Stefan Schmidt

Stefan Schmidt
University of KwaZulu-Natal | ukzn · Discipline of Microbiology, School of Life Sciences, Pietermaritzburg

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94
Publications
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Introduction
Stefan Schmidt currently works at the Discipline of Microbiology, School of Life Sciences, Pietermaritzburg, University of KwaZulu-Natal.
Skills and Expertise

Publications

Publications (94)
Article
Full-text available
The fungal genus Basidiobolus is typically associated with ectothermic animals such as amphibians and reptiles. In rare cases, it can cause infections in humans, which are often misdiagnosed. Although usually restricted to tropical and subtropical countries, infections have recently been more frequently reported in hot-dry regions such as Arizona a...
Article
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Farmer practices may influence the microbial quality and safety of fresh produce. The increasing demands to create ready-to-eat (RTE) fresh produce while providing potential niche markets for smallholder farmers might be contributing to increased numbers of fresh produce-associated foodborne disease outbreaks. This study determined the demographic...
Article
Many studies have shown the efficacy of phage therapy in reducing intestinal pathogens. However, phage-based probiotic treatment is poorly studied in view of effects on the gut microbiota and intestinal inflammation. In this study, a lytic or a temperate phage (each at 4×10⁸ PFU per day) or a streptomycin solution (40 mg per day) were administered...
Article
The presence of Escherichia coli and Staphylococcus spp. was determined on the skin, personal protective equipment, the municipal vehicle, and various surfaces at ten households in a peri-urban community (KwaZulu-Natal, South Africa) before and after manual emptying of ventilated improved pit latrines. Surface samples (n = 14) were collected using...
Article
Microplastics are considered environmental pollutants of serious concern. In freshwater environments, they can affect aquatic biota and accumulate along the food web. Therefore, this study investigated the capacity of bacterivorous freshwater ciliates, essential members of the aquatic food chain, to ingest plain and fluorescently-labeled polystyren...
Article
Extensive usage of fossil fuels in sub-Saharan Africa (SSA) has led to increasing greenhouse gas (GHG) emissions that might adversely affect numerous sustainable development goals. However, biofuels produced from energy crops are carbon-neutral because the plants assimilated the CO2 released subsequently in the combustion process, therewith reducin...
Article
To assess the contamination of lettuce with norovirus in Nanjing city (China), two hundred and eighty one lettuce samples were collected between 2017 and 2018 from production sites (preharvest) and retail outlets (postharvest) and analyzed. The presence of norovirus was confirmed in 26.9% (71/264) of lettuce samples, with norovirus genogroup I dete...
Article
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Objectives: Klebsiella michiganensis is an emerging pathogen implicated in nosocomial infections. Here we report on the resistome, virulome and mobilome of a carbapenemase-producing K. michiganensis isolate from urban hospital effluent in Pietermaritzburg, KwaZulu-Natal, South Africa. Klebsiella sp. isolate KP124 was originally isolated from the fi...
Article
Full-text available
The genus Basidiobolus, known since 1886, is primarily associated with reptiles and amphibians. Although globally distributed, rare infections caused by members of this genus mainly occur in tropical and subtropical regions. Morphological and physiological characteristics were used in the past for the description of species. However, some of these...
Article
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Many studies have shown the efficacy of phage therapy in reducing gastrointestinal pathogens. However, it is unclear whether phages can successfully colonize the gut when administered in an adequate amount for a long time. About 1 × 10 ⁸ PFU/mL of purified lytic phage PA13076 or temperate phage BP96115 were fed daily to mice via drinking water over...
Article
S. Enteritidis continues to be the most common pathogen of farm animals and a major public health burden worldwide. Using bacteriophages is a potential alternative to antibiotics against S. Enteritidis infection. In this study, the genome analysis of the lytic phage vB_SenM-PA13076 (PA13076) infecting S. Enteritidis revealed a linear, double-strand...
Article
Hospital effluents are crucial hotspots for the dissemination of antibiotic resistant microorganisms. This study analysed hospital effluent and proximate wastewater treatment plants for the presence of antibiotic resistant Klebsiella spp. Water samples were obtained twice over a three-month period from an urban and rural hospital at three effluent...
