13693780310001610056

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Prevalence ofMalassezia species on various body sites in

clinically healthy subjects representing different age

groups

ADITYA K. GUPTA*,$ & YATIKA KOHLI$,%

*Division of Dermatology, Department of Medicine, Sunnybrook and Womens College Health Science Center (Sunnybrook

site) and the University of Toronto, Toronto, $Mediprobe Laboratories, London, Ontario and%The Hospital for Sick Children,

Toronto, Ontario, Canada

To investigate the distribution of Malassezia species on four body sites (scalp,

forehead, chest and back), we employed contact plates filled with Leeming/

Notman agar to sample 245 clinically healthy subjects, representing six age groups

(AG) (AG I, 0/3 years; AG II, 4/14 years; AG III, 15/25 years; AG IV, 26/40

years; AG V, 41/60 years; AG VI, over 60 years). The number of colony forming

units was recorded for every plate positive for Malassezia species, and the species

were identified. Younger individuals (B/14 years) yielded a culture positive forMalassezia significantly less frequently than did older individuals (]/15 years). M.

globosa was cultured at significantly elevated frequency on younger subjects. M.

sympodialis was present at low frequency on younger subjects, but was found in

higher amounts on the skin of adolescents and adults. The amount and kind of

Malassezia species that can be recovered from human skin varies with age and

body site.

Keywords age, contact plates, Malassezia, skin, yeasts

Introduction

Yeasts of the genus Malassezia are a normal part of the

flora of human skin. In susceptible individuals, how-

ever, these yeasts appear to play a causative role in

various superficial dermatoses, including pityriasis

versicolor, seborrheic dermatitis, Malassezia folliculitis,

and some variants of psoriasis and atopic dermatitis

[1]. The yeasts have been found on upwards of 90% of

normal adults and are also commonly isolated from

lesional skin [2]. While Malassezia species tend to

colonize lipid-rich body sites such as the chest, back,

face and scalp [3], the relationship between coloniza-

tion patterns and age group is less clear. A number of

studies indicate that there is a difference in the

colonization pattern of Malassezia species in different

age groups, with an increase in colonization appearing

to occur at puberty when quantities of skin lipidsincrease [4,5]. In addition, when colonization does

occur in children, it appears to more likely to happen

on the head than on the trunk [6]. With the recent

reclassification of the genus Malassezia , there has been

a resurgence of interest in these yeasts and in the

possibility of variation in species distribution in differ-

ent body sites and dermatoses. This study investigates

whether there is a difference in the amount and kinds of

Malassezia species in different age groups.

Previous studies investigating the relationship be-

tween age and colonization with Malassezia species

were based on an older classification in which the

yeasts were classified as the genus Pityrosporum [4,7].

In the previous nomenclature, the two lipophilic

variants were known as P. ovale and P. orbiculare;

however, there was controversy over whether these

variants represented different species, or simply differ-

ent variants of a single species. The relative prevalence

of these yeasts in human hosts has been found to vary

with age, body site and geographical location [2,4,8].

Correspondence: Dr Aditya K. Gupta, Suite 6, 490 Wonderland

Road South, London, Ontario, Canada, N6K 1L6. Tel.: 519 657

4222; E-mail: [email protected]

Received 8 November 2002; Accepted 2 July 2003

2004 ISHAM DOI: 10.1080/13693780310001610056

Medical Mycology February 2004, 42, 35/42

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Age has also been implicated as a factor in the

amount of Malassezia isolated from the skin. In

general, colony counts are higher in adults than in

children, though the amount of yeast obtained de-

creases again in elderly individuals [9]. The yeasts are

less frequently isolated from infants and children,

though Bergbrant and Broberg found P. ovale to be

quite common in children [7].

The taxonomy of Malassezia is now quite different

than that used in these studies. Despite the controversy

over the relationship between P. orbiculare and P.

ovale, most investigators believed that the two forms

represented a single species [10]. However, there was

also controversy over whether the genus should be

named Pityrosporum or Malassezia . Some investiga-

tors even used both designations, describing the yeasts

cultivated from healthy skin as P. orbiculare or P. ovale

and reserving the name Malassezia furfur to indicate

the pathogenic mycelial form of the organism cultured

from lesions of pityriasis versicolor. The currentlyaccepted generic name is Malassezia [11].

