Diagnosis and treatment of extended-spectrum and AmpC beta-lactamase-producing organisms

Clinical Outcomes of Patients with AmpC-Beta-Lactamase-Producing Enterobacterales Bacteremia Treated with Carbapenems versus Non-Carbapenem Regimens: A Single-Center Study

INTRODUCTION

Bloodstream infections caused by AmpC-producing Enterobacterales pose treatment challenges due to the risk of AmpC overproduction and treatment failure. Current guidelines recommend carbapenems or cefepime as optimal therapy. We aimed to evaluate empiric and definitive non-carbapenem regimens for these infections.

METHODS

In a retrospective study from June 2014 to March 2023, adult bacteremic patients with Enterobacter cloacae complex strains and Morganella morganii were evaluated. Demographic, clinical and lab data and outcomes were assessed.

RESULTS

The cohort comprised 120 bacteremic patients, 17 receiving empiric carbapenem and 103 non-carbapenem regimens. Both groups had similar Charlson and Norton scores and previous antimicrobial exposure. The most common sources of bacteremia were urinary, abdominal and central-line-associated sources. Empiric non-carbapenem regimens (primarily piperacillin-tazobactam and cephalosporins) were not associated with recurrent bacteremia or 30-day mortality. Definitive regimens included mainly carbapenems (n = 41) and ciprofloxacin (n = 46). Beta-lactams were administered to 25 patients. Recurrent bacteremia and 30-day mortality rates were similar among treatment groups. Ciprofloxacin showed comparable outcomes to carbapenems, however, severity of illness among these patients was lower.

CONCLUSIONS

Empiric and definitive non-carbapenem regimens for bacteremia with AmpC-producing organisms were not associated with treatment failure or increased 30-day mortality. Ciprofloxacin appears promising for selected, stable patients, potentially enabling early discharge.

Systematic Review of Plasmid AmpC Type Resistances in Escherichia coli and Klebsiella pneumoniae and Preliminary Proposal of a Simplified Screening Method for ampC

Beta-lactamase (BL) production is a major public health problem. Although not the most frequent AmpC type, AmpC-BL is increasingly isolated, especially plasmid AmpC-BL (pAmpC-BL). The objective of this study was to review information published to date on pAmpC-BL in Escherichia coli and Klebsiella pneumoniae, and on the epidemiology and detection methods used by clinical microbiology laboratories, by performing a systematic review using the MEDLINE PubMed database. The predictive capacity of a screening method to detect AmpC-BL using disks with cloxacillin (CLX) was also evaluated by studying 102 Enterobacteriaceae clinical isolates grown in CHROMID ESBL medium with the addition of cefepime (FEP), cefoxitin (FOX), ertapenem (ETP), CLX, and oxacillin with CLX. The review, which included 149 publications, suggests that certain risk factors (prolonged hospitalization and previous use of cephalosporins) are associated with infections by pAmpC-BL-producing microorganisms. The worldwide prevalence has increased over the past 10 years, with a positivity rate ranging between 0.1 and 40%, although AmpC was only detected when sought in a targeted manner. CMY-2 type has been the most prevalent pAmpC-BL-producing microorganism. The most frequently used phenotypic method has been the double-disk synergy test (using CLX disks or phenyl-boronic acid and cefotaxime [CTX] and ceftazidime) and the disk method combined with these inhibitors. In regard to screening methods, a 1-µg oxacillin disk with CLX showed 88.9% sensitivity, 100% specificity, 100% positive predictive value (PPV), 98.9% negative predictive value (NPV), and 98.9% validity index (VI). This predictive capacity is reduced with the addition of extended-spectrum beta-lactamases, showing 62.5% sensitivity, 100% specificity, 100% PPV, 93.5% NPV, and 94.1% VI. In conclusion, there has been a worldwide increase in the number of isolates with pAmpC-BL, especially in Asia, with CMY-2 being the most frequently detected pAmpC-BL-producing type of microorganism. Reduction in its spread requires routine screening with a combination of phenotypic methods (with AmpC inhibitors) and genotypic methods (multiplex PCR). In conclusion, the proposed screening technique is an easy-to-apply and inexpensive test for the detection of AmpC-producing isolates in the routine screening of multidrug-resistant microorganisms.

Evidence of potentially unrelated AmpC beta-lactamase producing Enterobacteriaceae from cattle, cattle products and hospital environments commonly harboring the blaACC resistance determinant

The occurrence and genetic relatedness of AmpC beta-lactamase producing Enterobacteriaceae isolated from clinical environments, groundwater, beef, human and cattle faeces were investigated. One hundred seventy-seven (177) samples were collected and cultured on MacConkey agar. A total of 203 non-repetitive isolates were characterised using genus/species-specific PCRs and the identified isolates were subjected to antibiotic susceptibility testing. The production of AmpC beta-lactamases was evaluated using cefoxitin disc, confirmed by the D96C detection test and their encoding genes detected by PCR. The D64C extended-spectrum beta-lactamases (ESBL) test was also performed to appraise ESBLs/AmpC co-production. The genetic fingerprints of AmpC beta-lactamase producers were determined by ERIC-PCR. A total of 116 isolates were identified as E. coli (n = 65), Shigella spp. (n = 36) and Klebsiella pneumoniae (n = 15). Ciprofloxacin resistance (44.4-55.4%) was the most frequent and resistance against the Cephem antibiotics ranged from 15-43.1% for E. coli, 25-36.1% for Shigella spp., and 20-40% for K. pneumoniae. On the other hand, these bacteria strains were most sensitive to Amikacin (0%), Meropenem (2.8%) and Piperacillin-Tazobactam (6.7%) respectively. Nineteen (16.4%) isolates comprising 16 E. coli and 3 Shigella spp. were confirmed as AmpC beta-lactamase producers. However, only E. coli isolates possessed the corresponding resistance determinants: blaACC (73.7%, n = 14), blaCIT (26%, n = 5), blaDHA (11%, n = 2) and blaFOX (16%, n = 3). Thirty-four (27.3%) Enterobacteriaceae strains were confirmed as ESBL producers and a large proportion (79.4%, n = 27) harboured the blaTEM gene, however, only two were ESBLs/AmpC co-producers. Genetic fingerprinting of the AmpC beta-lactamase-producing E. coli isolates revealed low similarity between isolates. In conclusion, the findings indicate the presence of AmpC beta-lactamase-producing Enterobacteriaceae from cattle, beef products and hospital environments that commonly harbour the associated resistance determinants especially the blaACC gene, nonetheless, there is limited possible cross-contamination between these environments.

