Benefit-risk Evaluation for Diagnostics: A Framework (BED-FRAME)

The medical community needs systematic and pragmatic approaches for evaluating the benefit-risk trade-offs of diagnostics that assist in medical decision making. Benefit-Risk Evaluation of Diagnostics: A Framework (BED-FRAME) is a strategy for pragmatic evaluation of diagnostics designed to supplement traditional approaches. BED-FRAME evaluates diagnostic yield and addresses 2 key issues: (1) that diagnostic yield depends on prevalence, and (2) that different diagnostic errors carry different clinical consequences. As such, evaluating and comparing diagnostics depends on prevalence and the relative importance of potential errors. BED-FRAME provides a tool for communicating the expected clinical impact of diagnostic application and the expected trade-offs of diagnostic alternatives. BED-FRAME is a useful fundamental supplement to the standard analysis of diagnostic studies that will aid in clinical decision making.

Rapid Molecular Diagnostics, Antibiotic Treatment Decisions, and Developing Approaches to Inform Empiric Therapy: PRIMERS I and II

BACKGROUND

Rapid molecular diagnostic (RMD) platforms may lead to better antibiotic use. Our objective was to develop analytical strategies to enhance the interpretation of RMDs for clinicians.

METHODS

We compared the performance characteristics of 4 RMD platforms for detecting resistance against β-lactams in 72 highly resistant isolates of Escherichia coli and Klebsiella pneumoniae (PRIMERS I). Subsequently, 2 platforms were used in a blinded study in which a heterogeneous collection of 196 isolates of E. coli and K. pneumoniae (PRIMERS II) were examined. We evaluated the genotypic results as predictors of resistance or susceptibility against β-lactam antibiotics. We designed analytical strategies and graphical representations of platform performance, including discrimination summary plots and susceptibility and resistance predictive values, that are readily interpretable by practitioners to inform decision-making.

RESULTS

In PRIMERS I, the 4 RMD platforms detected β-lactamase (bla) genes and identified susceptibility or resistance in >95% of cases. In PRIMERS II, the 2 platforms identified susceptibility against extended-spectrum cephalosporins and carbapenems in >90% of cases; however, against piperacillin/tazobactam, susceptibility was identified in <80% of cases. Applying the analytical strategies to a population with 15% prevalence of ceftazidime-resistance and 5% imipenem-resistance, RMD platforms predicted susceptibility in >95% of cases, while prediction of resistance was 69%-73% for ceftazidime and 41%-50% for imipenem.

CONCLUSIONS

RMD platforms can help inform empiric β-lactam therapy in cases where bla genes are not detected and the prevalence of resistance is known. Our analysis is a first step in bridging the gap between RMDs and empiric treatment decisions.

Are Staphylococcus intermedius Infections in Humans Cases of Mistaken Identity? A Case Series and Literature Review

Staphylococcus intermedius and Staphylococcus pseudintermedius are difficult to distinguish using conventional microbiological methods. Molecular diagnostic tools change our understanding of the epidemiology of these 2 organisms. In this study, we present (1) a detailed review of the current literature on molecular diagnostics and (2) a case series in which misidentification was proven in 1 case. We conclude that S pseudintermedius is a more common human pathogen than previously recognized.

Fulminant endocarditis and disseminated infection caused by carbapenem-resistant Acinetobacter baumannii in a renal-pancreas transplant recipient

Acinetobacter baumannii is an important cause of healthcare-associated infections, and is particularly problematic among patients who undergo organ transplantation. We describe a case of fulminant sepsis caused by carbapenem-resistant A. baumannii harboring the blaOXA-23 carbapenemase gene and belonging to international clone II. This isolate led to the death of a patient 6 days after simultaneous kidney-pancreas transplantation. Autopsy findings revealed acute mitral valve endocarditis, myocarditis, splenic and renal emboli, peritonitis, and pneumonia. This case highlights the severe nature of certain A. baumannii infections and the vulnerability of transplanted patients to the increasingly intractable "high-risk" clones of multidrug-resistant organisms.

