Aleksandra Wierzbowski

Antimicrobial-Resistant Pathogens in Intensive Care Units in Canada: Results of the Canadian National Intensive Care Unit (CAN-ICU) Study, 2005-2006

ABSTRACT Between 1 September 2005 and 30 June 2006, 19 medical centers collected 4,180 isolates recovered from clinical specimens from patients in intensive care units (ICUs) in Canada. The 4,180 isolates were collected from 2,292 respiratory specimens (54.8%), 738 blood specimens (17.7%), 581 wound/tissue specimens (13.9%), and 569 urinary specimens (13.6%). The 10 most common organisms isolated from 79.5% of all clinical specimens were methicillin-susceptible Staphylococcus aureus (MSSA) (16.4%), Escherichia coli (12.8%), Pseudomonas aeruginosa (10.0%), Haemophilus influenzae (7.9%), coagulase-negative staphylococci/Staphylococcus epidermidis (6.5%), Enterococcus spp. (6.1%), Streptococcus pneumoniae (5.8%), Klebsiella pneumoniae (5.8%), methicillin-resistant Staphylococcus aureus (MRSA) (4.7%), and Enterobacter cloacae (3.9%). MRSA made up 22.3% (197/884) of all S. aureus isolates (90.9% of MRSA were health care-associated MRSA, and 9.1% were community-associated MRSA), while vancomycin-resistant enterococci (VRE) made up 6.7% (11/255) of all enterococcal isolates (88.2% of VRE had the vanA genotype). Extended-spectrum β-lactamase (ESBL)-producing E. coli and K. pneumoniae occurred in 3.5% (19/536) and 1.8% (4/224) of isolates, respectively. All 19 ESBL-producing E. coli isolates were PCR positive for CTX-M, with blaCTX-M-15 occurring in 74% (14/19) of isolates. For MRSA, no resistance against daptomycin, linezolid, tigecycline, and vancomycin was observed, while the resistance rates to other agents were as follows: clarithromycin, 89.9%; clindamycin, 76.1%; fluoroquinolones, 90.1 to 91.8%; and trimethoprim-sulfamethoxazole, 11.7%. For E. coli, no resistance to amikacin, meropenem, and tigecycline was observed, while resistance rates to other agents were as follows: cefazolin, 20.1%; cefepime, 0.7%; ceftriaxone, 3.7%; gentamicin, 3.0%; fluoroquinolones, 21.1%; piperacillin-tazobactam, 1.9%; and trimethoprim-sulfamethoxazole, 24.8%. Resistance rates for P. aeruginosa were as follows: amikacin, 2.6%; cefepime, 10.2%; gentamicin, 15.2%; fluoroquinolones, 23.8 to 25.5%; meropenem, 13.6%; and piperacillin-tazobactam, 9.3%. A multidrug-resistant (MDR) phenotype (resistance to three or more of the following drugs: cefepime, piperacillin-tazobactam, meropenem, amikacin or gentamicin, and ciprofloxacin) occurred frequently in P. aeruginosa (12.6%) but uncommonly in E. coli (0.2%), E. cloacae (0.6%), or K. pneumoniae (0%). In conclusion, S. aureus (MSSA and MRSA), E. coli, P. aeruginosa, H. influenzae, Enterococcus spp., S. pneumoniae, and K. pneumoniae are the most common isolates recovered from clinical specimens in Canadian ICUs. A MDR phenotype is common for P. aeruginosa isolates in Canadian ICUs.

The ketolides: a critical review.

