Effect of Lactic Acid Bacteria on Growth of Staphylococcus aureus

Cultures of lactic acid bacteria, mostly from foods, were tested for their effect on the growth of Staphylococcus aureus in Trypticase Soy Broth (BBL). Some of the effectors, e.g., Streptococcus faecalis, S. faecium, Lactobacillus lactis, L. brevis, and Leuconostoc mesenteroides, stimulated growth of S. aureus during early hours of growth, especially at higher temperatures of incubation, but most cultures were inhibitory, and some (S. faecium and L. mesenteroides) were even killing by the time of attainment of the maximal phase of growth of the Staphylococcus. Low-temperature meat lactobacilli and Leuconostoc dextranicum inhibited S. aureus at 10, 15, 20, and 25 C throughout its growth. Streptococcus faecalis var. liquefaciens inhibited at these temperatures and at 30 and 37 C, as well. When the ratio of effectors to staphylococci in the inoculum was 100:1, the three enterococci, the meat Lactobacillus, and L. dextranicum prevented the attainment of 5 x 10(6) staphylococci per milliliter at 15 C, and all but the meat Lactobacillus did so at 22 C. A ratio of 1:1 accomplished similar results at 15 C, except that S. aureus was only delayed for 12 hr by S. faecalis. A ratio of 1:100 usually was ineffective. In general, the more effector bacteria there were in the inoculum, the greater was the overall inhibition (or stimulation) of S. aureus. Inhibition was most effective at 10 or 15 C, less so at 20 or 25 C, and least at 30 or 37 C, whereas stimulation during early growth was greater at the higher temperatures. Results with different strains of the effectors and with two strains of S. aureus were similar, for the most part.     

Formation of Protoporphyrin from Coproporphyrinogen in Extracts of Various Bacteria

The enzyme system capable of converting coproporphyrinogen to protoporphyrin was demonstrated in the soluble fraction of extracts of Pseudomonas fluorescens grown aerobically, of P. denitrificans grown anaerobically under denitrifying conditions, and of Escherichia coli grown both aerobically and anaerobically. Protoporphyrin accumulation by each of these extracts occurred only if the assay was conducted aerobically. Attempts to replace this oxygen requirement with several alternate electron acceptors were not successful. The conversion of coproporphyrinogen to protoporphyrin could not be demonstrated in extracts of the heme-containing organisms Staphylococcus epidermidis and Bacillus subtilis.     

Effect of Selected Lactic Acid Bacteria on Growth of Staphylococcus aureus and Production of Enterotoxin

Representative strains of 15 species of lactic acid bacteria were examined for their ability to influence growth of Staphylococcus aureus and production of enterotoxin in associative culture. Among the organisms used as effectors the streptococci were most inhibitory, followed by Pediococcus cerevisiae. The lactobacilli and Leuconostoc citrovorum were not inhibitory to growth and only slightly inhibitory to production of enterotoxin. Enterotoxin was detected in all cultures in which the population of S. aureus reached 8 x 10(7) per ml. At lower S. aureus populations no enterotoxin was detected after incubation for 48 h. Mechanisms of inhibition of growth and enterotoxin production by S. aureus strain 243 grown in association with Streptococcus lactis A64 or P. cerevisiae 10791 in APT broth were investigated. Competition for vital nutrients, especially niacin and biotin, and probably production of hydrogen peroxide contribute to inhibition. Production of lactic acid appears to inhibit growth of S. aureus in the early but not the late stages of incubation.     

Comparison of Purified Alpha-Toxins from Various Strains of Staphylococcus aureus

Alpha-toxin from five strains of Staphylococcus aureus, including Wood 46, was purified by isoelectric focusing. The alpha-toxins obtained from different strains were similar. The isoelectric point of the purified toxins was 8.65 +/- 0.15. Sharp concentration peaks were not always obtained. In the ultracentrifuge the alpha-toxins migrated usually as three peaks which could be dissociated with propionic acid to yield one peak. A single line of identity was obtained in immunoelectrophoresis when a heterologous antiserum was reacted with the five purified toxins. It was concluded that the widespread use of the Wood 46 strain for the production of alpha-toxin is justified.     

Repression of Staphylococcus aureus by Food Bacteria: I. Effect of Environmental Factors on Inhibition1

The effects of environmental factors on the inhibition of an enterotoxin-producing strain of Staphylococcus aureus by food bacteria were investigated. Type of medium and temperature of incubation were important factors in determining the amount of inhibition. The pH range of maximal inhibition was found to be 7.4 to 6.2. Availability of oxygen was not a factor. As the ratios of inhibitor to staphylococcus were increased from 1:1 to 10:1 and 100:1, the amount of inhibition was markedly increased. Inhibition occurred in custard, where it increased with increasing ratios of effector to staphylococcus. The repression of the staphylococcus in all media usually was sufficient to be of practical significance.     

