Dual infection with Pneumocystis carinii and Pasteurella pneumotropica in B cell-deficient mice:: Diagnosis and therapy

Background and Purpose: The clinical presentation, diagnosis, histopathologic findings, and elimination of dual respiratory tract infection with Pasteurella pneumotropica and Pneumocystis carinii were studied in 100 adult barrier-reared C.B17 and MRL-1pr mice homozygous for a targeted mutation of the J(H) region of the immunoglobulin heavy chain. Methods: Necropsy, aerobic bacteriologic culture of hematogenous and pulmonary tissues, histochemical staining of pulmonary tissues, polymerase chain reaction analysis of pulmonary tissues and feces, and viral serologic testing were performed on 19 clinically affected mice and 8 clinically normal mice, then later on antibiotic-treated and caesarian re-derived mice. Therapeutic strategies included sequential administration of trimethoprim/sulfamethoxazole and enrofloxacin or enrofloxacin administration and caesarian rederivation, Results: Clinically affected mice had diffuse, nonsuppurative, interstitial pneumonia with superimposed pyogranulomatous lobar pneumonia that was detected microscopically. Affected lung tissue yielded pure culture of P. pneumotropica. Aged-matched, clinically normal mice of both genotypes had interstitial histiocytic pneumonia without lobar pneumonia, and P. pneumotropica was not isolated. Histochemical staining of lung tissues from normal and clinically affected mice revealed scattered cysts consistent with P. carinii, principally in the interstitium, Treatment with sulfamethoxazole/trimethoprim and enrofloxacin eliminated bacteriologic detection of P pneumotropica, decreased mortality from 50% to 6%, and improved breeding performance. Conclusion: A successful antibiotic therapy and rederivation approach, incorporating enrofloxacin, cesarian section, and isolator rearing, was developed for B cell-deficient mice with opportunistic infections.