Spread in an Italian hospital of a clonal Acinetobacter baumannii strain producing the TEM-92 extended-spectrum beta-lactamase

Clinical isolates of Acinetobacter baumannii (n = 470) were collected during a 7-year period and investigated for the genetic determinants of resistance to expanded-spectrum beta-lactams. Thirty-one isolates produced the TEM-92 extended-spectrum beta-lactamase (ESBL) and were clonally related. This is the first report of A. baumannii producing a TEM-type ESBL.

Microbiology of Postoperative Infections

BACKGROUND

Surgical infections, accounting for approximately one quarter of all nosocomial infections, contribute to longer hospital stays and higher medical costs. Clinical failure of antibiotic treatment often is associated with increasing drug resistance.

METHODS

Non-duplicated microbial isolates obtained at our institution from surgical patients were identified and tested for antimicrobial susceptibility using the Sceptor system in 2001-2002 and the Phoenix system in 2003-2005. Epidemiologic data were extracted using Epicenter and Powerlab. During selected periods, genetic and biochemical characterization was performed by pulsed-field gel electrophoresis, colony blot hybridization, gene amplification and sequencing, isoelectric focusing, and enzyme kinetics.

RESULTS

The specimens were most commonly isolated from infections at surgical sites (24.0%), the urinary tract (19.0%), and blood stream (10.6%). Isolates of Escherichia coli showed an increasing prevalence of resistance to penicillins, third-generation cephalosporins, ciprofloxacin, and gentamicin, whereas the prevalence of resistant Staphylococcus aureus generally declined. Highly aggressive multi-drug-resistant (MDR) Pseudomonas aeruginosa strains were widespread, although colistin remained effective in 100% of cases. A significant increase was seen in infections attributable to S. epidermidis and Candida albicans. The overall number of Enterobacteriaceae carrying extended-spectrum beta-lactamases increased continuously, and new resistance traits emerged. It appeared that the TEM-92 determinant moved from Enterobacteriaceae to nonfermenting gram-negative rods such as Acinetobacter baumannii.

CONCLUSION

The number and type of antimicrobial-resistance determinants are increasing.

Performance in detection and reporting beta-lactam resistance phenotypes in Enterobacteriaceae: a nationwide proficiency study in Italian laboratories

We evaluated the ability of 60 Italian clinical microbiology laboratories in detecting and reporting beta-lactam resistance phenotypes in Enterobacteriaceae. Laboratories received 5 well-characterized isolates producing extended-spectrum beta-lactamases (ESBLs), 2 hyperproducers of chromosomal enzymes, and 3 quality control strains. The performances in antimicrobial susceptibility testing (AST) were different depending on the species and type of ESBL produced. High rates of very major errors (up to 56%) were observed for ESBL producers when testing cephalosporins and aztreonam, especially in the case of CTX-M-1-producing Escherichia coli and TEM-52-producing Proteus mirabilis. Isolates hyperproducing chromosomal enzymes were erroneously reported as ESBL producers in approximately 20% of cases. Detection of ESBLs is still a problem for clinical microbiology laboratories. Overall, performances in AST appear to be better with Klebsiella spp. producing well-known enzymes (e.g., SHV type) than with strains producing emerging enzymes (e.g., CTX-M type) or organisms not well recognized as ESBL producers (e.g., P. mirabilis).

Pseudomonas aeruginosa bloodstream infections: risk factors and treatment outcome related to expression of the PER-1 extended-spectrum beta-lactamase

BACKGROUND

Bloodstream infection (BSI) due to Pseudomonas aeruginosa (Pa) has relevant clinical impact especially in relation to drug resistance determinants. The PER-1 extended-spectrum beta-lactamase (ESBL) is a common enzyme conferring high-level resistance to anti-pseudomonal cephalosporins. Risk factors and treatment outcome of BSI episodes caused by PER-1-positive Pa (PER-1-Pa) strains were compared to those caused by ESBL-negative Pa isolates (ESBL-N-Pa).

METHODS

Twenty-six BSI cases due to ceftazidime-resistant Pa strains have been investigated. MIC values of anti-pseudomonal drugs were determined by the Etest method (AB Biodisk, Solna, Sweden). The double-disk synergy test was used to detect ESBL production. PCR amplification and DNA sequencing were used to characterize ESBL types. Clinical records of BSI-patients were examined retrospectively. Demographic data, underlying diseases (McCabe-Jackson classification and Charlson weighted index), risk factors, antimicrobial therapy, and treatment outcome were evaluated in cases due to ESBL-positive and cases due to ESBL-N-Pa isolates. Unpaired Student's t-test, Mann-Whitney U-test, Fisher's exact test and the chi2 test were used for statistical analysis.

