SUMMARY Although Escherichia coli can be an innocuous resident of the gastrointestinal tract, it also has the pathogenic capacity to cause significant diarrheal and extraintestinal diseases. Pathogenic variants of E. coli (pathovars or pathotypes) cause much morbidity and mortality worldwide. Consequently, pathogenic E. coli is widely studied in humans, animals, food, and the environment. While there are many common features that these pathotypes employ to colonize the intestinal mucosa and cause disease, the course, onset, and complications vary significantly. Outbreaks are common in developed and developing countries, and they sometimes have fatal consequences. Many of these pathotypes are a major public health concern as they have low infectious doses and are transmitted through ubiquitous mediums, including food and water. The seriousness of pathogenic E. coli is exemplified by dedicated national and international surveillance programs that monitor and track outbreaks; unfortunately, this surveillance is often lacking in developing countries. While not all pathotypes carry the same public health profile, they all carry an enormous potential to cause disease and continue to present challenges to human health. This comprehensive review highlights recent advances in our understanding of the intestinal pathotypes of E. coli .

Escherichia coli is a remarkable and diverse organism. This normally harmless commensal needs only to acquire a combination of mobile genetic elements to become a highly adapted pathogen capable of causing a range of diseases, from gastroenteritis to extraintestinal infections of the urinary tract, bloodstream and central nervous system. The worldwide burden of these diseases is staggering, with hundreds of millions of people affected annually. Eight E. coli pathovars have been well characterized, and each uses a large arsenal of virulence factors to subvert host cellular functions to potentiate its virulence. In this Review, we focus on the recent advances in our understanding of the different pathogenic mechanisms that are used by various E. coli pathovars and how they cause disease in humans.

Nitazoxanide (NTZ) exhibits broad-spectrum activity against anaerobic bacteria and parasites and the ulcer-causing pathogen Helicobacter pylori. Here we show that NTZ is a noncompetitive inhibitor (K i , 2 to 10 M) of the pyruvate:ferredoxin/flavodoxin oxidoreductases (PFORs) of Trichomonas vaginalis, Entamoeba histolytica, Giardia intestinalis, Clostridium difficile, Clostridium perfringens, H. pylori, and Campylobacter jejuni and is weakly active against the pyruvate dehydrogenase of Escherichia coli. To further mechanistic studies, the PFOR operon of H. pylori was cloned and overexpressed in E. coli, and the multisubunit complex was purified by ion-exchange chromatography. Pyruvate-dependent PFOR activity with NTZ, as measured by a decrease in absorbance at 418 nm (spectral shift from 418 to 351 nm), unlike the reduction of viologen dyes, did not result in the accumulation of products (acetyl coenzyme A and CO 2 ) and pyruvate was not consumed in the reaction. NTZ did not displace the thiamine pyrophosphate (TPP) cofactor of PFOR, and the 351-nm absorbing form of NTZ was inactive. Optical scans and 1 H nuclear magnetic resonance analyses determined that the spectral shift (A 418 to A 351 ) of NTZ was due to protonation of the anion (NTZ ؊ ) of the 2-amino group of the thiazole ring which could be generated with the pure compound under acidic solutions (pK a ‫؍‬ 6.18). We propose that NTZ ؊ intercepts PFOR at an early step in the formation of the lactyl-TPP transition intermediate, resulting in the reversal of pyruvate binding prior to decarboxylation and in coordination with proton transfer to NTZ. Thus, NTZ might be the first example of an antimicrobial that targets the "activated cofactor" of an enzymatic reaction rather than its substrate or catalytic sites, a novel mechanism that may escape mutation-based drug resistance.Nitazoxanide [2-acetyloxy-N-(5-nitro-2-thiazolyl) benzamide] (NTZ) is a broad-spectrum drug that is efficacious for the treatment of infections caused by amitochondriate luminal parasites and helminths (8,15,21,26) and that shows promise as an alternative therapy for treating infections caused by Clostridium difficile (20). More generally, NTZ appears to be an effective treatment for persistent diarrhea (35) and even infections caused by rotavirus (26). NTZ shares some structural similarities with thiamine pyrophosphate (TPP) (Fig. 1) and exhibits a spectrum of activity similar to those of metronidazole (MTZ) and nitrofuran drugs (22), but several lines of evidence suggest that this drug is mechanistically different from the redox-active prodrugs (8,18,28). For example, NTZ does not increase the mutation frequency or produce DNA damage in Helicobacter pylori (28), and there is no cross-resistance with MTZ, as MTZ-resistant strains of Trichomonas vaginalis and H. pylori remain susceptible to NTZ (1,18,28,34). Unlike MTZ, resistance to NTZ has not been observed clinically or generated by in vitro methods commonly used to isolate MTZ r mutants of H. pylori (18). Despite the ever widening spe...