Bacterial nutritional approach to mechanisms of oxygen toxicity

Effect of total and partial pressure (oxygen and carbon dioxide) on aerobic microbial processes

In industrial bioreactors, levels and gradients of total and partial pressures are considerably higher than on the laboratory scale. In the relevant range (in general up to 2 or 3 bar, maximum approx. 10 bar), effects of total pressure on aerobic cultures are negligibly small. CO2 partial pressures of more than approx. 100 mbar may have inhibitory effects on aerobic cultures. Growth of aerobic cultures can be enhanced by O2 partial pressures higher than 210 mbar (corresponding to air at 1 bar), if oxygen transfer is limited. In many cases, however, increased O2 partial pressure (higher than approx. 1 bar) is toxic to aerobic cultures and inhibits microbial growth and product formation. Stepwise and cyclic variations of O2 partial pressure may have positive or negative effects, depending on strain of microorganism, culturing conditions, and range of dissolved oxygen concentration. Knowledge of these effects is required in process development and bioreactor scale-up.

Rheology of filamentous fermentations

The performance of a bioreactor containing a filamentous fermentation broth is greatly influenced by the rheological properties of the broth. These properties are determined mainly by the concentration of biomass, its growth rate and morphology. Included in the morphology are such factors as the geometry of hyphae (length, diameter, branching frequency), hyphal flexibility and hyphal-hyphal interactions, which can all be affected by the operational design of the reactor. Thus, correlations describing viscosity as a function of biomass only are of limited value. A better understanding of the relations between morphology and rheology may be achieved by a combination of rheological and morphological studies. Rheological properties are normally determined using off-line measurements in-spite of associated problems with sample treatment influencing the results. Equipment for dynamic, on-line, measurement of morphology and rheology is available, but little used in filamentous fermentations. Controlling the rheological properties of mycelial fermentations may be difficult because of the great number of factors influencing mycelial development and/or hyphal-hyphal interactions.Polymer solutions are often used to simulate flow behaviour of filamentous fermentations and scale-up and mass transfer considerations are based on these studies. Although much information has been gained this way, the predictions developed do not include the effect of an active biomass on the mass transfer and flow properties of the culture. It is important to carry out studies on the non-homogeneous fermentation fluids, and develop correlations based on these studies.

Effect of trimethoprim/sulphamethoxazole and hyperbaric oxygen on experimental Spiroplasma mirum encephalitis

This study was undertaken to determine the susceptibility of experimentally induced Spiroplasma mirum infection in the rat to trimethoprim/sulfamethoxazole (TMP/SMX) in combination with hyperbaric oxygen (HBO). One-day-old Fisher 344 rats were intracerebrally inoculated with the GT-48 strain of S. mirum and were exposed to regimens employed combined antibiotic and HBO treatments. The exclusive use of TMP/SMX produced a significant reduction in mortality (P less than 0.0001) and an absence of clinical signs of infection. HBO in combination with TMP/SMX showed similar effect on mortality and no evident clinical disease. The addition of HBO did result in a significant decrease in spiroplasma brain titres but was no more effective in preventing the spiroplasma-induced fatal microcystic encephalopathy than when the antibiotics were used alone. The exclusive use of HBO produced a catastrophic mortality rate in the spiroplasma-infected rats, which is contrary to the effect of HBO on conventional bacterial infections.

Investigations of the structure of 3-methylcrotonyl-CoA carboxylase from Achromobacter

It was shown by gel electrophoresis in sodium dodecylsulphate solution that 3-methylcrotonyl-CoA carboxylase from Achromobacter IVS is composed of two different subunits with molecular weights of about 78000 and 96000, respectively. The biotin is bound to the heavier subunit. It was previously found that 3-methylcrotonyl-CoA carboxylase contains four biotin molecules per complex. A complex composed of four of each subunit would thus have a molecular weight of about 700000. This is compatible with the molecular weight of 760000 determined earlier by analytical ultracentrifugation. Both subunits were isolated preparatively. As the subunits, unlike the complex, are very sensitive to oxygen, special precautions had to be taken during isolation. The biotin-containing subunit was isolated by chromatography on DEAE-cellulose in 5 M urea. It no longer catalyzed the overall reaction, yet could still carboxylate free biotin. The biotin-free subunit was separated after dissociation of the enzyme by three-days' dialysis at pH 9.8 under nitrogen. On chromatography over a Sepharose-bound avidin column, the biotin-subunit was fixed and the biotin-free subunit was eluted unretarded. The latter subunit showed no enzymic activity. After the addition of the biotin-containing subunit, overall activity was regenerated. The speed of reassociation is very much enhanced by 3-methylcrotonyl-CoA. It was shown by reassociation experiments under different conditions that probably an initial complex, AxBy is formed, possessing a binding site for 3-methylcrotonyl-CoA. Upon the binding of this substrate the conformation may be changed to a form favourable for reconstitution. Finally, the structures of biotin enzymes from different sources are compared. In the course of evolution there is a tendency toward integration of the different constituent proteins into only one polypeptide chain.

