed by blaIMP-7 (53.6%) and blaOXA-50 (42.8%). Ginger oil is the most efficient antibacterial agent and its antibacterial action mechanism is attributed to the morphological changes in bacterial cells. The oil characterization revealed that 9,12-Octadecadienoic acid methyl ester is the major fatty acid (50.49%) identified.

CONCLUSION

The high incidence of drug-resistance in ESβL-producing P. aeruginosa isolated from burn wounds is alarming. As proven in vitro, EOs may represent promising natural alternatives against ESβL-producing PDR or MDR P. aeruginosa isolates.

Outpatient management of cholesteatoma with canal wall reconstruction tympanomastoidectomy

Objectives

The postoperative wound infection rate for canal wall reconstruction (CWR) tympanomastoidectomy with mastoid obliteration in the treatment of chronic otitis media with cholesteatoma has been reported to be 3.6%. Postoperative administration of 24–48 hours of intravenous antibiotics has been recommended. We aim to determine the infection rate of CWR with postoperative outpatient oral antibiotics.

Study Design

Institutional review board—approved retrospective case review.

Setting

Tertiary referral center.

Patients: Retrospective review of consecutive patients who underwent CWR tympanomastoidectomy with mastoid obliteration at a single institution from 2014 to 2016.

Main Outcome Measure: Patient characteristics (age, sex) were calculated. Rate of postoperative complications and infections within 1 month of surgery were calculated. Comparison to previous published infection rates with postoperative intravenous antibiotics.

Results

51 patients underwent CWR followed by outpatient oral antibiotics with a mean age of 25.9 years (16 patients were less than 10 years old). There were no postoperative wound infections. Outpatient antibiotics showed non‐inferiority to IV antibiotic historic controls (0% vs. 3.6%; 95% confidence interval [CI], 0–6.09%; p = 0.03). One patient had small postoperative wound dehiscence with CSF leak that was managed conservatively. One patient developed Clostridium difficile colitis on postoperative day 2.

Conclusions

The infection rate after CWR tympanomastoidectomy with use of outpatient antibiotics is low and is non‐inferior to a historic cohort treated with inpatient intravenous antibiotics. A larger randomized controlled trial is warranted.

Level of Evidence

4.

Distribution of the Strains of Multidrug-resistant, Extensively Drug-resistant, and Pandrug-resistant Pseudomonas aeruginosa Isolates from Burn Patients

Background:

Pseudomonas aeruginosa is an opportunistic and Gram-negative pathogen that is used as the most important factor in burn wound infections, and due to the rapid acquisition of multidrug resistance (MDR), it causes high mortality rates in these sectors. Thus, diagnosis and assessment of antibiotic resistance patterns are very important in these patients. The aim of this study was to evaluate antibiotic resistance pattern and determining P. aeruginosa MDR.

Materials and Methods:

In this study, phenotypic, biochemical, and polymerase chain reaction tests were used to identify P. aeruginosa from 120 wound burn samples that 96 samples were detected to P. aeruginosa species. In the next step, according to the Clinical and Laboratory Standard Institute standard guidelines, antibiogram test was performed by disk diffusion method for amikacin, ciprofloxacin, norfloxacin, gentamicin, cefepime, aztreonam, meropenem, colistin, ceftazidime, and piperacillin-tazobactam antibiotics. Antibiotic data were analyzed by WHONET software; finally, the rate of antibiotic resistance and MDR strains was determined.

Results:

The highest antibiotic resistance belonged to amikacin (94.8%) and norfloxacin (90.6%); in contrast, colistin (8.3%) had the lowest and the MDR strains were MDR (95.8%) and extensively drug resistance (XDR) (87.5%).

Conclusion:

In this study, there was MDR with an alarming rate including MDR (95.8%), XDR (87.5%), and pan-drug resistance (0%). As a result, given antibiotics to patients should be controlled by the antibiogram results to avoid increasing MDR strains.

Prevalence and risk factors associated with colonization and infection of extensively drug-resistant Pseudomonas aeruginosa: a systematic review

Pseudomonas aeruginosa is a Gram-negative human pathogen with extensively drug-resistant (XDR) strains emerging in hospitals across the globe. This systematic review is focused on the worldwide prevalence of XDR P. aeruginosa (XDR-PA) and on the risk factors associated with its colonization and infection, based on literature available through PubMed, Web of Science and BioMed Central databases. An overview of surveillance systems is provided as well as a synopsis on the prevalence of XDR-PA, showing an increase in recent reports. Risk factors independently associated with XDR-PA colonization or infections are described in four groups with reference to antimicrobial therapy, medical devices as well as patient- and hospital environment-related factors.

Evaluation of regional antibiograms to monitor antimicrobial resistance in Hampton Roads, Virginia

We studied recent antibiograms (2010 to 2011) from 12 hospitals in the Hampton Roads area, Virginia, that refer patients to a tertiary-care facility affiliated with Eastern Virginia Medical School. The data was compiled into a regional antibiogram, and sensitivity rates of common isolates from the tertiary-care facility (central) were compared to those of referring hospitals grouped by locale. Staphylococcus aureus was the most common Gram- positive and E. coli the most common Gram- negative organism grown from clinical samples in the area. Overall 53% of S.aureus isolates were resistant to oxacillin. There was a broad scatter of MIC (minimum inhibitory concentration) for vancomycin within the susceptibility range, and MIC of 4 μg/mL was reported in 2012. Penicillin resistance was seen in 50% and erythromycin resistance in 45% of Streptococcus pneumoniae. Vancomycin resistance was seen in 75% of Enterococcus faecium and 2% of Enterococcus faecalis respectively. Acinetobacter baumannii was the most resistant Gram negative organism in the data compiled. Among the Escherichia coli, 26%, 44% and 52%were resistant to Trimethoprim/Sulfamethoxazole ( SXT) ampicillin- sulbactam and ampicillin respectively. We found significant differences in methodology, interpretation and antibiotic panels used by area laboratories. Based on these findings, we are now prospectively following resistance patterns in the tertiary-care facility, sharing data, and creating a consistent approach to antimicrobial susceptibility testing in the region.

