Abstract
Antibiotic resistance and mechanisms involved were studied in
Escherichia coli
isolates from fecal samples of healthy children. Fifty fecal samples were analyzed, and one colony per sample was recovered
and identified by biochemical and molecular tests. Forty-one
E. coli
isolates were obtained (82%). MIC testing was performed by agar dilution with 18 antibiotics, and the mechanisms of resistance
were analyzed. Ampicillin resistance was detected in 24 isolates (58.5%), and
bla
TEM
,
bla
SHV
, and
bla
OXA
type genes were studied by PCR and sequencing.
The following
β
-lactamases were detected (number of isolates): TEM (20), SHV-1 (1), and OXA-30 (1). The number of aminoglycoside-resistant isolates detected was as follows: streptomycin (15),
tobramycin (1), gentamicin (1), and kanamycin (4). The
aac(3)-IV
gene was detected in the only gentamicin-resistant isolate. Nine (22%) and 2 (5%) isolates showed nalidixic acid (NAL
R
)
and ciprofloxacin resistance (CIP
R
), respectively. Mutations in GyrA and ParC proteins were shown in both NAL
R
-CIP
R
isolates and were the following: (1) GyrA (S83L + D87N),
ParC (S80I); and (2) GyrA (S83L + A84P), ParC (S80I + A108V). A single mutation in the S83 codon of the
gyrA
gene was found in the remaining seven NAL
R
-CIP
S
isolates. Tetracycline
resistance was identified in 21 isolates (51%) and the following resistance genes were found (number of isolates):
tetA
(12),
tetB
(5), and
tetD
(1). Chloramphenicol resistance was
detected in five isolates (12%). These results show that the intestinal tract of healthy children constitutes a reservoir of resistant bacteria and resistance genes.