The RAPD process uses PCR with random oligonucleotide
primers to amplify genomic DNA and analyze sequence polymorphisms.
RAPD is easy to perform, is cost-effective, does not
require prior sequence knowledge and requires only a small
amount of template genomic DNA [15]. The RAPD method has
become widely accepted as a valid taxonomic and phylogenetic tool
for a large range of organisms, including lactobacilli [14,16e18].However, RAPD reproducibility is variable and the process is sensitive
to reaction conditions, including template DNA quality,
ramping speed and the type of instrument used. Therefore, it is
more efficient to clone the RAPD markers and convert them into
sequence characterized amplified regions (SCARs). Long complementary
primers permit a more stringent annealing temperature
than that used with the RAPD analysis and typically results in the
amplification of a single locus [19].The template DNA of the
Lactobacillus strains was amplified with the OPD-3 primer (50-GTCGCCGTCA-30) by RAPD-PCR. This amplification produced a
species-specific band specific for L. pentosus (Fig. 1). This specific
fragment was then isolated and ligated into the pCR2.1-TOPO
vector for nucleotide sequencing. The cloned DNA was sequenced
(Fig. 2), entered into the GenBank database and aligned to homologs
using the BLAST analysis. These sequences showed high
congruence with the ABC transporter, an ATP-binding and
permease protein of L. pentosus, which is known to play a critical
role in multidrug resistance (MDR). From this, we deduced that
these cloned sequences likely exhibit high variation, which would
make them ideal templates for designing specific primers to
discriminate among species within the L. plantarum group. A
primer pair, SpOPD3Lpen-F1/R1, was designed from the cloned
sequences, and these primers successfully generated a single
species-specific band when used in PCR reactions with L. pentosus
DNA (Fig. 3). Annealing temperatures may influence PCR specificity,
and determining the optimal annealing temperature is a time
consuming process [20]. Lower annealing temperatures and additional
PCR amplification cycles may lead to non-specific PCR
products. Thus, either a high annealing temperature or a short
annealing time should be used. In the present study, we found that
the most appropriate annealing temperature for SpOPD3Lpen-F1/
R1was 65 C, with 20 cycles of PCR amplification. Moreover, to
confirm the species specificity of this set of primers, 34 Lactobacillus
strains were tested and demonstrated accuracies reaching 100%
(Table 1).
In conclusion, we have developed a pair of species-specific
primers based on RAPD fingerprinting. These novel speciesspecific
primers can be a rapid, cost-effective, accurate and reliableway
to distinguish the L. pentosus species from the L. plantarum
group.