Serum bactericidal activity against multi-drug resistant Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus, and Pseudomonas aeruginosa

Abstract

Antibiotic resistance has become a matter of utmost concern. Many disease-causing pathogens are becoming resistant to multiple antibiotics, referred to as multi-drug resistant (MDR) bacteria. The purpose of this study is to know the immunity against MDR bacteria among normal healthy individuals. Bacterial samples were collected from tertiary care hospitals. Gram staining followed by biochemical tests were performed to confirm the identity of the four different organisms- Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus and Pseudomonas aeruginosa. After identification, antibiogram was performed to confirm that they are MDR bacteria. From normal individuals’ blood was collected and centrifuged at 4000 rpm for 10 min to obtain serum. All serum samples were incubated with four different bacterial suspensions. All sera samples were heated at 56℃ for 30 minutes to inactivate them and then incubated with bacterial suspension. Lastly, bacterial suspension was incubated with sera to which ethylene glycol-bis (β-aminoethyl ether)-N, N, N′, N′-tetraacetic acid (EGTA) had been added. This was done to inhibit the classical pathway of the complement system. For Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and Staphylococcus aureus, 67.82%, 99.56%, 48.33% and 93.38% highest inhibition was observed respectively. No inhibition of bacterial growth was observed when treated with inactivated sera. Incubation with EGTA-added sera showed uncontrolled bacterial growth which suggests that the observed bactericidal effect of sera was due to the classical pathway and no other pathway of the complement system was involved.