Monica Lobo

Treatment of experimental staphylococcal infection with rifampin.

Bacteria surviving within leukocytes are protected from the lethal action of high concentrations of most antibiotics, which may explain, in part, the failure of bactericidal antibiotics to eradicate staphylococci from abscesses. Since rifampin is unique in its ability to kill intraleukocytic bacteria, the efficacy of this drug was tested in the treatment of staphylococcal infections in mice. Groups of mice infected intravenously with Staphylococcus aureus were treated with rifampin (20 mg/kg), procaine penicillin (937.5 mg/kg), or methicillin (200 mg/kg). All untreated mice died with disseminated visceral abscesses. After 10 days of therapy, survival in groups treated with penicillin and methicillin was 16 and 20%, respectively, whereas with rifampin it was 80% (P < 0.0005). Antibiotic concentrations in the serum of mice treated with penicillin, methicillin, or rifampin were bactericidal for the strain of S. aureus used. Serial bacterial counts of kidney, lung, and spleen homogenates showed that neither penicillin nor methicillin was able to eradicate staphylococci, whereas rifampin completely sterilized those organs in many mice. When abscess contents and infected peritoneal washings were incubated with high concentrations of penicillin, methicillin, or rifampin, only rifampin killed all of the bacteria. The capacity of rifampin to eradicate staphylococci from pus in vitro and from abscesses in mice appears to be related to the ability of rifampin to kill intraleukocytic bacteria.

The Effect of Antibiotics on Escherichia coli Ingested by Macrophages

Summary Macrophages obtained from mouse peritoneal washings or the culture of human peripheral monocytes, were incubated in vitro with opsonized E. coli. Macrophages containing viable E. coli were then incubated with either rifampin, gentamicin or ampicillin. Only rifampin killed all intracellular and extracellular bacteria whereas gentamicin and ampicillin eradicated only extracellular bacteria. Rifampin is able to penetrate macrophages and kill bacteria that have survived phagocytosis.

Low Plasma Levels of Adrenocorticotropic Hormone in Patients with Acute Influenza

Plasma levels of adrenocorticotropic hormone (ACTH) and cortisol were measured in young adults with influenza virus type A (H3N2) infection for whom cultures were positive and in comparable controls without symptoms or other evidence of illness. The mean plasma ACTH level +/- SE in 19 patients with acute influenza was 13.5 +/- 2.1 pg/mL compared with 23 +/- 3.2 pg/mL in 11 controls (P = .02). Mean plasma ACTH levels +/- SE had risen to 21 +/- 4.1 pg/mL in specimens obtained from patients during convalescence. The mean plasma cortisol level +/- SE in patients with acute influenza was 13.7 +/- 1.4 micrograms/dL compared with 10.8 +/- 1.0 micrograms/dL in controls (P = not significant). ACTH levels in individual controls were relatively higher than their cortisol levels, but ACTH levels in patients tended to be lower than cortisol levels in paired specimens. These findings suggest that influenza virus type A infection may have an inhibitory effect on the production or release of ACTH.