Resistance Of Lactic Acid Bacteria Research Articles

Antibiotic Resistance in Lactic Acid Bacteria

Most starter cultures belong to the lactic acid bacteria recognized as safe by the US Food and Drug Administration (FDA) and the European Food safety Authority. However, LAB may act as intrinsic reservoirs for antibiotic resistance (AR) genes. This fact may not constitute a safety concern itself, as the resistance gene transfer is vertical. Nevertheless, external genetic elements may induce changes that favour the horizontal transfer transmission of resistance from pathogens as well as from the human intestinal microbiota, which represents a severe safety issue. Some genus of AR LAB includes Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Pediococcus, and Streptococcus isolated from fermented meat and milk products. Currently, the WHO recommends that LAB used in the food industry should be free of resistance.

Increased Survival of Lactococcus lactis Strains Subjected to Freeze-Drying after Cultivation in an Acid Medium: Involvement of Membrane Fluidity Cultivation in Acid Medium to Improve Bacterial Survival of Freeze-Drying.

SUMMARYResearch backgroundFreeze-drying is the most widely used dehydration process in the food industry for the stabilization of bacteria. Studies have shown the effectiveness of an acid prestress in increasing the resistance of lactic acid bacteria to freeze-drying. Adaptation of bacteria to an acid stress is based on maintaining the properties of the plasma membrane. Indeed, the fatty acid composition of the membrane of lactic acid bacteria is often changed after an acid prestress. However, few studies have measured membrane fluidity after an acid stress during lactic acid bacterial strain cultivation.Experimental approachIn order to use two pH profiles, the strains Lactococcus lactis NCDO 712 and NZ9000 were cultivated in two media, without any pH control. The two pH profiles obtained were representative of the initial medium composition, medium buffering properties and strain metabolism. Absorbance at 600 nm and pH were measured during bacterial cultivation. Then, the two strains were freeze-dried and their survival rates determined. Membrane fluidity was evaluated by fluorescence anisotropy measurements using a spectrofluorometer.Results and conclusionsCultivation under more acidic conditions significantly increased the survival during freeze-drying (p<0.05, ANOVA) of both strains. Moreover, in both strains of L. lactis, a more acidic condition during cultivation significantly increased membrane fluidity (p<0.05, ANOVA). Our results revealed that cultivation under such conditions, fluidifies the membrane and allows a better survival during freeze-drying of the two L. lactis strains. A more fluid membrane can facilitate membrane deformation and lateral reorganization of membrane components, critical for the maintenance of cellular integrity during dehydration and rehydration.Novelty and scientific contributionA better understanding of the involvement of membrane properties, especially of membrane fluidity, in bacterial resistance to dehydration is provided in this study.

The study of antibacterial, fungicidal and cytotoxic properties of antagonist microorganisms

Microorganisms isolated from natural sources that have antagonistic properties are the objects of the research in this paper. The main objective of the study was to screen and characterize the antagonistic properties of microorganisms isolated from natural sources in connection with the creation of new pharmaceutical substances. Methods of cultivating strains of microorganisms, chromatographic methods, spectrometric, electrophoretic methods of analysis, and methods of cryopreservation of accumulative cultures were applied. In the course of the experiment, nutrient media for cultivating strains of antagonist microorganisms were optimized, and the physiological and biochemical properties of lactic acid bacteria and other antagonist microorganisms were studied. It is proved that lactic acid bacteria and other antagonist microorganisms show antimicrobial properties on a solid medium. The antibiotic resistance of lactic acid bacteria and other antagonist microorganisms was studied, the biocompatibility of lactic acid bacteria and other antagonist microorganisms was proved. During the investigation, the antibacterial properties of the isolated peptide fractions were determined, the fungicidal properties of the isolated peptide fractions were established, and low-molecular protein compounds with antibacterial and antifungicidal activity were identified; the toxicity indicators of identified bacteriocins and fungicides were studied in vitro. The novelty of this work consists in the development of scientifically based approaches to screening and characterization of antagonistic properties of microorganisms isolated from natural sources, as well as to the cultivation of antagonist microorganisms in connection with the creation of new pharmaceutical substances of antimicrobial action.

