Multidrug-resistant enterobacterales in Oman : molecular epidemiology and therapeutic insights

The spread of antibiotic resistance is a concerning issue causing limited treatment options for bacterial infections, particularly with Gram-negative bacteria. Surveillance and epidemiological studies help to determine the magnitude of the problem as well as to establish early measures to slow down the spread of resistance and consequently increase antibiotic lifespan. Currently, there is a visible paucity of published data about resistance from the Arabian Peninsula. In this thesis, we studied a collection of carbapenem nonsusceptible E. coli (n=35) and K. pneumoniae (n=237) isolated in 2015 from various hospitals in Oman. We aimed at identifying resistance mechanisms, mapping the bacterial population structure, investigating bacterial fitness, and studying potential treatment options available to tackle infections caused by such multidrug-resistant strains. These aims were addressed in five papers as discussed below. NDM and OXA-48 were the only carbapenemases we found in this collection, both among E. coli (Paper I) and K. pneumoniae (Paper II). The pattern of resistance among the isolates from Arabian Peninsula mimics the pattern reported from the Indian subcontinent, most likely due to the close socioeconomic interactions between them. Both regions lack KPC enzymes, which are commonly seen in China and the US from strains belong to ST11 and ST258, respectively. Despite ST11 being predominant in this collection, we did not detect KPC. Yet, we detected a high-risk clone of E. coli, ST131-H30Rx-CTX-M-15. Additionally, we identified newly emerging clones of K. pneumoniae and E. coli such as ST231 and ST1193-H64RxC, respectively. Nearly 10% of the K. pneumoniae isolates in our collection were colistin resistant which prompted us to study the mechanisms of colistin resistance (Paper III). MgrB-inactivation by insertion elements was seen in 8 isolates while other mutations were seen in other chromosomal genes known to be involved in colistin resistance e.g. pmrB, phoPQ and crrB. However, we did not detect mcr genes. Collectively, the genetic alterations are thought to reduce the net negative charge in bacterial cell wall, hence lowering the binding affinity of colistin. Our data underscores that there is no reduction in the surface charge in colistinresistant K. pneumoniae, due to the MgrB-insertion (Paper IV). The genetic alteration might lead to other structural changes in the cell wall such as altering hydrophobicity, which required further investigation. Also, our data shows no difference in the survival rates of colistin resistant and susceptible strains in blood, serum and zebrafish model. Thus, gaining resistance against colistin does not infer a fitness cost in K. pneumoniae with MgrB-insertion (Paper IV). Additionally, colistin and LL-37 share similar binding mechanism which suggest there might be a cross-resistance between them. Our data supported this hypothesis, but only at high concentrations of LL-37 ( ≥ 50 mg/L) (Paper IV). Finally, we studied available options to treat infections caused by multidrug-resistant strains. Combining colistin and rifampicin showed good in vitro activity against multidrug-resistant strains of E. coli (Paper V) and K. pneumoniae (Paper III). To summarise, we conducted comprehensive genomic analysis of E. coli and K. pneumoniae isolates from Oman to reveal the resistance mechanism, their impact on bacterial cell structural and if there is a fitness cost inferred by the resistance mechanisms. Finally, we studied combination therapy as an available option at hand for tackling infections caused by multidrug-resistant strains

Combustion and emission studies of a common-rail direct injection diesel engine with various injector nozzles

Fuel injection has a critical role in an internal combustion engine and a significant effect on the quality of the fuel spray. In turn, fuel spray directly affects an engine´s combustion, efficiency, power and emissions. This study evaluated three different injector nozzles in a highspeed, non-road diesel engine. It was run on diesel fuel oil (DFO) and testing was conducted at three different engine loads (100%, 75% and 50%) and at two engine speeds (2,200 rpm and 1,500 rpm). The nozzles had 6, 8 and 10 holes and a relatively high mass flow rate (HF). The study investigated and compared injection and combustion characteristics, together with gaseous emissions. The combustion parameters seemed to be very similar with all studied injector nozzles. The emission measurements indicated general reductions in hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx) at most load/speed points when using the 6- and 10-hole nozzles instead of the reference 8-hole nozzles. However, smoke number increased when the alternative nozzles were used

Combustion property analyses with variable liquid marine fuels in combustion research unit