Overcoming drug resistance in multi-drug resistant cancers and microorganisms: a conceptual framework

Resistance development against multiple drugs is a common feature among many pathogens--including bacteria such as Pseudomonas aeruginosa, viruses, and parasites--and also among cancers. The reasons are two-fold. Most commonly-used rationally-designed small molecule drugs or monoclonal antibodies, as well as antibiotics, strongly inhibit a key single step in the growth and proliferation of the pathogen or cancer cells. The disease agents quickly change or switch off this single target, or activate the efflux mechanisms to pump out the drug, thereby becoming resistant to the drug. A second problem is the way drugs are designed. The pharmaceutical industry chooses to use, by high-throughput screening, compounds that are maximally inhibitory to the key single step in the growth of the pathogen or cancer, thereby promoting selective pressure. An ideal drug would be one that inhibits multiple steps in the disease progression pathways with less stringency in these steps. Low levels of inhibition at multiple steps provide cumulative strong inhibitory effect, but little incentives or ability on the part of the pathogen/cancer to develop resistance. Such intelligent drug design involving multiple less stringent inhibitory steps is beyond the scope of the drug industry and requires evolutionary wisdom commonly possessed by bacteria. This review surveys assessments of the current clinical situation with regard to drug resistance in P. aeruginosa, and examines tools currently employed to limit this trend. We then provide a conceptual framework in which we explore the similarities between multi-drug resistance in pathogens and in cancers. We summarize promising work on anti-cancer drugs derived from the evolutionary wisdom of bacteria such as P. aeruginosa, and how such strategies can be the basis for how to look for candidate protein/peptide antibiotic drugs from bioengineered bugs. Such multi-domain proteins, unlike diffusible antibiotics, are not diffusible because of their large size and are often released only on contact with the perceived competitor. Thus, multi-domain proteins are missed during traditional methods of looking for growth zone inhibition of susceptible bacteria as demonstrated by antibiotics, but may represent the weapons of the future in the fights against both drug-resistant cancers and pathogens such as P. aeruginosa.

Cefepime-resistant Pseudomonas aeruginosa

Resistance to extended-spectrum cephalosporins complicates treatment of Pseudomonas aeruginosa infections. To elucidate risk factors for cefepime-resistant P. aeruginosa and determine its association with patient death, we conducted a case-control study in Philadelphia, Pennsylvania. Among 2,529 patients hospitalized during 2001-2006, a total of 213 (8.4%) had cefepime-resistant P. aeruginosa infection. Independent risk factors were prior use of an extended-spectrum cephalosphorin (p<0.001), prior use of an extended-spectrum penicillin (p = 0.005), prior use of a quinolone (p<0.001), and transfer from an outside facility (p = 0.01). Among those hospitalized at least 30 days, mortality rates were higher for those with cefepime-resistant than with cefepime-susceptible P. aeruginosa infection (20.2% vs. 13.2%, p = 0.007). Cefepime-resistant P. aeruginosa was an independent risk factor for death only for patients for whom it could be isolated from blood (p = 0.001). Strategies to counter its emergence should focus on optimizing use of antipseudomonal drugs.

Antibiotic resistance in Pseudomonas aeruginosa related to quinolone formulary changes: an interrupted time series analysis

Pseudomonas aeruginosa is a nosocomial pathogen capable of exhibiting a variety of resistance mechanisms against multiple classes of antibiotics. Fluoroquinolones, commonly used to treat a variety of infections in both ambulatory and hospitalized patients, have been increasingly linked to the development of resistance, both to fluoroquinolones and to other classes of antibiotics including β-lactams, cephalosporins, and carbapenems. In turn, as many as 95% of multidrug-resistant pseudomonal isolates may be resistant to fluoroquinolones. Although research has examined the effect of fluoroquinolone use on P. aeruginosa resistance, to our knowledge, no work has been published describing possible differences among individual fluoroquinolones related to resistance to other antibiotic classes. The purpose of this analysis was to assess the possible effects of varying usage of levofloxacin, gatifloxacin, and moxifloxacin on P. aeruginosa susceptibility to piperacillin-tazobactam, cefepime, and tobramycin. Data from January 2000 through December 2008 were obtained from clinical microbiology and pharmacy databases of the Medical University of South Carolina Medical Center, which is a 689-bed academic medical center and level 1 trauma center with adult and pediatric beds. This study was approved by the institution's institutional review board.

Pneumonia due to Pseudomonas aeruginosa: part II: antimicrobial resistance, pharmacodynamic concepts, and antibiotic therapy

Pseudomonas aeruginosa carries a notably higher mortality rate than other pneumonia pathogens. Because of its multiple mechanisms of antibiotic resistance, therapy has always been challenging. This problem has been magnified in recent years with the emergence of multidrug-resistant (MDR) pathogens often unharmed by almost all classes of antimicrobials. The objective of this article is to assess optimal antimicrobial therapy based on in vitro activity, animal studies, and pharmacokinetic/pharmacodynamic (PK/PD) observations so that evidence-based recommendations can be developed to maximize favorable clinical outcomes. Mechanisms of antimicrobial resistance of P aeruginosa are reviewed. A selective literature review of laboratory studies, PK/PD concepts, and controlled clinical trials of antibiotic therapy directed at P aeruginosa pneumonia was performed. P aeruginosa possesses multiple mechanisms for inducing antibiotic resistance to antimicrobial agents. Continuous infusion of antipseudomonal β-lactam antibiotics enhances bacterial killing. Although the advantages of combination therapy remain contentious, in vitro and animal model studies plus selected meta-analyses of clinical trials support its use, especially in the era of MDR. Colistin use and the role of antibiotic aerosolization are reviewed. An evidence-based algorithmic approach based on severity of illness, Clinical Pulmonary Infection Score, and combination antibiotic therapy is presented; clinical outcomes may be improved, and the emergence of MDR pathogens should be minimized with this approach.

