Comparative ceftaroline activity tested against pathogens associated with community-acquired pneumonia: results from an international surveillance study

OBJECTIVES

To document the spectrum of activity of ceftaroline, the active form of the prodrug, ceftaroline fosamil, a new cephalosporin with anti-methicillin-resistant staphylococcal activity, against a surveillance collection of clinical isolates obtained from the USA and Europe during 2008-09.

METHODS

A selected group of species associated with community-acquired pneumonia (CAP; 6496 of 17 326 monitored strains) were tested for susceptibility in a central laboratory using CLSI broth microdilution methods. Organisms were sampled from 55 medical centres, 27 in the USA and 28 (12 countries) in Europe. Ceftaroline and comparator agents were tested and interpretations of MIC endpoints made by applying current CLSI (2010) and EUCAST (2010) breakpoint criteria.

RESULTS

Against 1340 Streptococcus pneumoniae, ceftaroline inhibited all isolates at ≤0.5 mg/L (MIC(50/90), ≤0.008/0.12 mg/L) and was 8-fold more active than ceftriaxone (MIC(90), 1 mg/L; only 79.2% coverage at EUCAST breakpoint). Haemophilus influenzae (n = 584; MIC(50/90), ≤0.008/0.015 mg/L), Moraxella catarrhalis (n = 377; MIC(50/90), 0.03-0.06/0.12 mg/L) and Staphylococcus aureus (n = 590; MIC(50/90), 0.5/1 mg/L) were very susceptible to ceftaroline, regardless of β-lactamase production or multidrug resistance (MDR) patterns. The potency of ceftaroline against three species of Enterobacteriaceae (Escherichia coli, Klebsiella pneumoniae and Enterobacter cloacae) was similar to that of ceftriaxone, ceftazidime and piperacillin/tazobactam. Only modest differences in rates of ceftaroline susceptibility (breakpoint ≤2 mg/L) were noted with extended-spectrum β-lactamase-negative Enterobacteriaceae strains between the USA and Europe (97.9% versus 97.0% for E. coli). Ceftaroline, like ceftriaxone, was not active against ceftazidime-resistant E. coli (10.2%-26.2% susceptible at ≤2 mg/L) or K. pneumoniae (5.3%-11.2%).

CONCLUSIONS

The ceftaroline surveillance for 2008-09 (USA and Europe) documented low MIC(50/90) values for S. aureus isolates at 0.5/1 and 0.25/1 mg/L, respectively. More importantly, ceftaroline MIC(90) results for S. pneumoniae (0.12 mg/L), H. influenzae (0.015 mg/L) and M. catarrhalis (0.12 mg/L) were very low, all MICs being ≤0.5 mg/L. Ceftaroline exhibited promising high potency and wide coverage against Gram-positive and -negative pathogens known to cause CAP, especially isolates of MDR pneumococci and methicillin-resistant S. aureus.

Telavancin Activity against gram-positive bacteria isolated from patients with skin and skin-structure infections

Telavancin is approved in the United States and Canada for the treatment of complicated skin and skin structure infections (cSSSI) in adults caused by susceptible Gram-positive organisms. The antimicrobial activity of telavancin and comparators was evaluated against 5,027 (2007-2008) Gram-positive bacteria responsible for SSSI in medical centers in Asia-Pacific, European, Latin American, and North American regions. Telavancin was active against Staphylococcus aureus (MIC₅₀(/)₉₀, 0.12/0.25 mg/l; 100.0% susceptible) and coagulase-negative staphylococci (MIC₅₀(/)₉₀, 0.12/0.25 mg/l). telavancin inhibited all Enterococcus faecalis, including four strains displaying a VanB phenotype, at ≤ 1 mg/L (MIC₅₀(/)₉₀, 0.25/0.5 mg/l), except for two isolates with a VanA phenotype (MIC, >2 mg/l). Vancomycin-susceptible and VanB vancomycin-resistant E. faecium were inhibited by telavancin at ≤ 0.25 mg/L, while this drug exhibited elevated MIC values (≥ 0.5 mg/l) against E. faecium of VanA phenotype (MIC₅₀(/)₉₀, 2/>2 mg/l). Telavancin was potent against β-haemolytic streptococci (MIC₅₀(/)₉₀, 0.03/0.12 mg/l; 100.0% susceptible) and viridans group streptococci (MIC₅₀(/)₉₀, 0.03/0.06 mg/l; 100.0% susceptible). These in vitro data document the activity of telavancin against contemporary Gram-positive isolates and support its clinical use for the treatment of cSSSI caused by the indicated pathogens.

Ceftaroline activity against pathogens associated with complicated skin and skin structure infections: results from an international surveillance study

OBJECTIVES

To assess the spectrum and potency of ceftaroline, a novel anti-methicillin-resistant staphylococcal cephalosporin, against a 2008 surveillance collection of clinical isolates from patients in the USA and Europe.

METHODS

A collection of 14 169 isolates of various bacterial species from complicated skin and skin structure infections (cSSSIs) was tested for susceptibility to ceftaroline and 19 comparator agents in a central reference laboratory using CLSI broth microdilution methods. Organisms were received from 55 medical centres; 27 in the USA and 28 in Europe (12 countries, including Israel). The clonality of isolates of Staphylococcus aureus with elevated ceftaroline MICs (4 mg/L) was determined by PFGE and single and multilocus sequence typing, and the mechanism of ceftaroline non-susceptibility was assessed by molecular methods (PCR amplification and sequencing).

RESULTS

Ceftaroline, the active component of the parenteral prodrug ceftaroline fosamil, was active against 2988 methicillin-resistant S. aureus (MRSA) isolates, with an MI₉₀ of 1 mg/L. The MIC₉₀ for methicillin-susceptible strains was 0.25-0.5 mg/L. Ceftaroline was additionally active against coagulase-negative staphylococci (MIC₉₀, 0.5-1 mg/L), Enterococcus faecalis (MIC₅₀, 2 mg/L), β-haemolytic and viridans group streptococci (MIC₉₀, 0.015-0.25 mg/L) and three commonly isolated Enterobacteriaceae (Escherichia coli, Klebsiella spp. and Proteus mirabilis; MIC₉₀ values of 0.25 to > 16 mg/L). All but four isolates of MRSA (0.13%) had ceftaroline MIC values of ≤ 2 mg/L. The isolates for which ceftaroline MICs were 4 mg/L were clonal (single Greek hospital) and had detectable mecA mutations (N146K, N204K, E150K and H351N).

CONCLUSIONS

The ceftaroline yearly (2008) surveillance for the USA and Europe documented low MIC₅₀/₉₀ values for MRSA isolates at 1/1 and 1/2 mg/L, respectively. Ceftaroline demonstrated promising potency and coverage against Gram-positive and -negative pathogens known to cause cSSSIs, including MRSA and β-haemolytic streptococci.

