Low prevalence of DHFR and DHPS mutations in Pneumocystis jirovecii strains obtained from a German cohort

Background Pneumocystis pneumonia (PCP) is an opportunistic and potentially life-threatening infection of immunocompromised individuals. A combination of trimethoprim–sulfamethoxazole is widely used for prophylaxis and treatment of PCP. Polymorphisms in the drug targets, the dihydropteroate synthase (DHPS) or the dihydrofolate reductase (DHFR) are presumably a reason for treatment failure. Methods We retrospectively examined the prevalence of DHPS and DHFR mutations in Pneumocystis jirovecii isolates obtained from HIV-infected and non-HIV-infected PCP patients. DHFR and DHPS genes were amplified using semi-nested PCR followed by sequencing. Obtained data were correlated with clinical findings. Results Sequencing of the DHPS gene was achieved in 81 out of 128 isolates (63%), the DHFR-gene was successfully sequenced in 96 isolates (75%). The vast majority of DHFR and DHPS sequences were either wild-type or showed synonymous single nucleotide polymorphisms. Only one sample contained a double mutation at DHPS codon 55 and codon 57 which was associated with treatment failure in some studies. No linkage of treatment failure to a DHFR or DHPS genotype was observed. In our cohort, 35 of 95 Patients (37%) were HIV-positive and 60 (63%) were HIV-negative. The overall mortality rate was 24% with a much higher rate among non-HIV patients. Conclusion DHPS and DHFR mutations exist but are infrequent in our cohort. The contribution of gene polymorphisms to treatment failure needs further research. In immunocompromised HIV-negative patients PCP is associated with high mortality rates. Prophylactic treatment is warranted in this patient subset.