Antimicrobial susceptibility of intra-abdominal gram-negative bacilli from Europe: SMART Europe 2008

As part of the worldwide Study for Monitoring Antimicrobial Resistance Trends (SMART), a total of 3,030 clinical isolates of gram-negative bacilli from intra-abdominal infections were collected from 43 hospital centres from 13 European countries during 2008. Of 51 species, the most commonly isolated species were Escherichia coli (49.3%), followed by Klebsiella pneumoniae (10.5%) and Pseudomonas aeruginosa (8.6%). Respectively, 17.9%, 11.6%, 5.5% and 4.5% of K. pneumoniae, E. coli, Proteus mirabilis and K. oxytoca were extended-spectrum beta-lactamase (ESBL)-positive. All isolates were tested using a panel of 12 antimicrobial agents, and susceptibilities were determined using European Committee on Antimicrobial Susceptibility Testing (EUCAST) clinical breakpoints. The most active agents against the study isolates (including those producing ESBLs) were amikacin, ertapenem and imipenem. Overall, with the exception of the carbapenems, most agents exhibited dramatically reduced susceptibilities against ESBL-positive and multi-drug-resistant isolates.

Multicenter, randomized study of the efficacy and safety of intravenous iclaprim in complicated skin and skin structure infections

Iclaprim is a novel antibacterial agent that is currently in development for the treatment of complicated skin and skin structure infections (cSSSI). Iclaprim specifically and selectively inhibits bacterial dihydrofolate reductase, a critical enzyme in the bacterial folate pathway, and exhibits an extended spectrum of activity against various resistant pathogens, including methicillin (meticillin)-resistant Staphylococcus aureus (MRSA). The objective of this randomized, double-blind phase II study was to compare the efficacy and safety of iclaprim to those of vancomycin in patients with cSSSI. Patients were randomized to receive 0.8 mg iclaprim/kg of body weight, 1.6 mg/kg iclaprim, or 1 g vancomycin twice a day for 10 days. Clinical cure rates for the 0.8- and 1.6-mg/kg-iclaprim treatment groups were comparable to that for the vancomycin treatment group (26/28 patients [92.9%], 28/31 patients [90.3%], and 26/28 patients [92.9%], respectively). Iclaprim also showed high microbiological eradication rates. Iclaprim exhibited an eradication rate of 80% and 72% versus 59% observed with vancomycin for S. aureus, the pathogen most frequently isolated at baseline. Five MRSA cases were observed, four in the 0.8-mg/kg-iclaprim arm and one in the vancomycin arm, and all were both clinically and microbiologically cured. Iclaprim exhibited a safety profile similar to that of vancomycin, an established drug for the treatment of cSSSI. Results from this study indicate that iclaprim is a promising new therapy for the treatment of cSSSI, in particular those caused by S. aureus, including MRSA.

Concentrations in plasma, epithelial lining fluid, alveolar macrophages and bronchial mucosa after a single intravenous dose of 1.6 mg/kg of iclaprim (AR-100) in healthy men

OBJECTIVES

A validated microbiological assay was used to measure concentrations of iclaprim (AR-100) in plasma, bronchial mucosa (BM), alveolar macrophages (AM) and epithelial lining fluid (ELF) after a single 1.6 mg/kg intravenous 60 min iv infusion of iclaprim.

METHODS

Male volunteers were randomly allocated to three nominal sampling time intervals 1-2 h (Group A), 3-4 h (Group B) and 5.5-7.0 h (Group C) after the start of the drug infusion.

RESULTS

Mean iclaprim concentrations in plasma, BM, AM and ELF, respectively, were for Group A 0.59 mg/L (SD 0.18), 0.51 mg/kg (SD 0.17), 24.51 mg/L (SD 21.22) and 12.61 mg/L (SD 7.33); Group B 0.24 mg/L (SD 0.05), 0.35 mg/kg (SD 0.17), 7.16 mg/L (SD 1.91) and 6.38 mg/L (SD 5.17); and Group C 0.14 mg/L (SD 0.05), no detectable level in BM, 5.28 mg/L (SD 2.30) and 2.66 mg/L (SD 2.08).

CONCLUSIONS

Iclaprim concentrations in ELF and AM exceeded the MIC(90) for penicillin-susceptible Streptococcus pneumoniae (MIC90 0.06 mg/L), penicillin-intermediate S. pneumoniae (MIC90 2 mg/L), penicillin-resistant S. pneumoniae (MIC90 4 mg/L) for 7, 7 and 4 h, respectively, and Chlamydia pneumoniae (MIC90 0.5 mg/L) for 7 h. Mean iclaprim concentrations in ELF exceeded the MIC90 for Haemophilus influenzae (MIC90 4 mg/L) and Moraxella catarrhalis (MIC90 8 mg/L) for up to 4 and 2 h, respectively; in AM the MIC90 was exceeded for up to 7 h. Furthermore, the MIC90 for methicillin-resistant Staphylococcus aureus of 0.12 mg/L was exceeded at all sites for up to 7 h. These data suggest that iclaprim reaches lung concentrations that should be effective in the treatment of community-acquired pneumonia.

