The development of functionalized electrospun nanofibers for the control of pathogenic microorganisms in water.
- Authors: Kleyi, Phumelele Eldridge
- Date: 2014
- Subjects: Electrospinning , Nanofibers , Pathogenic microorganisms , Pathogenic microorganisms -- Detection , Drinking water -- Microbiology , Water quality -- Measurement , Imidazoles , Spectrum analysis , Anti-infective agents , Polymerization
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4497 , http://hdl.handle.net/10962/d1013134
- Description: The thesis presents the development of functionalized electrospun nylon 6 nanofibers for the eradication of pathogenic microorganisms in drinking water. Imidazole derivatives were synthesized as the antimicrobial agents and were characterized by means of NMR spectroscopy, IR spectroscopy, elemental analysis and X-ray crystallography. The first set of compounds (2-substituted N-alkylimidazoles) consisted of imidazole derivatives substituted with different alkyl groups (methyl, ethyl, propyl, butyl, heptyl, octyl, decyl and benzyl) at the 1-position and various functional groups [carboxaldehyde (CHO), alcohol (CH2OH) and carboxylic acid (COOH)] at the 2-position. It was observed that the antimicrobial activity of the compounds increased with increasing alkyl chain length and decreasing pKa of the 2-substituent. It was also observed that the antimicrobial activity was predominantly against a Gram-positive bacterial strains [Staphylococcus aureus (MIC = 5-160 μg/mL) and Bacillus subtilis subsp. spizizenii (MIC = 5-20 μg/mL)], with the latter being the more susceptible. However, the compounds displayed poor antimicrobial activity against Gram-negative bacterial strain, E. coli (MIC = 150- >2500 μg/mL) and did not show any activity against the yeast, C. albicans. The second set of compounds consisted of the silver(I) complexes containing 2-hydroxymethyl-N-alkylimidazoles. The complexes displayed a broad spectrum antimicrobial activity towards the microorganisms that were tested and their activity [E. coli (MIC = 5-40 μg/mL), S. aureus (MIC = 20-80 μg/mL), Bacillus subtilis subsp. spizizenii (MIC = 5-40 μg/mL) and C. albicans (MIC = 40-80 μg/mL)] increased with the alkyl chain length of the 2-hydroxymethyl-N-alkylimidazole. The third set of compounds consisted of the vinylimidazoles containing the vinyl group either at the 1-position or at the 4- or 5- position. The imidazoles with the vinyl group at the 4- or 5-position contained the alkyl group (decyl) at the 1-position. For the fabrication of the antimicrobial nanofibers, the first two sets of imidazole derivatives (2-substituted N-alkylimidazoles and silver(I) complexes) were incorporated into electrospun nylon 6 nanofibers while the third set (2-substituted vinylimidazoles) was immobilized onto electrospun nylon 6 nanofibers employing the graft polymerization method. The antimicrobial nylon nanofibers were characterized by IR spectroscopy and SEM-EDAX (EDS). The electrospun nylon 6 nanofibers incorporated with 2-substituted N-alkylimidazoles displayed moderate to excellent levels of growth reduction against S. aureus (73.2-99.8 percent). For the electrospun nylon 6 nanofibers incorporated with silver(I) complexes, the levels of growth reduction were >99.99 percent, after the antimicrobial activity evaluation using the shake flask method. Furthermore, the grafted electrospun nylon 6 nanofibers showed excellent levels of growth reduction for E. coli (99.94-99.99 percent) and S. aureus (99.93-99.99 percent). The reusability results indicated that the grafted electrospun nylon 6 nanofibers maintained the antibacterial activity until the third cycle of useage. The cytotoxicity studies showed that grafted electrospun nylon 6 nanofibers possess lower cytotoxic effects on Chang liver cells with IC50 values in the range 23.48-26.81 μg/mL. The thesis demonstrated that the development of antimicrobial electrospun nanofibers, with potential for the eradication of pathogenic microoganisms in water, could be accomplished by incorporation as well as immobilization strategies.
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- Date Issued: 2014
Comparative in-vitro activities of trimethoprimsulfamethoxazole and the new fluoroquinolones against confirmed extended spectrum beta-lactamase producing Stenotrophomonas maltophilia in Nkonkobe Municipality, Eastern Cape environment
- Authors: Adeyemi, Oluwatosin Oluwakemi
- Date: 2012
- Subjects: Antibiotics , Microbial sensitivity tests , Drug resistance in microorganisms , Pathogenic microorganisms , Gram-negative bacterial infections
- Language: English
- Type: Thesis , Masters , MSc (Microbiology)
- Identifier: vital:11275 , http://hdl.handle.net/10353/d1007576 , Antibiotics , Microbial sensitivity tests , Drug resistance in microorganisms , Pathogenic microorganisms , Gram-negative bacterial infections
- Description: Stenotrophomonas maltophilia is increasingly emerging as an opportunistic pathogen of global concern. Due to its inherent resistance to several classes of antibiotics including carbapenems and its ability to acquire mobile resistance elements, treatment of infections caused by S. maltophilia is a constant challenge for clinicians. Trimethoprim-sulphamethoxazole (TMP-SMX) is the generally accepted antibiotic of choice for the treatment of infections caused by this organism, but resistance to the drug is increasingly being reported; hence, the need for alternative therapeutic options. In this study, the antimicrobial susceptibility profile of 110 commensal S. maltophilia isolates obtained from Nkonkobe municipality, Eastern Cape Province, Republic of South Africa was investigated. Twenty-one antibiotics including TMP-SMX and the newer fluoroquinolones; levofloxacin, gatifloxacin and moxifloxacin were included in the antibiotic panel. About 63.4 percent of the isolates were susceptible to TMP-SMX with a resistance rate of 28.2 percent. The fluoroquinolones were more effective with susceptibilities ranging from 76 percent to 94.7 percent. Resistance to the fluoroquinolones ranged from 1.3 percent to 2.7 percent. Levofloxacin was the most effective fluoroquinolone tested. Phenotypic dectection of extended spectrum β-lactamases (ESBLs) showed double disc synergy test (DDST) positivity in 59.5 percent of the isolates. Cefepime was the most sensitive indicator cephalosporin in the DDST with 77.3 percent of suspected ESBL-producing isolates showing cefepime-clavulanic acid synergy. Isolates exhibited nine different ESBL phenotypes, however, PCR amplification of the bla genes revealed four isolates that possessed genes belonging to the CTX-M group (CTX-M-1 and CTX-M-8 groups). ESBL genes are usually carried on mobile elements such as plasmids and transposons which may also bear genes that mediate resistance to aminoglycosides, tetracyclines, TMP-SMX and fluoroquinolones. ESBL positive isolates appeared more susceptible to the fluoroquinolones compared to TMP-SMX but there was no significant relationship between ESBL production and susceptibility to these drugs (p > 0.05). The newer fluoroquinolones are a possible alternative treatment option for S. maltophilia infections in this environment but further studies and clinical investigations are needed to determine the in vivo efficacy of these drugs.
