Resistance Of Lactic Acid Bacteria Research Articles

Antibiotic resistance of lactis acid bacteria and the risk of its transmission with fermented dairy products

Bacterial resistance to antimicrobials is a global health problem that affects not only on humane and veterinary medicine, but also on food products. The food chain can be by transmission of antibiotic resistance from bacterial populations to animals and humans. Literary data on the current state of the problem of antibiotic resistance of lactic acid bacteria (LAB) in Ukraine and in the world are given in the review. Possible ways of transferring resistance to antibiotics through fermented dairy products are shown. The main aspects of the danger of transmission of antibiotic resistance genes through the LAB and fermented dairy products are revealed. The main modern approaches to the definition of antibiotic resistance of microorganisms with the use of classical and modern research methods are described. The article provides the main sources of information on the safety of use of LAB as starter cultures and probiotics for the production of fermented dairy products. The hypothesis of the resistance gene's reservoir suggests that LAB can be a reservoir of sustainability genes, and the subsequent transfer of such genes to pathogenic and opportunistic microorganisms. The presence of antibiotic resistance genes transposed horizontally is inadmissible for lactobacilli, which are used as commercial bacterial agents for the production of fermented dairy products. According to the literature data, the absence of acquired antimicrobial resistance has become an important criterion for assessing the safety of lactobacilli, which are used as starting cultures for the production of fermented dairy products or probiotics. It has been established that it is obligatory to study the antibiotic resistance gene in addition to clinical and laboratory methods of studying the antibiotic resistance of LAB. To minimize the formation of antibiotic-resistant bacteria in food products of plant and animal origin it is possible by careful monitoring of residues of antibiotics in raw materials and finished products. This will prevent the entry of antibiotic resistant strains into the natural cycle.

Determination of antibiotic resistance of lactic acid bacteria isolated from traditional Turkish fermented dairy products.

In this study, the antibiotic resistance (AR) of lactic acid bacteria (LAB) isolated from traditional Turkish fermented dairy products was investigated. Yogurt, white cheese, tulum cheese, cokelek, camız cream and kefir as dairy products were collected from various supermarkets. Lactic acid bacteria such as Lactobacillus spp., Streptococcus spp., Bifidobacterium spp., and Enterecoccus spp. were isolated from these dairy products. Lactobacillus spp. were resistant to vancomycin (58%), erythromycin (10.8%), tetracycline (4.3%), gentamicin (28%), and ciprofloxacin (26%). Streptococcus spp. were resistant to vancomycin (40%), erythromycin (10%), chloramphenicol (10%), gentamicin (20%), and ciprofloxacin (30%). Bifidobacterium spp. were resistant to vancomycin (60%), E 15 (6.6%), gentamicin (20%), and ciprofloxacin (33%). Enterococcus spp. were resistant to vancomycin (100%), erythromycin (100%), rifampin (100%), and ciprofloxacin (100%). As a result, LAB islated from dairy products in this study showed mostly resistance to vancomycin.

Adaptation to Aerobic Environment of Lactobacillus johnsonii/gasseri Strains.

Oxygen is considered one of the main factors affecting probiotic bacteria survival due to the induction of oxidative damages caused by the action of reactive oxygen species (ROS). It has been shown that oxidative stress resistance in lactic acid bacteria is strongly dependent on the type of cell metabolism. Shift from fermentative to respiratory metabolism (through the addition of heme and menaquinone and in presence of oxygen) was associated to increase in biomass, long-term survival, and production of antioxidant enzymes. The aim of this work was to investigate the effect of aerobic (presence of oxygen) and respiratory (presence of oxygen, heme, and menaquinone) cultivation on the growth kinetic, catalase production, oxygen uptake, and oxidative stress response of Lactobacillus johnsonii/gasseri strains previously isolated from infant feces. Seven strains showed to consume oxygen under aerobic and respiratory conditions. The strain AL5 showed a catalase activity in both growth conditions, while AL3 showed this activity only in respiratory condition. Respiratory condition improved their tolerance to oxidative compounds (hydrogen peroxide and ROS generators) and further they showed promising probiotic features. The exploration of respiratory competent phenotypes with probiotic features may be extremely useful for the development of competitive starter or probiotic cultures.

