Article Elective and Selective media for lactic acid bacteria

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Thank you Nikolay Vassilev and Alaa Kareem Niamah

I appreciate your kind help :)

Lactic acid bacteria comprise a heterogeneous group of microorganisms. Isolates from food include representatives of the genera Lactobacillus, Streptococcus, Pediococcus and Leuconostoc. As no universal selective medium exists for the cultivation of all lactic acid bacteria the well-known media for lactobacilli may be modified by changing the pH value, the concentrations of inhibitory agents and the incubation time and temperature. It may be necessary to select media for special fields of application, e.g. milk and milk products, meat and meat products. Surface plating under microaerophilic or anaerobic conditions is generally recommended. Generally suitable as selective media for lactic acid bacteria are MRS-medium, adapted to a lower pH (e.g. 5.7) with the addition of an inhibitor (e.g. sorbic acid) or a modified Rogosamedium with increased pH (e.g. 6.2). The LaS (lactobacilli-sorbic acid) medium (pH 5.0) incubated for at least 48 h is also suitable but fails to recover enterococci. However, this can be compensated by a special enterococcus medium used in parallel. Elective media for defined groups of lactic acid bacteria such as lactic streptococci or yoghurt bacteria have recently been used successfully. One of those is the M 17 medium for lactic streptococci which must be used strictly according to the recommendations of the authors. Good growth can also be obtained with the BRIGGS or RCM medium, the latter supplemented with 1% dextrose or lactose. For the differentiation of the yoghurt lactic acid bacteria the TPPY medium proved suitable as well as the LSD medium which was introduced recently.

MRS broth and gelose for Lactobacillus

M17 for Streptococcus

I used to isolate LAB on MRS, M17 but it is not selective enough, you should adapt the pH add some vitamines and adjust the temperature,. you can use the two toghether to have a better isolation of a large spectrum of LAB (almost all the genera exept streptococcus, tha hardest to obtain for me), but for more precise results you can adapt PCA with milk powder , i used to add an anti fungic , sodium azid, and a colored indicator (bromocresol), you can use Elliker rogosa for lactobacilli, PCA-milk for lactococci, MSE or Nikels and leesment are media for Leuconostoc isolation.you have to try, and adjust your medium using bacteria specificities, don't just use standards ones because it is on books. You can also prepare your samples according to the genera you are looking for, imerge them in milk and incubate at a cetrain temperature, or heat it before incubation (until 72°C for streptococci) and before isolation.

Thank you very much for all your feedback: Basil A. Abbas Zohra Boukefoussa Muhammad Saleem Kalhoro

Ami Rameshbhai Patel

Regards

You should try MRS agar.

In that case, I would like to prefer MRS broth for Lactobacillus plantrum .

MRS agar can be used to enumerate Lactobacillus species. You can search this link for further details

https://himedialabs.com/TD/M641.pdf

Other than this following articles would be helpful to you

Article Medium for selective enumeration of lactic acid bacteria in foods

https://www.tandfonline.com/doi/pdf/10.1080/1040-840291046759?needAccess=true

You can use MRS agar and M17 agar.

MRS medium is selective for lactobacilli but some growth of leuconostocs and pediococci may occur. Selectivity can be altered by pH adjustment. Lactobacilli will tolerate lower pH levels than streptococci (pH 5.0-6.5) with pediococci and leuconostocs growing best within this range. Inhibitors of the main groups of competitor microflora include thallous acetate, sodium acetate, sorbic acid, acetic acid, sodium nitrite, cycloheximide and polymyxin. These substances can be used at varying concentrations and combinations but, inevitably, a compromise has to be reached between selectivity and productivity of the organism(s) sought3. MRS Agar with sorbic acid has been described3,4. This is MRS medium with its pH reduced to 5.7 and 0.14% sorbic acid added (equating to 0.2% potassium sorbate).