In Vitro Testing of Aspergillus fumigatus Clinical Isolates for Susceptibility to Voriconazole,Amphotericin B and Itraconazole: Comparison of Sensititre versus NCCLS M38-A Using Two Different Inocula

Abstract

Voriconazole, amphotericin B and itraconazole were tested In Vitro against 18 strains of Aspergillus fumigatus isolated from cystic fibrosis patients. Susceptibility was tested with the broth microdilution method (M38-A protocol- NCCLS). Results of this reference method were compared with those of an experimental commercial microdilution broth method (Sensititre). Two different inocula, prepared from 2- and 7-day cultures, were used. Minimum inhibitory concentrations (MICs) of the reference method ranged from 0.25 to 2 μg/ml for voriconazole, 0.06 to 1 μg/ml for amphotericin B, 0.016 to >16 μg/ml for itraconazole. There were no significant differences in the MIC ranges or MIC₉₀ values obtained with the two testing methods or with the two types of inocula. These findings confirm the good In Vitro activity of voriconazole, itraconazole and amphotericin B against A. fumigatus. They also indicate that reliable susceptibility data can be generated more rapidly by commercial systems and use of 2-day cultures for inoculum preparation.     

Susceptibility profile and epidemiological cut‐off values of Cryptococcus neoformans species complex from Argentina

Epidemiological cut‐off values (ECVs) based on minimal inhibitory concentration (MIC) distribution have been recently proposed for some antifungal drug/Cryptococcus neoformans combinations. However, these ECVs vary according to the species studied, being serotypes and the geographical origin of strains, variables to be considered. The aims were to define the wild‐type (WT) population of the C. neoformans species complex (C. neoformans) isolated from patients living in Argentina, and to propose ECVs for six antifungal drugs. A total of 707 unique C. neoformans isolates obtained from HIV patients suffering cryptococcal meningitis were studied. The MIC of amphotericin B, flucytosine, fluconazole, itraconazole, voriconazole and posaconazole was determined according to the EDef 7.2 (EUCAST) reference document. The MIC distribution, MIC₅₀, MIC₉₀ and ECV for each of these drugs were calculated. The highest ECV, which included ≥95% of the WT population modelled, was observed for flucytosine and fluconazole (32 μg ml^?1 each). For amphotericin B, itraconazole, voriconazole and posaconazole, the ECVs were: 0.5, 0.5, 0.5 and 0.06 μg ml^?1 respectively. The ECVs determined in this study may aid in identifying the C. neoformans strains circulating in Argentina with decreased susceptibility to the antifungal drugs tested.     

In vitro susceptibility of Cryptococcus neoformans clinical isolates from Egypt to seven antifungal drugs

The in vitro susceptibility of 29 clinical isolates of Cryptococcus neoformans to fluconazole, miconazole, itraconazole, ketoconazole, flucytosine, nystatin and amphotericin B was tested by broth and colorimetric microdilution methods. Most of the isolates showed uniform patterns of susceptibility to the used antifungal agents. Only three isolates exhibited resistance [fourfold or greater rise in the minimum inhibitory concentrations (MICs)] to the tested antifungal drugs. The MIC50 and MIC90 were 0.5-8 mg l(-1) for 5-flucytosine, 0.2-8.25 mg l(-1) for nystatin, 0.5-16 mg l(-1) for fluconazole and 0.2-12.5 mg l(-1) for miconazole. However, MIC50 and MIC90 were in narrow range for the clinical yeast isolates in both methods used and showed 0.5-1 mg l(-1) for amphotericin B and 0.016-0.25 mg l(-1) for both ketoconazole and itraconazole. The combination of fluconazole plus flucytosine showed greater synergistic and fungicidal activity compared with that of fluconazole plus amphotericin B or the use of individual drugs.     