Probiotic Potential and Antibiotic Resistance of Lactic Acid Bacteria Isolated from Curd in Sri Lanka

Lactic acid bacteria (LAB) are organisms beneficial to the human beings as probiotics which the organism can remain viable under stress conditions in the gastrointestinal tract.The aim of this study was to characterize and evaluate probiotic properties, and antibiotic resistance of thirteen isolates of lactic acid bacteria obtained from curd. In order to characterize the lactic acid bacteria isolates from curd; Gram’s staining, endospore staining, motility, catalase reaction, indole production, methyl red test, Voges-Proskauer test, citrate utilization, oxidase activity, urease activity, H2S production, arginine hydrolysis, growth at different temperatures, gas production from glucose and fermentation pattern of different carbohydrates were performed. In order to screen the probiotic potential of the isolates; tolerance to pH, bile, and phenol, survival in the presence of simulated gastric and pancreatic juices were examined. Antibiotic resistance of selected isolates was evaluated using 12 antibiotics. Results of biochemical tests and physiochemical tests revealed that all thirteen isolates (ITI_CD001, ITI_CD 002, ITI_CD 003, ITI_CD 004, ITI_CD 005,ITI_CD006, ITI_CD 009, ITI_CD 010, ITI_CD 011, ITI_CD 012 ITI_CD013, ITI_CD 014, andITI_CD 015) are belonged to the genus Lactobacillus. Species were identified as Lactobacillus plantarum, Lactobacillus brevis and Lactobacillus delbrukeii lactis. Most of the isolates were able to tolerate and grow well under low pH conditions (1.5 - 3.0), high pH (9.0), extremes of bile up to 0.5% and phenol up to 0.6%.The isolates were able to growin the presence of simulated gastric and pancreatic juices too. Results for the antibiotic resistance varied among isolates. Isolates ITI_CD004, ITI_CD 009, ITI_CD 010, ITI_CD 011, ITI_CD 012 and ITI_CD 015 were identified as higher probiotic isolates. The study revealed that the tested LAB isolates possess desirable probiotic properties. Hence, these isolates can be used to produce foods high in probiotics.

Mechanisms and improvement of acid resistance in lactic acid bacteria.

Lactic acid bacteria (LAB) can take advantage of fermentable carbohydrates to produce lactic acid. They are proverbially applied in industry, agricultural production, animal husbandry, food enterprise, pharmaceutical engineering and some other important fields, which are closely related to human life. For performing the probiotic functions, LAB have to face the low pH environment of the gastrointestinal tract. Therefore, acid resistance of LAB is of great importance not only for their own growth, but also for fermentation and preparation of probiotic products. Recent research studies on acid resistance mechanisms of LAB are mainly focused on neutralization process, biofilm and cell density, proton pump, protection of macromolecules, pre-adaptation and cross-protection, and effect of solutes. In this context, biotechnological strategies such as synthetic biology, genome shuffling, high pressure homogenization and adaptive laboratory evolution were also used to improve the acid resistance of LAB to respond to constantly changing low pH environment.

Isolation and Analysis of Salt Response of Lactobacillusplantarum FS5-5 from Dajiang.

From 15 samples of dajiang collected in northeast of China, three salt resistant lactic acid bacteria were isolated and identified as Lactobacillusplantarum through physiological studies and 16S rDNA sequence alignment. L. plantarum FS5-5 showed better growth in an environment with 12% (w/v) NaCl than the other two strains. The expression of proteins extracted from L.plantarum FS5-5 cultured in de Man, Rogosa, and Sharp (MRS) containing 0, 3, 6 and 9% (w/v) NaCl was analyzed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS). The results showed that 42 kinds of proteins were identified, which could be divided into three groups: 27 kinds of proteins related to protein synthesis and degradation, six kinds of proteins related to carbohydrate metabolism and energy metabolism, nine proteins related to nucleic acid metabolism. Overexpression of these proteins imply that a series of changes have occurred in the process of protein synthesis and degradation, carbohydrate metabolism, energy metabolism and nucleic acid metabolism after L.plantarum FS5-5 exposed to salt stress. All these proteins may have effects on the salt-tolerant characteristics of the L.plantarum FS5-5.

