Susceptibility Testing of Fungi and Correlation with Clinical Outcome

Antimicrobial and anti-biofilm properties of oleuropein against Escherichia coli and fluconazole-resistant isolates of Candida albicans and Candida glabrata

BACKGROUND

Side effects associated with antimicrobial drugs, as well as their high cost, have prompted a search for low-cost herbal medicinal substances with fewer side effects. These substances can be used as supplements to medicine or to strengthen their effects. The current study investigated the effect of oleuropein on the inhibition of fungal and bacterial biofilm in-vitro and at the molecular level.

MATERIALS AND METHODS

In this experimental study, antimicrobial properties were evaluated using microbroth dilution method. The effect of oleuropein on the formation and eradication of biofilm was assessed on 96-well flat bottom microtiter plates and their effects were observed through scanning electron microscopy (SEM). Its effect on key genes (Hwp1, Als3, Epa1, Epa6, LuxS, Pfs) involved in biofilm formation was investigated using the quantitative reverse transcriptase-polymerase chain reaction (RT-qPCR) method.

RESULTS

The minimum inhibitory concentration (MIC) and minimum fungicidal/bactericidal concentration (MFC/MBC) for oleuropein were found to be 65 mg/ml and 130 mg/ml, respectively. Oleuropein significantly inhibited biofilm formation at MIC/2 (32.5 mg/ml), MIC/4 (16.25 mg/ml), MIC/8 (8.125 mg/ml) and MIC/16 (4.062 mg/ml) (p < 0.0001). The anti-biofilm effect of oleuropein was confirmed by SEM. RT-qPCR indicated significant down regulation of expression genes involved in biofilm formation in Candida albicans (Hwp1, Als3) and Candida glabrata (Epa1, Epa6) as well as Escherichia coli (LuxS, Pfs) genes after culture with a MIC/2 of oleuropein (p < 0.0001).

CONCLUSIONS

The results indicate that oleuropein has antifungal and antibacterial properties that enable it to inhibit or destroy the formation of fungal and bacterial biofilm.

Evaluation of the Drug Utilization Pattern of Pre and Post Operative Medicines used in Surgical Department: A Prospective Observational Study

Background:

Surgery is the art of treating lesions and malformations of the human body which involves various surgical techniques. Various classes of drugs are being used in the surgery but unfortunately, the drug utilization pattern of these drugs particularly in developing countries like India is still unsatisfactory. Thus, there is a need to conduct drug utilization studies of various medicines used in the surgical department.

Objective:

The main objective of the current study is to evaluate the drug utilization pattern of pre and post- operative medicines used in surgery to promote the rational use of medicines.

Material and Methods:

A prospective observational study was carried out over a period of 6 months (November 2017 to April 2018) from in Global Hospital, Jalandhar, Punjab, India. A consent form has been designed and filled by the patients after explaining the aims and objectives of the study. The case record form (CRF) has been designed to collect all the relevant information from the surgery patients.

Results:

A total of 271 cases have been reported and evaluated. 58.0% of patients were female and 42.0% of patients were male. The most common surgery was nailing, plating and knee replacement. In pre and post-operative procedures, the most common medicines prescribed were a combination of antimicrobials and antacids followed by anti-emetics, analgesics.

Conclusion:

The prescribed medicines were less from the National Essential Medical List (EML) which should be increase in future.

Study of Pathogens of Fungal Keratitis and the Sensitivity of Pathogenic Fungi to Therapeutic Agents with the Disk Diffusion Method

PURPOSE/AIM OF THE STUDY

To identify the causative fungi of fungal keratitis, test their susceptibility to antifungal agents with the disk diffusion method and study the relationship between the organisms, the inhibition zones and the clinical outcomes.

MATERIALS AND METHODS

535 patients with fungal keratitis in one eye were included in this study. Pathogenic fungi were isolated by corneal scraping, identified by fungal cultivation and subjected to drug sensitivity tests conducted with the disk diffusion method. The patients were treated initially with voriconazole, terbinafine and natamycin eye drops for one week. Further treatment continued using the most effective drug according to the drug sensitivity results. The patients were followed up every week until three months after cured. The inhibition zones of fungi cultured with voriconazole, terbinafine and natamycin were compared. The relationship between inhibition zones and organism, organism and treatment results measure, and each treatment results measure and inhibition zones were evaluated.