Assessment of linezolid resistance mechanisms among Staphylococcus epidermidis causing bacteraemia in Rome, Italy

OBJECTIVES

To characterize linezolid resistance among blood cultured Staphylococcus epidermidis from patients at the Polyclinic Agostino Gemelli (2006-08). Isolates also showed elevated MICs of macrolide, lincosamide and streptogramin (MLS) compounds, which were investigated.

METHODS

Ten S. epidermidis exhibiting linezolid MICs ≥ 4 mg/L were included. Isolates were screened for cfr mutations in 23S rRNA, L3, L4 and L22, and MLS genes by PCR/sequencing. Ribosomal proteins were compared with those from a linezolid-susceptible (MIC, 1 mg/L) clinical strain and ATCC 12228. cfr location was determined by Southern blot/hybridization. The cfr strain was submitted to plasmid curing. Epidemiology was assessed by PFGE and multilocus sequence typing (MLST).

RESULTS

S. epidermidis displayed linezolid MICs of 4 or 8 mg/L, except for strain 4303A (MIC, 64 mg/L). These organisms and a linezolid-susceptible strain exhibited L3 Leu101Val compared with ATCC 12228. Isolates also showed L3 Phe147Leu and Ala157Arg, and L4 Asn158Ser. Strain 12375A possessed L4 Lys68Arg. Isolates were wild-type for 23S rRNA and L22. cfr was plasmid located in strain 4303A and the plasmid-cured strain exhibited a linezolid MIC (4 mg/L) similar to that for cfr-negative strains (4-8 mg/L). All organisms harboured erm(A) and msr(A), while vga(A) was detected in several isolates. All isolates were clonally related and ST-23.

CONCLUSIONS

L3 Phe147Leu and/or Ala157Arg appeared responsible for the elevated linezolid MIC, since adjacent alterations have been associated with resistance. L4 Asn158Ser has been reported in a linezolid-susceptible isolate and Lys68Arg detected here did not seem to provide an additive effect. Acquisition of cfr markedly increased (8- to 16-fold) the linezolid MICs. vga(A) was associated with higher MICs of quinupristin/dalfopristin and retapamulin.

Sustained antimicrobial activity of tigecycline against methicillin-resistant Staphylococcus aureus (MRSA) from United States Medical Centers from 2004 through 2008

Tigecycline, a glycylcycline, has been approved by the United States Food and Drug Administration (USA-FDA) for the treatment of complicated skin and skin structure infections, intra-abdominal infections and community-acquired bacterial pneumonia. based on broth microdilution minimum inhibitory concentration (MIC) testing, tigecycline demonstrated sustained high activity (MIC(50/90), 0.12/0.25 mg/L) against a contemporary collection (10,242) of methicillin (oxacillin)-resistant Staphylococcus aureus (MRSA) collected from 32 USA hospitals over a 5-year period (2004-2008). Tigecycline MIC distribution did not vary significantly during the study period and only three isolates (0.03%) were non-susceptible at USA-FDA breakpoints. Vancomycin (MIC(90), 1 mg/L), trimethoprim/sulfamethoxazole (MIC( 90), <0.5 mg/L) and linezolid (MIC(90), 2 mg/L) were also very active. The results of this study indicate that tigecycline potency and spectrum against MRSA have not changed since its initial regulatory approval by the USA-FDA.

Evolving trends in Streptococcus pneumoniae resistance: implications for therapy of community-acquired bacterial pneumonia

Pneumonia is a major infectious disease associated with significant morbidity, mortality and utilisation of healthcare resources. Streptococcus pneumoniae is the predominant pathogen in community-acquired pneumonia (CAP), accounting for 20-60% of bacterial cases. Emergence of multidrug-resistant S. pneumoniae has become a significant problem in the management of CAP. Although pneumococcal conjugate vaccine usage in children has led to significant decreases in morbidity and mortality due to S. pneumoniae in all age groups, disease management has been further complicated by the unexpected increase in resistant serotypes, such as 19A, in some regions. Until rapid and accurate diagnostic tests become available, initial treatment of CAP will remain empirical. Thus, selection of appropriate antimicrobial therapy for CAP must be based on prediction of the most likely pathogens and their local antimicrobial susceptibility patterns. This article reviews information on antimicrobial resistance patterns amongst S. pneumoniae and implications for managing CAP.

Antimicrobial susceptibility patterns of KPC-producing or CTX-M-producing Enterobacteriaceae

Enterobacteriaceae clinical isolates harboring KPC-(178 strains) or CTX-M-encoding (67 strains) genes were collected during surveillance programs in the 2000-2007 period; and susceptibility was tested by broth microdilution methods. Organisms were dominantly collected in U.S. hospitals (93%). CTX-M-15 and -14 were the most prevalent CTX-M types (97%), all collected from the United States. KPC producers were isolated in the United States (160/178), Israel, China, and Argentina. bla(CTX-M)-carrying isolates were 95.5 and 98.5%, susceptible to Imipenem and meropenem respectively, and were all susceptible to tigecycline, whereas KPC-producing isolates were highly resistant to all antimicrobials tested except polymyxin B and tigecycline (90.6% and 99.4% susceptibility, respectively). The occurrence of KPC-producing and CTX-M-producing isolates has rapidly increased especially in U.S. hospitals, and expanded therapeutic options are needed to treat infections caused by these emerging organisms.

Activity of ceftaroline against recent emerging serotypes of Streptococcus pneumoniae in the United States

The in vitro activity of ceftaroline against 891 pneumococci collected in 2008 from 22 centers in the United States was investigated. Ceftaroline was the most potent agent tested, with the MICs being <0.008 to 0.5 microg/ml and the MIC(90)s being <0.008 to 0.25 microg/ml against 11 prevailing serotypes. The overall rates of susceptibility were as follows: penicillin G, 86.2%; ceftriaxone, 90.7%; cefuroxime, 70.1%; erythromycin, 61.6%; clindamycin, 79.2%; levofloxacin, 99.4%; and vancomycin, 100%. Serotype 19A isolates were the least susceptible. These results support the use of ceftaroline for the treatment of pneumococcal infections, including those caused by pneumococci resistant to other agents.

