Lactobacilli and bifidobacteria are known to exert various health benefits via the production of antimicrobial compounds that are able to inhibit growth of some pathogenic
bacteria such as Escherichia coli, Staphylococcus aureus
and Pseudomonas aeruginosa (Tham et al. 2011). They
are also capable of producing compounds that are beneficial
to the skin such as acetic acid, lactic acid, and diacetyl
which could inhibit the invasion of various dermal pathogens (Pasricha et al. 1979; Nagoba et al. 2008; Lanciotti et
al. 2003). Production of lactic acid and acetic acid by
lactobacilli and bifidobacteria is one of the most important
properties contributing to their antimicrobial activities. It
has been reported that acetic acid showed excellent bactericidal effect even at low concentration, especially on Gramnegative bacteria, and thus may inhibit opportunistic dermal
pathogens. The inhibitory effect of acetic and lactic acids is
mainly attributed to interference with essential metabolic functions, dissipation of cell membrane permeability, and
reduction of intracellular pH (Suskovic et al. 2010). Moreover, lactic acid, as one of the α-hydroxy acids, has potential
in skin applications, attributed to its ability to improve the
stratum corneum barrier function and enhance the production of ceramides by keratinocytes (Rawlings et al. 1996).
Diacetyl on the other hand is a product of citrate metabolism
and is one of the identified antimicrobial compounds produced by lactobacilli and bifidobacteria during fermentation. It plays a role in controlling the growth of Gramnegative skin bacteria such as Escherichia coli by inhibiting
arginine utilization