RESULTS

Of 535 patients, 53.84%, 19.25% and 26.91% were infected with Aspergillus, Fusarium and other fungi, respectively. Keratitis patients infected with Aspergillus keratitis had the worst outcome. The size of the inhibition zones of Aspergillus spp., Fusarium spp. and other fungal genera differed significantly in response to voriconazole, terbinafine and natamycin. The inhibition zone associated with natamycin correlated significantly with the clinical outcome of fungal keratitis (OR = 0.925), but no other such correlations were found for the other drugs tested.

CONCLUSIONS

Aspergillus and Fusarium were the predominant pathogenic genera causing fungal keratitis in our patients. Among the causative fungi, infections due to Aspergillus spp. were associated with the worst outcomes. The inhibition zones of fungal isolates in response to natamycin significantly correlated with the treatment outcomes of keratitis. Specifically, the smaller the natamycin inhibition zone, the lower the probability that the fungal keratitis had been eliminated.

Combination treatment of invasive fungal infections

The persistence of high morbidity and mortality from systemic fungal infections despite the availability of novel antifungals points to the need for effective treatment strategies. Treatment of invasive fungal infections is often hampered by drug toxicity, tolerability, and specificity issues, and added complications often arise due to the lack of diagnostic tests and to treatment complexities. Combination therapy has been suggested as a possible approach to improve treatment outcome. In this article, we undertake a historical review of studies of combination therapy and also focus on recent studies involving newly approved antifungal agents. The limitations surrounding antifungal combinations include nonuniform interpretation criteria, inability to predict the likelihood of clinical success, strain variability, and variations in pharmacodynamic/pharmacokinetic properties of antifungals used in combination. The issue of antagonism between polyenes and azoles is beginning to be addressed, but data regarding other drug combinations are not adequate for us to draw definite conclusions. However, recent data have identified potentially useful combinations. Standardization of assay methods and adoption of common interpretive criteria are essential to avoid discrepancies between different in vitro studies. Larger clinical trials are needed to assess whether combination therapy improves survival and treatment outcome in the most seriously debilitated patients afflicted with life-threatening fungal infections.

Effects of antifungal interventions on the outcome of experimental infections with phenotypic switch variants of Cryptococcus neoformans

In cryptococcal infection, phenotypic switching from a smooth to a mucoid variant can occur in vivo, producing variants with enhanced virulence that are subsequently selected and affect the outcome of infection. Here, we demonstrate that antifungal treatment of the chronically infected host can promote this phenomenon. Amphotericin B treatment reduces fungal burden less effectively in mucoid variant-infected than in smooth variant-infected mice. Consequently, amphotericin B treatment resulted in a more pronounced prolongation of survival in smooth variant-infected than in mucoid variant-infected mice (20 versus 42 days; P < 0.05). Administration of anticapsular monoclonal antibody mediated better protection in smooth variant-infected than in mucoid variant-infected mice, although a protective effect was not consistently observed at all doses. Most interestingly, both antifungal drug therapy and administration of anticapsular monoclonal antibody promoted the selection of mucoid variants in smooth variant-infected mice, a phenomenon manifested by a statistically higher percentage of mucoid colonies in smooth variant-infected mice than in nontreated control mice. This finding suggests that both chemotherapeutic and immunological antifungal interventions may promote the selection of the more virulent mucoid variant, which could affect the outcome of infection in chronically infected hosts.

Identification of Antifungal Compounds from Ferula persica. var. persica

In this investigation, the antifungal activities of chloroform and water extracts of Ferula persica. var. persica. Willd. roots were studied using conventional disk diffusion method. The chloroform extract showed antifungal activity at concentrations tested. Bioassay-guided fractionation study of the chloroform extract by preparative thin-layer chromatography (PTLC) detected two antifungal fractions that were effective against some fungi. Using conventional spectroscopy methods, the active fractions were identified as t-butyl 3-[(1-methylpropyl)dithio]-2-propenyl malonate (persicasulfide A) (1) and t.-butyl 3-[(1-methylthiopropyl)dithio]-2-propenyl malonate (persicasulfide B) (2), recently isolated from Ferula persica. var. latisecta.. These compounds showed the most potent antifungal activity with MICs of ≤ 62.5 µg/ml against filamentous fungi.

