- Volume 4, Issue 4, 1971

The activity of clindamycin, a new lincomycin derivative, was measured against over 500 strains of bacteria. The assessment was quantitative in terms of drug concentration and bacterial population size, and comparative in that the major groups of bacteria were tested simultaneously for their sensitivity to lincomycin, erythromycin, benzylpenicillin and oxacillin. Clindamycin at a low concentration was highly active against most Gram-positive cocci excepting Strep. faecalis, and showed appreciable activity against H. influenzae, but was inactive against enterobacteria. Two strains of coagulase-positive staphylococci out of 300 tested were highly resistant to clindamycin; a further seven showed a low degree of resistance. Resistance to lincomycin and erythromycin was considerably commoner. Variation in inoculum size produced a small change in MIC comparable with that found for lincomycin and erythromycin, but much less than that found for benzylpenicillin. On a weight-for-weight basis clindamycin was from 4 to 16 times more active than lincomycin against staphylococci.

Lysogenicity in coagulase-negative staphylococci was tested by incubating the strains in the presence of Mitomycin C. Among 173 strains examined, 45 were found to release phage. Twenty-eight of these phages were obtained from 90 strains belonging to Staphylococcus epidermidis biotype 1 (Baird-Parker, 1965).

Further study of the phages isolated from lysogenic strains of Staphylococcus epidermidis confirms that they are of at least two classes: (1) phages active only on other Staph. epidermidis strains and (2) phages initially active only on Staph. aureus strains but sometimes adaptable to lyse Staph. epidermidis strains. Ten phages of the first class, five adapted phages of the first class and three adapted phages of the second class could all be propagated on strains of Staph. epidermidis of biotype 1. They are all adsorbed by strains of Staph. epidermidis and belong to a single serological group that is distinct from the groups A, B, F and L of Staph. aureus phages.

A provisional set of 18 phages proposed for typing Staph. epidermidis is described and characterised.

The injection of galactan extracted from Mycoplasma mycoides into cattle subsequently infected with M. mycoides induced lesions in joints and kidneys and a prolonged mycoplasmaemia. Several treated animals developed pleurisy, but the only lung lesions were small and were present in both galactantreated and control animals. These effects occurred with galactan prepared from both virulent and avirulent strains and were evident at a dose rate of 0.66 mg per kg but not at 0.22 mg per kg. The supernatant fraction galactan F and the cell fraction L, which might be the same as the supernatant fraction, were equally active. The other cell fraction W did not induce lesions nor mycoplasmaemia.

The galactan had no effect on the rate of clearance of M. mycoides injected intravenously into cattle, nor did it reduce the resistance of vaccinated cattle.

Although the W fraction, when injected with Freund’s adjuvant into cattle, provoked CF antibody production, it did not induce resistance to airborne CBPP infection. It suppressed or delayed the complement-fixing antibody response to M. mycoides in those cattle that became infected after exposure to airborne infection.

The growth and pathogenicity of Mycoplasma gallisepticum were studied in chicken embryo tracheal organ cultures. In these cultures M. gallisepticum attained titres of 106-107 CCU per ml of Eagle’s medium and there was inhibition of ciliary activity. The cilia-stopping effect (CSE) was not closely related to dose, as a 50 per cent. reduction of ciliary activity occurred at about the same time after inoculation of organisms differing in number by as much as 100- to 10,000-fold. The addition of neuraminidase or catalase to the cultures did not inhibit the CSE of M. gallisepticum; in fact, the CSE was potentiated in cultures containing catalase. The CSE was present but delayed in organ cultures maintained in medium that contained M. gallisepticum, the continued multiplication of which was suppressed by tetracycline. Thus it seems that either the accumulation of toxic products in the medium contributes to tissue damage, or that the organisms themselves do so; but neither cytadsorption nor peroxide production appears to be important in the pathogenicity of M. gallisepticum.

As part of a study of the metabolic activities of intestinal bacteria, the activity of the principal glycosidases produced by the major groups of intestinal bacteria has been estimated. The results are discussed in terms of the toxicological and pharmacological effects of various ingested glycosides and of the enterohepatic circulation of compounds by four laboratory animal species commonly used in toxicological studies.

Pregnant sows were immunised either actively by injecting a bacterial extract or a killed bacterial suspension prepared from Escherichia coli serotype O138 :K81(B), or passively by injecting antiserum or immunoglobulins prepared against an extract of the same organism. Antibodies to this organism were detected in serum from the colostrum-deprived piglets of these sows by means of bactericidal, passive cutaneous anaphylaxis, haemagglutination, and antiglobulin-haemagglutination tests. The evidence suggests that piglets may be passively sensitised in utero as a result of the transfer of maternal antibody and that factors such as the character of the antibody and its fixation in the tissues may influence its detection in piglet serum. These results are discussed in relation to the role of hypersensitivity in the pathogenesis of E. coli disease in the newborn piglet.

Strains of Escherichia coli containing different combinations of the transmissible plasmids governing production of α-haemolysin (Hly), enterotoxin (Ent) and K88 antigen (K88) were prepared by the selective addition or removal of these plasmids and tested for ability to produce diarrhoea when given orally to naturally reared piglets and to recently weaned pigs.