Killing of Staphylococcus aureus via Magnetic Hyperthermia Mediated by Magnetotactic Bacteria

Staphylococcus aureus is a common hospital and household pathogen. Given the emergence of antibiotic-resistant derivatives of this pathogen resulting from the use of antibiotics as general treatment, development of alternative therapeutic strategies is urgently needed. Here, we assess the feasibility of killing S. aureus cells in vitro and in vivo through magnetic hyperthermia mediated by magnetotactic bacteria that possess magnetic nanocrystals and demonstrate magnetically steered swimming. The S. aureus suspension was added to magnetotactic MO-1 bacteria either directly or after coating with anti-MO-1 polyclonal antibodies. The suspensions were then subjected to an alternating magnetic field (AMF) for 1 h. S. aureus viability was subsequently assessed through conventional plate counting and flow cytometry. We found that approximately 30% of the S. aureus cells mixed with uncoated MO-1 cells were killed after AMF treatment. Moreover, attachment between the magnetotactic bacteria and S. aureus increased the killing efficiency of hyperthermia to more than 50%. Using mouse models, we demonstrated that magnetic hyperthermia mediated by antibody-coated magnetotactic MO-1 bacteria significantly improved wound healing. These results collectively demonstrated the effective eradication of S. aureus both in vitro and in vivo, indicating the potential of magnetotactic bacterium-mediated magnetic hyperthermia as a treatment for S. aureus-induced skin or wound infections.     

Effect of Gramicidin on Methanogenesis by Various Methanogenic Bacteria

Methanogenesis by Methanobacterium thermoautotrophicum strains was extremely sensitive to gramicidin, total inhibition being observed at 0.2 μg/ml. In contrast, methane synthesis by Methanococcus voltae, Methanogenium marisnigri, Methanosarcina mazei, and Methanospirillum hungatei were resistant to the highest concentrations of gramicidin tested (40 μg/ml), although spheroplasts of Methanospirillum hungatei were extremely sensitive. Other species tested showed intermediate sensitivity to gramicidin, methanogenesis inhibition occurring at 4 to 20 μg/ml.     

Effect of High Oxygen Concentration on Virulence of Staphylococcus aureus

Cultures of Staphylococcus aureus were agitated and treated with oxygen or air for a period of 29 days. At intervals of 1, 3, 9, 15, and 29 days, samples of washed cells were tested for coagulase activity and for abscess-producing ability. It was found that aeration with agitation initially increased abscess formation and that the increase was of the same magnitude for oxygen and air. Continued treatment beyond 1 day resulted in a progressive decrease in this activity which was more pronounced in the oxygenated cultures. Throughout the treatment, the bound coagulase activity remained constant. Thus, there appeared to be no quantitative relationship of coagulase titer with virulence as expressed by lesion formation.     

Effect of Staphylococcus aureus serine proteinase on human lymphocyte impairment

Assessment of lymphocyte surface membrane integrity by means of trypan exclusion test and longer term survival studies based on 3HTdR uptake and Con A stimulation test were used to estimate effect of Staphylococcus aureus serine proteinase on human lymphocytes in vitro. At concentration of proteinase as high as 10 micrograms/ml, the percentage of trypan-stained lymphocytes increase with enzyme level. In contrast, decrease of 3HTdR level and Con A stimulation is already apparent at concentrations of proteinase ten times lower. Autologous serum exerts strong protective effect. Observed impairment is discussed as significant for local response in inflammation.     

Effect of mild acid on gene expression in Staphylococcus aureus

During staphylococcal growth in glucose-supplemented medium, the pH of a culture starting near neutrality typically decreases by about 2 units due to the fermentation of glucose. Many species can comfortably tolerate the resulting mildly acidic conditions (pH, approximately 5.5) by mounting a cellular response, which serves to defend the intracellular pH and, in principle, to modify gene expression for optimal performance in a mildly acidic infection site. In this report, we show that changes in staphylococcal gene expression formerly thought to represent a glucose effect are largely the result of declining pH. We examine the cellular response to mild acid by microarray analysis and define the affected gene set as the mild acid stimulon. Many of the genes encoding extracellular virulence factors are affected, as are genes involved in regulation of virulence factor gene expression, transport of sugars and peptides, intermediary metabolism, and pH homeostasis. Key results are verified by gene fusion and Northern blot hybridization analyses. The results point to, but do not define, possible regulatory pathways by which the organism senses and responds to a pH stimulus.