Diversity and antibiotic resistance patterns of Lactobacillus species in traditional curd in Sri Lanka
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Date
2015
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Uva Wellassa University of Sri Lanka
Abstract
In their fermentative pathways, main metabolic end product is Lactic acid. The fermentation
process of Lactobacillus increases the shelf-life of the fermented dairy product, as well as
adds the taste and improves the digestibility of milk. There are adequate evidences to prove
that traditionally fermented milk products have been produced for a long time in different
countries. Curd (Sri Lanka and India), Kefer (Russia), Yakult, Yogurt, Kumisss (Russia),
Tarhana (Turkey) are some examples.
There are Lactobacillus species that have achieved GRAS (Generally Recognized as Safe) or
QPS (Qualified Presumption of Safety) status. However, during the past few decades there
has been an emerging concern on spreading the antibiotic resistance in the environment. Due
to the increasing use of antibiotics and disposing them in to the environment in a considerably
inappropriate manner, concerns have arisen on the possibility and probability of spreading the
antibiotic resistance genes to Lactobacillus in fermented food (Farthing, 2004). The main
threat associated with these bacteria is that they can transfer resistance genes to pathogenic
bacteria as well as to the commensal flora in the intestinal tract. A number of initiatives have
been recently launched across the globe to address the biosafety concerns of starter cultures
and probiotic microorganisms. The European Food safety Authority (2007) considers
transferable antibiotic resistances as a safety concern. Many studies have detected the acquired
antibiotic resistance in fermented food products. Nevertheless, the tetracycline resistance was
shown to be able to transferred in vitro to Enterococcous faecalis from Lactobacillus species
isolated from fermented sausages (Gevers et al., 2003).
The objective of this study was to find out the diversity of Lactobacillus species in curd
prepared by small and medium scale producers in Sri Lanka and to detect their antibiotic
resistances.
Methodology
Total number of 32 curd samples representing different areas of the country were collected
from small and medium scale produces (SMS) who do not use starter cultures directly for the
process. Samples were enriched in modified Man Rogosa Sharpe broth at 37 C at room
temperature for 24 h, under anaerobic conditions and plated on modified MRS agar medium
Results
For morphological characteristics, shape and colour of the colonies, Gram’s reaction, shape
and arrangement of cells, motility and endospore formation were observed. For the
biochemical characteristics, reaction in the Gibson’s medium, oxidase test, catalase test,
Arginine utilization, sugar fermentation tests (Arabinose, Cellobioose , Esculin, Galactose,
Maltose, Mannose, Melibiose, Raffinose, Ribose, Sucrose, Trehalose, Xylose, Salicin,
Sorbitol, Mannitol, Rhamnose, Lactose ) were detected.
A total Number of 51 Lactobacillus isolates were obtained in this study and all the 51 isolates
were comprised with 16 different bacterial species. Lactobacillus fermentum (35%)
Lactobacillus acidophilus (11.11%), Lactobacillus plantarum (5.55%) and Lactobacillus
amylolyticus (8.33%) represented majority. When compare the antibiotic resistance patterns
(Table 01), Polymixine B was reported to have 94.44% overall resistance. All the 51 isolates
were reported to score 100% of overall resistance for both Vancomycin and Nalidixic Acid.
Minimum percentages of antibiotic resistances were observed for Tetracycline (22.22%) and
Erythromycin (27.78%).
Discussion
Considering the prevalence of different Lactobacillus species, the results obtained in this
study correlate to a significant extent to some research carried out on traditional fermented
dairy products (Yu, 2011). Conversely, several research studies have been disclosed that L.
delbrueckii subsp. bulgaricus is the most abundant Lactobacilli in traditionally fermented
milk products (Tendakyi et al., 2001) and this species was not identified in this study.
Though the present study reveals less abundance of Tetracycline and Erythromycin resistance
compared to that of most other countries it can be considered as an important finding.
Correlate with the Tet- resistant species identified in this study, R-plasmids encoding Tet-
resistance have been reported in L. fermentum L. planatarum and L. amylolyticus. Because
the Tet-resistance has been transferred from Lactobacillus to E. faecalis in vitro it shows the
possibility of in vivo process. Further studies can be aimed at determining the transferability
of the Tet-resistance from Lactobacillus to commensal flora in vitro.
Description
Keywords
Animal Sciences, Veterinary Sciences, Milk, Food Science, Food Technology