Clostridium is a genus of spore forming Gram-positive bacteria that grow under anaerobic conditions comprising more than 100 species. There are four main species responsible for diseases in humans and other warm-blooded animals: C. botulinum, an organism producing a toxin in food or wounds that causes botulism; C. difficile, which can cause pseudomembraneous colitis, toxic megacolon and antibiotic associated diarrheas; C. tetani, which is the causative organism of tetanus; and C. perfringens, which can cause enterotoxemia, necrotizing enteritis, and gas gangrene.
C. perfringens is ubiquitous in the environment and is found in soil, dust, raw ingredients such as spices used in food processing, and in the intestines of humans and animals. It produces over 15 different toxins resulting in various enteric conditions. C. perfringens infections can also cause gut health problems in broiler flocks with significant negative economic consequences.
C. difficile is an opportunistic gram positive, anaerobic, spore forming bacillus, and causes Clostridium difficile infections (CDI) such as antibiotic-associated diarrhoea (CDAD) and colitis which burdens healthcare systems across the globe. In the last decade, rates of C. difficile infections have increased dramatically, particularly hospital-acquired infection (nosocomial infection), resulting in increased morbidity, an increased incidence of complications requiring colectomy, and rising mortality.
It is estimated that 3 to 15% of the normal population is infected with C. difficile. However, rates of infection are much higher in hospitalised patients. C. difficile colonises the intestine and in many subjects infected the bacteria lives in equilibrium with other gut flora and is asymptomatic. However, if the homoeostasis of the normal intestinal flora is disturbed, for example as a result of previous antibiotic use, the use of drugs which alter the gastric pH (for example proton pump inhibitors), or gastrointestinal surgery, symptomatic CDI can arise as a result of the proliferation of the C. difficile in the intestine. Toxins produced by the C. difficile disrupt the colonic epithelium, leading to an inflammatory response and clinical symptoms varying from mild diarrhoea to severe life-threatening pseudomembranous colitis.
C. difficile bacteria produce toxins, which can cause inflammation and damage to the lining of the lower gastro-intestinal tract, including the colon. There are a number of different strains of C. difficile, some of which can cause more serious illnesses than others. Strain NAP1/027/BI 027 (NAP1/027) produces particularly high levels of toxins and is associated with particularly severe CDI and high levels of mortality.
C. difficile infections are particularly associated with the clinical use of broad spectrum antibiotics, for example clindamycin, cephalosporins and amoxicillin-clavulinic acid). Fluoroquinolone antibiotics have been identified as a particular risk factor for CDI. Antibiotics commonly used to treat a primary infection in a subject (for example a urinary infection, a skin infection or other infection), kill the bacteria that cause the primary infection. However, they may also kill many of the bacteria present in the flora of the GI tract. Because C. difficile bacteria are not affected by many commonly used antibiotics this can result in the proliferation of C. difficile in the intestine and the presence of high levels of associated toxins resulting in the emergence of symptoms of a CDI.
C. difficile infection is the most common infectious cause of nosocomial diarrhoea in elderly patients, accounting for 15% to 25% of all cases of antibiotic-induced diarrhoea. Patients undergoing total joint arthroplasty are at particular risk of CDI because of the advanced age of the patients, the use of prophylactic antibiotic coverage in the perioperative period, multiple comorbid conditions, and length of hospital stay required for recovery.
The treatment of C. difficile infections depends on the severity of the associated symptoms or disease. Generally asymptomatic infections are not treated. However, if symptoms develop treatments are generally required to reduce the symptoms and prevent the infection from worsening.
Generally a first step in the treatment of CDI is the cessation of the inciting antibiotic. Treatment with concomitant antibiotics (i.e. antibiotics other than those given to treat C. difficile infection) is associated both with significant prolongation of diarrhoea and with an increased risk of recurrent CDI. If concomitant antibiotics are essential for treatment of the primary infection, it is generally prudent, if possible, to use an antibiotic therapy that is less frequently implicated in antibiotic-associated CDI, such as parenteral aminoglycosides, sulfonamides, macrolides, vancomycin, or tetracycline (Läkartidningen, 103(46), 2006).
C. difficile infection, such as CDAD is usually treated with metronidazole or oral vancomycin. A new antibiotic against C. difficile has recently been approved, fidaxomicin (OPT-80, PAR-101), a macrocyclic antibiotic. In phase III clinical trials, fidaxomicin was non-inferior to vancomycin in achieving clinical cure of CDAD. Fidaxomicin treatment was also superior to vancomycin in preventing recurrence of CDAD. These results, combined with the ease of administration and a somewhat better safety profile has made fidaxomicin an attractive treatment option for treating CDAD. (Louie, T. J., Miller, M. A., Mulvane, K. M., Weiss, K., Lenten, A. Shoe, Y. K. (2011). Fidaxomicin versus Vancomycin for Clostridium difficile infection. New England Journal of Medicine, 364, 422-431). However, resistance towards metronidazole, vancomycin and fidaxomicin has been observed.
Rifamycins and derivatives, for example rifampicin and rifaximin, have been successfully used to treat recurrent CDI. However, rapid spontaneous resistance evolution has also been observed with this class of antibiotic and the spread of, for example rifampicin-resistant C. difficile in hospitals is an increasing concern.