The removal of the K88 plasmid from an O141 :K85ab,88ab strain was accompanied by the loss of its diarrhoea-producing capacity. It was restored by introducing a K88 plasmid from another strain of E. coli. The removal of the Hly plasmid had no observable effect. Neither did its removal from another wild enteropathogenic strain of antigenic formula O141 :K85ac; the Hly− form of this strain, like the Hly+ form, produced oedema disease in addition to diarrhoea.

As a consequence of receiving an Ent plasmid, a non-haemolytic O8 :K40, 88ab:H9 strain produced diarrhoea more frequently and more severely in piglets than hitherto; after the removal of the K88 plasmid it became non-enteropathogenic.

A non-pathogenic O9 :K36:H19 strain was rendered enteropathogenic by the introduction of plasmids. The K88+ Ent+ form produced moderately severe diarrhoea in piglets. A smaller proportion of those given the K88+ Ent− form developed a milder diarrhoea. The K88− Ent+ and the K88− Ent− forms had no observable ill-effect.

Bacteriological examinations on the animals given the different forms of the O141 :K85ab,88ab, the O8 :K40,88ab:H9 and the O9 :K36:H19 strains revealed that it was the K88 antigen that enabled the organisms to proliferate high up in the small intestine, an essential prerequisite in the pathogenesis of E. coli diarrhoea. The Ent plasmid appeared to play no part in this proliferation, only in the diarrhoea that followed.

The introduction of Hly into strains of E. coli was usually accompanied by an increase in virulence for mice challenged intraperitoneally, the extent of the increase varying according to the particular Hly plasmid introduced. Virulence was not related directly to haemolytic activity.

K88+ forms of strains of E. coli were less virulent for mice on intraperitoneal injection than were the corresponding K88− forms. So were K88+ forms of Salmonella typhimurium and S. choleraesuis after intraperitoneal and oral infection; the K88+ organisms were less able to survive in the alimentary tract and in the tissues than were the K88− ones. A K88+ form of S. choleraesuis was also less virulent for pigs than was the corresponding K88− form.

Parenteral administration of antiserum usually prevented pigs developing diarrhoea or oedema disease after experimental oral infection with entero-pathogenic strains of Escherichia coli, provided the antiserum had been prepared against the strain of E. coli used to produce the infection. The protection appeared to be principally bactericidal in nature. The antisera might also have had a protective effect against oedema disease that was not strain-specific, presumably by neutralising the metabolites of E. coli that cause this disease.

Rabbits were given an intravenous injection of sheep red cells. Some received red cells only, others were given, at the same time or at 24 hr or at 4 or 6 days after the red cells, an intravenous injection of a saline emulsion of a tubercle bacillary lipid. The haemolysin and haemagglutinin titres against sheep red cells were determined for serum samples taken before and at 2-day intervals after injection of red cells.

Animals given lipid at the same time as red cells showed an antibody response significantly greater in rate and magnitude than that in animals given red cells only. Lipid given 24 hr or more after injection of red cells had no effect on the antibody response.

The MIC of nystatin was determined for 1389 successive isolates of candida from clinical specimens, and of amphotericin B for 1307 successive isolates. A further 626 isolates of C. albicans were tested for sensitivity to nystatin and a further 708 to amphotericin B. All these were shown to be sensitive. After gradual exposure on solid media to increased antibiotic concentrations, isolates of seven candida species became resistant to nystatin, amphotericin B, candicidin, pimaricin, and filipin. Compared with the polyene-sensitive parent isolates, the resistant cultures showed decreased growth rate, reduced production of germ tubes, slower production of chlamydospores, reduced suspension stability, reduced ergosterol content, and reduced pathogenicity. Isolates resistant to one polyene were found to show cross-resistance to other polyenes. The fluctuation and Newcombe tests suggested that the development of resistance was due to mutation. Resistant isolates showed reversion to sensitivity and some return of their normal properties when no longer exposed to polyenes. There was no evidence of the transfer of resistance from one isolate to another.

Diphtheria toxin was titrated in primary cells, cell-lines and known tumour cell-cultures from nine animal species. The effects of toxin were assayed by the conventional cytotoxic test and by a dye-uptake method. Both tests placed the various cell-cultures in the same order of sensitivity to toxin, reflecting the sensitivity of the donor animals. The dye-uptake technique was found to be as reproducible as the cytotoxic test, and more precise, for calculating the sensitivity of cell cultures to diphtheria toxin.

Comparison of primary cells and cell-lines from the same animal species showed no constant pattern of sensitivity to toxin. For example, primary mouse cells were more sensitive than a mouse cell-line, and vice versa with rabbit cells. There was also variability in relative sensitivity of normal and tumour cells from the same species.

Incubation with Streptococcus pyogenes type 12 was shown to lead to marked alterations of the fucose, galactose, and total hexose content of human immunoglobulin G (IgG). Immunological studies showed at least partial identity of this altered IgG and normal IgG. Streptococcal antigen was not found in the altered immunoglobulin. We suggest that if such alterations occurred in vivo, the altered immunoglobulin might become autoimmunogenic or might possess the biological properties of immune complexes and thus be of immunopathological significance in post-streptococcal glomerulonephritis.

The resistance of vegetative cells of CI. welchii to low pH was tested in gastric juice and in peptone water of pH 1.5–3.6. The results showed that, for any given strain the death rate increased with decreasing pH; the death rate was dependent on the age of the culture—for cells grown in cooked-meat medium a 5-hr culture was more susceptible to low pH than a 24-hr culture of the same strain; the cells were more susceptible to gastric juice than to peptone water of the same pH.