| Summary: | <p><b>Background: </b>To identify the microorganisms that can grow rapidly in total parenteral nutrition (TPN) solutions, we investigated the growth of the major causes of catheter-related blood stream infection (<i>Staphylococcus aureus</i>, <i>Serratia marcescens</i>, <i>Bacillus cereus</i>, and <i>Candida albicans</i>) in TPN solutions containing lipid. <b>Methods:</b> The pH value of a TPN solution containing lipid (pH 6.0, containing 20 ppm of NaHSO<sub>3</sub>) was adjusted by the addition of HCl to 5.7, 5.4, or 4.9. The pH value of another TPN solution (pH5.5, containing 400 ppm of NaHSO<sub>3</sub>) was adjusted by the addition of NaOH to 5.9, 6.3, or 6.8. A specific number of each microorganism was added to 10 mL of each test solution and incubated at room temperature. The number of microorganisms was counted as colony forming units at 0, 24, and 48 hrs later. <b>Results:</b> <i>C albicans</i> increased similarly at any pH values in the TPN solution. The bacterial species also increased rapidly at pH6.0 in the solution containing 20 ppm of NaHSO<sub>3</sub>, but growth was suppressed as the pH value was reduced, with growth halted at pH4.9. However, these bacterial species did not increase, even at pH5.9, in the other solution containing 400 ppm of NaHSO<sub>3</sub>. <b>Conclusions:</b> These results suggest that <i>Candida</i> species can grow rapidly in almost all TPN solutions regardless of the acidity, lipid, and NaHSO<sub>3</sub>; also, some bacterial species may grow in TPN solutions containing lipid unless the pH value is 5.0 or less. Therefore, each TPN solution should be examined whether or not the bacterial species can proliferate.</p>
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