RESULTS

Nine Pa isolates expressed the PER-1 ESBL; the remaining 17 isolates did not produce ESBLs. Severe sepsis (P = 0.03), bladder and intravascular catheters (both P = 0.01), immunosuppressive therapy (P = 0.04), and mechanical ventilation (P = 0.03) were significantly associated with BSI due to PER-1-Pa. Empirical treatment (P = 0.02) and treatment after ID/AST (P < 0.01) were rarely adequate in PER-1-Pa cases. With regard to treatment outcome, 77.8% BSI cases due to PER-1-Pa vs. 28.6% cases due to ESBL-N-Pa isolates failed to respond (P < 0.03). All cases due to PER-1-Pa that were treated with carbapenems (alone or in combination with amikacin) failed to respond. In contrast, 7/8 cases due to ESBL-N-Pa given carbapenems were responders.

CONCLUSION

Therapeutic failure and increased hospital costs are associated with BSI episodes caused by PER-1-Pa strains. Thus, recognition and prompt reporting of ESBL-production appears a critical factor for the management of patients with serious P. aeruginosa infections.

Failure of levofloxacin treatment in community-acquired pneumococcal pneumonia

Background

Streptococcus pneumoniae is the leading cause of community-acquired pneumonia (CAP). High global incidence of macrolide and penicillin resistance has been reported, whereas fluoroquinolone resistance is uncommon. Current guidelines for suspected CAP in patients with co-morbidity factors and recent antibiotic therapy recommend initial empiric therapy using one fluoroquinolone or one macrolide associated to other drugs (amoxicillin, amoxicillin/clavulanate, broad-spectrum cephalosporins). Resistance to fluoroquinolones is determined by efflux mechanisms and/or mutations in the parC and parE genes coding for topoisomerase IV and/or gyrA and gyrB genes coding for DNA gyrase. No clinical cases due to fluoroquinolone-resistant S. pneumoniae strains have been yet reported from Italy.

Case presentation

A 72-year-old patient with long history of chronic obstructive pulmonary disease and multiple fluoroquinolone treatments for recurrent lower respiratory tract infections developed fever, increased sputum production, and dyspnea. He was treated with oral levofloxacin (500 mg bid). Three days later, because of acute respiratory insufficiency, the patient was hospitalized. Levofloxacin treatment was supplemented with piperacillin/tazobactam. Microbiological tests detected a S. pneumoniae strain intermediate to penicillin (MIC, 1 mg/L) and resistant to macrolides (MIC >256 mg/L) and fluoroquinolones (MIC >32 mg/L). Point mutations were detected in gyrA (Ser81-Phe), parE (Ile460-Val), and parC gene (Ser79-Phe; Lys137-Asn). Complete clinical response followed treatment with piperacillin/tazobactam.

Conclusion

This is the first Italian case of community-acquired pneumonia due to a fluoroquinolone-resistant S. pneumoniae isolate where treatment failure of levofloxacin was documented. Molecular analysis showed a group of mutations that have not yet been reported from Italy and has been detected only twice in Europe. Treatment with piperacillin/tazobactam appears an effective means to inhibit fluoroquinolone-resistant strains of S. pneumoniae causing community-acquired pneumonia in seriously ill patients.

Proteus mirabilis bloodstream infections: risk factors and treatment outcome related to the expression of extended-spectrum beta-lactamases

Bloodstream infection (BSI) due to Proteus mirabilis strains is a relatively uncommon clinical entity, and its significance has received little attention. This study was initiated to evaluate risk factors and treatment outcome of BSI episodes due to P. mirabilis producing extended-spectrum beta-lactamases (ESBLs). Twenty-five BSI episodes caused by P. mirabilis occurred at our hospital (Ospedale di Circolo e Fondazione Macchi, Varese, Italy) over a 7.5-year period. Phenotypic and molecular methods were used to assess ESBL production. Clinical records of BSI patients were examined retrospectively. Demographic data, underlying diseases (according to McCabe and Jackson classification and Charlson weighted index), risk factors, and treatment outcome were investigated by comparing cases due to ESBL-positive strains to cases due to ESBL-negative strains. Eleven isolates were found to express ESBLs (TEM-52 or TEM-92). The remaining 14 isolates were ESBL negative and were uniformly susceptible to extended-spectrum cephalosporins and monobactams. Comparison of the two groups showed that previous hospitalization in a nursing home (P = 0.04) and use of bladder catheter (P = 0.01) were significant risk factors for infections due to ESBL-positive strains. In addition, cases due to ESBL-positive strains showed a significantly higher mortality attributable to BSI (P = 0.04). BSI cases due to ESBL-negative isolates uniformly responded to therapy, whereas 5/11 cases due to ESBL-positive isolates failed to respond (P < 0.01). Use of carbapenems was associated with complete response independently of ESBL production. Therapeutic failure and mortality may occur in BSI episodes caused by ESBL-positive P. mirabilis isolates. Thus, recognition of ESBL-positive strains appears to be critical for the clinical management of patients with systemic P. mirabilis infections.