Assessment of Acid, Bile tolerance and Antibiotic resistance of Lactic acid Bacteria isolated from Fermented Foods

With the aim of selecting potential probiotic cultures, 19 different bacteria were isolated from different fermented foods like curd, semolina, paneer whey and sour milk. Among the isolates, the 7 isolates identified as Streptococcus infantarius BBE2 (from curd), Enterococcus faecium BBE3 (from curd), Lactobacillus fermentum BBE4 (from curd), Lactobacillus fermentum BBE5 (from sour milk), Lactobacillus fermentum BBE6 (from curd), Lactobacillus plantarum BBE7 (from paneer whey) and Bacillus cereus (from fermented semolina) were tested for their tolerance against acidic/gastric conditions, bile and assessed for their bile salt hyrolase activity and antibiotic resistance pattern. Among all the strains, the isolates B. cereus and L. fermentum BBE5 showed maximum survival at pH2 and bile tolerance. Isolate L. fermentum BBE5 showed maximum tolerance to gastric juice and bile salt hydrolase activity. None of the isolates showed resistance towards all the tested antibiotics. Based on their survival in pH 2 and in 0.3% bile, the tested isolates may be able to resist passage through the gastro-intestinal tract. Further, the isolate L. fermentum BBE5 may be a potential probiotic.

Susceptibility and resistance of lactic acid bacteria and yeasts against preservatives with potential application in table olives

In the present study, a dose-response model was used to investigate the susceptibility (NIC) and resistance (MIC) of the lactic acid bacteria and yeast populations with respect to five chemical preservatives (fumaric and pyruvic acids, cinnamaldehyde, sodium metabisulphite and natamycin) with potential application in table olives. Results were compared with respect to potassium sorbate, a well-known preservative habitually used in olive packaging. Sodium metabisulphite was the most efficient preservative to control lactic acid bacteria growth (MIC, 50 ppm), followed by cinnamaldehyde (1060 ppm) while pyruvic acid required higher concentrations (3211 ppm). Natamycin (25 ppm) was highly efficient against yeasts, followed by cinnamaldehyde (125 ppm), potassium sorbate (553 ppm), sodium metabisulphite (772 ppm) and pyruvic acid (3038 ppm). Fumaric acid, in the range assayed (0–2000 ppm), did not show any inhibitory effect against these two microbial groups. This survey presents for the first time a comparative study of the efficiency of potential preservatives to control the growth of table olive related microorganisms. Further studies should be performed to validate their effects and interactions in the food matrix.

Antibiotic resistance of lactic acid bacteria isolated from dry-fermented sausages

Dry-fermented sausages are meat products highly valued by many consumers. Manufacturing process involves fermentation driven by natural microbiota or intentionally added starter cultures and further drying. The most relevant fermentative microbiota is lactic acid bacteria (LAB) such as Lactobacillus, Pediococcus and Enterococcus, producing mainly lactate and contributing to product preservation. The great diversity of LAB in dry-fermented sausages is linked to manufacturing practices. Indigenous starters development is considered to be a very promising field, because it allows for high sanitary and sensorial quality of sausage production.LAB have a long history of safe use in fermented food, however, since they are present in human gastrointestinal tract, and are also intentionally added to the diet, concerns have been raised about the antimicrobial resistance in these beneficial bacteria. In fact, the food chain has been recognized as one of the key routes of antimicrobial resistance transmission from animal to human bacterial populations. The World Health Organization 2014 report on global surveillance of antimicrobial resistance reveals that this issue is no longer a future prediction, since evidences establish a link between the antimicrobial drugs use in food-producing animals and the emergence of resistance among common pathogens. This poses a risk to the treatment of nosocomial and community-acquired infections. This review describes the possible sources and transmission routes of antibiotic resistant LAB of dry-fermented sausages, presenting LAB antibiotic resistance profile and related genetic determinants. Whenever LAB are used as starters in dry-fermented sausages processing, safety concerns regarding antimicrobial resistance should be addressed since antibiotic resistant genes could be mobilized and transferred to other bacteria.

