| 1. |
- Al-Saai, Salma, et al.
(författare)
-
Distinct haplotypes of dhfr and dhps among Plasmodium falciparum isolates in an area of high level of sulfadoxine-pyrimethamine (SP) resistance in eastern Sudan
- 2009
-
Ingår i: Infection, Genetics and Evolution. - : Elsevier BV. - 1567-1348 .- 1567-7257. ; 9:5, s. 778-783
-
Tidskriftsartikel (refereegranskat)abstract
- Typing of polymorphic microsatellites that are linked to drug resistance genes has shed light on the origin and pattern of spread of some anti-malarial drugs. Recent surveys revealed spread of a high-level pyrimethemine resistant lineage of Plasmodium falciparum, of Asian origin, across Africa. Here, we examined mutations in dihydrofolate reductase, dhfr [chromsosome 4], the dihydropteroate synthase, dhps [chromosome 8] associated with resistance to sulfadoxine-pyrimethamine (SP), and neighboring microsatellites among P. falciparum isolates in Asar village, eastern Sudan. This area lies at the fringes of malaria endemicity, where the remote P. falciparum parasites have some distinct genetic characteristics. Overall, 89% (84/94) of the examined isolates carried double mutations at dhfr (N51I and S108N), but the 59R and I164L mutations were not seen. Similarly, the majority, 43% (35/81) of the isolates carried double mutations at dhps (437G, 540E). Analysis of neighboring microsatellites revealed one major dhfr haplotype with mutations (51I, 108N) and one dhps haplotype with mutations (436S, 437G, 540E). These haplotypes differ from the major ones thought to drive resistance to SP across Africa. The resistant haplotypes of dhfr and dhps, in Asar, share some microsatellites with the wild genotypes suggesting that they were generated locally. Among isolates successfully examined, 40% shared identical haplotypes of the 2 loci, comprising a dominant resistant lineage. Undoubtedly, this lineage plays an important role in clinical failure to SP in this area.
|
|
| 2. |
|
|
| 3. |
- Babiker, Hamza A., et al.
(författare)
-
Impaired fitness of drug-resistant malaria parasites : evidence and implication on drug-deployment policies
- 2009
-
Ingår i: Expert review of anti-infective therapy. - 1478-7210. ; 7:5, s. 581-593
-
Forskningsöversikt (refereegranskat)abstract
- Malaria, a leading parasitic disease, inflicts an enormous toll on human lives and is caused by protozoal parasites belonging to the genus Plasmodium. Antimalarial drugs targeting essential biochemical processes in the parasite are the primary resources for management and control. However, the parasite has established mutations, substantially reducing the efficacy of these drugs. First-line therapy is faced the with the consistent evolution of drug-resistant genotypes carrying these mutations. However, drug-resistant genotypes are likely to be less fit than the wild-type, suggesting that they might disappear by reducing the volume of drug pressure. A substantial body of epidemiological evidence confirmed that the frequency of resistant genotypes wanes when active drug selection declines. Drug selection on the parasite genome that removes genetic variation in the vicinity of drug-resistant genes (hitch-hiking) is common among resistant parasites in the field. This can further disadvantage drug-resistant strains and limit their variability in the face of a mounting immune response. Attempts to provide unequivocal evidence for the fitness cost of drug resistance have monitored the outcomes of laboratory competition experiments of deliberate mixtures of sensitive and resistant strains, in the absence of drug pressure, using isogenic clones produced either by drug selection or gene manipulation. Some of these experiments provided inconclusive results, but they all suggested reduced fitness of drug-resistant clones in the absence of drug pressure. In addition, biochemical analyses provided clearer information demonstrating that the mutation of some antimalarial-targeted enzymes lowers their activity compared with the wild-type enzyme. Here, we review current evidences for the disadvantage of drug-resistance mutations, and discuss some strategies of drug deployment to maximize the cost of resistance and limit its spread.
|
|
| 4. |
- Buwembo, William, et al.
(författare)
-
Point Mutations in the folP Gene Partly Explain Sulfonamide Resistance of Streptococcus mutans
- 2013
-
Ingår i: International Journal of Microbiology. - : Hindawi Limited. - 1687-918X .- 1687-9198. ; 2013, s. 367021-
-
Tidskriftsartikel (refereegranskat)abstract
- Cotrimoxazole inhibits dhfr and dhps and reportedly selects for drug resistance in pathogens. Here,Streptococcus mutansisolates were obtained from saliva of HIV/AIDS patients taking cotrimoxazole prophylaxis in Uganda. The isolates were tested for resistance to cotrimoxazole and theirfolPDNA (which encodes sulfonamide-targeted enzyme dhps) cloned in pUC19. A set of recombinant plasmids carrying different point mutations in cloned folP were separately transformed intofolP-deficientEscherichia coli. Using sulfonamide-containing media, we assessed the growth offolP-deficient bacteria harbouring plasmids with differingfolPpoint mutations. Interestingly, clonedfolPwith three mutations (A37V, N172D, R193Q) derived fromStreptococcus mutans8 conferred substantial resistance against sulfonamide tofolP-deficient bacteria. Indeed, change of any of the three residues (A37V, N172D, and R193Q) in plasmid-encodedfolPdiminished the bacterial resistance to sulfonamide while removal of all three mutations abolished the resistance. In contrast, plasmids carrying four other mutations (A46V, E80K, Q122H, and S146G) infolPdid not similarly confer any sulfonamide resistance tofolP-knockout bacteria. Nevertheless, sulfonamide resistance (MIC = 50 μM) offolP-knockout bacteria transformed with plasmid-encodedfolPwas much less than the resistance (MIC = 4 mM) expressed by chromosomally-encodedfolP. Therefore,folPpoint mutations only partially explain bacterial resistance to sulfonamide.