CEM-101, a novel fluoroketolide: antimicrobial activity against a diverse collection of Gram-positive and Gram-negative bacteria

CEM-101 is a novel fluoroketolide with reported high potency against diverse groups of Gram-positive (Micrococcus spp., viridans group streptococci, Corynebacterium spp. Listeria monocytogenes, Clostridium spp., etc.) and Gram-negative bacteria (Neisseria gonorrhoeae, Campylobacter jejuni, Helicobacter pylori, Bacteroides fragilis, Shigella spp., etc.), including mycoplasma and ureaplasma, as well as bacteria commonly associated with community-acquired respiratory tract infections and skin and skin structure infections. In this study, CEM-101 and comparator antimicrobials were tested against a collection of very low prevalence aerobic and anaerobic bacteria collected via the SENTRY Antimicrobial Surveillance Program platform. CEM-101 was highly active against all Gram-positive organisms (MIC(50), 0.015 microg/mL) as compared with telithromycin (MIC(50), 0.06 microg/mL), clarithromycin (MIC(50), 0.12 microg/mL), and erythromycin (MIC(50), 0.25 microg/mL). Among Gram-negative pathogens, CEM-101 also displayed a high potency against most strains (MIC(50), 4 microg/mL) but was found to be equivalent or less active when compared with other antimicrobials tested with MIC(50) values ranging from < or =0.12 microg/mL for levofloxacin to 8 microg/mL for telithromycin. Among the strict anaerobic species, CEM-101 activity mirrored that of the aerobic species: high activity against the Gram-positive anaerobes (MIC(50) results ranging from < or =0.03 microg/mL to 0.12 microg/mL) and equivalent or less susceptible against Gram-negative anaerobes. Our in vitro antimicrobial susceptibility results for CEM-101 demonstrate better activity compared with other MLS(B) class agents among a diverse group of uncommonly isolated bacterial pathogens; these results provide an impetus for possible expanded indications during Phase 2 and 3 clinical trials.

Antimicrobial susceptibility of Gram-positive cocci isolated from skin and skin-structure infections in European medical centres

Skin and skin-structure infections (SSSIs) usually involve Gram-positive organisms. Prompt initiation of appropriate antimicrobial treatment is essential for achieving a favourable outcome in severe cases. Empirical antibacterial therapy should be based on several considerations, including patient risk factors, expected pathogens and local/regional susceptibility profiles, among others. In the present study, we evaluated the antimicrobial susceptibility patterns of Gram-positive bacteria isolated from patients with SSSIs hospitalised in European medical centres. A total of 3573 bacterial isolates were collected from 33 medical centres located in 13 European countries as well as Israel over a 6-year period (2003-2008) and were tested for susceptibility to daptomycin and other comparator agents by reference broth microdilution methods in a central laboratory. The most frequently isolated organisms were Staphylococcus aureus (71.1%), beta-haemolytic streptococci (10.5%) and enterococci (9.3%). Overall, rates of methicillin-resistant S. aureus (MRSA) and vancomycin-resistant enterococci (VRE) were 22.5% and 5.1%, respectively, but with great intercountry variation. The overall MRSA rate varied slightly during the study period, but with no overall tendency toward increase or decrease, whilst the overall VRE rate consistently increased from 1.5% in 2003 to 11.0% in 2008. Daptomycin and linezolid were the most active agents tested overall. All isolates monitored were considered susceptible to daptomycin, and only one isolate (Enterococcus faecium) was categorised as non-susceptible to linezolid. In conclusion, the results of this contemporary surveillance study indicate that daptomycin and linezolid retain sustained in vitro activity against Gram-positive cocci isolated from patients hospitalised with SSSI in numerous European medical centres.

Comparison of European Committee on Antimicrobial Susceptibility Testing (EUCAST) and Etest methods with the CLSI broth microdilution method for echinocandin susceptibility testing of Candida species

The antifungal broth microdilution (BMD) method of the European Committee on Antibiotic Susceptibility Testing (EUCAST) and the Etest agar diffusion method were compared with the Clinical and Laboratory Standards Institute (CLSI) BMD method M27-A3 for anidulafungin, caspofungin, and micafungin susceptibility testing of 133 clinical isolates of Candida species. The isolates were characterized for the presence or absence of fks1 and/or fks2 gene mutations and included 34 isolates of C. glabrata (4 mutant strains), 32 of C. albicans (1 mutant strain), 25 of C. parapsilosis, 19 of C. guilliermondii, 12 of C. tropicalis (2 mutant strains), and 11 of C. krusei. Excellent essential agreement (EA; within 2 dilutions) between the CLSI and EUCAST and CLSI and Etest MIC results was observed. The overall EA between the EUCAST and CLSI results ranged from 89.5% (caspofungin) to 99.2% (micafungin), whereas the EA between the Etest and CLSI results ranged from 90.2% (caspofungin) to 93.2% (anidulafungin). The categorical agreement (CA) between methods for each antifungal agent was assessed using previously determined epidemiological cutoff values (ECVs). Excellent CA (>90%) was observed for all comparisons between the EUCAST and CLSI results with the exceptions of C. glabrata and caspofungin (85.3%) and C. krusei and caspofungin (54.5%). The CA between the Etest and CLSI results was also excellent for all comparisons, with the exception of C. krusei and caspofungin (81.8%). All three methods were able to differentiate wild-type (WT) strains from those with fks mutations. With anidulafungin as the test reagent, the CLSI method identified 5 of 7 mutant strains, whereas the EUCAST method and the Etest identified 6 of 7 mutant strains. With either caspofungin or micafungin as the test reagent, the CLSI method identified all 7 mutant strains and the EUCAST method identified 6 of 7 mutant strains. The Etest identified all 7 mutant strains using caspofungin as the reagent. All three test methods showed a high level of agreement and of ability to distinguish fks mutant strains of Candida species from WT strains using each of the echinocandins.

The in vitro evaluation of tigecycline tested against pathogens isolated in eight countries in the Asia-Western Pacific region (2008)

OBJECTIVES

To determine the in vitro activity of tigecycline and comparator common use antimicrobial agents tested against contemporary bacterial pathogens from the Asia-Western Pacific region.

METHODS

As part of the SENTRY Antimicrobial Surveillance Program, a total of 5759 Gram-positive and Gram-negative isolates were collected from 28 medical centers in eight Asia-Western Pacific countries during 2008. Minimum inhibitory concentrations (MICs) were determined using Clinical and Laboratory Standards Institute (CLSI) broth microdilution method and interpreted using CLSI breakpoints. United States Food and Drug Administration (US-FDA) breakpoints were used to interpret tigecycline susceptibility.

RESULTS

Antimicrobial resistance was found to be widespread and prevalence varied considerably between the eight countries. Against pathogens for which breakpoints were available, >98% of all isolates were susceptible to tigecycline. Against all Gram-positive isolates, including methicillin (oxacillin)-resistant Staphylococcus aureus, penicillin- and multidrug-resistant pneumococci, and vancomycin-resistant enterococci, the highest tigecycline MIC found was 1 microg/ml. Against all Enterobacteriaceae, including extended-spectrum beta-lactamase phenotypes, tigecycline susceptibility was 97.5%. Tigecycline had good activity against Acinetobacter spp. but was much less active against Pseudomonas aeruginosa.

CONCLUSION

Tigecycline demonstrated excellent sustained in vitro activity against a wide spectrum of contemporary Gram-positive and -negative pathogens from Asia-Western Pacific countries.

