Obligate anaerobes metabolise energy by anaerobic respiration or fermentation. Currently known "Shewanella" species are heterotrophic facultative anaerobes. The least common were infections caused exclusively by anaerobes and facultative organisms. CHG is active against Gram-positive and Gram-negative organisms, facultative anaerobes, aerobes, and yeasts. This allows the differentiation of obligate aerobes, obligate anaerobes, facultative anaerobes, microaerophiles, and aerotolerant organisms. Some obligate anaerobes use fermentation, while others use anaerobic respiration. This is observable when facultative anaerobes are cultured in thioglycolate broth. However, microaerophiles metabolise energy aerobically, and obligate anaerobes metabolise energy anaerobically. They are obligate anaerobes capable of producing endospores. There are organisms that can adjust their metabolism to their environment, such as facultative anaerobes. Metronidazole&colon; This is an antimicrobial effective against some protozoa and strict anaerobes. Some fermentation processes involve obligate anaerobes, which cannot tolerate oxygen. It is commonly isolated from dental abscesses, where obligate anaerobes predominate. Biogas is methane produced by the process of anaerobic digestion of organic material by anaerobes. Pasteurellaceae are typically rod-shaped, and are a notable group of facultative anaerobes.