Modelling inactivation of wild-type and clinical Escherichia coli O26 strains using UV-C and thermal treatment and subsequent persistence in simulated gastric fluid.

AIMS: First, two inactivation models were compared for different phenotypic profiles of Escherichia coli O26 using ultraviolet-C light (UV-C) and thermal treatment (T), by means of Central Composite Rotatable Design of Experiment (CCRD). Second, we aimed to evaluate the subsequent survival and persistence of cells in simulated gastric fluid (SGF). METHODS AND RESULTS: Two strains of E. coli O26, a wild-type strain and a clinical ATCC strain were used in both steps. A CCRD was used in a 22 arrangement in random order. The goodness-of-fit of the models was determined. The lack of fit, and the normality of residual data were checked with the Shapiro-Wilk test, and the model accuracy factor, bias factor and the model mean square error (MSE) were measured. Subsequently, the resistance capacity of the strains was evaluated after exposure to simulated gastric acid. The CCRD results obtained indicate that the mild heat (<70°C) has a recovery effect. In addition, for the clinical strain, the UV-C and heat (above 70°C) has an additive inactivation effect. Moreover, temperature (65°C) induced SGF resistance by the wild-type and clinical strain. For the clinical strain, cells exposed to UV-C were more sensitive to SGF. In contrast to clinical strain, exposing cells of the wild-type strain to UV-C increased the survival capacity in the SGF. CONCLUSION: Response surface analyses showed that the wild-type O26 strain has higher persistence under unfavourable conditions than the clinical strain, and the stresses caused by applied microbial control technologies can increase the survival capacity in the SGF. SIGNIFICANCE AND IMPACT OF THE STUDY: The present study shed light on different phenotypic responses in the same bacterium serogroup. Moreover, the impact of the study was that strain selection criteria must be adequate to develop effective models of inactivation.

Bacteriological and molecular detection of Mycobacterium bovis in cattle with inconclusive results to intradermal tuberculin tests.

A dairy herd (77 cows) from Rio de Janeiro, Brazil, with a history of tuberculosis infection was tested by a comparative cervical test (CCT). Seventeen cows were reactive and seven were inconclusive (swelling ≥ 2.0 mm and ≤ 3.9 mm, respectively). All of these 24 cows were slaughtered and necropsied ; samples from lungs and lymph nodes were collected for multiplex polymerase chain reaction (PCR) and culturing. Infection was confirmed in 23/24 (95.8%) of the slaughtered animals (five by culturing, four by PCR, and 14 by both tests). All cows with inconclusive results at CCT were confirmed as infected. Although slaughter of inconclusive reactor cows is not mandatory in many countries, our study provided evidence to support the slaughter of these cows, at least during an outbreak.

Prevalência de tuberculose bovina em animais e rebanhos abatidos em 2009 no estado de Mato Grosso, Brasil / Prevalence of bovine tuberculosis in herds and animals slaughtered in 2009 in the State of Mato Grosso, Brazil

Estimou-se a prevalência de tuberculose em bovinos, e em seus respectivos rebanhos, abatidos em 2009 no estado de Mato Grosso, utilizando como diagnóstico confirmatório o exame bacteriológico e o molecular a partir de fragmentos de tecidos lesionados. Nos sete abatedouros selecionados, detentores de serviço de inspeção federal (SIF), foram inspecionados 41.193 bovinos, sadios ao exame ante mortem, procedentes de 492 rebanhos originários de 85 (60%) municípios mato-grossenses. Um total de 198 carcaças apresentaram lesões suspeitas. Apenas três carcaças (3/198) apresentaram lesões confirmadas como tuberculosas pelos diagnósticos laboratoriais. A prevalência aparente de tuberculose bovina em animais e rebanhos abatidos no estado de Mato Grosso foi de 0,007% [IC 95% = -0,001%; 0,016%] e 0,61% [IC 95% = -0,08%; 1,30%], respectivamente. O estado do Mato Grosso possui, naturalmente, um status sanitário considerado de baixa prevalência.

The prevalence of bovine tuberculosis in cattle, and its herds, slaughtered in 2009 in the state of Mato Grosso, Brazil, was estimated using bacteriological analysis and molecular test, from fragments of injured tissues as well as direct DNA templates. 41,193 cattle, which appeared healthy in the ante mortem examination, from seven selected slaughterhouses, under Brazilian federal inspection services (SIF), were inspected. The animals were from 492 herds located in 85 (60%) different cities of Mato Grosso. A total of the 198 carcasses had suspicious lesions. Three carcasses (3/198) had lesions that were found to be tuberculous in laboratory diagnosis. The apparent prevalence of bovine tuberculosis in the total number of animals and in herds slaughtered in Mato Grosso was 0.007% [IC 95% = -0.001%; 0.016%] and 0.61% [IC 95% = -0.08%; 1.30%], respectively. The sanitation status demonstrated in Mato Grosso indicates the progress in this state toward the eradication of bovine tuberculosis.