|
|
| 5. |
|
|
| 6. |
- Enweji, Nizar
(författare)
-
Dynamics of Resistant Plasmodium falciparum Parasites
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Persistence of drug resistant Plasmodium falciparum is a major problem to management and control malaria in endemic areas. The focus of this thesis was to study the dynamics of resistant P. falciparum parasites. The study was performed in two African countries: 1) Sudan: Asar village in eastern Sudan, here we examined the persistence of drug sensitive and resistant P. falciparum genotypes among individuals with single-clone and multiple clones infection during the dry season. We genotyped microsatellite loci in the vicinity of the dihydrofolate reductase gene (dhfr) and the dihydropteroate synthase gene (dhps). Microsatellite investigation showed that asymptomatic parasitemia persisted in some patients for several months throughout the dry season and into the next transmission season. In some samples mixed infections were detected, and we noted several cases where the microsatellite haplotype varied from month to month, suggesting turnover of different parasite populations in the blood. This demonstrates that even during asymptomatic infections there can be dynamics within the parasite population in an individual. In addition, we calculated the parasite density throughout the dry season to the next transmission season by using allele-specific quantitative PCR. Parasite density during the dry season fluctuated, but was generally lower than in the first transmission season. A significant difference (P<0.05) between dry and first transmission season was found in regard to the parasite density, whereas no significant difference was observed when dry and second transmission season were compared (P>0.05). 2) Ethiopia: West Arsi zone, one of the malaria endemic zones of the Oromia region. In the first study we determined the prevalence of asymptomatic malaria carriages from November-December 2012. According to PCR the prevalence of sub-microscopic P. falciparum carriage was 19.2%, microscopy-based prevalence was 3.7% while the prevalence was 6.9% using RDT. Based on this, PCR was considered a better tool for measuring Plasmodium prevalence than microscopy and RDT. A second study addressed the genetic diversity of chloroquine resistance (CQR) in P. falciparum by analysing four microsatellite markers in and around the pfcrt gene. Although CQ was withdrawn for more than a decade, 100% of the parasites still carried the Pfcrt K76T mutation. Only the CVIET haplotype was identified. Based on combinations of MS markers, seven different Ethiopian CQR variants (E1-E7) were identified. Both intronic and MS flanking the pfcrt gene showed low levels of diversity.
|
|
| 7. |
|
|
| 8. |
- Eriksen, J, et al.
(författare)
-
Antimalarial resistance and DHFR/DHPS genotypes of Plasmodium falciparum three years after introduction of sulfadoxine-pyrimethamine and amodiaquine in rural Tanzania.
- 2008
-
Ingår i: Transactions of the Royal Society of Tropical Medicine and Hygiene. - : Oxford University Press (OUP). - 0035-9203 .- 1878-3503. ; 102:2, s. 137-142
-
Tidskriftsartikel (refereegranskat)abstract
- We assessed the efficacy of sulfadoxine-pyrimethamine (SP) and amodiaquine (AQ) and DHFR/DHPS genotypes of Plasmodium falciparum in rural Tanzania, 3 years after their introduction as first- and second-line treatments for uncomplicated malaria, respectively. Under five children with uncomplicated malaria were given standard treatments of either SP (n=66) or AQ (n=30) and treatment outcomes after 14 and 28 days were determined. Total treatment failure of 18 and 42.5% was observed for SP on days 14 and 28, respectively. For AQ, total treatment failure of 27 and 53% was found on day 14 and 28, respectively. On day 14, significantly lower SP total treatment failures were observed in 2004 compared with results from a study conducted in 1999 in the same location. No relationship was detected between clinical outcome and DHFR/DHPS genotypes, but the point mutation prevalence in parasites was higher than in 1999. Pre-treatment blood levels of SP were detected in a quarter of the study children: less than expected. We report unacceptably high levels of total treatment failures, both for first- and second-line treatments for uncomplicated malaria in Tanzania 3 years after their introduction, supporting the decision to replace them with artemisinin-based combination therapy.
|
|
| 9. |
- Farzana, Refath, et al.
