- Volume 20, Issue 1, 1985

A microbiological survey has been undertaken of comedones isolated by micro-dissection from skin biopsies. Of closed comedones 10.7% and of open comedones 7.1% did not contain Pityrosporum spp., Propionibacterium spp. or Staphylococcus spp., the organisms most frequently associated with the pathogenesis of acne. Mature comedones were more frequently colonised than were young comedones. These results support the argument that the presence of microorganisms is not a prerequisite for comedo formation. Other pathological and ecological implications of these results are discussed.

To test the hypothesis that the in-vivo antibiotic action of tetracycline might be affected by ferric iron and the enhancement of infection by ferric iron by tetracycline, the actions of intraperitoneal antibiotic and local ferric ammonium citrate, given separately and together, were measured in the dorsal skin of guinea-pigs bearing lesions due to staphylococci, streptococci, a Proteus sp., an Erysipelothrix sp., Clostridium perfringens, Pseudomonas aeruginosa, Aeromonas hydrophila and Klebsiella pneumoniae.

Tetracycline, given in two intraperitoneal doses of 25 mg/kg at 0 and 2 h after intracutaneous challenge, maintained plasma concentrations of 4-6 μg/ml for more than the first 4 h of infection, after which the local lesions had become largely insusceptible to the antibiotic. The intracutaneous injection of Fe+++ 10 μg in a volume of 0·1 ml containing the bacteria was sufficient to enhance infection by those strains susceptible to this effect.

The in-vivo efficacy of tetracycline was not always related to low MIC; a low MIC was sometimes associated with little action and a high MIC with moderate action.

Sixteen organisms were tested. The iron diminished the tetracycline effect only feebly with one staphylococcal strain and the strain of E. rhusiopathiae. In only one case, with a strain of Proteus sp., was the tetracycline action grossly diminished. On the other hand, tetracycline diminished the enhancement effect of iron moderately with three strains of staphylococci and one strain each of K. pneumoniae, P. aeruginosa and C. perfringens, and strongly with two strains of staphylococci, a group-C streptococcus and one strain each of K. pneumoniae, E. rhusiopathiae and A. hydrophila.

It is evident that the diminution of tetracycline action by moderate excess of readily available Fe+++, whether endogenous or administered, is an unlikely event (three instances among the 16 tested) whereas the diminution of the infection-enhancing effect of iron by tetracycline is much more likely (12 instances among the 16). Insofar as a decrease in iron available for enhancement of infection is valid evidence of a

Herpes simplex virus (HSV) type-1 was isolated from a fatal case of herpes simplex encephalitis (case 1) and from a fatal case of disseminated herpes simplex (case 2). The virus was isolated from the lip lesion, the frontal lobe and the temporal lobe of the brain in case 1 and from a mesenteric node, myocardium and salivary gland in case 2. Restriction endonuclease digestion analysis showed that each case was infected with different substrains of HSV. The changes in band pattern in isolates from case 1 occurred in the “variable” region of the genome, showing that viruses with such variations can be isolated simultaneously from different tissues. The changes in band patterns in isolates from case 2 indicated the presence of two virus substrains, one in the mesenteric node and salivary gland and a second in the myocardium.

Neutrophil chemiluminescence was used to assess the opsonins required for phagocytosis of non-typable Haemophilus influenzae isolated from sputum samples of patients with hypogammaglobulinaemia. Immunoglobulin was the major opsonin, whereas complement was relatively unimportant. Evidence was found for a heat-labile opsonin other than complement that enhanced phagocytosis of these organisms. Tuftsin was shown to aid phagocytosis of H. influenzae without triggering chemiluminesence.

A screening method for plasmids in the fragilis group of Bacteroides spp. was developed, taking account of the lysozyme resistance of these species; 26 strains, 24 of them B. fragilis, were investigated by this method. Eleven strains contained plasmids and up to three different plasmids were found in individual strains. The plasmids belonged to five different size classes of mol. wt (106) 2·8, 3·5, 3·6, 4·2 and 19. Plasmids of equal size showed homology; no homology was found between plasmids of different sizes. Plasmids of equal size showed identical restriction patterns with 17 restriction endonucleases. Restriction maps were constructed for the five classes of plasmid.

Methicillin-resistant Staphylococcus aureus (MRSA), currently causing problems in Australian hospitals, have chromosomal penicillinase and carry a new family of incompatibility group I (IncI) plasmids that encode resistance to nucleic acid-binding compounds (NAB). These plasmids may carry additional determinants for penicillinase production and resistance to gentamicin and trimethoprim. By comparison, earlier MRSA isolates from Australia were NAB-sensitive and the penicillinase determinants were carried on IncI plasmids. The possibility that these newer MRSA isolates have the same ‘clonal’ origin as other MRSA isolates has been investigated. Forcible maintenance of IncI penicillinase plasmids and NAC-resistance plasmids in the same cells resulted in various recombination events. Similar recombination events to those generated in the laboratory have been found in MRSA isolates.