Linezolid surveillance program results for 2008 (LEADER Program for 2008)

The LEADER Program was initiated in 2004 and monitors emerging linezolid resistance in sampled US medical centers. This report summarizes the data obtained in 2008, the 5th consecutive year. A total of 57 institutions participated in 2008 representing all 9 US census regions with 100 target organisms per site (6113 isolates, 101.9% compliance to protocol design). The organisms tested by reference broth microdilution methods were Staphylococcus aureus (3156), coagulase-negative staphylococci (CoNS; 856), enterococci (901), Streptococcus pneumoniae (619), and viridans group (223) or beta-hemolytic streptococci (358); also, D-test was used to determine inducible clindamycin resistance in Staphylococcus aureus. Linezolid remained very potent against all sampled species with MIC(90) results ranging from 1 microg/mL (streptococci and CoNS) to 2 microg/mL (Staphylococcus aureus and enterococci). Only 0.36% of sampled strains were nonsusceptible to linezolid, a slight decrease from 0.45% and 0.44% in 2006 and 2007, respectively. The nonsusceptible strains (22) were Staphylococcus aureus (3), CoNS (14), and Enterococcus faecium (5) each with defined target mutations (G2576T in 19 strains; T2504A in 1 strain), mobile cfr element (1 strain Staphylococcus epidermidis with an identical pulsed-field gel electrophoresis pattern to a cfr-positive Staphylococcus epidermidis isolated from the same center in LEADER 2007), or an unknown (1 strain) mechanism. The mobile cfr resistance found in a Staphylococcus aureus strain in 2007 was not observed in 2008. In conclusion, linezolid activity sampled by the 5th year of this LEADER Program showed sustained potency and spectrum (99.64% susceptibility levels). The nonsusceptible strain isolation rates remained stable and the plasmid-mediated ribosomal-based resistance mechanism that emerged in Staphylococcus aureus and Staphylococcus epidermidis strains in 2007 showed no evidence of dissemination or increased prevalence. However, there was evidence of cfr persistence with the S. epidermidis strain. The LEADER Program continues to be an effective and sensitive surveillance tool to detect and monitor novel oxazolidinone resistance phenotypes and genotypes.

Summary trends for the Meropenem Yearly Susceptibility Test Information Collection Program: a 10-year experience in the United States (1999-2008)

The Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program was a global, longitudinal antimicrobial resistance surveillance network of more than 100 medical centers worldwide monitoring the susceptibility of meropenem and selected other broad-spectrum comparator agents. In 1999, and from 2000 through 2008, a total of 10 or 15 United States (USA) medical centers each forwarded 200 nonduplicate clinical isolates from serious infections to a central processing laboratory. Over the 10-year period of this surveillance program, the activity of meropenem and an average of 11 other antimicrobial agents were assessed against a total of 27 289 bacterial isolates using Clinical and Laboratory Standards Institute reference methods. Meropenem consistently demonstrated low resistance rates against Enterobacteriaceae species isolates through 2008 and did not exhibit a widespread change in resistance rates over the monitored interval. In fact, the incidence of emerging carbapenemase-producing (KPC-type) Klebsiella spp. showed a decline in 2008 compared to the steeply increasing rates observed from 2004 to 2007. Moreover, the KPC serine carbapenemases have spread to other Enterobacteriaceae species monitored by the MYSTIC Program. Greatest increases in antimicrobial resistance rates were observed for the fluoroquinolones (ciprofloxacin, levofloxacin) among all species monitored by the MYSTIC Program. Current susceptibility rates for meropenem when tested against prevalent pathogens were Pseudomonas aeruginosa (439 strains, 85.4% susceptible), Enterobacteriaceae (1537 strains, 97.3% susceptible), methicillin-susceptible staphylococci (460 strains, 100.0% susceptible), Streptococcus pneumoniae (125 strains, 80.2% at meningitis susceptibility breakpoints), other streptococci (159 strains, 90.0-100.0% susceptible), and Acinetobacter spp. (127 strains, 45.7% susceptible), the widest spectrum among beta-lactams tested in 2008 and throughout the last decade. Continued local surveillance of broad-spectrum agents following the completion of the MYSTIC Program (USA) appears critical to detect emerging resistances among pathogens causing the most serious infections requiring carbapenem agents.

Wild-type MIC distributions and epidemiological cutoff values for the echinocandins and Candida spp

We tested a global collection of Candida sp. strains against anidulafungin, caspofungin, and micafungin, using CLSI M27-A3 broth microdilution (BMD) methods, in order to define wild-type (WT) populations and epidemiological cutoff values (ECVs). From 2003 to 2007, 8,271 isolates of Candida spp. (4,283 C. albicans, 1,236 C. glabrata, 1,238 C. parapsilosis, 996 C. tropicalis, 270 C. krusei, 99 C. lusitaniae, 88 C. guilliermondii, and 61 C. kefyr isolates) were obtained from over 100 centers worldwide. The modal MICs (in microg/ml) for anidulafungin, caspofungin, and micafungin, respectively, for each species were as follows: C. albicans, 0.03, 0.03, 0.015; C. glabrata, 0.06, 0.03, 0.015; C. tropicalis, 0.03, 0.03, 0.015; C. kefyr, 0.06, 0.015, 0.06; C. krusei, 0.03, 0.06, 0.06; C. lusitaniae, 0.05, 0.25, 0.12; C. parapsilosis, 2, 0.25, 1; and C. guilliermondii, 2, 0.5. 05. The ECVs, expressed in microg/ml (percentage of isolates that had MICs that were less than or equal to the ECV is shown in parentheses) for anidulafungin, caspofungin, and micafungin, respectively, were as follows: 0.12 (99.7%), 0.12 (99.8%), and 0.03 (97.7%) for C. albicans; 0.25 (99.4%), 0.12 (98.5%), and 0.03 (98.2%) for C. glabrata; 0.12 (98.9%), 0.12 (99.4%), and 0.12 (99.1%) for C. tropicalis; 0.25(100%), 0.03 (100%), and 0.12 (100%) for C. kefyr; 0.12 (99.3%), 0.25 (96.3%), and 0.12 (97.8%) for C. krusei; 2 (100%), 0.5 (98.0%), and 0.5 (99.0%) for C. lusitaniae; 4 (100%), 1 (98.6%), and 4 (100%) for C. parapsilosis; 16 (100%), 4 (95.5%), and 4 (98.9%) for C. guilliermondii. These WT MIC distributions and ECVs will be useful in surveillance for emerging reduced echinocandin susceptibility among Candida spp. and for determining the importance of various FKS1 or other mutations.

Order out of chaos in the hybrid plant nucleus

The plant nucleus is a highly ordered and dynamic structure, with a considerable level of variation between species in terms of genome size, genome organisation, chromosome territories and patterns associated with developmental changes. Diploids naturally represent the simplest state of affairs, but in the plant world more than 70% of species may have been involved in polyploidisation events at some stage during their evolution. Autopolyploids have multiple sets of chromosomes from a single species, and aside from the complexities of meiosis we may expect them to accommodate their polysomic state as well as their disomic relatives. Allopolyploids are at the other extreme, with multiple sets of chromosomes from 2 or more species, embedded in the cytoplasm of the maternal parent following hybridisation, and this presents the nucleus of nascent allopolyploids with certain zones of conflict. Nature has found ways to make the accommodation, and recent developments in molecular analysis have now opened a window for the experimenter to view the process of this adjustment, and to see how rapidly it takes place and what processes are involved. The nature of the resolution of nuclear conflicts in diploid hybrids and in allopolyploids is discussed.

