Increased Antibiotic Resistance of Methicillin-Resistant Staphylococcus aureus USA300 Δpsm Mutants and a Complementation Study of Δpsm Mutants Using Synthetic Phenol-Soluble Modulins

Abstract

Phenol-soluble modulins (PSMs) are responsible for regulating biofilm formation, persister cell formation, pmtR expression, host cell lysis, and anti-bacterial effects. To determine the effect of psm deletion on methicillin-resistant Staphylococcus aureus, we investigated psm deletion mutants including Δpsmα, Δpsmβ, and Δpsmαβ. These mutants exhibited increased β-lactam antibiotic resistance to ampicillin and oxacillin that was shown to be caused by increased Nacetylmannosamine kinase (nanK) mRNA expression, which regulates persister cell formation, leading to changes in the pattern of phospholipid fatty acids resulting in increased anteiso-C 15:0 , and increased membrane hydrophobicity with the deletion of PSMs. When synthetic PSMs were applied to Δpsmα and Δpsmβ mutants, treatment of Δpsmα with PSMα1-4 and Δpsmβ with PSMβ1-2 restored the sensitivity to oxacillin and slightly reduced the biofilm formation. Addition of a single fragment showed that α1, α2, α3, and β2 had an inhibiting effect on biofilms in Δpsmα; however, β1 showed an enhancing effect on biofilms in Δpsmβ. This study demonstrates a possible reason for the increased antibiotic resistance in psm mutants and the effect of PSMs on biofilm formation.

Intracellular persistence of Staphylococcus aureus in endothelial cells is promoted by the absence of phenol-soluble modulins

“…Thus, the downregulation of psmαβ could represent an important bacterial strategy that contributes to the intracellular persistence of S. aureus . Recently, persisting S. aureus deficient in psmαβ was shown to be less susceptible for intracellularly acting antibiotics [ 53 , 54 ]. PSMs are transcriptionally controlled directly by Agr [ 24 ], and their expression is boosted during the stringent response [ 19 ].…”

Comparative Study of the Difference in Behavior of the Accessory Gene Regulator (Agr) in USA300 and USA400 Community-Associated Methicillin-Resistant Staphylococcus aureus (CA-MRSA)

“…For pre-culture, a single colony of the strain from a TSB agar plate was inoculated with 5 ml of TSB medium using a sterilized inoculation loop. One percent (v/v) of the cell culture suspension was inoculated in TSB for subsequent cell cultivation at 37°C in a shaking incubator (200 rpm) [ 24 ].…”

“…Thereafter, 0.2% of crystal violet solution was added to each well to stain the biofilm. After 5 min, the remaining dye was removed with distilled water and the absorbance was measured at 595 nm using a 96-well microplate reader (Thermo Fisher Scientific) [ 24 ]. For disc diffusion method, to inoculate each strain onto TSB agar plate sterile swab was used.…”

“…The injector port temperature was set at 210°C. For the internal standard, 1 μl of methyl heneicosanoate (10 mg/ml) and bacterial acid methyl ester mix (Merck-Millipore, USA) was used [ 24 , 25 , 36 ].…”

Isolation of Microbulbifer sp. SOL66 with High Polyhydroxyalkanoate-Degrading Activity from the Marine Environment

“…The structural assignments were based on the interpretation of the mass spectrometric fragmentation and confirmed by comparison with the retention times and fragmentation patterns of the standards and spectral data obtained from the Wiley ( , accessed on 6 August 20) and National Institute of Standards and Technology ( , accessed on 6 August 20) online libraries. Methyl heneicosanoate (10 mg/mL; 10 μL) was used as an internal standard [ 21 ].…”