Article
For effective use of phages as antimicrobial agents for controlling multidrug resistant S. Pullorum, it is important to understand phage biology. A lytic S. Pullorum phage was isolated and characterized from chicken feces, and its whole genome was sequenced and analyzed. A new lytic phage-vB_SPuM_SP116 (in brief SP116)- isolated and characterized u...
Article
Members of the genus Basidiobolus are potentially pathogenic fungi, known to cause mycoses in tropical and subtropical countries. Basidiobolus spp. can be associated with animals, and reptiles and amphibians are candidate vectors for the distribution of this fungus. The presence of Basidiobolus spp. was described for different reptiles in several A...
Article
Full-text available
Phages, the most abundant species in the mammalian gut, have numerous advantages as biocontrol agent over antibiotics. In this study, mice were orally treated with the lytic gut phage PA13076 (group B), the temperate phage BP96115 (group C), no phage (group A), or streptomycin (group D) over 31 days. At the end of the experiment, fecal microbiota d...
Article
Increasing demands for “minimally processed” fresh produce create a potential market niche in high-value markets for South African smallholder farmers. Fresh produce not meeting required microbiological quality criteria causes consumer health concerns and therefore limits market access. This study determined selected smallholder farmer pre-and-post...
Article
The aim of this study was to assess pit latrine samples from a peri-urban community in KwaZulu-Natal (South Africa) for the presence of multidrug-resistant (MDR) Staphylococcus spp. Standard procedures were used to isolate Staphylococcus spp. from pit latrine fecal sludge samples, with confirmation at genus level by polymerase chain reaction (PCR)....
Article
Introduction: PiAstra is a simulated flash-heat (FH) pasteurization temperature monitoring system designed using Raspberry Pi technology for the pasteurization of human milk. This study analyzed the effect of the PiAstra FH method on human milk immune components (immunoglobulin A [IgA] and lactoferrin activity). Methods: Donor milk samples (N =...
Article
Anaerobic digestion is a process, which leads to energy generation as well as pollution minimization. Both industrial and agricultural wastes can be digested anaerobically due to the presence of biodegradable materials. However, the presence of potential chemical inhibitors has been identified as one of the primary factors contributing to process i...
Article
Due to the frequent use of antibiotics and recurring illnesses related to multidrug-resistant (MDR) bacteria in South Africa, we determined if MDR Escherichia coli were present in pit latrine fecal sludge samples obtained from a peri-urban community in KwaZulu-Natal, South Africa. The abundance of E. coli in pit latrine samples was established usin...
Article
Artificial Neural Network (ANN) and Response Surface Methodology (RSM) modeling was employed in an Upflow Anaerobic Sludge Blanket (UASB) bioreactor for optimization of hydrogen yield and COD (Chemical Oxygen Demand) removal efficiency. Experimental data were generated by running seventeen fermentation experiments at varying hydraulic retention tim...
Article
Full-text available
Due to limited data available on the presence of antibiotic-resistant (ABR) bacteria in faeces of wild herbivores in South Africa, this study analysed resistance patterns for Escherichia coli isolates from wildebeest, zebra and giraffe in addition to pet and farm pig faeces. Total and faecal coliforms and E. coli were quantified in faecal matter us...
Article
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A pasteurization temperature monitoring system has been designed using FoneAstra, a cellphone-based networked sensing system, to monitor simulated flash-heat (FH) pasteurization. This study compared the effect of the FoneAstra FH (F-FH) method with the Sterifeed Holder method currently used by human milk banks on human milk immune components (immun...
Article
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Postharvest microbial spoilage due to suboptimal transportation and packaging conditions is a key concern for the South African tomato industry. This study investigated the influence of washing with tap water or aqueous disinfectant solutions (chlorinated and anolyte water) on the microbiological quality of tomatoes during storage after transportat...
Chapter
Full-text available
Free-living amoebae are part of the microscopic environment and typically act as predators. They show a great variety of cell morphologies and can be differentiated into naked amoebae, testate amoebae (testacea), foraminifera, radiolaria and heliozoa. Amoebae are single-celled organisms, which can form pseudopodia as temporary cell extensions that...
Article
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Two infrared systems set at an intensity of 4777 W/m²with peak emission wavelengths of 2.5 μm and 3.5 μm were used to produce biltong by drying differently pre-treated meat. In addition to meat texture and colour, the microbial quality of the biltong produced was assessed by quantifying viable heterotrophic microorganisms using a most probable numb...
