Image: E.coli on growing on various agar media

Description: Escherichia coli grows on many commonly used cultivation media. Examples of these media are: Fig. A1 Brain heart infusion agar (BHIA), A2 Trypticase soy agar (TSA), A3 MacConkey agar (MCA), A4 Endo agar Fig. B shows growth of a common E. coli strain on these media. Note the different size of colonies as nutriet and selective properties of these media vary. Colonies on brain heart infusion agar (B1) are larger in comparison with colonies on trypticase soy agar (B2), MacConkey (B3) and Endo agar (B4). MacConkey (Fig. C1, C4) and Endo agar (Fig. C2, C3) represent diagnostic selective media. Both of them typically inhibit growth of Gram positive bacteria and enable differentiation between lactose positive and lactose negative bacteria (E. coli is typically lactose positive).Colonies are smallest on Endo agar as this medium has higher selectivity for Enterobacteriaceae in comparison with MacConkey agar. Size of colonies is also influenced by numbers of colonies growing on a defined surface of agar medium (higher numbers usually mean smaller colonies). (Competition for nutrients) Fig. C E. coli growing on MacConkey (C1) and Endo agar (C2) in comparison with Klebsiella pneumoniae (C3 MacConkey, C4 Endo). Both of them are lactose positive. Fig. D, G, H Colonies of lactose-negative and positive E. coli on MacConkey agar. E. coli strains are typically lactose positive. Colonies apperaing lactose-negative are usually delayed lactose fermentors giving positive ONPG test. Fig. E Staphylococcus aureus (yellow), Enterococcus faecalis (small) and E. coli on trypticase soy agar after 24 h at 37°C. Seen with reflected light. Fig. F E. coli and Pseudomonas aeruginosa (smaller greenish colonies) in mixed culture on brain heart infusion agar. 24 h, 37°C, seen with both reflected and transmitted light. Fig. I E. coli and Klebsiella pneumoniae (larger), yellow, lactose-positive colonies on CLED agar. Bluish lactose-negative colonies of Serratia marcescens. Fig. J Lactose-fermenting colonies of E.coli with a gold metallic sheen on Endo agar.
Title: E.coli on growing on various agar media
Credit: Own work
Author: HansN.
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