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The growth of 20 strains of Shigella, representing the four species, was evaluated by the inoculation of pure cultures of single strains on Tryptic Soy agar (TSA) and four selective plating media. Colony counts of 18 strains were highest on TSA. While recovery on MacConkey (MAC) and Xylose Lysine Desoxycholate (XLD) agars was intermediate, very low counts occurred on Desoxycholate Citrate (DCA) and Salmonella-Shigella (SS) agars. Six strains plated on MAC and four strains plated on XLD gave colony counts 10% lower than TSA. With DCA and SS 15 and 16 strains, respectively, gave colony counts 50% lower than TSA. In fact seven strains failed to grow on DCA and nine strains failed to grow on SS. This inhibition was observed by strains from all species; although Shigella boydii and Shigella sonnei were most susceptible to inhibitors. By observing changes in optical density over a 24 hr period, it was possible to evaluate the growth response of three strains which differed in their sensitivity to selective media to the inhibitors in the selective media. Lag phases of over 15 hr were observed in some strains when sodium desoxycholate (0.5%) was added to Tryptic Soy broth (TSB). No inhibition of growth was observed when bile salts (0.15% or 0.85%) were added to TSB; however the addition of sodium citrate (0.85%) plus bile salts (0.85%) to the basal medium did extend the lag phase of all strains by about 3 hr. Strains having a low plate count efficiency on selective media failed to grow when desoxycholate (0.85%) plus sodium citrate (2%) was added to TSB. On the other hand strains not apparently affected by inhibitors in the selective media required 24 hr to initiate growth. When mannitol, lactose, or glucose was added to Trypticase Soy broth (TCSB) aerobic growth was greatest with glucose. Those strains capable of fermenting mannitol also grew well on mannitol. Growth of aerobic cultures on media containing lactose was not greater than that observed on TCSB with no added carbohydrate. When Shigella sonnei was grown on mannitol containing media, an enzyme was detected in cell-free extracts which reduces nicotinamide adenine dinucleotide in the presence of mannitol-1-phosphate or mannitol. Cell-free extracts of Shigella dysenteriae and Shigella sonnei grown on glucose did not exhibit this enzyme activity.



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Department Name

UNM Biology Department

First Committee Member (Chair)

Larry L. Barton

Second Committee Member

John August Ulrich

Third Committee Member

Eugene Weston Rypka

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