Kinetics of bacterial growth in simple intravenous solutions and admixtures.

The growth of bacteria in intravenous solutions and admixtures has been studied under stationary conditions of incubation. All the solutions were inoculated with 100 organisms/ml, incubated at room temperature (27 degrees C) or (37 degrees C), with samples withdrawn at specified time intervals, and plated in quadruplicates. The simple intravenous (i.v.) solutions did not support significant growth (P greater than 0.05) of any of the micro-organisms. Growth in i.v. solutions containing 1% blood was very significant (P greater than 0.05), as demonstrated by the high apparent growth rate constants (K). The ratio of K for beta-lactamase producing bacteria (beta-lac+) over that for non-beta-lactamase producing bacteria (beta-lac-) was significant (P less than 0.05) at 37 degrees C compared to that at 27 degrees C. The higher K values for B. cereus in benzylpenicillin and cefuroxime solutions, respectively, compared to those in antibiotic-free solutions, may be attributable to hydrolysis of the drugs, while the low K values for B. subtilis in the same solutions may be attributed to the inhibitory effects of the drugs. In conclusion, minute quantities of blood in i.v. solution tend to cause bacteria to multiply rapidly. The presence of beta-lactamase producing species might, in addition, hydrolyse susceptible beta-lactam antibiotics which are common additives to i.v. fluids.

Survival of beta-lactamase-producing and -nonproducing bacteria in intravenous solutions.

The survival of beta-lactamase-producing (beta-lac+) and non-beta-lactamase-producing (beta-lac-) Bacillus and Staphylococcus spp. has been investigated in dextrose 5% injection, NaCl 0.9%, and dextrose 5% in NaCl 0.9% solutions. Tests were performed under static and turbulent conditions of incubation, with and without antibiotics added to the fluids, and with or without 1% citrated blood. All solutions were inoculated with about 1000 organisms/mL, and sampled for viable bacteria at specific time intervals. Under static conditions, there was no significant decrease in viability (p greater than 0.01) of the bacilli, except for the staphylococci (p less than 0.01). However, when cultures were agitated, all species showed significant decline in viability (p less than 0.01). When antibiotics were present, S. aureus (beta-lac+) declined gradually throughout 24 hours (p greater than 0.01). B. cereus (beta-lac+) concentrations were static in all solutions. All organisms multiplied rapidly in solutions containing blood. The results suggest that the growth characteristics of both beta-lac+ and beta-lac- bacteria in intravenous fluids are essentially similar, except in solutions containing beta-lactamase-sensitive antibiotics in which beta-lac+ bacteria tend to survive.