Risk factors for pneumonia caused by multidrug-resistant Gram-negative bacilli among liver recipients

Pneumonia caused by multidrug-resistant (MDR) Gram-negative bacilli is associated with a higher mortality rate. The appropriate empiric therapy is based on the understanding of local etiology and MDR pattern. This study was to evaluate the spectrum of Gram-negative bacilli, MDR rate, risk factors and mortality in 475 liver transplantation (LT) recipients. In the first six months after LT, the incidence of bacterial pneumonia was 21.3% (101/475). The overall infectious incidence during the first post-transplant month was 80.2%. The most frequent pneumonia isolates were Enterobacteriaceae, Acinetobacter baumannii, Pseudomonas aeruginosa and Staphylococcus aureus. Gram-negative bacilli accounted for 69.6% of all pneumonia pathogens. Of the main 124 Gram-negative bacilli isolates, MDR rate was 58.9%. Four risk factors for post-LT pneumonia caused by MDR Gram-negative bacilli were LT candidates with grade II-IV encephalopathy (OR 2.275, 95%CI 1.249-4.124, p = 0.006), prolonged duration of endotracheal intubation (OR 8.224, 95%CI 4.276-15.815, p = 0.013), tracheostomy (OR 4.929, 95%CI 1.099-18.308, p = 0.027) and post-LT episode(s) of reoperations (OR 10.597, 95%CI 3.726-30.134, p < 0.001). MDR Gram-negative bacterial pneumonia-related mortality was significantly higher than that because of antibiotic-susceptible bacilli (45.6% vs. 11.4%, p = 0.010). Our data suggest that pneumonia caused by MDR Gram-negative bacilli after LT is common, and associated with the severity of underlying disease, prolonged mechanical ventilation and upper abdominal surgery.

[Evolution of antimicrobial resistance against Pseudomonas aeruginosa in a French university hospital between 2002 and 2006]

AIM OF STUDY

Monitor evolution of antibiotic resistance of Pseudomonas aeruginosa from 2002 to 2006 in our hospital to optimize antibiotherapy.

PATIENTS AND METHOD

The infections/colonizations with P. aeruginosa have been identified by the hospital's informatic database. Bacteriological samples realized 48hours after patient's admission was considered as nosocomial. A Cochran-Armitage test was conducted to assess the evolution of resistance.

RESULTS

During this period, 2098 infections/colonizations with P. aeruginosa have been identified. Bacteriological samples (68.5%) were nosocomial. Among the beta-lactam antibiotics, ceftazidime and imipenem were the most active (R=16.8% and 15.2%, respectively), followed by piperacillin and piperacillin-tazobactam (R=24.8%, 18.4%, respectively). Amikacin and tobramycin were more active than gentamicin (R=19.9%; 22.2% and 40.6%, respectively). 28.9% of strains were resistant to ciprofloxacin. Nosocomial strains were significantly more resistant than non-hospital strains: ceftazidime: 17.9% versus 14.2%, p=0.0346; ticarcillin-clavulanic acid: 47.5% versus 39.6%, p=0.0009; piperacillin-tazobactam: 20.0% versus 14.8%, p=0.0046; ciprofloxacin: 30.7% versus 25.2%, p=0.0112. A significant increase in the resistance of nosocomial strains to ceftazidime, ticarcillin-clavulanic acid and piperacillin-tazobactam was noted. Resistance from non-hospital strains to fluoroquinolones, aminoglycosides, ceftazidime, piperacillin and ticarcillin-clavulanic acid decreased significantly.

CONCLUSION

P. aeruginosa is a predominantly nosocomial microorganism. There is a decrease of resistance for non-hospital strains. But the resistance of nosocomial strains to antibiotics widely prescribed in hospital is worrying.

Antimicrobial susceptibility and ESBL prevalence in Pseudomonas aeruginosa isolated from burn patients in the North West of Pakistan

Pseudomonas aeruginosa is one of the most prevalent pathogen in burn infections. Infections with P. aeruginosa are associated with higher mortality rate and antibiotic costs in hospitalized patients. These bacteria also produce enzymes called Expanded Spectrum Beta-Lactamases (ESBL) which render penicillins and cephalosporins inactive. The aim of this study was to assess the antimicrobial susceptibility pattern and prevalence of ESBL in P. aeruginosa in Peshawar, North West of Pakistan. During 2005-2006, one hundred and six P. aeruginosa isolates were collected from burn patients at a tertiary care hospital. Antibiotic susceptibility testing and ESBL detection were carried out according to Clinical Laboratory and Standards Institute (CLSI) criteria. Eighteen antibiotics were tested in this study. A total of 38 (35.85%) isolates were found to be ESBL producers. Thirty one (29.24%) isolates were resistant to 3 or more antibiotics (multidrug resistance). Meropenem and imipenem showed high potency with 99% and 96% isolates being susceptible respectively. Susceptibility to amikacin was 70%; gentamicin 25%; ciprofloxacin 49%; enoxacin 47%; gatifloxacin 42%; doxycycline 21% and to co-trimoxazole only 16%. This study reveals that P. aeruginosa isolated from burns in this region are multidrug resistant and produce ESBL in large proportions.