Cyclopropanation of unsaturated fatty acids and membrane rigidification improve the freeze-drying resistance of Lactococcus lactis subsp. lactis TOMSC161.

This work aimed at characterizing the biochemical and biophysical properties of the membrane of Lactococcus lactis TOMSC161 cells during fermentation at different temperatures, in relation to their freeze-drying and storage resistance. Cells were cultivated at two different temperatures (22 and 30°C) and were harvested at different growth phases (from the middle exponential phase to the late stationary phase). Bacterial membranes were characterized by determining the fatty acid composition, the lipid phase transition, and the membrane fluidity. Cultivability and acidification activity losses of L. lactis were quantified after freezing, drying, and 3months of storage. The direct measurement of membrane fluidity by fluorescence anisotropy was linked to lipid composition, and it was established that the cyclopropanation of unsaturated fatty acids with concomitant membrane rigidification during growth led to an increase in the freeze-drying and storage resistance of L. lactis. As expected, cultivating cells at a lower fermentation temperature than the optimum growth temperature induced a homeoviscous adaptation that was demonstrated by a lowered lipid phase transition temperature but that was not related to any improvement in freeze-drying resistance. L. lactis TOMSC161 was therefore able to develop a combined biochemical and biophysical response at the membrane level during fermentation. The ratio of cyclic fatty acids to unsaturated fatty acids (CFA/UFA) appeared to be the most relevant parameter associated with membrane rigidification and cell resistance to freeze-drying and storage. This study increased our knowledge about the physiological mechanisms that explain the resistance of lactic acid bacteria (LAB) to freeze-drying and storage stresses and demonstrated the relevance of complementary methods of membrane characterization.

Prevalence of antibiotic resistance in lactic acid bacteria isolated from the faeces of broiler chicken in Malaysia.

BackgroundProbiotics are commonly used as feed additive to substitute antibiotic as growth promoter in animal farming. Probiotic consists of lactic acid bacteria (LAB), which enhance the growth and health of the animal. Probiotic also have higher possibility to become pathogenic bacteria that may carry antibiotic resistant gene that can be transmitted to other LAB species. The aim of this study was to identify the LAB species in the faeces of broiler chicken and to determine the prevalence of antibiotic resistant in LAB of broiler chicken.MethodsSixty faeces samples were collected from wet markets located in Klang Valley of Malaysia for the isolation of LAB using de-Mann Rogosa Sharpe medium. Thirteen species of LAB were obtained in this study and the identification of LAB was performed by using API test kit on the basis of carbohydrate fermentation profile. Antibiotic susceptibility assay was then carried out to determine the prevalence of LAB antibiotic resistance.ResultsLactococcus lactis subsp lactis was found in nine out of sixty faecal samples. Lactobacillus paracasei was the second common LAB species isolated from chicken faecal. No significant difference (P > 0.05) was found between the occurrence of Lactobacillus brevis, Lactobacillus curvatus, Lactobacillus plantarum, Leuconostoc lactis mesenteroides subsp mesenteroides/dectranium and Pediococcus pentosaceus isolated from 5 different locations. Most of the isolated LAB was resistant to antibiotic and high variability of the antibiotic resistance was observed among the LAB against 15 types of antibiotics. Penicillin, amoxicillin, chloramphenicol, and ampicillin had significant higher (P< 0.05) inhibitory zone than nalidixic acid, gentamycin, sulphamethoxazole, kanamycin, and streptomycin.ConclusionsMany species of LAB were isolated from the faecal samples of broiler chicken that resistance to the common antibiotics used in the farm. The development of resistant against antibiotics in LAB can be attributed to the long term exposure of antibiotic as growth promoter and therapeutic agents. Thus, it is essential to advise farmer the safety measure of antibiotic application in animal farming. Additionally, the supplementation of probiotic in animal feeding also needs more attention and close monitoring.