Comparison of outcomes in urinary tract infections caused by AmpC-harboring organisms treated with AmpC stable versus AmpC susceptible agents

There is minimal data on the optimal treatment of lower inoculum infections such as urinary tract infections (UTIs) caused by SPICE organisms which encode the betalactamase enzyme, AmpC. This single-center, retrospective review of adult hospitalized patients with UTIs caused by a SPICE organism compared outcomes amongst patients treated with drugs susceptible to AmpC hydrolysis versus drugs stable against AmpC. Of 156 patients, similar rates of clinical response, 30-day infection related readmission, 30-day infection recurrence, 30-day mortality rates, and median length of hospital stay were found between the two groups. Notably, 44% of patients with ceftriaxone resistance reported had recent β-lactam exposure versus only 11% of patients without ceftriaxone resistance (P = 0.002). Based on our data, there does not appear to be a difference in clinical response or any of the secondary outcomes in patients with UTIs treated with AmpC stable and AmpC susceptible agents.

Adverse clinical outcomes associated with infections by Enterobacterales producing ESBL (ESBL-E): a systematic review and meta-analysis

OBJECTIVES

Enterobacterales producing ESBL (ESBL-E) have been notable for their rapid expansion in community settings. This systematic review and meta-analysis aimed to summarize evidence investigating the association between ESBL-E infection and adverse clinical outcomes, defined as bacteraemia, sepsis or septic shock, and all-cause mortality in adult patients.

METHODS

Database search was conducted in PubMed, Scopus and EMBASE. In general, studies were screened for effect estimates of ESBL-E colonization or infection on clinical outcomes with non-ESBL-producing Enterobacterales as comparator, adult populations and molecular ascertainment of ESBL gene. Meta-analysis was performed using the inverse variance heterogeneity model.

RESULTS

Eighteen studies were identified, including 1399 ESBL-E and 3200 non-ESBL-E infected patients. Sixteen of these studies included only bacteraemic patients. Mortality was studied in 17 studies and ESBL-E infection was significantly associated with higher odds of mortality compared with non-ESBL-producing Enterobacterales infection (OR = 1.70, 95% CI: 1.15-2.49, I 2=58.3%). However, statistical significance did not persist when adjusted estimates were pooled (aOR = 1.67, 95% CI: 0.52-5.39, I 2=78.1%). Septic shock was studied in seven studies and all included only bacteraemic patients. No association between ESBL-E infection and shock was found (OR = 1.23, 95% CI: 0.75-2.02, I 2=14.8%). Only one study investigated the association between ESBL-E infection and bacteraemia.

CONCLUSIONS

Infections by ESBL-E appear to be significantly associated with mortality but not septic shock. Available studies investigating bacteraemia and shock as an intermediate outcome of ESBL-E infections are lacking. Future studies investigating the relationship between clinical outcomes and molecular characteristics of resistant strains are further warranted, along with studies investigating this in non-bacteraemic patients.

Towards the Identification of Antibiotic-Resistant Bacteria Causing Urinary Tract Infections Using Volatile Organic Compounds Analysis-A Pilot Study

Antibiotic resistance is an unprecedented threat to modern medicine. The analysis of volatile organic compounds (VOCs) from bacteria potentially offers a rapid way to determine antibiotic susceptibility in bacteria. This study aimed to find the optimal conditions to obtain the maximum number of VOCs detected which next allowed the assessment of differences in VOC profiles between susceptible and resistant isolates of Escherichia coli causing urinary tract infections. The analysis of VOCs in the headspace above the bacterial cultures allowed the distinguishing of resistant and susceptible bacteria based on the abundance of six VOCs with 85.7% overall accuracy. The results of this preliminary study are promising, and with development could lead to a practical, faster diagnostic method for use in routine microbiology.

Multicenter, Observational Cohort Study Evaluating Third-Generation Cephalosporin Therapy for Bloodstream Infections Secondary to Enterobacter, Serratia, and Citrobacter Species

OBJECTIVES

There is debate on whether the use of third-generation cephalosporins (3GC) increases the risk of clinical failure in bloodstream infections (BSIs) caused by chromosomally-mediated AmpC-producing Enterobacterales (CAE). This study evaluates the impact of definitive 3GC therapy versus other antibiotics on clinical outcomes in BSIs due to Enterobacter, Serratia, or Citrobacter species.

METHODS

This multicenter, retrospective cohort study evaluated adult hospitalized patients with BSIs secondary to Enterobacter, Serratia, or Citrobacter species from 1 January 2006 to 1 September 2014. Definitive 3GC therapy was compared to definitive therapy with other non-3GC antibiotics. Multivariable Cox proportional hazards regression evaluated the impact of definitive 3GC on overall treatment failure (OTF) as a composite of in-hospital mortality, 30-day hospital readmission, or 90-day reinfection.