In vitro resistance of lactic acid bacteria carried in kefir appetizer enriched with agroindustrial by-products

This study aimed to develop a salty type appetizer and evaluate its physicochemical, sensorial and instrumental characteristics and the resistance of the lactic acid bacteria (LAB) to the gastrointestinal tract (GIT) simulated in vitro. Five formulations were prepared after desorbed of kefir: F0: kefir, salt, garlic and herbs (control); F1: F0 and Lactobacillus acidophilus; F2: F1 and green banana flour; F3: F1 and passion fruit albedo flour; F4: F1 and orange peel flour. The formulations were stored refrigerated for 28 days and realized analyzes. Resistance of the LAB to GIT conditions was done for F0 and F4 at 0, 14 and 28 days. The formulations didn't differ (p > 0.05) for pH, acidity and texture at zero time, however, F3 presented greater firmness and gumminess at 28 days. The formulations were safe for consumption and F0 and F1 were the most acceptable. The addition of fruit flour didn't influence the viability of the bacteria. In the in vitro GIT test, at 28 days, > 8.5 Log CFU/g of LAB was available to promote consumer benefits. There are no any negative impact using of these by-products is environmental friendly and will help to avoid production of food industry nus-products in great extent.

Comparative Assessment of Antibiotic Resistance in Lactic Acid Bacteria Isolated from Healthy Human Adult and Infant Feces

Lactic acid bacteria are normal inhabitants of the gastrointestinal tract of humans. Their occurrence in infant and adult feces is abundant. The current study assesses and compares the antibiotic resistance in lactic acid bacteria isolated from healthy human adult and healthy infant fecal samples. A total of 255 lactic acid bacteria isolates (126 from adult feces and 129 from infant feces) were isolated and characterized from 60 fecal samples. Lactobacillus spp., Pediococcus spp. and Enterococcus spp. were included in the study. The study was done using the WHONET software for the analysis of antibiotic susceptibility data of lactic acid bacteria. Most of the Lactobacillus and Pediococcus strains were sensitive to vancomycin. Enterococcus strains showed resistance against vancomycin. Ampicillin, ciprofloxacin and cefuroxime resistance were significantly (p&lt;0.05) higher in Lactobacillus strains isolated from adult fecal samples than those isolated from infant fecal samples. A similar pattern was observed in Enterococcus strains with erythromycin, gentamycin and tobramycin resistance. Pediococcal isolates from adult feces showed significantly higher resistance against tobramycin, ciprofloxacin, gentamycin, cefotaxime and cefuroxime in comparison with infant fecal isolates. Antibiotic resistance was exhibited by lactic acid bacteria against most commonly used antibiotics and it was higher in strains isolated from adult fecal samples than in the strains isolated from infant fecal samples. The increasing trend in antibiotic resistance from infant to adult might be due to food habits and antibiotic intakes. Thus, the widespread antibiotic resistance in different lactic acid bacteriamay pose a food safety concern as well.

Antibiotic activity and resistance of lactic acid bacteria and other antagonistic bacteriocin-producing microorganisms

Introduction. Increased resistance of microorganisms to traditional antibiotics has created a practical need for isolating and synthesizing new antibiotics. We aimed to study the antibiotic activity and resistance of bacteriocins produced by lactic acid bacteria and other microorganisms.&#x0D; Study objects and methods. We studied the isolates of the following microorganism strains: Bacillus subtilis, Penicillium glabrum, Penicillium lagena, Pseudomonas koreenis, Penicillium ochrochloron, Leuconostoc lactis, Lactobacillus plantarum, Leuconostoc mesenteroides, Pediococcus acidilactici, Leuconostoc mesenteroides, Pediococcus pentosaceus, Lactobacillus casei, Lactobacillus fermentum, Bacteroides hypermegas, Bacteroides ruminicola, Pediococcus damnosus, Bacteroides paurosaccharolyticus, Halobacillus profundi, Geobacillus stearothermophilus, and Bacillus caldotenax. Pathogenic test strains included Escherichia coli, Salmonella enterica, Staphylococcus aureus, Pseudomonas aeruginosa, Bacillus mycoides, Alcaligenes faecalis, and Proteus vulgaris. The titer of microorganisms was determined by optical density measurements at 595 nm. &#x0D; Results and discussion. We found that eleven microorganisms out of twenty showed high antimicrobial activity against all test strains of pathogenic and opportunistic microorganisms. All the Bacteroides strains exhibited little antimicrobial activity against Gramnegative test strains, while Halobacillus profundi had an inhibitory effect on Gram-positive species only. The Penicillium strains also displayed a slight antimicrobial effect on pathogenic test strains.&#x0D; Conclusion. The antibiotic resistance of the studied lactic acid bacteria and other bacteriocin-producing microorganisms allows for their use in the production of pharmaceutical antibiotic drugs.