Occurrence of vancomycin-tolerant and heterogeneous vancomycin-intermediate strains (hVISA) among Staphylococcus aureus causing bloodstream infections in nine USA hospitals

BACKGROUND

The bactericidal activities of vancomycin and daptomycin were evaluated in a large collection of methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia strains from nine major USA medical centres.

OBJECTIVES

To evaluate the occurrence of heterogeneous vancomycin-intermediate S. aureus (hVISA) among MRSA strains tolerant to vancomycin and/or with increased vancomycin or daptomycin MIC values. The accuracy of the macro Etest method (MET) compared with population analysis profiling (PAP) for the detection of hVISA was also assessed.

METHODS

A total of 1800 MRSA strains were collected from bloodstream infections at the nine sites (40 strains per year, per medical centre during the 2002-06 study period). Vancomycin and daptomycin MIC testing was performed by reference broth microdilution (all strains) and MBC tests on 50% of strains (randomly selected). A subset of isolates (n = 268) having an increased vancomycin MBC (> or =16 mg/L), an increased vancomycin MIC (> or =1 mg/L) and/or an increased daptomycin MIC (>0.5 mg/L) were tested for susceptibility to vancomycin and teicoplanin by MET.

RESULTS

Overall, 181 of 900 (20.1%) MRSA tested exhibited vancomycin tolerance, varying from 10% to 43% among the medical centres evaluated, and from 11.7% in 2004 to 27.8% in 2005. No resistance trend was observed in any medical centre or in the overall study data. Daptomycin showed bactericidal activity against all strains tested. The accuracy of MET for identifying hVISA strains varied significantly with the criteria applied for positivity.

CONCLUSIONS

The most frequently used criteria to define hVISA, i.e. MET reading values > or =8 mg/L for both vancomycin and teicoplanin or > or =12 mg/L for teicoplanin only, detected 20 of 36 PAP-positive strains (55.6% sensitivity), indicating that the prevalence of hVISA could be higher than currently appreciated. Daptomycin was bactericidal against hVISA strains.

Global view of antimicrobial resistance. Findings of the SENTRY Antimicrobial Surveillance Program, 1997-1999

The SENTRY Antimicrobial Surveillance Program, originated in 1997, currently encompasses 74 sentinel sites in 22 nations. SENTRY was designed to track antimicrobial resistance globally over a 5- to 10-year period. Isolates from bloodstream infections (BSIs), community-acquired lower respiratory tract infections, pneumonia in hospitalized patients, skin and soft tissue infections, and urinary tract infections are collected by each participating center and sent to the central monitoring laboratory for identification and antimicrobial susceptibility testing. Since 1997 more than 93,000 isolates have been processed by the SENTRY monitoring laboratories. Over the past 3 years (1997-1999), considerable data about BSI pathogens have been generated by the SENTRY program. Antimicrobial resistance among gram-positive cocci, especially Staphylococcus aureus, enterococci, and Streptococcus pneumoniae, constitutes a pressing concern worldwide. Among the S aureus organisms, methicillin resistance exceeds 30% of BSI isolates in most regions. Resistant gram-negative bacilli pose considerable problems, especially in Latin America and the Asia-Pacific region. Both enteric and nonenteric gram-negative pathogens resistant to ss-lactams, fluoroquinolones, and even carbapenems appear to be especially prevalent in those regions. In contrast, Canadian isolates of S aureus, enterococci, and gram-negative bacilli were considerably more susceptible to the agents tested when compared with isolates from the United States, Europe, Latin America, and the Asia-Pacific region. Given the regional differences in BSI pathogens and antimicrobial susceptibility observed thus far, further investigation directed at determining the reasons for such differences is warranted.

Dissemination and genetic context analysis of bla(VIM-6) among Pseudomonas aeruginosa isolates in Asian-Pacific Nations

VIM-6, previously reported in two strains from Singapore recovered in 2000, was detected in 16 isolates collected in 2006 in India (12 isolates), Indonesia (two), Korea and the Philippines (one each). High genetic variability was observed among VIM-6-producing isolates (12 ribotypes and 11 pulsed-field gel electrophoresis types), but clones were observed in India and Indonesia; bla(VIM-6)-carrying integrons of 3.9 kb and 5 kb were detected, and two of five Indian hospitals yielded isolates with both integrons. These two integrons, bla(VIM-6) was located in the first position, followed by bla(OXA-10) and aacA4. The 5-kb integrons also harboured aadA1 and a 331-bp open reading frame encoding a putative efflux pump.

ZAAPS International Surveillance Program (2007) for linezolid resistance: results from 5591 Gram-positive clinical isolates in 23 countries

The 2007 ZAAPS Program reports the results from the 6th year of oxazolidinone (linezolid) resistance surveillance among Gram-positive pathogens from 23 nations. For 2007, a total of 5591 organisms were systematically sampled from Asia, Australia, Canada, Europe, and Latin America including Staphylococcus aureus (3000 isolates, 38.2% methicillin resistant), coagulase-negative staphylococci (CoNS, 716 isolates), enterococci (906 isolates), Streptococcus pneumoniae (452 isolates), viridans group streptococci (155 isolates), and beta-hemolytic streptococci (362 isolates). The overall linezolid MIC distribution (MIC(50) and MIC(90) at 1 and 2 microg/mL, respectively) was unchanged since 2002. At published linezolid breakpoints (, or = 2 microg/mL), all streptococci were susceptible; however, resistance was observed very rarely among S. aureus (0.03%), CoNS (0.28%), and the enterococci (0.11%, 0.55% intermediate). These oxazolidinone-nonsusceptible isolates occurred in Ireland, Italy, China, and Brazil (9 strains), and the rate was not increased since 2006. The detected mechanism of resistance was G2576 target mutations; no cfr-mediated patterns were observed. Clonal outbreaks with patient-to-patient dissemination were documented in 1 Italian site. Linezolid appears to retain excellent activity against monitored Gram-positive pathogens at a level of >99.8%.

Delirium accelerates cognitive decline in Alzheimer disease

OBJECTIVE

To examine the impact of delirium on the trajectory of cognitive function in a cohort of patients with Alzheimer disease (AD).

METHODS

A secondary analysis of data collected from a large prospective cohort, the Massachusetts Alzheimer's Disease Research Center's patient registry, examined cognitive performance over time in patients who developed (n = 72) or did not develop (n = 336) delirium during the course of their illnesses. Cognitive performance was measured by change in score on the Information-Memory-Concentration (IMC) subtest of the Blessed Dementia Rating Scale. Delirium was identified using a previously validated chart review method. Using linear mixed regression models, rates of cognitive change were calculated, controlling for age, sex, education, comorbid medical diagnoses, family history of dementia, dementia severity score, and duration of symptoms before diagnosis.