RESULTS

A total of 381 patients from 18 institutions in the southeastern United States were enrolled. Common sources of BSIs were the urinary tract and central venous catheters (78 (20.5%) patients each). Definitive 3GC therapy was utilized in 65 (17.1%) patients. OTF occurred in 22/65 patients (33.9%) in the definitive 3GC group vs. 94/316 (29.8%) in the non-3GC group (p = 0.51). Individual components of OTF were comparable between groups. Risk of OTF was comparable with definitive 3GC therapy vs. definitive non-3GC therapy (aHR 0.93, 95% CI 0.51-1.72) in multivariable Cox proportional hazards regression analysis.

CONCLUSIONS

These outcomes suggest definitive 3GC therapy does not significantly alter the risk of poor clinical outcomes in the treatment of BSIs secondary to Enterobacter, Serratia, or Citrobacter species compared to other antimicrobial agents.

Evaluation of modified carbapenem inactivation method for suspected carbapenemase among Enterobacteriaceae clinical isolates

Modified carbapenem inactivation method (mCIM) testing was currently recommended by Clinical and Laboratory Standards Institute (CLSI) for detection of carbapenemase among Enterobacteriaceae clinical isolates. In this study, a panel of 145 clinical strains were collected for evaluating the mCIM for detection of carbapenemase. Antimicrobial susceptibility testing were performed by microbroth dilution and the results were interpreted according to CLSI guidelines. All strains were resistant to ertapenem with high MIC₅₀ and MIC₉₀ (64 mg/L –>128 mg/L). For bla_NDM-1-positive or bla_OXA-232-positive strains, the zone of inhibition of meropenem were all 6 mm despite the incubation time of 6 h, 18 h or 24 h. For 6 h, the zone of meropenem inhibition for most of carbapenemase-positive isolates were meet the positive criteria 6–15 mm. However, for carbapenemase-negative isolates, the zone of meropenem inhibition were 16–18 mm after 6 h incubation which should be considered indeterminate for standard incubating time such as 18 h or 24 h. After incubating for 18 h or 24 h, the zone of meropenem inhibition were 22–25 mm for carbapenemase-negative isolates and meet the negative criteria. Our study indicate mCIM is a simple and effective method to identify the carbapenemases producers among Enterobacteriaceae clinical isolates.

Isolation of ESBL-producing Bacteria from Sputum in Community-acquired Pneumonia or Healthcare-associated Pneumonia Does Not Indicate the Need for Antibiotics with Activity against This Class

Objective In the past decade, extended-spectrum β-lactamase (ESBL)-producing bacteria have increasingly frequently been isolated from various kinds of clinical specimens. However, the appropriate treatment of pneumonia in which ESBL-producing bacteria are isolated from sputum culture is poorly understood. To investigate whether or not ESBL-producing bacteria isolated from sputum in pneumonia cases should be treated as the causative bacteria. Methods and Patients In this retrospective study, we screened for patients, admitted between January 2009 and December 2015 in whom pneumonia was suspected and for whom sputum cultures yielded Escherichia coli or Klebsiella spp. isolates. We identified patients with community-acquired pneumonia (CAP) or healthcare-associated pneumonia (HCAP) from whom ESBL-producing bacteria had been isolated from sputum culture and to whom antibiotic treatment had been given with a diagnosis of pneumonia. We analyzed the patients' backgrounds and the effect of the antibiotic treatment for the initial 3-5 days. Results From 400 patients initially screened, 27 with ESBL-producing bacteria were secondarily screened. In this subset of patients, 15 were diagnosed with pneumonia, including 7 with CAP (5 E. coli and 2 K. pneumoniae) and 8 with HCAP (8 E. coli). These patients exhibited an average age of 84.1 years old, and 9 of 15 were men. No patients were initially treated with antimicrobials that are effective against isolated ESBL-producing bacteria. However, 13 of 15 patients showed improvement of pneumonia following the initial antibiotic treatment. Conclusion ESBL-producing bacteria isolated from sputum are not likely to be the actual causative organisms of pneumonia.

Empiric Piperacillin-Tazobactam versus Carbapenems in the Treatment of Bacteraemia Due to Extended-Spectrum Beta-Lactamase-Producing Enterobacteriaceae

Extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae are a common cause of bacteraemia in endemic countries and may be associated with high mortality; carbapenems are considered the drug of choice. Limited data suggest piperacillin-tazobactam could be equally effective. We aimed to compare 30-day mortality of patients treated empirically with piperacillin-tazobactam versus a carbapenem in a multi-centre retrospective cohort study in Singapore. Only patients with active empiric monotherapy with piperacillin-tazobactam or a carbapenem were included. A propensity score for empiric carbapenem therapy was derived and an adjusted multivariate analysis of mortality was conducted. A total of 394 patients had ESBL-Escherichia.coli and ESBL-Klebsiella pneumoniae bacteraemia of which 23.1% were community acquired cases. One hundred and fifty-one received initial active monotherapy comprising piperacillin-tazobactam (n = 94) or a carbapenem (n = 57). Patients who received carbapenems were less likely to have health-care associated risk factors and have an unknown source of bacteraemia, but were more likely to have a urinary source. Thirty-day mortality was comparable between those who received empiric piperacillin-tazobactam and a carbapenem (29 [30.9%] vs. 17 [29.8%]), P = 0.89). Those who received empiric piperacillin-tazobactam had a lower 30-day acquisition of multi-drug resistant and fungal infections (7 [7.4%] vs. 14 [24.6%]), P<0.01). After adjusting for confounders, use of empiric piperacillin-tazobactam was not associated with increased 30-day mortality (OR 1.00, 95% CI; 0.45–2.17). Empiric piperacillin-tazobactam was not associated with increased 30-day mortality and may result in fewer multi-drug resistant and fungal infections when compared with a carbapenem.

