Determination of Microbial Contaminants and Aflatoxins
Medicinal plants may be associated with a broad variety of microbial contaminants,
represented by bacteria, fungi, and viruses. Inevitably, this microbiological back-
ground depends on several environmental factors and exerts an important impact
on the overall quality of herbal products and preparations. Risk assessment of the
microbial load of medicinal plants has therefore become an important subject in
the establishment of modern Hazard Analysis and Critical Control Point (HACCP)
schemes.
2.3 Quality Control of Herbal Drugs
Herbal drugs normally carry a number of bacteria and molds, often originating
in the soil. Poor methods of harvesting, cleaning, drying, handling, and storage
may also cause additional contamination, as may be the case with Escherichia coli
or Salmonella spp. While a large range of bacteria and fungi are from naturally oc-
curring microflora, aerobic spore-forming bacteria frequently predominate.
Laboratory procedures investigating microbial contaminations are laid down in
the well-known pharmacopeias, as well as in the WHO guidelines [17, 65]. Limit
values can also be found in the sources mentioned. In general, a complete proce-
dure consists of determining the total aerobic microbial count, the total fungal
count, and the total Enterobacteriaceae count, together with tests for the presence
of Escherichia coli, Staphylococcus aureus, Shigella, and Pseudomonas aeruginosa and
Salmonella spp. The European Pharmacopoeia also specifies that E. coli and Salmo-
nella spp. should be absent from herbal preparations [66]. However it is not always
these two pathogenic bacteria that cause clinical problems. For example, a fatal
case of listeriosis was caused by contamination of alfalfa tablets with the Gram-
positive bacillus Listeria monocytogenes [67].
Materials of vegetable origin tend to show much higher levels of microbial con-
tamination than synthetic products and the requirements for microbial contami-
nation in the European Pharmacopoeia allow higher levels of microbial contami-
nation in herbal remedies than in synthetic pharmaceuticals. The allowed contam-
ination level may also depend on the method of processing of the drug. For exam-
ple, higher contamination levels are permitted if the final herbal preparation in-
volves boiling with water [66].
The presence of fungi should be carefully investigated and/or monitored, since
some common species produce toxins, especially aflotoxins. Aflatoxins in herbal
drugs can be dangerous to health even if they are absorbed in minute amounts [65,
68]. Aflatoxin-producing fungi sometimes build up during storage [61]. Procedures
for the determination of aflatoxin contamination in herbal drugs are published by
the WHO [65]. After a thorough clean-up procedure, TLC is used for confirmation.
In addition to the risk of bacterial and viral contamination, herbal remedies may
also be contaminated with microbial toxins, and as such, bacterial endotoxins and
mycotoxins, at times may also be an issue [61, 69–72]. There is evidence that me-
dicinal plants from some countries may be contaminated with toxigenic fungi (As-
pergillus, Fusarium). Certain plant constituents are susceptible to chemical trans-
formation by contaminating microorganisms.
Withering leads to enhanced enzymic activity, transforming some the constitu-
ents to other metabolites not initially found in the herb. These newly formed con-
stituent(s) along with the molds such as Penicillium nigricans and P. jensi may then
have adverse effects
Medicinal plants may be associated with a broad variety of microbial contaminants,
represented by bacteria, fungi, and viruses. Inevitably, this microbiological back-
ground depends on several environmental factors and exerts an important impact
on the overall quality of herbal products and preparations. Risk assessment of the
microbial load of medicinal plants has therefore become an important subject in
the establishment of modern Hazard Analysis and Critical Control Point (HACCP)
schemes.
2.3 Quality Control of Herbal Drugs
Herbal drugs normally carry a number of bacteria and molds, often originating
in the soil. Poor methods of harvesting, cleaning, drying, handling, and storage
may also cause additional contamination, as may be the case with Escherichia coli
or Salmonella spp. While a large range of bacteria and fungi are from naturally oc-
curring microflora, aerobic spore-forming bacteria frequently predominate.
Laboratory procedures investigating microbial contaminations are laid down in
the well-known pharmacopeias, as well as in the WHO guidelines [17, 65]. Limit
values can also be found in the sources mentioned. In general, a complete proce-
dure consists of determining the total aerobic microbial count, the total fungal
count, and the total Enterobacteriaceae count, together with tests for the presence
of Escherichia coli, Staphylococcus aureus, Shigella, and Pseudomonas aeruginosa and
Salmonella spp. The European Pharmacopoeia also specifies that E. coli and Salmo-
nella spp. should be absent from herbal preparations [66]. However it is not always
these two pathogenic bacteria that cause clinical problems. For example, a fatal
case of listeriosis was caused by contamination of alfalfa tablets with the Gram-
positive bacillus Listeria monocytogenes [67].
Materials of vegetable origin tend to show much higher levels of microbial con-
tamination than synthetic products and the requirements for microbial contami-
nation in the European Pharmacopoeia allow higher levels of microbial contami-
nation in herbal remedies than in synthetic pharmaceuticals. The allowed contam-
ination level may also depend on the method of processing of the drug. For exam-
ple, higher contamination levels are permitted if the final herbal preparation in-
volves boiling with water [66].
The presence of fungi should be carefully investigated and/or monitored, since
some common species produce toxins, especially aflotoxins. Aflatoxins in herbal
drugs can be dangerous to health even if they are absorbed in minute amounts [65,
68]. Aflatoxin-producing fungi sometimes build up during storage [61]. Procedures
for the determination of aflatoxin contamination in herbal drugs are published by
the WHO [65]. After a thorough clean-up procedure, TLC is used for confirmation.
In addition to the risk of bacterial and viral contamination, herbal remedies may
also be contaminated with microbial toxins, and as such, bacterial endotoxins and
mycotoxins, at times may also be an issue [61, 69–72]. There is evidence that me-
dicinal plants from some countries may be contaminated with toxigenic fungi (As-
pergillus, Fusarium). Certain plant constituents are susceptible to chemical trans-
formation by contaminating microorganisms.
Withering leads to enhanced enzymic activity, transforming some the constitu-
ents to other metabolites not initially found in the herb. These newly formed con-
stituent(s) along with the molds such as Penicillium nigricans and P. jensi may then
have adverse effects
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