- Volume 30, Issue 3, 1989

The epidemiology of 10 episodes of CAPD peritonitis caused by coagulase-negative staphylococci was studied. The infecting micro-organism was found in prospective skin swabs in six episodes, widely distributed and as the predominant, or equally predominant, organism at each site but was not detected in swabs taken more than 12 weeks before the episode of peritonitis; this suggests recent acquisition. Infecting strains were no more likely to be adherent or to produce slime than non-infecting strains, nor had they any other characteristic detected in our typing scheme that might lead to their detection before peritonitis developed.

Radiometric selective inhibition tests were developed and evaluated for the rapid differentiation of Mycobacterium spp. Both a p-nitrobenzoic acid (PNB) test and a commercially-prepared p-nitro-α-acetylamino-β-hydroxypropiophenone (NAP) test successfully differentiated M. tuberculosis and M. bovis from ‘atypical’ mycobacteria or mycobacteria other than tubercle bacilli (MOTT). Thiophene-2-carboxylic acid hydrazide (TCH) readily distinguished human M. tuberculosis strains from M. bovis, irrespective of resistance to isoniazid. Both PNB and TCH tests were utilised in a routine radiometric susceptibility testing scheme over a period of 1 year in which 110 isolates of M. tuberculosis, 10 of M. bovis and one isolate of BCG were correctly differentiated from 10 isolates of MOTT. The rapidity, sensitivity and specificity of these radiometric tests can play a useful role in mycobacterial identification.

We studied the influence of cyclosporin-A (Cy-A) on resistance of mice to systemic infection with Candida albicans. Cy-A clearly inhibited resistance to C. albicans. The effect was dose-dependent and time and route of administration of the drug were important. This immunodepressive effect was due, at least in part, to an impairment of polymorphonuclear leucocyte (PMNL) candidacidal activity, as demonstrated in vitro by a reduction of phagocytic and cytotoxic activity and in vivo by protection when PMNL from untreated mice were transferred into cyclophosphamide-treated hosts challenged with C. albicans. The decreased activity of PMNL could be partly restored by adoptive transfer of normal T-lymphocytes into Cy-A-treated mice, as well as by exposure of PMNL to gamma-interferon (IFN-γ) in vitro.

Survival of mice infected with an intravenous injection of Candida albicans was observed in a short-term (21-day) survival study. Concentration of C. albicans in the kidneys, liver, and spleen was determined at various times. The effects of treatment with the commercial formulation of amphotericin B (fAMB), liposomal amphotericin B (LAMB), and liposomal amphotericin B bearing external antibody specific for C. albicans (LAMB-Ab) were compared. In single intravenous treatment dosages of 0.6 mg of amphotericin B/kg, the liposomal forms of the drug (LAMB and LAMB-Ab) enhanced the percentage survival and mean survival time of mice in comparison with those treated with the unencapsulated antifungal compound, fAMB (p <0.03 and p<0.001, respectively). LAMB-Ab, at this dosage, produced an increase in the survival (p<0.007) of mice over that produced by LAMB. LAMB-Ab treatment caused a greater than 3-fold increase over fAMB. The percentage of LAMB-Ab-treated mice which survived for 21 days was almost double that of the LAMB-treated mice. The increase in survival following this treatment did not, however, lead to the eradication of C. albicans in all mice which survived to the end of the experiment.

An infant mouse model has been used to investigate the colonisation of the intestine by Campylobacter jejuni and the effect of endotoxin (Escherichia coli O26: B6) on the initial stage of this process. Endotoxin injected 1 or 16 h before the bacterial challenge had no effect on the growth of campylobacters but endotoxin injected 4 to 10 h before the bacterial challenge caused a bacteriostatic effect on the growth of campylobacters which lasted for one day. The bacteriostatic effect was evident both in the small intestine and in the distal part of the intestine containing caecum and colon. The mechanism of the bacteriostatic effect of endotoxin could not be explained in the study, but is thought to be non-immunological because it developed so rapidly. Oral and parenteral iron administered as ammonium ferric citrate or iron dextran, respectively, were used in an attempt to reverse the bacteriostatic effect. High oral doses of iron (0.5 mg per animal) were effective but small doses (0.5 mg per animal) were ineffective. Parenteral iron administration had a delayed effect on the reversal of the bacteriostatic effect of endotoxin. Transferrin administered orally caused a clear bacteriostatic effect in both endotoxin pretreated and untreated mice. Campylobacter counts were always lower in the small intestine than in the large intestine both in control and in endotoxin pretreated mice. This indicates that the large intestine is the primary ecological niche where campylobacters colonise mice.