Incidence of Antibiotic Resistance of Lactic Acid Bacteria (LAB) Isolated from Various Sudanese Fermented Foods

Incidence of Antibiotic Resistance of Lactic Acid Bacteria (LAB) Isolated from Various Sudanese Fermented Foods Antimicrobial resistance is one of the most increasing problems worldwide that has been created due to the extensive use of antibiotics in both human and animal treatment. This could lead to the transmission of antibiotic resistant strains to the human body through food. Therefore, the aim of the present study was to investigate the antibiotic resistance of LAB of fermented foods (sorghum dough, mish, yoghurt, cucumber pickles, cheese and meat sausage) consumed regularly in Sudan. In this regard, 25 strains of LAB were isolated from six types of Sudanese fermented foods. The isolates were tested for their susceptibility to 8 antibiotics including amoxicillin, ceftriaxone, ciprofloxacin, chloramphenicol, erythromycin, tetracycline, tobramycin, and vancomycin by standard disk diffusion method. All isolates showed multiple resistances to the antibiotics used, specifically, tobramycin, ceftriaxone and ciprofloxacin. However, the results demonstrated that none of the isolates were totally susceptible to all antibiotics tested.

Antibiotic resistance in lactic acid bacteria isolated from some pharmaceutical and dairy products.

A total of 244 lactic acid bacteria (LAB) strains were isolated from 180 dairy and pharmaceutical products that were collected from different areas in Minia governorate, Egypt. LAB were identified phenotypically on basis of morphological, physiological and biochemical characteristics. Lactobacillus isolates were further confirmed using PCR-based assay. By combination of phenotypic with molecular identification Lactobacillus spp. were found to be the dominant genus (138, 76.7%) followed by Streptococcus spp. (65, 36.1%) and Lactococcus spp. (27, 15%). Some contaminant organisms such as (Staphylococcus spp., Escherichia coli, Salmonella spp., mould and yeast) were isolated from the collected dairy samples but pharmaceutical products were free of such contaminants. Susceptibility of LAB isolates to antibiotics representing all major classes was tested by agar dilution method. Generally, LAB were highly susceptible to Beta-lactams except penicillin. Lactobacilli were resistant to vancomycin, however lactococci and streptococci proved to be very susceptible. Most strains were susceptible to tetracycline and showed a wide range of streptomycin MICs. The MICs of erythromycin and clindamycin for most of the LAB were within the normal range of susceptibility. Sixteen Lactobacillus, 8 Lactococcus and 8 Streptococcus isolates including all tetracycline and/or erythromycin resistant strains were tested for the presence of tetracycline and/or erythromycin resistant genes [tet(M) and/or erm(B)]. PCR assays shows that some resistant strains harbor tet(M) and/or erm(B) resistance genes.

Progress in engineering acid stress resistance of lactic acid bacteria

Lactic acid bacteria (LAB) are widely used for the production of a variety of fermented foods, and are considered as probiotic due to their health-promoting effect. However, LAB encounter various environmental stresses both in industrial fermentation and application, among which acid stress is one of the most important survival challenges. Improving the acid stress resistance may contribute to the application and function of probiotic action to the host. Recently, the advent of genomics, functional genomics and high-throughput technologies have allowed for the understanding of acid tolerance mechanisms at a systems level, and many method to improve acid tolerance have been developed. This review describes the current progress in engineering acid stress resistance of LAB. Special emphasis is placed on engineering cellular microenvironment (engineering amino acid metabolism, introduction of exogenous biosynthetic capacity, and overproduction of stress response proteins) and maintaining cell membrane functionality. Moreover, strategies to improve acid tolerance and the related physiological mechanisms are also discussed.

Significant effect of Ca2+on improving the heat resistance of lactic acid bacteria

The heat resistance of lactic acid bacteria (LAB) has been extensively investigated due to its highly practical significance. Reconstituted skim milk (RSM) has been found to be one of the most effective protectant wall materials for microencapsulating microorganisms during convective drying, such as spray drying. In addition to proteins and carbohydrate, RSM is rich in calcium. It is not clear which component is critical in the RSM protection mechanism. This study investigated the independent effect of calcium. Ca(2+) was added to lactose solution to examine its influence on the heat resistance of Lactobacillus rhamnosus ZY, Lactobacillus casei Zhang, Lactobacillus plantarum P8 and Streptococcus thermophilus ND03. The results showed that certain Ca(2+) concentrations enhanced the heat resistance of the LAB strains to different extents, that is produced higher survival and shorter regrowth lag times of the bacterial cells. In some cases, the improvements were dramatic. More scientifically insightful and more intensive instrumental study of the Ca(2+) behavior around and in the cells should be carried out in the near future. In the meantime, this work may lead to the development of more cost-effective wall materials with Ca(2+) added as a prime factor.