Unexpected challenges in treating multidrug-resistant Gram-negative bacteria: resistance to ceftazidime-avibactam in archived isolates of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a notoriously difficult-to-treat pathogen that is a common cause of severe nosocomial infections. Investigating a collection of β-lactam-resistant P. aeruginosa clinical isolates from a decade ago, we uncovered resistance to ceftazidime-avibactam, a novel β-lactam/β-lactamase inhibitor combination. The isolates were systematically analyzed through a variety of genetic, biochemical, genomic, and microbiological methods to understand how resistance manifests to a unique drug combination that is not yet clinically released. We discovered that avibactam was able to inactivate different AmpC β-lactamase enzymes and that blaPDC regulatory elements and penicillin-binding protein differences did not contribute in a major way to resistance. By using carefully selected combinations of antimicrobial agents, we deduced that the greatest barrier to ceftazidime-avibactam is membrane permeability and drug efflux. To overcome the constellation of resistance determinants, we show that a combination of antimicrobial agents (ceftazidime/avibactam/fosfomycin) targeting multiple cell wall synthetic pathways can restore susceptibility. In P. aeruginosa, efflux, as a general mechanism of resistance, may pose the greatest challenge to future antibiotic development. Our unexpected findings create concern that even the development of antimicrobial agents targeted for the treatment of multidrug-resistant bacteria may encounter clinically important resistance. Antibiotic therapy in the future must consider these factors.

Salvage microbiology: opportunities and challenges in the detection of bacterial pathogens following initiation of antimicrobial treatment

Broad-range 16S ribosomal RNA gene PCR coupled with Sanger sequencing was originally employed by soil scientists and was subsequently adapted for clinical applications. PCR coupled with electrospray ionization mass spectrometry has also progressed from initial applications in the detection of organisms from environmental samples into the clinical realm and has demonstrated promise in detection of pathogens in clinical specimens obtained from patients with suspected infection but negative cultures. We review studies of multiplex PCR, 16S ribosomal RNA gene PCR and sequencing and PCR coupled with electrospray ionization mass spectrometry for detection of bacteria in specimens that were obtained from patients during or after administration of antibiotic treatment, and examine the role of each for assisting in antimicrobial treatment and stewardship efforts. Following an exploration of the available data in this field, we discuss the opportunities that the preliminary investigations reveal, as well as the challenges faced with the implementation of these strategies in clinical practice.

Culture negative empyema in a critically ill child: an opportunity for rapid molecular diagnostics

Background

Nucleic acid amplification technologies (NAAT) are advancing our ability to make rapid molecular diagnoses in patients with serious culture negative infections. This is the first report of PCR coupled to electrospray ionization mass spectrometry use in the evaluation of complicated community acquired pneumonia in a pediatric patient.

Case presentation

We present a case of culture negative empyema in a critically ill, Caucasian, 2-year-old girl who was treated with broad-spectrum empiric antibiotics, in which the length of stay was prolonged by adverse effects of the empiric antibiotic treatment. PCR coupled to electrospray ionization mass spectrometry was applied to culture negative fluid and tissue samples from the patient in order to determine the etiology of the empyema.

Conclusions

Using this method, Streptococcus mitis/viridans was identified as the pathogen. A retrospective review of cases of empyema in children at our institution found that 87.5% of cases were negative for identification of a pathogen and antibiotics were administered to 100% of cases prior to collecting pleural fluid for culture. Understanding the role of Streptococcus mitis/viridans group in the etiology of empyema using an advanced NAAT coupled with mass spectrometry can enlighten clinicians as to the impact of this pathogen in community acquired pneumonia and help assist with antibiotic stewardship.

Infections caused by fluoroquinolone-resistant Escherichia coli following transrectal ultrasound-guided biopsy of the prostate

An increase in the number of infections with fluoroquinolone (FQ)-resistant Escherichia coli following transrectal ultrasound-guided biopsy of the prostate (TRUBP) was observed in Louis Stokes Cleveland Department of Veterans Affairs Medical Center. This study investigated whether these infections were caused by a single strain of E. coli possessing distinct resistance and virulence determinants. Of 15 patients with urinary tract infection, 5 were complicated with bacteraemia and 1 with prostate abscess. Thirteen FQ-resistant isolates demonstrated mutations in the quinolone resistance-determining regions (QRDRs) of gyrA and parC but did not contain plasmid-mediated quinolone resistance determinants; bla_CTX-M and bla_CMY as well as genes coding for extended-spectrum β-lactamases were also absent. Genes encoding aminoglycoside-modifying enzymes were discovered in an isolate that was gentamicin-resistant. The most prevalent sequence type (ST) was ST43 (n = 7), corresponding to ST131 in Achtman's multilocus sequence typing (MLST) scheme. These isolates (i) were distinguished as >95% similar by repetitive sequence-based PCR (rep-PCR), (ii) belonged to the virulent phylogenetic group B2 and (iii) contained plasmid types FIB, FIA and Frep. Several other strain types were present (ST2, ST27, ST30, ST44, ST472, ST494, ST511 and ST627). Non-ST43 isolates infected patients with more co-morbidities but contained similar virulence factors (kpsMTII, iutA, papAH/papC and sfa/focDE). In our hospital, E. coli isolates causing TRUBP-related infection are quite heterogeneous (ST131 and other ST types) and are part of phylogenetic groups containing multiple virulence factors.