Emergence of Resistance to Amphotericin B and Triazoles in Candida glabrata Vaginal Isolates in a Case of Recurrent Vaginitis

Abstract

Emergence of resistance to triazoles and amphotericin B in Candida glabrata vaginal isolates is documented by Etest. During the 18-month follow-up of a case of vaginitis, 14 consecutive isolates of C. glabrata were examined. The isolates exhibited development of in vitro resistance beginning with itraconazole (>32 μg/ml), followed by fluconazole (>256 μg/ml), amphotericin B (>32 μg/ml), and voriconazole (>32 μg/ml). The DNA sequence analyses and finger printing of the isolates strongly suggest that our patient remained colonized with a single strain. The report underscores the propensity of C. glabrata to acquire resistance during antifungal therapy and the importance of susceptibility testing in the management of infections caused by this species.     

Antifungal activity of miconazole against recent Candida strains

Miconazole (MICON) has long been used for the topical treatment of mucosal candidiasis. However, the preponderance of MICON susceptibility data was generated before standard methodology was established, and prior to the emergence of fluconazole (FLU)‐resistant strains. The objective of this study was to determine the antifungal activity of MICON and comparators against recent clinical isolates of Candida spp. using standard Clinical and Laboratory Standards Institute methodology. One hundred and fifty isolates, consisting of 25 strains each of Candida albicans, C. krusei, C. glabrata, C. tropicalis, C. parapsilosis and C. dubliniensis, were tested. Of these, twenty‐two strains were known to be FLU‐resistant. Minimum inhibitory concentrations (MICs) were determined for MICON, amphotericin B (AM), caspofungin (CAS), clotrimazole (CLOT), FLU, itraconazole (ITRA), nystatin (NYS) and voriconazole (VOR). MICON demonstrated potent inhibitory activity against all of the strains tested. The MIC₉₀ for MICON was 0.12 μg ml^?1 against FLU‐susceptible strains, which was comparable to that of AM, CAS, CLOT, ITRA and VOR. The MICON MIC₉₀ against FLU‐resistant strains was 0.5 μg ml^?1, which was 12‐fold lower than the FLU MIC₉₀. Our study showed that MICON possesses potent activity against all of the Candida isolates tested, including those with known FLU resistance. This indicates that recent clinical isolates remain susceptible to this antifungal and that MICON could be used as first‐line treatment for oropharyngeal candidiasis.     

In vitro evaluation of antifungal susceptibility and keratinase,elastase, lipase and DNase activities of different dermatophyte species isolated from clinical specimens in Iran

The aims of this study were to evaluate the enzymatic activity of various dermatophyte species and their antifungal susceptibility profiles. A total of 60 dermatophyte isolates, including Trichophyton mentagrophytes, Trichophyton rubrum, Microsporum canis and Microsporum gypseum, were examined. Fungal isolates were analysed for the production of keratinase, lipase, elastase and deoxyribonuclease (DNase). A broth microdilution method was performed on the basis of M38‐A2 Clinical and Laboratory Standards Institute (CLSI) guidelines. T. mentagrophytes, M. canis and M. gypseum isolates were capable of producing keratinase, lipase, elastase and DNase, while T. rubrum isolates were elastase negative. The highest mean diameter of the clear zone around the colonies (PZ) was associated with keratinase (PZ: 4.56 ± 1.29 mm), followed by lipase (PZ: 1.53 ± 0.90 mm), DNase (PZ: 0.65 ± 0.54 mm) and elastase (PZ: 0.22 ± 0.27 mm) (P < 0.05). The mean minimum inhibitory concentration 90 (MIC₉₀) of all strains were as follows: itraconazole (MIC₉₀: 0.28 ± 0.31 μg ml^?1), ketoconazole (MIC₉₀: 0.48 ± 0.51 μg ml^?1), griseofulvin (MIC₉₀: 0.86 ± 1.00 μg ml^?1) and fluconazole (MIC₉₀: 18.57 ± 20.10 μg ml^?1). Dermatophyte isolates had higher keratinolytic activity than other enzymes. Itraconazole was the most effective antifungal drug and fluconazole had the poorest activity.     