In 1996, the genus Malassezia was reclassified and

seven species were delineated [12,13]. M. pachydermatis

remains the sole recognized species that does not

require exogenous lipids in order to grow. The remain-

ing six lipophilic species are M. furfur, M. sympodialis,

M. restricta , M. slooffiae, M. obtusa and M. globosa .

All of these species have been isolated from human

skin, though with varying frequencies.

Since this reclassification, several studies have begun

to determine the differences in prevalence of the six

lipophilic Malassezia species. Some progress has been

made in discovering the geographical variation inspecies distribution; in addition, there are indications

that the dominant species may vary at different body

sites and in different skin conditions [3,14]. To our

knowledge, however, this is the first study to investigate

differences in the type and amount of Malassezia

species in different age groups. Because the amount

and composition of skin surface lipids varies with age

[15,16]. we hypothesized that alterations in the habitat

provided by human skin will affect the amount and

species of Malassezia yeasts present on the skin.

Materials and methods

Preparation of contact plates

BBL RODAC (Beckton Dickinson, MD, USA)

contact plates (4.5 cm diameter) filled with Leeming/

Notman agar were used for sampling, as described

previously [3].

Sample and sampling procedure

We sampled 245 individuals from six different age

groups (AG). These six age groups were: AG I, 0/3

years (n0/33); AG II, 4/14 years (n0/55); AG III, 15/

25 years (n0/43); AG IV, 26/40 years (n0/40); AG V,

41/60 years (n0/44); AG VI, over 60 years (n0/30). All

of the individuals sampled were clinically healthyindividuals (i.e. with no Malassezia -related skin condi-

tions) and informed consent (on the protocol approved

by an independent Review Board) was obtained from

the volunteers or their guardians. All of the individuals

were being seen for conditions other than a dermatosis

(i.e. individuals with psoriasis, atopic dermatitis, sebor-

rheic dermatitis, etc., were excluded).

For each individual, four body sites (scalp, forehead,

chest and back) were sampled by pressing the contact

plates filled with Leeming/Notman agar on the skin

for 20 s. The flattest available surface of the body site

was sampled in order to maximize the recovery of yeast

in each sample. The sampling procedure, incubation of

contact plates, counting the colony forming units

(c.f.u.), and identification of Malassezia species among

selected colonies was performed as described previously

[3]. Contact plates were incubated at 358C for 7 days.

Prior to starting the experiment we had done a pilot

study to determine the appropriate incubation period.

Our pilot data indicated that all six lipophilic species

could be grown adequately and form colonies in this

time frame. Moreover, with longer incubation times

(i.e. 10/14 days) the medium in Rodac plates (/9/9.5

ml medium) usually dries out at 358C. Up to five

isolated single colonies with varied macromorphologywere picked from the contact plates and subcultured on

Leeming/Notman agar slants before processing them

for species identification. Malassezia species were

identified on the basis of their micromorphology (shape

and size of cells), physiological features (catalase

reaction and ability to grow on Tween 20, 40, 60 and

80, as described by Guillot et al. [17]), and molecular

characteristics (based on PCR-restriction enzyme ana-

lysis [REA] of the nuclear ribosomal internal tran-

scribed spacer [ITS] and large subunit [LSU] regions as

described previously [18]).

Statistics

Statistical tests were performed as follows: (i) Samples

from individuals in different age groups and from

different body sites that yielded a positive culture for

Malassezia species were compared using a chi-squared

test, with standardized residuals computed for each

cell. Phi-coefficients were computed to estimate the

strength of relationship between variables. (ii) A uni-

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variate analysis of variance was conducted to compare

the mean c.f.u. and adjusted c.f.u. from each age group.

(iii) A univariate analysis of variance was conducted to

evaluate the effect of age and sex on total c.f.u.,

followed by multivariate analysis to evaluate the effects

of age and sex on the c.f.u. counts from each of the four

body sites. (iv) Chi-square tests, with standardized

residuals for each cell, were calculated to analyze the

differential likelihood of Malassezia species, if any, to

be recovered across different age groups and from

different body regions. Phi coefficients were computed

to estimate the strength of relationship between vari-

ables.

Tests mentioned in points (i) and (ii) were performed

using density data (i.e. data recorded as the number of

Malassezia c.f.u. obtained within the sample categories

(Tables 1 and 2). Statistical tests based on the specificity

of individual Malassezia species as mentioned in point

(iii) were carried out using frequency data (data based

on the number of contact plates yielding at least oneisolate of the species in question; Tables 3 and 4).

