Abstract
Sperm immobilization factor (SIF) causing 100% immobilization of spermatozoa isolated from Staphylococcus aureus when characterized using LC-MS (Liquid chromatography-mass spectrometry) showed that this 20 kDa protein had peptide sequence similarity with hsp-70 protein. It was found to completely (100%) inhibit Mg++ ATPase activity of spermatozoa at concentration of 100 μg mL−1. Sperm samples treated with SIF also showed reduction in calcium ionophore-induced acrosome reaction as compared to control samples (treated with calcium ionophore alone). Binding studies of FITC labelled SIF with spermatozoa using fluorescent microscopy showed binding of SIF to the surface of spermatozoa indicating the presence of SIF binding receptor. The receptor was extracted by 3M NaCl and purified by gel permeation chromatography. Characterization of the receptor by MALDI-TOF (Matrix-assisted laser desorption ionization-time of flight) indicated that the receptor shared sequence similarity with MHC class II antigen. A calorimetric study showed that the receptor moiety on spermatozoa was specific for the purified ligand as binding of the receptor to ligand was enthalpically (−11.9 kJ mole−1) as well as entropically (21.53 J mole−1 K−1) favored resulting in the Gibb's free energy of −18.57 kJ mole−1.
Highlights
Staphylococcus aureus is amongst the most versatile and successful of the human pathogens
Similar studies were done by Liu et al on the effect of certain uropathogenic microorganisms on human sperm motility parameters and found significant decrease in sperm motility when spermatozoa were coincubated with S. aureus [6]
According to Liquid Chromatography-Mass Spectrometry (LC-MS) measurements of the 20 kDa band, the protein showed the peptide sequence similarity with hsp-70 protein when matched with proteins in the NCBInr database, using the Mascot search program
Summary
Staphylococcus aureus is amongst the most versatile and successful of the human pathogens. S. aureus has been observed as causative organism accounting for 68.2% of seminal fluid infections [2]. This is consistent with that reported by Okon et al, where S. aureus was isolated from 62.5% of the seminal fluids [3]. Huwe et al studied the influence of different uropathogenic microorganisms on human sperm motility parameters by means of CASA and reported that S. aureus retards the sperm motility [5]. Similar studies were done by Liu et al on the effect of certain uropathogenic microorganisms on human sperm motility parameters and found significant decrease in sperm motility when spermatozoa were coincubated with S. aureus [6]. Some authors have suggested that direct interaction between bacteria and spermatozoa facilitates immobilization of spermatozoa [7,8,9], while others have reported evidence for soluble spermicidal factor produced and secreted by bacteria in the extracellular medium [10]
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