Screening and Characterization of the Antagonistic Properties of Microorganisms Isolated From Natural Sources

BACKGROUND: Human infectious diseases caused by antibiotic-resistant bacterial pathogens present a serious problem for clinical medicine. Causative agents of nosocomial infections, such as Escherichia coli, Klebsiella pneumoniae, Enterobacter spp., are the most common among them. An active search for antimicrobial agents that can effectively combat drugresistant pathogens is underway. Antimicrobial substances of bacterial origin are of particular interest. Promising sources of microorganisms with antibiotic properties are natural sources: Soil, water, plants, etc.&#x0D; AIM: The purpose of this work is to screen and characterize the antagonistic properties of microorganisms isolated from natural sources in connection with the creation of new pharmaceutical substances.&#x0D; METHODS: The material for the isolation of microorganisms was the soil, water bodies, and plant objects of various municipal districts of the Kemerovo Region. Identification of the isolated microorganisms was carried out using the methods proposed in the directory “Bergey’s Manual of Determinative Bacteriology” and in the monograph Nesterenko et al. The selection of strains from soil samples was carried out according to standard methods described in “Methods of soil microbiological control. Methodical recommendations,” cultural-morphological properties of isolates were studied using conventional microbiological methods.&#x0D; RESULTS: The following results are obtained: (1) Lactic acid bacteria and other microorganisms antagonists from natural sources were isolated: Soil, water bodies, and plant objects; 20 isolates were isolated, their cultural and morphological properties were studied; isolated microorganisms were found to belong presumably to the genera Bacillus, Leuconostoc, Pedio-coccus, Lactobacillus, and Bacteroides; (2) Antimicrobial properties of lactic acid bacteria and other antagonistic microorganisms isolated from natural sources on solid and liquid nutrient media were studied; (3) 12 strains of 20 isolates with maximum antimicrobial properties were selected for further studies.&#x0D; CONCLUSION: Further research on the biochemical properties of lactic acid bacteria and other antagonist microorganisms isolated from natural sources, the study of antibiotic resistance of lactic acid bacteria and other antagonist microorganisms isolated from natural sources, as well as other more detailed studies will be conducted with selected 12 strains with maximum antimicrobial properties.

Microbial dynamics in durum wheat kernels during aging

In the present work the microbial dynamics in wheat kernels were evaluated over time. The main aim of this research was to study the resistance of lactic acid bacteria (LAB) and yeasts associated to unprocessed cereals used for bread making during long term conservation. To this purpose four Triticum durum Desf. genotypes including two modern varieties (Claudio and Simeto) and two Sicilian wheat landraces (Russello and Timilia) were analysed by a combined culture-independent and -dependent microbiological approach after one, two or three years from cultivation and threshing. DNA based MiSeq Illumina technology was applied to reveal the entire bacterial composition of all semolina samples. The samples showed a different distribution of bacterial taxa per variety and time of storage. The groups mostly represented were Stenotrophomonas, Pseudomonas, Erwinia, Delftia and Sphingomonas genera, Enterobacteriaceae and Oxalobacteriaceae families, and Actinobacteria phylum. Among LAB, only Enterococcus genus was detected barely in a single sample (Simeto stored for one year) by the next generation sequencing, indicating that LAB remained unassigned or their abundances were below 0.1% or their DNAs were rendered inaccessible. Plate counts showed consistent differences in relation to genotypes and duration of storage, with the highest levels found for total mesophilic microorganisms detected up 6.8 Log CFU/g. Colonies of presumptive sourdough LAB were detected only in a few samples. Cocci constituted the major group of LAB in almost all samples. Following the enrichment procedure, almost all samples were characterised by the presence of acidifying microorganisms. All isolates collected before and after enrichment represented 28 different strains belonging to 10 species of Enterococcus, Lactobacillus and Pediococcus genera. The most resistant species during aging were Enterococcus faecium, Enterococcus durans, Lactobacillus brevis, Lactobacillus pentosus and Lactobacillus paracasei demonstrating that lactobacilli and enterococci are able to overcome the stressing conditions represented by cereal storage better than other LAB genera commonly found associated to cereals after harvest. Yeast community included mostly species with no interest in bread making.