Results

Recovery of Malassezia species from individuals of different

age groups

Overall, a positive culture was obtained from 70% of

individuals sampled in all age groups from one or more

body sites. Occurrence of a positive culture was highest

(93.3%) in AG VI (over 60 years) and lowest (36.3%) in

AG-I and II (0/14 years) (Table 1). Based on a

calculation of standardized residual scores, signifi-cantly fewer than expected AG-I and AG-II individuals

yielded a positive culture.

Mean and adjusted c.f.u.

The mean c.f.u. for each age group was calculated by

dividing the total c.f.u. count by the number of

individuals sampled in each age category. This was

further adjusted (adjusted c.f.u.) by limiting the max-

imum counts from each contact plate to 100. Overall,

the anova indicated a significant difference among the

age groups for both the mean c.f.u. (F [5,238]0/7.714;

PB/0.0001) and the adjusted c.f.u. (F [5,239]0/9.997;

PB/0.0001). The mean c.f.u. in AG-1 and AG-II was

significantly lower than in AG-III and AG-VI. Simi-

larly, the adjusted c.f.u. in AG-I and AG-II was

significantly lower than in AG-III, IV, V and VI. (Table

1).

Colony forming units from different body sites and variation

among age groups

Table 2 summarizes the data for mean c.f.u. from each

age group and different body sites. We conducted a

multivariate anova, using c.f.u. scores (both adjusted

and unadjusted) from scalp, forehead, chest and back

as dependent variables. A significant difference was

found between age groups when all body parts were

considered as an optimally weighted composite for

both adjusted c.f.u. (F [20,952]0/2.486; PB/0.0001)

and unadjusted c.f.u. (F [20,952]0/2.522; PB/0.0001).

Based on a pairwise comparison of means from

different age groups, the mean c.f.u. on the scalp,

back, and chest of individuals in AG-III and VI were

significantly higher than the counts for individuals in

AG-I and II (Table 2).

Interaction between age and sex

There was no significant difference in the number of

men and women sampled for each of the age groups

(Table 1; x2 [5]0/3.5; P0/0.6). While the main effect of

sex was not significant, the interaction between age and

sex was significant with women in AG-V and VI having

significantly lower mean c.f.u. than men. (F [5,233]0/

2.554; PB/0.05). The same trend was noted for the

forehead (P0/0.02) and the chest (P0/0.006).

Table 1 Malassezia colony forming units (c.f.u.) from contact plate samples of individuals from different age groups

Age group Age (years) No.

individuals

sampled (M/F)

No. positive for

Malassezia (%)

No. negative for

Malassezia (%)

Total

c.f.u.

count

Mean c.f.u.

(standard

error)

Adjusted c.f.u.

(standard

error)

Tukeys

HSD**

I 0/3 33 (15/18) 12 (36.3) 21 (63.6)* 228 6.9 (4.0) 6.1 (3.3) IB/III, IV, V, VIII 4/14 55 (27/28) 20 (36.3) 35 (63.6)* 466 8.5 (3.3) 8.2 (3.1) IIB/III, IV, V, VI

III 15/25 43 (18/25) 39 (90.7) 4 (9.3) 2000 47.6 (8.5) 38.3 (5.8) III!/I, II

IV 26/40 40 (14/26) 36 (90) 4 (10) 1427 35.7 (6.0) 33.8 (5.2) IV!/I, II

V 41/60 44 (17/27) 37 (84.1) 7 (15.9) 1502 34.1 (20.7) 27.3 (5.4) V!/I, II

VI Over 60 30 (16/14) 28 (93.3) 2 (6.7) 2233 74.4 (113.2) 45.7 (7.4) VI!/I, II

*Represent values of statistical significance where significantly less growth was observed than would be expected due to chance alone. **Tukeys

HSD was computed, in the post hoc testing of the mean scores to do a pairwise comparison of adjusted means from different age groups.

M/F: Males/Females.


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Association of Malassezia species with different age groups

and body sites

All six known lipophilic Malassezia species were

recovered (Table 3). In many individuals, more than

one Malassezia species was recovered from any given

body site. Different Malassezia species were recoveredamongst the different colonies picked from the same

plate from a given body site. We did not find any

evidence of mixed colonies containing more than one

species. The most common species were M. sympodialis

(56.9%) and M. globosa (31.8%) followed by M. furfur

(6.1%), M. slooffiae (2.7%), M. obtusa (1.8%), and M.

restricta (0.7%).