Inhibition of pathogenic enteric bacteria by hyperbaric oxygen: enhanced antibacterial activity in the absence of carbon dioxide

The antibacterial effects of 24-h exposures to high-pressure oxygen in relation to environmental CO(2) were studied at 3 atm absolute (ata) and at 1 ata. Eight gram-negative, aerobic and facultatively aerobic, pathogenic enteric bacteria (Salmonella typhosa, Salmonella paratyphi, Salmonella schottmuelleri, Shigella dysenteriae, Shigella flexneri, Proteus vulgaris, Pseudomonas aeruginosa, and Escherichia coli) were exposed as shallow-broth cultures and agar surface cultures. Although broths supplemented with 0.2% glucose permitted some growth of Salmonella typhosa, Salmonella schottmuelleri, Shigella dysenteriae, and Shigella flexneri during exposure to high-pressure oxygen in the presence of CO(2), the other species grew only after the exposure, indicating a bacteriostatic effect. Both bacteriostatic and bactericidal effects were demonstrated on the surface of Trypticase soy agar, where killing of Salmonellea typhosa, Proteus vulgaris, and Pseudomonas aeruginosa was significantly greater after exposure to pure O(2) at 3 ata than at 1 ata. At 3 ata, significantly more killing occurred upon exposure of all species (except Shigella dysenteriae and S. flexneri) on an agar surface to 100% O(2) as compared with exposure to a mixture of 95% O(2) + 5% CO(2). Thus, deprivation of CO(2) during exposure to pure O(2) enhanced the bactericidal effect of high-pressure oxygen.

Inhibition of Pseudomonas aeruginosa by hyperbaric oxygen. I. Sulfonamide activity enhancement and reversal

To elucidate an explanation for in vitro sulfonamide enhancement by high-pressure oxygen (HPO) and the reported absence of enhancement with in vivo therapy, Pseudomonas aeruginosa cultures were exposed to selected antifolate antimicrobials in the presence of 1.87 atm absolute of O(2) and compared with non-HPO treated controls. Under these conditions, HPO alone retarded growth. Trimethoprim, a non-sulfonamide which inhibits dihydrofolate reductase, was not bactericidal, nor did HPO enhance existent bacteriostatic activity. The sulfonamide, sulfisozazole, was not bactericidal, but HPO enhanced bacteriostatic activity twofold; bacteriostasis was mitigated in HPO-treated and control cultures by p-aminobenzoate but not by a mixture of compounds involved in folate-mediated "1-C" biosynthesis. Mafenide, a unique sulfonamide, at high concentrations with HPO, was synergistically bactericidal; non-HPO-treated cultures were bacteriostatically inhibited. Bacteriostatic activity of lower mafenide concentrations was also enhanced at least twofold by HPO. These inhibitory effects of mafenide, acting with or without HPO, were mitigated by the above mixture, but not by p-aminobenzoate. This may explain the lack of in vivo HPO-mafenide enhancement in burn-wound sepsis where exudates would contain such a mixture. Lastly, HPO itself was largely bactericidal at 2.87 atm absolute of O(2). This was reversed to various degrees by the above mixture, or its components, or by folic, folinic, or p-aminobenzoic acids. These in vitro interactions suggest HPO per se may act at the same site as some sulfonamides to inhibit folate synthesis (not primarily at the dihydrofolate reductase level), or coenzyme functions of folate, or both.

