There are a few most common supplements:

- Chloramphenicol you can add to a medium before autoclaving.

- Kanamycin, but this you will need to add after sterilization

- Acidification of culture media.You can use HCL to acidify culture media to pH 4-4.5. Alternatively, organic acids such as Lactic and Citric can be used (despite some critique). Acids should be also added after autoclaving.

If you want cultivate fungi chloramphenicol is a good alternative. 1000 ug/L added before autoclave.

I have an old paper in which different antibiotics are used to inhibit the growth of Gram+ cocci, Gram + rods and Gram- rods. The reference is: Casey & Ingledew (1981). The use and understanding of media used in brewing bacteriology. II Selective media for the isolation of lactic acid bacteria Brewers Digest March: 38-45.

If you can’t get it, I shall send you a scanned copy.

Florin, antibiotics are not always the best option to prevent contamination. Many antibiotics could have an unexpected side effect and majority of antibiotics are self-degrading (activity is declining with time). What medium you are using and what are the cultured organisms (pure, mixed, fungi, plant tissues)? What is the goal of your study?

you can use pénicillin (0.05 g/L) + streptomycine (0.05

g/L) and chlorotétracycline (0.05 g/L) to inhibit bacteria if you want to isolate fungi on Potato Dextrose Agar

You must added both sterile streptomycin and pincillin(50ug/ml:100ug /l) after autoclaving at temp 60

Thank you for yours answers!

Nicolai, I will use Potato Dextrose Agar which will be inoculated with 1 ml soil dilution (mixed microbiota). My final goal is to isolate soil yeasts.

Also, I would like to know if is possible to growth on the nutritive media (PDA) only the Gram positive bacteria and to block reproduction of Gram negative bacteria (inoculation with soil dilution).

Florin, now I see the problem: you want to create a selective advantage for yeasts when use regular soil plating on a generic medium. Sure, you can use a wide range of antibiotics (A) against prokaryotes (see advices above) but you still face at least two problems: presence of A-resistant bacteria and self-decay of A (long incubation times to isolate slowly growing yeasts are not allowed because A will disappear after few days). Besides, it could be expensive. Much simpler way would be to use a selective medium, e.g. malt extract agar acidified by lactic acid (with or without sugars). Bacteria will grow really rarely. To avoid spread of mycelial fungi, experienced mycologists incubate the inoculated Petri dishes at low temperature, e.g. at 5 to 10 oC in a regular fridge. Yeasts tend to be more resistant to cold than mycelial fungi. Sure, it works only as a trend, do not expect miracles. I mean, you give advantage to yeasts but do not eliminate other groups completely. Some other useful tricks you can find in papers published by soil mycologists Bab'eva, Chernov, Lodder, and many other in 1950-1990.

Finally, no insults, I'm sure you are aware that plating as enumeration/isolation technique is not as popular as before. Now we have molecular tools (SSU rRNA gene) to detect various taxonomic groups in situ. If you want to isolate some special bugs, then use narrow-defined isolation conditions. For example, if you want to isolate yeasts from the anthill, then use formic acid as a specific C-source.

Good luck

what is your aim?Whether you are medium especially for culturing fungi or bacteria strain؟

Gentamicin will cover most of the Gram negative and Gram positive organisms. U can try that.

There are commercially available culture media containing various antibiotics inhibiting certain bacterial species. If you are aiming to isolate yeasts there is a ready-made Sabauraud agar supplemented with chlolamphenicol. If you are targeting other microorganisms you can try the commercial mediums supplemented with certain antibiotics or buy the commercially available antibiotices for use as supplements in different culture media. I should advise you contact your culture media suppliers and they will provide you with an array of solutions for your problem.

Instead of using PD I would rather go for YM. The problem is that PD is frequently used to induce (or facilitate the development of) filamentous stage by fungi. This might cause a problem as molds (as well as dimorphic fungi) will start spreading over plates and make the isolation of pure cultures difficult.

PD is absolutely OK when you work with pure cultures.

Regarding the acidification, you will need to decide yourself. I am using this inhibition method and it worked well for my soils. However, there is always some critique. One point is that some soil yeasts are able to produce anti-fungal substances such as mycocins and glycolipids, and these are produces better on acidified medium. Therefore, there is always a risk that by using acidification you will loose certain "sensitive" strains and species. I have to mention that I did not observe antagonistic effects in my soil samples so far.

Indeed, there are older studies on soil yeasts that are worth to read. I would add one more name to the list above - Margaret E di Menna.

You can use advantage of methods these authors tried but you have to keep in mind that the number of recognized yeast species has increased dramatically since that time. I would not take comments on species observation and diversity values too close.

Although culture-independent techniques are more fashionable nowadays, cultivation approaches have their own advantages. Also, all currently used culture-independent techniques are still biased. You can still use cultivation-based approaches as soon as you can show that you are using them properly. One of the most important issues will be species identification (ITS and LSU rDNA) and sufficient statistical support.

I used chlortetracycline-HCL and chloramphenicol at the same time to prevent the growth of gram positive and gram negative bacteria in the medium used for enumeration of yeast and mold (American Public Health Association (1993). Standard Methods for the Examination of Dairy Products, 16th ed. APHA. Washington, DC.)

Gentamicin for Gram negative and Vancomycin for Gram positive

Best results with chloramphenicol (500 mg/L) and gentamicin (50 mg/L); they are heat-stable, so you can add to the medium before autoclaving. Another method is the reduction of medium pH using lactic acid.

I suggest the use of choloramphenicol

also, you use YGC medium ( Yeast extract, Glucose , choloramphinicol) for isolate yeast of soil

Streptomycin.....I use it

I suggest you in your nutritive media, the use of antibiotics'mix : streptomycine, Penicilin and choramphenicol in order to control the growth of bacteria.

definetivellly...gentamicin

Try reading the literature

Dear Ron ,

thank you for your answer!!!!

Dear friend, If it is fungal media, generally chloramphenicol is used to suppress the bacterial growth.

CHLORAMPHENICOL.....at 50 mg/L or you can use CTAB(hexadécyltriméthylammonium bromide) instead....

Please, be careful with CTAB as this selects towards a few phylogenetic groups only, e.g. Metschnikowia yeasts. See for details papers by Marc-André Lachance & William T Starmer (https://www.researchgate.net/profile/William_Starmer/).

Penicillin and streptomycin............

Neomycin (1% in water) and streptomycin (5% in water)

Chloramphenicol should be a good alternative.

Chloramphenicol is OK, but you can use other antibiotics and their combinations too, controlling their concentrations.

You can use Oxytetracyclin

to control bacterial growth why not try vancomycin/kanamycin: vancomycin inhibits gram positive kanamycin inhibits gram negative: can also try polymixinB, Colistin for Gramnegative