Cultivation Methods

Cultivation relies on the growth of micro-organisms in the laboratory under artificial growth conditions. This technique has some advantages:

1) It allows identification of a great diversity of microbial species in a sample, including those not being sought.

2) Also allows determination of the antimicrobial susceptibilities of the isolates.

Nevertheless, cultivation methods have a number of drawbacks:

1) They are scarcely able or unable to grow many micro-organisms, thus may lead to false-negative and underestimation of the pathogenic micro-organisms.

2) They are slow to provide diagnostic result.

3) They have low specificity and therefore have limitations in distinguishing among microbial species and strains.

4) They have low sensitivity i.e., failure to detect small numbers of microorganisms.

5) They strictly depend on the mode of sample transport, which must allow the survival of anaerobic bacteria but not favour overgrowth of facultative bacteria.

6) They are time-consuming, laborious, and expensive.

In the past two decades a number of methods based on molecular biology have been introduced for microbial identification. However, researchers have also shown that 40-50 percent of bacterial clones in the oral cavity represent unknown and as yet uncultivable species. The question no longer is whether uncultivable micro-organisms exist but why huge proportion of the species living in diverse environments cannot be grown under laboratory conditions. Some micro-organisms may be uncultivable for a number of reasons:

1) The artificial culture medium may lack the required nutrients or growth factors.

2) Other micro-organisms in the sample may produce substances that may inhibit the target species e.g., Bacteriocins.

3) A species may depend on another species for growth.

4) Bacterial intercommunication may be disrupted, such as present in natural biofilms.