Effect of high oxygen tensions on the growth of selected, aerobic, gram-negative, athogenic bacteria

The in vitro effects of high O(2) tensions (P(O2)) on aerobic, enteric pathogens were examined at pressures of up to 3 atm absolute. Organisms from the genera Salmonella, Shigella, and Vibrio were usually subjected to 24-hr exposures. Tensions of 0.87, 1.87, and 2.87 atm absolute of O(2) (plus traces of CO(2) and N(2)) became progressively inhibitory for Salmonella and Shigella growth, but were bactericidal only for V. comma strains at tensions greater than 0.87 atm absolute of O(2). Growth inhibition of enteric organisms resulted from increased P(O2), rather than pressure per se, and could be mitigated nutritionally; an appropriate carbohydrate source is at least partially involved. Further studies with vibrios indicated that such mitigation was independent of medium pH. In addition, a synergistic relationship existed between O(2) and sulfisoxazole when tensions from 0.87 to 2.87 atm absolute of O(2) were maintained for 3 to 24 hr. Synergism occurred even under nutritional conditions which negated growth inhibition by O(2) alone. Bactericidal concentrations of sulfisoxazole, in the presence of increased P(O2), were reducible up to 4,000-fold. The combined procedure employed in this investigation, by use of an antimicrobial drug of known action, which also synergizes with O(2), plus nutritional studies, suggests a means for establishing a site of O(2) toxicity. These data support the concept that O(2) inhibition of growth represents a metabolic disturbance and that metabolic pathways involving p-aminobenzoic acid may be O(2)-labile. Such an approach could also guide development of antimicrobial agents as O(2) substitutes for promoting synergism.

Synthesis of M protein by group A hemolytic streptococci in completely synthetic media during steady-state growth

Strains of type 6 (S 43) and type 14 group A streptococci were grown with M-protein production in the presence of chemically defined synthetic media slightly modified from that previously employed for the growth of a nonproducer of M protein (type 4). The M protein, which is associated with virulence in group A streptococcus, was previously produced in growing cultures only with complex media. The bacterial growth with the biosynthesis of M protein in synthetic medium was obtained by successive adaptation in steady-state culture with decreasing amounts of Todd-Hewitt broth. The synthesis continued for at least 480 generations at pH 7.3 and with a generation time of 84 min. Glucose was the limiting nutrilite and the concentration of reducing agents in the medium was critical. The M protein was identified by gel diffusion against type-specific antisera from the Communicable Disease Center and from R. Lancefield. The yield of M protein obtained from organisms grown in the continuous-culture device was comparable to that from standard broth stationary cultures.

Some effects of hyperbaric oxygenation on bacteria at increased hydrostatic pressures

The adverse effects of hyperbaric oxygenation on the reproduction and survival of bacteria are augmented by increased hydrostatic pressure. Different bacterial species differ considerably in their tolerance of increased hydrostatic pressure as well as for increased partial pressure of oxygen. Although their generation times may be lengthened and their reproduction rates retarded by increased pressures, most species of well-known bacteria are able to grow at hydrostatic pressures as high as 200–400 atm. In closed systems at 1 atm, certain aerobic bacteria grow well, or sometimes better, in nutrient media in which the partial pressure of oxygen is 5 to 10 times higher than that in the normal atmosphere (-Po2ca. 0.2 atm, equivalent to a dissolved oxygen content of ca. 7 μg/ml), but such increased concentrations of oxygen (35–70 μg/ml) are injurious at substantially increased hydrostatic pressures, for example, 5–25 atm. Escherichia coli, Bacillus subtilis, Bacillus megaterium, Pseudomonas enalia, Pseudomonas perfectomarinus, and Serratia marinorubra were sterilized within a day or two by compression to 100 atm in media having a dissolved oxygen content of 35 μg/ml. All six species thrived at 100 atm in nutrient media having an initial oxygen content of 7 μg/ml and they grew well in media with an oxygen content of 35 μg/ml at 1 atm.

Enhancement of antibiotic activity against Staphylococcus aureus by exposure to hyperbaric oxygen

Growth of Staphylococcus aureus ATCC 6538P was studied in stationary broth cultures (11 mm deep) exposed to hyperbaric oxygen (100% O(2) at 3 atm absolute). The minimal inhibitory concentration (MIC) of the following antibiotics was determined after exposure to high-pressure oxygen (HPO) for 3, 6, and 12 hr: penicillin, streptomycin, tetracycline, oxytetracycline, kanamycin, and cephalothin. Logarithmic growth during exposure to HPO was retarded 60%. Air at 3 atm absolute did not retard growth. The longer the exposure of tube dilution tests to HPO, the lower the MIC. Regardless of the antibiotic used, MIC values relative to 100% for unexposed controls were similar for given exposures, and averaged 73% after 3 hr of exposure to HPO, 53% after 6 hr, and 34% after 12 hr. Similar enhancement with HPO and an iodophor suggests occurrence of a general phenomenon with antibacterial agents. Although HPO alone is primarily bacteriostatic, combined therapy with antibiotics and HPO may be useful against bacterial infections because the therapeutic effectiveness of a maximal dosage of antibiotic could be increased.