Alessandro Capone

High rate of colistin resistance among patients with carbapenem-resistant Klebsiella pneumoniae infection accounts for an excess of mortality

Carbapenem-resistant Klebsiella pneumoniae (CR-KP) is becoming a common cause of healthcare-associated infection in Italy, with high morbidity and mortality. Prevalent CR-KP clones and resistance mechanisms vary between regions and over time. Therapeutic approaches and their impact on mortality have to be investigated. We performed a prospective study of patients with CR-KP isolation, hospitalized in nine hospitals of Rome, Italy, from December 2010 to May 2011, to describe the molecular epidemiology, antibiotic treatment and risk factors for mortality. Overall, 97 patients (60% male, median age 69xa0years) were enrolled. Strains producing blaKPC-3 were identified in 89 patients, blaVIM in three patients and blaCTX-M-15 plus porin defects in the remaining five patients. Inter-hospital spread of two major clones, ST512 and ST258, was found. Overall, 36.1% and 20.4% of strains were also resistant to colistin and tigecycline, respectively. Infection was diagnosed in 91 patients who received appropriate antibiotic treatment, combination therapy and removal of the infectious source in 73.6%, 59.3% and 28.5% of cases, respectively. Overall, 23 different antibiotic regimens were prescribed. In-hospital mortality was 25.8%. Multivariate analysis adjusted for appropriate treatment, combination therapy and infectious-source removal, showed that Charlson comorbidity score, intensive-care unit onset of infection, bacteraemia and infection due to a colistin-resistant CR-KP strain were independent risk factors for mortality. The spread of clones producing K.xa0pneumoniae carbapenemases, mainly ST258, is currently the major cause of CR-KP infection in central Italy. We observed a high rate of resistance to colistin that is independently associated with worse outcome.

In vitro activity of tigecycline in combination with various antimicrobials against multidrug resistant Acinetobacter baumannii

BackgroundInfections sustained by multidrug-resistant (MDR) and pan-resistant Acinetobacter baumannii have become a challenging problem in Intensive Care Units. Tigecycline provided new hope for the treatment of MDR A. baumannii infections, but isolates showing reduced susceptibility have emerged in many countries, further limiting the therapeutic options. Empirical combination therapy has become a common practice to treat patients infected with MDR A. baumannii, in spite of the limited microbiological and clinical evidence supporting its efficacy. Here, the in vitro interaction of tigecycline with seven commonly used anti-Acinetobacter drugs has been assessed.MethodsTwenty-two MDR A. baumannii isolates from Intensive Care Unit (ICU) patients and two reference strains for the European clonal lineages I and II (including 3, 15 and 6 isolates that were resistant, intermediate and susceptible to tigecycline, respectively) were tested. Antimicrobial agents were: tigecycline, levofloxacin, piperacillin-tazobactam, amikacin, imipenem, rifampicin, ampicillin-sulbactam, and colistin. MICs were determined by the broth microdilution method. Antibiotic interactions were determined by chequerboard and time-kill assays. Only antibiotic combinations showing synergism or antagonism in both chequerboard and time-kill assays were accepted as authentic synergistic or antagonistic interactions, respectively.ResultsConsidering all antimicrobials in combination with tigecycline, chequerboard analysis showed 5.9% synergy, 85.7% indifference, and 8.3% antagonism. Tigecycline showed synergism with levofloxacin (4 strains; 16.6%), amikacin (2 strains; 8.3%), imipenem (2 strains; 8.3%) and colistin (2 strains; 8.3%). Antagonism was observed for the tigecycline/piperacillin-tazobactam combination (8 strains; 33.3%). Synergism was detected only among tigecycline non-susceptible strains. Time-kill assays confirmed the synergistic interaction between tigecycline and levofloxacin, amikacin, imipenem and colistin for 5 of 7 selected isolates. No antagonism was confirmed by time-kill assays.ConclusionThis study demonstrates the in vitro synergistic activity of tigecycline in combination with colistin, levofloxacin, amikacin and imipenem against five tigecycline non-susceptible A. baumannii strains, opening the way to a more rationale clinical assessment of novel combination therapies to combat infections caused by MDR and pan-resistant A. baumannii.