In vitro antifungal activity of amphotericin B and 11 comparators against Aspergillus terreus species complex

Aspergillus terreus infections are difficult to treat because of the intrinsic resistance to amphotericin B, and higher mortality compared to infections caused by other Aspergillus species. The aim of the present study was to determine the in vitro antifungal activity of amphotericin B and 11 comparators against clinical (n = 36) and environmental (n = 45) A. terreus isolates. In vitro antifungal susceptibility was performed using the CLSI M38‐A2 procedure. Amphotericin B exhibited the highest MICs (MIC range, 0.125‐4 μg/mL; MIC₉₀, 2 μg/mL), followed by terbinafine (MIC range, 0.002‐1 μg/mL; MIC₉₀, 1 μg/mL). Only one isolate (1/81) showed amphotericin B MIC above the epidemiologic cut‐off value (ECV; 4 μg/mL). None of the isolates had a MIC of ≥ ECV for voriconazole, itraconazole and posaconazole. The reasons for the difference in amphotericin B susceptibility patterns between studies remain unknown. The genetic and species diversity, clinical, environmental and ecological factors in Terrei section on various amphotericin B susceptibility profiles in different countries should be considered more as the main reasons associated with these differences.     

Comparative In Vitro Activity of Cefepime against Nosocomial Isolates

Abstract

Cefepime, a new parenteral cephalosporin, was evaluated for its In Vitro antibacterial activity in comparison with other broad-spectrum antibiotics against a total of 445 recently isolated microorganisms of nosocomial origin. Cefepime was highly active against all species of Enterobacteriaceae with minimum inhibitory concentrations (MIC₉₀s) ranging from 0.25-8 μ/ml. Cefepime showed moderate activity against Acinetobacter spp (MIC₅₀ and MIC₉₀, 16 μ/ml) but its activity was superior to that of any drug tested, except imipenem. Against Pseudomonas aeruginosa its activity was comparable to that of ceftazidime and was greater than that of cefotaxime, aztreonam, ciprofloxacin and aminoglycosides. Of all the agents tested, imipenem was the most active compound. Cefepime was active against Staphylococcus aureus and coagulase-negative methicillin-susceptible staphylococci but it had no activity against methicillin-resistant staphylococci and enterococci.     

In vitro interactions between amphotericin B and other antifungal agents and rifampin against Fusarium spp.

Fusarium species are common hyaline soil saprophytes and plant pathogens that are opportunistic fungal pathogens of immunocompromised patients. The treatment for fusariosis remains uncertain with an unfavourable prognosis; new possibilities for treatment, such as various synergistic drug interactions, must be uncovered. In this study, we evaluated the in vitro interactions of amphotericin B with caspofungin, ketoconazole, 5‐flucytosine, itraconazole, miconazole, rifampin, fluconazole, terbinafine and voriconazole against isolates of Fusarium spp. using the chequerboard method with interactions evaluated by fractional inhibitory concentration indices. The highest percentages of synergistic interactions were observed for the combinations of amphotericin B and caspofungin (68.7%), amphotericin B and rifampin (68.7%), amphotericin B plus 5‐flucytosine (59.3%) and amphotericin B with voriconazole (37.5%). The pattern of susceptibility to antifungal agents among Fusarium species and their consequence on the effects of drug combinations are also discussed.     

Activity of Plazomicin (ACHN-490) against MDR clinical isolates of Klebsiella pneumoniae,Escherichia coli,and Enterobacter spp. from Athens,Greece

Abstract

The in vitro activity of plazomicin was evaluated against 300 multidrug resistant (MDR) (carbapenemase and/or ESBL-producing) isolates from four hospitals in Athens, an area where carbapenemase-producing organisms are endemic. Most of the isolates were also resistant to the legacy aminoglycosides with the MIC₅₀/MIC₉₀ to tobramycin, amikacin and gentamicin being 32/>32, 32/>32 and 4/>8 μg/ml, respectively. ACHN-490 retained activity (MICs?4 μg/ml) against all isolates of Klebsiella pneumoniae, Escherichia coli, and Enterobacter spp. tested with MIC₅₀ and MIC₉₀ of 1 and 2 μg/ml, respectively, irrespective of their MDR phenotype and it represents a promising alternative for the treatment of the most problematic Gram-negative pathogens.     

