Bactericidal Effect Of Serum Research Articles

Effect of Serum and Blood on Enterobacteriaceae Grown in the Presence of Subminimal Inhibitory Concentrations of Ampicillin and Mecillinam

Bacteria from the strains of five species of Enterobacteriaceae grown in the presence of subminimal inhibitory concentrations of ampicillin or mecillinam formed into filamentous or round cells. These filamentous and round cells as well as normal control bacteria were incubated with either fresh human serum or blood, the bactericidal effects of which were then determined. In most cases, the bactericidal effect of either serum or blood on filamentous or round cells was less than the effect on control cells. In some cases, the effect on these drug-exposed cells was similar to that on control cells, but in no instance was the effect greater for the drug-exposed cells than for the control cells. However, in all cases in which the bactericidal effect of either serum or blood on the control cells was greater than or equal to 99%, the bactericidal effect on the drug-exposed cells was close to 90%. Although drug-exposed cells were not much more resistant to the bactericidal effect of serum or blood than were normal bacteria, they clearly were not more susceptible to these effects.

Susceptibility of Isolates of Bacteroides to the Bactericidal Activity of Normal Human Serum

Seventy-one strains of species from the Bacteroides fragilis group, including 46 isolates of B. fragilis, were tested for susceptibility to the bactericidal effect of serum from healthy subjects. Twenty-seven (38%) of the isolates were killed by serum. Isolates from feces were significantly more sensitive to serum than were isolates from patients with clinical infections. Killing of bacteria required heat-labile serum components and was an exponential function of serum concentration. Among the various species tested, B. fragilis was clearly the most resistant to bactericidal activity of serum. These observations may be important to the understanding of infections caused by the B. fragilis group, which contains the anaerobes of greatest clinical importance.

Tetracycline interference with the bactericidal effect of serum.

INTACT host defence mechanisms are vitally important in the eradication of invading microbes. Certain drugs such as methimazole and phenylbutazone2 are known to interfere with the intracellular killing of microbes, but little attention has been paid to possible interactions between antibiotics and the complement system. We have shown (our unpublished results) that tetracyclines interfered with the bactericidal action of complement in vitro. Here we show the effect of ‘Doxycycline’ on the serum bactericidal system in vivo.

Specificity of opsonic and bactericidal response of gnotobiotic rat sera.

Using an indirect in vitro system, the bactericidal activity of gnotobiotic rat sera towards 22P‐labelled E. coli was tested. Furthermore, the opsonic effect of such sera was studied, measuring phagocytosis by rat peritoneal polymorphonuclear leucocytes. Monocontamination of germfree rats with different strains of E. coli resulted in a significant augmentation of both activities. The highest bactericidal and opsonic activities were obtained in sera from rats monocontaminated with the strain of E. coli used in the test system. The results also indicated that specific antibodies might be more important for the opsonic than the bactericidal effect of serum.

The effects of serum components on the agglutination of Gram-negative bacteria.

Fresh normal guinea pig serum was found to increase the agglutination titer of antiserum. Absorption of fresh serum with homologous bacterial cells did not remove the activity. Exposure of fresh serum to 56 C for 30 min, 0.01 M ethylenediaminetetraacetic acid (EDTA), or 150 μg/ml of lipopolysaccharide significantly decreased its activity. This reaction was shown to be initiated at 37 C, but not at 0 C, thus indicating an enzymatic reaction, possibly that of the complement system. Other sources of fresh serum were also found to mediate this reaction. Although this phenomenon requires further investigation, it should be considered when evaluating the bactericidal effect of serum from plate counts, as some decrease in numbers could be due to agglutination.

Endotoxic properties of gramnegative bacteria and their susceptibility to the lethal effect of normal serum.

effect of normal serum (Rowley, 1956), (b) an array of normal serum components including specific antibody, complement and lysozyme are required for conversion of Gram-negative bacteria to spheroplasts (Michael and Braun, 1959; Carey et al, 1960), and (c) in the course of the bactericidal action of serum there occurs a striking reduction in the endotoxic and antigenic properties of the bacteria (Landy et al, 1960). In the light of these developments implicating the somatic complexes as at least the primary target for the bactericidal effects of serum, an attempt was made to determine whether marked differences in the bactericidal effectiveness of serum on members of antigenically related bacterial strains are related to the content of endotoxin in these bacteria.