- Volume 5, Issue 3, 1972

The effect of food and water deprivation (stress) on asymptomatic carriage of Salmonella was investigated in mice given Salmonella typhimurium intra-nasally. Groups of mice were killed and examined by cultural and serological techniques before, during, and after a 3-day stress period. The numbers of salmonellae in the stomach, small intestine, and caecum+large intestine increased during the stress period, with the greatest increases occurring after 2–3 days. Stress-induced changes within the carrier animal apparently allo wthe multiplication of salmonellae to occur throughout the gastro-intestinal tract.

The pathogenic avian mycoplasma M. gallisepticum caused a 50 per cent. reduction of ciliary activity in chicken tracheal organ cultures after 4–5 days. Nine days were required for a similar loss of activity when the non-pathogenic mycoplasma M. gallinarum was introduced into the cultures 24 to 48 hr before M. gallisepticum. The protective effect occurred only with viable M. gallinarum organisms and did not involve inhibition of the growth of M. gallisepticum. The phenomenon was observed with most strains of M. gallisepticum and all strains of M. gallinarum tested. A single strain of M. hominis failed to protect the ciliary activity of M. gallisepticum-infected cultures. Chicken tracheal organ cultures infected with M. gallinarum alone showed more prolonged ciliary activity than cultures uninfected with any mycoplasma. The possible reasons for these phenomena are discussed.

Strains of Escherichia coli K12F- to which Ent plasmids from a human and a porcine enteropathogenic strain of E. coli had been transmitted yielded cellfree preparations that produced diarrhoea when administered orally to baby rabbits. The preparations obtained from the strain containing the “porcine” plasmid was more active in this respect than were those of the strain containing the “human” plasmid. This difference was also observed when preparations of wild human and porcine enteropathogenic strains were compared. The diarrhoea produced in the baby rabbits resembled that produced by Vibrio cholerae enterotoxin.

The diarrhoea-producing activity of cell-free preparations of the K12 strain that contained the “porcine” Ent plasmid could be neutralised by antiserum against either this strain or V. cholerae; so could cell-free preparations of V. cholerae, but more heterologous than homologous antiserum was required in each case to achieve neutralisation.

A simple method is described for the inactivation of contaminating bacteriophage in concentrated pyocin preparations prepared from induced lysates of Pseudomonas aeruginosa. It is possible to destroy the plaque-forming ability of the bacteriophage by treatment with ultraviolet light and at the same time to preserve approximately 65 per cent. of the pyocin activity.

The effect of ultraviolet light on a concentrated bacteriophage preparation was studied, and it was shown that some residual inhibition activity remained. However, it is not likely that the lysogenic phage in concentrated pyocin preparations will be of a high enough titre to produce inhibition reactions.

It is now proposed to use pyocin extracts prepared in this way as typing reagents in a pyocin typing scheme based on the inhibition patterns produced when a number of different pyocins are spotted on to lawns of unknown test strains.

Sera from 303 pregnant women were examined for antibodies to Candida by means of a precipitin test in gel. Three preparations derived from C. albicans, type A (mannan antigen, cytoplasmic antigen and culture-filtrate antigen), were used, each at two concentrations.

Precipitins to all three antigens were found more frequently in the sera of women with mycotic vulvovaginitis than of other women. When serum precipitins were present and C. albicans was isolated from the vagina there was nearly always clinical evidence of vaginal thrush.

Strains of Escherichia coli showed two types of response to erythromycin in conventional doubling-dilution titrations. For 11 of 16 strains, the original inoculum could be wholly or largely recovered from tubes in which there was no growth after overnight incubation. For the remaining five strains, no survivors could be recovered from tubes in which growth was inhibited. Two strains selected as typifying the bacteristatic and bactericidal responses behaved differently when exposed to erythromycin and continuously diluted with fresh medium as in the urinary bladder. Growth, and also lysis by ampicillin, of a strain showing the bactericidal response were inhibited by lower concentrations of erythromycin than those required to produce comparable effects in a strain showing the bacteristatic effect. On the other hand, the inhibitory effects on growth and ampicillin lysis disappeared as continuing dilution reduced the concentration of erythromycin below the MIC for a strain showing the bactericidal effect but not for the strain showing the bacteristatic effect.

