Eradication of nasopharyngeal carriage of penicillin-non-susceptible Streptococcus pneumoniae--is it possible?

BACKGROUND: The South Swedish Pneumococcal Intervention Project (SSPIP) was started in 1995 with the aim of limiting the spread of penicillin-non-susceptible pneumococci (PNSP) in Skåne County, Sweden. As part of the SSPIP, eradication therapy with rifampicin in combination with 1 more antibiotic was considered on a social indication after prolonged carriage of 2-3 months. METHODS: In this retrospective study, 125 medical records were analyzed. Children aged 0-10 y referred for eradication therapy in Malmö and Lund, due to a prolonged nasopharyngeal carriage of PNSP with a penicillin G minimum inhibitory concentration of ≥ 0.5 mg/l, between the y 1997 and 2011 were included. Two consecutive negative cultures, with the second one no shorter than 7 days after treatment completion, were required for the carriage to be considered eradicated. RESULTS: Out of 125 children, 71 received treatment with rifampicin in combination with amoxicillin (n = 44), erythromycin (n = 22), or clindamycin (n = 5) for 7 days. Eradication treatment was successful in 91.5% of the children. Six children (8.5%) had treatment failure with amoxicillin and rifampicin; 3 were found by late follow-up. There was a trend towards a better outcome with erythromycin and clindamycin combinations in comparison to amoxicillin. CONCLUSIONS: Eradication therapy was successful, but a proper follow-up is essential.

Selection of resistant Streptococcus pneumoniae during penicillin treatment in vitro and in three animal models.

Pharmacokinetic (PK) and pharmacodynamic (PD) properties for the selection of resistant pneumococci were studied by using three strains of the same serotype (6B) for mixed-culture infection in time-kill experiments in vitro and in three different animal models, the mouse peritonitis, the mouse thigh, and the rabbit tissue cage models. Treatment regimens with penicillin were designed to give a wide range of T(>MIC)s, the amounts of time for which the drug concentrations in serum were above the MIC. The mixed culture of the three pneumococcal strains, 10(7) CFU of strain A (MIC of penicillin, 0.016 micro g/ml; erythromycin resistant)/ml, 10(6) CFU of strain B (MIC of penicillin, 0.25 micro g/ml)/ml, and 10(5) CFU of strain C (MIC of penicillin, 4 micro g/ml)/ml, was used in the two mouse models, and a mixture of 10(5) CFU of strain A/ml, 10(4) CFU of strain B/ml, and 10(3) CFU of strain C/ml was used in the rabbit tissue cage model. During the different treatment regimens, the differences in numbers of CFU between treated and control animals were calculated to measure the efficacies of the regimens. Selective media with erythromycin or different penicillin concentrations were used to quantify the strains separately. The efficacies of penicillin in vitro were similar when individual strains or mixed cultures were studied. The eradication of the bacteria, independent of the susceptibility of the strain or strains or the presence of the strains in a mixture or on their own, followed the well-known PK and PD rules for treatment with beta-lactams: a maximum efficacy was seen when the T(>MIC) was >40 to 50% of the observation time and the ratio of the maximum concentration of the drug in serum to the MIC was >10. It was possible in all three models to select for the less-susceptible strains by using insufficient treatments. In the rabbit tissue cage model, a regrowth of pneumococci was observed; in the mouse thigh model, the ratio between the different strains changed in favor of the less-susceptible strains; and in the mouse peritonitis model, the susceptible strain disappeared and was overgrown by the less-susceptible strains. These findings with the experimental infection models confirm the importance of eradicating all the bacteria taking part in the infectious process in order to avoid selection of resistant clones.