RESULTS

A significant acceleration in the slope of cognitive decline occurs following an episode of delirium. Among patients who developed delirium, the average decline at baseline for performance on the IMC was 2.5 points per year, but after an episode of delirium there was further decline to an average of 4.9 points per year (p = 0.001). Across groups, the rate of change in IMC score occurred about three times faster in those who had delirium compared to those who did not.

CONCLUSIONS

Delirium can accelerate the trajectory of cognitive decline in patients with Alzheimer disease (AD). The information from this study provides the foundation for future randomized intervention studies to determine whether prevention of delirium might ameliorate or delay cognitive decline in patients with AD.

In vitro activity of ceftaroline alone and in combination against clinical isolates of resistant gram-negative pathogens, including beta-lactamase-producing Enterobacteriaceae and Pseudomonas aeruginosa

Ceftaroline is a novel broad-spectrum cephalosporin that exhibits bactericidal activity against many gram-positive and -negative pathogens. However, the activity of ceftaroline cannot be solely relied upon for eradication of multidrug-resistant gram-negative isolates, such as Pseudomonas aeruginosa and extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae, which represent a current clinical concern. As drug combinations might be beneficial by potential synergy, we evaluated the in vitro activity of ceftaroline combined with meropenem, aztreonam, cefepime, tazobactam, amikacin, levofloxacin, and tigecycline. Susceptibility testing was performed for 20 clinical P. aeruginosa isolates, 10 ESBL-producing Escherichia coli isolates, 10 ESBL-producing Klebsiella pneumoniae isolates, and 10 AmpC-derepressed Enterobacter cloacae isolates. Time-kill experiments were performed for 10 isolates using antimicrobials at one-fourth the MIC. Ceftaroline exhibited a MIC range of 0.125 to 1,024 microg/ml and was reduced 2- to 512-fold by combination with tazobactam (4 microg/ml) for ESBL-producing strains. In time-kill experiments, ceftaroline plus amikacin was synergistic against 90% of the isolates (and indifferent for one P. aeruginosa isolate). Ceftaroline plus tazobactam was indifferent for E. cloacae and P. aeruginosa strains but synergistic against 100% of E. coli and K. pneumoniae isolates. Combinations of ceftaroline plus meropenem or aztreonam were also synergistic for all E. coli and E. cloacae isolates, respectively, but indifferent against 90% of the other isolates. Finally, combinations of ceftaroline plus either tigecycline, levofloxacin, or cefepime were indifferent for 100% of the isolates. No antagonism was observed with any combination. Ceftaroline plus amikacin appeared as the most likely synergistic combination. This represents a promising therapeutic option, and further studies are warranted to elucidate the clinical value of ceftaroline combinations against resistant gram-negative pathogens.

Update of cefditoren activity tested against community-acquired pathogens associated with infections of the respiratory tract and skin and skin structures, including recent pharmacodynamic considerations

Antimicrobial resistance rates have noticeably increased among commonly isolated species associated with respiratory tract infections and skin and skin structure infections, particularly Streptococcus pneumoniae and Staphylococcus aureus. Cefditoren, an oral 3rd-generation-like cephalosporin, has been shown to be very active against many Gram-positive and Gram-negative species with favorable attributes including bactericidal activity and stability against many beta-lactamase enzymes. Clinical trial data worldwide support the use of cefditoren for infections and species that have been approved by the US Food and Drug Administration (US-FDA). This review and a contemporary study report provide an update of clinical trial and in vitro data for cefditoren especially against pathogens within the spectrum of activity since 2002. A large collection of 7279 clinical isolates collected during 2002 and 2003 from medical centers in North and Latin America and Europe were tested to confirm cefditoren potency and spectrum compared with other oral cephalosporins and other class agents. Isolates were tested at a reference laboratory using reference broth microdilution methods. Cefditoren was shown to be active against nearly all (>99%) isolates of penicillin-susceptible S. pneumoniae isolates (MIC(90), < or = 0.03 microg/mL) and was the most potent orally administered cephalosporin against this organism. Cefditoren was the most active oral cephem tested against Haemophilus influenzae (MIC(90), < or = 0.03 microg/mL) and had >99% activity versus both beta-lactamase-positive and beta-lactamase-negative isolates. The potency of cefditoren (MIC(90), 0.5 microg/mL) was similar to that of amoxicillin/clavulanate and cefdinir (MIC(90), 0.25 microg/mL) when tested against Moraxella catarrhalis. Cefditoren was the most potent cephalosporin tested against oxacillin-susceptible S. aureus with an MIC(90) value of only 1 microg/mL, and it was 100% active against the tested beta-hemolytic streptococci. Using the data generated from the large collection of isolates tested in this global surveillance collection, as well as other summarized supporting studies and clinical trial information, we show that cefditoren has sustained in vitro activity and documented clinical efficacy for indications that have been approved by regulators (US-FDA).

Frequency of occurrence and daptomycin susceptibility rates of Gram-positive organisms causing bloodstream infections in cancer patients

We evaluated the pathogen frequency and the antimicrobial susceptibility patterns of Gram-positive bacteria causing infections in cancer patients. We also compared the antimicrobial susceptibility of isolates from cancer patients to those from non-cancer patients and evaluated the activity of the novel lipopeptide daptomycin against these isolates. A total of 1,222 Gram-positive isolates were collected (one per patient) from bloodstream infections (BSI) in cancer patients at 33 United States (USA) medical centers in 2002-2006 and susceptibility tested by the broth microdilution method. Frequency of occurrence and susceptibility patterns of strains from cancer patients were compared to those from non-cancer patients collected in the same hospitals (10,684 strains). Staphylococcus aureus (39.2%) ranked first among Gram-positive pathogens from cancer patients, followed by Enterococcus spp. (32.2%) and coagulase-negative staphylococci (CoNS; 20.4%). Daptomycin was active against 99.8% of Gram-positive strains collected from patients with cancer at USA hospitals, but vancomycin was only active against 87.6% of strains and showed limited activity against Enterococcus spp.(61.4% susceptible). Only three daptomycin non-susceptible isolates were detected, all with MIC values at one doubling dilution above the susceptible breakpoint. These results indicate that daptomycin has an appropriate spectrum and potency to be used for empirical coverage of Gram-positive infections (especially BSI) in cancer patients in the hospitals surveyed in the USA.

Antimicrobial activity of prulifloxacin tested against a worldwide collection of gastroenteritis-producing pathogens, including those causing traveler's diarrhea

Prulifloxacin, the prodrug of ulifloxacin (active component), is a newer fluoroquinolone with broad activity against enteric and nonenteric gram-negative bacilli. Ulifloxacin and other oral comparator agents were tested for activity against 582 gastroenteritis strains from global surveillance studies. Ulifloxacin was highly active against Escherichia coli, Salmonella spp., Shigella spp., Yersinia spp., Vibrio spp., Aeromonas spp., and Plesiomonas spp. (MIC(50)s and MIC(90)s, or=4 microg/ml). Ciprofloxacin exhibited similar activity but was two- to fourfold less potent. Presently approved for clinical use in certain European countries and Japan, ulifloxacin was the most active of the antimicrobial agents tested against these gastroenteritis-causing pathogens.