Changing carbapenemase gene pattern in an epidemic multidrug-resistant Acinetobacter baumannii lineage causing multiple outbreaks in central Italy

OBJECTIVESninfections caused by multidrug-resistant (MDR) Acinetobacter baumannii are a challenging problem worldwide. Here, the molecular epidemiology and the genetic basis of antibiotic resistance in 111 MDR A. baumannii strains isolated from June 2005 to March 2009 from infected patients in 10 intensive care units (ICUs) in central Italy were investigated.nnnMETHODSnepidemiological typing was performed by random amplification of polymorphic DNA, PCR-based sequence grouping and macrorestriction analysis. MICs of antibiotics were determined by the broth microdilution method. Genes for OXA carbapenemases, metallo-β-lactamases and the CarO porin were searched for by PCR.nnnRESULTSnmolecular genotyping identified one predominant A. baumannii lineage, related to the international clonal lineage II, accounting for 95.6% of isolates. Isolates referable to this lineage were recovered from all ICUs surveyed and were resistant to nearly all classes of antimicrobials, with the exception of tigecycline and colistin. A high percentage (60.5%) of A. baumannii isolates showed elevated resistance to imipenem (MICs ≥u200a 128 mg/L), concomitant with resistance to meropenem. Carbapenem resistance was associated with the presence of either bla(OXA-58)-like (22.8%) or bla(OXA-23)-like (71.1%) carbapenemase genes. Molecular typing showed that the epidemic lineage encoding OXA-23 emerged in 2007 and displaced a genetically related clone encoding OXA-58 that had been responsible for previous ICU outbreaks in the same region.nnnCONCLUSIONSnemergence of the OXA-23 epidemic lineage could result from selective advantage conferred by the bla(OXA-23)-like determinant, which provides increased resistance to carbapenems.

Characterization of pABVA01, a Plasmid Encoding the OXA-24 Carbapenemase from Italian Isolates of Acinetobacter baumannii

ABSTRACT Two epidemiologically unrelated carbapenem-resistant Acinetobacter baumannii isolates were investigated as representatives of the first Italian isolates producing the OXA-24 carbapenemase. Both isolates were of European clonal lineage II and carried an identical OXA-24-encoding plasmid, named pABVA01. Comparative analysis revealed that in pABVA01, blaOXA-24 was part of a DNA module flanked by conserved inverted repeats homologous to XerC/XerD binding sites, which in other Acinetobacter plasmids flank different DNA modules, suggesting mobilization by a novel site-specific recombination mechanism.

Reversion to susceptibility of a carbapenem-resistant clinical isolate of Klebsiella pneumoniae producing KPC-3

OBJECTIVESnWe report the case of a kidney-transplant patient, suffering an intra-abdominal abscess at the surgical site caused by a carbapenem-resistant ST258 Klebsiella pneumoniae clone, producing the KPC-3 carbapenemase. Under tigecycline treatment, the patient developed a sepsis caused by a carbapenem-susceptible ST258 K. pneumoniae strain. Complete DNA sequences of the plasmids carried by the resistant and susceptible strains from this patient were determined.nnnMETHODSnThe complete DNA sequences of plasmids were obtained by applying the 454 Genome Sequencer FLX-PLUS procedure on a library constructed of total plasmid DNA purified from the carbapenem-resistant and -susceptible strains.nnnRESULTSnIn the carbapenem-resistant strain, four plasmids encoding 24 resistance genes, including blaKPC-3, and two putative virulence clusters were detected. In the susceptible strain, large rearrangements occurred in the KPC-carrying plasmid, causing the deletion of the entire Tn4401::blaKPC-3 transposon, with the consequent reversion of the strain to carbapenem susceptibility. The patient was successfully treated with carbapenems and fully recovered.nnnCONCLUSIONSnThe description of the plasmid content in these two strains gives interesting insights into the plasticity of KPC-carrying plasmids in K. pneumoniae.

Daptomycin for the treatment of infective endocarditis: results from a European registry

OBJECTIVESnInfective endocarditis (IE) is a complex infection associated with high mortality. Daptomycin, a cyclic lipopeptide antibiotic highly active against Gram-positive bacteria, has recently been incorporated into IE treatment guidelines. This retrospective analysis provides insights into the use of daptomycin in IE in the European Cubicin(®) Outcomes Registry Experience (EU-CORE(SM)) between 2006 and 2010.nnnPATIENTS AND METHODSnThree hundred and seventy-eight (10%) of 3621 enrolled patients received daptomycin for treatment of IE. Two hundred and fifty-nine (69%) had left-sided IE (LIE) and 182 patients (48%) underwent concomitant surgery.nnnRESULTSnStaphylococcus aureus was the most frequently identified pathogen (n=92; methicillin susceptible, n=50) and daptomycin was used empirically in 134 patients. Among cases of second-line therapy (n=312), the most common reason for switching to daptomycin was failure of the previous regimen (including glycopeptides and penicillins). Daptomycin was administered at 6 mg/kg in 224 patients and at ≥ 8 mg/kg in 72 patients. Clinical success rates were 80% overall, 91% for right-sided IE (RIE) and 76% for LIE, with similar rates seen for infections caused by methicillin-susceptible S. aureus (84%) and methicillin-resistant S. aureus (81%). The clinical success rate in patients treated with ≥ 8 mg/kg daptomycin was 90% [n=72 (RIE, 91%; LIE, 89%)]. No new safety signals were observed.nnnCONCLUSIONSnIn patients with IE registered in EU-CORE, daptomycin was most frequently used as second-line treatment after treatment failure. The majority of patients had LIE and most commonly received daptomycin for the treatment of staphylococcal infections. Clinical success was high in this difficult-to-treat population. The role of doses ≥ 8 mg/kg per day in the empirical treatment of IE deserves further investigation.