Article
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South Africa is a water-scarce country with increasing pressure on its water resources. Urgent interventions are needed to protect water security within this rapidly developing country. This paper reports on an interdisciplinary Water Security Colloquium, convened by the South African Young Academy of Science in 2014. A selected group of water prof...
Article
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This study assessed faecal matter from three indigenous South African herbivores—zebra, giraffe and impala—as a potential source for hydrolytically active aerobic and facultatively anaerobic bacteria. Herbivore droppings were collected freshly in a local nature reserve in Pietermaritzburg, South Africa. Soil samples adjacent to faecal collection si...
Article
Full-text available
To assess the microbiological status of a biofiltration system used to treat borehole water, filter matrix samples were analyzed after staining for the presence of active biofilms using confocal laser scanning microscopy (CLSM). CLSM revealed the presence of biofilms on the filter matrix with actively metabolizing microbial cells present. Thereafte...
Conference Paper
Full-text available
A huge chunk of African countries' national budget which could have gone into development is spent on fossil fuel energy import. This leads to poor infrastructural development, in-fighting (wars) and spread of lethal diseases. Conversion of biomass to energy will help reduce the dependence on fossil fuels as well as mitigate the negative social and...
Article
The interactive effect of a hybrid pH and microwave pre-treatment on a mixed inoculum for biohydrogen production was investigated. Response surface methodology (RSM) was employed to obtain the optimum pre-treatment conditions of pH, microwave duration and microwave intensity for maximum hydrogen yield. The obtained model had a coefficient of correl...
Article
Density functional theory (DFT) calculations were used to explore the relationship between the biotransformation of dibenzo-p-dioxin and selected chlorinated derivatives by resting cells of Sphingomonas wittichii RW1 and measuring the thermodynamic properties of the biotransformation substrates. Sphingomonas wittichii RW1 can aerobically catabolize...
Article
Full-text available
OPSOMMING Produksie van goeie gehalte voedselprodukte is van kritieke belang in die verbetering van toegang tot die mark en voedselsekuriteit. Boerderypraktyke beïnvloed die gehalte van die finale produk, wat op sy beurt sukses in die mark bepaal. Dit is dus belangrik dat boere voedsel van goeie higiëniese gehalte produseer as hulle van plan is om...
Chapter
Full-text available
The isolation of bacteriolytic prokaryotes from herbivore droppings collected in South Africa (Pietermaritzburg) was undertaken by using inactivated or active microbial cells as the bait embedded in water agar. Using Zebra droppings as the source for predatory bacteria feeding on the microbial bait, a Gram negative isolate was obtained. Based on it...
Chapter
Full-text available
The presence of antibiotic residues in food and feed can cause serious problems for consumers (e.g. penicillin allergy) or by giving rise to the development and spread of antibiotic resistances. To safeguard food quality and consumer safety, the EU implemented regulations governing maximum residue levels in certain food products of animal origin su...
Article
As little is known about the potential risks associated with the use of microbiologically contaminated river water for recreation, irrigation, or domestic purposes, the Msunduzi River in Pietermaritzburg (KwaZulu-Natal, South Africa) was evaluated. In addition to pH, temperature, and chemical oxygen demand, quantitative and qualitative microbiologi...
Article
Inoculum pre-treatment is a crucial aspect of hydrogen fermentation processes to establish the required microbial community for hydrogen production. This paper models and optimizes two hybrid techniques of inoculum pre-treatment for fermentative hydrogen production: (1)pH and Autoclave (PHA); (2)pH and heat shock (PHS) using Response Surface Method...
Article
Full-text available
During October, November and December 2011 (when highest sales of Agri-Hub fresh produce are observed), irrigation water, compost, lettuce and spinach sampled from four different farmer cooperatives supplying the local Agri-Hub in uMbumbulu (KwaZulu-Natal, South Africa) were analyzed monthly for the presence of total and fecal coliforms and Escheri...
Data
Individual MALDI-TOF MS spectra obtained for protein extracts of 15 randomly selected Msunduzi River E. coli isolates (M1-M15) and two E. coli reference strains
Article
A web-enabled software was developed for continuous online monitoring of biohydrogen, biomethane and carbon dioxide gas fractions, temperature, Dissolved Oxygen (DO), pH, conductivity and gas volume for biogas fermentations. The cumulative gas volumes are computed recursively at 1 min intervals. Process data streamed into a MySQL database are acces...
