Identification and characterisation of microbial contaminants of herbal medicines in Kenya
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With the ever increasing use of herbal medicines and the global expansion of the herbal medicines market, safety has become a concern for both health authorities and the public in many countries. This is because many contaminants and residues that may cause harm to the consumers have been reported. Many are natural such as naturally occurring radioxides, toxic metals, bacteria and fungi. Some arise from past and present use of agents or materials that pollute the environment and subsequently medicinal plants, such as emissions from factories or the residues of certain pesticides. Microbial contamination of herbal medicines can be influenced by environmental factors such as temperature, humidity and extent of rainfall during pre-harvesting and post-harvesting periods, handling practices and the storage conditions of crude and processed medicinal-plant materials. For these reasons, there is currently a global danger to the health and well-being of the people. The World Health Organization, British Pharmacopoeia and the United States Pharmacopoeia have recommended tolerable microbial limits in non-sterile pharmaceutical products which include 107 cfu/ml bacteria and 105 cfu/ml fungi. These risks can be reduced by ensuring that there is enough surveillance of herbal medicines so that those with harmful contaminants and residues above recommended limits do not reach the public. This study therefore was aimed at identification and characterization of the microbial contaminants in herbal medicines sold in Kenyan herbal clinics, Chemists, supermarkets and streets. The microbial loads were established and the contaminants isolated and identified.

Thirty (30) herbal products collected by purposive random sampling were analyzed for their microbial contaminants. Microbial load analysis was done and interpreted based on the methods recorded by the USP and BP while isolation of pure cultures was done based on morphological differences where form, elevation, pigmentation and size were the major distinguishing factors for both fungal and bacterial contaminants. The pure isolates were then stocked in glycerol and stored in a freezer at -23 °C from where they were used for subsequent identifications. Gram-staining procedure was used to classify bacteria into Gram-negative and Gram-positive while microscopic and macroscopic observations formed the basis for fungal identification. Specific microbes were then characterized using differential and selective media and later confirmed using API 20 E strip following procedures by the manufacturer. Molecular characterization of the microbes that were not identified using the above techniques was done using the QiaAmp procedures for DNA extraction, agarose gel analysis and cleaning of the PCR products. Sequencing was then done in Segolip (Ilri).

Fourteen (47 %) of the analyzed samples were powders, nine (30 %) liquids, five (16 %) tablets, one balm and capsule each (3 %). Blood purifiers, food supplements and antidiabetics formed the majority of herbal products in the market (50 %) while the rest claimed to manage blood pressure, STD and GIT problems among others. Ten (33 %) of the samples had a colony count of below 30 cfu/ml, these were interpreted as free from contamination. Twenty (67 %) of the samples however had bacterial counts in the range of 6.00 × 105 to 1.56 × 1010 cfu/ ml and fungal count in the range of 5.30 × 104 to 1.56 × 109 cfu/ ml.  Of the 19 different types of bacteria identified, 13 (68 %) were Gram-negative rods while 6 (32 %) were Gram-positive rods and cocci.

 The tests for specified microorganisms using differential and selective media confirmed the presence of Staphylococcus aureus, Klebsiella pneumonia, Escherichia coli, Shigella and Candida spp. in abundant growths. Microscopic and macroscopic examinations confirmed the presence of fungi i.e. Rhizopus, Candida, Fusarium, Aspergillus, Torula, Penicillium and Alternaria also in abundance. Biochemical tests by API 20 E confirmed the presence of Enterobacter agglomerurans, Serratia marsensens, Klebsiella oxytocca, Chryseomonus luteola, Flavobacterium spp and Enterobacter cloacae. Further genotypic analyzes of the isolates that were not identified and characterized by morphological and biochemical methods revealed the presence of Kocuria rosea, Bacillus pumilus, Cronobacter sakazakii, Bacillus safensis, Bacillus subtilis and Bacillus flexus some of the microbes isolated and characterized are pathogenic especially to immune-compromised individuals.

 From this study, it is evident that herbal medicines sold in Kenya without control or regulations are contaminated with microbes which are potential pathogens hence pose a threat to patients. It is therefore recommended that a policy be established to enable regulation of these products. Herbalists should be trained to apply Good Manufacturing Practices, good harvesting practices and the safe handling and storage of herbal medicinal products. Further studies are recommended for herbal products to establish other contaminants and ways in which the contaminants can be reduced to recommended levels.