RESEARCH

Molecular genetic studies on the anaerobic bacteria Bacteroides fragilis and Bifidobacterium spp.

B. fragilis
This Gram-negative, clinically important intestinal bacterium accounts for approximately 80% of post-operative abdominal bacteraemias. Under normal circumstances, however, the organism is commensal in the gut and is thought to play a significant role in nitrogen assimilation.

The research being carried out, therefore, focuses on the molecular features of B. fragilis which enable it to function under these different growth conditions. The pathogenic aspects of the organism are being studied with a view to understanding drug resistance in organisms isolated from infected patients. These studies include molecular characterization of the mechanisms of drug resistance to metronidazole (a DNA damaging antibiotic). We are investigating the role of B. fragilis in the assimilation of nitrogen in the gut. We are doing this by cloning and characterizing the structure-function relationships of proteins involved in this process, including the glutamine synthetase and glutamate dehydrogenase enzymes.

Bifidobacterium spp (in collaboration with A/Prof Sharon Reid)
Bifidobacterium spp are nonpathogenic microorganisms that, when ingested, exert a positive influence on the health or physiology of the host. These bacteria are natural inhabitants of the intestines of warm-blooded animals and have been used successfully to prevent post-antibiotic complications as well as intestinal disease, and are reported to play a possible role in preventing cancer, hypertension and in lowering blood cholesterol levels, all of which are prevalent medical problems in South Africa. Recent work has also shown that these probiotic organisms of the gut may also play a role in preventing kidney stone formation by preventing the absorption of oxalate into the body.

Our research focuses on molecular aspects of the antibiotic resistance of these bacteria, the carbohydrates that are most suited to their survival in the gut, and oxalate degradation by them in the gut of patients suffering from kidney stone disease.

PUBLICATIONS

Dachs, G.U., Abratt, V.R., and Woods, D.R. (1995) Mode of action of metronidazole and a Bacteroides fragilis metA resistance gene in Escherichia coli. Journal of Antimicrobial Chemotherapy, 35: 483 - 496.

Abratt VR, Mbewe M, Woods DR (1998) Cloning of an EF-P homologue from Bacteroides fragilis that increases B. fragilis glutamine synthetase activity in Escherichia coli. Molecular and General Genetics 258:363-372

Abrahams GL, Abratt VR (1998) The NADH-dependent glutamate dehydrogenase enzyme of Bacteroides fragilis Bf1 is induced by peptides in the growth medium. Microbiology 144:1659-1667

Koch CL, Derby P and Abratt, VR (1998) Antibiotic susceptibility of anaerobic bacteria isolated in Cape Town, South Africa. Journal of Antimicrobial Chemotherapy 42: 245-248.

Mulder, M. , Abratt, V.R., Zappe, H., and Steyn, LM. (1999) The Mycobacterium tuberculosis katG gene protects mutant E. coli against DNA damaging Agents. Microbiology 145: 2011-2021.

GL Abrahams, KD Iles, VR Abratt (2001) The Bacteroides fragilis NADH-specific glutamate dehydrogenase enzyme is cell-surface associated and regulated by peptides at the protein level. Anaerobe 7, 135 - 142.

Trindade, M.I., Abratt, V.R., and Reid, S.J. (2003) Induction of sucrose-utilisation genes from Bifidobacterium lactis by sucrose and raffinose. Appl. Environ. Microbiol, 69, 24-32.

Published Book

Abratt V, Collett, H, Miller-Butterworth, C, and Suiro-Stheeman V. (2002) “Practical Biology: a classroom resource for teachers” Francolin Publishers, Cape Town; ISBN 1-86859-077-1.

LAB MEMBERS

Bacteroides fragilis

1. Wellcome Trust research group
Metronidazole resistance in Bacteroides fragilis:
Research students: Lynthia Paul (PhD), Ana Casanueva (PhD), Ekta Patel (MSc)

2. Structure- function analysis of the B. fragilis glutamine synthetase protein.
Research student: Jason van Rooyen (MSc)

Bifidobacterium spp

1. Antibiotic resistance and multidrug efflux systems in Bifidobacteria.
Research student: Claire Price (MSc)

2. Carbohydrate metabolism in Bifidobacterium longum
Research student: Brian Kullin (BSc Hons).

3. Probiotic organisms and kidney stone disease
Research students: Sonja Lewendowski (Post doc), Thokozile Lewanika (MSc), Sarah Griffin (BSc Hons).