In vitro activity of tigecycline against multidrug-resistant Acinetobacter baumannii

Sir, Acinetobacter baumannii has emerged as a leading nosocomial pathogen, particularly in intensive care units (ICUs), where several outbreaks have been described. Treatment of severe A. baumannii infection represents a difficult clinical challenge due to the propensity of this organism to acquire antimicrobial resistance, resulting in the emergence of multiand pan-resistant clones. There are few therapeutic options to combat multidrug-resistant (MDR) A. baumannii. Tigecycline, a new semi-synthetic tetracycline, has provided hope for the treatment of bacterial infections. Literature data on the in vitro activity of tigecycline against MDR A. baumannii shows variable susceptibility, – 7 likely resulting from different susceptibility testing methods and high clonal correlation among epidemic strains. Indeed, early studies have reported excellent in vitro activity of tigecycline against isolates of the A. baumannii complex (MIC90 2 mg/L). 3 However, A. baumannii isolates showing reduced susceptibility to tigecycline (MIC90 32 mg/L) have recently been identified, posing the risk for selection and spreading of resistance in this notoriously adaptable species. Therefore, we investigated the in vitro activity of tigecycline against a collection of 80 presumed MDR A. baumannii isolates and compared the activity between tigecycline and 17 other antimicrobials, including three tetracyclines. A. baumannii primary isolates were obtained between January 2004 and June 2005 from ICU patients cared for in six general hospitals of the Rome (Italy) urban area. None of the patients had undergone previous treatment with tigecycline. Bacteria were identified by the Vitek II system (bioMerieux, Marcy l’Etoile, France) and Amplified Ribosomal DNA Restriction Analysis. Although all isolates had been provided as MDR by collaborating centres, antimicrobial susceptibility testing was re-assessed using ampicillin/ sulbactam, piperacillin, piperacillin/tazobactam, cefepime, ceftazidime, aztreonam, imipenem, meropenem, amikacin, gentamicin, ciprofloxacin, levofloxacin, trimethoprim/sulfamethoxazole, colistin, tetracycline, doxycycline, minocycline and tigecycline. For all drugs, except colistin, doxycycline, minocycline and tigecycline, susceptibility tests were performed by the Vitek II ID-GNB and AST-GN09 cards. Doxycycline and minocycline susceptibility was determined by the disc diffusion method. Tigecycline and colistin susceptibility was determined by the broth microdilution method, according to the CLSI guidelines. The US FDA breakpoints approved for Enterobacteriaceae were applied to define tigecycline susceptibility ( 2 mg/L susceptibility; 8 mg/L resistance). Colistin susceptibility was interpreted according to Gales et al. The MDR phenotype was defined as diminished susceptibility to more than one of the following five drug classes: antipseudomonal cephalosporins, antipseudomonal carbapenems, b-lactam/b-lactamase inhibitor combinations, antipseudomonal fluoroquinolones and aminoglycosides. The in vitro activity of individual antimicrobial agents against A. baumannii clinical isolates is summarized in Table 1. Seventy-eight isolates were definitively defined as MDR. The most common phenotype ( 90% of the isolates) was resistant to piperacillin, piperacillin/tazobactam, cefepime, ceftazidime, aztreonam, ciprofloxacin and levofloxacin. Individual resistance to imipenem, amikacin, trimethoprim/sulfamethoxazole and tetracycline was observed in 70% to 86.2% of the isolates. Approximately 50% of the A. baumannii isolates were resistant to gentamicin and 22.5% to ampicillin/sulbactam. A high level of carbapenem resistance was observed, with 77.5% and 81.3% of isolates resistant to imipenem and meropenem, respectively. Concerning tigecycline, 27.5% of the isolates were nonsusceptible, including 23.7% intermediate and 3.7% fully resistant isolates. The MIC50 and MIC90 values were 2 and 4 mg/L, respectively, with a unimodal distribution of tigecycline MICs in the 0.125–8 mg/L range. These findings are in the middle-upper range of previously reported tigecycline resistance data.3 – 7 Notably, the only isolate resistant to colistin was susceptible to tigecycline. Recent data on the activity of tetracyclines against A. baumannii are conflicting. In large surveys from the UK, the USA, Germany and Italy, the frequency of A. baumannii isolates resistant to tigecycline, minocycline and doxycycline varied in the ranges 4% to 6%, 0% to 18% and 6% to 44%, respectively, in association with high overall rates of resistance to tetracycline. – 7 Conversely, a study conducted in Israel showed that 66% and 37% of the MDR A. baumannii isolates were resistant to tigecycline and minocycline, respectively. Here, we report that 3 (3.8%), 13 (16.3%) and 69 (86.3%) out of the 80 presumed MDR A. baumannii isolates were resistant to minocycline, doxycycline and tetracycline, respectively. Taking into account non-susceptible isolates (intermediate and fully resistant), the relative activities of tetracyclines were minocycline . tigecycline doxycycline . tetracycline, with an overall decreased susceptibility to tigecycline among A. baumannii isolates resistant to other tetracyclines. In fact, all isolates susceptible to minocycline, doxycycline and tetracycline were highly susceptible to tigecycline (MIC range 0.125–1 mg/L), whereas only 6 of 16 (37.5%) isolates non-susceptible to the three tetracyclines were susceptible to tigecycline (MIC range Journal of Antimicrobial Chemotherapy (2008) 62, 422–425 doi:10.1093/jac/dkn172 Advance Access publication 19 April 2008