Multicenter evaluation of the in vitro activity of dalbavancin tested against staphylococci and streptococci in 5 European countries: results from the DECIDE Surveillance Program (2007)

Dalbavancin is an antimicrobial lipoglycopeptide agent that has proven activity against Gram-positive pathogens and a once weekly dosing advantage compared with other agents in the glycopeptide class. The most common pathogens isolated from skin and skin structure infections (SSSIs) include Staphylococcus aureus and beta-hemolytic streptococci (betaHS), and dalbavancin has demonstrated excellent activity against these species. This study used 18 medical center laboratories in 5 European countries to assess the activity of dalbavancin, vancomycin, and teicoplanin against S. aureus, coagulase-negative staphylococci (CoNS), and betaHS. The rank order of potency was dalbavancin (MIC(50), 0.06 microg/mL) > teicoplanin (MIC(50), 0.5 microg/mL) > vancomycin (MIC(50), 2 microg/mL) and dalbavancin (MIC(50), 0.06 microg/mL) > teicoplanin and vancomycin (MIC(50), 2 microg/mL) against S. aureus and CoNS, respectively. Dalbavancin was the most active glycopeptide tested against betaHS with all strains inhibited by < or = 0.12 microg/mL. Susceptibility to other antimicrobial classes was also evaluated with noticeable differences demonstrated between countries. Higher methicillin-resistant S. aureus (MRSA) rates were observed in Italy (44.2%) and the United Kingdom (36.8%) compared with other countries, but resistance to erythromycin (51.6-83.1%) and clindamycin (5.7-68.4%) among MRSA also varied significantly between countries. The excellent contemporary activity of dalbavancin against common Gram-positive pathogens collected in European countries suggests that dalbavancin could have a role in the treatment of various types of SSSIs.

United States resistance surveillance results for linezolid (LEADER Program for 2007)

The LEADER Program (2007) monitors for emerging linezolid resistance in sampled US medical centers, initiated in 2004. For the current reported year, the number of sites participating was increased from 50 to 60 institutions representing all 9 US census regions with 100 target organisms per site (6305 isolates, 105.1% compliance to protocol design). The organisms tested by reference broth microdilution methods were Staphylococcus aureus (3318), coagulase negative staphylococci (CoNS, 1020), enterococci (705), Streptococcus pneumoniae (622), and viridans group (249) or beta-hemolytic streptococci (391); also, D-test was used to determine inducible clindamycin resistance in S. aureus strains. Linezolid remained very potent against all sampled species with MIC(90) results ranging from 1 microg/mL (streptococci and CoNS) to 2 microg/mL (S. aureus and enterococci). Only 0.44% of sampled strains were nonsusceptible to linezolid, compared with 0.45% in 2006. The nonsusceptible strains (23) were usually staphylococci (20) or Enterococcus faecium (8), each with defined target mutations (G2576T, 24 strains) or a novel mobile cfr element in staphylococci (2 strains). In conclusion, linezolid activity sampled by the 4th year of this LEADER Program showed sustained potency and spectrum (99.56% susceptibility). Although the nonsusceptible strain isolation rates remained stable, a new plasmid-mediated ribosomal-based resistance mechanism emerged in S. aureus and Staphylococcus epidermidis strains from Arizona and Ohio. The LEADER Program appears to be an effective and sensitive surveillance tool to detect novel resistance phenotypes and genotypes.

Comparison of 2002–2006 OPTAMA Programs for US Hospitals: Focus on Gram-Negative Resistance

Background:

Resistance among gram-negative bacteria is increasing within the US.

Objective:

To determine pharmacodynamic target attainment rates for 10 antimicrobials against selected gram-negative bacilli and compare these results with previous Optimizing Pharmacodynamic Target Attainment Using the MYSTIC Antibiogram (OPTAMA) assessments.

Methods:

A 5000-patient Monte Carlo simulation using data from population pharmacokinetic studies was employed to estimate the pharmacokinetic profiles for standard and/or prolonged infusion (PI) regimens of cefepime, ceftazidime, ceftriaxone, ciprofloxacin, ertapenem, imipenem, levofloxacin, meropenem, piperacillin–tazobactam, and tigecycline. Minimum inhibitory concentration data were obtained from intensive care units of 15 US hospitals participating in the 2006 MYSTIC (Meropenem Yearly Susceptibility Test Information Collection) study for 640 Escherichia coli, 618 Klebsiella spp., and 606 Pseudomonas aeruginosa isolates. Cumulative fraction of response (CFR) was calculated using pharmacodynamic targets for each antibiotic and compared with results from the 2002 and 2004 OPTAMA studies.

Results:

Against E. coli, CFRs greater than 92% were maintained for all regimens except the fluoroquinolones (CFR range 69.4–72%), which showed a 7% decrease compared with 2004. The presence of Klebsiella spp. producing KPC-type carbapenemases with associated multidrug resistance resulted in a 7% or greater drop in CFR of standard regimens relative to 2004. Despite these resistant phenotypes, high-dose PI regimens (2 g every 8 hours as 3-hour PI) of cefepime and meropenem achieved CFRs of 97% and 95.8%, respectively. Excluding 3 KPC-harboring hospitals resulted in CFR increases to greater than 98% for carbapenems and cefepime and greater than 88% for all other agents tested, except tigecycline. Against P. aeruginosa, the fluoroquinolones had the lowest CFR (55.8–63.9%), followed by imipenem (74.6-80.4%). The most predictable activity was seen with cefepime 2 g every 12 hours or higher (>90%), ceftazidime 2 g every 8 hours (97.9%), and meropenem 1-2 g every 8 hours (86.7–92.6%). Use of PI for piperacillin-tazobactam and meropenem increased CFRs by 6% and 4%, respectively, over standard infusions.

Conclusions:

Relative to previous years, an increase in resistance was noted among gram-negative bacilli to common antibiotics, resulting in disproportionate decreases in pharmacodynamic target attainment. The use of PI for β-lactams may help to overcome these decreases.