The Association of Biofilm Formation with Antibiotic Resistance in Lactic Acid Bacteria from Fermented Foods

AbstractFifty‐three lactic acid bacteria (LAB) strains from five species of bacteria were isolated and identified from yogurt and Chinese pickled vegetables. Susceptibility of all the isolates to five antibiotics (ampicillin, erythromycin, tetracycline, vancomycin, streptomycin) was tested with disc diffusion methods. All LAB were resistant to streptomycin. Thirty‐seven strains were resistant to vancomycin, seven strains were resistant to tetracycline and erythromycin, and six strains were resistant to ampicillin. The corresponding genetic determinants were characterized by polymerase chain reaction. No antibiotic resistant gene was detected among all resistant strains. Biofilm‐forming ability was monitored by a modified crystal violet staining method. Among the 53 strains, 32 strains showed different levels of biofilm‐forming ability, while 21 strains did not form biofilms. The minimal inhibitory concentration of antibiotics (MIC) and the biofilm inhibitory concentration (BIC) were determined in the 32 strains which can form biofilms. There are significance correlations between biofilm formation and BIC/MIC for all antibiotics (P &lt; 0.05) except vancomycin. Biofilms exhibited increased antimicrobial resistance compared with planktonic isolates, but the extent of enhanced antibiotic resistance in biofilms is different with different antibiotics.Practical ApplicationRecently, there are increasing researches focusing on the safety of LAB, due to their antibiotic resistance. However, effects of antibiotic resistance in LAB were different in different application fields. So it is necessary to understand the mechanism of resistance all sidedly. In this study, we found those LAB isolates, which exhibiting antibiotics resistance in the susceptive tests, carried no transferable antibiotic resistance determinant, while there was a significant positive correlation between four antibiotics resistance and biofilm‐forming ability. Data derived from this study can be used as a basis for assessing the safety of LAB applied in fermented food.

유산균에서 Bacteriophage의 중요성

Lactic acid bacteria as probiotics contribute to various food and medicine industry. Recently, many groups reported effects of lactic acid bacteria are the results of in vitro and clinical experiments. To apply lactic acid bacteria in food and medicine industry, the genome based research might be need for understand physiological and metabolic capabilities of lactic acid bacteria in the future. Also, study of bacteriophages for stable fermentation of lactic acid bacteria have to be performed the bacteriophage molecular characterization, relation of lactic acid bacteria, bacteriophage resistant lactic acid bacteria. Therefore, these studies would provide the various functional aspects of lactic acid bacteria to improve food quality and safety in the food industry.

50. Relevance of cell biophysical behaviour and membrane fluidity for explaining freezing resistance of lactic acid bacteria