Multi-drug-resistant Klebsiella pneumoniae pancreatitis: a new challenge in a serious surgical infection

BACKGROUND

Klebsiella pneumoniae is an important cause of nosocomial infections, but its role in severe acute pancreatitis (SAP) is not well defined. Few cases of K. pneumoniae associated SAP have been reported. Due to the emergence of extended-spectrum beta-lactamases (ESBLs) and carbapenemases, treatment of multidrug-resistant (MDR) K. pneumoniae presents a challenge. Tigecycline and colistin have gained recent attention for their broad-spectrum antimicrobial activity.

METHODS

We describe a case of SAP due to K. pneumoniae bearing K. pneumoniae carbapenemase (KPC) treated successfully with colistin plus tigecycline and offer a review of similar experiences published in the literature.

RESULTS

The case reported herein required surgical drainage of multiple pancreatic abscesses and treatment with tigecycline and colistin. Our comparative analysis revealed a number of unique features associated with SAP due to K. pneumoniae: 1) underlying pancreatic injury, 2) multiple drug resistance determinants and virulence factors that complicate treatment, and 3) surgical debridement as a requirement for cure.

CONCLUSION

As the prevalence of K. pneumoniae bearing KPC continues to increase in the healthcare setting, SAP caused by this MDR pathogen will become more common. Tigecycline plus colistin was a successful antibiotic regimen for the treatment of SAP due to K. pneumoniae bearing KPC.

Pseudo-outbreak of Klebsiella oxytoca spontaneous bacterial peritonitis attributed to contamination of multidose vials of culture medium supplement

OBJECTIVE

To determine the source of a cluster of Klebsiella oxytoca isolates cultured from peritoneal fluid of 3 patients with cirrhosis on a single day.

DESIGN

Outbreak investigation and before-after study.

SETTING

A Veterans Affairs medical center.

METHODS

Epidemiologic investigation, analysis of antimicrobial susceptibility testing results and molecular typing of K. oxytoca isolates with repetitive sequence-based polymerase chain reaction (rep-PCR), review of microbiology laboratory procedures for processing peritoneal fluid cultures, and comparison of peritoneal fluid contamination rates 18 months before and after modification of laboratory procedures for culturing peritoneal fluid.

RESULTS

Each of the peritoneal fluid samples that grew K. oxytoca was inoculated into blood culture bottles by different clinicians at different hospital locations. None of the patients had clinical findings suggestive of peritonitis or elevated polymorphonuclear cell counts in peritoneal fluid (range, 3-25 cells/μL). Molecular typing with rep-PCR demonstrated that the K. oxytoca isolates were genetically related (greater than 95% similarity). Laboratory procedures included the routine addition of a culture medium supplement of yeast extract and dextrose from a multidose vial into blood culture bottles with peritoneal fluid. After discontinuing use of the culture medium supplement, there was a marked reduction in the number of peritoneal fluid cultures deemed as contaminants (14.3% vs 0.9%; [Formula: see text]).

CONCLUSION

A pseudo-outbreak of K. oxytoca peritonitis and high rates of contamination of peritoneal fluid were attributable to contamination of a multidose culture medium supplement. This article highlights the importance of discouraging the use of multidose vials in all clinical settings.

