Which of the following is NOT an anaerobe?

Campylobacter is the correct choice as it is NOT an anaerobe. This genus of bacteria is characterized as a microaerophilic organism, which means it requires a reduced level of oxygen for growth, rather than completely anaerobic conditions. Microaerophilic organisms thrive in environments with lower oxygen concentrations compared to atmospheric levels, typically around 5-10% oxygen, which distinguishes them from strict anaerobes that cannot tolerate any oxygen exposure.

In contrast, the other options listed are indeed anaerobic bacteria. Veillonella and Fusobacterium are both obligate anaerobes, meaning they can only survive in environments devoid of oxygen. Actinomyces can be classified as a facultative anaerobe or obligate anaerobe, depending on the species, but generally prefers environments without oxygen. Therefore, Campylobacter stands out as the only bacterium in the list that requires some oxygen for survival and growth, highlighting its unique metabolic needs among the options provided.