Carbapenem-nonsusceptible Enterobacteriaceae in Taiwan

A total of 1135 carbapenem-resistant (nonsusceptible) Enterobacteriaceae (CRE) isolates were recovered between November 2010 and July 2012 (517 from 2010-2011 and 618 from 2012) from 4 hospitals in Taiwan. Carbapenemase-producing Enterobacteriaceae (CPE) comprised 5.0% (57 isolates), including 17 KPC-2 (16 Klebsiella pneumoniae and 1 Escherichia coli), 1 NDM-1 (K. oxytoca), 37 IMP-8 (26 Enterobacter cloacae, 4 Citrobacter freundii, 4 Raoultella planticola, 1 K. pneumoniae, 1 E. coli and 1 K. oxytoca), and 2 VIM-1 (1 E. cloacae, 1 E. coli). The KPC-2-positive K. pneumoniae were highly clonal even in isolates from different hospitals, and all were ST11. IMP-8 positive E. cloacae from the same hospitals showed higher similarity in PFGE pattern than those from different hospitals. A total of 518 CRE isolates (45.6%) were positive for blaESBL, while 704 (62.0%) isolates were blaAmpC-positive, 382 (33.6% overall) of which carried both blaESBL and blaAmpC. CTX-M (414, 80.0%) was the most common blaESBL, while DHA (497, 70.6%) and CMY (157, 22.3%) were the most common blaAmpC. Co-carriage of blaESBL and blaAmpC was detected in 31 (54.4%) and 15 (26.3%) of the 57 CPE, respectively. KPC-2 was the most common carbapenemase detected in K. pneumoniae (2.8%), while IMP-8 was the most common in E. cloacae (9.7%). All KPC-2-positive CRE were resistant to all three tested carbapenems. However, fourteen of the 37 IMP-8-positive CRE were susceptible to both imipenem and meropenem in vitro. Intra- and inter-hospital spread of KPC-2-producing K. pneumoniae and IMP-8-producing E. cloacae likely occurred. Although the prevalence of CPE is still low, careful monitoring is urgently needed. Non-susceptibility to ertapenem might need to be considered as one criterion of definition for CRE in areas where IMP type carbapenemase is prevalent.

A statistical approach for determination of disk diffusion-based cutoff values for systematic characterization of wild-type and non-wild-type bacterial populations in antimicrobial susceptibility testing

In this study, we introduce a new approach for determination of epidemiologic cutoffs (ECOFFs) and resistant-population cutoffs (RCOFFs) based on receiver operating characteristic (ROC) curves. As an example, the method was applied for determination of ECOFFs for seven different beta-lactam antibiotics and wild-type populations of Escherichia coli, Klebsiella pneumoniae, and Enterobacter cloacae. In addition, RCOFFs were determined for bacterial populations with defined resistance mechanisms ("resistotypes"), i.e., extended-spectrum beta-lactamase (ESBL)-positive E. coli, ESBL-positive K. pneumoniae, and ESBL-positive E. cloacae; AmpC cephalosporinase-positive E. coli and AmpC-positive K. pneumoniae; and broad-spectrum beta-lactamase (BSBL)-positive E. coli. RCOFFs and ECOFFs are instrumental for a systematic characterization of associations between resistotypes and wild-type populations.

Clinical Efficacy of Ertapenem for Recurrent Cystitis Caused by Multidrug-Resistant Extended-Spectrum β-Lactamase-Producing Escherichia coli in Female Outpatients

Purpose

To evaluate the clinical outcomes of ertapenem administered as an outpatient parenteral antibiotic therapy for intractable cystitis caused by extended-spectrum β-lactamase (ESBL)-producing Escherichia coli.

Materials and Methods

We retrospectively reviewed a case series of 3 years of therapeutic experience with ertapenem for intractable recurrent cystitis caused by ESBL-producing E. coli. Ertapenem 1 g/d was parenterally administered to the patients on an outpatient basis until the acquisition of symptomatic improvement and negative conversion of urine culture. Demographic and clinical characteristics of patients, antimicrobial resistance, and clinical response data were analyzed from the patients' medical records.

Results

During the course of this study, a total of 383 patients were diagnosed with cystitis, and 24 of them showed ESBL-producing E. coli (6.26%). The mean treatment duration of all patients was 8.5 days. The early clinical and microbiological cure rates 0 to 7 days after the end of treatment were 91.7% (22/24) and 90.9% (20/22), respectively. The late clinical and microbiological cure rates 4 to 6 weeks after the end of treatment were 72.2% (13/18) at both time points.

Conclusions

Parenteral ertapenem treatment can be an effective and well-tolerated treatment option for intractable recurrent cystitis by multidrug-resistant ESBL-producing E. coli.

Hospital clonal dissemination of Enterobacter aerogenes producing carbapenemase KPC-2 in a Chinese teaching hospital

Carbapenems are first-line agents for the treatment of serious nosocomial infections caused by multidrug-resistant Enterobacteriaceae. However, resistance to carbapenems has increased dramatically among Enterobacteriaceae in our hospital. In this study, we report clonal dissemination caused by carbapenem-resistant Enterobacter aerogenes (CREA). In 2011, CREA was identified from 12 patients admitted to the neurosurgical ward. All 12 clinical isolates were non-susceptible to cefotaxime, ceftazidime, cefoxitin, ertapenem, imipenem or meropenem. All isolates carried the gene encoding Klebsiella pneumoniae carbapenemase-2 (KPC-2), except for the isolate E4. However, a remarkably lower expression level of the porin OmpF was detected in the non-KPC-2-producing isolate E4 on SDS-PAGE compared with the carbapenem-susceptible isolate. Epidemiological and molecular investigations showed that a single E. aerogenes strain (PFGE type A), including seven KPC-2-producing clinical isolates, was primarily responsible for the first isolation and subsequent dissemination. In a case-control study, we identified risk factors for infection/colonization with CREA. Mechanical ventilation, the changing of sickbeds and previous use of broad-spectrum antibiotics were identified as potential risk factors. Our findings suggest that further studies should focus on judicious use of available antibiotics, implementation of active antibiotic resistance surveillance and strict implementation of infection-control measures to avoid the rapid spread or clonal dissemination caused by carbapenem-resistant Enterobacteriaceae in healthcare facilities.

