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Year : 2002  |  Volume : 20  |  Issue : 3  |  Page : 160--162

Evaluation of fungichrom 1: A new yeast identification system

P Umabala, T Satheeshkumar, V Lakshmi 
 Department of Microbiology, Nizam's Institute of Medical Sciences, Punjagutta, Hyderabad - 500 082, India

Correspondence Address:
V Lakshmi
Department of Microbiology, Nizam«SQ»s Institute of Medical Sciences, Punjagutta, Hyderabad - 500 082
India

Abstract

Advances in anti-fungal therapy necessitate the need for accurate identification of fungi especially yeasts to their species level for more effective management. Unlike the time consuming conventional methods of yeast identification using fermentation and assimilation patterns of various carbohydrates, the new commercialized yeast identification systems are simpler, rapid and are particularly easy to interpret. In our study, a new colorimetric yeast identification system-Fungichrom 1(International microbio, Signes, France) was evaluated against the conventional method to identify 50 clinical isolates of yeasts belonging to the genera -Candida, Cryptococcus, Geotrichum. 96% agreement was found between the two methods.

How to cite this article:
Umabala P, Satheeshkumar T, Lakshmi V. Evaluation of fungichrom 1: A new yeast identification system.Indian J Med Microbiol 2002;20:160-162

How to cite this URL:
Umabala P, Satheeshkumar T, Lakshmi V. Evaluation of fungichrom 1: A new yeast identification system. Indian J Med Microbiol [serial online] 2002 [cited 2020 Dec 1 ];20:160-162
Available from: https://www.ijmm.org/text.asp?2002/20/3/160/6943

Full Text

Recent years have shown a global increase in the incidence of mycotic infections.[1],[2] In patients suffering from immunocompromising diseases or undergoing immunosuppressive therapy, not only cellular and humoral immune functions are compromised but the normal microbial flora is altered and destroyed. This leads to an increased susceptibility to opportunistic mycotic infections, of which majority are caused by yeasts and yeast like fungi.[1],[2],[3],[4]

Candida albicans and Cryptococcus neoformans are the most important yeast pathogens but the so-called non-albicans yeasts are being implicated with greater frequency as opportunistic pathogens in the compromised host.[4],[5],[6] Some of these species have been associated with certain diseases and devices[5],[6] and some species like C. glabrata and C.krusei have been noted to be naturally resistant to fluconazole. Rapid and accurate identification of yeasts have thus become important not only for effective management of yeast infections, as various species respond differently to various antifungals[7],[8],[9] but also to prevent emergence of drug resistance. The aim of the present study was to compare Fungichrom 1, a new yeast identification system, with the conventional method, for the speciation of yeasts and yeast like fungi isolated from clinical specimens.

 Materials and Methods



Fifty yeast isolates from sputum, urine, oropharyngeal swabs, blood, pus, CSF from patients admitted in the Nizam's Institute of Medical Sciences (NIMS), Hyderabad, AP, were tested by the conventional methods and by the Fungichrom 1, a commercial yeast identification system.

Conventional tests

These methods are based on the study of the different phenotypic properties of the yeasts that include colony morphology and microscopic morphology on corn meal agar supplemented with tween 80, germ tube test, growth on special media such as caffeic acid agar, sugar assimilation and fermentation reactions.[10]

Fungichrom 1

(International Microbio, Parcd'activites-allee D'athenes, 83870 Signes, France) is a polystyrene microtitre plate with 16 wells. The enzymatic activities are revealed by 3 kinds of reactions [Figure].

a) Hydrolysis of chromogenic substrates

[Wells GAL (contains a chromogenic substrate for N-acetyl-B-d-galactosaminidase), PRO (contains a chromogenic substrate for L-proline-amidase), ONPG (contains a chromogenic substrate for ortho-phenyl-b-d-galactosidase), EPA (contains a chromogenic substrate for a peptidase), SGL (contains a chromogenic substrate for a peptidase), GLY (contains a chromogenic substrate for glycine-amidase)]: the oxidase and peptidase activities of the yeasts hydrolyse these chromogenic substrates and lead to the release of para-nitroaniline, para-nitrophenol or ortho- nitrophenol, all end products giving a yellow colour.

b) The assimilation of carbohydrate substrates:

[Wells GAL- SAC (galactose-sucrose and Bromocresol purple), TRE (trehalose and bromocresol purple), MAL (maltose and bromocresol purple), CEL (cellobiose and BCP), RAF (raffinose and BCP), LAC (lactose and BCP)] the use of these sugars by the yeasts is revealed by the colour change of Bromocresol purple (BCP) from violet to yellow or an absence of colour.

c) The resistance to cycloheximide (actidione - well ACT) is revealed by the same principle of substrate utilization.

d) The hydrolysis of urea (well URE) releases ammonia, which alkalinizes the medium and makes phenol red (PR) turn to fuchsia-pink.

e) Oxidation of synthetic substrates (well POX): The activity of phenol oxidase, produced by the yeasts, in the presence of caffeic acid produces a brown colour.

Each Fungichrom 1 tray also includes a positive control well (C+) which reveals the assimilation of glucose.

The interpretation of the reactions is performed either by a coding system or by the yeast identification table, provided along with the kit. If at the 24-hour mark the code identified was not referenced, incubation was continued for another 24 hours. If at the 48-hour mark, the code was still not itemized, the identification chart was referred to. For a given yeast isolate, all the predominant characteristics mentioned in the identification table should be positive except when a positivity percentage is mentioned in the chart.

When the results of Fungichrom-1 did not match the conventional tests, both the test methods were repeated.

 Results



Out of the 50 yeast and yeast like isolates tested, same species identification was obtained by both the test methods for 48 isolates [Table].

One isolate identified as Geotrichum candidum by Fungichrom 1, could not be definitely identified by the conventional method. For one isolate identified as C.tropicalis by conventional methods, no match was found by the Fungichrom 1.

 Discussion



Unlike the time consuming conventional methods of microbial identification, the new commercialized microbial identification systems are simpler, rapid and are particularly easy to interpret. The various commercial identification systems introduced for yeast identification are based on color changes denoting the utilization of the several kinds of substrates by the metabolizing yeast.[11] Some of the disadvantages of these systems, apart from the higher cost per test compared to conventional method, is that all require careful standardization of the inoculum. High density inocula often require 48 hours of subculture, which can delay identification and limit classification of the corresponding methods as rapid techniques. Some of the systems also present difficulties in reading the colour reactions leading to some misidentifications. The rate of correct identification is also based on whether strains tested were included in the manufacturer's data base. Some of the widely evaluated systems are the API-20C AUX yeast identification system, API Candida, Uni-Yeast Tek identification system, Microscan Yeast Identification panel, Vitek Yeast biochemical card , CHROMagar, Rapid ID Yeast Plus system and Fungichrom 1.The results of this study show that Fungichrom 1, a commercial yeast identification, could identify 98% of the commonly isolated yeasts in our hospital and the results showed 96% correlation with the conventional method of yeast identification. The sensitivity observed in the present study was comparable with those observed in previous studies 95.5%[11] and 99%.[12]

Fungichrom 1 provides a rapid, simple and accurate method for identification of medically important yeasts that can be routinely used in clinical laboratories. The time required was considerably less about 24- 48 hours when compared with the time consuming conventional methods of identification. As the reading is manual, expensive automation is also avoided, unlike the other commercially available systems. Further evaluation of the system with larger number of isolates representing additional species of yeasts needs to be done. Also, the cost effectiveness of routine use of Fungichrom 1 should be assessed depending upon the type of patients being catered to by a particular laboratory.

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