Ketolides are a new class of macrolides designed particularly to combat respiratory tract pathogens that have acquired resistance to macrolides. The ketolides are semi-synthetic derivatives of the 14-membered macrolide erythromycin A, and retain the erythromycin macrolactone ring structure as well as the D-desosamine sugar attached at position 5. The defining characteristic of the ketolides is the removal of the neutral sugar, L-cladinose from the 3 position of the ring and the subsequent oxidation of the 3-hydroxyl to a 3-keto functional group. The ketolides presently under development additionally contain an 11, 12 cyclic carbamate linkage in place of the two hydroxyl groups of erythromycin A and an arylalkyl or an arylallyl chain, imparting in vitro activity equal to or better than the newer macrolides.Telithromycin is the first member of this new class to be approved for clinical use, while ABT-773 is presently in phase III of development. Ketolides have a mechanism of action very similar to erythromycin A from which they have been derived. They potently inhibit protein synthesis by interacting close to the peptidyl transferase site of the bacterial 50S ribosomal subunit. Ketolides bind to ribosomes with higher affinity than macrolides.The ketolides exhibit good activity against Gram-positive aerobes and some Gram-negative aerobes, and have excellent activity against drug-resistant Streptococcus pneumoniae, including macrolide-resistant (mefA and ermB strains of S. pneumoniae). Ketolides such as telithromycin display excellent pharmacokinetics allowing once daily dose administration and extensive tissue distribution relative to serum. Evidence suggests the ketolides are primarily metabolised in the liver and that elimination is by a combination of biliary, hepatic and urinary excretion. Pharmacodynamically, ketolides display an element of concentration dependent killing unlike macrolides which are considered time dependent killers.Clinical trial data are only available for telithromycin and have focused on respiratory infections including community-acquired pneumonia, acute exacerbations of chronic bronchitis, sinusitis and streptococcal pharyngitis. Bacteriological and clinical cure rates have been similar to comparators. Limited data suggest very good eradication of macrolide-resistant and penicillin-resistant S. pneumoniae. As a class, the macrolides are well tolerated and can be used safely. Limited clinical trial data suggest that ketolides have similar safety profiles to the newer macrolides. Telithromycin interacts with the cytochrome P450 enzyme system (specifically CYP 3A4) in a reversible fashion and limited clinically significant drug interactions occur.In summary, clinical trials support the clinical efficacy of the ketolides in upper and lower respiratory tract infections caused by typical and atypical pathogens including strains resistant to penicillins and macrolides. Considerations such as local epidemiology, patterns of resistance and ketolide adverse effects, drug interactions and cost relative to existing agents will define the role of these agents. The addition of the ketolides in the era of antibacterial resistance provides clinicians with more options in the treatment of respiratory infections.

Prevalence of Antimicrobial-Resistant Pathogens in Canadian Hospitals: Results of the Canadian Ward Surveillance Study (CANWARD 2008)

ABSTRACT A total of 5,282 bacterial isolates obtained between 1 January and 31 December 31 2008, inclusive, from patients in 10 hospitals across Canada as part of the Canadian Ward Surveillance Study (CANWARD 2008) underwent susceptibility testing. The 10 most common organisms, representing 78.8% of all clinical specimens, were as follows: Escherichia coli (21.4%), methicillin-susceptible Staphylococcus aureus (MSSA; 13.9%), Streptococcus pneumoniae (10.3%), Pseudomonas aeruginosa (7.1%), Klebsiella pneumoniae (6.0%), coagulase-negative staphylococci/Staphylococcus epidermidis (5.4%), methicillin-resistant S. aureus (MRSA; 5.1%), Haemophilus influenzae (4.1%), Enterococcus spp. (3.3%), Enterobacter cloacae (2.2%). MRSA comprised 27.0% (272/1,007) of all S. aureus isolates (genotypically, 68.8% of MRSA were health care associated [HA-MRSA] and 27.6% were community associated [CA-MRSA]). Extended-spectrum β-lactamase (ESBL)-producing E. coli occurred in 4.9% of E. coli isolates. The CTX-M type was the predominant ESBL, with CTX-M-15 the most prevalent genotype. MRSA demonstrated no resistance to ceftobiprole, daptomycin, linezolid, telavancin, tigecycline, or vancomycin (0.4% intermediate intermediate resistance). E. coli demonstrated no resistance to ertapenem, meropenem, or tigecycline. Resistance rates with P. aeruginosa were as follows: colistin (polymyxin E), 0.8%; amikacin, 3.5%; cefepime, 7.2%; gentamicin, 12.3%; fluoroquinolones, 19.0 to 24.1%; meropenem, 5.6%; piperacillin-tazobactam, 8.0%. A multidrug-resistant (MDR) phenotype occurred frequently in P. aeruginosa (5.9%) but uncommonly in E. coli (1.2%) and K. pneumoniae (0.9%). In conclusion, E. coli, S. aureus (MSSA and MRSA), P. aeruginosa, S. pneumoniae, K. pneumoniae, H. influenzae, and Enterococcus spp. are the most common isolates recovered from clinical specimens in Canadian hospitals. The prevalence of MRSA was 27.0% (of which genotypically 27.6% were CA-MRSA), while ESBL-producing E. coli occurred in 4.9% of isolates. An MDR phenotype was common in P. aeruginosa.