In vitro activity of a novel diaminopyrimidine compound, iclaprim, against Chlamydia trachomatis and C. pneumoniae

The in vitro activities of iclaprim, a novel dihydrofolate reductase inhibitor, azithromycin, and levofloxacin were tested against 10 strains of Chlamydia trachomatis and 10 isolates of Chlamydia pneumoniae. For C. trachomatis and C. pneumoniae, the iclaprim MIC and minimal bactericidal concentration at which 90% of isolates were inhibited (MIC(90) and MBC(90)) were 0.5 micro g/ml, compared to an azithromycin MIC(90) and MBC(90) of 0.125 micro g/ml and levofloxacin MIC(90)s and MBC(90)s of 1 micro g/ml for C. trachomatis and 0.5 micro g/ml for C. pneumoniae.

Anidulafungin (Eli Lilly & Co)

The pentyloxyterphenyl side chain derivative of echinocandin B, anidulafungin, is a 1,3-alpha-glucan synthesis inhibitor undergoing phase II clinical trials by Versicor and Eli Lilly, in various formulations, for the potential treatment of fungal and protozoal infections. Eli Lilly has retained options to the oral formulation of the compound, but development, clinical registration and marketing rights were licensed to Versicor in June 1999. The primary target of this compound is Candida, but Eli Lilly also intends to develop the drug for Aspergillus infections. No activity has been shown against Cryptococcus. The oral activity of anidulafungin is compromised by a low bioavailability, a decreased absorption when taken with food, and gastrointestinal side effects at higher doses. The development of a phosphorylated prodrug, LY-307853, which is converted in the body to anidulafungin by tissue and serum phosphatases, was discontinued in favor of an oral formulation, which uses anidulafungin directly. In February 1999, Deutsche Bank predicted sales of $100 million in 2001, rising to $300 million in 2003.

Comparisons of the effects of fungicidal and fungistatic antifungal agents on the morphogenetic transformation of Candida albicans

Eleven different antifungal agents were compared, and their ability to inhibit the morphogenetic transformation of Candida albicans was examined together with their ability to inhibit growth, as measured by MIC methodology. The fungicidal potential of each agent was also determined. Of the antifungal agents tested, only amphotericin B, mulundocandin and aculeacin inhibited the transformation at sub-MIC values; all three agents showed fungicidal activity at concentrations close to the MIC. All other agents were fungicidal only at concentrations much higher than the MIC and inhibited the morphogenetic transformation only at concentrations above the MIC. These data suggest that fungicidal antifungal agents are more likely to act by inhibiting the morphogenetic transformation of C. albicans while fungistatic agents are unable to do so and are more likely to block growth by budding.

Mulundocandin, an echinocandin-like lipopeptide antifungal agent: biological activities in vitro

Mulundocandin (MCN) is an antifungal lipopeptide which belongs to the echinocandin class of antimycotic agents. MCN exhibited good in vitro activity against Candida albicans and C. glabrata isolates with MIC ranges of 0.5-4.0 microg/ml and 2.0-4.0 microg/ml, respectively. MCN also exhibited some activity against C. tropicalis isolates (MIC range 1.0-8.0 microg/ml). However, MCN was poorly active against other non-albicans isolates and was inactive against Cryptococcus neoformans, Aspergillus species and Trichophyton. MCN appeared to exert its antifungal activity through preferential inhibition of germ tube formation (MIC-HY 0.015-0.03 microg/ml) and was typically less active on the yeast form (MIC 0.5-4.0 microg/ml). In kill-curve experiments 99.9% reductions in cell viability were observed following 8 hours exposure to MCN at 4 x MIC and 8 x MIC and after 5 hours exposure to 16 x MIC.

3874 H1 and H3, novel antifungal heptaene antibiotics produced by Streptomyces sp. HAG 003874

New antifungal antibiotics, designated as 3874 H1 and H3, were discovered in the fermentation broth of the strain Streptomyces sp. HAG 003874. The compounds were obtained as yellow powders after sequential purification by chromatography on MCI Gel CHP20P, Fractogel HW-40 and ODS reversed phase chromatography. On the basis of the results of spectroscopic analysis, it was found that 3874 H1, C58H86N2O18, MW 1098, belongs to the p-aminoacetophenone containing family of heptaene antibiotics, while 3874 H3, C57H87NO18, MW 1073, is a non-aromatic heptaene. In addition to these, a minor component, 3874 H2, C59H88N2O18, MW 1112, a N-methyl derivative of 3874 H1 has been detected. The structures were elucidated through mass spectral analyses and 1-D and 2-D homonuclear and heteronuclear NMR data. The outstanding physico-chemical feature of 3874 H3 is its improved solubility. The new heptaenes are potent antifungal compounds with broad activity spectra, encompassing dermatophytes, yeasts and filamentous fungi.

