Increased resistance of a methicillin-resistant Staphylococcus aureus Δagr mutant with modified control in fatty acid metabolism

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) strains are distinct from general Staphylococcus strains with respect to the composition of the membrane, ability to form a thicker biofilm, and, importantly, ability to modify the target of antibiotics to evade their activity. The agr gene is an accessory global regulator of gram-positive bacteria that governs virulence or resistant mechanisms and therefore an important target for the control of resistant strains. However, the mechanism by which agr impacts resistance to β-lactam antibiotics remains unclear. In the present study, we found the Δagr mutant strain having higher resistance to high concentrations of β-lactam antibiotics such as oxacillin and ampicillin. To determine the influence of variation in the microenvironment of cells between the parental and mutant strains, fatty acid analysis of the supernatant, total lipids, and phospholipid fatty acids were compared. The Δagr mutant strain tended to produce fewer fatty acids and retained lower amounts of C16, C18 fatty acids in the supernatant. Phospholipid analysis showed a dramatic increase in the hydrophobic longer-chain fatty acids in the membrane. To target membrane, we applied several surfactants and found that sorbitan monolaurate (Span20) had a synergistic effect with oxacillin by decreasing biofilm formation and growth. These findings indicate that agr deletion allows for MRSA to resist antibiotics via several changes including constant expression of mecA, fatty acid metabolism, and biofilm thickening.

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

“…PSMs are related to biofilm structure and dispersion in that they support the biofilm structure by generating an amyloid structure and are capable of disseminating the biofilm by virtue of their surfactant properties [ 21 ]. psm null mutants lose their surfactant ability and are therefore unable to disperse biofilms; this results in biofilm thickening, which might eventually culminate in increased antibiotic resistance [ 18 ]. Therefore, the antibiotic resistance of Δ psm mutants was compared to that of the wild-type MRSA LAC strain to determine how psm deletions would affect the antibiotic sensitivity.…”

“…Biofilm formation, fatty acid synthesis, CSH, membrane fluidity, and membrane permeability are the major factors responsible for antibiotic resistance [ 23 - 26 ]. To check if a compositional change in fatty acids is responsible for the development of antibiotic resistance, membrane fatty acids are analyzed using GC-MS [ 18 ]. Additionally, CSH and membrane fluidity were investigated as CSH is known to be related to biofilms, which result in lower exposure to the surroundings and a less fluid membrane in some isolated MRSA strains that are known to have higher resistance.…”

“…PSMs are involved in host cell lysis, anti-bacterial effects, control of biofilm formation and persister cell formation and are produced more in CA-MRSA than in HA-MRSA [ 28 ]. Without PSM, MRSA lose their ability to release cytoplasmic proteins and lipids into the supernatant [ 18 , 29 ]. In addition, psm mutants produce thicker biofilms compared to the wild type [ 15 ].…”

“…Gas chromatography (GC)/mass spectrometry (MS) was used for the detection and quantification of fatty acids, in accordance with a previously described method, with a slight modification [ 18 ]. For methanolysis of fatty acids, approximately 10 mg of freeze-dried cells was weighed and placed in Teflon-stoppered glass vials.…”

The Inhibition Effect of Linezolid With Reyanning Mixture on MRSA and its Biofilm is More Significant than That of Linezolid Alone

“…agrA and agrB genes are significantly associated with markers of metabolic pathways of amino acid metabolism and fatty acid metabolism. Current studies have shown that the level of long-chain fatty acids in the plasma membrane of the agr mutant strain is higher than that of the wild type ( Song et al, 2020 ). Long-chain fatty acids help reduce cell membrane permeability and stability, which may be related to the resistance of MRSA to antibiotics ( Meadows and Wargo, 2015 ).…”