Killing of oxacillin-exposed staphylococci in human polymorphonuclear leukocytes

Abstract

Twelve strains of Staphylococcus aureus isolated from patients and two collection strains were grown on membranes placed on agar containing subminimal inhibitory concentrations of oxacillin. Clusters of staphylococci held together by thick cross walls resulted. These organisms, as well as the same strains grown in the same way on drug-free medium (control), were eluted from the membranes and were incubated with human polymorphonuclear leukocytes (PMNs) from various donors. Phagocytosis was comparable for both staphylococci exposed to oxacillin and control staphylococci, but the killing effect was different. The staphylococci grown on membranes in the presence of oxacillin were less susceptible to killing than the control staphylococci. After 0.5 and 1 h of incubation with PMNs, the killing rates for oxacillin-grown versus control staphylococci were 52 and 70% and 65 and 85%, respectively (P < 0.01). After 2 and 3 h of incubation, the killing was similar. Most clusters of staphylococci contain a few individual cells that are located in the center of the cluster and are surrounded by other staphylococci; therefore, they are protected from adverse agents in the environment. This could explain why the phagocytized clusters are less susceptible than control staphylococci to the killing effect of PMNs during the first hour of incubation. Oxacillin does not penetrate into PMNs and in the absence of the drug the cross walls lyse, liberating the constituent staphylococci. This coincides with the increase in the percentage of cluster killing by PMNs after 2 and 3 h of incubation.

The Role of Antibiotics in Modulating Virulence in Staphylococcus aureus

“…Three different protocols were used in these studies. In the first protocol, S. aureus isolates were previously cultured with or without antibiotics at sub-MICs and subsequently incubated with PMNs or macrophages (32,(53)(54)(55)(56)(57)(58)(59)(60)(61)(62), allowing measurement of the effects of antibiotics on the susceptibility of bacteria to opsonization and opsonophagocytosis or phagocytosis. In the second protocol, S. aureus and phagocytic cells were simultaneously cocultivated with antibiotics at sub-MICs (63), enabling study of the synergic effect of antibiotics and phagocytic cells on bacterial survival.…”

Influence of subinhibitory concentrations of penicillin, cephalothin, and clindamycin on Staphylococcus aureus growth in human phagocytic cells

“…It is reported that phagocytized bacteria are protected from the effect of antibiotics (5,10,19,21); however, enhancement of the bactericidal capacity of polymorphonuclear leukocytes (PMN) may be secondary to the effect of antibiotic-exposed bacteria before phagocytosis. Even at subinhibitory concentrations of antibiotics, bacterial morphology (2,9,18), adherence properties (15), opsonic requirements (2), and kinetics of phagocytosis and killing by PMN are altered (1,2,6,9,11,17,18).…”

Synergistic Effect of Romurtide with Ampicillin against Pneumococcal Pneumonia in Mice

“…Finally, the results of experimental chemo therapy tested here verify the hypothesis that the total efficacy of antibiotic therapy in in fectious diseases is due mainly to the com bined effect of the antimicrobial activity of a drug and the cellular defense of the host [28,34,36]. Thus, romurtide with a potent hemato poietic activity may create an innovative clin ical chemotherapy for the future, especially in the field where current chemotherapy faces difficulties treating patients with decreased host defenses [30, 35,39] …”

“…These results should be interpreted with caution, since augmenta tion of body defense alone is not sufficient, and, similarly, the antibiotic alone is not al ways successful in the treatment of the pneu monia developed in mice with an impaired phagocytosis due to depletion of C3 [28][29][30]. One possible interpretation for the efficacy of the combination therapy is that pneumococci in suppressive state either quantitatively (de creased surface protein synthesis) or qualita tively (morphological changes such as elonga tion and unusual septal formation) or both be came easily phagocytosed by treatment with ABPC and were killed efficiently by the acti vated macrophages [35][36][37], Such an assumed underlying mechanism of the efficacy should be studied in in vitro or ex vivo cell culture sys tems in the future. Also, though the serum C3 level was assumed insignificant in this study, the involvement of local C3 in the pneumonic lungs in the efficacy of the combination ther apy should be clarified, since activated macro phages after stimulation with romurtide were reported to produce significant amounts of complement components [38].…”