In vitro activity of doripenem in combination with various antimicrobials against multidrug-resistant Acinetobacter baumannii: possible options for the treatment of complicated infection.

AIMSnThe aim of this study was to evaluate the in vitro activity of doripenem (DOR) alone and in combination with a variety of commonly used anti-Acinetobacter chemotherapeutic agents against 22 primary multidrug-resistant (MDR) Acinetobacter baumannii isolates (including 17 isolates that were resistant to DOR) from Intensive Care Unit patients. Antibiotic interactions were evaluated using the chequerboard method and the time-kill assay.nnnRESULTSnConsidering all antimicrobials in combination with DOR, chequerboard analysis showed synergy in 13 A. baumannii strains (54.2%). Seven strains (29.2%) showed ≥2 synergistic interactions. DOR showed synergy in combination with tigecycline (TIG) (eight strains), colistin (COL) (eight strains), amikacin (AMK) (four strains), ampicillin/sulbactam (two strains), and rifampicin (one strain). Remarkably, synergistic effects were detected only in DOR nonsusceptible strains. Time-kill assays confirmed synergy in eight isolates (giving 10 synergistic interactions) for DOR in combination with TIG (n=4), COL (n=5), and AMK (n=1). No antagonistic interactions were observed with both methods.nnnCONCLUSIONSnThis study demonstrates the in vitro synergistic activity of DOR in combination with TIG, COL, and AMK against DOR-resistant A. baumannii strains, opening the way to in vivo assessment of novel combination therapies for treatment of infections caused by MDR A. baumannii.

Management of antibiotic resistance in the intensive care unit setting

Over the past few decades, an alarming increase of infections caused by antibiotic-resistant pathogens, including methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus species, carbapenem-resistant Pseudomonas aeruginosa, extended-spectrum β-lactamase-producing Escherichia coli and Klebsiella spp., and multidrug-resistant Acinetobacter spp., has been observed, particularly in intensive care units. For clinicians, the rising resistance rate observed in nosocomial pathogens, when coupled with the lack of effective antimicrobials, represents the real challenge in the therapeutic management of critically ill patients. The contribution of clinicians in minimizing the increasing trend of resistance is represented by reduction of the patients’ exposure to antibiotics, which reduces the resistance-selecting pressure, and by avoiding unnecessary antibiotic treatments. Recent issues on strategies to minimize resistance development and to appropriately manage critically ill patients with infections caused by multidrug-resistant organisms in the intensive care unit setting are discussed in this article.

Isolation of NDM-1-producing Pseudomonas aeruginosa sequence type ST235 from a stem cell transplant patient in Italy, May 2013

We describe the first isolation of an NDM-1-producing Pseudomonas aeruginosa in Italy. In May 2013, a patient with acute lymphoblastic leukaemia and history of prior hospitalisation in Belgrad, Serbia, underwent stem cell transplantation at a tertiary care hospital in Rome, Italy. After transplantion, sepsis by NDM-1-producing P. aeruginosa occurred, leading to septic shock and fatal outcome.