Gentamicin, at concentrations up to 500 ,g/ml, showed no effect on the replication, yield, or infectivity of seven viruses or on the agents of psittacosis and men-ngopneumonitis when grown in mice or embryonated eggs. At the 500 ,ug/ml level, lymphogranuloma venereum cultures had a slight reduction in infectivity. Rickettsia akari demonstrated susceptibility at the 5 ug/ml level, whereas R. rickettsii, R. mooseri, and R. canada grown in embryonated eggs were susceptible in varying degrees to gentamicin at or above the 50 ,ug/ml concentration.Gentamicin sulfate, an aminoglycoside antibiotic, is readily soluble in water, autoclavable, and highly stable at wide pH and temperature ranges. It has been reported (4,6,11) to inhibit the in vitro growth of a wide range of grampositive and gram-negative bacteria. Other investigators (5, 7) have described the effectiveness of gentamicin in eliminating mycoplasmas from cell cultures. Its use in virological studies with cell cultures as reported by Schafer et al. (10) showed neither cytotoxic effects nor virucidal activity at concentrations as high as 2,000 ,ug/ml. The routine recommended dose of50 ,ug/ ml in cell cultures was found to be bactericidal for a wide range of organisms. Wentworth (12) described the use of 10 ,ug of gentamicin per ml for the isolation in McCoy cell cultures of subgroup A Chlamydia from clinical specimens. Acute and subacute toxicity studies conducted in mice by Black et al. (1) revealed that the lethal dose of gentamicin sulfate administered by parenteral routes exceeded 400 mg/kg of body weight.These reports led us to consider applying gentamicin in the large-scale production of viral, chlamydial, and rickettsial diagnostic reagents from fluids and tissues of mice and embryonated chicken eggs. Penicillin and streptomycin are routinely used to control contamination in the production of viral reagents; however, these antibiotics cannot be used in the production ofchlamydial and rickettsial reagents. The purpose of this report is to describe the effect of gentamicin on the replication of several viral, rickettsial, and chlamydial agents in mice and embryonated eggs. The chlamydial agents included were those of psittacosis, strain DD-34; meningopneumonitis, strain Francis; and lymphogranuloma venereum, strain JH.
MATERIALS AND METHODS
Organisms. The viruses included in these investiThe four rickettsiae included were Rickettsia akari, strain Hartford; R. rickettsii, strain Shelia Smith; R. mooseri, strain Wilmington; and R. canada.Host systems. Embryonated eggs were obtained from chicken flocks maintained on antibiotic-free feed. The viral agents and psittacosis were grown in the allantoic cavity of either 8-or 10-day-old eggs incubated at 33 to 35°C. The other chlamydiae were grown in the yolk sacs of 8-day-old eggs incubated at 36°C. The rickettsial agents were cultivated in the yolk sacs of 5-to 6-day-old eggs at 35°C.Random-bred, ICR, weanling mice weighing approximately 15 to 18 g were inoculated intracranially with 0.03 ml of rabies, psittaco...