Minimum inhibitory concentrations of amphotericin B against Candida krusei isolates from a French teaching hospital laboratory: a retrospective study over 8 years

Recent studies have shown decreased susceptibility of Candida krusei to amphotericin B (AmB), in addition to its inherent resistance to fluconazole. The susceptibility of C. krusei to AmB was studied in the Parasitology–Mycology laboratory of Grenoble Teaching Hospital, France. Between 2003 and 2011, we analysed 200 C. krusei isolates from 130 patients. The isolates were mainly collected in intensive care, cardio‐thoracic and cancer/haematology units. Minimum inhibitory concentrations (MICs) were determined by the E‐test method. The modal MIC was 0.5 μg ml^?1; the MIC₅₀ and MIC₉₀ (MICs encompassing 50% and 90% of all isolates tested, respectively) were 0.5 μg ml^?1 and 1 μg ml^?1. The Cuzick’s and Kendall’s tests showed a significant increase in MIC values between 2003 and 2011 (P = 0.001 and P ≤ 0.001, respectively), regardless of age or gender. No statistical difference was reached with these tests when the first 100 or 50 data were excluded. Despite the increase observed in the first period of the study, our results confirm the low AmB MICs reported in previous studies. However, some authors have recently reported much higher MICs. This discrepancy cannot be explained by method biases and could reflect C. krusei epidemiological differences among populations.     

In vitro susceptibility patterns of clinically important Trichophyton and Epidermophyton species against nine antifungal drugs

Despite the common, worldwide, occurrence of dermatophytes, little information is available regarding susceptibility profiles against currently available and novel antifungal agents. A collection of sixty‐eight clinical Trichophyton species and Epidermophyton floccosum were previously identified and verified to the species level by sequencing the internal transcribed spacer (ITS) regions of rDNA. MICs of amphotericin B, fluconazole, itraconazole, voriconazole, posaconazole, isavuconazole, terbinafine and MECs of caspofungin and anidulafungin were performed based on CLSI M38‐A2. The resulting MIC₉₀s of all strains were, in increasing order, as follows: terbinafine (0.063 mg l^?1); posaconazole (1 mg l^?1); isavuconazole and anidulafungin (2 mg l^?1); itraconazole, voriconazole, amphotericin B, and caspofungin (4 mg l^?1) and fluconazole (>64 mg l^?1). These results confirm that terbinafine is an excellent agent for treatment of dermatophytosis due to T. rubrum, T. mentagrophytes, T. verrucosum, T. schoenleinii and E. floccosum. In addition, the new azoles POS and ISA are potentially useful antifungals to treat dermatophytosis. However, the clinical effectiveness of these novel antifungals remains to be determined.     

Antifungal drug susceptibility of Cryptococcus neoformans from clinical sources in Nairobi, Kenya

The serotypes and mating types of 80 clinical isolates of Cryptococcus neoformans from Kenya were studied and subjected to broth microdilution susceptibility testing to amphotericin B (AMP), flucytosin, fluconazole (FLC), itraconazole (ITC) and miconazole (MCZ). The isolates included C. neoformans var. grubii- 75 of 80 (serotype A; 93.7%), C. neoformans var. neoformans- three of 80 (3.8%) and C. neoformans var. gattii- two (serotype B; 2.5%). Mating experiment confirmed all the isolates to be alpha-mating type. Seventy-eight (97.5%) of the isolates had minimum inhibitory concentration (MIC) of < or =0.5 microg ml(-1) to AMP and at 1 microg ml(-1), 100% of the isolates were inhibited. Flucytosin resistance was observed in 21% with MIC in which 90% of the isolates were inhibited (MIC90) of 64 microg ml(-1). Only 23.8% of the strains were susceptible to FLC with 65% susceptible dose-dependent (SDD) and 11.2% resistant. Itraconazole susceptibility was 61.3% while the rest were either SDD or resistant. The MIC90 for ITC and MCZ were 0.5 and 2 microg ml(-1) respectively. The study reports the serotypes, mating types and highlights the existence of azoles resistance in C. neoformans in Nairobi which calls for antifungal drug resistance surveillance as prophylactic use of FLC increases because of human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) epidemic in sub-Saharan Africa.     