A kinetic analysis of the inhibition of FOX-4 β-lactamase, a plasmid-mediated AmpC cephalosporinase, by monocyclic β-lactams and carbapenems

OBJECTIVES

Class C β-lactamases are prevalent among Enterobacteriaceae; however, these enzymes are resistant to inactivation by commercially available β-lactamase inhibitors. In order to find novel scaffolds to inhibit class C β-lactamases, the comparative efficacy of monocyclic β-lactam antibiotics (aztreonam and the siderophore monosulfactam BAL30072), the bridged monobactam β-lactamase inhibitor BAL29880, and carbapenems (imipenem, meropenem, doripenem and ertapenem) were tested in kinetic assays against FOX-4, a plasmid-mediated class C β-lactamase (pmAmpC).

METHODS

The FOX-4 β-lactamase was purified. Steady-state kinetics, electrospray ionization mass spectrometry (ESI-MS) and ultraviolet difference (UVD) spectroscopy were conducted using the β-lactam scaffolds described.

RESULTS

The K(i) values for the monocyclic β-lactams against FOX-4 β-lactamase were 0.04 ± 0.01 μM (aztreonam) and 0.66 ± 0.03 μM (BAL30072), and the Ki value for the bridged monobactam BAL29880 was 8.9 ± 0.5 μM. For carbapenems, the Ki values ranged from 0.27 ± 0.05 μM (ertapenem) to 2.3 ± 0.3 μM (imipenem). ESI-MS demonstrated the formation of stable covalent adducts when the monocyclic β-lactams and carbapenems were reacted with FOX-4 β-lactamase. UVD spectroscopy suggested the appearance of different chromophoric intermediates.

CONCLUSIONS

Monocyclic β-lactam and carbapenem antibiotics are effective mechanism-based inhibitors of FOX-4 β-lactamase, a clinically important pmAmpC, and provide stimulus for the development of new inhibitors to inactivate plasmidic and chromosomal class C β-lactamases.

Characterisation and clinical features of Enterobacter cloacae bloodstream infections occurring at a tertiary care university hospital in Switzerland: is cefepime adequate therapy?

Despite many years of clinical experience with cefepime, data regarding the outcome of patients suffering from bloodstream infections (BSIs) due to Enterobacter cloacae (Ecl) are scarce. To address the gap in our knowledge, 57 Ecl responsible for 51 BSIs were analysed implementing phenotypic and molecular methods (microarrays, PCRs for bla and other genes, rep-PCR to analyse clonality). Only two E. cloacae (3.5%) were ESBL-producers, whereas 34 (59.6%) and 18 (31.6%) possessed inducible (Ind-Ecl) or derepressed (Der-Ecl) AmpC enzymes, respectively. All isolates were susceptible to imipenem, meropenem, gentamicin and ciprofloxacin. Der-Ecl were highly resistant to ceftazidime and piperacillin/tazobactam (both MIC₉₀≥256 μg/mL), whereas cefepime retained its activity (MIC₉₀ of 3 μg/mL). rep-PCR indicated that the isolates were sporadic, but Ecl collected from the same patients were indistinguishable. In particular, three BSIs initially due to Ind-Ecl evolved (under ceftriaxone or piperacillin/tazobactam treatment) into Der-Ecl because of mutations or a deletion in ampD or insertion of IS4321 in the promoter. These last two mechanisms have never been described in Ecl. Mortality was higher for BSIs due to Der-Ecl than Ind-Ecl (3.8% vs. 29.4%; P=0.028) and was associated with the Charlson co-morbidity index (P=0.046). Using the following directed treatments, patients with BSI showed a favourable treatment outcome: cefepime (16/18; 88.9%); carbapenems (12/13; 92.3%); ceftriaxone (4/7; 57.1%); piperacillin/tazobactam (5/7; 71.4%); and ciprofloxacin (6/6; 100%). Cefepime represents a safe therapeutic option and an alternative to carbapenems to treat BSIs due to Ecl when the prevalence of ESBL-producers is low.

"Silent" dissemination of Klebsiella pneumoniae isolates bearing K. pneumoniae carbapenemase in a long-term care facility for children and young adults in Northeast Ohio

BACKGROUND

Klebsiella pneumoniae isolates harboring the K. pneumoniae carbapenemase gene (bla(KPC)) are creating a significant healthcare threat in both acute and long-term care facilities (LTCFs). As part of a study conducted in 2004 to determine the risk of stool colonization with extended-spectrum cephalosporin-resistant gram-negative bacteria, 12 isolates of K. pneumoniae that exhibited nonsusceptibility to extended-spectrum cephalosporins were detected. All were gastrointestinal carriage isolates that were not associated with infection.