Locally derived versus guideline-based approach to treatment of hospital-acquired pneumonia in the trauma intensive care unit

BACKGROUND

Appropriate initial antibiotic therapy for presumed pneumonia in critically ill patients decreases the mortality rate. To achieve this goal, treatment guidelines developed by groups such as the American Thoracic Society (ATS) have been stressed. However, often overlooked is the importance of incorporating local microbiologic data into an empiric algorithm. Our hypothesis was that an empiric algorithm supported by our locally-driven analysis would predict more accurate coverage than one defined strictly by an unmodified guideline-driven approach.

METHODS

Retrospective review of all first hospital-acquired (HAP) and ventilator-associated pneumonia (VAP) pathogens in consecutive trauma intensive care unit (TICU) patients over 18 months. Microbiologic data were analyzed to update our TICU-specific empiric algorithm. The ATS guidelines define patients at risk for multidrug-resistant (MDR) organisms on the basis of standardized criteria and time since admission (early <5 days; late ≥5 days).

RESULTS

A total of 164 pathogens caused 117 pneumonias. For early coverage, ATS guidelines stress identification of MDR risks; these criteria failed to identify 8 of 13 (62%) early MDR pneumonias. For early HAP/VAP with no MDR risks, the ATS guidelines recommend monotherapy; susceptibility differed (49% to ciprofloxacin, 68% to ampicillin-sulbactam, 83% to ceftriaxone). A total of 15% of early pathogens were MDR gram-positive, so addition of vancomycin resulted in adequate predicted coverage of 100%, 79%, and 95% for ciprofloxacin, ampicillin-sulbactam, and ceftriaxone, respectively. For late HAP/VAP, ATS recommends regimens based on broad-spectrum drugs. Vancomycin with ciprofloxacin, cefepime, or piperacillin-tazobactam had predicted coverage of 95%, 94%, and 93%, respectively.

CONCLUSIONS

The empiric algorithm derived from analysis of local microbiologic data predicted significantly better coverage than one defined by an unmodified guideline-driven approach for early HAP/VAP. Our locally-derived TICU algorithm of ceftriaxone+vancomycin for early pneumonia and piperacillin-tazobactam+vancomycin for late pneumonia optimizes the adequacy of initial therapy. Understanding local patterns of pneumonia ensures the creation and maintenance of empiric algorithms that achieve the best clinical outcomes.

[Nocosomial urinary tract infections]

Nosocomial urinary tract infections (UTI) are mainly related to urinary catheterisation. In this paper we review the pathogenic mechanisms, particularly the route by which the microorganisms colonise the urinary tract, their adhesion ability, and their capacity to form biofilms, and are related not only to the microorganism but also to the type of urinary catheter. The aetiology of catheter related UTI is variable, and multiresistant microorganisms are often isolated, making empirical antibiotic therapy complex. Clinical findings are frequently atypical, and its diagnosis is difficult. The therapeutic management of catheter-related UTI should be stratified according to the type of UTI: asymptomatic bacteriuria should not be habitually treated, but patients with septic shock should receive a broad spectrum antibiotic. In this review, the value of the different preventive measures are discussed.

Combination antibiotic therapy for empiric and definitive treatment of gram-negative infections: insights from the Society of Infectious Diseases Pharmacists

The widespread emergence of antibiotic-resistant gram-negative organisms has compromised the utility of current treatment options for severe infections caused by these pathogens. The rate of gram-negative multidrug resistance is worsening, threatening the effectiveness of newer broad-spectrum antibiotic agents. Infections associated with multidrug-resistant Pseudomonas aeruginosa, Acinetobacter baumannii, and Enterobacteriaceae are having a substantial impact on hospital costs and mortality rates. The potential for these resistant gram-negative nosocomial pathogens must always be a primary consideration when selecting antibiotic therapy for critically ill patients. Empiric combination therapy directed at gram-negative pathogens is a logical approach for patients with suspected health care-associated infections, particularly those with risk factors for infections caused by multidrug-resistant pathogens. Although in vitro synergy tests have shown potential benefits of continued combination therapy, convincing clinical data that demonstrate a need for combination therapy once susceptibilities are known are lacking. Thus, deescalation to a single agent once susceptibilities are known is recommended for most patients and pathogens. Use of polymyxins, often in combination with other antimicrobials, may be necessary for salvage therapy.

