Incidência da colonização de crianças de creche por Staphylococcus aureus

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Rev Panam Infectol 2008;10(1):20-23
artículo original/artigo original
Incidence of Staphylococcus aureus colonization in 
children attending day-care centers
Incidência da colonização de crianças de creche por Staphylococcus aureus
Maria de Fátima Bernardo1
Mariko Ueno2*
1Estudante de Graduação, Departamento de 
Biologia, Universidade de Taubaté., Taubaté, 
SP, Brasil.
2Professor Assistente Doutor, Instituto Bási-
co de Biociências, Universidade de Taubaté, 
Taubaté, SP, Brasil.
Rev Panam Infectol 2008;10(1):20-23
Conflicto de intereses: ninguno
Recibido en 3/7/2007.
Aceptado para publicación en 21/11/2007.
Resumo
Nosso objetivo, neste trabalho, é apresentar a incidência de 
portadores de Staphylococcus aureus entre crianças saudáveis, 
com idade entre 1 a 6 anos, que freqüentam creches. Swabs foram 
utilizados para a coleta de amostras da cavidade nasal e garganta de 
76 crianças. Os resultados mostraram que 37 (48,7%) das crianças 
eram portadoras de S. aureus. Todas as cepas apresentaram-se 
sensíveis a amicacina, ciprofloxacina, imipenem, gentamicina, 
mupirocina, teicoplanina, rifampicina e vancomicina, e resistentes 
a ampicilina, amoxicilina, aztreonam e penicilina G. Uma cepa 
resistente à oxacilina foi isolada da garganta de uma criança de 
6 anos de idade; sendo resistente também a: outros antibióticos 
b-lactâmicos, clindamicina, ciprofloxacina, eritromicina e trime-
toprima. Observou-se multirresistência a até nove antibióticos. A 
colonização de crianças de creches por S. aureus é alta, sobretudo 
por cepas resistentes aos antibióticos. 
Palavras-chave: Staphylococcus aureus, portadores assintomá-
ticos, crianças, resistência a antibióticos.
Abstract
Our objective in this report is to present the incidence of Sta-
phylococcus aureus carriage among 1-6 age healthy children atten-
ding day-care centers. Nasal and throat swabs were collected from 
76 healthy children. The samples were inoculated in Baird-Parker 
agar. Typical colonies of S. aureus were identified by biochemical 
tests. The results showed that 37 (48.7%) children were carriers 
of S. aureus. 31 (83.8%) presented the microorganism only in the 
anterior nares, 1 (2.7%) presented in the throat and 5 (13.5%) in 
both body sites. All strains were sensitive to amikacin, ciprofloxacin, 
gentamycin, imipenem, mupirocin, rifampicin, teicoplanin, and 
vancomycin and all of them was resistant to penicillin G, ampi-
cillin, aztreonam and amoxicillin. One strain resistant to oxacillin 
(methicillin) was isolated, from the throat of a 6 years old child, 
and it was resistant to others b-lactams, erytromicin, clindamycin, 
ciprofloxacin and trimethoprim. Multiresistance to 9 antibiotics 
was observed in one strain. The rates of colonization by S. aureus, 
especially by antibiotic-resistant strains, were high in children 
attending day-care centers. 
Key words: Staphylococcus aureus, asymptomatic carriers, chil-
dren, antibiotic resistance. 
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Bernardo MF, et al • Incidence of Staphylococcus aureus colonization in children...
Introduction
Many younger children attending day-care centers 
tend to frequently experience acute respiratory infec-
tions. Colonization of S. aureus in children is a matter 
of constant concern. S. aureus is a common cause of 
disease, particularly for colonized persons. Infections 
caused by S. aureus, either hospital-acquired or com-
munity-acquired, cause high morbidity and mortality. 
The anterior nares are considered to be the primary 
site(1) and the most important screening site of coloni-
zation. Mertz et al.(2) screened individuals for S. aureus 
carriage of both nares and throat. A total of 37.1% of 
persons were nasal carriers, and 12.8% were solely 
throat carriers.
The human throat is less well studied as a carriage 
site. Uemura et al.(3) reported an isolation rate of 29% 
in a group of healthy volunteers. Berkovitch et al.(4) 
found the bacteria in 10% of healthy children younger 
than 7 years of age. There have also been observations 
of higher than expected rates of methicillin-resistant 
S. aureus (MRSA) in infants’ throats.(5)
Most studies on colonization of Staphylococci 
focused mainly on methicillin susceptible strains. 
Colonization may be either transient or persistent, at a 
single site or multiple body sites. In addition, patients 
may carry multiple strains of S. aureus.(6)
Nasal colonization with MRSA occurs infrequen-
tly in the healthy pediatric population (0.2-2.2%). 
