Molecular and Functional Profiling of the Polyamine Content in Enteroinvasive E. coli : Looking into the Gap between Commensal E. coli and Harmful Shigella

Abstract

Polyamines are small molecules associated with a wide variety of physiological functions. Bacterial pathogens have developed subtle strategies to exploit polyamines or manipulate polyamine-related processes to optimize fitness within the host. During the transition from its innocuous E. coli ancestor, Shigella, the aetiological agent of bacillary dysentery, has undergone drastic genomic rearrangements affecting the polyamine profile. A pathoadaptation process involving the speG gene and the cad operon has led to spermidine accumulation and loss of cadaverine. While a higher spermidine content promotes the survival of Shigella within infected macrophages, the lack of cadaverine boosts the pathogenic potential of the bacterium in host tissues. Enteroinvasive E. coli (EIEC) display the same pathogenicity process as Shigella, but have a higher infectious dose and a higher metabolic activity. Pathoadaption events affecting the cad locus have occurred also in EIEC, silencing cadaverine production. Since EIEC are commonly regarded as evolutionary intermediates between E. coli and Shigella, we investigated on their polyamine profile in order to better understand which changes have occurred along the path to pathogenicity. By functional and molecular analyses carried out in EIEC strains belonging to different serotypes, we show that speG has been silenced in one strain only, favouring resistance to oxidative stress conditions and survival within macrophages. At the same time, we observe that the content of spermidine and putrescine, a relevant intermediate in the synthesis of spermidine, is higher in all strains as compared to E. coli. This may represent an evolutionary response to the lack of cadaverine. Indeed, restoring cadaverine synthesis decreases the expression of the speC gene, whose product affects putrescine production. In the light of these results, we discuss the possible impact of pathoadaptation events on the evolutionary emergence of a polyamine profile favouring to the pathogenic lifestyle of Shigella and EIEC.

Shifting national surveillance of Shigella infections toward geno‐serotyping by the development of a tailored Luminex assay and NGS workflow

“…It has been demonstrated that a higher level of spermidine increases Shigella survival within macrophages and confers higher resistance to oxidative stress (Barbagallo et al., ), indicating that the loss of speG function is an emerging trait. As predicted, EIEC have an intermediate position as active N‐acetylspermidine is still present in most EIEC strains (68.7% in our dataset), yet intracellular spermidine tends to be higher as compared to commensal E. coli (Campilongo et al., ). Interestingly, among all non‐ Shigella strains that were sent to the NRCS by peripheral Belgian laboratories, not a single strain with defective speG was detected (Appendix 2), strongly suggesting that the large majority are non‐EIEC strains.…”

Salmonella, Shigella, and Yersinia

“…Enteroinvasive E. coli are evolutionary intermediates between E. coli and Shigella . 78 Some of the enteroinvasive E. coli (EIEC) may cross-react with Shigella anti-sera. It should be noted that serological testing of the serum of an infected individual is generally not useful for diagnosis.…”

One Gene and Two Proteins: a Leaderless mRNA Supports the Translation of a Shorter Form of the Shigella VirF Regulator

“…(E) Identification of the VirF 21 binding site on the virF promoter based on DNase I footprinting results. Plasmid pMYSH6504 DNA (41) was incubated with 0, 10 or 20 µl of in vitro -translated VirF 21 . The samples were DNase I treated and subsequently analyzed as described in Materials and Methods, using ML-U30 and ML-U29 as primers.…”

“…Total RNA from exponentially growing plasmid-carrying E. coli strains was extracted (41). Total RNA (10 to 20 µg) was hybridized with 5′- 32 P-labeled ML-512 and ML-1314 primers.…”