Experimental lobar pneumonia due to penicillin-susceptible and penicillin-resistant Streptococcus pneumoniae in immunocompetent and neutropenic rats: efficacy of penicillin and teicoplanin treatment

Lobar pneumonia models were established in rats by intratracheal inoculation of either penicillin-susceptible (immunocompetent model) or penicillin-resistant (immunocompetent and neutropenic models) Streptococcus pneumoniae. Untreated animals maintained a relatively high bacterial load in the lungs but only occasionally developed bacteraemia or pleurisy. The infection was rarely fatal in immunocompetent rats, but immunocompromised rats frequently died. Treatment i.m. with 10,000 IU/kg of procaine penicillin G (12 h after infection then bid for 3 days) or with a single i.v. dose of 5 or 10 mg/kg of teicoplanin significantly reduced lung bacterial loads of rats infected with the penicillin-susceptible strain. Against the penicillin-resistant strain, teicoplanin displayed a significant activity regardless of the immununological status of the animals. Penicillin G significantly reduced lung bacterial load of the penicillin-resistant strain only in immunocompetent rats and at a higher dose than needed in treatment of the penicillin-susceptible infection. The experimental models described here could be suitable for studying the efficacy of antibacterial agents against pulmonary infections caused by penicillin-susceptible and penicillin-resistant S. pneumoniae strains.