Rickettsia tsutsugamushi infection in cell culture: antibiotic susceptibility determined by flow cytometry.

Recent unpublished reports from northern Thailand of severe and sometimes fatal cases of scrub typhus, despite appropriate antibiotic therapy, suggest that resistance may occur. Current antibiotic susceptibility methods that use direct microscopic counts of Giemsa-stained cells or mouse protection assays are slow, labor-intensive, and expensive. We explored the use of flow cytometry to measure rickettsial infection in vitro in L-929 cells treated with and without doxycycline, ciprofloxacin, erythromycin, and chloramphenicol. It was possible to detect the rickettsiae down to a level of 83% of the cells infected, mean of 37 rickettsiae per cell, and 40% of cells with too many rickettsiae to count. This level of sensitivity was sufficient to determine the inhibitory effect of all four drugs at standard screening concentrations. At lower concentrations of doxycycline, flow cytometry detected inhibition of rickettsial growth at a concentration of 6.25 x 10(-2) micrograms/ml but not at 6.25 x 10(-3) micrograms/ml, suggesting that the minimum inhibitory concentration is somewhere between these two values. The data from this study show that flow cytometry permits the rapid screening of numerous rickettsial isolates for their susceptibility to a variety of antibiotics, but that visual counts of infected cells provide a more precise indication of rickettsial growth.

Mosquito bite anaphylaxis: immunotherapy with whole body extracts.

BACKGROUND: Adverse reactions to mosquito bites have been recognized for some time. These usually consist of large local swellings and redness, generalized urticaria, angioedema and less easily definable responses such as nausea, dizziness, headaches, and lethargy. METHODS: We report two patients who experienced systemic anaphylaxis from mosquito bites. Both were skin tested and given immunotherapy using whole body mosquito extracts. RESULTS: Skin testing using whole body mosquito extracts was positive to Aedes aegypti at 1/1,000 weight/volume (wt/vol) in one patient and to Aedes aegypti at 1/100,000 wt/vol, and Culex pipiens at 1/10,000 wt/vol in the other. Skin testing of ten volunteers without a history of adverse reactions to mosquito bites was negative. Immunotherapy using these extracts resulted in resolution of adverse reactions to mosquito bites in one patient and a decrease in reactions in the other. CONCLUSIONS: Immunotherapy with whole body mosquito extracts is a viable treatment option that can play a role in patients with mosquito bite-induced anaphylaxis. It may also result in severe side effects and one must determine the benefit versus risks for each individual patient.