Monoclonal Antibodies against Accumulation-Associated Protein Affect EPS Biosynthesis and Enhance Bacterial Accumulation of Staphylococcus epidermidis

Jian Hu,Wenyan Tong,Yang Wu,Yalin Huang,Xueqin Wang,Fangyou Yu,Huayong Liu,Baixing Ding,Qiang Lou,Renzheng Huang,Di Qu,Tao Zhu,Jingran Liu,Tao Xu,Sarah K Highlander

doi:10.1371/journal.pone.0020918

Jian Hu, Wenyan Tong + Show 13 more

Open Access

https://doi.org/10.1371/journal.pone.0020918

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Abstract

Because there is no effective antibiotic to eradicate Staphylococcus epidermidis biofilm infections that lead to the failure of medical device implantations, the development of anti-biofilm vaccines is necessary. Biofilm formation by S. epidermidis requires accumulation-associated protein (Aap) that contains sequence repeats known as G5 domains, which are responsible for the Zn2+-dependent dimerization of Aap to mediate intercellular adhesion. Antibodies against Aap have been reported to inhibit biofilm accumulation. In the present study, three monoclonal antibodies (MAbs) against the Aap C-terminal single B-repeat construct followed by the 79-aa half repeat (AapBrpt1.5) were generated. MAb18B6 inhibited biofilm formation by S. epidermidis RP62A to 60% of the maximum, while MAb25C11 and MAb20B9 enhanced biofilm accumulation. All three MAbs aggregated the planktonic bacteria to form visible cell clusters. Epitope mapping revealed that the epitope of MAb18B6, which recognizes an identical area within AapBrpt constructs from S. epidermidis RP62A, was not shared by MAb25C11 and MAb20B9. Furthermore, all three MAbs were found to affect both Aap expression and extracellular polymeric substance (EPS, including extracellular DNA and PIA) biosynthesis in S. epidermidis and enhance the cell accumulation. These findings contribute to a better understanding of staphylococcal biofilm formation and will help to develop epitope-peptide vaccines against staphylococcal infections.

Highlights

Staphylococcus epidermidis, an opportunistic pathogen, has become one of the most prevalent causes of nosocomial infections, especially in patients with prosthetic medical devices [1,2]
General characteristics of the MAbs against AapBrpt1.5 To locate the epitopes of the anti-biofilm antibodies, three mouse monoclonal antibodies against AapBrpt1.5 from S. epidermidis ATCC 12228 were prepared and termed MAb18B6, MAb25C11, and MAb20B9
The precise epitopes of MAb25C11 and MAb20B9 were located between aa 71–80 (Figure 2B), which are in a non-identical area within AapBrpt constructs from S. epidermidis RP62A (Figure 2D, E)

Summary

Introduction

Staphylococcus epidermidis, an opportunistic pathogen, has become one of the most prevalent causes of nosocomial infections, especially in patients with prosthetic medical devices [1,2]. S. epidermidis colonization of these devices is complicated by the formation of biofilms, which render it increasingly resistant to multiple antibiotics and host defenses [3,4]. Replacement of the indwelling medical devices after S. epidermidis biofilm infection is generally necessary, and the development of biofilm-preventing vaccines is imperative. Biofilms are bacterial communities that adhere to biological or abiotic substrata and are stabilized by extracellular polymeric substances (EPSs), typically composed of polysaccharides and extracellular DNA [2,5,6,7,8]. The formation of staphylococcal biofilms involves two phases: primary adhesion followed by biofilm accumulation [4,9,10,11]. Polysaccharide intercellular adhesin (PIA), which is synthesized by proteins encoded in the ica operon [12,13,14,15,16], and extracellular DNA (eDNA)

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