Prevalence and characterization of metallo-beta-lactamases in clinical isolates of pseudomonas aeruginosa

The prevalence and the type(s) of metallo-beta-lactamases (MBLs) produced by isolates of Pseudomonas aeruginosa were investigated. During 2001, 506 nonduplicate isolates were obtained from hospitalized patients. Eighty-two strains were selected because of resistance to carbapenems and/or ceftazidime. Screening for MBL production was performed in the latter isolates by the Etest MBL strips (AB Biodisk, Solna, Sweden) and by a broth microdilution method measuring minimum inhibitory concentrations (MICs) of imipenem alone and in the presence of metal-chelating agents (EDTA and o-phenanthroline). Specific DNA probes were used to investigate the presence of genes coding for IMP- or VIM-type enzymes. Overall, four isolates of P. aeruginosa (obtained from independent patients) were found to carry a blaVIM gene. Polymerase chain reaction (PCR) experiments and DNA sequencing revealed that the VIM-2 determinant was present in three cases, whereas VIM-1 was detected in one isolate. Surveillance programs should be adopted to avoid the spread of these worrisome resistance genes.

Emergence in Klebsiella pneumoniae and Enterobacter cloacae clinical isolates of the VIM-4 metallo-beta-lactamase encoded by a conjugative plasmid

Resistance to carbapenems is an emerging problem among gram-negative hospital pathogens. A transferable plasmid encoding the VIM-4 metallo-beta-lactamase was detected in isolates of Klebsiella pneumoniae and Enterobacter cloacae obtained from a single patient under carbapenem therapy. Thus, enterobacteria appear to increasingly contribute to the spread of VIM-type enzymes.

Bacteremia Due toKlebsiella pneumoniaeIsolates Producing the TEM‐52 Extended‐Spectrum β‐Lactamase: Treatment Outcome of Patients Receiving Imipenem or Ciprofloxacin

The treatment outcome of 35 cases of bacteremia due to Klebsiella pneumoniae isolates producing TEM-52 extended-spectrum beta-lactamase was studied. Twenty-eight cases, classified as "nonfatal disease" using the McCabe and Jackson classification, were investigated with regard to ciprofloxacin and imipenem response. Because ciprofloxacin was active in vitro against 21 of 28 isolates, only the treatment outcome of the ciprofloxacin-susceptible subgroup was evaluated. Eight of 10 cases occurred in patients who experienced a complete response to imipenem; 2 of 10 failed to respond. In contrast, only 2 of 7 cases had a partial response to ciprofloxacin, and, in 5 of 7 cases, the treatment failed. Statistical analysis revealed a significant difference in the treatment outcome of the 2 groups (P=.03). Because the isolates had minimum inhibitory concentrations of ciprofloxacin close to the susceptibility breakpoint, treatment failure could be ascribed to the inability of the drug to reach therapeutic concentrations at infected sites.

IMP-12, a new plasmid-encoded metallo-beta-lactamase from a Pseudomonas putida clinical isolate

A Pseudomonas putida strain showing broad-spectrum resistance to beta-lactams, including expanded-spectrum cephalosporins and carbapenems, was isolated from a patient with a urinary tract infection at the University Hospital of Varese in northern Italy. The isolate was found to produce metallo-beta-lactamase activity and to harbor a 50-kb plasmid, named pVA758, carrying a new bla(IMP) determinant, named bla(IMP-12). Plasmid pVA758 was not self-transferable by conjugation to either Escherichia coli or Pseudomonas aeruginosa but could be introduced by electroporation and maintained in the latter host, where it conferred resistance or decreased susceptibility to various beta-lactams. The IMP-12 enzyme is quite divergent from other IMP variants: its closest relatives are IMP-8 and IMP-2 (89 and 88% sequence identity, respectively), and IMP-1 is 85% identical to IMP-12. The bla(IMP-12) determinant is carried on an integron-borne gene cassette whose attC recombination site is related to those present in cassettes containing bla(IMP-1), bla(IMP-6), bla(IMP-7), bla(IMP-10), and bla(IMP-11) and unrelated to that present in cassettes containing bla(IMP-2) and bla(IMP-8). IMP-12 was overproduced in E. coli by using a T7-based expression system and was purified by cation-exchange chromatography followed by gel filtration. Kinetic analysis revealed that, like other IMP variants, IMP-12 exhibits an overall preference for cephalosporins and carbapenems rather than for penicillins and does not hydrolyze temocillin and aztreonam. However, IMP-12 also exhibits some notable functional differences from other IMP variants, including uniformly poor activity toward penicillins (k(cat)/K(m) values, around 10(4) M(-1). s(-1)) and a remarkably high K(m) (around 900 micro M) for imipenem.

