T.G. Barnard

The viable but non-culturable state in pathogenic Escherichia coli: A general review

Background The persistence and pathogenicity of pathogenic bacteria are dependent on the ability of the species to survive in adverse conditions. During the infectious process, the organism may need to pass through certain hostile anatomical sites, such as the stomach. Under various environmental stresses, many bacteria enter into the viable but non-culturable (VBNC) state, where they are ‘alive’ or metabolically active, but will not grow on conventional media. Escherichia coli bacteria encounter several diverse stress factors during their growth, survival and infection and thus may enter into the VBNC state. Objectives This review discusses various general aspects of the VBNC state, the mechanisms and possible public health impact of indicator and pathogenic E. coli entering into the VBNC state. Method A literature review was conducted to ascertain the possible impact of E. coli entering into the VBNC state. Results Escherichia coli enter into the VBNC state by means of several induction mechanisms. Various authors have found that E. coli can be resuscitated post-VBNC. Certain strains of pathogenic E. coli are still able to produce toxins in the VBNC state, whilst others are avirulent during the VBNC state but are able to regain virulence after resuscitation. Conclusion Pathogenic and indicator E. coli entering into the VBNC state could have an adverse effect on public health if conventional detection methods are used, where the number of viable cells could be underestimated and the VBNC cells still produce toxins or could, at any time, be resuscitated and become virulent again.

UV-assisted reduction of in situ electrospun antibacterial chitosan-based nanofibres for removal of bacteria from water

A greener synthesis of low-swelling uniformly-sized chitosan (CTS)-based nanofibres decorated with silver (Ag) and silver/iron (Ag/Fe) nanoparticles is reported. The synthesis was achieved by electrospinning a solution of CTS blended with varying amounts of polyacrylamide (PAA), polyethylene glycol (PEG) and Ag+ or Ag+/Fe3+ ions. These nanofibres were subjected to UV irradiation under ionised water vapour at low temperature (70 °C). The effect of UV irradiation time on the reduction of the NPs was confirmed using UV-Vis spectroscopy. The microstructure and chemical composition of the Ag and Ag/Fe modified nanofibres was studied using transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and ultraviolet-visible spectroscopy (UV-Vis). TEM revealed that the average diameter of the CTS-based nanofibres, AgNPs, and Ag/Fe NPs supported on the CTS-based nanofibres were 471 ± 89 nm, 18 ± 2.5 and 32 ± 8.7 nm respectively. XRD and EDS analysis confirmed the presence of Ag and Fe in the nanofibers. The biocidal effect of the Ag and Ag/Fe NPs supported on the CTS-based nanofibres was investigated using Gram positive (Bacillus cereus, Enterococcus faecalis) and Gram negative (Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Pseudomonas aeruginosa, Proteus mirabilis, Shigella boydii, Shigella sonnei, Enterobacter cloacae) bacterial strains. The nanofibres exhibited a strong biocidal effect on the bacteria suggesting that they can be used as efficient antimicrobial materials in water systems that are contaminated by bacteria.

Antimicrobial Properties of Chitosan-Alumina/f-MWCNT Nanocomposites

Antimicrobial chitosan-alumina/functionalized-multiwalled carbon nanotube (f-MWCNT) nanocomposites were prepared by a simple phase inversion method. Scanning electron microscopy (SEM) analyses showed the change in the internal morphology of the composites and energy dispersive spectroscopy (EDS) confirmed the presence of alumina and f-MWCNTs in the chitosan polymer matrix. Fourier transform infrared (FTIR) spectroscopy showed the appearance of new functional groups from both alumina and f-MWCNTs, and thermogravimetric analysis (TGA) revealed that the addition of alumina and f-MWCNTs improved the thermal stability of the chitosan polymer. The presence of alumina and f-MWCNTs in the polymer matrix was found to improve the thermal stability and reduced the solubility of chitosan polymer. The prepared chitosan-alumina/f-MWCNT nanocomposites showed inhibition of twelve strains of bacterial strains that were tested. Thus, the nanocomposites show a potential for use as a biocide in water treatment for the removal of bacteria at different environmental conditions.

Detection of amoeba-associated Legionella pneumophila in hospital water networks of Johannesburg

The prevalence of free-living amoeba and associated Legionella spp. in hospital water systems may pose a risk of Legionnaires’ disease to immuno-compromised patients. This study investigated the oc...

Flow cytometric assessment of the effect of simulated gastric fluid (SGF) on the survival of Salmonella typhimurium, Shigella dysenteriae and Shigella flexneri

T stomach is considered as the first line of defense against bacterial infection, however during the intake of food or water the pH increases, offering the ideal time for bacterial pathogens to pass through. This study investigated the ability of stationary phase non-acid adapted, diarrhoea causing Shigella dysenteriae, Shigella flexneri and Salmonella typhimurium cells to tolerate an environment mimicking the human stomach. Flow cytometric (FCM) analysis was used to investigate bacterial response to the challenge of simulated gastric fluid (SGF) at varying pH for physiological heterogeneity and survival. FCM established that the SGF challenged bacterial cells, at two inoculum sizes, consisted of a mixture of three sub-populations (intact, stressed, and damaged cells) stained with Propidium iodide (PI) and Thiazole orange (TO). Eighty percent of the bacterial cells suffered partial loss of cell membrane integrity and shifted to the stressed state throughout SGF exposure, up to 180 min. All pathogens were culturable from 60 min of SGF (pH 2.5-4.5) exposure, with growth increasing at inoculum size of 102 CFU/ml. A general trend of acid tolerance was seen amongst all three strains, with an increase in culturability occurring after 60 min. We found that non-acid adapted bacteria can activate its tolerance mechanisms and survive throughout low pH SGF exposure, even though the numbers of cells decreases to a certain extent or changes to a stressed state, those that did survive were more resistant to acid challenge. The study foresees a potential increase in diarrheal diseases in immune-compromised individuals that depend on the stomach barrier as protection against bacterial pathogens.Objectives: The increasing rate of antimicrobial resistance among A. baumannii species is a serious concern in treatment worldwide. Carbapeneme-hydrolyzing class D β-lactamases (CHDLs) encoded by OXA genes and some genetic elements like the insertion sequences (ISs) have an important role in resistance. The purpose of this study was to determine the antimicrobial susceptibility patterns and identify the OXA-carbapenemases genes and their related ISs that have an important role in drug resistance.