Antibiotic resistance in vancomycin‐resistant lactic acid bacteria (VRLAB) isolated from foods of animal origin

In this study, antibiotic resistance in 47 vancomycin-resistant lactic acid bacteria (VRLAB), isolated from 340 foods of animal origin obtained in Turkey, were investigated. VRLAB isolates were molecularly identified as Enterococcus gallinarum (44.68%), Pediococcus pentosaceus (25.53%), P. acidilactici (12.77%), E. casseliflavus (6.38%), E. casseliflavus/E. gallinarum (4.26%), Weissella cibaria (2.13%), W. confusa (2.13%), and W. minor (2.13%). The disk diffusion test results showed that 57.45%, 53.19%, 44.68%, and 44.68% of VRLAB were resistant to ciprofloxacin, norfloxacin, teicoplanin, and vancomycin, respectively. It was found that all the Pediococcus and Weissella isolates and 53.85% of the Enterococcus isolates had multiple antibiotic resistance. Various transferable antibiotic resistance genes were found in the VRLAB using polymerase chain reaction (PCR). The most common antibiotic resistance genes in the VRLAB isolates were vanC1 (46.81%), tetM (23.4%), and ermB (19.15%). Practical applications Lactic acid bacteria (LAB) play a key role in food fermentations. However, antibiotic resistance in LAB is a concern because these bacteria can, potentially, be a reservoir that facilitates the spread of antibiotic resistance genes to pathogenic bacteria. Vancomycin is a glycopeptide antibiotic that is used as a last resort in the cure of multidrug-resistant enterococci. In this study, vancomycin-resistant Enterococcus, Pediococcus, and Weissella strains were isolated from foods of animal origin. Several transferable antibiotic resistance genes were detected in these isolates. The results of this study indicated that VRLAB strains isolated from foods of animal origin may be the reservoirs for antibiotic resistance genes. Our findings suggest that antibiotic resistance profiles and resistance genes, in addition to industrial characteristics, should be investigated when selecting LAB from foods of animal origin to be used as starter cultures.

The Analysis of Drug Resistance of the Strains of Lactic Acid Bacteria Isolated from Yoghurt Made in China and Outside of China

To analysis and compare the drug resistance of lactic acid bacteria isolated from yoghurt made in China and outside of China. Yoghourt products were purchased from Nanchang supermarkets. The Lactic acid bacteria bacterias in yoghourt were isolated by MRS, MC and M17 medium. The isolated strains were identified by gram’s stain, colony morphology observation and biochemistry reaction test. Drug resistance analysis of the identified strains were analyzed by K-B method. 26 kinds of Lactic acid bacteria, 13 strains of cocci and 13 strains of bacillus, were isolated. All strains were identified by physiology and biochemistry test. They were Lactic acid bacteria bulgaricus, Lactic acid bacteria delbrueckii subsp. Bulgaricus, Streptococcus thermophilus. Bifidobacteria (Bacillus bifidus). Drug resistance analysis revealed that the 26 strains of Lactic acid bacteria showed multiple drug resistance to 13 kinds of antibiotics, such as kanamycin. And all of these Lactic acid bacteria were completely resistant to kanamycin, ampicillin and oxacillin. The drug resistance spectrum of China’s Lactic acid bacteria is similar to that of foreign Lactic acid bacteria, but the drug resistance of China’s Lactic acid bacteria is significantly stronger than that of foreign Lactic acid bacteria. The abuse of antibiotics is serious in dairy industry. We should strengthen the management of antibiotics, reduce the chance of super resistant bacteria, and maintain the food health of the general public.

