The apicoplast link to fever-survival and artemisinin-resistance in the malaria parasite

The emergence and spread of Plasmodium falciparum parasites resistant to front-line antimalarial artemisinin-combination therapies (ACT) threatens to erase the considerable gains against the disease of the last decade. Here, we develop a large-scale phenotypic screening pipeline and use it to carry out a large-scale forward-genetic phenotype screen in P. falciparum to identify genes allowing parasites to survive febrile temperatures. Screening identifies more than 200 P. falciparum mutants with differential responses to increased temperature. These mutants are more likely to be sensitive to artemisinin derivatives as well as to heightened oxidative stress. Major processes critical for P. falciparum tolerance to febrile temperatures and artemisinin include highly essential, conserved pathways associated with protein-folding, heat shock and proteasome-mediated degradation, and unexpectedly, isoprenoid biosynthesis, which originated from the ancestral genome of the parasite’s algal endosymbiont-derived plastid, the apicoplast. Apicoplast-targeted genes in general are upregulated in response to heat shock, as are other Plasmodium genes with orthologs in plant and algal genomes. Plasmodium falciparum parasites appear to exploit their innate febrile-response mechanisms to mediate resistance to artemisinin. Both responses depend on endosymbiont-derived genes in the parasite’s genome, suggesting a link to the evolutionary origins of Plasmodium parasites in free-living ancestors.

The endosymbiotic origins of the apicoplast link fever-survival and artemisinin-resistance in the malaria parasite

ABSTRACTBackgroundThe emergence and spread of Plasmodium falciparum parasites resistant to front-line antimalarial artemisinin-combination therapies (ACT) threatens to erase the considerable gains against the disease of the last decade. We developed a new large-scale phenotypic screening pipeline and used it to carry out the first large-scale forward-genetic phenotype screen in P. falciparum to identify genes that allow parasites to survive febrile temperatures.ResultsScreening identified more than 200 P. falciparum mutants with differential responses to increased temperature. These mutants were more likely to be sensitive to artemisinin derivatives as well as to heightened oxidative stress. Major processes critical for P. falciparum tolerance to febrile temperatures and artemisinin included highly essential, conserved pathways associated with protein-folding, heat-shock and proteasome-mediated degradation, and unexpectedly, isoprenoid biosynthesis, which originated from the parasite’s algal endosymbiont-derived plastid, the apicoplast. Apicoplast-targeted genes in general were up-regulated in response to heat shock, as were other Plasmodium genes with orthologs in plant and algal genomes.ConclusionsPlasmodium falciparum parasites appear to exploit their innate febrile-response mechanisms to mediate resistance to artemisinin. Both responses depend on endosymbiotic cyanobacterium-related ancestral genes in the parasite’s genome, suggesting a link to the evolutionary origins of Plasmodium parasites in free-living ancestors.

Antimicrobial Activity of Ceftolozane–Tazobactam Tested against Contemporary (2012–2016) Enterobacteriaceae and Pseudomonas aeruginosa Isolates by US Census Division

Background Ceftolozane-tazobactam (C-T) is a combination of a novel antipseudomonal cephalosporin and a well-described β-lactamase inhibitor. C-T was approved by the United States (US) Food and Drug Administration in 2014 for complicated urinary tract infections, including acute pyelonephritis and complicated intra-abdominal infections. C-T is currently in clinical trials for the treatment of nosocomial pneumonia. The Program to Assess Ceftolozane-Tazobactam Susceptibility (PACTS) monitors C-T resistance to gram-negative (GN) isolates worldwide. In this study, the activities of C-T and comparators vs. GN isolates from each of the 9 US Census divisions were compared. Methods A total of 18,856 Enterobacteriaceae (ENT) and 4,735 Pseudomonas aeruginosa (PSA) isolates were collected from 32 US hospitals in 2012–2016. Isolates were tested for susceptibility (S) to C-T and comparators by CLSI broth microdilution methodology in a central monitoring laboratory. Other antibiotics tested included amikacin (AMK), ceftazidime (CAZ), colistin (COL), meropenem (MER), and piperacillin-tazobactam (TZP). The following resistant phenotypes were analyzed for ENT: carbapenem resistant (CRE); extended-spectrum β-lactamase phenotype screen-positive (ESBL); and ESBL, nonCRE. or PSA, MER-nonsusceptible (NS), TZP-NS, and CAZ-NS isolates were analyzed. CLSI (2017) interpretive criteria were used. Results For all ENT, 94.2% were S to C-T, 91.5% were S to TZP, 98.0% were S to MER, and 98.8% were S to AMK; 1,697 (9.0%) were ESBL, nonCRE and 356 (1.9%) were CRE. For all PSA isolates, 97.4% were S to C-T, 99.3% were S to COL, 96.9% were S to AMK, and 81.2% were S to MER. The % C-T S for each division (DIV) are shown in the table. The % C-T S for ENT ranged from 98.1% (DIV 4) to 87.4% (DIV 2) and % C-T S for ESBL, nonCRE ranged from 93.8% in DIV 4 to 79.8% in DIV 7. For PSA, the % C-T S ranged from 99.6% in DIV 4 to 94.9% in DIV 9. Activity of C-T against PSA NS to MER, CAZ or TZP varied by division and was >80% for all except DIV 9. Conclusion Against PSA, only COL was more active than C-T. C-T demonstrated potent activity against PSA NS to other β-lactams. For ENT, overall activity was good. For both PSA and ENT, C-T varied by DIV. Disclosures D. Shortridge, Merck: Research Contractor, Research grant; L. R. Duncan, Merck: Research Contractor, Research grant; M. A. Pfaller, Merck: Research Contractor, Research grant; R. K. Flamm, Merck: Research Contractor, Research grant