Which micro-organism is likely to be involved in cases of ANUG?

The correct choice is Borrelia vincenti, which is significantly associated with Acute Necrotizing Ulcerative Gingivitis (ANUG). This micro-organism is part of the normal oral flora but can become pathogenic under certain conditions, such as poor oral hygiene, stress, smoking, and immune suppression. Borrelia vincenti is known for its role in periodontal diseases, particularly those characterized by ulceration and necrosis of the gingiva, leading to the symptoms seen in ANUG, such as pain, bleeding, and foul breath.

In contrast, Treponema pallidum is primarily known for causing syphilis, Streptococcus mutans is primarily associated with dental caries through the formation of dental plaque, and Escherichia coli is mainly a gastrointestinal pathogen. While they are all harmful under specific circumstances, none are directly linked to the pathogenesis of ANUG as Borrelia vincenti is. Understanding the specific organisms involved in dental diseases is crucial for effective diagnosis and treatment in dental nursing practice.