- Volume 33, Issue 1, 1990

The frequency of electrophoretic types B1 (fast mobilities) and B2 (slow mobilities) of carboxylesterase B, and α-haemolysin and mannose-resistant haemagglutinin (MRHA) production were compared in 705 strains of Escherichia coli isolated from cases of septicaemia, urinary tract infection (UTI) and other extra-intestinal infections from different geographical origins, in particular France, America (USA and Canada) and Oceania (Australia and New Zealand). In all groups of strains, whether classified according to their clinical or their geographical origin, electrophoretic type B2 was phenotypically linked with α-haemolysin and MRHA production. Haemolytic type B2 strains were isolated more frequently from France and Oceania than America whereas the proportions demonstrating production of MRHA were similar among the three groups. Type B2 strains were more frequently isolated from UTI and other infections than from septicaemia. This is attributed to the high frequency of immunocompromised subjects in the septicaemia group. Our results establish the suitability of using the type B2 of carboxylesterase B as a molecular marker for highly pathogenic E. coli strains implicated in extra-intestinal infections in man.

The growth of nine species of colonic bacteria—Escherichia coli, Enterococcus faecalis, Bacteroides ovatus, Fusobacterium varium, Clostridium perfringens, Klebsiella pneumoniae, Proteus vulgaris, Staphylococcus aureus and Bifidobacterium adolescentis—was examined after concomitant injection to form experimental subcutaneous abscesses in mice. Injection of a mixture of c. 105 cfu of each of the first five strains (E. coli, Ent. faecalis, B. ovatis, F. varium and C. perfringens) resulted in abscess formation in all mice tested when the E. coli strain was haemolytic. E. coli and B. ovatus multiplied and reached a maximum population of c. 108 cfu/abscess. When non-haemolytic E. coli was used, injection of ≥107 cfu was required for abscess formation. The inclusion of partially purified E. coli haemolysin (125 HU 50) with c. 105 cfu of bacteria including non-haemolytic E. coli resulted in abscess formation in most mice tested. These results indicate that E. coli haemolysin is one factor that may potentiate pathogenic synergy among colonic bacteria especially between E. coli and B. ovatus, during abscess formation.

A marked increase in the prevalence of bacteraemia due to Escherichia coli of serogroup O 15 was noted during November and December 1986 at Charing Cross Hospital. This multiresistant strain had been reported by several hospitals in south London. All isolates of E. coli from patients with bacteraemia between October 1986 and the end of September 1988 were assessed for the presence of the O 15 antigen and for the unusual pattern of resistance to six antimicrobial agents. As a guide to faecal carriage, isolates from urine were similarly assessed during seven 4-week periods between January 1987 and June 1988. Of the 123 E. coli isolates from blood, 25 (20%) were serogroup O 15 and 20 of these expressed the same pattern of multiresistance; 17 of these multiresistant isolates occurred in the 4-month period 1 Nov. 1986-28 Feb. 1987. During the remaining 19 months of the study only eight isolates were serogroup O 15 of which only three were multiresistant. In the first 4-week period that urine isolates were studied 21 Jan. 1987-17 Feb. 1987, 26 (13-2%) of the 195 isolates were serogroup O 15 of which 20 were multiresistant. The proportion of serogroup O 15 isolates fell gradually until, in June 1988, the last period studied, only 8 (4.2%) of the 189 isolates were serogroup O 15 of which only one was multiresistant. In a preliminary study of plasmids in six serogroup O 15 isolates from blood, three multiresistant isolates and one that was sensitive to chloramphenicol appeared to carry a similar plasmid of c. 100 Mda. A strain that expressed the multiresistance pattern except for tetracycline sensitivity carried four plasmids, the largest of which was c. 70 Mda. No plasmids were found in the one fully sensitive strain studied.

Extracts of 19 samples of pus which showed red fluorescence with ultraviolet light were screened for the presence of porphyrins by absorption spectrophotometry. All those which showed spectra typical of metal-free porphyrins were analysed by high performance liquid chromatography to identify the porphyrins present. These were predominantly the di-carboxylic porphyrins, deuteroporphyrin and mesoporphyrin, and another which was thought to be pemptoporphyrin. This combination matched those reported previously in normal stools. Protoporphyrin IX was shown not to be the most common fluorescent pigment in pus and was never present alone. However, the di-carboxylic porphyrins may be produced by bacterial metabolism of its labile vinyl side-chains. Black-pigmented bacteroides (the melaninogenicus group of Bacteroides spp. and Porphyromonas spp.) were isolated from 12 (63%) of the 19 pus samples; these may produce protoporphyrin IX by the demetallation of haem.