In vitro activities of voriconazole (UK-109, 496), fluconazole, itraconazole and amphotericin B against 132 non-albicans bloodstream yeast isolates (CANARI study)

The aim was to evaluate the in vitro activity of voriconazole compared with those of amphotericin B, itraconazole and fluconazole against 132 bloodstream isolates of Candida non-albicans and Saccharomyces cerevisiae species. The minimal inhibitory concentrations (MICs) were determined by an adapted National Committee for Clinical Laboratory Standards (NCCLS) M27-A method using RPMI 1640 as test medium supplemented with 2% glucose. MIC end-points were determined with a spectrophotometer after incubation for 48 h at 35 degrees C. Optical density data were used for the calculation of the MIC end-points. For amphotericin B, the end-point was defined as the minimal antifungal concentration that exerts 90% inhibition compared with the control well growth. For the azoles, the end-points were determined at 50% inhibition of growth. Amphotericin B is highly active with 97% of isolates inhibited by < or =1 microg ml(-1). Decreased susceptibility or resistance to fluconazole was the rule among C. krusei, which is intrinsically resistant to fluconazole. For C. glabrata isolates, resistance to fluconazole and itraconazole was measured in 13% and 17% of the isolates respectively. Voriconazole was quite active in vitro against all the isolates with a MIC90% of < or =1 microg ml(-1) and we conclude that it may be useful in the treatment of non-albicans bloodstream infections.     

In vitro activity (MIC and MFC) of voriconazole, amphotericin B, and itraconazole against 192 filamentous fungi: the GISIA-2 study

We evaluated the in vitro activity of voriconazole, amphotericin B, and itraconazole against 192 clinical mould isolates recovered in twenty Italian microbiology laboratories. The vast majority of isolates belonged to the genus Aspergillus (94.2%) with A. fumigatus (58.3%) being the most frequently isolated species. Antifungal susceptibility testing was performed using the broth microdilution method defined by the CLSI M38-A standard, and results were compared to those obtained with Sensititre panels. Aspergillus flavus ATCC 204304 was employed as reference strain and results were within all expected ranges. Voriconazole's activity against the 192 mould isolates was comparable to that of amphotericin B and itraconazole: voriconazole MIC90 (CLSI 1 microg/ml, Sensititre 1 microg/ml), itraconazole MIC90 (CLSI 0.5 microg/ml, Sensititre 0.5 microg/ml), amphotericin B MIC90 (CLSI 1 microg/ml, Sensititre 1 microg/ml). In conclusion, these in vitro data highlight voriconazole's broad spectrum activity against filamentous fungi and support its use as a first line agent for the treatment of fungal diseases.     

In vitro susceptibilities of Malaysian clinical isolates of Cryptococcus neoformans var. grubii and Cryptococcus gattii to five antifungal drugs

The in vitro susceptibilities of Malaysian clinical isolates of Cryptococcus neoformans var. grubii and C . gattii to five antifungal drugs (amphotericin B, flucytosine, fluconazole, itraconazole and ketoconazole) were determined using the Etest method. None of the Malaysian isolates was resistant to amphotericin B and ketoconazole. Isolates resistant to flucytosine, fluconazole and itraconazole were observed in this study. Minimum inhibition concentrations (MICs) of > or = 32 microg ml(-1) against flucytosine, > or = 64 microg ml(-1) against fluconazole and > or = 1 microg ml(-1) against itraconazole were noted in four (8.3%), two (4.2%) and one (2.1%) isolates respectively. There was no significant difference in the MICs for both Cryptococcus species (P > 0.05), indicating that C. gattii was as susceptible as var. grubii to all the antifungal drugs tested. No significant difference in the MICs for both Cryptococcus species collected from 1980 to 1990 and 2002 to 2004 were observed (P > 0.05).     

