INVESTIGADORES
GALLI Lucia
congresos y reuniones científicas
Título:
Prevalence and Characterization of Shiga toxin-producing Escherichia coli O157:H7/NM in commercial beef abattoirs of Argentina
Autor/es:
MASANA MO; LEOTTA GA; DEL CASTILLO LL; D´ASTEK BA; PALLADINO PM; GALLI L; VILACOBA E; CARBONARI CC; TEITELBAUM D; RIVAS M
Lugar:
CABA
Reunión:
Simposio; 7th International Symposium on Shiga Toxin (Verocytotoxin) - Producing Escherichia coli Infections. Buenos Aires; 2009
Institución organizadora:
Asosiación Argentina de Microbiología
Resumen:
In Argentina, the
information on the prevalence of Shiga toxin-producing Escherichia coli (STEC)
O157 in the beef chain has been scarce, and non-systematic. Therefore, the aim
of this study was to determine the prevalence of STEC O157:H7/NM under the current
commercial operation of national abattoirs. This goal was achieved by sampling
for STEC O157 the bovine fecal content of cattle at the abattoir, and the
carcasses produced. Six animals from a lot of 30-60 bovines of identified
origin were sampled in each visit to an abattoir in such a way to obtain fecal
and carcass samples from the same animal. Fecal samples (FS) were collected
from the descendent colon near to the rectum, while carcasses samples were
obtained by swabbing the carcass surface (CS) with a humidified sponge
according to USDA. Enrichment procedures were conducted as follows: 10 g of the feces were
incubated in 90 ml of GN Hajna (Difco, USA) at 37ºC for 5 h; for carcass
sponges incubation took place in 90 ml of mEC for 2 h at 37ºC. After the primary
enrichment, noboviocin was added up to 20 µg/ml and the enrichment broths were
further incubated for 18 h at 37ºC.
Enriched samples (1 ml) were then processed by immunomagnetic separation (IMS)
according to a modification of the USDA/FSIS procedure for STEC O157:H7/NM
isolation from foods. Confluent growth zone and colony pools were screened for stx1,
stx2 and rfbO157 genes by a multiplex
polymerase chain reaction. At least 20 colonies per PCR-positive sample were
performed for confirmation. Isolates were characterized by biochemical tests,
and the genetic profile (stx1, stx2, ehxA,
eae, rfbO157), and H7 flagellar antigen (fliCH7)
was established by PCR. Between November 2006 and April 2008, 1622 samples (811
CS, 811 FS) were collected in nine abattoirs from Argentina. These abattoirs, all
working under HACCP, contribute with approximately the 18% of the animals
slaughtered per year. Bovines were typified as steers (46%), young steers
(17%), cows (24%), calves (6%), and heifers (7%), and originated from 9
provinces, being Buenos Aires
the biggest supplier (43%). STEC O157 was isolated from 49 samples (3.0%), 20
from CS (2.5 %) and 29 of FS (3.6 %). The carriage of STEC O157 in FS
varied in the different types of cattle: steers (3.2%), young steers (4.4%),
cows (1.5%), calves (6.4%), and heifers (8.8%). The contamination of carcasses
also varied between abattoirs from 0% to 11.1%. In the biochemical
characterization all STEC O157 isolates were sorbitol and β-glucoronidase-negative,
while toxicity on Vero cells was also demonstrated for all isolates. The
prevalent genotype was stx2/stx2c (vh-a) /eae/ehxA/fliCH7
(23/49, 47%), while stx1/stx2 genes
were carried out by 8 strains. These results are important as in Argentina the
genotype stx2/stx2c (vh-a) is also
prevalent in more than 90% of O157-HUS cases. The cattle tested in this
work is representative of the common grass feeding production systems, and that
the degree of carriage of STEC O157 in cattle is comparable to other
international reports.