Impact of healthcare-associated acquisition on community-onset Gram-negative bloodstream infection: a population-based study: healthcare-associated Gram-negative BSI

We performed a population-based study to examine the influence of healthcare-associated acquisition on pathogen distribution, antimicrobial resistance, short- and long-term mortality of community-onset Gram-negative bloodstream infections (BSI). We identified 733 unique patients with community-onset Gram-negative BSI (306 healthcare-associated and 427 community-acquired) among Olmsted County, Minnesota, residents from 1 January 1998 to 31 December 2007. Multivariate logistic regression was used to examine the association between healthcare-associated acquisition and microbiological etiology and antimicrobial resistance. Multivariate Cox proportional hazards regression was used to evaluate the influence of the site of acquisition on mortality. Healthcare-associated acquisition was predictive of Pseudomonas aeruginosa (odds ratio [OR] 3.14, 95% confidence intervals [CI]: 1.59-6.57) and the group of Enterobacter, Citrobacter, and Serratia species (OR 2.23, 95% CI: 1.21-4.21) as causative pathogens of community-onset Gram-negative BSI. Healthcare-associated acquisition was also predictive of fluoroquinolone resistance among community-onset Gram-negative bloodstream isolates (OR 2.27, 95% CI: 1.18-4.53). Healthcare-associated acquisition of BSI was independently associated with higher 28-day (hazard ratio [HR] 3.73, 95% CI: 2.13-6.93) and 1-year mortality (HR 3.60, 95% CI: 2.57-5.15). Because of differences in pathogen distribution, antimicrobial resistance, and outcomes between healthcare-associated and community-acquired Gram-negative BSI, identification of patients with healthcare-associated acquisition of BSI is essential to optimize empiric antimicrobial therapy.

Antibiotic Collateral Damage: Resistance and Antibiotic-Associated Diarrhea

The purpose of this review is to describe dilemmas associated with antibiotic collateral damage and provide clinical pharmacists with information to improve antibiotic utilization. The clinical use of antibiotics has been associated with acquisition and spread of nosocomial pathogens and multidrug-resistant strains, such as extended-spectrum beta-lactamases, AmpC hyper-producers, carbapenemases, and resistant gram-positive organisms. The mobility of plasmid-mediated resistance, such as extended-spectrum beta-lactamases and the more recently isolated Klebsiella pneumoniae carbapenemases, have been well-demonstrated with worldwide distribution across several different species. The challenges surrounding antibiotic-associated diarrhea, particularly Clostridium difficile infection (CDI), continue to evolve with outbreaks of hypervirulent strains linked to the use of less commonly implicated antibiotics. Published literature was searched and reviewed using PubMed. Undesirable attributes related to antibiotic use can have broad consequences in addition to their effect on individual patients. This collateral damage can evolve over time, and prescribers must be aware of current concerns and be diligent in their judicious use of antibiotics.

Efficacy and safety of tigecycline for the treatment of infectious diseases: a meta-analysis

BACKGROUND

Multidrug resistance among bacteria increases the need for new antimicrobial drugs with high potency and stability. Tigecycline is one candidate drug, and a previous meta-analysis of only published randomised controlled trials suggested that it might as effective as comparator treatments; we did a meta-analysis to include new and unpublished trials to assess its efficacy for the treatment of adult patients with serious bacterial infection.

METHODS

We searched PubMed, Cochrane Central Register, and Embase up to March 30, 2011, to identify published studies, and we searched clinical trial registries to identify completed unpublished studies, the results of which were obtained through the manufacturer. Eligible studies were randomised trials assessing the clinical efficacy, safety, and eradication efficiency of tigecycline versus other antimicrobial agents for any bacterial infection. The primary outcome was treatment success in patients who received at least one dose of the study drug, had clinical evidence of disease, and had complete follow-up (the clinically assessable population). Meta-analysis was done with random-effects models because of heterogeneity across the trials.

FINDINGS

14 randomised trials, comprising about 7400 patients, were included. Treatment success was lower with tigecycline than with control antibiotic agents, but the difference was not significant (odds ratio 0·87, 95% CI 0·74-1·02). Adverse events were more frequent in the tigecycline group than in the control groups (1·45, 1·11-1·88), with significantly more vomiting and nausea. All-cause mortality was higher in the tigecycline group than in the comparator groups, but the difference was not significant (1·28, 0·97-1·69). Eradication efficiency did not differ between tigecycline and control regimens, but the sample size for these comparisons was small.

INTERPRETATION

Tigecycline is not better than standard antimicrobial agents for the treatment of serious infections. Our findings show that assessment with unpublished studies is needed to make appropriate decisions about new agents.

FUNDING

None.

Pathogens resistant to antibacterial agents

Resistance to antimicrobial drugs is increasing at an alarming rate among both gram-positive and gram-negative bacteria. Traditionally, bacteria resistant to multiple antimicrobial agents have been restricted to the nosocomial environment. A disturbing trend has been the recent emergence and spread of resistant pathogens in nursing homes, in the community, and in the hospital. This article reviews the epidemiology, molecular mechanisms of resistance, and treatment options for pathogens resistant to antimicrobial drugs.

Investigating the impact of the definition of previous antibiotic exposure related to isolation of extended spectrum β-lactamase-producing Klebsiella pneumoniae

BACKGROUND

Previous antibiotic exposure is a risk factor for extended spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae isolation, but the optimal definition of previous antibiotic exposure remains unclear.

METHODS

This was a retrospective, case-control study comparing 88 patients with ESBL-producing K pneumoniae (cases) and 88 patients with non-ESBL-producing K pneumoniae (controls). Three previous antibiotic exposure definitions were analyzed, including durations of 30, 60, and 90 days prior to organism isolation.

RESULTS

The mean cohort age was 63.6 ± 16.9 years, 43% were male, and 86% were black. In bivariate analysis, third-generation cephalosporins and cefepime were associated with ESBL-producing K pneumoniae isolation, and the odds ratios (OR) were significant regardless of previous antibiotic exposure definition. However, for fluoroquinolones and ampicillin/sulbactam, the ORs varied as a function of previous antibiotic exposure definition. In multivariate analysis, third-generation cephalosporin usage was a risk factor for ESBL-producing K pneumoniae isolation, whereas ampicillin/sulbactam usage was protective against these organisms, regardless of the time frame analyzed. Other independent predictors of ESBL-producing K pneumoniae included nursing home residence (OR, 9.30 [95% confidence interval: 3.69-23.43]) and hemodialysis (OR, 13.60 [95% confidence interval: 4.29-43.17]).