Solutions of Clinifeed ISO, Triosorbon, Vivonex Standard (full- and half-strength) and Vivonex HN were experimentally contaminated with two strains each of Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella aerogenes, Escherichia coli and Enterobacter cloacae at concentrations of 102-103 organisms/ml. Samples were incubated at 4,25 or 37°C and viable counts were made at 0, 4, 8 and 24 h.

No increase in numbers of any of the organisms was observed in any of the feeds during 24 h at 4°C. All organisms multiplied rapidly in Clinifeed ISO and in Triosorbon at 25 and 37°C. There was less rapid growth in half-strength Vivonex Standard at 25°C, although at 37°C all strains multiplied rapidly except for the two S. aureus strains, the growth of which was inhibited in half-strength Vivonex Standard at both 25 and 37°C. In full-strength Vivonex Standard at 25°C, only P. aeruginosa showed any increase in numbers during 24 h, whereas P. aeruginosa, K. aerogenes and E. cloacae all multiplied at 37°C. None of the test organisms multiplied in full strength Vivonex HN at any of the temperatures studied.

The results of the study show that bacteria survive and may multiply even in feeds with low pH and high osmolarity, and emphasise the importance of strict hygiene during the preparation and handling of all enteral feeds.

A competitive ELISA procedure for the detection of Escherichia coli heat stable enterotoxin (ST) with monoclonal antibody has been developed. This test is 10 times more sensitive than the suckling-mouse bioassay and it is specific, simple and cheap. A set of 882 strains of E. coli isolated from man were tested both by ST-ELISA and suckling-mouse bioassay, the latter serving as the reference method. Positive results in both tests were obtained with 152 strains. The remaining strains gave negative results in both tests, with the exception of two strains, known to be ST producers, that gave negative results in the suckling-mouse assay, but gave positive results by the ELISA method.

API and morphological tests were examined for their ability to distinguish between 37 Bacillus anthracis strains (virulent and avirulent) and 194 strains of closely related Bacillus species (B. cereus, B. mycoides and B. thuringiensis). In addition, 34 strains of B. anthracis and four of B. cereus were tested by several other methods that included capsule formation, ability to grow on a selective medium, and sensitivity to phage. It was found that virulent strains of B. anthracis were easily separated from the closely related Bacillus species by most of the test methods; but separation of slightly virulent and avirulent strains of B. anthracis from the closely related species could be done only by API and phage-sensitivity tests.

Seven materials used in the manufacture of tampons-four rayon, one modified rayon, one cotton and one carboxy-methyl cellulose (a modified cotton)-were compared for their effects in vitro on the physiology of a strain of Staphylococcus aureus isolated from a patient with Toxic Shock Syndrome. Experiments were performed in broth culture and, with the exception of two rayon samples, all of the materials tested reduced growth rate and cell yield compared with control values.

Exocellular acid phosphatase, lipase, proteinase, hyaluronate lyase and haemolysin in culture filtrates were measured and the lethality of filtrates was determined in mice. The tampon materials had different effects on the levels of exocellular products. Cotton and carboxy-methyl cellulose cotton materials reduced the levels of all of the activities tested. The activities of the other enzymes were reduced or increased, depending on which material was present. All materials reduced both haemolytic activity and lethality of the culture filtrates.

The in-vitro data suggest an extremely complex interaction between tampon materials and S. aureus.

The effect of pretreatment of denture acrylic with chlorhexidine gluconate on the subsequent adherence of Candida albicans GDH 2346 was measured in vitro. Adherence was significantly reduced by pretreatment with chlorhexidine; maximal inhibition was achieved by incubation at room temperature for 30 min in 2% chlorhexidine. Inhibition of adherence was greatest when the organisms were grown in conditions that enhanced adherence the most, i.e., growth to stationary phase in high concentrations of galactose and sucrose. Yeasts grown in high concentrations of galactose, which were the most adherent to acrylic, were also the most sensitive to the fungicidal action of chlorhexidine gluconate, whereas those grown in a low concentration of glucose were the least adherent and also the most resistant. Adherence to acrylic of seven strains of C. albicans isolated from active infections (I strains) and grown in medium containing 500 mm sucrose was significantly higher than that of four strains obtained from asymptomatic carriers (C strains). A spectrum of adherence values was obtained when various yeasts other than C. albicans were tested.

Sera from 489 trainee nurses were examined, by the ELISA technique, for the presence of varicella-zoster virus specific antibody; antibody was found in 446 (91.2%). In more detailed investigations of specific immunity in 33 healthy adults with a past history of chickenpox, 32 (97%) showed a positive lymphocyte transformation test, but only 11 out of 23 examined (48%) demonstrated mononuclear cell production of specific antibody in vitro; serum antibody was found in 30 (91%) by the ELISA and in 25 out of 26 examined (96%) by the FAMA technique. A high degree of correlation was found between both a positive lymphocyte transformation and the presence of serum antibody and a past history of chickenpox.

Antigenic relationships among type-3 fimbriae of 31 strains, representing 19 species and eight genera of Enterobacteriaceae, were investigated by immunoelectronmicroscopy in tests with 17 different type-3 fimbrial antisera. At least nine antigenically distinct groups among type-3 fimbriae were distinguished. The constituent membership of some groupings did not conform with current views on the taxonomy of Enterobacteriaceae.