Antimicrobial susceptibility of 15,644 pathogens from Canadian hospitals: results of the CANWARD 2007-2009 study.

The CANWARD study (Canadian Ward Surveillance Study) assessed the antimicrobial susceptibility of a variety of available agents against 15 644 pathogens isolated from patients in Canadian hospitals between 2007 and 2009. The most active (based on MIC data) agents against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci were daptomycin, linezolid, tigecycline, and vancomycin (MRSA only) with MIC(90)s (μg/mL) of 0.25 and 2, 2 and 2, 0.5 and 0.12, and 1, respectively. The most active agents against extended-spectrum β-lactamase-producing Escherichia coli were colistin (polymyxin E), doripenem, ertapenem, meropenem, and tigecycline with MIC(90)s (μg/mL) of 1, ≤ 0.12, 0.25, ≤ 0.12, and 1, respectively. The most active agents against Pseudomonas aeruginosa were amikacin, cefepime, ceftazidime, colistin, doripenem, meropenem, and piperacillin-tazobactam with MIC(90)s (μg/mL) of 32, 16, 32, 2, 4, 8, and 64, respectively. Overall, the most active agents versus Gram-positive cocci from Canadian hospitals were vancomycin, linezolid, daptomycin, and tigecycline and versus Gram-negative bacilli were amikacin, cefepime, doripenem, ertapenem (excluding Pseudomonas aeruginosa), meropenem, piperacillin-tazobactam, and tigecycline (excluding Pseudomonas aeruginosa).

Macrolide-Resistant Streptococcus pneumoniae in Canada during 1998-1999: Prevalence of mef(A) and erm(B) and Susceptibilities to Ketolides

ABSTRACT In this study (1998–1999), we collected 215 macrolide-resistantStreptococcus pneumoniae isolates from an ongoing Canadian Respiratory Organism Surveillance Study involving 23 centers representing all regions of Canada. The prevalence of erythromycin-resistant S. pneumoniae was 8% (215 of 2,688). Of the 215 isolates, 48.8% (105 of 215) were PCR positive formef(A) and 46.5% (100 of 215) were PCR positive forerm(B). The ketolides telithromycin and ABT-773 demonstrated excellent activity against both mef(A) (MIC for 90% of strains [MIC90], 0.06 and 0.03 μg/ml, respectively) and erm(B) (MIC90, 0.06 and 0.03 μg/ml, respectively) strains of S. pneumoniae.

Antimicrobial susceptibility of 3931 organisms isolated from intensive care units in Canada: Canadian National Intensive Care Unit Study, 2005/2006

We tested the in vitro activity of 15 antimicrobials against Gram-positive cocci and 12 antimicrobials against Gram-negative bacilli versus 3931 isolates (20 most common organisms) obtained between September 1, 2005, and June 30, 2006, from 19 intensive care units (ICUs) across Canada. The most active (based upon MIC only) agents against methicillin-resistant Staphylococcus aureus and methicillin-resistant Staphylococcus epidermidis were dalbavancin, daptomycin, linezolid, tigecycline, and vancomycin with MIC(90) (microg/mL) of 0.06 and < or =0.03, 0.25 and 0.12, 2 and 1, 0.5 and 0.5, and 1 and 2, respectively. The most active agents against vancomycin-resistant enterococci were daptomycin, linezolid, and tigecycline with MIC(90) (microg/mL) of 1, 4, and 0.12, respectively. The most active agents against Escherichia coli were amikacin, cefepime, meropenem, piperacillin/tazobactam, and tigecycline with MIC(90) (microg/mL) of 4, < or =1, < or =0.12, 8, and 0.5, respectively. The most active agents against extended-spectrum beta-lactamase-producing E. coli were meropenem and tigecycline with MIC(90) (microg/mL) of < or =0.12 and 1, respectively. The most active agents against Pseudomonas aeruginosa were amikacin, cefepime, meropenem, and piperacillin/tazobactam with MIC(90) (microg/mL) of 16, 32, 16, and 64, respectively. The most active agents against Stenotrophomonas maltophilia were tigecycline and trimethoprim/sulfamethoxazole with MIC(90) (microg/mL) of 4 and 4, respectively. The most active agents against Acinetobacter baumannii were fluoroquinolones (e.g., levofloxacin), meropenem, and tigecycline with MIC(90) (microg/mL) of 0.5, 1, and 2, respectively. In conclusion, the most active agents versus Gram-positive cocci and Gram-negative bacilli obtained from Canadian ICUs were daptomycin, linezolid, tigecycline, dalbavancin and amikacin, cefepime, meropenem, piperacillin/tazobactam, and tigecycline (not P. aeruginosa), respectively.