METHODS

Reassessment of the carbapenem minimum inhibitory concentrations using revised 2011 Clinical Laboratory Standards Institute breakpoints uncovered carbapenem resistance. To further investigate, a DNA microarray assay, PCR-sequencing of bla genes, immunoblotting, repetitive-sequence-based PCR (rep-PCR) and multilocus sequence typing (MLST) were performed.

RESULTS

The DNA microarray detected bla(KPC) in all 12 isolates, and bla(KPC-3) was identified by PCR amplification and sequencing of the amplicon. In addition, a bla(SHV-11) gene was detected in all isolates. Immunoblotting revealed "low-level" production of the K. pneumoniae carbapenemase, and rep-PCR indicated that all bla(KPC-3)-positive K. pneumoniae strains were genetically related (≥98% similar). According to MLST, all isolates belonged to sequence type 36. This sequence type has not been previously linked with bla(KPC) carriage. Plasmids from 3 representative isolates readily transferred the bla(KPC-3) to Escherichia coli J-53 recipients.

CONCLUSIONS

Our findings reveal the "silent" dissemination of bla(KPC-3) as part of Tn4401b on a mobile plasmid in Northeast Ohio nearly a decade ago and establish the first report, to our knowledge, of K. pneumoniae containing bla(KPC-3) in an LTCF caring for neurologically impaired children and young adults.

Acinetobacter baumannii rOmpA vaccine dose alters immune polarization and immunodominant epitopes

BACKGROUND

The rOmpA vaccine has been shown to protect mice from lethal infection caused by extreme-drug-resistant (XDR) Acinetobacter baumannii. The role of dose in immunology of the rOmpA vaccine was explored.

METHODS

Mice were vaccinated with various doses of rOmpA plus aluminum hydroxide (Al(OH)(3)) adjuvant. The impact of dose on antibody titers, cytokine production, and immunodominant epitopes was defined.

RESULTS

Anti-rOmpA IgG and IgG subtype titers were higher at larger vaccine doses (30 and 100 μg vs. 3 μg). The 3 μg dose induced a balanced IFN-γ-IL-4 immune response while the 100 μg dose induced a polarized IL-4/Type 2 response. Epitope mapping revealed distinct T cell epitopes that activated IFN-γ-, IL-4-, and IL-17-producing splenocytes. Vaccination with the 100 μg dose caused epitope spreading among IL-4-producing splenocytes, while it induced fewer reactive epitopes among IFN-γ-producing splenocytes.

CONCLUSIONS

Vaccine dose escalation resulted in an enhanced Type 2 immune response, accompanied by substantial IL-4-inducing T cell epitope spreading and restricted IFN-γ-inducing epitopes. These results inform continued development of the rOmpA vaccine against A. baumannii, and also are of general importance in that they indicate that immune polarization and epitope selectivity can be modulated by altering vaccine dose.

"Swimming in resistance": Co-colonization with carbapenem-resistant Enterobacteriaceae and Acinetobacter baumannii or Pseudomonas aeruginosa

BACKGROUND

Co-colonization of patients with carbapenem-resistant Enterobacteriaceae (CRE) and Acinetobacter baumannii (AB) or Pseudomonas aeruginosa (PA) is reported to be associated with increased antibiotic resistance and mortality.

METHODS

CREs isolated between September 2008 and September 2009 were analyzed at Detroit Medical Center. Patients who had an additional isolation of AB or PA during the period spanning 7 days before to 7 days after CRE isolation were considered co-colonized. Molecular typing was used to determine genetic similarity among CRE strains.

RESULTS

Eighty-six unique patient isolates of CREs were analyzed. Thirty-four patients (40%) were co-colonized, and 26 (79%) had AB or PA isolated on the same day as the CRE. High Charlson Comorbidity Index score was an independent predictor for co-colonization. Recent stay at a long-term acute-care facility and previous therapy with antimicrobials with activity only against gram-positive microorganisms also were associated with co-colonization, but did not remain significant independent predictors. Co-colonization was associated with higher levels of resistance to carbapenems among CREs and increased 90-day mortality. Molecular typing revealed CRE polyclonality in co-colonized patients.

