Provided herein are methods and compositions for the treatment or prevention of a skin disease (e.g., acne) in a subject by administering to the subject a composition comprising a strain of P. granulosum, a strain of P. avidum, and/or a strain of P. humerusii. Also provided herein are methods of determining whether a subject has a skin condition, the method comprising measuring the amount of P. granulosum on the skin of the subject.