The distributions of M. sympodialis and M. globosa

were significantly different among individuals from

different age groups (Table 3). In AG-I, M. globosa

and M. furfur were the predominant species account-

ing for 54.5% and 36.4%, respectively, of all the species

recovered. M. furfur was recovered significantly more

frequently from AG-I members than would be expected

by chance (PB/0.0001). M. sympodialis on the other

hand, was not cultured from individuals aged 0/3

years. In AG-II, again M. globosa was the predominant

species (59.7%) and occurred more frequently than

expected by chance alone (PB/0.0001). In AGs III to

VI, M. sympodialis was observed approximately twice

as often as M. globosa (Table 3).

Table 2 Means and standard errors for c.f.u. by age group and body site

Body site Mean adjusted c.f.u. (standard error) anova Tukeys

AG-I AG-II AG-III AG-IV AG-V AG-VI F (P)* HSD$

Scalp 0.6 2.7 4.2 3.1 3.8 11.5 2.67 I, II B/III,VI

(0.3) (1.4) (1.7) (1.5) (0.9) (5.2) (0.001)

Forehead 4.4 2.4 5.5 5.0 2.7 12.2 1.3 I, II B/III,VI

(3.1) (1.6) (2.1) (2.0) (1.3) (7.1) (0.02)Back 0.4 0.9 17.4 15.3 14.4 26.9 4.004 I, II B/III, VI

(0.2) (1.5) (3.7) (3.5) (3.7) (5.5) (0.000)

Chest 1.6 2.5 19.6 12.4 13.2 23.7 7.24 I, IIB/III, VI

(1.0) (1.7) (5.7) (3.6) (4.2) (8.3) (0.000)

*F-statistics for univariate anova calculations with unadjusted c.f.u. as a variable; P-value in parentheses represent the probability value of

statistical significance. $Tukeys honestly significant difference (HSD) was computed in the post hoc testing of the mean scores to do a pairwise

comparison of means from different age groups.

Table 3 Distribution of Malassezia species in individuals from different age groups

Characteristics AG-I AG-II AG-III AG-IV AG-V AG-VI Total

No. individuals sampled 33 55 43 40 44 30 245

No. individuals that cultured

positive for Malassezia spe-

cies

12 20 39 36 37 28 172

No. colonies examined 22 57 161 143 155 123 661

No. individuals with positive

species identification for

yeast colonies.

5 13 33 27 29 27 134

No. species identified 3 4 5 6 5 5 6

Malassezia species No. colonies (% of total number of colonies for stated age group)

[No. individuals from whom species isolated]*

M. furfur 8(36.4%) [1] 3(5.3%) [3] 5(3.1%) [4] 2(1.4%) [2] 11(7.1%) [7] 11(8.9%) [4] 40{6.1}$

M. globosa 12(54.5%) [5] 34(59.7%) [11] 41(25.5%) [17] 42(29.4%) [3] 52(33.5%) [17] 29(23.6%) [13] 210{31.8%}

M. obtusa 0 2(3.5%) [2] 4(2.5%) [3] 1(0.07%) [1] 2(1.3%) [1] 3(2.4%) [2] 12{1.8%}

M. restricta 0 0 2(1.2%) [2] 3(2.1%) [2] 0 0 5{0.7%}M. slooffiae 2(9.1%) [1] 0 0 3(2.1%) [3] 3(1.9%) [3] 10(8.1%) [2] 18{2.7%}

M. sympodialis 0 18(31.6%) [6] 109(67.7%) [28] 92(64.3%) [26] 87(56.1%) [24] 70(56.9%) [19] 376{56.9%}

Total 22 57 161 143 155 123 661

*In some individuals more than one colony was isolated. $Percent of total number of colonies (n0/661).


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All correlations of Malassezia species with body site

were more prominent after combining the data across

age groups (Table 4). For all age groups combined, M.

globosa was recovered significantly more often from

scalp and forehead and less frequently from the back

(PB/0.0001). M. sympodialis, on the other hand, was

recovered more frequently from the back and less

frequently from the scalp and forehead (PB/0.0001).

Discussion

This is the first study that evaluates the type and

amount of Malassezia species in the different age

groups using the new taxonomy. The results of our

study replicate and expand on the findings of some of

the earlier studies [9,14,19/22]. While our results and

those of investigators using the old taxonomy show

similarities in the number of yeasts found in different

age groups, caution should be used in any attempts to

compare the species-level results generated using the

two classification systems.

