Extended spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae: considerations for diagnosis, prevention and drug treatment

First isolation of metallo-beta-lactamase-producing multiresistant Klebsiella pneumoniae from a patient in Brazil

A multiresistant Klebsiella pneumoniae isolate was taken from the blood of a 75-year-old patient with nosocomial pneumonia who developed septic shock and failed therapy with imipenem. The isolate presented an MIC of imipenem of 128 microg/ml, and the production of a metallo-beta-lactamase was confirmed by phenotypic and genotypic techniques. We here report, for the first time, the detection of a metalloenzyme (IMP-1)-producing K. pneumoniae clinical strain in Latin America. The gene responsible for this phenotype was found to be bla(IMP-1), carried in a class 1 integron.

Evolution and dissemination of extended-spectrum β-lactamase-producing Klebsiella pneumoniae: Epidemiology and molecular report from the SENTRY Antimicrobial Surveillance Program (1997–2003)

During 2001, occurrences of extended-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae isolates were detected in a single medical center (Hospital A) from the SENTRY Antimicrobial Surveillance Program that became endemic in long-term acute care areas and in the intensive care unit in 2002-2003. Between 2001 and 2003, 123 patients were infected or colonized with ESBL-positive K. pneumoniae. Resistance profiles were determined by reference broth microdilution methods, and automated ribotyping and pulsed-field gel electrophoresis (PFGE) were performed. The ESBL-positive K. pneumoniae isolates were resistant to aztreonam, ceftazidime, aminoglycosides, and trimethoprim/sulfamethoxazole and susceptible to ciprofloxacin and tetracycline. In 1997, 1998, and 2000, 9 ESBL-producing K. pneumoniae strains from 2 New York City hospitals shared the same antibiograms and ribotype (204.2) as the strains from Hospital A. PFGE patterns divided Hospital A isolates into 2 subtypes (A and A1) and 3 New York City strains were similar to the Hospital A isolates (A2, A3, and A4). Isoelectric focusing studies of 1 New York City isolate (A4) revealed pIs at 5.4, 7.7, and 8.2. PCR and sequencing results from 1 strain of each Hospital A and 1 New York PFGE pattern determined that TEM-1 and SHV-5 (ESBL) were present in all strains. In addition, 2 New York isolates from 1998 (A3 and A4) also had an OXA-2 enzyme. ESBL-producing K. pneumoniae isolates with ribotype 204.2 from SENTRY Program sites have been recognized in New York only since 1997 and in Hospital A beginning in 2001. The similarities of the antibiogram and epidemiological patterns suggest that these isolates have persisted over time and may have evolved into different but genetically related endemic ESBL-positive K. pneumoniae clones that have the ability to cause sustained epidemic outbreaks in US medical centers.

Characteristics, epidemiology and clinical importance of emerging strains of Gram-negative bacilli producing extended-spectrum beta-lactamases

Beta-lactam antimicrobial agents represent the most common treatment for bacterial infections and continue to be the leading cause of resistance to beta-lactam antibiotics among Gram-negative bacteria worldwide. The persistent exposure of bacterial strains to a multitude of beta-lactams has induced dynamic and continuous production and mutation of beta-lactamases in these bacteria, expanding their activity even against the newly developed beta-lactam antibiotics. These enzymes are known as extended-spectrum beta-lactamases (ESBLs). The majority of ESBLs are derived from the widespread broad-spectrum beta-lactamases TEM-1 and SHV-1. There are also new families of ESBLs, including the CTX-M and OXA-type enzymes as well as novel unrelated beta-lactamases. In recent years, there has been an increased incidence and prevalence of ESBLs. ESBLs are mainly found in strains of Escherichia coli and Klebsiella pneumoniae but have also been reported in other Enterobacteriaceae strains and Pseudomonas aeruginosa. Infections with ESBL-producing bacterial strains are encountered singly or in outbreaks, especially in critical care units in hospitals, resulting in increasing cost of treatment and prolonged hospital stays. Not only may nursing home patients be an important reservoir of ESBL-containing multiple antibiotic-resistant organisms, but ambulatory patients with chronic conditions may also harbor ESBL-producing organisms.

Canine model for investigating the impact of oral enrofloxacin on commensal coliforms and colonization with multidrug-resistant Escherichia coli

A model was developed in dogs to determine the impact of oral enrofloxacin administration on the indigenous coliform population in the gastrointestinal tract and subsequent disposition to colonization by a strain of multidrug-resistant Escherichia coli (MDREC). Dogs given a daily oral dose of 5 mg enrofloxacin kg−1 for 21 consecutive days showed a significant decline in faecal coliforms to levels below detectable limits by 72 h of administration. Subsequently, faecal coliforms remained suppressed throughout the period of enrofloxacin dosing. Upon termination of antibiotic administration, the number of excreted faecal coliforms slowly returned over an 8-day period, to levels comparable to those seen prior to antibiotic treatment. Enrofloxacin-treated dogs were more effectively colonized by MDREC, evidenced by a significantly increased count of MDREC in the faeces (7.1 ± 1.5 log10 g−1) compared with non-antibiotic-treated dogs (5.2 ± 1.2; P = 0.003). Furthermore, antibiotic treatment also sustained a significantly longer period of MDREC excretion in the faeces (26.8 ± 10.5 days) compared with animals not treated with enrofloxacin (8.5 ± 5.4 days; P = 0.0215). These results confirm the importance of sustained delivery of an antimicrobial agent to maintain and expand the colonization potential of drug-resistant bacteria in vivo, achieved in part by reducing the competing commensal coliforms in the gastrointestinal tract to below detectable levels in the faeces. Without in vivo antimicrobial selection pressure, commensal coliforms dominated the gastrointestinal tract at the expense of the MDREC population. Conceivably, the model developed could be used to test the efficacy of novel non-antibiotic strategies aimed at monitoring and controlling gastrointestinal colonization by multidrug-resistant members of the Enterobacteriaceae that cause nosocomial infections.

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.

Colistin forKlebsiella pneumoniae–Associated Sepsis

Klebsiella pneumoniae that was resistant to all available antibiotics (minimum inhibitory concentration of imipenem, 32 microg/mL), including carbapenems, was isolated from blood samples obtained from a 48-year-old patient in the intensive care unit. The patient developed septic shock, which was successfully treated with colistin, the only antibiotic with activity against this multidrug-resistant strain.

Basic pharmacodynamics of antibacterials with clinical applications to the use of β-lactams, glycopeptides, and linezolid

Time above MIC for free drug concentrations is the important PK-PD parameter correlating with the efficacy of beta-lactam antibiotics. The duration of time plasma concentrations needed to exceed the MIC is relatively similar for most organisms except staphylococci. Neutrophils contribute very little to the overall activity of beta-lactams. The appearance of increasing antimicrobial resistance can challenge the efficacy of these drugs when concentrations do not exceed the MIC for 40% to 50% of the dosing interval. Time above MIC with oral amoxicillin and amoxicillin-clavulanate can be enhanced with high-dose formulations. Time above MIC with parenteral preparations can be enhanced by longer intravenous infusions or even continuous infusion. The 24-hour AUC-MIC is probably the important PK-PD parameter correlating with the efficacy of vancomycin and teicoplanin. It clearly is the important parameter for the efficacy of linezolid. Usual doses of these drugs generally provide adequate plasma concentrations to treat effectively infections in which plasma concentrations are predictive of tissue concentrations. Penetration of these drugs into respiratory secretions, such as ELF, is enhanced for linezolid and reduced for vancomycin. This may give linezolid an advantage over vancomycin in certain respiratory infections.