Abstract
We assessed the anti-Listerial activities of crude n-hexane and aqueous extracts of Garcinia kola seeds against a panel of 42 Listeria isolates previously isolated from wastewater effluents in the Eastern Cape Province of South Africa and belonging to Listeria monocytogenes, Listeria grayi and Listeria ivanovii species. The n-hexane fraction was active against 45% of the test bacteria with zones of inhibition ranging between 8–17 mm, while the aqueous fraction was active against 29% with zones of inhibition ranging between 8–11 mm. The minimum inhibitory concentrations (MIC) were within the ranges of 0.079–0.625 mg/mL for the n-hexane extract and 10 to >10 mg/mL for the aqueous extract. The rate of kill experiment carried out for the n-hexane extract only, revealed complete elimination of the initial bacterial population for L. grayi (LAL 15) at 3× and 4× MIC after 90 and 60 min; L. monocytogenes (LAL 8) at 3× and 4× MIC after 60 and 15 min; L. ivanovii (LEL 18) at 3× and 4× MIC after 120 and 15 min; L. ivanovii (LEL 30) at 2, 3 and 4× MIC values after 105, 90 and 15 min exposure time respectively. The rate of kill activities were time- and concentration-dependant and the extract proved to be bactericidal as it achieved a more than 3log10 decrease in viable cell counts after 2 h exposure time for all of the four test organisms at 3× and 4× MIC values. The results therefore show the potential presence of anti-Listerial compounds in Garcinia kola seeds that can be exploited in effective anti-Listerial chemotherapy.
Highlights
The genus Listeria consists of Gram-positive, non-sporeforming rod shaped bacteria which are facultatively anaerobic, catalase positive, oxidase negative and ubiquitous in nature [1]
There are six characterized Listeria species, namely Listeria monocytogenes, Listeria ivanovii, Listeria seeligeri, Listeria innocua, Listeria grayi and Listeria welshimeri [1,2]. Among these six species only two species L. ivanovii and L. monocytogenes are regarded as pathogenic; L. monocytogenes is pathogenic to humans and animals whilst L. ivanovii is pathogenic to animals mainly sheep and cattle causing the bacteremia listeriosis [2,3]
Listeriosis is a severe food-borne disease characterized by bacteremia, meningitis and encephalitis individuals usually at high risk are those with impaired cell-mediated immunity, including neonates, pregnant woman, elderly persons, and the immune-compromised patients [10]
Summary
The genus Listeria consists of Gram-positive, non-sporeforming rod shaped bacteria which are facultatively anaerobic, catalase positive, oxidase negative and ubiquitous in nature [1]. There are six characterized Listeria species, namely Listeria monocytogenes, Listeria ivanovii, Listeria seeligeri, Listeria innocua, Listeria grayi and Listeria welshimeri [1,2]. Among these six species only two species L. ivanovii and L. monocytogenes are regarded as pathogenic; L. monocytogenes is pathogenic to humans and animals whilst L. ivanovii is pathogenic to animals mainly sheep and cattle causing the bacteremia listeriosis [2,3]. L. monocytogenes is an invasive, intracellular pathogen that can transverse the placenta in pregnant women and infect the fetus, some intrauterine infection may be the result of ascending spread of the bacteria from vaginal colonization resulting in abortion, birth of a stillborn fetus or a baby with generalized infection (granulomatosis infantiseptica), and sepsis or meningitis in the neonate such that it is of particular high risk for pregnant women [11,12,13]
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