Characterisation of a Transposon-induced Pleiotropic Mutant ofClostridium acetobutylicumP262

Metronidazole: an update on metabolism, structure-cytotoxicity and resistance mechanisms

Metronidazole, a nitroimidazole, remains a front-line choice for treatment of infections related to inflammatory disorders of the gastrointestinal tract including colitis linked to Clostridium difficile. Despite >60 years of research, the metabolism of metronidazole and associated cytotoxicity is not definitively characterized. Nitroimidazoles are prodrugs that are reductively activated (the nitro group is reduced) under low oxygen tension, leading to imidazole fragmentation and cytotoxicity. It remains unclear if nitroimidazole reduction (activation) contributes to the cytotoxicity profile, or whether subsequent fragmentation of the imidazole ring and formed metabolites alone mediate cytotoxicity. A molecular mechanism underpinning high level (>256 mg/L) bacterial resistance to metronidazole also remains elusive. Considering the widespread use of metronidazole and other nitroimidazoles, this review was undertaken to emphasize the structure-cytotoxicity profile of the numerous metabolites of metronidazole in human and murine models and to examine conflicting reports regarding metabolite-DNA interactions. An alternative hypothesis, that DNA synthesis and repair of existing DNA is indirectly inhibited by metronidazole is proposed. Prokaryotic metabolism of metronidazole is detailed to discuss new resistance mechanisms. Additionally, the review contextualizes the history and current use of metronidazole, rates of metronidazole resistance including metronidazole MDR as well as the biosynthesis of azomycin, the natural precursor of metronidazole. Changes in the gastrointestinal microbiome and the host after metronidazole administration are also reviewed. Finally, novel nitroimidazoles and new antibiotic strategies are discussed.

Physical and genetic map of the Clostridium saccharobutylicum (formerly Clostridium acetobutylicum) NCP 262 chromosome

A physical and genetic map of the Clostridium saccharobutylicum NCP 262 chromosome was constructed. The order of macrorestriction fragments was determined by analysing fragments generated after single and double digestion with the restriction enzymes BssHII, I-CeuI, Sse8387I, RsrII and SfiI and separation by PFGE. The I-CeuI backbone of C. saccharobutylicum was constructed by indirect end-labelling with rrs- and 3' rrl-specific probes located on either side of the I-CeuI site in the rrn operon, and reciprocal separation of BssHII and I-CeuI digestion products by two-dimensional PFGE. The positions of BssHII fragments on the physical map were determined using a library of linking clones containing BssHII cleavage sites. The size of the circular genome was estimated to be 5.3 Mb with a mean resolution of approximately 140 kb. The chromosome of C. saccharobutylicum contains 12 rrn operons, located on 46% of the chromosome, which are transcribed divergently from the deduced origin of replication. The genetic map was constructed by determining the location of 28 genes involved in house-keeping, heat-shock response, sporulation, electron transfer and acid- and solvent-formation. Comparison of the C. saccharobutylicum genetic map with those of the spore-forming bacteria Bacillus subtilis, Clostridium acetobutylicum, Clostridium perfringens and Clostridium beijerinckii indicated C. saccharobutylicum to be most similar to the latter two Clostridium species, with the order of the genes within the gyrAB and recA loci being conserved.