lithium-chloride and propionic-acid

Bifidobacteria are commonly used for the production of fermented milks, alone or in combination with other lactic acid bacteria. Bifidobacteria populations in fermented milks should be over 10(6) bifidobacteria/g at the time of consumption of strain added to the product. Hence, rapid and reliable methods are needed to routinely determine the initial inoculum and to estimate the storage time period bifidobacteria remain viable. Plate count methods are still preferable for quality control measurements in dairy products. It is, therefore, necessary to have a medium that selectively promotes the growth of bifidobacteria, whereas other bacteria are suppressed. The present paper is an overview of media and methods including summaries of published comparisons between different selective media. Culture media for bifidobacteria may be divided into basal, elective, differential and selective culture medium. Non-selective media are useful for routine enumeration of bifidobacteria when present in non-fermented milks. Reinforced Clostridial Agar and De Man Rogosa Sharpe (MRS) supplemented with cysteine and agar available commercially are the media of choice for industrial quality control laboratories. Several media for selective or differential isolation have been described for enumeration of bifidobacteria from other lactic acid bacteria. From the large number of selective media available, it can be concluded that there is no standard medium for the detection of bifidobacteria. However, Columbia agar base media supplemented with lithium chloride and sodium propionate and MRS medium supplemented with neomycin, paromomycin, nalidixic acid and lithium chloride can be recommended for selective enumeration of bifidobacteria in dairy products.

Topics: Animals; Bifidobacterium; Colony Count, Microbial; Culture Media; Dairy Products; Fermentation; Food Microbiology; Food Preservation; Lithium Chloride; Propionates

Propionic acid, an enteric bacterial fermentation product, has received recent attention in regards to satiety and obesity in humans. The possibility that propionic acid might produce internal aversive cues was investigated in two experiments using conditioned taste avoidance and place avoidance procedures to index the potential aversive nature of systemic treatment with propionic acid in male rats. Experiment 1 examined the effect of systemic treatment with propionic acid (500 mg/kg), LiCl (95 mg/kg) or vehicle (all corrected to pH 7.5) on the formation of conditioned taste avoidance using a lickometer procedure. On 3 acquisition days three groups of rats were injected with propionic acid, LiCl or vehicle, following 30 min access to 0.3M sucrose solution. Both the Propionic acid group and the LiCl group evidenced a conditioned taste avoidance by the end of the acquisition period. During a drug free extinction phase the Propionic acid group showed extinction of the taste avoidance whereas the LiCl group did not. Experiment 2 involved place preference conditioning with propionic acid treatment associated with one novel context and vehicle with a different novel context on 6 conditioning trials for each type of injection. Place avoidance was assessed on two drug free extinction trials. Multi-variable assessment of the unconditioned (Acquisition Trials) and conditioned effects (Extinction Trials) of propionic acid on locomotor activity was quantified as was chamber choice time on the extinction trials. Propionic acid induced a significant place avoidance and significantly reduced locomotor activity on some acquisition trials. During the extinction trials rats exhibited enhanced locomotor activity levels in the propionic acid associated chamber, likely due to the conditioned aversive nature of this chamber.

Topics: Analysis of Variance; Animals; Avoidance Learning; Conditioning, Classical; Conditioning, Operant; Drinking; Extinction, Psychological; Injections, Intraperitoneal; Lithium Chloride; Male; Motor Activity; Propionates; Rats; Rats, Long-Evans; Taste; Water Deprivation

A new selective antibiotic-free medium for Bifidobacterium spp. is defined. This medium has lactulose as the main carbon source and includes methylene blue, propionic acid, and lithium chloride as inhibitors of some related bacterial species. The low pH of the medium contributes to the inhibition of the growth of Enterobacteriaceae. This new selective medium has a simple composition, and the level of recovery it yields is similar to those yielded by nonselective media for Bifidobacterium strains. It could thus be used for routine analysis in environmental or food microbiology.

Topics: Bacteriological Techniques; Bifidobacterium; Culture Media; Enterobacteriaceae; Environmental Monitoring; Food Microbiology; Humans; Hydrogen-Ion Concentration; Intestines; Lactulose; Lithium Chloride; Methylene Blue; Propionates

Lithium chloride-sodium propionate agar has been developed for the enumeration of bifidobacteria in fermented dairy products. The medium contains lithium chloride and sodium propionate to inhibit the growth of other lactic acid bacteria. Pure cultures of bifidobacteria, lactobacilli, and streptococci were tested for growth in this medium. With one exception, all bifidobacteria were able to grow in this medium and in a nonselective agar with a difference not exceeding .4 log units. However, none of the lactobacilli tested and only one strain each of Streptococcus salivarius ssp. thermophilus and Lactococcus lactis ssp. cremoris grew in lithium chloride-sodium propionate agar. In those cases, the numbers of colonies were lower in lithium chloride-sodium propionate agar by 1.26 and 2.51 log units, respectively, compared with a nonselective agar. Bifidobacteria were also selectively isolated from all fermented milks and cheeses analyzed.

Topics: Animals; Bifidobacterium; Cheese; Chlorides; Colony Count, Microbial; Culture Media; Dairy Products; Fermentation; Food Microbiology; Lithium; Lithium Chloride; Propionates; Yogurt