Nosocomial outbreak of a non-cefepime-susceptible ceftazidime-susceptible Pseudomonas aeruginosa strain overexpressing MexXY-OprM and producing an integron-borne PSE-1 betta-lactamase

Cefepime (FEP) and ceftazidime (CAZ) are broad-spectrum cephalosporins that display similar MICs for wild-type Pseudomonas aeruginosa strains. Recently, P. aeruginosa isolates showing a discordance in susceptibility to CAZ and FEP have been noted at the Hospital de Bellvitge in Barcelona, Spain, and a clustering was suspected. During the study period (March to December 2007), 51 patients, particularly those in an intensive care units (ICUs) (n = 29 [57%]), infected or colonized with at least one P. aeruginosa non-FEP-susceptible and CAZ-susceptible (Fep(ns) Caz(s)) phenotype strain were detected. Twenty-three (45%) patients were infected, and the respiratory tract was the most frequent site of infection. Changes in the consumption of antimicrobials in the ICUs were observed over time: a progressive reduction in the levels of consumption of carbapenems (247 defined daily doses [DDD]/1,000 patient days to 66 DDD/1,000 patient days; P = 0.008), after restriction of its use in 2006, and an expected increase in the rate of piperacillin-tazobactam use (42 DDD/1,000 patient days in 2004 to 200 DDD/1,000 patient days in 2007; P < 0.001). Throughout the whole study period, only a single clone of a P. aeruginosa Fep(ns) Caz(s) phenotype strain was identified by pulsed-field gel electrophoresis analysis to be associated with the hyperexpression of MexXY-OprM and the production of an integron-borne PSE-1 ss-lactamase. In conclusion, we identified an epidemic P. aeruginosa clone of an Fep(ns) Caz(s) phenotype strain involving 51 patients, in particular, ICU patients. The combination of the overexpression of an efflux pump and PSE-1 ss-lactamase production is associated with the multidrug-resistant phenotype. The dominant use of a single class of antibiotics could have provided the selective pressure required for the emergence and spread of this P. aeruginosa strain.

The Utility of Fluoroquinolones in the Critically Ill

Fluoroquinolone antibiotics have been used for more than 40 years to treat a variety of infections from simple uncomplicated urinary tract infections to infections as severe as nosocomial-acquired pneumonia. Their availability both orally and intravenously, ease of dosing, favorable safety profile, and broad spectrum of activity have led to the pervasive use of these agents in both the community and institutions. Unfortunately, this widespread use has led to the development of resistance and subsequently, increased mortality. Resistance, specifically with Pseudomonas aeruginosa and Escherichia coli, as well as their association with the development of Clostridium difficile–associated diarrhea, has led many clinicians to question the use of fluoroquinolones in the critically ill. This article will review these issues related to the use of fluoroquinolones, in an effort to better define their role among institutionalized patients.

Efficacy and safety of doripenem versus piperacillin/tazobactam in nosocomial pneumonia: a randomized, open-label, multicenter study

OBJECTIVE

Doripenem is a new carbapenem that has broad-spectrum activity against bacterial pathogens commonly responsible for nosocomial pneumonia (NP). It has several advantages over currently available carbapenems and other classes of drugs used in this indication. This prospective, randomized, open-label, multicenter study was designed to establish whether doripenem was noninferior to piperacillin/tazobactam in NP.

METHODS

Adults (n=448) with signs and symptoms of NP, including non-ventilated patients and those ventilated for <5 days, were stratified by ventilation mode, illness severity (Acute Physiology and Chronic Health Evaluation II score), and geographic region and then randomly allocated to treatment with doripenem 500 mg every 8 h by a 1-h intravenous (IV) infusion or piperacillin/tazobactam 4.5 g every 6 h by 30-min IV infusion. After receiving IV study drug for at least 72 h, eligible patients could be switched to oral levofloxacin 750 mg once daily. Antibiotic therapy was continued for a total of 7-14 days. The primary endpoint was the clinical cure rate, assessed 7-14 days after treatment completion, in clinically evaluable patients and in the clinical modified intent-to-treat population (cMITT).

TRIAL REGISTRATION

ClinicalTrials.gov, NCT00211003.

RESULTS

Doripenem was noninferior to piperacillin/tazobactam. Clinical cure rates in clinically evaluable patients (n=253) were 81.3% in the doripenem arm and 79.8% in the piperacillin/tazobactam arm (between-treatment difference: 1.5%; 95% confidence interval [CI], -9.1 to 12.1%) and in the cMITT population 69.5% and 64.1%, respectively, (between-treatment difference: 5.4%; 95% CI, -4.1 to 14.8%). Baseline resistance of Klebsiella pneumoniae and Pseudomonas aeruginosa to piperacillin/tazobactam was 44% and 26.9%, respectively; a doripenem minimum inhibitory concentration (MIC) >8 mug/mL occurred in 0% and 7.7%, respectively. Favorable microbiological outcome rates against Gram-negative pathogens were numerically higher with doripenem than with piperacillin/tazobactam, but the difference was not statistically significant. Both study drugs were generally well tolerated, as only 16.1% and 17.6% of patients receiving doripenem and piperacillin/tazobactam, respectively, had a drug-related adverse event. Study limitations included the open-label design, the low rate of monotherapy (adjunctive use of aminoglycoside was required when P. aeruginosa was suspected), and the exclusion of the most critically ill and immunocompromized patients.

CONCLUSIONS

Doripenem was clinically and microbiologically effective in patents with NP, including those with early-onset ventilator-associated pneumonia, and was therapeutically noninferior to piperacillin/tazobactam.