ВПЛИВ ДЕЯКИХ ЧИННИКІВ ШЛУНКОВО-КИШКОВОГО ТРАКТУ НА ЖИТТЄЗДАТНІСТЬ ЛАКТОБАЦИЛ, ВИДІЛЕНИХ ІЗ РІЗНИХ ЕКОЛОГІЧНИХ НІШ

The aim of our work was to study the resistance of lactobacilli strains to some aggressive factors of gastrointestinal tract. The use of lactobacilli as a probiotic submits a number of requirements to this group of microorganisms associated with their ability to survive in conditions of high acidity and in the presence of enzymes of the gastrointestinal tract. 13 lactobacilli strains isolated from different sources (auto-fermenting vegetables, children feces and raw meat material) were used in this work. Resistance to secretions of the macroorganism affecting to lactobacilli during their transit through the gastrointestinal tract was investigated in vitro using different pH values (3,0–8,0) and digestive enzymes – pepsin and trypsin. It has been experimentally established and statistically confirmed that the tested lactobacilli strains showed a variable response to the action of different pH values and digestive enzymes, which was determined between a certain strain and the active factor. It was found that strains isolated from raw meat had the highest levels of resistance to different pH values, and strains isolated from auto-fermented vegetables were more resistant to digestive enzymes. It was shown that despite this dependence, there was a heterogeneous response of the strains to each aggressive factor, confirming the variability of the lactic acid bacteria strains. The mathematical analysis showed that the tested studied lactobacilli form several clusters and subclusters depending on the studied features. It has been shown that the primary source of lactobacilli isolation partially influences the formation of resistance of lactic acid bacteria to aggressive factors of the gastrointestinal tract. The obtained results indicate the feasibility of further studies that required for the selection of lactobacillus strains to produce probiotic preparations, and contribute to a more rational approach to the search for potential probiotic strains with predetermined properties.

Антибиотикорезистентность молочнокислых бактерий с пробиотическими свойствами

Антибиотикорезистентность молочнокислых бактерий с пробиотическими свойствами

Antibiotic resistance of lactic acid bacteria isolated from dairy products in Tianjin, China

Abstract Antibiotic resistance poses safety risk to public health. Limited studies have considered the spread of resistance due to bacteria used in food production. We conducted a study investigating the antibiotic resistance of lactic acid bacteria from fermented dairy products in Tianjin. A total of 9 strains (3 Lactobacillus bulgaricus and 6 Streptococcus thermophilus) were isolated from commercial yogurt and cheese. Antibiotic resistance to 4 antibiotics of all isolates was analyzed by disc diffusion method and the corresponding resistance genes were determined using PCR and sequencing. Eight of 9 isolates were identified to be resistant to at least one antibiotic and 6 isolates displayed multi-drug resistance. Occurrence rate of antibiotic resistant strains to vancomycin, neomycin, gentamycin and streptomycin were 11.1%, 77.8%, 66.7% and 44.4%, respectively. The presence of antibiotic resistance genes van, aph or aadA2 were identified in 6 resistant strains. Sequencing results of aph and aadA2 amplicon demonstrated 100% and 99% identity to the resistant genes in vector pEXKm4 and Lactococcus lactis subsp. cremoris, respectively. L. bulgaricus and S. thermophilus used in dairy products can harbour antibiotic resistance genes and disseminate the resistance through food. Screening for antibiotic resistance in fermented foods should be a routine inspection for food safety.

Prevalence of Multi-Drug Resistance Traits in Probiotic Bacterial Species from Fermented Milk Products in Bangladesh