Teicoplanin (although not widely available and expensive) is another antibiotic with high reported efficacy against CDI, and limited data suggest that it may be effective in recurrent CDI.
Patients who have had one CDI are at risk of recurrence of the infection. The rate of recurrent CDI (RCDI) is estimated to be 15% to 30%. Patients with recurrent C. difficile infections in hospitals and the community constitute an increasing treatment problem. Whilst most patients with a first infection respond to either metronidazole or oral vancomycin, current therapeutic approaches to recurrent C. difficile infections are prone to failure, increasing the risk of antibiotic resistance emerging. Most treatment guidelines recommend prolonged oral vancomycin pulse and/or tapering dosage regimens. However, evidence supporting the effectiveness of such dosage regimens is limited.
The spores formed by C. difficile are thought to be the primary mechanism for the transmission or spread of infection. Additionally spores present in the colon of a patient may be responsible for recurrence of C. difficile infections, even after elimination of the bacterial with antibiotic treatment. Fidaxomycin has been shown to inhibit C. difficile spore formation (Babakhani et al, S162 CID 2012:55 (suppl 2)). There is however a need for additional agents that can inhibit spore formation and thus minimise the risk of transmission and/or recurrence of C. difficile infections.
U.S. Pat. No. 8,618,100 discloses chromanyl derivatives described as having antibacterial activity against Clostridium bacteria, in particular Clostridium perfringens. 
PCT patent application WO2008/039640 discloses the compound 5-[3-((R)(+)-6,8-dibromo-chroman-4-ylamino)-propylamino]-4H-thieno[3,2-b]pyridine-7-one, which is also known as REP3123, and its antibacterial activity against Clostridium difficile. In vitro tests of the antibacterial activity of the REP3123 compound demonstrate that said compound is active against bacteria of the Clostridium genus however REP3123 also has antibacterial activity against a wide variety of bacteria that are present in the gut.
U.S. Pat. No. 8,796,292 discloses that certain 7-substituted-2-(benzylamino)-6-oxopurines have potent activity against the growth of the intestinal anaerobe C. difficile, but weak activity against other, intestinal Gram-positive anaerobes. The compounds are described to be useful in reducing the likelihood of developing or to treat C. difficile infections.
PCT application WO2014135891 describes the rectal administration of compositions comprising fidaxomicin. The compositions are described as useful for the treatment or maintenance of remission of infections such as diarrhea caused by C. difficile. 
PCT application WO2012/050826 describes the use of reutericyclin or reutericyclin analogs in order to kill C. difficile organisms and thus alleviate the signs and symptoms of C. difficile infection.
There is however a need for new treatments for C. difficile. 
Halogenated salicylanilides such as niclosamide, closantel and rafoxanide, are important anthelmintics that are used extensively in the control of Haemonchus spp. and Fasciola spp. infestation in sheep and cattle, and Oestrus ovis in sheep.
Niclosamide is commercially available in a number of formulations including, but not limited to Bayer73®, Bayer2353®, Bayer25648®, Bayluscid®, Baylucide®, Cestocid®, Clonitralid, Dichlosale®, Fenasal®, HL 2447®, Iomesan®, Iomezan®, Manosil®, Nasemo®, Niclosamid®, Phenasal®, Tredemine®, Sulqui®, Vermitid®, Vermitin® and Yomesan®.
Niclosamide has been proposed as a possible systemic treatment for chronic lung infections caused by the proteobacterium Pseudomonas aeruginosa and the actinobacterium Mycoplasmum tuberculosis (F. Imperi et al., Antimicrobial, Agents and Chemotherapy, 557(2), 996-1005 (2013)).
J. Vinsova et al. (Molecules, vol. 12, no. 1, pp. 1-12, 2007; Bioorganic and Medicinal Chemistry Letters, vol. 19, no. 2, pp. 348-351, 2009; European Journal of Medicinal Chemistry, vol. 45, no. 12, pp. 6106-6113, 2010) describe certain antibacterial activity of salicylanilides, however, there is no disclosure of the treatment of CDI.
Ghazi et al. (Zentralbl. Mikrobiol. 141 (1986), 225-232) have tested the antibacterial effect and toxicity of synthesized salicylanilide derivatives against Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa and Staphylococcus aureus. 
M. J. Macielag et al. tested for antibacterial activity of closantel and related derivatives against the drug-resistant organisms, methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecium (VREF) (J. Med. Chem., 41(16), 2939-45 (1998)).
D. J. Hlasta et al. found that closantel had antibacterial activity against drug resistant S. aureus and E. faecium (Bioorg. Med. Chem. Letters, 8(14), 1923-28 (1998)).
R. Rajamuthiah et al. (PloS One, 2014, 9(2): e89189) identified closantel as a hit in a high throughput liquid screening assay and found anti-staphylococcal activity of closantel against vancomycin-resistant S. aureus isolates and other Gram-positive bacteria.
R. Rajamuthiah et al. (PloS One, 2015, 10(4):e0124595) describe that niclosamide and oxyclosanide have activity against MRSA.
Pauk et al. Bioorg. & Med. Chem. 23, 6574-6581 (2013), discloses the in-vitro antimicrobial activity of certain halogenated salicylanilides and derivatives.
WO 2008/155535 describes the use of halogenated salicylanilides for the treatment of acne resulting from propioni bacterial infection.