intracellular SA protected from abx in experimental infection

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J Dairy Res. 1984 Nov;51(4):513-23. Related Articles, Links

Phagocytosis of Staphylococcus aureus by bovine mammary gland

macrophages and intracellular protection from antibiotic action in

vitro and in vivo.

Craven N, JC.

Macrophages isolated from the involuted bovine mammary gland were

cultured in vitro. Phagocytosis of opsonized Staphylococcus aureus

occurred rapidly, but intracellular killing of bacteria was slow.

Many intracellular staphylococci survived for up to 4 d exposure to

extracellular cloxacillin and emerged from within the macrophages to

multiply extracellularly when the antibiotic was inactivated.

Rifampicin was significantly more efficient than cloxacillin in

killing intracellular S. aureus after 18 h incubation, but it too

failed to sterilize the cultures within 3 d. Staphylococci, which had

remained viable within macrophages during 20 h incubation with

extracellular cloxacillin, showed an increased sensitivity to dilute

lysostaphin on subsequent exposure. A 3 d course of intramammary

therapy with cloxacillin, commencing simultaneously with an infecting

inoculum of approximately 10(8) colony forming units (c.f.u.) S.

aureus, apparently eliminated the infection from one quarter of the

udders of each of three lactating cows, but bacteria were re-isolated

from two cows after a delay of several days. However, when other

quarters of the same cows were infected with approximately 10(8)

c.f.u. S. aureus which had been phagocytosed by autologous mammary

macrophages, similar simultaneous antibiotic therapy failed to affect

these infections. The in vitro and in vivo findings indicate the

significance of intracellular survival of S. aureus as a factor

contributing to failure of antibiotic therapy.

PMID: 6569065 [PubMed - indexed for MEDLINE]