Aims: Matured nourishment like yogurt and cheese are great wellsprings of probiotic living beings. The present study was carried out for isolation, identification and antibiotic profiling of some important bacteria in, local fermented milk-products sold in the market of Dhaka, Bangladesh.&#x0D; Methodology: Twenty types of yogurt and fifteen types of cheese samples were collected from two different local market. De Man, Rogosa and Sharpe agar (MRS agar) and Streptococcus thermophilus agar (ST agar) were used for the isolation of probiotic micro-organisms from these different fermented dairy products. Characterization of lactic acid bacteria belonging to the species of Lactobacillus acidophilus, Lactobacillus bulgaricus and Streptococcus thermophilus was done by using morphological feature, Gram staining, biochemical tests (catalase test, some carbohydrate fermentation tests, alpha haemolysis test, starch hydrolysis test, bile salt tolerance test). The antibiotic profiling was performed by utilizing twelve distinct antibiotics: amikacin (10 μg), amoxicillin (15 μg), azithromycin (30 μg), bacitracin (30 μg), chloramphenicol (30 μg), ciprofloxacin (10 μg), erythromycin (30 μg), gentamicin (30 μg), kanamycin (30 μg), penicillin g (30 μg), tetracycline (15 μg), vancomycin (15 μg) to identified the multi-drug resistance of probiotic micro-organisms.&#x0D; Results: The outcomes demonstrated that specific bacterial species (L. acidophilus, L. bulgaricus and S. thermophilus) were utilized in the production of yogurt and cheese samples, that may have unnecessary antibiotic resistances which can be a risk if they transfer antibiotic resistance genes to pathogenic microbes. Notably, L. bulgaricus was effectively susceptible against bacitracin and penicillin g.&#x0D; Conclusion: Yogurt and cheese are one kind of probiotic source, made up by using probiotic starter cultures (Lactobacillus spp. and Streptococcus thermophilus) which were identified in this study. Most of the probiotic micro-organisms were resistant against these widely accepted commercial antibiotics. These resistant lactic acid bacteria may transfer their resistance genes to pathogenic microorganisms. It can be a significant cause of concern for human and animal health.

Factors influencing the membrane fluidity and the impact on production of lactic acid bacteria starters.

Production of lactic acid bacteria starters for manufacturing food, probiotic, and chemical products requires the application of successive steps: fermentation, concentration, stabilization, and storage. Despite process optimization, losses of bacterial viability and functional activities are observed after stabilization and storage steps due to cell exposure to environmental stresses (thermal, osmotic, mechanical, and oxidative). Bacterial membrane is the primary target for injury and its damage is highly dependent on its physical properties and lipid organization. Membrane fluidity is a key property for maintaining cell functionality, and depends on lipid composition and cell environment. Extensive evidence has been reported on changes in membrane fatty acyl chains when modifying fermentation conditions. However, a deep characterization of membrane physical properties and their evolution following production processes is scarcely reported. Therefore, the aims of this mini-review are (i) to define the membrane fluidity and the methods used to assess it and (ii) to summarize the effect of environmental conditions on membrane fluidity and the resulting impact on the resistance of lactic acid bacteria to the stabilization processes. This will make it possible to highlight existing gaps of knowledge and opens up novel approaches for future investigations.

Antimicrobial activity and antibiotic resistance of lactic acid bacteria isolated from Malaysian stingless bee’s gut

Antimicrobial activity and antibiotic resistance of lactic acid bacteria isolated from Malaysian stingless bee’s gut

Polyphasic characterization of Enterococcus strains isolated from traditional Moghan cheese in Iran

AbstractTraditional Moghan cheese is made from unpasteurized milk in the rural areas and nomadic tribes of Moghan region in Iran. In this study, we used a simple and rapid method for isolation of acid resistant lactic acid bacteria from traditional Moghan cheese. The six distinct isolates differentiated based on RAPD‐PCR were identified as members of Enterococcus faecium, E. faecalis, and E.durans species using classical phenotypic and biochemical tests as well as molecular methods. Based on the antibiotic susceptibility, the isolates were classified as resistant, intermediate, and sensitive. Cell‐free culture supernatants of isolates showed different antagonistic activity against the growth of some spoilage and food‐borne pathogens at two natural and neutralized pH conditions. Considering their tolerance to acid and bile, antagonistic effects on some spoilage and food‐borne pathogens and susceptibility to vancomycin, E. faecium strain ABRIINW.M (isolate IE2) and E. faecium strain ABRIINW.N (isolate FE1) are proposed as adjunct cultures to prevent the growth of spoilage and food‐borne pathogens.Practical applicationsThis study aimed to provide the first data on prevalence, acquired antibiotic‐resistance, and probiotic potential of Enterococcus spp. isolated from Moghan cheese in Iran. Such observations contribute to understanding the functional characteristics of Enterococci isolated from Moghan cheese. We also showed that polyphasic characterization of Enterococci provides significant information for species assignment and could be used as a strategy to differentiate between strains of isolates. The results of our study provide a useful setting for further investigations on antibiotic‐resistance and antimicrobial activity of Moghan cheese Enterococci as well as evaluation of their technological activities and probiotic potential.

