Penetration of antibiotics into bovine neutrophils and their activity against intracellular Staphylococcus aureus

Abstract

The penetration of three antibiotics, penicillin, chloramphenicol and erythromycin into bovine neutrophils, either alone or containing previously ingested Staphylococcus aureus, was determined, and their intracellular activity against these bacteria was measured. Uptake of radiolabelled antibiotics was assessed by rapidly separating neutrophils from extracellular antibiotic by centrifugation through silicone oil. Intracellular activity was estimated by comparing the numbers of bacteria surviving intracellularly in neutrophils exposed to antibiotic for 3 h at ten times the MBC, with those surviving intracellularly in untreated neutrophils. Penicillin was slightly concentrated within the neutrophils, reaching a maximum intracellular concentration 1.75 times that of the extracellular concentration; this is the C/E ratio. Chloramphenicol entered to a greater extent with a maximum C/E ratio of 7.08. Erythromycin became highly concentrated within the neutrophils with a C/E ratio of 11.46 after 90 min incubation. The presence of ingested staphylococci significantly reduced the uptake of chloramphenicol, but had no significant effect on the penetration of the other antibiotics. Intracellular activity studies indicated that, at ten times MBC, only penicillin had any significant activity against intracellular staphylococci, reducing survival by 28%. This work demonstrates that penetration of certain antibiotics can be altered by the presence of ingested staphylococci and that high intracellular levels of antibiotics do not necessarily ensure good intracellular activity against pathogenic micro-organisms.

Uptake of cefepime by phagocytosing polymorphonuclear neutrophils and subsequent intracellular killing

“…Therefore, ␤-lactam antibiotics have intracellular-toextracellular ratios of less than one, and it has been generally accepted that they have little effect on bacteria residing within cells. Much of the evidence for this has been derived from antibiotic uptake studies utilizing nonphagocytosing neutrophils (7,12,15,19) or PMN preloaded with bacteria, usually S. aureus (1,9,16,23). Several studies have shown that there is no difference in penetration of penicillin G into resting neutrophils and neutrophils containing ingested S. aureus (16,26), and Madgwick et al (16) showed that preingested S. aureus actually decreased uptake of chloramphenicol by bovine neutrophils, although penicillin was not significantly affected.…”

A New Model Examining Intracellular and Extracellular Activity of Amoxicillin, Azithromycin, and Clarithromycin in Infected Cells

“…Perhaps they are extremely effective extracellularly because so little drug enters the cell. However, agents such as Legio nella -and even organisms such as Staphylo coccus -which frequently grow intracellularly, can be problematic for drugs with limited in tracellular penetration [4,9,10]. Ideally, then, an antimicrobial agent would be able to pene trate cells while maintaining adequate extra cellular concentrations.…”

Macrolide antibiotics in food-animal health

“…This situation creates an equilibrium between extracellular drug and the two-compartment intracellular system of cytosol and lysosome, in which the acidity of the latter drives the uptake of macrolide into the lysosome and enables greater antibiotic persistence in the phagocyte [128,129]. The intracellular concentrations of antibiotic may be increased, decreased, or unchanged by the presence of intracellular bacteria [154][155][156][157][158]. The uptake mechanism of four macrolides into PMNs has been recently linked to the required presence of extracellular calcium ions [159].…”

“…Problems that may diminish intracellular killing by a well-accumulated antibiotic include: its intracellular degradation or metabolism, sequestration in an ineffective intracellular location away from the pathogen, and negative effects on intracellular functions necessary for microbial killing within the phagocytic cell. The low efficacy of erythromycin against bovine mastitis caused by S. aureus has been attributed to some extent to ineffective killing of S. aureus inside PMNs [154,155]. In contrast, uptake of tilmicosin into mouse macrophages and human monocytes exceeded that of erythromycin and tylosin while intracellular killing of Toxoplasma gondii was demonstrated within bovine turbinate cells [160,161].…”