Pankaj Jha

Changes associated with cell membrane composition of Staphylococcus aureus on acquisition of resistance against class IIa bacteriocin and its in vitro substantiation

The emergence and spread of bacteria resistant to bacteriocins would threaten the safety of using them as food preservatives. To determine the physiological characteristics of resistant strain, resistance of Staphylococcus aureus NCDC 133 against pediocin, a class IIa bacteriocin, was isolated. A significant amplification in unsaturated fatty acid and hydroxy fatty acid in addition to branched chain fatty acid was observed in resistant which validates enhanced fluid membrane of resistant strain. Increased membrane fluidity leads to unstable oligomerization of bacteriocin which ceases pore formation. The composition of the phospholipids in resistant strain also differed from those in the wild-type strain. The putative zwitterionic amino-containing phospholipid in the resistant significantly increased, whereas amounts of amino-lacking phospholipids decreased which could be correlated to reduced negative charge making bacteriocin unable to associate optimally with bacterial membrane. Increased percent colorimetric response in resistant variant indicates that bacteriocin was positioned predominantly at the lipid–water interface rather than penetrating deep inside. Both physiological study and in vitro results confirm membrane changes during resistance acquisition which could be utilized to establish structure activity relationship and henceforth to develop potent peptide with suitable amino acid substitutes with enhanced stability and activity features.

Contribution of Cell Surface Hydrophobicity in the Resistance of Staphylococcus aureus against Antimicrobial Agents

Staphylococcus aureus is found in a wide variety of habitats, including human skin, where many strains are commensals that may be clinically significant or contaminants of food. To determine the physiological characteristics of resistant strain of Staphylococcus aureus against pediocin, a class IIa bacteriocin, a resistant strain was compared with wild type in order to investigate the contribution of hydrophobicity to this resistance. Additional clumping of resistant strain relative to wild type in light microscopy was considered as an elementary evidence of resistance attainment. A delay in log phase attainment was observed in resistant strain compared to the wild type strain. A significant increase in cell surface hydrophobicity was detected for resistant strain in both hexadecane and xylene indicating the contribution of cell surface hydrophobicity as adaptive reaction against antimicrobial agents.