Pharmacodynamic Modeling of Clarithromycin against Macrolide-Resistant [PCR-Positive mef(A) or erm(B)] Streptococcus pneumoniae Simulating Clinically Achievable Serum and Epithelial Lining Fluid Free-Drug Concentrations

ABSTRACT The association between macrolide resistance mechanisms and clinical outcomes remains understudied. The present study, using an in vitro pharmacodynamic model, assessed clarithromycin (CLR) activity against mef(A)-positive and erm(B)-negative Streptococcus pneumoniae isolates by simulating free-drug concentrations in serum and both total (protein-bound and free) and free drug in epithelial lining fluid (ELF). Five mef(A)-positive and erm(B)-negative strains, one mef(A)-negative and erm(B)-positive strain, and a control [mef(A)-negative and erm(B)-negative] strain of S. pneumoniae were tested. CLR was modeled using a one-compartment model, simulating a dosage of 500 mg, per os, twice a day (in serum, free-drug Cp maximum of 2 μg/ml, t1/2 of 6 h; in ELF, CELF(total) maximum of 35μg/ml, t1/2 of 6 h; CELF(free) maximum of 14 μg/ml, t1/2 of 6 h). Starting inocula were 106 CFU/ml in Mueller-Hinton broth with 2% lysed horse blood. With sampling at 0, 4, 8, 12, 20, and 24 h, the extent of bacterial killing was assessed. Achieving CLR T/MIC values of ≥90% (AUC0-24/MIC ratio, ≥61) resulted in bacterial eradication, while T>MIC values of 40 to 56% (AUC0-24/MIC ratios of ≥30.5 to 38) resulted in a 1.2 to 2.0 log10 CFU/ml decrease at 24 h compared to that for the initial inoculum. CLR T/MIC values of ≤8% (AUC0-24/MIC ratio, ≤17.3) resulted in a static effect or bacterial regrowth. The high drug concentrations in ELF that were obtained clinically with CLR may explain the lack of clinical failures with mef(A)-producing S. pneumoniae strains, with MICs up to 8 μg/ml. However, mef(A) isolates for which MICs are ≥16 μg/ml along with erm(B) may result in bacteriological failures.

Ketolides: an emerging treatment for macrolide-resistant respiratory infections, focusing on S. pneumoniae

Resistance to antibiotics in community acquired respiratory infections is increasing worldwide. Resistance to the macrolides can be class-specific, as in efflux or ribosomal mutations, or, in the case of erythromycin ribosomal methylase (erm)-mediated resistance, may generate cross-resistance to other related classes. The ketolides are a new subclass of macrolides specifically designed to combat macrolide-resistant respiratory pathogens. X-ray crystallography indicates that ketolides bind to a secondary region in domain II of the 23S rRNA subunit, resulting in an improved structure–activity relationship. Telithromycin and cethromycin (formerly ABT-773) are the two most clinically advanced ketolides, exhibiting greater activity towards both typical and atypical respiratory pathogens. As a subclass of macrolides, ketolides demonstrate potent activity against most macrolide-resistant streptococci, including ermB- and macrolide efflux (mef)A-positive Streptococcus pneumoniae. Their pharmacokinetics display a long half-life as well as extensive tissue distribution and uptake into respiratory tissues and fluids, allowing for once-daily dosing. Clinical trials focusing on respiratory infections indicate bacteriological and clinical cure rates similar to comparators, even in patients infected with macrolide-resistant strains.

