Study on the bactericidal activity and synergistic effect of neutropenic rat serum with gentamicin

It is well known that normal rat serum (NRS) shows an antibacterial activity because of the presence of endogenous substances that are able to express a defence against pathogenic microorganisms. Moreover, in former studies, we observed that NRS presents a synergistic activity with some antibiotics (thus able to lower minimum inhibitory concentration values). The aim of this research was to study the antibacterial activity and synergistic effect of neutropenic rat sera (NPRS) with gentamicin. The animals were made neutropenic by the i.p. injection of cyclophosphamide (100 mg/kg on day 0 and 75 mg on day 4). At all tested concentrations (from 0.25% to 5%) NPRS showed lower antibacterial activity than NRS with differences which were always statistically significant. The synergistic activity of NPRS with gentamicin was still present and quite similar to that of NRS, in spite of many altered blood parameters showing evident immunodepression. Some possible interpretations of these results are discussed.