However, infections caused by community-associated 
MRSA have increased remarkably in recent years.(7,8)
S. aureus was isolated from 17 (25%) nasal swabs. 
Nine (13.2%) of the 68 children had community-
acquired (CA) - MRSA carriage.(9) 
Two (3%) of 61 children at child care center had 
MRSA. Colonization with MRSA was not associated with 
health care contact by subjects or by members of their 
households. MRSA in child day care centers indicates 
accelerated spread of MRSA in the community.(10)
In Brazil, about 37% of hospital-acquired S. aureus 
are resistant to methicillin(11) and most community-
acquired strains are sensitive to oxacillin.(12) 
The extent of MRSA carriage in Brazilian infants is 
largely unknown. Evaluation of the presence of MRSA na-
sopharyngeal carriage in children younger than 5 years in 
Brazil showed that S. aureus was isolated in 93 (13.5%) 
of which 7 (1.02%) were identified as MRSA.(13)
Material and Methods
Samples were collected from children, attending 
two day-care centers. The study was carried out with 76 
children, divided into 3 groups: a) group 1, consisting 
of 21 children between 1 and 2 years old; b) group 2, 
comprising 29 children between 3 and 4 years; and, c) 
group 3 consisting of 26 children aged 5 to 6 years old. 
Two samples were collected from each individual: one 
from the anterior nares and another from the throat. Sam-
ples were collected with a swab moistened in physiologic 
solution and inoculated in Baird Parker agar (DIFCO), 
enriched with 1% potassium tellurite and 5% emulsion 
of egg yolk, and incubated at 37º C for 24 hours.
Typical colonies of Staphylococcus that appears 
shiny black with a clear halo surrounding them as a 
result of lecithinase production by the colonies were 
selected for further identification using the catalase, 
coagulase, Voges Proskauer and fermentation of trealo-
se. Five colonies of each plate were selected. However, 
in those cases where less than 5 colonies had grown, 
all colonies were collected.
Carrier frequencies were compared using the tests 
for two independent proportions, chi-square or Fisher’s 
exact test (Fisher-Freeman-Halton). In all cases a sig-
nificance level of a = 0,05 was used.
Subjects participated after providing informed con-
sent to the study protocol. The protocol was approved 
by the Ethic Committee of Universidade de Taubaté. 
Results and Discussion
The presence of Staphylococcus aureus in children 
colonized, in the nare and throat, by age is showed in 
table 1.
a) Carrier frequency by age 
In this study 37 (48.7%) children were colonized 
with S. aureus; 17 (45.9%) of these children per-
tained to age group 1, 14 (37.8%) to age group 2 
and 6 (16.2%) to age group 3. Although incidence 
of Staphylococcus tended to decrease with age, this 
tendency was not statistically significant (x² = 3.25; 
p = 0.20 test). 
b) Carrier frequency by anatomic site
Among the 37 children identified as carriers of S. 
aureus, 31 (83.8%) presented the microorganism only 
in the anterior nares, 1 (2.7%) presented in the throat 
and 5 (13.5%) in both body sites (table 1). The nasal 
carrier rate was higher than that of the other anatomic 
sites (x² = 43.03; p = 0.000).
c) Association between carrier frequency by anato-
mic site and by age
The occurrence of S. aureus by type of anatomicTable 1. Number of Staphylococcus aureus carriers by 
anatomic site by age
Group Age (years) Nasal carriers
Throat 
carriers
Either sites 
carriers
1 1-2 12 0 4
2 3-4 13 1 1
3 5-6 6 0 0
Total - 31 1 5
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Rev Panam Infectol 2008;10(1):20-23
site did not vary with the age of the children (Fisher’s 
exact test, p = 0.45, table 1).
S. aureus was isolated more frequently from the 
anterior nares 36 (47.4%) of children studied than 
from the throat 6 (7.9%). Lo et al.(9) reported that 25% 
of children are nasal carriers of S. aureus. Nilsson, 
Ripa(6) isolated S. aureus more frequently from the 
throat than from the anterior nares.
Our results demonstrate that S. aureus rarely was 
carried only in the throat (2,7%). This could have 
some important implications. Since nasal carriage of 
S. aureus is a well-documented risk factor for S. aureus 
infections,(1) prophylactic decolonization of carriers has 
been tried with different patient groups.(14)
Two children presented S. aureus and S. schleiferi 
subsp. coagulans in the anterior nares. S. schleiferi 
subsp. coagulans is an organism with limited human 
pathogenicity;(15) associated with wound infections.(16) 
Although it is considered non-pathogenic by some 
ones,(17) by others it is responsible for post-operative 
infections in patients submitted to thoracic surgery 
and systemic abscesses.(18)
95 (76%) strains were confirmed as S. aureus, 
distributed among the three age groups as follows: 39 
strains isolated from group 1; 35 strains from group 2 
and 21 strains from group 3.
d) Carrier frequency by sex
As for carrier frequency by sex, the proportion of 
male carriers (0.47; n = 15) is not different (p = 0.74) 
from that of female carriers (0.53; n = 17). 
e) Antibiotic resistance
A resistance profile of strains isolated from children 
attending day-care centers limited to b-lactams (table 
2). In the past, the increased consumption of peni-
cillin and ampicillin was accompanied by increased 
resistance to these drugs.
