Transcriptome analysis of the responses of Staphylococcus aureus to antimicrobial peptides and characterization of the roles of vraDE and vraSR in antimicrobial resistance.
BACKGROUND
Understanding how pathogens respond to antimicrobial peptides, and how this compares to currently available antibiotics, is crucial for optimizing antimicrobial therapy. Staphylococcus aureus has several known resistance mechanisms against human cationic antimicrobial peptides (CAMPs). Gene expression changes in S. aureus strain Newman exposed to linear CAMPs were analyzed by DNA microarray. Three antimicrobial peptides were used in the analysis, two are derived from frog, temporin L and dermaseptin K4-S4(1-16), and the ovispirin-1 is obtained from sheep.


RESULTS
The peptides induced the VraSR cell-wall regulon and several other genes that are also up-regulated in cells treated with vancomycin and other cell wall-active antibiotics. In addition to this similarity, three genes/operons were particularly strongly induced by the peptides: vraDE, SA0205 and SAS016, encoding an ABC transporter, a putative membrane-bound lysostaphin-like peptidase and a small functionally unknown protein, respectively. Ovispirin-1 and dermaseptin K4-S4(1-16), which disrupt lipid bilayers by the carpet mechanism, appeared to be strong inducers of the vraDE operon. We show that high level induction by ovispirin-1 is dependent on the amide modification of the peptide C-terminus. This suggests that the amide group has a crucial role in the activation of the Aps (GraRS) sensory system, the regulator of vraDE. In contrast, temporin L, which disrupts lipid bilayers by forming pores, revealed a weaker inducer of vraDE despite the C-terminal amide modification. Sensitivity testing with CAMPs and other antimicrobials suggested that VraDE is a transporter dedicated to resist bacitracin. We also showed that SA0205 belongs to the VraSR regulon. Furthermore, VraSR was shown to be important for resistance against a wide range of cell wall-active antibiotics and other antimicrobial agents including the amide-modified ovispirin-1, bacitracin, teicoplanin, cefotaxime and 10 other beta-lactam antibiotics, chlorpromazine, thioridazine and EGTA.


CONCLUSIONS
Defense against different CAMPs involves not only general signaling pathways but also CAMP-specific ones. These results suggest that CAMPs or a mixture of CAMPs could constitute a potential additive to standard antibiotic treatment.
Pietiäinen
Milla
M
Antimicrobial Resistance Unit, Department of Infectious Disease Surveillance and Control, National Institute for Health and Welfare (THL), PL 30, 00271 Helsinki, Finland.
François
Patrice
P
Hyyryläinen
Hanne-Leena
HL
Tangomo
Manuela
M
Sass
Vera
V
Sahl
Hans-Georg
HG
Schrenzel
Jacques
J
Kontinen
Vesa P
VP
D018528:ATP-Binding Cassette Transporters / Q000235:genetics*; D029845:Amphibian Proteins / Q000494:pharmacology*; D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics*; D002473:Cell Wall / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D024881:Drug Resistance, Bacterial; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D008826:Microbial Sensitivity Tests; D009154:Mutation; D020411:Oligonucleotide Array Sequence Analysis; D009876:Operon; D011506:Proteins / Q000494:pharmacology; D012329:RNA, Bacterial / Q000235:genetics; D018085:Regulon; D013211:Staphylococcus aureus / Q000187:drug effects / Q000235:genetics*; D037521:Virulence Factors / Q000235:genetics
D018528:ATP-Binding Cassette Transporters; D029845:Amphibian Proteins; D023181:Antimicrobial Cationic Peptides; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D011506:Proteins; D012329:RNA, Bacterial; D037521:Virulence Factors; C478170:VraR protein, Staphylococcus aureus; C478169:VraS protein, Staphylococcus aureus; C440189:ovispirin; C104501:temporin; C070905:dermaseptin