Mannitol Utilisation is Required for Protection of Staphylococcus aureus from Human Skin Antimicrobial Fatty Acids

John G Kenny,Malcolm J Horsburgh,Josephine Moran,Stacey L Kolar,Alexander Ulanov,Elisabet Josefsson,Lindsey N Shaw,Zhong Li,Michael Otto

doi:10.1371/journal.pone.0067698

Abstract

Mannitol (Mtl) fermentation, with the subsequent production of acid, is a species signature of Staphylococcus aureus, and discriminates it from most other members of the genus. Inactivation of the gene mtlD, encoding Mtl-1-P dehydrogenase was found to markedly reduce survival in the presence of the antimicrobial fatty acid, linoleic acid. We demonstrate that the sugar alcohol has a potentiating action for this membrane-acting antimicrobial. Analysis of cellular metabolites revealed that, during exponential growth, the mtlD mutant accumulated high levels of Mtl and Mtl-P. The latter metabolite was not detected in its isogenic parent strain or a deletion mutant of the entire mtlABFD operon. In addition, the mtlD mutant strain exhibited a decreased MIC for H2O2, however virulence was unaffected in a model of septic arthritis.

Highlights

S. aureus is a common skin and soft tissue pathogen capable of causing more severe infections including sepsis, osteomyelitis, and endocarditis [1]
The metabolite levels were evident in strain Liv1023 (mtlD) mutant suvB24 (SH1000 mtlD::Tn917) selected for further study showed clearly reduced survival on linoleic acid agar compared to its isogenic parent strain (Figure 2)
Culture Phenotypes of mtl Mutants To investigate the role of the mtlD gene product in host cell physiology and to help explain the mechanism for reduced linoleic acid agar survival, growth of the suvB24 mutant was compared with its isogenic parental strain using a Biolog phenotype array

Summary

Introduction

S. aureus is a common skin and soft tissue pathogen capable of causing more severe infections including sepsis, osteomyelitis, and endocarditis [1]. One focus for study of survival is the antimicrobial activity of long chain (typically C$16) unsaturated free fatty acids that generate the acid mantle on skin [5,6,7,8,9] These antimicrobial fatty acids (AFAs) are components of the innate immune system that function on skin and in abscesses [9,10,11,12,13,14,15,16,17,18]. The transcript encoding the cell surface protein SasF is upregulated .30 fold after addition of linoleic acid and inactivation of the gene decreases survival, but not via detectable changes to surface hydrophobicity [6]. Inhibitory concentrations of AFAs cause leakage of proteins and inhibit respiration [20,21,22,23]

Methods

Results

Conclusion