Another factor that makes it difficult to generalize

among studies is the different sampling procedures

used. While we have used contact plates in this study,

other studies have used skin scrapings [23] or tape

samples [24], the detergent scrub technique [25] and

even contact plates (with either Leeming/Notman [26]

or a different medium) [27]. Aspiroz [20] used a cotton

ball impregnated with 1 ml TritonX-100 and Naka-

bayashi et al. [14] used several methods: swab, tape and

Table 4 Prevalence of Malassezia species on body sites of members of different age groups

Malassezia species AG-I AG-II AG-III AG-IV AG-V AG-VI Total

M. furfur

Scalp / / / / 3 3 6

Forehead 3 1 / 1 1 / 6

Chest 2 / 2 1 3 4 12

Back 3 2 3 1 4 3 16

Total 8* 3 5 3$ 11 10

M. globosa

Scalp 4 16 9 6 16 8 59*

Forehead 4 9 9 11 16 3 52*

Chest 3 5 13 18 7 6 52

Back 1 4 10 7 11 8 41$

Total 12 34* 41 42 50 25

M. obtusa

Scalp / 1 2 / / 2 5

Forehead / / 2 / / / 2

Chest / 1 / 1 2 1 5

Back / / / / / / 0$

Total 0 2 4 1 2 3

M. restricta

Scalp / / / 1 / / 1

Forehead / / / 1 / / 1

Chest / / 1 / / / 1

Back / / 1 / / / 1

Total 0 0 2 2 0 0

M. slooffiae

Scalp / / / 1 / 5 6

Forehead / / / / 1 / 1

Chest / / / / 1 / 1

Back 2 / / 2 1 4 9

Total 2 0 0 3 3 9*

M. sympodialis

Scalp / 2 14 4 8 9 37$

Forehead / 3 13 6 7 8 37$

Chest / 7 44 38 28 15 132Back / 6 38 44 44 35 167*

Total 0$ 18$ 109 92 87 67

*Based on the standardized residual scores by computing z-test, a significantly greater number of cases than expected were observed. $Based on

the standardized residual scores by computing z-test, a significantly lower number of cases than expected were observed.



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hairbrush (for scalp). Recently, Gemmer et al. [28] have

described a new molecular technique named terminal

fragment length polymorphism (tFLP), which allows

the molecular detection and differentiation of Malas-

sezia yeast species from dandruff. Whether this techni-

que will be helpful in isolating and identifying

Malassezia yeasts from samples other than dandruff

remains to be investigated. The tFLP method, however,

is not suitable for quantitative culturing of yeasts.

While no studies have been performed comparing the

contact plates with the detergent scrub technique, an

animal study has shown a high correlation in yields

provided by the two methods (PB/0.001) [29]. Contact

plates were chosen for sampling because: (i) we [3] and

others [22] have used contact plates successfully for

quantitative culturing; (ii) the use of a contact plate

minimizes the chances of losing a part or whole sample

in the transit from the clinic to the laboratory; and (iii)

in our experience, this sampling method was found to

be best tolerated by children.In the various age groups that we have studied, there

is a difference in both the amount as well as the kind of

Malassezia species found on the skin. The two young-

est age groups, representing individuals from 0 to 3 and

4 to 14 years of age, had significantly lower mean c.f.u.

(6.12 and 8.20, respectively; mean adjusted c.f.u.) than

groups III through VI. Our study shows some striking

similarities and differences when contrasted with a

study by Bergbrant and Broberg [7], who also used

contact plates (containing peptone, ox bile, bacto agar,

glucose and yeast extract supplemented with glycerol,

glycerol monostearate, Tween 60 and cows milk) to

investigate the prevalence of P. ovale in childrenbetween 2 months and 15 years of age. The colony

counts in our two youngest age groups were similar to

those of Bergbrant and Broberg [7]. They reported a

mean c.f.u. of 10 for children between the ages of 2 and

7 years; in our study the mean c.f.u. were 6.9 and 8.5 for

AG I and II, respectively. Our results however, differ

from those of Bergbrant and Broberg [7] in the number

of individuals who sampled positive for Malassezia in

younger age groups (0/14 years). In our study, while a

positive culture was obtained from 70% of individuals

sampled over all age groups, only 36.3% of individuals

of younger ages (0/14 years) were positive for Malas-

sezia , which is in contrast with the 87% positive

recovery rate observed by Bergbrant and Broberg [7].

