Activated ADI pathway: the initiator of intermediate vancomycin resistance in Staphylococcus aureus

Abstract

Comparative proteomic profiling between 2 vancomycin-intermediate Staphylococcus aureus (VISA) strains, Mu50Ω-vraSm and Mu50Ω-vraSm-graRm, and vancomycin-susceptible S.aureus (VSSA) strain Mu50Ω revealed upregulated levels of catabolic ornithine carbamoyltransferase (ArcB) of the arginine catabolism pathway in VISA strains. Subsequent analyses showed that the VISA strains have higher levels of cellular ATP and ammonia, which are by-products of arginine catabolism, and displayed thicker cell walls. We postulate that elevated cytoplasmic ammonia and ATP molecules, resulting from activated arginine catabolism upon acquisition of vraS and graR mutations, are important requirements facilitating cell wall biosynthesis, thereby contributing to thickened cell wall and consequently reduced vancomycin susceptibility in VISA strains.

Full text

NOTE
Activated ADI pathway: the initiator of intermediate
vancomycin resistance in Staphylococcus aureus
Xin-Ee Tan, Hui-min Neoh, Mee-Lee Looi, Siok Fong Chin, Longzhu Cui, Keiichi Hiramatsu,
Salasawati Hussin, and Rahman Jamal
Abstract: Comparative proteomic profiling between 2 vancomycin-intermediate Staphylococcus aureus (VISA)
strains, Mu50⍀-vraSm and Mu50⍀-vraSm-graRm, and vancomycin-susceptible S. aureus (VSSA) strain Mu50⍀
revealed upregulated levels of catabolic ornithine carbamoyltransferase (ArcB) of the arginine catabolism
pathway in VISA strains. Subsequent analyses showed that the VISA strains have higher levels of cellular ATP
and ammonia, which are by-products of arginine catabolism, and displayed thicker cell walls. We postulate
that elevated cytoplasmic ammonia and ATP molecules, resulting from activated arginine catabolism upon
acquisition of vraS and graR mutations, are important requirements facilitating cell wall biosynthesis, thereby
contributing to thickened cell wall and consequently reduced vancomycin susceptibility in VISA strains.
Key words: vancomycin-intermediate Staphylococcus aureus, arginine catabolism, ammonia, ATP, cell wall thickening.
Résumé : Le profilage protéomique comparatif de deux souches de Staphylococcus aureus de résistance inter-
médiaire a
`la vancomycine (SARIV), Mu50⍀-vraSm et Mu50⍀-vraSm-graRm, et d’une souche susceptible a
`la
vancomycine (SASV), Mu50⍀, a mis au jour une hausse de la quantité d’ornithine carbamoyltransférase
catabolique (ArcB) de la voie du catabolisme de l’arginine chez les SARIV. Des analysées ultérieures ont révélé
que les souches SARIV renferment des taux plus élevés d’ATP cellulaire et d’ammoniac, des sous-produits du
catabolisme de l’arginine, et étaient dotées d’une paroi cellulaire plus épaisse. Nous postulons que la sur-
abondance d’ammoniac cytoplasmique et de molécules d’ATP, résultant d’une activation du catabolisme de
l’arginine rendue possible par l’acquisition de mutations dans vraS et graR, serait un important facteur
facilitant la biosynthèse de la paroi cellulaire, contribuant ainsi a
`l’épaississement de la paroi cellulaire lequel
conduirait a
`une diminution de la susceptibilité a
`la vancomycine chez les SARIV. [Traduit par la Rédaction]
Mots-clés : Staphylococcus aureus de résistance intermédiaire a
`la vancomycine, catabolisme de l’arginine, ammoniac,
ATP, épaississement de la paroi cellulaire.
Various genetic determinants have been reported to
be associated with intermediate vancomycin resistance
in Staphylococcus aureus (Kuroda et al. 2003;Neoh et al.
2008;Shoji et al. 2011;Watanabe et al. 2011). In 2005, we
published our discovery of higher expression of the vraS
and graR genes in vancomycin-intermediate S. aureus
(VISA) strain Mu50 than vancomycin-susceptible S. aureus
(VSSA) N315, and subsequently showed that genome en-
gineering of mutated Mu50 vraS and graR into VSSA
Mu50⍀converted it into a VISA strain (Cui et al. 2005,
2009). However, the exact mechanism regulated by VraS
and GraR that contributes towards vancomycin inter-
mediate resistance in the Mu50 lineage of strains is
still unclear.
In this study, we employed a proteomic approach to
elucidate the mechanism behind VraSR- and GraRS-
mediated intermediate vancomycin resistance. Total
proteins were extracted from Mu50⍀, a VSSA strain, and
from VISA strains Mu50⍀-vraSm and Mu50⍀-vraSm-
graRm. These 2 VISA strains were generated via Mu50
Received 11 July 2016. Revision received 23 September 2016. Accepted 27 September 2016.
X.-E. Tan, S.F. Chin, and R. Jamal. UKM Medical Molecular Biology Institute (UMBI), Universiti Kebangsaan Malaysia, Malaysia.
H.-m. Neoh. UKM Medical Molecular Biology Institute (UMBI), Universiti Kebangsaan Malaysia, Malaysia; Department of Bacteriology,
School of Medicine, Juntendo University, Japan.
M.-L. Looi. UKM Medical Molecular Biology Institute (UMBI), Universiti Kebangsaan Malaysia, Malaysia; Taylor’s University Lakeside
Campus, School of Biosciences, Malaysia.
L. Cui. Division of Bacteriology, Department of Infection and Immunity, School of Medicine, Jichi Medical University, Japan.
K. Hiramatsu. Department of Bacteriology, School of Medicine, Juntendo University, Japan.
S. Hussin. Department of Medical Microbiology and Immunology, Universiti Kebangsaan Malaysia, Malaysia.
Corresponding author: Hui-min Neoh (email: hui-min@ppukm.ukm.edu.my).
Copyright remains with the author(s) or their institution(s). Permission for reuse (free in most cases) can be obtained from RightsLink.
260
Can. J. Microbiol. 63: 260–264 (2017) dx.doi.org/10.1139/cjm-2016-0439 Published at www.nrcresearchpress.com/cjm on 19 October 2016.