I have a strain of bacteria. it's just a common bacteria without any genetic engineering or other processing. The instruction said that it can grow in normal LB broth. But I just worried if there is no antibiotic resistance, other bacteria could grow in the media that contaminate the broth. So how should I culture the bacteria and make sure it is not contaminated? Thanks!!!
Most bacterial cultures can be propagated in liquid culture without antibiotic selection with minimal risk of contamination. I would streak your bacteria on an LB Agar plate, select an isolated colony and, using sterile technique, transfer it to your liquid media.
If you are concerned about introducing contaminants you can transfer your sterile liquid media to your sterile vessel (test tube, flask...) the day before introducing your colony (i.e. the day you streak your strain for isolation on solid agar). If it is clear in the morning, your media is almost certainly still sterile. If you are concerned about the transfer, you can homogenize the colony in a small volume of sterile media and transfer that into your flask or test tube to avoid the risk of contacting the sterile inner surfaces. Keep in mind that bacteria will grow best when the dilution is less than about 1:100 (so you wouldn't want to inoculate a 4 L flask directly from a small colony - ideally, you would start a 50 mL starter culture and dilute ~ 40 mL of that into the 4 L flask the next day).
The only times I have had contamination issues is when I had a slow-growing strain that required several days of growth before turning cloudy. In that scenario, even small amounts of contaminant can overtake the culture (usually on day 7 of a 7-day fermentation, of course!) Good luck!
You can check sterility of LB media and if you carry out aseptic conditions, there is no risk for contamination of other bacteria if your culture is pure. Andrew also explained in detail.
Best regards.
A side comment: Even if a strain is antibiotic resistant, that does not make it impervious to contamination. As a matter of fact, if you are working with several clones on the same plasmid backbone, most potential contaminants around are already resistant to the same antibiotic. There is no substitute for good aseptic practice.
Practice proper sterile technique. If you have access to an autoclave at your place of experimentation utilize that after initial preparation of the LB-broth. After your broth has been sterilized, inoculate it and utilize an open flame from a bunsen burner to maintain the sterility of the inoculated culture broth. Assure that the lid or film covering the opening is air-tight and incubate preferably with agitation at an optimal temperature should you know the organism. If you do not know the organism I would recommend 34-37 degrees Celsius. If sterile you may also store at length at 0-5 degrees Celsius. At this temperature the bacteria will not cease growth but it shall slow down significantly. Once incubated in broth form you may choose to quantify the bacterial growth via a spectrophotometer or hemocytometer.
While streaking your bacteria also throw in a petri dish with no bacteria in the incubator. Next day is the plate has no growth that means you made the agar plate aseptically.
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