In Vitro Activity of Cefpirome (HR 810) against Enterococci and Staphylococci

Summary

The inhibitory activity of cefpirome (HR 810), a new cephalosporin derivative for parenteral use, was tested by agar dilution methods against Enterococcus faecatis (100 strains), Staphylococcus aureus (40 strains) and coagulase-negative staphylococcal species (60 strains) in comparison with other beta-lac ta m antibiotics.

For E. faecalls, the cefpirome minimum inhibitory concentration (MIC) range was 2-128 μg/ml, with an MIC,, of 8 μg/ml, and an MIC₉₀, of 64 μg/ml. The optimal bactericidal activity against strains with MICs of ≤ 8 μg/ml occurred at 2-4 times the MIC, and the reduction in the initial inoculum was 99.9-99.7% after 24 h incubation at these concentrations.

Mec gene-negative staphylococci (both S. aureus and coagulase- negative species) had cefpirome MICs of 0.25-2 μg/ml (MIC₅₀ 0.5 μg/ml, MIC₉₀ 1 μg/ml). Mec gene-positive strains had MICs of 0.5-128 μg/ml (MIC₅₀ 2 μg/ml, MIC₉₀ 32 μg/ml). Strains with borderline resistance to oxacillin which did not harbor the mec gene and which were susceptible to cefpirome maintained their susceptibility even when high-density inocula were used and after several passages in media containing the antibiotic.

These studies present some potential advantages of cefpirome over other cephalosporins in the inhibitory activity against Gram-positive cocci.     

In vitro antifungal activity of Indian liposomal amphotericin B against clinical isolates of emerging species of yeast and moulds,and its comparison with amphotericin B deoxycholate,voriconazole, itraconazole and fluconazole

Fungisome^TM is a liposomal preparation of amphotericin B (AMB), already marketed in India. However, its antifungal activity has not been evaluated against a wide range of fungal pathogens. The study was planned to elucidate the in vitro antifungal activity of Fungisome^TM against wide range of fungi and compare it with AMB deoxycholate (AMB‐d), voriconazole (VOR), itraconazole (ITR) and fluconazole (FLU). Minimum inhibitory concentrations (MICs) of the drugs were determined for 262 clinical fungal isolates, including yeast, dimorphic and filamentous fungi, by broth microdilution method approved by Clinical and Laboratory Standards Institute, USA (yeast, M27‐A3; filamentous fungi, M38‐A2). The MIC_90s of Fungisome^TM were 0.125, 0.5 and 0.25 mg l^?1 against yeast, filamentous and dimorphic fungi respectively. In comparison, MIC_90s of AMB‐d, FLU, ITR and VOR were 1, 1 and 1 mg l^?1 (AMB‐d), 4, 64 and 64 mg l^?1 (FLU), 1, 16 and 16 mg l^?1 (ITR) and 0.5, 4 and 16 mg l^?1 (VOR) against yeast, filamentous and dimorphic fungi respectively. The MIC of Fungisome^TM was two to 16‐fold lower than AMB‐d. These results reveal an efficient in vitro activity of Fungisome^TM.     

Emergence of resistance to amphotericin B and triazoles in Candida glabrata vaginal isolates in a case of recurrent vaginitis

Emergence of resistance to triazoles and amphotericin B in Candida glabrata vaginal isolates is documented by Etest. During the 18-month follow-up of a case of vaginitis, 14 consecutive isolates of C. glabrata were examined. The isolates exhibited development of in vitro resistance beginning with itraconazole (>32 microg/ml), followed by fluconazole (>256 microg/ml), amphotericin B (>32 microg/ml), and voriconazole (>32 microg/ml). The DNA sequence analyses and finger printing of the isolates strongly suggest that our patient remained colonized with a single strain. The report underscores the propensity of C. glabrata to acquire resistance during antifungal therapy and the importance of susceptibility testing in the management of infections caused by this species.