(författare)
-
Molecular and genetic characterization of emerging carbapenemase-producing Acinetobacter baumannii strains from patients and hospital environments in Bangladesh
- 2022
-
Ingår i: Infection Prevention in Practice. - : Elsevier. - 2590-0889. ; 4:2
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Carbapenemase-producing multidrug-resistant (MDR) Acinetobacter bau-mannii is a global health care problem. MDR A. baumannii has emerged as an important nosocomial pathogen, costing many lives worldwide including Bangladesh.Aim: To investigate the detailed molecular epidemiology of carbapenem-resistant A. baumannii (CRAB) both from patients and the hospital environment, to shed light on genetic characteristics and transmission dynamics.Methods: A set of 49 clinical A. baumannii strains collected during early 2015 was received from the clinical microbiology laboratory of Dhaka Medical College Hospital (DMCH) in Bangladesh. Additionaly, 100 environmental samples were also collected from the hospital surfaces of Dhaka Medical College Hospital and analyzed for carbapenamase-producing A. baumannii. CRAB were identified by culture on selective plates, biochemical testing and MALDI-TOF. All isolates were characterized by susceptibility testing, realtime-PCRs, conventional PCR, MLST and sequencing.Findings: Clinical A. baumannii were resistant to ciprofloxacin (100%), imipenem (91.8%), meropenem (91.8%), gentamicin (91.8%), amikacin (87.7%), and trimethoprim-sulfamethoxazole (61.2%). The majority (59%) of the isolates were MDR. All environ-mental A. baumannii (n1/410) were resistant to imipenem, meropenem, gentamicin, ami-kacin, and ciprofloxacin. Strains carried the following antibiotic resistant genes; blaOXA-23, blaOXA-58, blaPER-7, qnrB1, qnrC1, aac(60)1b-cr and armA. A total of 36 different clones were identified by rep-PCR and common clonal clusters were found both in patients and hospital environments. MLST analysis revealed different sequence types (ST2, ST10, ST149, ST575, ST1063 and ST1065). In clinical and environmental settings. A. baumannii ST2 dominated in both clinical and environmental settings. Both clinical and environmental A. baumannii strains with known STs carried several biofilm-related genes; bap, csuE, and pgaB. Conclusion: Widespread dissemination of MDR A. baumannii in the DMC hospital of Ban-gladesh is a serious problem.
|
|
| 10. |
- Golassa, Lemu, et al.
(författare)
-
Detection of a substantial number of sub-microscopic Plasmodium falciparum infections by polymerase chain reaction : a potential threat to malaria control and diagnosis in Ethiopia
- 2013
-
Ingår i: Malaria Journal. - : Springer Science and Business Media LLC. - 1475-2875 .- 1475-2875. ; 12, s. 352-
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Prompt and effective malaria diagnosis not only alleviates individual suffering, but also decreases malaria transmission at the community level. The commonly used diagnostic methods, microscopy and rapid diagnostic tests, are usually insensitive at very low-density parasitaemia. Molecular techniques, on the other hand, allow the detection of low-level, sub-microscopic parasitaemia. This study aimed to explore the presence of sub-microscopic Plasmodium falciparum infections using polymerase chain reaction (PCR). The PCR-based parasite prevalence was compared against microscopy and rapid diagnostic test (RDT). Methods: This study used 1,453 blood samples collected from clinical patients and sub-clinical subjects to determine the prevalence of sub-microscopic P. falciparum carriages. Subsets of RDT and microscopy negative blood samples were tested by PCR while all RDT and microscopically confirmed P. falciparum-infected samples were subjected to PCR. Finger-prick blood samples spotted on filter paper were used for parasite genomic DNA extraction. Results: The prevalence of sub-microscopic P. falciparum carriage was 19.2% (77/400) (95% CI = 15.4-23.1). Microscopy-based prevalence of P. falciparum infection was 3.7% (54/1,453) while the prevalence was 6.9% (100/1,453) using RDT alone. Using microscopy and PCR, the estimated parasite prevalence was 20.6% if PCR were performed in 1,453 blood samples. The prevalence was estimated to be 22.7% if RDT and PCR were used. Of 54 microscopically confirmed P. falciparum-infected subjects, PCR detected 90.7% (49/54). Out of 100 RDT-confirmed P. falciparum infections; PCR detected 80.0% (80/100). The sensitivity of PCR relative to microscopy and RDT was, therefore, 90.7% and 80%, respectively. The sensitivity of microscopy and RDT relative to PCR was 16.5 (49/299) and 24.2% (80/330), respectively. The overall PCR-based prevalence of P. falciparum infection was 5.6- and 3.3 fold higher than that determined by microscopy and RDT, respectively. None of the sub-microscopic subjects had severe anaemia, though 29.4% had mild anaemia (10-11.9 g/dl). Conclusions: Asymptomatic, low-density malaria infection was common in the study area and PCR may be a better tool for measuring Plasmodium prevalence than microscopy and RDT. The inadequate sensitivity of the diagnostic methods to detect substantial number of sub-microscopic parasitaemia would undoubtedly affect malaria control efforts, making reduction of transmission more difficult. RDT and microscopy-based prevalence studies and subsequent reports of reduction in malaria incidence underestimate the true pictures of P. falciparum infections in the community. PCR, on the other hand, seems to have reasonable sensitivity to detect a higher number of infected subjects with low and sub-microscopic parasite densities than RDTs or microscopy.
|
|