Antifungal susceptibility survey of 2,000 bloodstream Candida isolates in the United States

Candida bloodstream isolates (n = 2,000) from two multicenter clinical trials carried out by the National Institute of Allergy and Infectious Diseases Mycoses Study Group between 1995 and 1999 were tested against amphotericin B (AMB), flucytosine (5FC), fluconazole (FLU), itraconazole (ITR), voriconazole (VOR), posaconazole (POS), caspofungin (CFG), micafungin (MFG), and anidulafungin (AFG) using the NCCLS M27-A2 microdilution method. All drugs were tested in the NCCLS-specified RPMI 1640 medium except for AMB, which was tested in antibiotic medium 3. A sample of isolates was also tested in RPMI 1640 supplemented to 2% glucose and by using the diluent polyethylene glycol (PEG) in lieu of dimethyl sulfoxide for those drugs insoluble in water. Glucose supplementation tended to elevate the MIC, whereas using PEG tended to decrease the MIC. Trailing growth occurred frequently with azoles. Isolates were generally susceptible to AMB, 5FC, and FLU. Rates of resistance to ITR approached 20%. Although no established interpretative breakpoints are available for the candins (CFG, MFG, and AFG) and the new azoles (VOR and POS), they all exhibited excellent antifungal activity, even for those strains resistant to the other aforementioned agents.

In vitro susceptibility testing of ciclopirox, terbinafine, ketoconazole and itraconazole against dermatophytes and nondermatophytes, and in vitro evaluation of combination antifungal activity

BACKGROUND

With the development of newer antifungal agents with activity against both yeasts and filamentous fungi, there is an increased need to develop and standardize in vitro assays that will evaluate the activity of antimycotics against filamentous fungi. In vitro analysis of antifungal activity of these agents would also allow for the comparison between different antimycotics, which in turn may clarify the reasons for lack of clinical response or serve as an effective therapy for patients with chronic infection.

OBJECTIVES

To determine the in vitro susceptibility of fungal organisms to ciclopirox, terbinafine, ketoconazole and itraconazole and to evaluate the in vitro activity and mode of interaction of ciclopirox in combination with either terbinafine or itraconazole.

MATERIALS AND METHODS

In the minimum inhibitory concentration (MIC) study 133 strains were evaluated, including dermatophytes (110 strains; 98 from Trichophyton spp.), Candida spp. (14 strains) and nondermatophyte moulds (nine strains). In vitro susceptibility testing was conducted in microbroth dilutions based on the National Committee for Clinical Laboratory Standards (NCCLS) M27-A proposed standard. The testing MIC ranges were 0.003-2 microg mL-1 for ciclopirox and terbinafine, and 0.06-32 microg mL-1 for itraconazole and ketoconazole. For inoculum preparation, dermatophytes were grown on Heinz oatmeal cereal agar slants. Inoculum suspensions of dermatophytes were diluted in RPMI 1640 (Sigma-Aldrich) with the desired final concentration being 2-5 x 103 c.f.u. mL-1. Once inoculated, the microdilution plates were set up according to the NCCLS M27-A method, incubated at 35 degrees C, and read visually following 7 days of incubation. For azole agents, the MIC was the lowest concentration showing 80% growth inhibition; for terbinafine and ciclopirox, the MIC was the lowest concentration showing 100% growth inhibition. In the synergy studies, 29 strains from nondermatophyte species were evaluated using a checkerboard microdilution method. The concentrations tested were: 0 and 0.06-32 microg mL-1 for itraconazole, and 0 and 0.003-4 microg mL-1 for both terbinafine and ciclopirox. Modes of interaction between drugs were classified as synergism, additivism, antagonism or indifference based on fractional inhibitory concentration index values (FIC index). Synergism was defined as an FIC index of < or = 0.50, additivity as an FIC index of < or = 1.0, and antagonism as an FIC index of > or = 2.0. The drug combination was interpreted as indifferent if neither of the drugs had any visible effect on the presence of the other drug.

RESULTS

In the MIC study, the dermatophyte MIC values (microg mL-1) (mean +/- SEM) were: ciclopirox (0.04 +/- 0.02), terbinafine (0.04 +/- 0.23), itraconazole (2.28 +/- 7.42) and ketoconazole (0.83 +/- 1.99). The yeast MIC values (microg mL-1) (mean +/- SEM) were: ciclopirox (0.05 +/- 0.02), terbinafine (1.77 +/- 0.58), itraconazole (0.18 +/- 0.27) and ketoconazole (0.56 +/- 0.60). The non-dermatophyte fungi MIC values (microg mL-1) (mean +/- SEM) were: ciclopirox (1.04 +/- 2.62), terbinafine (1.04 +/- 0.95), itraconazole (17.87 +/- 16.75) and ketoconazole (10.69 +/- 13.09). In the synergy study, with ciclopirox in combination with terbinafine, mainly a synergistic or additive reaction was observed; there were no cases of antagonism. For ciclopirox in combination with itraconazole, there were some instances of additivism or synergism, with indifference in the majority of instances; there were no cases of antagonism.