CONCLUSIONS

Co-colonization is found in patients with the greatest disease burden in the hospital and occurs due to the dissemination of multiple CRE strains. This finding calls into question the practice of cohorting patients with CRE in close proximity to patients with AB or PA.

Exploring the role of a conserved class A residue in the Ω-Loop of KPC-2 β-lactamase: a mechanism for ceftazidime hydrolysis

Gram-negative bacteria harboring KPC-2, a class A β-lactamase, are resistant to all β-lactam antibiotics and pose a major public health threat. Arg-164 is a conserved residue in all class A β-lactamases and is located in the solvent-exposed Ω-loop of KPC-2. To probe the role of this amino acid in KPC-2, we performed site-saturation mutagenesis. When compared with wild type, 11 of 19 variants at position Arg-164 in KPC-2 conferred increased resistance to the oxyimino-cephalosporin, ceftazidime (minimum inhibitory concentration; 32→128 mg/liter) when expressed in Escherichia coli. Using the R164S variant of KPC-2 as a representative β-lactamase for more detailed analysis, we observed only a modest 25% increase in k(cat)/K(m) for ceftazidime (0.015→0.019 μm(-1) s(-1)). Employing pre-steady-state kinetics and mass spectrometry, we determined that acylation is rate-limiting for ceftazidime hydrolysis by KPC-2, whereas deacylation is rate-limiting in the R164S variant, leading to accumulation of acyl-enzyme at steady-state. CD spectroscopy revealed that a conformational change occurred in the turnover of ceftazidime by KPC-2, but not the R164S variant, providing evidence for a different form of the enzyme at steady state. Molecular models constructed to explain these findings suggest that ceftazidime adopts a unique conformation, despite preservation of Ω-loop structure. We propose that the R164S substitution in KPC-2 enhances ceftazidime resistance by proceeding through "covalent trapping" of the substrate by a deacylation impaired enzyme with a lower K(m). Future antibiotic design must consider the distinctive behavior of the Ω-loop of KPC-2.

Longitudinal analysis of the temporal evolution of Acinetobacter baumannii strains in Ohio, USA, by using rapid automated typing methods

Genotyping methods are essential to understand the transmission dynamics of Acinetobacter baumannii. We examined the representative genotypes of A. baumannii at different time periods in select locations in Ohio, using two rapid automated typing methods: PCR coupled with electrospray ionization mass spectrometry (PCR/ESI-MS), a form of multi-locus sequence typing (MLST), and repetitive-sequence-based-PCR (rep-PCR). Our analysis included 122 isolates from 4 referral hospital systems, in 2 urban areas of Ohio. These isolates were associated with outbreaks at 3 different time periods (1996, 2000 and 2005–2007). Type assignments of PCR/ESI-MS and rep-PCR were compared to each other and to worldwide (WW) clone types. The discriminatory power of each method was determined using the Simpson's index of diversity (DI). We observed that PCR/ESI-MS sequence type (ST) 14, corresponding to WW clone 3, predominated in 1996, whereas ST 12 and 14 co-existed in the intermediate period (2000) and ST 10 and 12, belonging to WW clone 2, predominated more recently in 2007. The shift from WW clone 3 to WW clone 2 was accompanied by an increase in carbapenem resistance. The DI was approximately 0.74 for PCR/ESI-MS, 0.88 for rep-PCR and 0.90 for the combination of both typing methods. We conclude that combining rapid automated typing methods such as PCR/ESI-MS and rep-PCR serves to optimally characterize the regional molecular epidemiology of A. baumannii. Our data also sheds light on the changing sequence types in an 11 year period in Northeast Ohio.

Longitudinal epidemiology of multidrug-resistant (MDR) Acinetobacter species in a tertiary care hospital

BACKGROUND

Acinetobacter species are well-known causes of health care-associated infections. The longitudinal epidemiology of this species in the hospital setting is poorly understood. A sudden, persistent increase in multidrug-resistant (MDR) A baumannii infections occurred beginning in June 2006 at Temple University Hospital in Philadelphia. An analysis was done to describe the longitudinal molecular epidemiology of MDR A baumannii in a tertiary care hospital.

METHODS

This was an epidemiologic investigation using repetitive extragenic palindromic-PCR (rep-PCR) of patients with a positive culture for MDR A baumannii admitted to the hospital between February 2006 and January 2010. MDR A baumannii were defined as susceptible only to colistin and/or tigecycline.