A two-year analysis of risk factors and outcome in patients with bloodstream infection

A two-year analysis was performed at our hospital to evaluate the incidence and clinical impact of bloodstream infections (BSI) in medical, surgical, and intensive care unit patients. During 1999-2000 there were 521 cases of BSI with an incidence of 10.1/1,000 admissions. The most frequent predisposing factors for BSI were intravascular catheter (56.4%) and previous use of antibiotics (50.9%). Infections were considered as primary in 67.9% of cases. Urinary tract and intravascular catheter were the most frequent source of secondary bacteremia (43.1% and 35.9%, respectively). At the time of the first positive blood culture, 83.5% of patients were receiving empirical treatment, but it was adequate in only 53.9% of cases. After antimicrobial susceptibility testing, adequate antibiotic treatment was given in 67.9% of cases. Statistical analysis of independent risk factors showed that mortality was significantly related to age (P < 0.048), rapidly-fatal diseases (P < 0.001), septic shock (P < 0.020), multiorgan failure (P < 0.001), previous use of antibiotics (P < 0.008), Enterobacteriaceae producing extended-spectrum beta-lactamases (P < 0.036), and inadequate empirical treatment (P < 0.039). Based on local epidemiology and susceptibility data, microbiology laboratories should periodically release recommendations on the optimal empirical treatment for different wards.

Identification and antimicrobial susceptibility testing of clinical isolates of nonfermenting gram-negative bacteria by the Phoenix Automated Microbiology System

The Phoenix Automated Microbiology System (Becton Dickinson, Sparks, MD) was evaluated for its ability to identify nonfermenting gram-negative pathogens and measure their drug susceptibility. Isolates producing rare extended-spectrum beta-lactamases (PER-1, IMP-2, VIM-1, and VIM-2) were included in the study. Species identification was compared to that given by the ATB System (bio-Mérieux, Marcy l'Etoile, France), whereas susceptibility results were compared to those produced by a reference broth microdilution test (panels manufactured by Pasco Laboratories, Becton Dickinson). The Phoenix system consistently identified all isolates of Pseudomonas aeruginosa (n = 55) and Stenotrophomonas maltophilia (n = 28), while in other cases species agreement was obtained for 47/53 isolates (Acinetobacter baumannii, 29/31; Pseudomonas putida, 10/11; Burkholderia cepacia, 6/7; and Pseudomonas fluorescens, 2/4). Overall, the Phoenix and ATB systems gave equal results in 130/136 cases (95.6%). For two isolates, consistent identification was obtained at the genus level, thus bringing the cumulative agreement to 97.1%. MIC values (interpreted according to NCCLS guidelines) gave essential and categorical agreement in 94.2% and 93.1% of cases, respectively. Minor and major errors were 5.1% and 5.2%, respectively. No very major errors were produced. The mean time to results (TTR) for the Phoenix system was 14.8 +/- 1.6 h (mean +/- SD), with the shortest TTR being observedfor A. baumannii (13.0 +/- 1.8 h) and the longest one for P. aeruginosa (15.6 +/- 1.2 h). In conclusion, the Phoenix system performed rapidly and correctly in the identification of clinical isolates of important opportunistic pathogens and in measuring their susceptibility to antipseudomonal drugs.

Epidemiology of bloodstream infections and time to detection of positive blood cultures: an evaluation of the automated BacT/Alert and BACTEC 9240 systems

Data of 3,097 blood culture sets processed with the BacT/Alert system in 1997 were compared to those of 3,158 blood culture sets processed with BACTEC 9240 in 1999. Agents responsible for bloodstream infections (BSI) were detected in 15.9% and 20.0% of blood cultures in 1997 and 1999, respectively. The incidence of BSI was 9.3 (1997) vs. 11.3 (1999) per 1,000 admissions. In both years, S. aureus was the most frequent isolate, followed by E. coli. Overall, the mean detection time (MDT) obtained with the BACTEC 9240 was significantly shorter than that of the BacT/Alert. Significant MDT differences were found for all organisms, except for Enterobacteriaceae (12.7 vs. 10.6 h). With both systems, over 95% positive samples were detected within 3 days, indicating that a 4-day incubation protocol may disclose most BSI agents. Thus, the added speed of the BACTEC 9240 allowed a particularly fast clinical management of septic patients.