All strains were sensitive to amikacin, ciprofloxacin, 
imipenem, gentamycin, mupirocin, rifampicin, teico-
planin and vancomycin, and resistant to ampicillin, 
aztreonam, penicillin G, and amoxicillin. These results 
exceed the data relative to antibiotics resistance pu-
blished in recent studies. 
In this study, one strain isolated from the throat 
of a 6 years old child were resistant to oxacillin (me-
thicillin). Throat is an important reservoir for MRSA 
and samples taken from the throat should be included 
in screening patients for MRSA. Ringberg et al.(19) 
reported that 53% of patients were positive for MRSA 
in their throat and in 40 patients (33%), throat was 
the only sample site with MRSA at the time when the 
patient was found to be MRSA positive. 
The isolated strain was resistant to others b-lactams, 
ciprofloxacin, clindamycin, erytromicin, and trimetho-
prim, the same antibiotics profile of CA-MRSA clone wi-
dely disseminated throughout Brazilian hospitals (BEC) 
described by Oliveira et al.(20) and Sola et al.,(21) Lo et 
al.(9) reported that CA-MRSA isolates had high resistance 
(100%) to both clindamycin and erythromycin.
In this study S. aureus was isolated in 37 (48.7%) 
subjects and CA-MRSA was isolated in (2.7%) of them. 
Lamaro-Cardoso et al.(13) isolated S. aureus in 93 (13.5%) 
of which 7 (1.02%) were identified as MRSA, in Brazilian 
children younger than 5 years old. Ciftci et al.(22) reported 
that 28.4% of children were nasal colonized with S. au-
reus in and MRSA was isolated in 3 (0.3%) of them.
Masuda et al.(23) and Toraño et al.(24) detected S. 
aureus in 17.9% and 18.7% of children, respectively, 
and MRSA was present in 42.9% and 2.2% of children 
attending day-care centers them, respectively.
Antimicrobial susceptibility testing revealed resis-
tant to nine antibiotics. 83 (87.4%) strains showed 
resistance to four antibiotics: amoxicillin, ampicillin, 
aztreonam and penicillin. One strain (1.1%) showed 
resistance to 9 antibiotics (amoxicillin, ampicillin, 
aztreonam, cefazolin, cephapirin, erythromycin, peni-
cillin, thiamphenicol, and trimethoprim).
Data collected in our study suggests that the mul-
tiresistance pattern of S. aureus strains increases with 
age, that means, the higher the age of the children, the 
higher the multiresistance of the strains they carry.
Table 2. Resistance of Staphylococcus aureus isolated from 
1 to 6 year old children
Antibiotic
Samples
n %
Penicillin G 95 100
Amoxicillin 95 100
Aztreonam 95 100
b-lactams Ampicillin 95 100
Oxacillin 1 1.1
Cefalotin 2 2.1
Cefazolin 1 1.1
Cefpiron 1 1.1
Gentamycin 0 0
Rifampicin 0 0
Tobramycin 3 3.2
Aminoglycosides Clindamycin 2 2.2
Streptomycin 5 5.3
Neomycin 2 2.1
Amikacin 0 0
Macrolides Mupirocin 0 0
Erytromycin 2 2.1
Tetracyclines Thianfenicol 3 3.2
Tetracycline 2 2.1
Glycopeptides Vancomycin 0 0
Teicoplanin 0 0
Antimetabolite Trimetoprim 3 3.2
Quinolone Ciprofloxacin 0 0
Carbapenem Imipenem 0 0
23
Bernardo MF, et al • Incidence of Staphylococcus aureus colonization in children...
Determination of phenotype characteristics, such as 
the morphology of colonies, biochemical analysis and 
antibiotic resistance pattern of 95 strains isolated clearly 
indicated the predominance of 1 strain, 24 (75%) chil-
dren carried the same strain of S. aureus. 14 (37.8%) 
children carried one single strain, 2 children (5.4%) 
were colonized with 4 strains in same anatomic site. 
In addition, it was observed distinct strains in different 
body site, whereas 2 children (5.4%) exhibited the same 
strain in both anatomic sites. By the way different strains 
might be present simultaneously at the same body site, 
as observed in 14 (37.8%) children. The diversity of 
strains present might be a result of the high degree of 
physical interaction since children attending day care 
centers share toys, cradles, clothes and others utensils, 
promoting cross transmission of strains.
This first assessment of this study is that nearly one 
half of the 1-6 age group healthy children population 
present nasal or throat carriage of S. aureus. However, it 
also shows that the rate of MRSA carriage remains low. 
We conclude that the rates of colonization by Sta-
phylococcus aureus, especially by antibiotic-resistant 
strains, were high in our study, suggesting their hori-
zontal spread among children in day-care centers.
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Correspondência:
Profa. Mariko Ueno
Instituto Básico de Biociências/Universidade de Taubaté
Av. Tiradentes, 500 - Campus Bom Conselho -
CEP 12030-180 - Taubaté - SP - Brasil.
e-mail: mariueno@unitau.com.br
mariueno@directnet.com.br