Characterization and transfer of antimicrobial resistance in lactic acid bacteria from fermented dairy products in China

Lactic acid bacteria (LAB) are commonly found in foods and are also natural intestinal inhabitants in humans and most animals. However, information regarding antimicrobial resistance and the transfer of resistance genes of LAB from fermented dairy products in China is limited. In this study, LAB isolates (n = 82) of Lactobacillus (n = 43) and Streptococcus thermophilus (n = 39) were isolated from 51 commercial fermented food samples in China. All isolates were subjected to pulsed-field gel electrophoresis (PFGE), antimicrobial susceptibility, detecting resistance genes, as well as investigating the transferability of resistance genes. The 43 Lactobacillus isolates yielded 24 PFGE patterns and the 34 isolates of S. thermophilus generated 32 different PFGE patterns. Among the 43 Lactobacillus strains, the most commonly observed resistance was that to streptomycin (83.7%) and gentamycin (83.7%). Among the 39 S. thermophilus strains, the most frequently observed resistance was that to streptomycin (92.3%), gentamycin (87.2%), ciprofloxacin (79.5%), and chloramphenicol (71.8%), whereas the lowest level of resistance was that against erythromycin (7.7%). Antimicrobial resistance genes for erythromycin (emrB), gentamycin (aac(6')-aph(2")), streptomycin (ant(6)), sulfamethoxazole (sulI and sulII), tetracycline (tetM and tetS) were detected in the 18 resistance LAB strains. Conjugation experiments showed that tetM from L. delbrueckii subsp. bulgaricus R6 and tetS from L. plantarum R41 were successfully transferred to L. monocytogenes by filter mating. LAB strains could potentially act as reservoirs of resistance genes and play an active role in the transfer of resistance to humans via the food chain.

Assessment of Antibiotic Susceptibility within Lactic Acid Bacteria and Coagulase-Negative Staphylococci Isolated from Hunan Smoked Pork, a Naturally Fermented Meat Product in China.

We evaluated the antibiotic resistance of lactic acid bacteria and coagulase-negative staphylococci strains isolated from Chinese naturally fermented smoked pork. Our results may provide important data on establishing breakpoint standards for LAB and CNS and evaluating the safety risk of these strains for commercial use.

Selection and Validation of Reference Genes for Quantitative Real-Time PCR Normalization Under Ethanol Stress Conditions in Oenococcus oeni SD-2a.

The powerful Quantitative real-time PCR (RT-qPCR) was widely used to assess gene expression levels, which requires the optimal reference genes used for normalization. Oenococcus oeni (O. oeni), as the one of most important microorganisms in wine industry and the most resistant lactic acid bacteria (LAB) species to ethanol, has not been investigated regarding the selection of stable reference genes for RT-qPCR normalization under ethanol stress conditions. In this study, nine candidate reference genes (proC, dnaG, rpoA, ldhD, ddlA, rrs, gyrA, gyrB, and dpoIII) were analyzed to determine the most stable reference genes for RT-qPCR in O. oeni SD-2a under different ethanol stress conditions (8, 12, and 16% (v/v) ethanol). The transcript stabilities of these genes were evaluated using the algorithms geNorm, NormFinder, and BestKeeper. The results showed that dnaG and dpoIII were selected as the best reference genes across all experimental ethanol conditions. Considering single stress experimental modes, dpoIII and dnaG would be suitable to normalize expression level for 8% ethanol shock treatment, while the combination of gyrA, gyrB, and rrs would be suitable for 12% ethanol shock treatment. proC and gyrB revealed the most stable expression in 16% ethanol shock treatment. This study selected and validated for the first time the reference genes for RT-qPCR normalization in O. oeni SD-2a under ethanol stress conditions.