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- Date Issued: 2012
The role of pacC in Aspergillus flavus
- Authors: Suleman, Essa
- Date: 2007
- Subjects: Fungi -- Biotechnology , Pathogenic microorganisms
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10332 , http://hdl.handle.net/10948/612 , Fungi -- Biotechnology , Pathogenic microorganisms
- Description: Many microorganisms, and in particular fungi, are able to grow over a wide pH range. Thus, these microorganisms must possess some regulatory mechanism or system that senses the environmental pH signal and ensures that gene expression of certain molecules is tailored to the pH of the environment (Penalva and Arst, 2002). In Aspergillus species and several other fungi, pH regulation is mediated by seven genes viz. palA, palB, palC, palF, palH, palI and the global pH regulatory gene, pacC (MacAbe et al, 1996; Negrete-Urtasun, 1999; Denison, 2000). The activated form of the PacC protein activates genes that are required at alkaline pH, e.g. genes coding for alkaline phosphatases, and represses certain genes that are functional at acidic pH, e.g. genes encoding acid phosphatases (Negrete-Urtasun, 1999). PacC (and its homologues) also positively regulates genes involved in penicillin biosynthesis, e.g. the isopenicillin N synthase gene, ipnA, in A. nidulans (Penalva and Arst, 2002). It has also been hypothesised that pacC may negatively regulate aflatoxin biosynthesis, a carcinogenic secondary metabolite in several species of Aspergillus (Keller et al, 1997). To elucidate the role of pacC a novel method of post-transcriptional gene silencing known as RNA interference was utilized. This method involved the cloning of a partial pacC gene fragment first in the forward and then the reverse orientations in a fungal expression cassette to create an RNA interference (RNAi) vector. The unique structure of this vector would allow the cloned fragments to be expressed and the resulting RNA to immediately form a double stranded stem-loop structure or short hairpin RNA (shRNA; McDonald et al, 2005). The formation of this shRNA, in turn, would be responsible for activating the endogenous RNA degradation complexes that would lead to mRNA degradation and subsequent gene silencing (Liu et al, 2003; Kadotoni et al, 2003; McDonald et al, 2005). The results presented here have shown that confirmed pacC RNAi mutants produced aflatoxins irrespective of environmental pH (i.e. the mutants produce aflatoxins under acidic and alkaline conditions). Thus, pacC is essential for pH regulation of aflatoxin production in A. flavus. There are numerous other biological (e.g. presence of oxylipins, lipooxygenases) and non-biological factors (pH, carbon source etc.) which affect maize colonisation and aflatoxin production by A. flavus (Burrow et al, 1996; Wilson et al, 2001; Calvo et al; 2002; Tsitsigiannis et al, 2006). However, all the genetic mechanisms involved have as yet not been identified. It has been shown by Caracuel et al (2003) that pacC acts as a negative virulence regulator in plants and these workers have hypothesised that PacC prevents expression of genes that are important for infection and virulence of the pathogen. Therefore the physiological effects that pacC silencing had on the growth, conidiation and pathogenicity of A. flavus mutants were also investigated. The results of this study showed that pacC does not play a significant role in primary growth and development but does affect conidial production. SEM results showed that mutants have many “open ended” phialides and poorly developed conidiophores. This would suggest that pacC activation of conidial production genes is also required. Furthermore, pacC RNAi silencing severely impaired the ability of the A. flavus mutants to infect and cause damage on maize. The results obtained here are similar to that of pacC null mutants in A. nidulans, C. albicans and F. oxysporum which also exhibited low pathogenicity (Davis et al, 2000; Fonzi, W.A, 2002; Caracuel et al, 2003; Bignell et al, 2005 and Cornet et al, 2005). This study indicates that pathogenicity of A. flavus on maize is directly related to the structural integrity of conidia, which in turn is greatly influenced by PacC. This gene is a global transcriptional regulator and may either repress or activate one or many genes in each of the above pathways (Penalva and Arst, 2002). Studies on the genetic mechanisms of pacC regulation on these pathways are needed to elucidate the mechanisms of activation or repression of these genes.
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- Date Issued: 2007