Downloaded from www.microbiologyresearch.org by IP: 54.70.40.11 On: Sat, 30 Mar 2019 20:49:22 D-Amino acids inhibit biofilm formation in Staphylococcus epidermidis strains from ocular infections Miriam L. Ramo ´ n-Pere ´z, 1 Francisco Diaz-Cedillo, 2 J. Antonio Ibarra, 1 Azael Torales-Carden ˜ a, 3 Sandra Rodrı ´guez-Martı ´nez, 3 Janet Jan-Roblero, 1 Mario E. Cancino-Diaz 3 and Juan C. Cancino-Diaz 1 Correspondence Juan C. Cancino-Diaz jccancinodiaz@hotmail.com Received 13 March 2014 Accepted 4 July 2014 1 Departments of Microbiology, Escuela Nacional de Ciencias Biolo ´ gicas-Instituto Polite ´ cnico Nacional, Carpio y Plan de Ayala S/N. Col. Santo Tomas. Deleg. Miguel Hidalgo. C.P. 11340 Mexico City, Mexico 2 Organic Chemistry, Escuela Nacional de Ciencias Biolo ´ gicas-Instituto Polite ´ cnico Nacional, Carpio y Plan de Ayala S/N. Col. Santo Tomas. Deleg. Miguel Hidalgo. C.P. 11340 Mexico City, Mexico 3 Immunology, Escuela Nacional de Ciencias Biolo ´ gicas-Instituto Polite ´ cnico Nacional, Carpio y Plan de Ayala S/N. Col. Santo Tomas. Deleg. Miguel Hidalgo. C.P. 11340 Mexico City, Mexico Biofilm formation on medical and surgical devices is a major virulence determinant for Staphylococcus epidermidis. The bacterium S. epidermidis is able to produce biofilms on biotic and abiotic surfaces and is the cause of ocular infection (OI). Recent studies have shown that D-amino acids inhibit and disrupt biofilm formation in the prototype strains Bacillus subtilis NCBI3610 and Staphylococcus aureus SCO1. The effect of D-amino acids on S. epidermidis biofilm formation has yet to be tested for clinical or commensal isolates. S. epidermidis strains isolated from healthy skin (n53), conjunctiva (n59) and OI (n519) were treated with D-Leu, D-Tyr, D-Pro, D-Phe, D-Met or D-Ala and tested for biofilm formation. The presence of D-amino acids during biofilm formation resulted in a variety of patterns. Some strains were sensitive to all amino acids tested, while others were sensitive to one or more, and one strain was resistant to all of them when added individually; in this way D-Met inhibited most of the strains (26/31), followed by D-Phe (21/31). Additionally, the use of D-Met inhibited biofilm formation on a contact lens. The use of L-isomers caused no defect in biofilm formation in all strains tested. In contrast, when biofilms were already formed D-Met, D-Phe and D-Pro were able to disrupt it. In summary, here we demonstrated the inhibitory effect of D-amino acids on biofilm formation in S. epidermidis. Moreover, we showed, for the first time, that S. epidermidis clinical strains have a different sensitivity to these compounds during biofilm formation. INTRODUCTION As for many other compounds, two chiral variants of amino acid exist in nature; the L- version is used for protein synthesis by ribosomes in living organisms, while the D- version is not involved in this pathway. Roles for D- amino acids have been described in both eukaryotic and bacterial cells (Kim et al., 2010; Kleckner & Dingledine, 1998; Wolosker et al., 2002; Wolosker, 2007). In bacteria, some peptides have D-amino acids that could be incor- porated through one of two mechanisms (Bodanszky & Perlman, 1969): (1) post-translational conversion from L- to D- inside the peptide or (2) activity of non-ribosomal peptide synthetases, this being the most common pathway in bacteria. D-Amino acids have multiple roles in bacterial homeostasis; they can be used as nutrients for growth (Chang & Adams, 1974; Conrad et al., 1974; Pioli et al., 1976; Roesch et al., 2003), allow germination of bac- terial spores, as in Bacillus anthracis with D-alanine (D-Ala) (Hills, 1949; Halvorson & Spiegelman 1952), and could also be a component of the cell wall (Veiga et al., 2006; Bellais et al., 2006). Moreover, D-amino acids can be secreted and have an inhibitory effect in cell division. This effect is caused by the incorporation of amino acids into the peptidoglycan layer causing destabilization of the whole structure (Izaki et al., 1968; Hammes, 1978; Caparros et al., 1991, 1992). Recently, it has been found that diverse bacterial phyla produce different types of D-amino acids in the stationary growth phase and this correlates with the Abbreviations: EPS, extracellular polysaccharide matrix; HC, healthy conjunctiva; HS, healthy skin; LTA, lipoteichoic acid; OI, ocular infection. Journal of Medical Microbiology (2014), 63, 1369–1376 DOI 10.1099/jmm.0.075796-0 075796 G 2014 The Authors Printed in Great Britain 1369