Antisera to two antigens of Giardia lamblia—plasma membrane (PM) protein and an affinity-purified surface antigen (SA56)—were raised in rabbits, and shown to agglutinate and kill trophozoites in vitro. These antibodies were also demonstrated by ELISA in the sera of paediatric patients with giardiasis. The titres of both antibodies were significantly higher in non-persistent (acute) and asymptomatic cases than in patients with persistent infection; and the latter group did not respond to anti-giardial therapy. The inability of this group to clear G. lamblia infection, in spite of therapy, may result from the low level of antibodies which mediate the killing of trophozoites.

The choice of strain, culture conditions, composition of medium and size of inoculum all affected the expression of a cholera-toxin-related antigen (CTRA) in Salmonella typhimurium. A previous study had shown that the number of organisms expressing CTRA in Casamino acid Yeast Extract (CYE) medium decreased between 4 h and 6 h in uninterrupted culture. In the present experiments, organisms harvested at 4-5 h were subcultured into fresh CYE medium and incubated for a further 2 h; the total number of organisms increased, and the decrease in the proportion of organisms expressing CTRA was reduced. Use of Hartley Digest Broth in place of CYE medium increased the proportion of organisms expressing CTRA in all strains tested, in both the uninterrupted and the subculture procedures. The higher the initial inoculum, the lower was the proportion of organisms expressing CTRA. The presence of the antigen in cells remained constant for about 18 h after transfer from 37°C to 4°C. These data have important implications for the production and purification of CTRA: they show that it was expressed during log-phase of growth, and they suggest that expression was regulated by a non-growth-limiting factor. Moreover, some avirulent strains were better producers of the antigen than virulent ones. The significance of the data is discussed in relation to the in-vivo situation.

Fourteen hybridoma cell lines were isolated that produced monoclonal antibodies (MAbs) to purified Verotoxins 1 and 2 (VT1, VT2) of Escherichia coli of serotype O157:H7. Of these MAbs, eight were obtained by immunisation of BALB/c mice with purified VT1, and six were obtained from BALB/c mice immunised with purified VT2. With the exception of MAb 1C5, with a heavy chain of IgG2b class, antibodies produced from mice immunised with heat-treated toxin were of IgM class. MAbs produced from mice immunised with heat-treated VT1 or VT2 reacted with both verotoxins in ELISA, and Western-blot analysis revealed that they reacted with subunit A and the A1 fragment of nicked subunit A of both toxins, but not with subunit B; furthermore, none of them neutralised Vero cytotoxicity or mouse lethality of either toxin. In contrast, MAbs produced from mice immunised with heat-treated and formalin-treated VT1 reacted in Western blots with subunits A and B of VT1 and subunit A, but not subunit B, of VT2, reacted in ELISA with VT1 only, and neutralised Vero cytotoxicity and mouse lethality of VT1 but not of VT2. Results indicate the existence of a common epitope on subunit A of VT1 and VT2 that is not responsible for the biological activity of these toxins, and that subunit B is essential for the biological activity of VT1. MAbs capable of reacting with both verotoxins from E. coli of serotype O157:H7 may be useful reagents for screening bacterial isolates capable of producing one or both of these toxins.

The bactericidal activity of compound DR-3355, an optically active isomer of ofloxacin, was measured against Escherichia coli, Staphylococcus aureus and S. epidermidis, in nutrient broth and in phosphate-buffered saline. DR-3355 was found to be approximately twice as active as ofloxacin in terms of the concentration at which maximum bacterial kill was achieved. Hence it appears that DR-3355 is twice as active as ofloxacin not only in terms of its ability to inhibit bacterial multiplication but also in its ability to kill bacteria. DR-3355 was found to be active against non-dividing bacteria and did not require either active RNA or protein biosynthesis in order to kill bacteria.

Conventionally reared female BALB/c mice, rendered susceptible to Mycoplasma hominis infection of the genital tract by treatment with oestradiol, have increased numbers of endogenous vaginal bacteria. The latter was reflected by the occurrence of bacterial growth in 95 (65.5%) of 145 cultures undertaken to isolate M. hominis from oestradiol-treated mice, but in only seven (4.8%) of 146 cultures from untreated animals. In addition, larger numbers of bacteria were seen in vaginal smears from oestradiol-treated mice than from untreated ones. Furthermore, abscesses developed in the genital region of 27 (17%) of 155 oestradiol-treated mice but in none of 50 that were untreated. However, such proliferation of the endogenous vaginal bacteria was not necessary for colonisation of the vagina by M. hominis. This was determined by showing that six germ-free, oestradiol-treated BALB/c mice given 2.5 x 105 ccu of M. hominis intravaginally became colonised vaginally for at least 14 days, with multiplication and spread of the organisms to the upper genital tract and elsewhere, whereas six similar untreated mice given the same inoculum remained uninfected.