Strategies for managing today's infections

Bacterial infections are becoming more difficult to treat. At the present time c. 70% of nosocomial infections are resistant to at least one antimicrobial drug that previously was effective for the causative pathogen. Pathogens that are notorious for their virulence and ability to develop resistance include Staphylococcus aureus, Enterococcus spp., members of the Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter species. Notable resistance patterns that have emerged include methicillin resistance in S. aureus, which started in the healthcare setting but has now moved into the community. Vancomycin resistance in enterococci is frequently seen, and vancomycin resistance in methicillin-resistant S. aureus is a public health threat. Resistance patterns seen in pseudomonal and Acinetobacter infections are rapidly shifting. The situation has become sufficiently serious for clinical opinion leaders to call upon governments for assistance in addressing the problem. In this worsening environment, in which patients are at progressively greater risk of untreatable infections, clear recommendations for prescribers are urgently needed. Severity of infection and underlying conditions are key issues, as patients with the most serious diseases are those in most urgent need, and improvements in our ability to predict likely infecting pathogens when empirical therapy is necessary are needed. Risk-factors and local resistance patterns must be accounted for, and initial empirical therapy should be adequately broad spectrum and adequately dosed. Agents must be highly active, able to penetrate adequately to the site of infection, safe, and well-tolerated.

Severe sepsis and septic shock in the emergency department

Increased attention has focused recently on the acute management of severe sepsis and septic shock, conditions that represent the end-stage systemic deterioration of overwhelming infection. Clinical trials have identified new therapies and management approaches that, when applied early, appear to reduce mortality. Practice guidelines have been advanced by critical care societies, and many of the proposed interventions involve therapies other than antimicrobials directed at hemodynamic resuscitation or addressing adverse effects of the inflammatory cascade. Although many emergency departments (EDs) are now adopting treatment protocols for sepsis that are based on published treatment guidelines, recent research calls many of the initial recommendations into question, and validation trials of some of these approaches are ongoing. This article reviews the initial evaluation and treatment considerations of sepsis in the ED setting.

Five-year report of national surveillance of antimicrobial resistance in Pseudomonas aeruginosa isolated from non-tertiary care hospitals in Korea (2002-2006)

A nationwide surveillance of the antimicrobial resistance of Pseudomonas aeruginosa isolates from non-tertiary care hospitals was conducted in Korea from 2002 to 2006. Resistance to almost all antimicrobial agents decreased significantly from 2003 (P < 0.01). Resistance rates to the major antipseudomonal agents, ceftazidime, imipenem, meropenem, and aztreonam, were 18.8%, 20.5%, 18.7%, and 19.7%, respectively, in 2003. However, they had all decreased to below 10% in 2006. The proportion of multidrug-resistant isolates that were resistant to at least 3 of 5 major antipseudomonal agent decreased from 33.5% in 2003 to 23.1% in 2006 (P < 0.05). In this study, we found a decreasing trend in resistance rates and low resistance rates in P. aeruginosa from non-tertiary care hospitals compared with those from general hospitals, including tertiary care hospitals, in Korea. Our data provide valuable information for the selection of reliable empiric therapies for P. aeruginosa infections in non-tertiary care hospital patients, including outpatients.

The current state of multidrug-resistant gram-negative bacilli in North America

Although much of today's media focuses on multidrug-resistant gram-positive bacteria such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus, resistance within gram-negative bacilli continues to rise, occasionally creating situations in which few or no antibiotics that retain activity are available. Extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli and Klebsiella sp are emerging threats nationally. Although carbapenems are considered the antibiotic class of choice to treat ESBL-producing Enterobacteriaceae, the ability of these organisms to produce carbapenemases has now become apparent in some regions throughout the United States. Although still rare, Klebsiella sp that produce KPC-2 retain susceptibility only to tigecycline, polymyxins, and occasionally aminoglycosides. Multidrug resistance among Pseudomonas aeruginosa and Acinetobacter sp has always been apparent across many hospitals in the United States. Recent surveillance indicates increasing resistance to all currently available antibiotics, including carbapenems, cephalosporins, penicillins, fluoroquinolones, and aminoglycosides. Against many strains, only polymyxins retain activity; however, resistance has also been reported to these agents. Fortunately, resistance mechanisms such as metallo-beta-lactamases are still rare in the United States. As no new antibiotics with novel mechanisms against many of these gram-negative bacilli are expected to be developed in the foreseeable future, careful and conservative use of agents combined with good infection control practices is required.

What are the most appropriate antibiotics for the treatment of acute exacerbation of chronic obstructive pulmonary disease? A therapeutic outcomes model

OBJECTIVES

To predict the clinical efficacy of several antimicrobials in the treatment of patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD).

METHODS

A probability model (therapeutic outcomes model) was used to predict the likelihood of clinical success with particular antimicrobial agents in the treatment of patients with AECOPD, both in those clinically diagnosed (total patients with an AECOPD diagnosis regardless of the cause) and in those with bacterial AECOPD. The model took into account the following variables: (i) the proportion of patients with a clinical diagnosis of AECOPD and non-bacterial disease; (ii) likelihood of spontaneous resolution of a non-bacterial infection; (iii) prevalence of subcauses (different bacterial species) in bacterial AECOPD; (iv) rates of spontaneous resolution of bacterial AECOPD; and (v) antimicrobial efficacy of each antibiotic against each bacterial species (susceptibility based on PK/PD breakpoints).

RESULTS

Fluoroquinolones (levofloxacin, ciprofloxacin and moxifloxacin), a new third-generation oral cephalosporin (cefditoren) and high doses of amoxicillin/clavulanate were the antimicrobials with the highest predicted clinical efficacy both in mild-moderate AECOPD and in severe AECOPD (rates of 89.2% to 90.5% and 80.3% to 88.1%, respectively), whereas cefaclor, azithromycin, erythromycin and clarithromycin had the lowest predicted clinical efficacy (rates of 79.1% to 81.3% and 51.8% to 55.6% for mild-moderate and severe AECOPD, respectively), which was not much higher than that predicted for placebo (73.6% and 45.5%, respectively).

