Tuesday, 20 March 2012

Specific Strains of Escherichia coli Are Pathogenic for the Endometrium of Cattle and Cause Pelvic Inflammatory Disease in Cattle and Mice

Pelvic inflammatory disease (PID) is an infection of the female genital tract caused by Escherichia coli in the uterus (Sheldon, et al., 2010). PID is an extremely uncomfortable and often painful infection in females which can lead to infertility and pre-term labour (Sheldon, et al., 2010). Observation of a herd of cattle during this study showed that 40% of the animals tested developed PID within a week of childbirth and 20% develop an irritated uterus for more than three weeks proceeding childbirth (Sheldon, et al., 2010). Pathogenic E. coli has a faecal-oral transmission system in cattle whereby the grass the animals digest has been infected with pathogenic E. coli contaminated manure by cattle farmers (Tilden, et al., 1996).

This study of the causes of PID in cattle tested the hypothesis that the there was a specific endometrial  pathogenic E. coli (EnPEC) strain causing the inflammation of the uterus and PID in cattle and not just a combination of random strains of genetically different E. coli (Sheldon, et al., 2010).

The experiment was conducted by studying a herd of 64 cattle for a year, taking 114 samples of uterine bacteria every week after childbirth  (Sheldon, et al., 2010). The samples were split into four phylogenetic groups (A, B1, B2, D) using Triplex PCR; a system of DNA amplification (Reece, et al., 2011); which each contained different strains of E. coli (Sheldon, et al., 2010). It was then noted that Group D came from the group of clinically unaffected cattle that were tested as a control (Sheldon, et al., 2010). Proceeding this, the bacterial samples were categorised using Random Amplification of Polymorphic DNA (RAPD) and multilocus sequence typing (MLST) into clusters of samples making it easier to test and categorise which strains of bacteria were most likely to be associated PID (Sheldon, et al., 2010).

The proceeding test in this experiment showed that the bacteria cells from Cluster 1 were totally disassociated with PID while the bacteria samples from Clusters 2, 3, and 4 were associated with PID (Cluster 3 was associated less than the remaining two however) (Sheldon, et al., 2010). These samples were tested against known pathogenic E. Coli strains. The results showed that the bacteria found in these Clusters were more adherent and invasive towards the endometrium cells and stimulated the greatest immune response in the animal (Sheldon, et al., 2010).

The effect of lipopolysacchrides (LPS), taken from the membrane of E. coli bacteria, was also tested on the endometrium of laboratory mice in vivo (Sheldon, et al., 2010). Most of the mice developed endometritis or PID indicating strong evidence to suggest that the E. coli causes PID in mice (Sheldon, et al., 2010).

The tests also showed that the bacteria use pili as an adhesion device (Sheldon, et al., 2010). A fimbrial inhibiting solution was added to the bacteria in some of the mice and this reduced the infection. This evidence could be used in treating PID in humans (Sheldon, et al., 2010).

PID does not just affect cattle and mice, it is a huge problem in humans as well, being one of the most important causes of infertility in female humans. This study concluded that there was in fact a specific strain of E. coli that was pathogenically adapted to cause PID in cattle.

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