Distribution and comparison of subtypes of STEC O157:H7 isolated from sporadic hemolytic uremic syndrome cases and healthy cattle in Argentina

D´ASTEK BA; MILIWEBSKY E; DEL CASTILLO LL; LEOTTA GA; CHINEN I; CARBONARI CC; DEZA N; PALLADINO PM; VILACOBA E; GALLI L; BASCHKIER A; MANFREDI E; MASANA MO; RIVAS M

CABA

Simposio; 7th International Symposium on Shiga Toxin (Verocytotoxin) - Producing Escherichia coli Infections; 2009

Asociaición Argentina de Microbiología

Shiga toxin-producing Escherichia coli (STEC) are the most important emerging food-borne pathogens. STEC is a major cause of gastroenteritis that may be complicated by hemorrhagic colitis, or hemolytic uremic syndrome (HUS). Ruminants, especially cattle, have been implicated as the main reservoir. Transmission occurs through the consumption of undercooked meat, unpasteurized dairy products, and vegetables or water contaminated by animal feces. In Argentina, where HUS is endemic, approximately 400 new cases are reported annually. STEC O157:H7 is the predominant serotype isolated from clinical cases, but little is known about the dominant subtypes in humans and animals or their genetic relatedness. The aim of this study was to determine the distribution of different subtypes of STEC O157:H7 strains among HUS cases and among healthy cattle, as well as, to compare the relationship of the strains of these two origins. This study was achieved between November 2006 and April 2008. A collection of 176 STEC O157:H7 strains included in this study were isolated from HUS cases (n=122) and from animals in the abattoirs (n=54) in different geographic regions of the country. These strains were previously subtyped by phage typing, stx genotyping, and XbaI-PFGE, methods. The strains were grouped into 17 phage types (PT) and six strains reacted with the typing phages but did not conform to any recognized PT. PT4 (41.8%), PT49 (22.1%) and PT2 (19.7%) were the most frequent PTs (83.6%) found in human strains. In the bovine isolates were also prevalent, but only 48.1% belonged to these PTs: PT2 (25.9%), PT4 (11.1%) and PT49 (11.1%). PT39 was predominant in bovine isolates (16.7%). The analysis of stx-genotype showed that stx2/stx2c(vh-a) and stx¬2 were prevalent in both sources: in human strains (74.9% and 22.7%, respectively) and bovine strains (47.5% and 17%). However, stx2c(vh-a) (17%) genotype only was found in cattle strains. The stx1 gene in combination with other genes was more detected in animal (17%) that in human (1.6%) strains. By XbaI-PFGE, a total of 92 different patterns were identified among the 176 STEC strains, within at least 75.5% similarity. The same PT-PFGE-stx profile combinations were detected in both origins: PT4-AREXH01.0543-stx2/stx2c(vh-a) (1 human and 4 bovines), PT4-AREXH01.0011-stx2 (1 human and 1 bovine), PT26-AREXH01.0458-stx1/stx2/stx2c(vh-a) (1 human and 1 bovine), PT49-AREXH01.0175-stx2/stx2c(vh-a) (5 humans and 1 bovine). In general, it was found that some strains could be discriminated by one of these subtyping methods. The overlap between PT-PFGE-stx profile combinations in bovine and human clinical isolates indicated that cattle are an important reservoir for human. This study showed that the use of phage typing, PFGE and stx genotyping methods, as epidemiological tools, may help to detect reservoirs, trace routes of transmission, and establish the temporal and geographical variations of newly emerging clones.