CONCLUSIONS

According to our model, fluoroquinolones (levofloxacin, ciprofloxacin and moxifloxacin), cefditoren and amoxicillin/clavulanate are the most appropriate antibiotics for the treatment of patients with AECOPD in terms of predicted clinical efficacy, with wide differences with respect to other antibiotics commonly used in the treatment of these patients, such as clarithromycin and azithromycin.

Levofloxacin pharmacokinetics in adult cystic fibrosis

BACKGROUND

Cystic fibrosis (CF) patients have enhanced renal clearance of aminoglycosides and several beta-lactams and require higher dosages. Levofloxacin is a fluoroquinolone with extensive renal elimination and enhanced penetration into lungs and Pseudomonas aeruginosa (PA) biofilms. We studied the preliminary pharmacokinetic and pharmacodynamic (PK/PD) relationship of levofloxacin in CF.

METHODS

Twelve patients at least 18 years old with a mild-to-moderate pulmonary exacerbation and fluoroquinolone-sensitive PA colonization received oral levofloxacin, 500 mg qd, for 14 days. Steady-state serum concentrations were collected after 3 to 7 days, and sputum samples for PA densities were collected before and after levofloxacin. PK/PD relationships for reducing PA sputum densities were evaluated.

RESULTS

When compared to published data on non-CF patients, CF patients had similar area under the curve for 24 h (AUC(24)), total clearance, volume of distribution, maximum serum concentration (Cpmax), and elimination half-life: mean, 7.33 microg x h/mL/kg (SD, 1.70); 2.43 mL/min/kg (SD, 0.74); 1.33 L/kg (SD, 0.37); 7.06 microg/mL (SD, 2.35); and 6.44 h (SD, 1.1), respectively. Time to reach maximum serum concentration (Tmax) in CF was longer: mean, 2.20 h (SD, 0.99) vs 1.1 h (SD, 0.4) [p < 0.01]. Preliminary PK/PD analysis failed to demonstrate trends for decreasing PA sputum densities with increasing Cpmax/minimum inhibitory concentration (MIC) ratio and AUC(24)/MIC ratio.

CONCLUSION

CF levofloxacin pharmacokinetics corrected for body weight are similar to non-CF, except for Tmax. Standard levofloxacin dosing (especially monotherapy) is unlikely to produce maximum therapeutic effectiveness. Additional levofloxacin studies in CF are necessary to evaluate its sputum concentrations; the benefits of higher daily dosages (>/= 750 mg); and establish PK/PD targets for managing PA pulmonary infections.

Optimizing the management of community-acquired respiratory tract infections in the age of antimicrobial resistance

Community-acquired respiratory tract infections (CARTIs) are the most common reason for prescribing antibiotics in the primary care setting. However, over the last decade, the management of CARTIs has become increasingly complicated by the steady increase in prevalence of drug-resistant pathogens responsible for these infections. As a result, significant attention has been directed at understanding the mechanisms of pathogen acquisition of resistance, drivers of resistance and methods for preventing the development of resistance. Data from recent surveillance studies suggest a slowing or decline in resistance rates to agents, such as beta-lactams, macrolides, tetracyclines and folic acid metabolism inhibitors. However, resistance to one antimicrobial family--the fluoroquinolones--while still low, appears to be on the increase. This is of significant concern given the rapid increase in resistance noted with older antibiotics in recent history. While the clinical implications of antibacterial resistance are poorly understood, the overall rates of antimicrobial resistance, as reported in recent surveillance studies, do not correspond to current rates of failure in patients with CARTIs. This disconnection between laboratory-determined resistance and clinical outcome has been termed the in vitro-in vivo paradox and several explanations have been offered to explain this phenomenon. Solving the problem of antimicrobial resistance will be multifactorial. Important factors in this effort include the education of healthcare providers, patients and the general healthcare community regarding the hazards of inappropriate antibiotic use, prevention of infections through vaccination, development of accurate, inexpensive and timely point-of-care diagnostic tests to aid in patient assessment, institution of objective treatment guidelines and use of more potent agents, especially those with a focused spectrum of activity, earlier in the treatment of CARTIs as opposed to reserving them as second-line treatment options. Ultimately, the single-most important factor will be the judicious use of antibiotics, as fewer antibiotic prescriptions lead to fewer antimicrobial-resistant bacteria.

Levofloxacin in the treatment of ventilator-associated pneumonia

The use of levofloxacin in critically ill patients has progressively increased since commercial marketing of the drug in 1999, despite the fact that few studies have been designed to assess the use of levofloxacin in this population. Pharmacological characteristics, broad spectrum of activity, and tolerability account for the high interest in the drug for the treatment of different infectious diseases, including ventilator-associated pneumonia (VAP), and the recommendation of levofloxacin in guidelines developed by a number of scientific societies. According to pharmacokinetic-pharmacodynamic data, it seems reasonable to assume that an increase in activity follows from a larger dose, so that 500 mg/12 h is adequate in patients with VAP. In critically ill patients with VAP, levofloxacin monotherapy is indicated for empirical treatment of patients with early onset pneumonia without risk factors for multiresistant pathogens, and in combination therapy for late onset VAP or for patients at risk for multiresistant pathogens. The use of levofloxacin in combination therapy is supported by multiple reasons, including: increased empirical coverage in infections with suspected intracellular pathogens; substitution for more toxic antimicrobial agents (e.g., aminoglycosides) in patients with renal dysfunction and in those at risk for renal insufficiency; and severity of systemic response to infection (septic shock) that justifies multiple treatment with better tolerated antibiotics. The availability of the oral formulation allows sequential therapy, switching from the intravenous route to the oral route. Levofloxacin is well tolerated by critically ill patients, with few adverse events of mild to moderate severity.

