Distribution of the stx1 and stx2 genes in Escherichia coli isolated from milk cattle according to season, age, and production scale in southwestern region of Goiás, Brazil / Distribuição dos genes stx1 e stx2 em Escherichia coli isoladas de bovinos de leite de acordo com a estação, idade e escala de produção na região sudoeste de Goiás, Brasil

This study determined the distribution of stx1 and stx2 genes in Escherichia coli isolated from dairy herds with regard to animal age, season, and farm production-scale, and analyzed the phylogenetic distribution of the groups A, B1, B2, and D of 276 isolates of bovine feces Shiga toxin-producing E. coli (STEC). The stx1 profile was the most common, detected in 20.4% (202/990) of the isolates, followed by stx2 (4.54%, 45/990) and stx1+stx2 (2.92%, 29/990). The stx1 gene was detected more frequently in calves than in adult animals. In the dry season (winter), the presence of stx1+stx2 profile in cattle feces was higher than in the rainy season (summer), while no significant changes were observed between seasons for the stx1 and stx2 profiles. The most predominant phylogenetic groups in adult animals were B1, A, and D, while groups A and B1 prevailed in calves. Our data highlight the importance of identifying STEC reservoirs, since 7.5% of the tested isolates were positive for stx2, the main profile responsible for the hemolytic-uremic syndrome (HUS). Moreover, these microorganisms are adapted to survive even in hostile environments and can contaminate the food production chain, posing a significant risk to consumers of animal products.(AU)

Esse estudo determinou a distribuição dos genes stx1 e stx2 em Escherichia coli isolados de rebanhos leiteiros em relação a idade, estação e produção, e analisaram a distribuição filogenética dos grupos A, B1, B2 e D de 276 E. coli produtoras de toxina Shiga (STEC). O perfil stx1 foi mais comum, detectado em 20,4% (202/990) dos isolados, seguido de stx2 (4,54%, 45/990) e stx1+stx2 (2,92%, 29/990). O gene stx1 foi detectado mais frequentemente em bezerros que animais adultos. No período de seca (inverno), a presença do perfil stx1+stx2 nas fezes dos bovinos foi mais prevalente que no período chuvoso (verão), apesar de não haver diferença significativa entre estações para os perfis stx1 e stx2. Os grupos filogenéticos mais predominantes em animais adultos foram B1, A e D, enquanto grupos A e B2 prevaleceram em bezerros. Nossos dados enfatizam a importância de se detectar reservatórios de STEC já que 7,5% dos isolados testados foram positivos para stx2, o perfil mais prevalente em casos de síndrome hemolítica-urêmica. Ademais, esses microorganismos são adaptados à sobreviver em ambientes hostis e contaminam a cadeia alimentar, levando a risco significativo para consumidores de alimentos de origem animal.(AU)

ppGpp and cytotoxicity diversity in Shiga toxin-producing Escherichia coli (STEC) isolates.

Shiga toxin-producing Escherichia coli (STEC) is a known food pathogen, which main reservoir is the intestine of ruminants. The abundance of different STEC lineages in nature reflect a heterogeneity that is characterised by the differential expression of certain genotypic characteristics, which in turn are influenced by the environmental conditions to which the microorganism is exposed. Bacterial homeostasis and stress response are under the control of the alarmone guanosine tetraphosphate (ppGpp), which intrinsic levels varies across the E. coli species. In the present study, 50 STEC isolates from healthy sheep were evaluated regarding their ppGpp content, cytotoxicity and other relevant genetic and phenotypic characteristics. We found that the level of ppGpp and cytotoxicity varied considerably among the examined strains. Isolates that harboured the stx2 gene were the least cytotoxic and presented the highest levels of ppGpp. All stx2 isolates belonged to phylogroup A, while strains that carried stx1 or both stx1 and stx2 genes pertained to phylogroup B1. All but two stx2 isolates belonged to the stx2b subtype. Strains that belonged to phylogroup B1 displayed on average low levels of ppGpp and high cytotoxicity. Overall, there was a negative correlation between cytotoxicity and ppGpp.

Virulence genes in isolates of Escherichia coli from samples of milk and feces from dairy cattle.

The aim of this work was to determine if Escherichia coli isolates carrying the virulence genes eae and eltB and exhibiting the Ehly phenotype are present in feces and milk samples from healthy dairy cattle on farms. Isolates from calves showed a statistically higher prevalence of eae and eltB compared with isolates from older animals. The other factors tested (stx(1), stx(2), and Ehly) were not statistically different between the two groups. Two isolates originating from calf feces were identified as serotype O157:H7; one of these isolates carried stx(1) and eae, the other stx(2) and eae. E. coli isolated from milk contained stx(1), stx(2), and eltB. The results show that feces or milk from healthy dairy cattle may contain E. coli pathotypes that express virulence genes, indicating that these materials have zoonotic potential. The results also reinforce the idea that host age can influence the dynamics of virulence genes in E. coli from cattle.

Characterization of Escherichia coli isolated from carcasses of beef cattle during their processing at an abattoir in Brazil.

Beef carcass sponge samples collected between March 2003 and August 2005 at an abattoir in Brazil were surveyed for the presence of Shiga toxin-producing Escherichia coli (STEC). Only one carcass among the 80 tested showed a STEC, stx2-encoding gene by PCR amplification. The frequency of carcass contamination by E. coli during processing was tested at three situations, respectively: preevisceration, postevisceration and postprocessing, during the rain and dry seasons. The prevalence of E. coli at the three points was of 30.0%, 70.0%, 27.5% in the rain season and of 22.5%, 55.0%, 17.5% during the dry season, respectively. The E. coli isolates exhibited a high level (45.0%) of multidrug resistance to two or more antimicrobial agents.