Expression of the mef(E) Gene Encoding the Macrolide Efflux Pump Protein Increases in Streptococcus pneumoniae with Increasing Resistance to Macrolides

ABSTRACT Active macrolide efflux is a major mechanism of macrolide resistance in Streptococcus pneumoniae in many parts of the world, especially North America. In Canada, this active macrolide efflux in S. pneumoniae is predominantly due to acquisition of the mef(E) gene. In the present study, we assessed the mef(E) gene sequence as well as mef(E) expression in variety of low- and high-level macrolide-resistant, clindamycin-susceptible (M-phenotype) S. pneumoniae isolates (erythromycin MICs, 1 to 32 μg/ml; clindamycin MICs, ≤0.25 μg/ml). Southern blot hybridization with mef(E) probe and EcoRI digestion and relative real-time reverse transcription-PCR were performed to study the mef(E) gene copy number and expression. Induction of mef(E) expression was analyzed by Etest susceptibility testing pre- and postincubation with subinhibitory concentrations of erythromycin, clarithromycin, azithromycin, telithromycin, and clindamycin. The macrolide efflux gene, mef(E), was shown to be a single-copy gene in all 23 clinical S. pneumoniae isolates tested, and expression post-macrolide induction increased 4-, 6-, 20-, and 200-fold in isolates with increasing macrolide resistance (erythromycin MICs 2, 4, 8, and 32 μg/ml, respectively). Sequencing analysis of the macrolide efflux genetic assembly (mega) revealed that mef(E) had a 16-bp deletion 153 bp upstream of the putative start codon in all 23 isolates. A 119-bp intergenic region between mef(E) and mel was sequenced, and a 99-bp deletion was found in 11 of the 23 M-phenotype S. pneumoniae isolates compared to the published mega sequence. However, the mef(E) gene was fully conserved among both high- and low-level macrolide-resistant isolates. In conclusion, increased expression of mef(E) is associated with higher levels of macrolide resistance in macrolide-resistant S. pneumoniae.

Pharmacodynamic activity of telithromycin at simulated clinically achievable free-drug concentrations in serum and epithelial lining fluid against efflux (mefE)-producing macrolide-resistant Streptococcus pneumoniae for which telithromycin MICs vary.

ABSTRACT The present study, using an in vitro model, assessed telithromycin pharmacodynamic activity at simulated clinically achievable free-drug concentrations in serum (S) and epithelial lining fluid (ELF) against efflux (mefE)-producing macrolide-resistant Streptococcus pneumoniae. Two macrolide-susceptible (PCR negative for both mefE and ermB) and 11 efflux-producing macrolide-resistant [PCR-positive for mefE and negative for ermB) S. pneumoniae strains with various telithromycin MICs (0.015 to 1 μg/ml) were tested. The steady-state pharmacokinetics of telithromycin were modeled, simulating a dosage of 800 mg orally once daily administered at time 0 and at 24 h (free-drug maximum concentration [Cmax] in serum, 0.7 μg/ml; half-life [t1/2], 10 h; free-drug Cmax in ELF, 6.0 μg/ml; t1/2, 10 h). Starting inocula were 106 CFU/ml in Mueller-Hinton Broth with 2% lysed horse blood. Sampling at 0, 2, 4, 6, 12, 24, and 48 h assessed the extent of bacterial killing (decrease in log10 CFU/ml versus initial inoculum). Free-telithromycin concentrations in serum achieved in the model were Cmax 0.9 ± 0.08 μg/ml, area under the curve to MIC (AUC0-24 h) 6.4 ± 1.5 μg · h/ml, and t1/2 of 10.6 ± 0.6 h. Telithromycin-free ELF concentrations achieved in the model were Cmax 6.6 ± 0.8 μg/ml, AUC0-24 h 45.5 ± 5.5 μg · h/ml, and t1/2 of 10.5 ± 1.7 h. Free-telithromycin S and ELF concentrations rapidly eradicated efflux-producing macrolide-resistant S. pneumoniae with telithromycin MICs up to and including 0.25 μg/ml and 1 μg/ml, respectively. Free-telithromycin S and ELF concentrations simulating Cmax/MIC ≥ 3.5 and AUC0-24 h/MIC ≥ 25 completely eradicated (≥4 log10 killing) macrolide-resistant S. pneumoniae at 24 and 48 h. Free-telithromycin concentrations in serum simulating Cmax/MIC ≥ 1.8 and AUC0-24 h/MIC ≥ 12.5 were bacteriostatic (0.1 to 0.2 log10 killing) against macrolide-resistant S. pneumoniae at 24 and 48 h. In conclusion, free-telithromycin concentrations in serum and ELF simulating Cmax/MIC ≥ 3.5 and AUC0-24 h/MIC ≥ 25 completely eradicated (≥4 log10 killing) macrolide-resistant S. pneumoniae at 24 and 48 h.