The pathogenesis of Mycoplasma pulmonis infection was studied in normal mice and in thymectomised, X-irradiated, anti-lymphocyte-treated mice. The immunosuppressed mice were more readily infected by the intranasal route than were normal mice, although the mycoplasmas multiplied to only a slightly greater extent in the lungs of the deficient animals. Spread of mycoplasmas from the lungs to other organs, such as the brain, occurred more frequently in the immunologically deficient mice. Cell-mediated immunity appeared to be important in the development of the pulmonary lesions. Thus, the lungs of normal mice showed marked peribronchiolar and perivascular cuffing by lymphocytes, but this was much less prominent in the immunosuppressed mice and macrophages were also fewer in number.

Immunofluorescence studies provided further evidence for the important role of cell-mediated immune mechanisms in M. pulmonis infections in mice. The way in which such mechanisms may operate is discussed.

A heat-stable enterotoxin from a strain of Escherichia coli enteropathogenic for calves was subjected to dialysis and ultrafiltration, and the resulting fractions were tested in Thiry-Vella loops in calves.

The active material was dialysable, and could be demonstrated in the dialysate. After 7 days’ dialysis, the activity remaining in the dialysand was not significant.

Ultrafiltration suggested that the molecular weight of most of the active material was between 1000 and 10,000, although a small amount appeared to have a molecular weight less than 1000.

Piglets immediately after normal birth were removed from their mothers and given Escherichia coli antisera by mouth and then infected, also by mouth, with an enteropathogenic strain of E. coli (O141: K85ab,88ab) mixed with larger numbers of a non-pathogenic E. coli strain and lactobacilli.

When antisera prepared against live, heat-killed or methanol-killed organisms of the O141: K85ab,88ab strain were used, the onset of diarrhoea was delayed or prevented. Antisera prepared against porcine enteropathogenic strains not possessing any of the O or K antigens of O141: K85ab,88ab had little effect. So did antiserum against E. coli K12 to which the plasmid responsible for porcine enterotoxin production (Ent) had been transmitted. Antiserum prepared against an enteropathogenic strain O8: K87,88ab had a definite controlling effect, the effect apparently being due to the K88ab antigen common to this strain and the infecting O141: K85ab,88ab strain.

Antisera administered subcutaneously also had a controlling effect on experimental E. coli diarrhoea, but their effect was markedly less than that of the same sera given orally.

Only low concentrations of enteropathogenic E. coli organisms were found in the contents of the small intestine of piglets in which the diarrhoea was controlled by antiserum, indicating that antibacterial antibody was important in his respect.

Sub-inhibitory concentrations of EDTA reduce the resistance of strains of Pseudomonas aeruginosa to carbenicillin in vitro. With strains made resistant by habituation, the extent of the reduction of carbenicillin resistance produced by a fixed subinhibitory dose of EDTA (200 μg per ml) did not vary with the degree of resistance even though the development of this habituated resistance was associated with a loss of sensitivity of the bacterial cells to EDTA. This suggests (1) that the reduction of habituated carbenicillin resistance by EDTA is due to a synergistic effect of the EDTA-carbenicillin combination, and (2) that the development of habituated carbenicillin resistance in Ps. aeruginosa is due to a change in type or amount, or in both, of cell-wall lipopolysaccharide.

In carbenicillinase-producing resistant strains of Ps. aeruginosa, the amount of reduction of carbenicillin resistance by EDTA is variable and appears to be inversely related to the quantity of carbenicillinase produced by the bacterial strain.

Cultures of Escherichia coli of human and animal origin were ingested by three normal persons. It was easy to produce temporary colonisation of the bowel by strains from both sources. Considerable variation in duration of carriage was observed. Some of the results were compatible with the view that colicines determined the fate of ingested strains. In other instances, however, colicines were ineffective in vivo although activity could be demonstrated in vitro.

A substance with the characteristics of a specific antibody was found in immune guineapig sera. It had inhibitory activity towards the growth of promastigotes and cytotoxicity to the amastigote form of Leishmania enriettii. The inhibitory effect was shown by direct counting of viable leptomonads. The cytotoxicity of immune sera on amastigotes was evaluated on the basis of morphological changes as well as of a decrease in the number of the organisms. The substance responsible was found to be heat stable and complement dependent. The activity could be removed by the specific absorption.

A method is described of inhibiting the swarming of Proteus in cultures of clinical material by the use of a flagellotropic phage, which has a wide range of activity on members of the Proteus-Providence group. The sensitive proteus strains formed isolated colonies, and the accompanying organisms could be obtained in pure culture.