CONCLUSIONS

In vitro susceptibility testing indicates that ciclopirox may have a broad antimicrobial profile including dermatophytes, yeasts and other nondermatophytes. Terbinafine is extremely potent against dermatophytes. In vitro evaluation of activity of ciclopirox and terbinafine suggests many instances of synergy or additivism; for ciclopirox and itraconazole there may be indifference, synergy or additivism.

In vitro pharmacodynamic properties of three antifungal agents against preformed Candida albicans biofilms determined by time-kill studies

We have examined the in vitro activities of fluconazole, amphotericin B, and caspofungin against Candida albicans biofilms by time-kill methodology. Fluconazole was ineffective against biofilms. Killing of biofilm cells was suboptimal at therapeutic concentrations of amphotericin B. Caspofungin displayed the most effective pharmacokinetic properties, with > or =99% killing at physiological concentrations.

Standardized method for in vitro antifungal susceptibility testing of Candida albicans biofilms

Candida albicans is implicated in many biomaterial-related infections. Typically, these infections are associated with biofilm formation. Cells in biofilms display phenotypic traits that are dramatically different from those of their free-floating planktonic counterparts and are notoriously resistant to antimicrobial agents. Consequently, biofilm-related infections are inherently difficult to treat and to fully eradicate with normal treatment regimens. Here, we report a rapid and highly reproducible microtiter-based colorimetric assay for the susceptibility testing of fungal biofilms, based on the measurement of metabolic activities of the sessile cells by using a formazan salt reduction assay. The assay was used for in vitro antifungal susceptibility testing of several C. albicans strains grown as biofilms against amphotericin B and fluconazole and the increased resistance of C. albicans biofilms against these antifungal agents was demonstrated. Because of its simplicity, compatibility with a widely available 96-well microplate platform, high throughput, and automation potential, we believe this assay represents a promising tool for the standardization of in vitro antifungal susceptibility testing of fungal biofilms.

Analysis of growth characteristics of filamentous fungi in different nutrient media

A microbroth kinetic model based on turbidity measurements was developed in order to analyze the growth characteristics of three species of filamentous fungi (Rhizopus microsporus, Aspergillus fumigatus, and Scedosporium prolificans) characterized by different growth rates in five nutrient media (antibiotic medium 3, yeast nitrogen base medium, Sabouraud broth, RPMI 1640 alone, and RPMI 1640 with 2% glucose). In general, five distinct phases in the growth of filamentous fungi could be distinguished, namely, the lag phase, the first transition period, the log phase, the second transition period, and the stationary phase. The growth curves were smooth and were characterized by the presence of long transition periods. Among the different growth phases distinguished, the smallest variability in growth rates among the strains of each species was found during the log phase in all nutrient media. The different growth phases of filamentous fungi were barely distinguishable in RPMI 1640, in which the poorest growth was observed for all fungi even when the medium was supplemented with 2% glucose. R. microsporus and A. fumigatus grew better in Sabouraud and yeast nitrogen base medium than in RPMI 1640, with growth rates three to four times higher. None of the media provided optimal growth of S. prolificans. The germination of Rhizopus spores and Aspergillus and Scedosporium conidia commenced after 2 and 5 h of incubation, respectively. The elongation rates ranged from 39.6 to 26.7, 25.4 to 20.2, and 16.9 to 9.9 microm/h for Rhizopus, Aspergillus, and Scedoporium hyphae, respectively. The germination of conidia and spores and the elongation rates of hyphae were enhanced in antibiotic medium 3 and delayed in yeast nitrogen base medium. In conclusion, the growth curves provide a useful tool to gain insight into the growth characteristics of filamentous fungi in different nutrient media and may help to optimize the methodology for antifungal susceptibility testing.

Correlation between in vitro and in vivo antifungal activities in experimental fluconazole-resistant oropharyngeal and esophageal candidiasis