The cell membrane is the primary site for freezing injury. During cooling, ice forms outside the cell resulting in an increase of the solutes concentration in the extracellular medium. This cryo-concentration of solutes induces water transport from the intracellular medium of cell to the extracellular medium and thus cell dehydration and cell injury. Cell membrane permeability to water is influenced by its fluidity property which is governed by the composition and the structure of the lipid bilayer. By changing the composition of the medium, the composition and organisation of the lipid bilayer of the cell membrane will be modified resulting in increasing or decreasing freezing resistance. Furthermore, another important phenomenon occurs during cooling of cell suspensions leading to the modification of membrane fluidity: the lipid phase transition from a liquid crystalline phase to a gel phase. The liquid crystalline state is characterized by increased lipid head group spacing, increased disorder in the lipid acyl chains, and a small bilayer thickness. In the gel phase the lipid head groups are very tightly packed, the lipid acyl chains become straighter and ordered, and the bilayer thickness increases. Our objective is to gain a better understanding of the relationships between membrane fluidity, lipid phase transition, membrane water permeability and freezing resistance of lactic acid bacteria. Two suspensions of Lactobacillus bulgaricus CFL1 were produced using either MRS broth or mild whey based culture media. The freezing resistance of both bacterial populations protected with sucrose was evaluated by measuring the cultivability and acidification activity of bacteria before and after freezing at −80 °C. The membrane lipid phase behaviour was studied in situ using Fourier transform infrared spectroscopy during freezing and thawing. Membrane fluidity was evaluated with fluorescence polarization using a lipophilic fluorescent probe embedded in the membrane, namely the DPH. The fluorescence measurements were performed on a flow cytometer at various temperatures. Bacterial cell dehydration was investigated by submitting cells to osmotic stress by increasing the concentration on a non penetrating solute (sucrose). The changes in cell volume with time were measured by Coulter techniques and the biophysical parameters of water transport were estimated. Bacterial population grown in MRS broth exhibited a better resistance to freezing than bacteria grown in mild whey. This better resistance can be ascribed to a lower lipid phase transition temperature and higher membrane fluidity. The detailed analysis of the results is in progress and will enable clarification of the relationships between freezing resistance, membrane fluidity and water permeability.

Antibiotic resistance of lactic acid bacteria isolated from Chinese yogurts

The aim of this study was to evaluate the susceptibility of 43 strains of lactic acid bacteria, isolated from Chinese yogurts made in different geographical areas, to 11 antibiotics (ampicillin, penicillin G, roxithromycin, chloramphenicol, tetracycline, chlortetracycline, lincomycin, kanamycin, streptomycin, neomycin, and gentamycin). The 43 isolates (18 Lactobacillus bulgaricus and 25 Streptococcus thermophilus) were identified at species level and were typed by random amplified polymorphic DNA analysis. Thirty-five genotypically different strains were detected and their antimicrobial resistance to 11 antibiotics was determined using the agar dilution method. Widespread resistance to ampicillin, chloramphenicol, chlortetracycline, tetracyclines, lincomycin, streptomycin, neomycin, and gentamycin was found among the 35 strains tested. All of the Strep. thermophilus strains tested were susceptible to penicillin G and roxithromycin, whereas 23.5 and 64.7% of Lb. bulgaricus strains, respectively, were resistant. All of the Strep. thermophilus and Lb. bulgaricus strains were found to be resistant to kanamycin. The presence of the corresponding resistance genes in the resistant isolates was investigated through PCR, with the following genes detected: tet(M) in 1 Lb. bulgaricus and 2 Strep. thermophilus isolates, ant(6) in 2 Lb. bulgaricus and 2 Strep. thermophilus isolates, and aph(3′)-IIIa in 5 Lb. bulgaricus and 2 Strep. thermophilus isolates. The main threat associated with these bacteria is that they may transfer resistance genes to pathogenic bacteria, which has been a major cause of concern to human and animal health. To our knowledge, the aph(3′)-IIIa and ant(6) genes were found in Lb. bulgaricus and Strep. thermophilus for the first time. Further investigations are required to analyze whether the genes identified in Lb. bulgaricus and Strep. thermophilus isolates might be horizontally transferred to other species.

Acquired resistance to macrolide-lincosamide-streptogramin antibiotics in lactic Acid bacteria of food origin.

Antibiotic resistance is a growing problem in clinical settings as well as in food industry. Lactic acid bacteria (LAB) commercially used as starter cultures and probiotic supplements are considered as reservoirs of several antibiotic resistance genes. Macrolide-lincosamide-streptogramin (MLS) antibiotics have a proven record of excellence in clinical settings. However, the intensive use of tylosin, lincomysin and virginamycin antibiotics of this group as growth promoters in animal husbandry and poultry has resulted in development of resistance in LAB of animal origin. Among the three different mechanisms of MLS resistance, the most commonly observed in LAB are the methylase and efflux mediated resistance. This review summarizes the updated information on MLS resistance genes detected and how resistance to these antibiotics poses a threat when present in food grade LAB.