Rapid emergence of blaCTX-M among Enterobacteriaceae in U.S. Medical Centers: molecular evaluation from the MYSTIC Program (2007)

A total of 220 gram-negative isolates showing distinct beta-lactam resistance profiles recovered in U.S. medical centers during the MYSTIC Program 2007 were evaluated to determine the presence of selected beta-lactamase genes. CTX-M-encoding genes, considered rare in the United States, were detected in 38.8% (28/70; three species) of the extended spectrum beta-lactamase-positive isolates and were observed in 80.0% of the participating hospitals. CTX-M-14 and -15 were found in multiple institutions (eight and nine medical centers, respectively), and CTX-M-3 was detected in only one isolate. The OXA-2 and -10 were identified in nine Enterobacteriaceae strains, and plasmid-mediated AmpC enzymes CMY-2 and FOX-5 were identified in six and four isolates, respectively, displaying negative clavulanate inhibition. Genes encoding OXA-23 and -24 were detected in 30.0% (15/50) of carbapenem-resistant Acinetobacter spp. strains. Retrospective sampling showed that these OXA enzymes were present since 2004 in the MYSTIC Program isolates. The KPC serine carbapenemases were observed in the majority of the carbapenem-resistant Enterobacteriaceae (usually Klebsiella pneumoniae), confirming an epidemic problem in the New York City area. The association of beta-lactamase production and transferable quinolone resistance genes (qnr; 6.7%) in Enterobacteriaceae strains was higher than previously reported. This study illustrates the emergence and rapid dissemination of some beta-lactamases, such as CTX-M, broad-spectrum oxacillinases, and serine carbapenemases, that compromised the treatment of gram-negative infections in numerous U.S. hospitals participating in the MYSTIC Program in 2007.

Interpretive categorical accuracy of fluoroquinolone reference broth microdilution MIC results when testing Streptococcus pneumoniae: selection of a surrogate testing agent

The categorical agreement among MIC results for the fluoroquinolones tested (levofloxacin, moxifloxacin, gatifloxacin and gemifloxacin) was high (99.16-99.85%), and error rates were nil or very low when 1 compound was used as a surrogate for predicting susceptibility (not resistance) to another agent in the class. No error was observed when levofloxacin was selected as the group surrogate for pneumococcal testing.

Emergence and widespread dissemination of OXA-23, -24/40 and -58 carbapenemases among Acinetobacter spp. in Asia-Pacific nations: report from the SENTRY Surveillance Program

OBJECTIVES

The aim of this study was to evaluate the occurrence and dissemination of acquired carbapenem-hydrolysing class D beta-lactamase (class D carbapenemase)- and metallo-beta-lactamase (MBL)-encoding genes among Acinetobacter spp. isolates recovered from medical centres in the Asia-Pacific (APAC) region.

METHODS

During 2006-07, 41 medical centres located in 10 countries in the APAC region forwarded to a central monitoring site 544 Acinetobacter spp. isolates, which were tested for susceptibility by the reference broth microdilution method. Isolates non-susceptible to imipenem or meropenem (MIC>or=8 mg/L) were screened for OXA-23-, OXA-24/40-, OXA-58- and MBL-encoding genes and confirmed by sequencing. Clonality was assessed by ribotyping and PFGE.

RESULTS

Polymyxins (99.1% susceptible) and tigecycline (98.9% susceptible) were the most active antimicrobial agents tested. Among the isolates, 230 (42.3%) were non-susceptible to imipenem or meropenem, and class D carbapenemase- or MBL-encoding genes were detected in 162 (70.4%). blaOXA-23 was found in isolates recovered from six countries, while blaOXA-24/40 and blaOXA-58 were less common. Several isolates harboured more than one class D carbapenemase, and MBL-encoding genes were detected in one Acinetobacter johnsonii from the Philippines (blaIMP-4) and one Acinetobacter baumannii from Korea (blaVIM-2)). Overall, clonal dissemination was noted within medical centres; however, genetic relatedness was also noted among class D carbapenemase-producing A. baumannii isolates recovered from different countries.

CONCLUSIONS

This study shows a high distribution of class D carbapenemase-encoding genes, mainly blaOXA-23, in Acinetobacter spp. isolates. In addition, clonal dissemination among medical centres located in different countries in the APAC region, previously documented in many regions of Europe, emphasizes the epidemic potential of these bacteria.

Strategic design of an effective beta-lactamase inhibitor: LN-1-255, a 6-alkylidene-2'-substituted penicillin sulfone

In an effort to devise strategies for overcoming bacterial beta-lactamases, we studied LN-1-255, a 6-alkylidene-2'-substituted penicillin sulfone inhibitor. By possessing a catecholic functionality that resembles a natural bacterial siderophore, LN-1-255 is unique among beta-lactamase inhibitors. LN-1-255 combined with piperacillin was more potent against Escherichia coli DH10B strains bearing bla(SHV) extended-spectrum and inhibitor-resistant beta-lactamases than an equivalent amount of tazobactam and piperacillin. In addition, LN-1-255 significantly enhanced the activity of ceftazidime and cefpirome against extended-spectrum cephalosporin and Sme-1 containing carbapenem-resistant clinical strains. LN-1-255 inhibited SHV-1 and SHV-2 beta-lactamases with nm affinity (K(I) = 110 +/- 10 and 100 +/- 10 nm, respectively). When LN-1-255 inactivated SHV beta-lactamases, a single intermediate was detected by mass spectrometry. The crystal structure of LN-1-255 in complex with SHV-1 was determined at 1.55A resolution. Interestingly, this novel inhibitor forms a bicyclic aromatic intermediate with its carbonyl oxygen pointing out of the oxyanion hole and forming hydrogen bonds with Lys-234 and Ser-130 in the active site. Electron density for the "tail" of LN-1-255 is less ordered and modeled in two conformations. Both conformations have the LN-1-255 carboxyl group interacting with Arg-244, yet the remaining tails of the two conformations diverge. The observed presence of the bicyclic aromatic intermediate with its carbonyl oxygen positioned outside of the oxyanion hole provides a rationale for the stability of this inhibitory intermediate. The 2'-substituted penicillin sulfone, LN-1-255, is proving to be an important lead compound for novel beta-lactamase inhibitor design.

Antimicrobial activity of daptomycin and selected comparators tested against bloodstream Staphylococcus aureus isolates from hemodialysis patients

BACKGROUND

Patients on long-term hemodialysis are at a significantly higher risk for catheter-related bloodstream infections (BSI) than the general population. These infections are generally caused by gram-positive organisms, especially Staphylococcus aureus. In the present study, we evaluated the antimicrobial susceptibility patterns of S. aureus causing BSI in dialysis patients compared to those causing BSI in other patient populations.

METHODS

The potencies of daptomycin and various comparator agents were evaluated by reference broth microdilution methods for S. aureus bloodstream isolates from dialysis patients (606 strains) in 43 hospitals in North America and Europe. Susceptibility patterns for the dialysis isolate set were compared to those S. aureus causing BSI in other patient populations in the same hospitals and time period.

RESULTS

Daptomycin was highly potent against S. aureus causing bacteremia in dialysis patients (MIC(50)/MIC(90), 0.25/0.5 microg/ml). Vancomycin (MIC(50)/MIC(90), 1/1 microg/ml) and linezolid (MIC(50)/MIC(90), 2/2 microg/ml) showed similar potency, and overall susceptibility rates for the three antibiotics were 99.8-100.0% susceptible. Linezolid and vancomycin were four- to eight-fold less potent than daptomycin.

CONCLUSIONS

The overall susceptibility patterns of S. aureus strains from dialysis patients were very similar to those of non-dialysis patients.