Oropharyngeal and esophageal candidiasis (OPEC) is a frequent opportunistic mycosis in immunocompromised patients. Azole-resistant OPEC is a refractory form of this infection occurring particularly in human immunodeficiency virus (HIV)-infected patients. The procedures developed by the Antifungal Subcommittee of the National Committee for Clinical Laboratory Standards (NCCLS) are an important advance in standardization of in vitro antifungal susceptibility methodology. In order to further understand the relationship between NCCLS methodology and antifungal therapeutic response, we studied the potential correlation between in vitro susceptibility to fluconazole and in vivo response in a rabbit model of fluconazole-resistant OPEC. MICs of fluconazole were determined by NCCLS methods. Three fluconazole-susceptible (FS) (MIC, </=0.125 microgram/ml) and three fluconazole-resistant (FR) (MIC, >/=64 microgram/ml) isolates of Candida albicans from prospectively monitored HIV-infected children with OPEC were studied. FR isolates were recovered from children with severe OPEC refractory to fluconazole, and FS isolates were recovered from those with mucosal candidiasis responsive to fluconazole. Fluconazole at 2 mg/kg of body weight/day was administered to infected animals for 7 days. The concentrations of fluconazole in plasma were maintained above the MICs for FS isolates throughout the dosing interval. Fluconazole concentrations in the esophagus were greater than or equal to those in plasma. Rabbits infected with FS isolates and treated with fluconazole had significant reductions in oral mucosal quantitative cultures (P < 0.001) and tissue burden of C. albicans in tongue, soft palate, and esophagus (P < 0.001). In comparison, rabbits infected with FR isolates were unresponsive to fluconazole and had no reduction in oral mucosal quantitative cultures or tissue burden of C. albicans versus untreated controls. We conclude that there is a strong correlation between in vitro fluconazole susceptibility by NCCLS methods and in vivo response to fluconazole therapy of OPEC due to C. albicans.

The Role of Resistance Testing in Clinical Trial Design and Product Labelling: A Regulatory Perspective

Assays that attempt to characterize HIV susceptibility or resistance are among the latest technologies that are likely to impact HIV clinical trial design, antiretroviral drug development and patient management. However, at present the Food and Drug Administration (FDA) have yet to approve any phenotypic or genotypic HIV resistance assay and the role of resistance testing in clinical management of patients and in drug development is ill defined. In November 1999, the Division of Antiviral Drug Products at the FDA convened a meeting of its advisory committee to consider the available information about HIV resistance testing, and to generate some recommendations about how these assays could be utilized in anti-retroviral drug development. In addition, the committee was presented with several hypothetical regulatory scenarios in order to illustrate how HIV resistance testing might be incorporated in antiretroviral drug development and drug labelling. In this article, we discuss the regulatory history of resistance testing in antimicrobial drug development, the current use of resistance testing for antiretrovirals, as well as a summary of the hypothetical scenarios that were presented to the committee and the discussion of the committee members regarding those scenarios.

Antifungal susceptibility testing of dermatophytes: establishing a medium for inducing conidial growth and evaluation of susceptibility of clinical isolates

A standardized reference method for dermatophyte in vitro susceptibility testing is lacking. In a previous study, Norris et al. (H. A. Norris, B. E. Elewski, and M. A. Ghannoum, J. Am. Acad. Dermatol. 40(6, part 2):S9-S13) established the optimal medium and other growth variables. However, the earlier study did not address two issues: (i) selection of an optimal medium for conidial formation by dermatophytes and (ii) validation of the method with a large number of dermatophytes. The present study addresses these two points. To select which agar medium best supported conidial growth, representative isolates of dermatophytes were grown on different agars. Preliminary experiments showed that only oatmeal cereal agar supported the production of conidia by Trichophyton rubrum. We tested the abilities of 251 T. rubrum isolates to form conidia using three different cereal agars and potato dextrose agar. Overall, oatmeal cereal and rice agar media were comparable in their abilities to support T. rubrum conidial growth. Next, we used the oatmeal cereal agar for conidial formation along with the optimal conditions for dermatophyte susceptibility testing proposed by Norris et al. and determined the antifungal susceptibilities of 217 dermatophytes to fluconazole, griseofulvin, itraconazole, and terbinafine. Relative to the other agents tested, terbinafine possessed the highest antifungal activity against all of the dermatophytes. The mean +/- standard error of the mean MICs of fluconazole, itraconazole, terbinafine, and griseofulvin were 2.07 +/- 0.29, 0.13 +/- 0.01, 0.002 +/- 0.0003, and 0.71 +/- 0.05 microgram/ml, respectively. This study is the first step in the identification of optimal conditions that could be used for the standardization of the antifungal susceptibility testing method for dermatophytes. Inter- and intralaboratory agreement as well as clinical correlations need to be established.

Novel strategies for treating candidiasis

In this review the recent achievements in the field of chemotherapy and immunotherapy of candidiasis are outlined. The current limitations of chemotherapeutic approaches and the lack of well defined preventive tools and strategies make it imperative to exploit the potential of novel immunotherapeutic venues. In this prospect the rather extensive work performed on cytokine patterns in experimental models and the upsurge of antibodies as one mechanism of anti-Candida protection raises great promise for the clinical use of immunotherapy possibly in conjunction with chemotherapy to improve the fight against this increasingly prevalent human opportunistic infection.