Involvement of the MexXY-OprM efflux system in emergence of cefepime resistance in clinical strains of Pseudomonas aeruginosa

Cefepime (FEP) and ceftazidime (CAZ) are potent beta-lactam antibiotics with similar MICs (1 to 2 mug/ml) for wild-type strains of Pseudomonas aeruginosa. However, recent epidemiological studies have highlighted the occurrence of isolates more resistant to FEP than to CAZ (FEPr/CAZs profile). We thus investigated the mechanisms conferring such a phenotype in 38 clonally unrelated strains collected in two French teaching hospitals. Most of the bacteria (n=32; 84%) appeared to stably overexpress the mexY gene, which codes for the RND transporter of the multidrug efflux system MexXY-OprM. MexXY up-regulation was the sole FEP resistance mechanism identified (n=12) or was associated with increased levels of pump MexAB-OprM (n=5) or MexJK (n=2), synthesis of secondary beta-lactamase PSE-1 (n=10), derepression of cephalosporinase AmpC (n=1), coexpression of both OXA-35 and MexJK (n=1), or production of both PSE-1 and MexAB-OprM (n=1). Down-regulation of the mexXY operon in seven selected strains by the plasmid-borne repressor gene mexZ decreased FEP resistance from two- to eightfold, thereby demonstrating the significant contribution of MexXY-OprM to the FEPr/CAZs phenotype. The six isolates of this series that exhibited wild-type levels of the mexY gene were found to produce beta-lactamase PSE-1 (n=1), OXA-35 (n=4), or both PSE-1 and OXA-35 (n=1). Altogether, these data provide evidence that MexXY-OprM plays a major role in the development of FEP resistance among clinical strains of P. aeruginosa.

Mechanisms of antimicrobial resistance in bacteria

The treatment of bacterial infections is increasingly complicated by the ability of bacteria to develop resistance to antimicrobial agents. Antimicrobial agents are often categorized according to their principal mechanism of action. Mechanisms include interference with cell wall synthesis (eg, beta-lactams and glycopeptide agents), inhibition of protein synthesis (macrolides and tetracyclines), interference with nucleic acid synthesis (fluoroquinolones and rifampin), inhibition of a metabolic pathway (trimethoprim-sulfamethoxazole), and disruption of bacterial membrane structure (polymyxins and daptomycin). Bacteria may be intrinsically resistant to > or =1 class of antimicrobial agents, or may acquire resistance by de novo mutation or via the acquisition of resistance genes from other organisms. Acquired resistance genes may enable a bacterium to produce enzymes that destroy the antibacterial drug, to express efflux systems that prevent the drug from reaching its intracellular target, to modify the drug's target site, or to produce an alternative metabolic pathway that bypasses the action of the drug. Acquisition of new genetic material by antimicrobial-susceptible bacteria from resistant strains of bacteria may occur through conjugation, transformation, or transduction, with transposons often facilitating the incorporation of the multiple resistance genes into the host's genome or plasmids. Use of antibacterial agents creates selective pressure for the emergence of resistant strains. Herein 3 case histories-one involving Escherichia coli resistance to third-generation cephalosporins, another focusing on the emergence of vancomycin-resistant Staphylococcus aureus, and a third detailing multidrug resistance in Pseudomonas aeruginosa-are reviewed to illustrate the varied ways in which resistant bacteria develop.

Resistance in nonfermenting gram-negative bacteria: multidrug resistance to the maximum

Nonfermenting gram-negative bacteria pose a particular difficulty for the healthcare community because they represent the problem of multidrug resistance to the maximum. Important members of the group in the United States include Pseudomonas aeruginosa, Acinetobacter baumannii, Stenotrophomonas maltophilia, and Burkholderia cepacia. These organisms are niche pathogens that primarily cause opportunistic healthcare-associated infections in patients who are critically ill or immunocompromised. Multidrug resistance is common and increasing among gram-negative nonfermenters, and a number of strains have now been identified that exhibit resistance to essentially all commonly used antibiotics, including antipseudomonal penicillins and cephalosporins, aminoglycosides, tetracyclines, fluoroquinolones, trimethoprim-sulfamethoxazole, and carbapenems. Polymyxins are the remaining antibiotic drug class with fairly consistent activity against multidrug-resistant strains of P aeruginosa, Acinetobacter spp, and S maltophilia. However, most multidrug-resistant B cepacia are not susceptible to polymyxins, and systemic polymyxins carry the risk of nephrotoxicity for all patients treated with these agents, the elderly in particular. A variety of resistance mechanisms have been identified in P aeruginosa and other gram-negative nonfermenters, including enzyme production, overexpression of efflux pumps, porin deficiencies, and target-site alterations. Multiple resistance genes frequently coexist in the same organism. Multidrug resistance in gram-negative nonfermenters makes treatment of infections caused by these pathogens both difficult and expensive. Improved methods for susceptibility testing are needed when dealing with these organisms, including emerging strains expressing metallo-beta-lactamases. Improved antibiotic stewardship and infection-control measures will be needed to prevent or slow the emergence and spread of multidrug-resistant, nonfermenting gram-negative bacilli in the healthcare setting.