CONCLUSION

Prior use of third-generation cephalosporins, nursing home residence, and hemodialysis were independent risk factors for isolation of an ESBL-producing K pneumoniae regardless of the time frame analyzed.

How I manage haematology patients with septic shock

Patients with a variety of haematological conditions are at risk of infection and its most serious complication: septic shock. Mortality for septic shock remains high and especially so in patients with haematological malignancy and following bone marrow transplantation. However, advances in the treatment of severe sepsis have improved mortality rates even though evidence for the management of severe sepsis in haematology patients is limited. Wherever possible this review will concentrate on evidence directly applicable to haematology patients but inevitably will have to extrapolate evidence from other patient groups. The Surviving Sepsis Guidelines 2008 provide information on best practice in the management of patients with severe sepsis and septic shock and are broadly applicable though not specific to haematology patients. This review summarizes a practical approach to the management of severe sepsis in haematology patients and highlights areas of research which may bring new treatments in the future. The review is limited to the management and initial resuscitation of septic shock in adult haematology patients and will not address the detailed intensive care management of these patients or the management of severe sepsis in children.

First detection of CTX-M and SHV extended-spectrum beta-lactamases in Escherichia coli urinary tract isolates from dogs and cats in the United States

One hundred fifty canine and feline Escherichia coli isolates associated with urinary tract infections were screened for the presence of extended-spectrum beta-lactamase (ESBL) genes. Out of 60 isolates suspected to be ESBL positive based on antimicrobial susceptibility testing, 11 ESBLs were identified, including one SHV-12 gene, one CTX-M-14 gene, and nine CTX-M-15 genes. This study provides the first report of CTX-M- and SHV-type ESBLs in dogs and cats in the United States.

Comparison of 3 phenotypic-detection methods for identifying plasmid-mediated AmpC beta-lactamase-producing Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis strains

BACKGROUND

Plasmid-mediated AmpC beta-lactamases (PABLs) have been detected in the strains of Escherichia coli, Klebsiella spp., Proteus mirabilis, and Salmonella spp. PABLs may be difficult to detect and might interfere in the therapeutic and infection-control processes. Although several PABL-detection methods based on phenotypes have been reported, the Clinical and Laboratory Standards Institute currently does not recommend a routine detection method for PABLs. The aim of this study is to compare the performances of 3 phenotypic PABL detection methods.

METHODS

Total 276 non-duplicated clinical isolates of E. coli (N=97), K. pneumoniae (N=136), and P. mirabilis (N=43) were collected from 14 hospitals in Korea between April and June 2007 in a non-consecutive and non-random manner. Multiplex PCR was performed to detect the PABL genes. Further, 3 phenotypic detection methods-cephamycin-Hodge test, Tris-EDTA (TE) disk test, and combination-disk test with 3-aminophenylboronic acid (BA)-were performed using cefoxitin and cefotetan disks.

RESULTS

PABL genes were detected by multiplex PCR in 122/276 isolates, including 14/97 E. coli, 105/136 K. pneumoniae, and 3/43 P. mirabilis isolates. The combination-disk test with BA showed higher sensitivity (98.4%), specificity (92.2%), and efficiency (96.3%) than the cephamycin-Hodge (76.2%, 96.1%, and 88.6%, respectively) and the TE-disk (80.3%, 91.6%, and 87.9%, respectively) tests.

CONCLUSIONS

The combination-disk test with BA is a simple, efficient, and interpretable test that can be applicable in clinical laboratories involved in the detection of PABLs in clinical isolates of E. coli, K. pneumoniae, and P. mirabilis.

Outbreaks of Serratia marcescens in neonatal and pediatric intensive care units: clinical aspects, risk factors and management

The following recommendations are derived from a systematic analysis of 34 Serratia marcescens outbreaks described in 27 publications from neonatal and pediatric intensive care units (NICU, PICU), in which genotyping methods were used to confirm or exclude clonality. The clinical observation of two or more temporally related cases of nosocomial S. marcescens infection should raise the suspicion of an outbreak, particularly in the NICU or PICU setting. Since colonized or infected patients represent the most important reservoir for cross transmission, hygienic barrier precautions (contact isolation/cohortation, the use of gloves and gowns in addition to strictly performed hand disinfection, enhanced environmental disinfection) should immediately be implemented and staff education given. Well-planned sampling of potential environmental sources should only be performed when these supervised barrier precautions do not result in containment of the outbreak. The current strategy of empiric antibiotic treatment should be reevaluated by a medical microbiologist or an infectious disease specialist. Empiric treatment of colonized children should use combination therapy informed by in vitro susceptibility data; in this context the high propensity of S. marcescens to cause meningitis and intracerebral abscess formation should be considered. In vitro susceptibility patterns do not reliably prove or exclude the clonality of the outbreak isolate. Genotyping of the isolates by pulse-field gel electrophoresis or PCR-based methods should be performed, but any interventions to interrupt further nosocomial spread should be carried out without waiting for the results.