Immunogold-silver staining is a sensitive staining technique that enables the visualisation of the presence of individual antigens by conventionallight microscopy. The application of this method to detect the antigenic heterogeneity of bacterial surface components and also the localisation of intracellular or extracellular bacteria is described. The latter applicationinvolved selective immuno-silver staining of the extracellular bacteria andcounterstaining of the intracellular bacteria and the eukaryotic cells bycrystal violet. The efficacy of the assay was confirmed by transmission electronmicroscopy of the silver-stained specimens. Immunogold-silver staining was shown to be useful for studying bacterial antigen variation and the uptake of bacteria by eukaryotic cells.

This study investigated whether oral candida infection in diabetics andadhesion of Candida albicans to buccal epithelial cells in vitro were related. Buccal cells from 50 patients with diabetes mellitus showed a significant increase in adhesion of C. albicans strain CDS 88 compared with those collected from 50 non-diabetic controls matched for age,sex and denture status. Oral candida carriage, candida infection and secretor status were also investigated in both groups. The frequency of carriage was increased, but not significantly, and there was a significantly higher incidence of candida infection in diabetic patients compared with controls.Diabetic patients who were non-secretors had a significantly increased frequency of oral candida carriage.

Listeria monocytogenes cells are ingested by protozoa such as Acanthamoeba sp. or Tetrahymena pyriformis. However, they are not killed, but survive within the protozoa and may multiply intracellularly. The protozoa are lysed within about 8 days, releasing viable L. monocytogenes. No co-existence was observed between L. monocytogenes and Tetrahymena. A co-culture of L. monocytogenes and Acanthamoeba sp. showed a decay of locomotive forms and release of listeria from vegetative protozoan cells whereas the bacteria were destroyed in cysts. These phenomena provide an insight into the pathogenesis of listeria infection in man and warmblooded animals because intracellular processes occurring in protozoa after ingestion of L. monocytogenes may be similar to those observed in mammalian cells.

Extracellular opacity factor (OF) from group-A Streptococcus M-type 22 was purified by ammonium sulphate precipitation followed byion-exchange on DE-52 cellulose and gel filtration on sephacryl S-400. OF was eluted near the void volume and shown to be heterogenous by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Antiserum to ammonium sulphate-purified OF from a cell-free culture supernate was prepared in rabbits. All preparations of OF from supernate and cell-extract were inhibited by the antiserum. No M protein was detected in the OF samples from various purification steps. The purified OF showed activity at a broad pH range with optimal activity at pH 6; it was inactivated considerably at high temperatures. Enzyme activity was inhibited by pepstatin A, but was unaffected by serine proteinase inhibitor, aprotinin, ethylene diamine trichloroacetic acid, N-ethylmaleimide, iodoacetamide and mercaptoethanol. This suggests that OF is an aspartic proteinase.

The ultrastructural features of a helical-shaped bacterium occurring inthe stomach of pigs, within the mucus on the mucosal surface of antral pits,were examined. The bacterial cell had three to eight spiral turns, flattened and truncated ends and was approximately 4.0 μm long and 0.6 μm wide.In some sections, up to six flagella, about 22 nm in diameter, were seen arising from each pole. The cytoplasm contained sparse, irregular granules,numerous ribosomes and large single-layered membrane-bound granules. In the flagella insertion area, there was a highly electron-dense component,the “polar membrane”. This micro-organism differed from similar bacteria described in cats, dogs and monkeys, and may cause inflammation in the antral mucosa of pigs similar to Helicobacter pylori infection in man. Furthermore, it was morphologically similar to the spiral micro-organism distinct from H. pylori which has been described recently in human antral mucosa from patients with gastritis and may be of potential significanceas a pathogen in man. The name “Gastrospirillum suis” is proposedfor this bacterium.

The 4-quinolone PD127,391 displays a biphasic effect on Escherichia coli, Staphylococcus aureus and S. epidermidis in nutrient broth.It is as active as ciprofloxacin in terms of its optimumbactericidal concentration against E. coli. However, against staphylococci it is six times as active as ciprofloxacin or any other 4-quinolone previously investigated. Although protein and RNA synthesis are not required for bactericidal activity, cell division is essential.