War has been declared against Staphylococcus aureus
Microbial imbalance–or dysbiosis– of the skin, caused particularly by Staphylococcus aureus, and atopic dermatitis, are closely linked. We now know that the imbalance precedes the onset of the disease in some individuals. An important step forward for basic research, and even more for the development of new therapeutic strategies.
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It has been established since the mid-1970s that the skin of individuals suffering from atopic dermatitis is generally colonized by Staphylococcus aureus. Highly pathogenic, its name often refers to tricky infections41. It is in particular responsible for the largest number of nosocomial infections (in hospitals), as well as skin or foodborne infections of variable severity. It was also recently discovered that the infection is more severe where these bacteria are present in greater numbers and belong to certain specific strains42. Meanwhile, technical progress made in the field of genetics has allowed the composition of the cutaneous flora of affected individuals to be better described, and has revealed a reduced bacterial diversity43. But up until now, it was not known whether the abundance of Staphylococcus aureus was the cause of atopic dermatitis or an observed consequence of the dysbiosis of the cutaneous microbiota.
Staphylococcus aureus, herald of the disease
A recent prospective clinical trial has just shown that colonization by Staphylococcus aureus precedes the onset of the disease in children44. This led to imparting a causal role to the bacterium in the onset of the disease, which partly contradicts the conclusion of another recent study45 (which however also incriminates Staphylococcus strains). It required two years of study to arrive at this conclusion: the researchers regularly analyzed skin samples taken from the elbow creases and the axillae, areas that are classically affected. First result: one child in four developed atopic dermatitis. Secondly: the proportion of Staphylococcus aureus increases markedly from the age of three months in infants who were subsequently reported to have atopic dermatitis. On the contrary, other bacteria, less abundant in infants suffering from atopic dermatitis, seem to have a potentially protective role46.
Other methods of eradication
Non-clinical and in vitro experiments have shown that Staphylococcus aureus could promote the disease in individuals with a genetic predisposition by triggering toxic and/or inflammatory reactions in skin cells exposed directly to the microbes47. By extrapolation, researchers thought that elimination of this bacterium could be beneficial in the treatment of atopic dermatitis. Relatively effective treatments already exist–topical antimicrobials, antibiotics, dilute bleach baths–but paradoxically, it is not known whether they really eliminate Staphylococcus aureus colonization nor what is their impact on the cutaneous microbiota. For this reason, similar to transplants of fecal flora, transplants of cutaneous microbiota48 containing bacteria known to act against Staphylococcus aureus is an emerging protocol. The first trials conducted on affected individuals led to a considerable reduction in colonization by Staphylococcus aureus. We wager that the next trials will validate this promising start and will be accompanied by improvements in treatment.
41. Leyden JJ, Marples RR, Kligman AM. Staphylococcus aureus in the lesions of atopic dermatitis. Br J Dermatol. 1974; 90:525–30
42. Byrd AL, Deming C, Cassidy SKB, Harrison OJ, Ng WI, Conlan S, et al. Staphylococcus aureus and Staphylococcus epidermidis strain diversity underlying pediatric atopic dermatitis. Sci Transl Med. 2017
43. Kong HH, Oh J, Deming C, Conlan S, Grice EA, Beatson MA, et al. Temporal shifts in the skin microbiome associated with disease flares and treatment in children with atopic dermatitis. Genome Res. 2012
44. Williams MR, Gallo R. Evidence that Human Skin Microbiome Dysbiosis Promotes Atopic Dermatitis. J Invest Dermatol. 2017 December
45. Kennedy EA, Connolly J, Hourihane JO, Fallon PG, McLean WH, Murray D, et al. Skin microbiome before development of atopic dermatitis: early colonization with commensal staphylococci at 2 months is associated with a lower risk of atopic dermatitis at 1 year. J Allergy Clin Immunol. 2017
46. Meylan P, Lang C, Mermoud S, Johannsen A, Norrenberg S, Hohl D, et al. eSkin colonization by Staphylococcus aureus precedes the clinical diagnosis of atopic dermatitis in infancy. J Invest Dermatol. 2017
47. Nakamura Y, Oscherwitz J, Cease KB, Chan SM, MunozPlanillo R, Hasegawa M, et al. Staphylococcus delta-toxin induces allergic skin disease by activating mast cells. Nature. 2013
48. Nakatsuji T, Chen TH, Narala S, Chun KA, Two AM, Yun T, et al. Antimicrobials from human skin commensal bacteria protect against Staphylococcus aureus and are deficient in atopic dermatitis. Sci Transl Med. 2017