Adhesion of different Candida spp. to plastic: XTT formazan determinations

Adhesion of synchronized yeast-phase Candida cells to tissue culture plastic was investigated using the tetrazolium salt, XTT. The procedure permits the direct enumeration of adherent yeasts following the metabolic conversion of the XTT tetrazolium salt, to its reduced formazan form, by mitochondrial dehydrogenases. Using this procedure, the formation of XTT formazan by Candida cells was typically related to the inoculum size. The adhesion of Candida yeast-phase cells from different Candida spp. to plastic was of the following order: C. krusei (n = 5) > C. albicans (n = 10) > C. glabrata (n = 6). Furthermore, preliminary experiments with several other species indicated that C. tropicalis (n = 2) may adhere as well as C. albicans and that one strain each of C. guilliermondii and C. parapsilosis appear to adhere to plastic in a similar fashion to C. glabrata. The data indicate the utility of the XTT tetrazolium based assay in enumerating the adhesion of different Candida spp. to plastic.

The effects of antifungal agents on the morphogenetic transformation by Candida albicans in vitro

The effects of antifungal agents, with different mechanisms of action, on the morphogenetic transformation by synchronised yeast-phase Candida albicans cells in vitro and their respective anti-Candida activities are described. MIC data demonstrated that the azoles, amphotericin B and echinocandin were the most active agents against four C. albicans strains. Morphogenetic transformation experiments demonstrated that amphotericin B was significantly better at preventing the transformation, under a variety of test conditions, than the azoles and flucytosine: amphotericin B abolished the transformation at low concentrations while the azoles only prevented the morphogenetic transformation at much higher concentrations (> 100 x MIC).

Spectrophotometric determination of the morphogenetic transformation by synchronous Candida albicans: effects of antifungal agents

A spectrophotometric method for studying the morphogenetic transformation by Candida albicans is described. Synchronous yeast-phase C. albicans cells incubated at 35 degrees C formed germ-tubes and resulted in an absorbance increase at 340 nm but not at 595 nm. Furthermore, measurements of germ tube length increases correlated strongly (r2 > 0.95) with increases in absorbance at 340 nm during the morphogenetic transformation. Amphotericin B significantly affected the morphogenetic transformation, at the MIC and 1/10 MIC, whereby no increase in absorbance was observed at 340 nm. In contrast, identical measurements demonstrated that ketoconazole, at the MIC and 1/10 MIC, did not exhibit the same effects on the morphogenetic transformation by C. albicans cells.

Comparisons of the susceptibilities of planktonic and adherent Candida albicans to antifungal agents: a modified XTT tetrazolium assay using synchronised C. albicans cells

Adhesion of synchronised yeast-phase Candida albicans cells to tissue culture plastic, and the susceptibility of planktonic and adherent cells to antifungal agents, was investigated using a modified tetrazolium (XTT) assay. MIC data demonstrated that ketoconazole and amphotericin B were highly active against planktonic C. albicans yeast-phase cells. XTT tetrazolium assays permitted comparisons of MIC values with XTT formazan IC50 and IC80 (percentage inhibitory concentrations); IC50 and IC80 values for amphotericin B and ketoconazole were similar. Furthermore, IC50 and IC80 values for 24 h incubation with antifungal agent were typically higher than corresponding IC50 and IC80 values for 48 h incubation. Furthermore, in comparison to values for planktonic Candida cells, adherent cells were typically less susceptible to amphotericin B and ketoconazole. For example, with increasing incubation time following the initial adhesion period, cells became progressively less susceptible to amphotericin B and ketoconazole: 24 h (P < 0.05) and 48 h (P < 0.001). Furthermore, other azoles showed the same activities compared with ketoconazole against both planktonic and adherent cells. Overall, the data demonstrate the usefulness of the XTT tetrazolium assay in describing comparisons of the susceptibility profiles for both planktonic and adherent synchronous yeast phase C. albicans in vitro.

Changes in internal and external pH accompanying growth of Candida albicans: studies of non-dimorphic variants

Non-dimorphic variants of Candida albicans, which were unable to form germ tubes or mature hyphae in media containing amino acids, glucose and salts or N-acetylglucosamine or serum, were prepared from two hyphal positive laboratory strains using a physical separation method. The hyphal-minus phenotype was stable and may be due to mutations or phenotypic variation. The variant strains maintained their internal pH within narrower bounds as compared to their parental wild-types. When exposed to conditions that normally supported the induction of germ tubes the cytoplasmic pH of the wild type strains increased from 6.8 to over pH 8.0 within 5 min while in the variants the rise in internal pH was only about 0.3 pH units. The wild type strains acidified the growth medium more rapidly than the variants. The results suggest that the control of internal pH is directly or indirectly associated with the regulation of dimorphism. The variants had unaltered cell volumes and specific growth rates. The hyphal-minus phenotype was however fully reversible since revertants occurred spontaneously on serum containing agar.