Article
Using minimal salts medium containing vitamins and pyruvate (MSVP) plus added manganese sulfate, a manganese (II) oxidizing bacterial strain was isolated from water samples of a biofiltration system treating borehole water in KwaZulu-Natal, South Africa. The nonmotile Gram-negative and oxidase-negative isolate was subsequently characterized microbi...
Article
Many aromatic hydrocarbons assigned to the so-called high production volume chemicals (HPVCs) are frequently encountered constituents of wastewaters that end up in the sea. Although the pollutant-degrading capabilities of freshwater bacteria are well known, the catabolism of pollutants by marine bacteria has received limited attention. A marine bac...
Article
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Mycobacteria are among the microorganisms least susceptible to biocides but cause devastating diseases, such as tuberculosis, and increasingly opportunistic infections. The exceptional resistance of mycobacteria to toxic solutes is due to an unusual outer membrane, which acts as an efficient permeability barrier, in synergy with other resistance me...
Article
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An automated biogas fermenter running continuously for about two years using fodder and sugar beet silage as mono-substrate without manure addition was analyzed simultaneously by amplified ribosomal DNA restriction analysis and microscopy. In this long-term fermentation study, an oscillating population of prokaryotes was observed. The presence of m...
Article
The antimicrobial agent triclosan is an emerging and persistent environmental pollutant. This study evaluated the susceptibility and biodegradation potential of triclosan by three bacterial strains (Sphingomonas wittichii RW1, Burkholderia xenovorans LB400 and Sphingomonas sp. PH-07) that are able to degrade aromatic pollutants (dibenzofuran, biphe...
Article
Full-text available
The present long-term study (about 1,100 days) monitored the diversity of methanogens during the mesophilic, anaerobic digestion of beet silage. Six fermentor samples were analyzed by ribosomal RNA gene restriction analysis, fluorescence in situ hybridization, and fluorescence microscopy. Hydrogenotrophic methanogens dominated within the population...
Article
Full-text available
Beet silage and beet juice were digested continuously as representative energy crops in a thermophilic biogas fermentor for more than 7 years. Fluorescence microscopy of 15 samples covering a period of 650 days revealed that a decrease in temperature from 60°C to 55°C converted a morphologically uniform archaeal population (rods) into a population...
Chapter
Full-text available
To lead a healthy lifestyle, it is essential to have a diet that includes fresh and minimally processed fruit and vegetables. A large proportion of the South African population exhibits suppressed immune systems, largely due to the HIV/AIDS epidemic. It is therefore imperative that minimally processed foods are not contaminated with potentially pat...
Article
Polybrominated diphenyl ethers (PBDEs) are common flame-retardant chemicals that are used in diverse commercial products such as textiles, circuit boards, and plastics. Because of the widespread production and improper disposal of materials that contain PBDEs, there has been an increasing accumulation of these compounds in the environment. The toxi...
Article
From water sampled in the River Elbe, we isolated a bacterial strain able to use the biocidal compound benzylbenzoate as its sole source of carbon and energy under aerobic conditions. This isolate was tentatively assigned to the genus Acinetobacter due to its morphological, physiological and partial SSU rRNA gene sequence properties. The productive...
Article
The effect of heavy metals on the degradation of dibenzofuran by Sphingomonas wittichii RW1 was determined in liquid cultures. The results showed that 10mg/L cadmium, mercury and copper not only affected the growth of RW1 with dibenzofuran but also the ability of resting cells to degrade this compound. Growth and degradation were strongly inhibited...
Article
Full-text available
Sphingomonas wittichii RW1 is able to catabolize 1,2,3,4-tetrachlorodibenzo-p-dioxin (H. B. Hong, Y. S. Chang, I. H. Nam, P. Fortnagel, and S. Schmidt, Appl. Environ. Microbiol. 68:2584-2588, 2002). Here we demonstrate the aerobic bacterial catabolism of the ubiquitous toxic diaryl ether pollutant 1,2,3,4,7,8-hexachlorodibenzo-p-dioxin by this stra...
