Post antibiotic effect and its efficacy on enhanced microbial susceptibility to phagocytosis

ABSTRACT

In the present work the in vitro post antibiotic effects of Amoxycillin/ Clavulanic acid [Augmentin] on Staphylococcus aureus and of Amikacin and Cefotaxime on Pseudomonas aeruginosa were determined by the broth technique. These organisms were hospital strains isolated from two patients in Ain Shams University Hospitals. The exposure of Staph. aureus to 5X minimum inhibitory concentration [MIC] of Augmentin for 2 hours produced a significant post-antibiotic effect [PAE] of 1.7 hour. As well as, exposure of Pseudomonas aeruginosa to 5X MIC of Amikacin and Cefotaxime for 1 hour produced a significant PAE of 2.4 hours and 1.8 hour respectively. Amikacin had a longer PAE than Cefotaxime under the same conditions. Moreover, post-antibiotic leucocyte enhancement [PALE] or the effect of previous exposure to antibiotics on the susceptibility of bacteria to the phagocytic and bactericidal activities of polymorphonuclear leucocytes [PMNL] had been tested. The PAE of Augmentin on S. aureus and of Amikacin or Cefotaxime on Ps. aeruginosa caused a significant increase in their susceptibility to the antibacterial activities of human PMNL, compared with the untreated control cells under the same test conditions. We concluded that, the PAE has many biological significances, this effect may justify the use of PAE inducing antimicrobial agents with longer dosing interval than those currently employed without loss of efficacy. Also, PAE induces the post-antibiotic leucocyte enhancement, organisms in the PAE phase are more susceptible to the antibacterial activity of human PMNL. Further studies are necessary to determine the full PAE clinical significances