The quality of ignition and co mbustion of four marine and power plant fuels were studied in a Combustion Research Unit, CRU. The fuels were low - sulphur Light Fuel Oil (LFO, baseline), Marine Gas Oil (MGO), kerosene and renewable wood - based naphtha. To meet climate change requirements a nd sustainability goals, combustion systems needs to be able to operate with a variety of renewable and ‘net - zero - carbon’ fuels. Due to the variations in the chemical and physical properties of the fuels, they generally cannot simply be dropped into existi ng systems. The aim of this research project was to understand how changes in fuel composition affect engine operation. The focus was on how various properties of the fuels impact on the combustion process – especially ignition delay and in - cylinder combus tion. The goal of the research project was to allow broad fuel flexibility without any or only minor changes to engine hardware. Before the engine tests, the CRU forms an easy and cost - effective device to find out the engine suitability of the fuel . The re sults showed that the ignition delay decreased expectedly with all fuels when the in - cylinder pressure and temperature increased. The differences in the maximum heat release rates between fuels decreased in high - pressure conditions. MGO had the shortest ig nition delay under both pressure and temperature conditions. Based on the CRU results MGO and kerosene are suitable to use in compression - ignited engines like the reference fuel LFO. In contrast renewable naphtha had a long ignition delay. If naphtha is us ed in a CI engine, the engine must be started and stopped with, e.g. LFO or MGO.fi=vertaisarvioitu|en=peerReviewed

Utveckling av temperaturreguleringskapacitet hos renkalvar

Utveckling av temperaturregleringskapacitet hos nyfodda renkalvar undersöktes vid Paliskuntain Yhdistys (Foreningen for Renbeteslagen) försoksstation i Kaamanen under maj-juli 1981-82

Waste fish oil as an alternative renewable fuel for IC engines

Received: January 31st, 2021 ; Accepted: April 10th, 2021 ; Published: April 30th, 2021 ; Correspondence: [email protected] are potential fuels for internal combustion engines because of they have advantageous properties such as biodegradability, renewability, high oxygen content and low sulphur. However, the high viscosity, surface tension, and density of crude bio-oils pose challenges for engine use. Those properties affect fuel spray characteristics, mixture formation and combustion. In turn, these impact engine, efficiency, power and emissions. This study investigated the use of crude fish oil (FO) at medium and low engine-loads at two engine speeds in an off-road engine. The injectors had 6-hole high flow rate tips. The results were compared with those of fossil diesel fuel oil (DFO). Fish oil increased hydrocarbon (HC), carbon monoxide (CO) and partly oxides of nitrogen (NOx) emissions. Smoke number, however, decreased. Crude fish oil also showed lowered total particle number (TPN) at low load at low engine-speed compared with DFO

Methanol-HVO blends for efficient low-temperature combustion: analytical research on fuel properties

Received: January 31st, 2023 ; Accepted: April 15th, 2023 ; Published: August 14th, 2023 ; Correspondence: [email protected] low-temperature combustion (LTC) engines can accommodate ultra-high efficiency with near-zero NOx and PM emissions. Reaction kinetics is the governing mechanism in LTC. Onboard fuel reactivity control is, thus, becoming an interesting concept that ultimately provides pathways toward a fully fuel-flexible engine. No matter the technical realisation - in-cylinder blending or pre-blending/emulsification - the reactivity control requires fuels with complementary properties. Methanol and hydrotreated vegetable oil (HVO) seem to be one of the most promising, yet under-studied combination for LTC engines. They are both renewable and can be mixed together. Methanol’s high knock resistance and large latent heat of evaporation enable a wide engine load range, with a propensity to reduce NOx emissions and mitigate thermal or mechanical stress. The same properties on the other hand require highly reactive fuel to enable the mixture to self-ignite controllably in LTC conditions. HVO is amongst the most reactive renewable alternatives and its clean paraffinic structure further mitigates particle matter formation. - Importantly, in pre-blending HVO emulsification can resolve the lubricity issues of methanol. In this paper, the aim was to study the engine-relevant properties of HVO-methanol fuel blends. The analysed properties were the distillation properties, density, kinematic viscosity, cetane index, and flash point. Based on the results, the suitability of the chosen blend shares for LTC concepts was evaluated

Soil organic carbon stocks under pasture atlantic forest in Rio de Janeiro state, Brazil.

The objective of this study is to perform a comparative analysis of the soil carbon stock under pasture (Brachiaria spp) and semideciduous broadleaf Atlantic Forest fragments

Carbon stock measurement to evaluate ecosystem service from carbon sequestration.

The aim of this study is to establish parameters to evaluate ecosystem service from carbon sequestration of the actions supported by the Sustainable Rural Development Program in watersheds of the state of Rio de Janeiro, southeastern Brazil – Rio-Rural