Spread of multidrug-resistant Proteus mirabilis isolates producing an AmpC-type beta-lactamase: epidemiology and clinical management

A remarkable increase in Proteus mirabilis strains producing acquired AmpC-type beta-lactamases (CBLs) has been observed at Ospedale di Circolo e Fondazione Macchi (Varese, Italy) over the last few years. The epidemiology and treatment outcome of infections associated with this unprecedented spread are reported. From 2004-2006, 2070 P. mirabilis isolates were investigated. Extended-spectrum beta-lactamases (ESBLs) and CBL resistance determinants were identified by gene amplification and direct sequencing. Clonal relatedness was evaluated by macrorestriction analysis. Overall, 43 CBL-positive isolates were obtained from hospitalised (n=22) and non-hospitalised (n=21) patients (median age 78.8 years). The prevalence of CBL-positive isolates increased from 0.3% in 2004 to 4.6% in 2006, whereas that of ESBL-positive isolates remained constant (ca. 10%). CBL-positive isolates were multidrug-resistant and carried the CMY-16 determinant. All but two isolates were genetically identical or closely related. Retrospective analysis of clinical records revealed that the majority of CMY-16-positive isolates were associated with urinary tract infections. Treatment with amikacin or carbapenems was consistently effective, whereas piperacillin/tazobactam produced a clinical response in seven of nine cases. This is the first report of a rapid spread of CBL-positive P. mirabilis strains endowed with remarkable antimicrobial resistance. Practical methods for CBL detection are needed for the appropriate management of related infections.

Establishment of in vitro susceptibility testing methodologies and comparative activities of piperacillin in combination with the penem {beta}-lactamase inhibitor BLI-489

The novel bicyclic penem inhibitor BLI-489 has demonstrated activity as an inhibitor of class A, C, and D beta-lactamases. To determine the combination of piperacillin and BLI-489 to be used in susceptibility testing that would most accurately identify susceptible and resistant isolates, a predictor panel of beta-lactamase-producing bacteria was utilized to determine the reliability of the combination of piperacillin-BLI-489 at a constant inhibitor concentration of 2 or 4 microg/ml and at ratios of 1:1, 2:1, 4:1, and 8:1. There were a number of strains that would be falsely reported as susceptible or intermediate if tested with the ratios of 1:1 and 2:1, whereas the constant concentration of 2 microg/ml of BLI-489 and the ratio of 8:1 had a tendency to overpredict resistance. Similar MICs were obtained with piperacillin-BLI-489 in a 4:1 ratio and when BLI-489 was held constant at 4 microg/ml. Based on these results, an in vitro testing methodology employing a constant concentration of 4 microg/ml BLI-489 was used to evaluate the combination of piperacillin-BLI-489 against a larger panel of recently identified clinical isolates. Approximately 55% of all of the enteric bacilli tested were nonsusceptible to piperacillin alone (MIC > or = 32 microg/ml). However, 92% of these piperacillin nonsusceptible strains were inhibited by < or =16 microg/ml piperacillin-BLI-489; in contrast, only 66% were inhibited by < or =16 microg/ml piperacillin-tazobactam. The combination of piperacillin-BLI-489 also demonstrated improved activity compared to that of piperacillin-tazobactam against the problematic extended-spectrum beta-lactamase- and AmpC-expressing strains.

[Infections associated with the use of indwelling urinary catheters. Infections related to intrauterine devices]

Hospital-acquired urinary tract infections (UTI) are mainly associated with indwelling urinary catheter use. In this chapter, the pathogenesis of hospital-acquired UTI in catheterized patients, the mechanisms by which microorganisms reach the urinary tract and are able to adhere and form biofilms, and the influence of other risk factors, such as time since catheter insertion and catheter composition, are reviewed. A wide variety of infecting microorganisms can affect patients with urinary catheters, making the choice of an adequate empirical antimicrobial course complex, particularly in cases of suspected multiresistant microorganisms. Moreover, the clinical symptoms are less characteristic in catheter infection and the diagnosis may be difficult. Treatment should be stratified according to the clinical features, which can vary from asymptomatic bacteriuria that may not require treatment, to severe septic episodes that need wide antibiotic coverage. The prevention measures for UTI in permanently catheterized patients are reviewed. Infections of the female genital tract associated with foreign bodies are mainly related to the use of intrauterine devices (IUDs). The epidemiology, microbiology profile, antimicrobial treatment, and prophylaxis of pelvic inflammatory disease related to IUD use in women are also reviewed.

Current Perspectives on Extended-Spectrum Beta-Lactamase–Producing Gram-Negative Bacilli

Beta-lactamase enzymes produced by gram-negative bacilli were identified before the first beta-lactam antibiotics were used to treat infections. As these enzymes adapted to available beta-lactam agents, newer beta-lactam agents were developed. Development and widespread use of the oxyimino-cephalosporins led to the emergence of extended-spectrum beta-lactamase enzymes that hydrolyze the penicillins, extended-spectrum cephalosporins, and aztreonam. There are now over 200 recognized ESBLs in a variety of gram-negative bacilli conferring resistance to penicillins, cephalosporins, a monobactam, and even carbapenems. The emergence of these enzymes is associated with poor patient outcomes, increased total health care costs, and more carbapenem use. Carbapenems should be selected judiciously to optimize outcomes while preventing further selection of extended-spectrum beta-lactamase resistance.

The role of carbapenems in the treatment of severe nosocomial respiratory tract infections

The prevalence of antibiotic-resistant bacteria continues to increase, particularly in patients in the intensive care unit with nosocomial pneumonia. The intention of this review is to provide an overview of severe nosocomial pneumonia, carbapenems and the problem of bacterial resistance to antimicrobial agents. Attention was focused on the efficacy, safety and pharmacodynamics of imipenem, meropenem, ertapenem and doripenem. Issues on the impact of appropriate empiric antibiotic therapy for nosocomial pneumonia patients considered at risk for resistant pathogens are discussed. Critical decision making regarding the use of carbapenems for treating severe nosocomial pneumonia requires careful consideration of the four Ds of optimal antimicrobial therapy: right Drug, right Dose, De-escalated to pathogen-directed therapy and right Duration of therapy.