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11.08.2012, 19:55 #1Üyelik tarihi: 09.08.2012 Son online zamanı: 28.04.2013
protozoa ders notu(İngilizce): Occurrence and diversity of free-living protozoa on butterhead lettuce [/TD][/TR]
: Pdf [/TD][/TR]
: Michael Jee [/TD][/TR]
To date, knowledge of quality, food safety and microbial
contamination of vegetables mainly concerns spoiling and pathogenic
bacteria, yeasts and molds, parasitic protozoa, nematodes and viruses
(Barth et al., 2009; Nguyen-the and Carlin, 2000). However, there is a
paucity of information about free-living protozoa (FLP) on vegetables.
Free-living protozoa (i.e., amoebae, flagellates, and ciliates) are singlecelled
eukaryotic microorganisms which are ubiquitous in aquatic and
terrestrial ecosystems, and are one of the main predators of bacteria.
Most of the studies about FLP on vegetables were focused on free-living
amoebae. Representatives of the genera Acanthamoeba, Hartmannella,
Naegleria and Vannellawere recovered frommushrooms and vegetables
such as carrots, cauliflower, lettuce, radishes, onions, spinach and
tomatoes (Ciurea-Van Saanen, 1981; Gourabathini et al., 2008;
Napolitano, 1982; Napolitano and Colletti-Eggolt, 1984; Rude et al.,
1984; Sharma et al., 2004). There are limited data on ciliate andflagellate
diversity on vegetables. Ciliates (Colpoda sp., holotrichs and hypotrichs)
were recovered from mushroom surfaces (Napolitano, 1982) but no
identification to species levelwas performed. Gourabathini et al. (2008)
reported high flagellate counts in drained water from spinach and
romaine lettuce and asmaller number of amoebae and ciliates in drained
water fromspinach. Two isolated ciliateswere identified asGlaucoma sp.
and Colpoda steinii. In a previous study, a high diversity of FLPwas found
on surfaces of vegetable trays in domestic refrigerators and it was
suggested that the protozoan diversity recorded may be related to FLP
present on vegetables (Vaerewijck et al., 2010).
Most FLP are not associated with foodborne illness. However, in
vitro studies showed that some FLP such as Acanthamoeba spp. and
Tetrahymena spp. are able to act as hosts for foodborne pathogens and
protect internalized bacteria against adverse conditions such as
desiccation and exposure to disinfectants (Snelling et al., 2006).
Gourabathini et al. (2008) documented that the ciliates Glaucoma sp.
and Tetrahymena pyriformis isolated from vegetables internalized
Escherichia coli O157:H7 and Salmonella enterica serovar Thompson,
and subsequently expelled small vesicles containing these bacteria. S.
enterica serovar Thompson entrapped in Tetrahymena sp. vesicles
were protected against low concentrations of calcium hypochlorite
(Brandl et al., 2005). In order to evaluate the role and potential risk of
FLP as reservoir or vector of foodborne pathogens, knowledge on the
occurrence and diversity of FLP in food-related habitats (Baré et al.,
2009; Vaerewijck et al., 2008; Vaerewijck et al., 2010) and raw food
products, such as fresh vegetables, is necessary.
The main objective of this study was to assess the occurrence and
provide an inventory of FLP diversity on leaves of commercially
available lettuce. Four different sampling methods were applied to
recover FLP from the leaves. The diversity was determined by light
microscopy (morphospecies) and sequencing (phylotypes) of excised
DGGE-separated 18S rRNA gene fragments. In addition, the effectiveness
of washing and spin-drying for removing FLP from lettuce leaves
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