RESULTS

The incidence rate of MDR A baumannii rose from 0.36 cases per 1,000 patient-days (pre-epidemic) to 0.86 cases per 1,000 patient-days, due mainly to an increase in the surgical intensive care unit. Enhanced infection control measures were implemented, but waves of MDR A baumannii continued to be documented through routine surveillance. Of 32 strains collected in 2006-2007, a single predominant clone and 2 minor clones accounted for almost all of the cases of MDR A baumannii studied. Of 24 strains collected in 2008-2009, another clone, different from those studied in the earlier period, predominated, and was accompanied by 3 minor variants.

CONCLUSION

Following an outbreak in the surgical intensive care unit, MDR A baumannii persisted in our institution for a 3-year period despite rigorous infection control measures. An unexpected strain replacement occurred during this period, with the original predominant strain disappearing completely and new minor clones displacing the original minor clones.

Outcomes and genetic relatedness of carbapenem-resistant enterobacteriaceae at Detroit medical center

BACKGROUND

Carbapenem-resistant Enterobacteriaceae (CRE) are rapidly emerging in hospitals in the United States and are posing a significant threat. To better understand the transmission dynamics and the acquisition of resistant strains, a thorough analysis of epidemiologic and molecular characteristics was performed.

METHODS

CRE isolated at Detroit Medical Center were analyzed from September 2008 to September 2009. bla(KPC) genes were investigated by polymerase chain reaction (PCR), and repetitive extragenic palindromic PCR (rep-PCR) was used to determine genetic similarity among strains. Epidemiologic and outcomes analyses were performed.

RESULTS

Ninety-two unique patient CRE isolates were recovered. Sixty-eight strains (74%) were Klebsiella pneumoniae, 7 were Klebsiella oxytoca, 15 were Enterobacter species, and 2 were Escherichia coli. Fifteen isolates (16%) were resistant to colistin, 14 (16%) were resistant to tigecycline, and 2 were resistant to all antimicrobials tested. The mean ± standard deviation age of patients was 63 ± 2 years. Sixty patients (68%) were admitted to the hospital from long-term care facilities. Only 70% of patients received effective antimicrobial therapy when infection was suspected, with a mean time to appropriate therapy of 120 ± 23 hours following sample culturing. The mean length of hospitalization after sample culturing was 18.6 ± 2.5 days. Of 57 inpatients, 18 (32%) died in the hospital. Independent predictors for mortality were intensive care unit stay (odds ratio [OR], 15.8; P = .003) and co-colonization with CRE and either Acinetobacter baumannii or Pseudomonas aeruginosa (OR, 17.2; P = .006). Among K. pneumoniae CRE, rep-PCR revealed 2 genetically related strains that comprised 70% and 20% of isolates, respectively.

CONCLUSIONS

In this large U.S. cohort of patients with CRE infection, which reflects the modern continuum of medical care, co-colonization with CRE and A. baumannii or P. aeruginosa was associated with increased mortality. Two predominant clones of K. pneumoniae accounted for the majority of cases of CRE infection.

Interlaboratory reproducibility of DiversiLab rep-PCR typing and clustering of Acinetobacter baumannii isolates

We have investigated the reproducibility of DiversiLab rep-PCR fingerprints between two laboratories with the aim of determining if the fingerprints and clustering are laboratory-specific or portable. One-hundred non-duplicate Acinetobacter baumannii isolates were used in this study. DNA isolation and rep-PCR were each performed separately in two laboratories and rep-PCR patterns generated in laboratory A were compared with those from laboratory B. Twelve A. baumannii isolates processed in laboratory A showed ≥98 % pattern similarity with the corresponding 12 isolates tested in laboratory B and were considered identical. Sixty-four isolates showed 95-97.9 % similarity with their corresponding isolates. Twenty-three isolates showed 90-94 % similarity with the corresponding isolates, while one isolate showed only 87.4 % similarity. However, intra-laboratory clustering was conserved: isolates that clustered in laboratory A also clustered in laboratory B. While clustering was conserved and reproducible at two different laboratories, demonstrating the robustness of rep-PCR, interlaboratory comparison of individual isolate fingerprints showed more variability. This comparison allows conclusions regarding clonality to be reached independent of the laboratory where the analysis is performed.