Several other studies have reported varied rates of

positive recovery from young children. Faergemann

and Fredrickson [4] found no Malassezia (P. orbicu-

lare/P.ovale) yeasts on children younger than 5 years of

age. Results of our study are closest to those of Silva et

al. [19], who found Malassezia yeasts in 23.3% of

children between the ages of 0 and 18 months and

26.7% of children between the ages of 11 and 15 years.

Because of the different ways in which subjects were

grouped according to age, comparison between these

studies is difficult. With the exception of the study by

Bergbrant and Broberg [7], in which the amount of

Malassezia species recovered from the skin of children

is quite high, other studies, including ours, show that

amount of Malassezia inoculum recoverable from

children is quite low. This may reflect the fact that

compared to other age groups, children have very little

sebum on their skin [16]. Both the amount and the

composition [16] of skin lipids changes at puberty.

With respect to the carriage of Malassezia species in

adolescents and adults, our study found no significant

difference between the four age groups (AG-III to AG-

VI). It is thought that the increase in skin lipid levels

that occurs at puberty may be responsible for the

increase in colonization of the skin by Malassezia

species [4]. A previous study [9] reported that there wasa decrease in Malassezia species colonization with

increasing age, with 30-year-olds having significantly

higher mean colony counts than persons aged 40, 50,

60, 70 or 80 years. By contrast, we found the highest

mean colony count in our age group VI (93.3%), which

contained individuals over 60 years of age, though,

again, differences between the four oldest age groups

were not significant. It is possible, however, that

differences in the techniques used to recover Malasse-

zia species from the skin, i.e., differences between

detergent scrub [9] and contact plate (present study)

results, may explain some of the observed differences.

For the various age groups, there were differencesamong body sites in the mean numbers of c.f.u. found.

The mean c.f.u. for AG-III and AG/IV were signifi-

cantly higher than those for AG-I and AG-II for the

back, chest, scalp and forehead. It is possible that these

differences are again due to puberty-related change in

skin lipid levels.

We also examined the relationship between the six

lipophilic Malassezia species, age group and body site.

All six species were recovered; however, the prevalence

rates were different. Overall, the most common species

was M. sympodialis (56.8%); M. globosa was the

second most common (31.7%). There were differences

in the prevalence of these species among age groups:

M. globosa was most common in AG-I and AG-II,

while M. sympodialis was most common in the other

four groups. The last result confirms an earlier report

by our group [3], but differs from the findings of other

studies. Aspiroz et al. [20] reported that M. globosa

was most frequently observed overall in normal in-

dividuals; however, M. sympodialis was more prevalent


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on the back. Crespo Erchiga et al. [21], from Spain,

found that M. sympodialis was the most common

species isolated from normal skin. In Sweden, Sand-

strom et al. [22] also reported that M. sympodialis was

frequently recovered from normal volunteers. It is

possible that climatic factors may play a role in the

type of Malassezia species present in skin, with M.sympodialis more common in temperate climates and

M. globosa occurring most frequently in warmer or

tropical locations.

The body sites sampled were combined into two

groups: head (forehead and scalp) and trunk (chest and

back). M. globosa was found in significantly higher

proportions than expected (according to the statistical

null hypothesis) on the head and in significantly lower

than expected amounts on the trunk. For M. sympo-

dialis, the reverse was true; this species was recovered

less often from the head and more frequently from the

trunk than would be expected by chance (data not

shown). Taken together, our results indicate that M.sympodialis is overall the most common Malassezia

species found on normal skin, and that it is most

frequently recovered from the chest and back. In

children, Malassezia colonization is more frequent on

the scalp and forehead than on the trunk, and is carried

out primarily by M. globosa . However, colonization by

Malassezia in children up to the age of approximately

14 years is much less common than in adults. Our

results indicate that the Malassezia species are not

interchangeable in their ecological relationships; they

have varying degrees of niche separation. Differences in

the amount and composition of skin lipids at different

ages and different body sites may account for part of

the variability we found. In addition, hygienic practices

change with age and with body site, possibly affecting

the habitat of the yeasts.

Following the completion of the study two other

Malassezia species have been reported, one from

humans and the other from the skin of horses [30,31].

As our study was carried out before these characteriza-

tions were published, we did not examine for the

presence of these yeasts.

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