Abdullahi Balarabe Inuwa

The global threat of antibiotic resistance in the high-priority pathogen Acinetobacter baumannii is intensifying, with research efforts and policy formulation largely driven toward addressing antibiotic misuse. However, it is now becoming increasingly evident that the contribution of biocides to the development of antibiotic resistance in bacteria is another significant factor to consider. The suboptimal use of biocides is also a powerful, independent selective pressure driving the evolution of antibiotic resistance, similar to antimicrobials. This chapter examines the key molecular and genetic pathways underlying this connection, including shared physiological defenses that indirectly confer resistance to clinically relevant antibiotics. Furthermore, the chapter presents a comprehensive synthesis of the mechanism of co-selection, where biocide resistance genes are genetically linked to antibiotic resistance genes on mobile elements such as plasmids and integrons, ensuring their co-inheritance and dissemination. A highlight is given on how environmental factors, including sublethal biocide concentrations and biofilm formation, create hot spots for the evolution and horizontal transfer of these resistance determinants, particularly in high-pressure healthcare settings such as intensive care units. Ultimately, this work calls for a paradigm shift in antimicrobial stewardship, urging the integration of biocide regulation and surveillance with current antibiotic-focused strategies to effectively combat the growing threat of multidrug-resistant A. baumannii.

Utilization of microalgae for simultaneous wastewater treatment and bioproducts accumulation has been a subject of research interest for a while. However, in order to successfully turn this into reality, development of strategies to maximize the yield and performance of the deployed microalgae remains paramount. Herein, the performances and yield of different artificial microalgae consortia were evaluated in a synthetic municipal wastewater medium. The results revealed that the performance of the best monoculture (KL10) was more or less comparable to that of the best binary culture (CK). However, the general pattern of the result revealed that regardless of the species diversity in all the cultures, the average reduction of chemical oxygen demand and total phosphorus, as well as the accumulation of protein, chlorophyll a, chlorophyll b and carotenoids content remined comparable (p > 0.05). Furthermore, the average PO43--P reduction efficiency and biomass productivity of the monocultures was higher than (p < 0.05) those of the co-cultures. Conversely, average NH4-N reduction efficiency and lipid productivity of the binary cultures were superior (p < 0.05) to those of the other culture combinations. Finally, the fatty acids composition, which revealed similar fatty acids profile in all the cultures, suggests the suitability of all the cultures for utilization as feedstock for biodiesel production. In conclusion, the findings of the current study suggest that contrary to the popular notion, raising species diversity in microalgae cultures does not always guarantee increased yield and performance.

Microalgae-based wastewater treatment systems (AWWTS) have recently shown promise in the mitigation of antibiotic resistance genes (ARGs) from municipal wastewater (MWW). However, due to the large number of ARGs that exist in MWW, the use of indirect conventional water quality parameters to monitor ARGs reduction in wastewater would make the process less burdensome and economically affordable. In order to establish a robust relationship between the ARGs and water quality parameters, the current study employed different microalgae strains in monoculture (CM2, KL10) and multi-species combinations (CK and WW) for the MWW treatment under outdoor environmental conditions. The studied genes were quantified in the MWW influents and effluents using real-time PCR. All the cultures substantially improved the physicochemical qualities of the MWW. Out of the 14 genes analyzed in this study, tetO, tetW, tetX and ermB were decreased beyond detection within the first 4 days of treatment in all the cultures. Other genes, including bla_CTX, sul1, cmlA, aadA, int1 and uidA were also decreased beyond a 2 log reduction value (LRV). The mobile genetic element, int1, correlated positively with most of the ARGs, especially sul1 (r ≤ 0.99, p < 0.01) and aadA (r ≤ 0.97, p < 0.01). Similarly, the Escherichia coli indicator gene, uidA, correlated positively with the studied genes, especially with aadA, bla_CTX, bla_TEM and cmlA (r ≤ 0.99 for each, p < 0.01). Some of the studied genes also correlated positively with total dissolved solids (TDS) (r ≤ 0.98, p < 0.01), and/or negatively with total suspended solids (TSS) (r ≤ −0.98, p < 0.01) and pH (r ≤ −0.98, p < 0.01). Among the tested cultures, both monocultures, i.e., KL10 and CM2 were found to be more consistent in gene suppression than their multi-species counterparts. The findings revealed water quality parameters such as TDS, TSS and E. coli as reliable proxies for ARGs mitigation in AWWTS and further highlight the superiority of monocultures over multi-species cultures in terms of gene suppression from the MWW stream.

Microalgal biomass provides a renewable source of biofuels and other green products. However, in order to realize economically viable microalgal biorefinery, strategic identification and utilization of suitable microalgal feedstock is fundamental. Here, a multi-step suboptimal screening strategy was used to target promising microalgae strains from selected freshwaters of the study area. The resulting strains were found to be affiliated to seven closely-related genera of the family Scenedesmaceae, as revealed by both morphologic and molecular characterization. Following initial screening under upper psychrophilic to optimum mesophilic (irregular temperature of 14.1 to 35.9°C) cultivation conditions, superior strains were chosen for further studies. Further cultivation of the selected strains under moderate to extreme mesophilic cultivation conditions (irregular temperature of 25.7 to 42.2°C), yielded up to 74.12 mgL^-1day^-1, 19.96 mgL^-1day^-1, 48.56%, 3.34 μg/mL and 1.20 μg/mL, for biomass productivity, lipid productivity, carbohydrate content, pigments content and carotenoids content respectively. These performances were deemed promising compared with some previous, optimum conditions-based reports. Interestingly, the fatty acids profile and the high carotenoids content of the studied strains revealed possible tolerance to the stress caused by the changing suboptimal cultivation conditions. Overall, strains AY1, CM6, LY2 and KL10 were exceptional and may present sustainable, promising feedstock for utilization in large-scale generation of green products, including biodiesel, bioethanol, pigments and dietary supplements. The findings of this study, which exposed promising, eurythermal strains, would expand the current knowledge on the search for promising microalgae strains capable of performing under the largely uncontrolled large-scale cultivation settings.

Endophytic microorganisms have continued to gain prominence as rich sources of useful compounds such as plant growth-promoting chemicals, bioactive compounds, among others. The present study aimed at evaluating the tomato seeds bio-priming and antagonistic potentials of endophytic bacteria isolated from Senna obtusifolia. Endophytic bacteria harbored in the roots and leaves of S. obtusifolia were isolated using a combination of cultural, biochemical, and microscopic techniques. The isolates were evaluated for possible applications as growth-promoting agents of tomato seeds and also, as antagonistic agents to the notorious plant pathogenic fungus Fusarium oxysporum. Diverse genera of bacteria were isolated from the plant, and these prominently include Bacillus spp; Staphylococcus aureus; Escherichia coli; Enterobacter spp; Rhizobium spp and Pseudomonas spp. Although tomato seeds bio-primed with Enterobacter spp germinated before all others, the germination period (4 days) was statistically the same (P< 0.05) as that yielded by the control (4.5). Similarly, tomato seeds treated with S. aureus yielded the highest number of leaves (2.5), and this was also statistically the same as that yielded by the control (P < 0.05). All the isolates used in the evaluation of antagonistic activity yielded significantly larger (P > 0.05) zones of inhibition than the control (11.0 mm). Among these, Bacillus spp yielded the largest zone (21.6 mm). The study revealed that S. obtusifolia harbors endophytic bacteria that could inhibit the growth of the plant pathogen, F. oxysporum.