Which of the following microorganisms causes acne?
a) Bacteria
b) Fungi
c) Protozoans
d) Virus

Hint:-A skin condition characterized by pimples, whiteheads, blackheads and scars is called acne. It causes when the oil secreting glands are overactive and their secretions clog hair follicles. Acne commonly occurs on the face, chest and upper back. The clogged pores of the skin are inhabited by spore forming microorganisms.

Complete Answer:-
Option (a) is correct. Bacteria of the genus Mycobacterium causes acne. They are Gram-positive rod-shaped bacteria present on the skin of human beings. The bacteria derive energy and nutrients from the sebum secreted by sebaceous glands. Over secretion of sebum and oil glands clogged hair follicles of the skin and facilitated excessive growth of Cutibacterium, which in turn causes inflammation and other symptoms of acne. Growth of Cutibacterium facilitates the growth of another opportunistic bacteria called Staphylococcus aureus that aggravates the symptoms of acne.
Option (b) is incorrect. Fungi are heterotrophic organisms. Fungi are eukaryotic organisms that belong to the decomposer level of the ecosystem. Many fungi live symbiotically with many plants and animals. They reproduce by means of spores. Common examples of fungi are moulds and yeasts.
Option (c) is incorrect. Protozoans are unicellular organisms that lack cell walls and belong to a separate kingdom called Protista. Protozoans are free living or parasitic in nature and are found in water, land and also inside bodies of multicellular animals. They reproduce sexually and asexually. Examples of protozoa are Plasmodium, Trypanosoma, Leishmania, etc.
Option (d) is incorrect. Virus is an infectious agent found inside bodies of a wide range of unicellular and multicellular organisms. Viruses are generally covered with a protective protein cover called capsid. The genetic material comprises either DNA or RNA. The viruses do not grow and divide independently. They use the machineries of the host to replicate and derive nutrition. Some common diseases caused by viruses are Ebola, Herpes, rabies, SARS, etc.
Thus, the right option is A.

Note:- Acne is a condition of skin caused by opportunistic bacteria. The condition is characterized by pimples, blackheads and whiteheads. It is caused due to over secretion of sebum followed by clogging of pores of skin. Acne often leads to depression, anxiety and lowered self esteem in affected individuals.