Resistance in nonfermenting gram-negative bacteria: multidrug resistance to the maximum

Nonfermenting gram-negative bacteria pose a particular difficulty for the healthcare community because they represent the problem of multidrug resistance to the maximum. Important members of the group in the United States include Pseudomonas aeruginosa, Acinetobacter baumannii, Stenotrophomonas maltophilia, and Burkholderia cepacia. These organisms are niche pathogens that primarily cause opportunistic healthcare-associated infections in patients who are critically ill or immunocompromised. Multidrug resistance is common and increasing among gram-negative nonfermenters, and a number of strains have now been identified that exhibit resistance to essentially all commonly used antibiotics, including antipseudomonal penicillins and cephalosporins, aminoglycosides, tetracyclines, fluoroquinolones, trimethoprim-sulfamethoxazole, and carbapenems. Polymyxins are the remaining antibiotic drug class with fairly consistent activity against multidrug-resistant strains of P aeruginosa, Acinetobacter spp, and S maltophilia. However, most multidrug-resistant B cepacia are not susceptible to polymyxins, and systemic polymyxins carry the risk of nephrotoxicity for all patients treated with these agents, the elderly in particular. A variety of resistance mechanisms have been identified in P aeruginosa and other gram-negative nonfermenters, including enzyme production, overexpression of efflux pumps, porin deficiencies, and target-site alterations. Multiple resistance genes frequently coexist in the same organism. Multidrug resistance in gram-negative nonfermenters makes treatment of infections caused by these pathogens both difficult and expensive. Improved methods for susceptibility testing are needed when dealing with these organisms, including emerging strains expressing metallo-beta-lactamases. Improved antibiotic stewardship and infection-control measures will be needed to prevent or slow the emergence and spread of multidrug-resistant, nonfermenting gram-negative bacilli in the healthcare setting.

Mechanisms of antimicrobial resistance in bacteria

The treatment of bacterial infections is increasingly complicated by the ability of bacteria to develop resistance to antimicrobial agents. Antimicrobial agents are often categorized according to their principal mechanism of action. Mechanisms include interference with cell wall synthesis (e.g., beta-lactams and glycopeptide agents), inhibition of protein synthesis (macrolides and tetracyclines), interference with nucleic acid synthesis (fluoroquinolones and rifampin), inhibition of a metabolic pathway (trimethoprim-sulfamethoxazole), and disruption of bacterial membrane structure (polymyxins and daptomycin). Bacteria may be intrinsically resistant to > or =1 class of antimicrobial agents, or may acquire resistance by de novo mutation or via the acquisition of resistance genes from other organisms. Acquired resistance genes may enable a bacterium to produce enzymes that destroy the antibacterial drug, to express efflux systems that prevent the drug from reaching its intracellular target, to modify the drug's target site, or to produce an alternative metabolic pathway that bypasses the action of the drug. Acquisition of new genetic material by antimicrobial-susceptible bacteria from resistant strains of bacteria may occur through conjugation, transformation, or transduction, with transposons often facilitating the incorporation of the multiple resistance genes into the host's genome or plasmids. Use of antibacterial agents creates selective pressure for the emergence of resistant strains. Herein 3 case histories-one involving Escherichia coli resistance to third-generation cephalosporins, another focusing on the emergence of vancomycin-resistant Staphylococcus aureus, and a third detailing multidrug resistance in Pseudomonas aeruginosa--are reviewed to illustrate the varied ways in which resistant bacteria develop.

Microbiological rationale for the utilisation of prulifloxacin, a new fluoroquinolone, in the eradication of serious infections caused by Pseudomonas aeruginosa

Minimal inhibitory concentrations (MICs) of prulifloxacin were evaluated in comparison with ciprofloxacin, levofloxacin and moxifloxacin against a large collection (N = 300) of Pseudomonas aeruginosa strains characterised according to the CLSI/NCCLS microdilution method. Additional in vitro tests (time-kill curves and mutant prevention concentration (MPC) determinations) were carried out. Assuming a susceptibility breakpoint for prulifloxacin identical to that of ciprofloxacin, the new fluoroquinolone emerged as the most potent antibiotic (72% of susceptible strains versus 65%, 61% and 23% for ciprofloxacin, levofloxacin and moxifloxacin, respectively). Time-kill tests at 4x MIC confirmed the pronounced bactericidal potency of the drug against P. aeruginosa. Amongst the members of the fluoroquinolone class assessed, prulifloxacin produced the lowest MPC values (< or = 4 mg/L). Our in vitro results indicate that prulifloxacin represents the most powerful antipseudomonal drug available today.

Update on Pseudomonas aeruginosa and Acinetobacter baumannii infections in the healthcare setting

PURPOSE OF REVIEW

Infections with Pseudomonas aeruginosa and Acinetobacter baumannii are of great concern for hospitalized patients, especially with multidrug-resistant strains. This review focuses on recent data that may help us to understand the emergence, spread, and persistence of antibiotic resistance, and summarizes the optional treatment feasible for these resistant bacteria.

RECENT FINDINGS

Multidrug-resistant P. aeruginosa and A. baumannii are increasingly causing nosocomial infections; multidrug-resistant clones are spreading into new geographic areas, and susceptible strains are acquiring resistance genes. New extended-spectrum beta-lactamases and carbapenemases are emerging, leading to pan-resistant strains. Current studies focus on the effect of antibiotics on gene expression in P. aeruginosa biofilms and their contribution to resistance to therapy. Treatment options for multidrug-resistant P. aeruginosa and A. baumannii infections are limited in most cases to carbapenems. Sulbactam is a treatment option for pan-resistant A. baumannii, and or renewed use of an old drug, colistin, is being entertained for pan-resistant A. baumannii and P. aeruginosa. Immunotherapy is a promising new modality being explored. Prevention of emergence of resistance through combination therapy and pharmacokinetic strategies are studied.

SUMMARY

The emergence and spread of multidrug-resistant P. aeruginosa and A. baumannii and their genetic potential to carry and transfer diverse antibiotic resistance determinants pose a major threat in hospitals. The complex interplay of clonal spread, persistence, transfer of resistance elements, and cell-cell interaction contribute to the difficulty in treating infections caused by these multidrug-resistant strains. In the absence of new antibiotic agents, new modalities of treatment should be developed.