Article
The bacterial catabolism of a technical formulation of alkylsulfonic acid phenyl esters employed as a general purpose plasticizer, Mesamoll, was elucidated. Two strains of the genus Rhodococcus were found able to utilize this substrate mixture as sole source of carbon and energy. Growth experiments along with enzymatic measurements indicated that b...
Article
We evaluated the High Production Volume (HPV)-compound 1,2,3- trichloropropane regarding its potential environmental impact by exploiting available data and by using the applicable EU guidelines for the risk assessment of new and existing substances. Consequently, a risk quotient of <1 was established by employing the PEC (predicted environmental c...
Article
Full-text available
The high production volume (HPV)-compound, p-chloroaniline, was evaluated with respect to its ecotoxicological impact upon aquatic systems. This was accomplished by employing the applicable EU-guidelines for the risk assessment of new and existing substances and by using available data. Accordingly, a risk quotient was obtained by employing a PEC a...
Article
This chapter aims to provide a brief overview of the biodegradability of the diaryl ester phenylbenzoate and some of its derivatives under aerobic conditions by comparing bacterial and fungal strategies. The ability of micro-organisms to degrade the simplest diaryl ester phenylbenzoate effectively, does suggest that this structure, and most probabl...
Article
Full-text available
Aerobic biotransformation of the diaryl ethers 2,7-dichlorodibenzo-p-dioxin and 1,2,3,4-tetrachlorodibenzo-p-dioxin by the dibenzo-p-dioxin-utilizing strain Sphingomonas wittichii RW1, producing corresponding metabolites, was demonstrated for the first time. Our strain transformed 2,7-dichlorodibenzo-p-dioxin, yielding 4-chlorocatechol, and 1,2,3,4...
Article
The role of green microalgae in the biotransformation of naphthalene (a polycyclic aromatic hydrocarbon) and diaryl ethers was investigated using axenic cultures of Chlorella vulgaris and two environmental isolates, Scenedesmus SI1 and Ankistrodesmus SI2. Biotransformation experiments with dense cell cultures showed that these three green algae tra...
Article
The dioxygenolytic catabolism of five C-methylated hydroquinones and 2,6-dichlorohydroquinone in Pseudomonas sp. strain HH35 was elucidated. This organism, which is known to catabolise 2,6-dimethylhydroquinone by 1,2-cleavage, accumulated metabolites from 2-methyl-, 2,3-dimethyl-, 2,5-dimethyl-, 2,3,5-trimethyl- and 2,3,5,6-tetramethylhydroquinone...
Chapter
Diaryl ethers such as dibenzo-p-dioxin (DD) and dibenzofuran (DF), particularly the chlorinated derivatives, are extremely persistent in the environment due to their high toxicity and limited biodegradation. These compounds may have significant deleterious effects upon green algae which are essential components of aquatic and soil ecosystems. There...
Article
Due to their physicochemical and toxicological properties, polychlorinated dibenzofurans are regarded as a class of compounds providing reason for serious environmental concern. While the nonhalogenated basic structure dibenzofuran is effectively mineralized by appropriate bacterial strains, its polychlorinated derivatives are not. To elucidate the...
Article
A bacterial isolate, tentatively identified as Pseudomonas sp. strain TR3, was found to utilize the diaryl ester phenylbenzoate as sole source of carbon and energy. This strain has the ability to productively degrade phenylbenzoate and some substituted derivatives by a catabolic sequence which was characterized biochemically. The biodegradation of...
Article
Scedosporium apiospermum, a recently isolated phenol-degrading hyphomycete, was shown to be able to productively utilise the diaryl ester phenylbenzoate as its sole source of carbon and energy. The characterisation of degradation intermediates together with the detection of the corresponding catabolic enzymes in crude extracts enabled us to propose...
Article
The microbial degradation of aromatic pollutants has been well characterized over a period of more than 30 years. The microbes of most interest have been bacteria and fungi. Only relatively recently has the question of how algae figure in the catabolism of these compounds attracted a degree of interest. The aim of this review is to highlight the bi...
Article
A hyphomycete with the ability to utilize phenol and p-cresol as carbon and energy source was isolated from soil and subsequently identified as Scedesporium apiospermum. The identification of degradation metabolites and the detection of the corresponding catabolic enzymes in crude extracts enabled us to propose different pathways for the degradatio...