MacConkey broth

Enterobacteriaceae sample of 100 ml shall be filtrated and placed the membrane filter into 50 ml of MacConkey broth, incubated for 20 to 28 hours at 35 2°C. Transfer into EMB agar for 40 to 48 hours at 35 2°C. If any characteristic colony is detected, identify using API and/or automated identification system... 

Enrichment cultures are intended to increase the dominance of a numerically minor component of a mixed culture such that it can be readily detected on an agar plate. Enrichment media are always liquid and are intended to provide conditions that are favourable for the growth of the desired organism and unfavourable for the growth of other likely isolates. This can be achieved either through manipulation of the pH and tonicity of the medium or by the inclusion of chemicals that inhibit the growth of unwanted species. Thus, MacConkey broth con-... 

A commonly used medium of this type is MacConkey broth. This contains the sugar lactose, the bile salt sodium taurocholate and an indicator. The bile salt only allows the growth of bile tolerant species i.e. enterobacteria, and metabolism of the sugar is shown by the acid colour of the indicator. Lactose is one of the... 

Samples from the presumptive positive tubes are then inoculated into further medium for confirmation tests for coliforms and also to determine whether E. coli is present. Results from the Voges Proskauer, Methyl Red, and Citrate tests (see later) are used to confirm the presence of coliforms. Positive results from growth on MacConkey broth at 44 °C are scored to give a statistical probability of the Most Probable Number (MPN) of E. coli per 100 ml of water sampled. 

To detect low levels of bacteria that might be missed with the quantitative technique, 5 pL of a biological fluid is inoculated into 5 mL of trypticase-soy broth and incubated overnight at 37°C. If bacterial growth is identified, the colonies are seeded onto a tryptic soy blood-MacConkey agar plate for further identification. 

Entero- bacteriaceae 1. MacConkey agar/broth 2. UBA agar 1. PCR 2. Automated ribo typing Jespersen and Jakobsen (1996), Maugueret and Walker (2002) and Koivula et al. (2006). 

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