- Volume 34, Issue 2, 1991

Summary. In the absence of antimicrobial therapy, bacteria such as Bacteroides fragilis, Escherichia coli and Proteus mirabilis may persist within an intra-abdominal abscess in the presence of large numbers of neutrophils which, under optimal conditions in vitro, can readily phagocytose and kill the same bacterial strains. Neutrophils taken from abscesses induced by gram-negative bacteria such as those above contain viable organisms. On incubation in vitro in the presence of serum, these neutrophils kill the bacteria phagocytosed in the abscess poorly, if at all, yet can readily kill organisms added in vitro. To determine possible mechanisms that might explain this, we examined the bactericidal activity in vitro of neutrophils from a range of abscesses induced by one or two species of bacteria plus an abscess-potentiating agent, bran. The organisms studied were B. fragilis, E. coli, P. mirabilis and Staphylococcus aureus. The killing in vitro of E. coli and P. mirabilis, engulfed within an abscess, was significantly less than that of the same organisms when they were added to the in-vitro assay. In contrast, the killing of S. aureus was similar, whether engulfed in vivo or in vitro. However, S. aureus was less susceptible to phagocytosis and killing in vitro than P. mirabilis or E. coli, and the killing of S. aureus during in-vitro incubation of neutrophils that had engulfed the organism within the abscess was similar to that of the gram-negative bacteria engulfed within the abscess. We examined whether organisms phagocytosed in vivo were within neutrophils which had diminished or no expression of cell surface Fc and C3 receptors, and might, therefore, be unresponsive to extracellular serum factors such as complement which stimulate intracellular killing. No population of neutrophils lacking CR3 complement receptors was detected. Furthermore, the expression of these receptors was enhanced on abscess neutrophils compared with peripheral blood neutrophils. FcγRII receptor expression was equivalent in the two populations. Extracellular serum was necessary for any abscess neutrophil bactericidal activity. To determine whether the bacteria within abscess neutrophils were a subpopulation selected for resistance to intracellular killing, we lysed the neutrophils and added the released bacteria to bactericidal assays with peritoneal exudate neutrophils. The bacteria were killed readily, but not as efficiently as log-phase organisms grown in vitro. As these studies have shown that neutrophils from abscesses are functional, with enhanced CR3 expression, and that bacteria persisting within abscesses are not resistant to intracellular killing, it is possible that the poor killing in vitro of bacteria engulfed in vivo by abscess neutrophils reflects depleted intracellular killing mechanisms in those particular neutrophils, or results from the phagocytosis of organisms under conditions prevailing within abscesses, or is due to as yet undefined bacterial virulence factors.

Summary. After growth in an iron-depleted chemically-defined medium Acinetobacter calcoaceticus expressed four high mol. wt outer-membrane proteins (OMPs) which were repressed under iron supplementation or in a complex laboratory medium. Immunoblotting with serum from a septicaemic patient infected with A. calcoaceticus revealed antibody binding to these iron-repressible OMPs, indicating that they were expressed in vivo, and also to the 42- and 18-Kda OMPs. Although the antibody response to the OMPs did not vary significantly during convalescence, the response to the O-polysaccharide component of lipopolysaccharide decreased significantly. However, antibodies in serum from patients with A. calcoaceticus wound infections reacted with the iron repressible OMPs and a 54-Kda antigen suggesting a difference in immune recognition between local and systemic infection.

Summary. Enterotoxigenic Escherichia coli (ETEC) strains of serotype O153:H45 have been found recently to be a frequent cause of sporadic cases and outbreaks of neonatal diarrhoea in Spain and the most important cause of infant diarrhoea in Chile. Relationships between sugar fermentation patterns, resistance to antibiotics and plasmid profiles were analysed in nine E. coli O153:H45 strains isolated in Spain that synthesised CFA/I antigen and STa enterotoxin. Derivative strains obtained by curing with acridine orange, and transconjugants rendered antibiotic resistant, were characterised phenotypically and analysed for plasmid content. Two fermentation patterns were recognised: rhamnose fermenters (four strains) and rhamnose non-fermenters (five strains). The ability to ferment rhamnose was the only differential characteristic found among 49 carbohydrate fermentation tests used to establish fermentation patterns. All nine strains possessed similar plasmid profiles of three or four plasmids of 52–87 Mda. A non-conjugative large plasmid of 82 Mda or 87 Mda, depending upon the strain, was identified as that responsible for production of both CFA/I and STa. Resistance to antibiotics was determined by plasmids other than those coding for CFA/I and STa. Two conjugative resistance factors were identified: a 52-Mda plasmid coding for resistance to ampicillin, streptomycin and sulphonamide in rhamnose-fermenting strains, and a 77-Mda plasmid coding for resistance to ampicillin, streptomycin, kanamycin, tetracycline and sulphonamide in rhamnose non-fermenting strains. Our results support the hypothesis that the prevalence and distribution of ETEC strains belonging to serotype O153:H45 in Spain and Chile could be due to the extensive cultural relations between Spain and South America from the past.

Summary. The haemolysin from a virulent strain of Treponema hyodysenteriae was extracted and injected into ligated loops of the ileum and colon of germ-free pigs. It caused severe epithelial damage, especially to the differentiated cells at the tips of the villi in the ileum and the cells in the intercrypt zones of the colon; goblet cells were less affected. The changes in the colon were similar to those seen in natural cases of swine dysentery. The ligated loop offers a means of investigating pathogenic mechanisms and the mode of action of the toxin. This study demonstrated that the haemolysin was a potent cytotoxin for pig enterocytes, and a probable virulence determinant in swine dysentery.

Summary. Factors that are known to influence plasmid transfer in bacterial populations were studied for the conjugative plasmid pWG613, which determined gentamicin resistance in Staphylococcus aureus. The transfer frequency was largely unaffected over a wide range of temperature (18–42°C); pH also had little effect on the transfer frequency in the range 5.0–8.5. High cell density and log phase cultures were required for optimal plasmid transfer, as were donor: recipient ratios of 0.003–3.3.

Summary. Of 166 strains of Staphylococcus aureus isolated from hospital patients and staff in Ile-Ife, Nigeria, 32% were non-typable (NT). The strains were isolated from skin lesions, eye infections, wounds and nasal flora. Isolates from skin lesions or eye and wound infections were more likely to produce protease (95% and 78% respectively) than nasal isolates (11%). Nearly all (99%) of the strains isolated were resistant to penicillin and 78% were resistant to tetracycline. Streptomycin resistance occurred in 25% of isolates; 19% were resistant to chloramphenicol and 9% to methicillin.

Summary. The growth inhibiting activity of transferrins, citrate, 2-2′ dipyridyl and desferrioxamine methanesulphonate towards Legionella spp. and their serogroups was investigated. The inhibitory activity of all these compounds depended upon the iron-free state of the molecules and was abolished by saturation with iron. No bactericidal effect by transferrins was observed at concentrations up to four times the minimal bacteriostatic concentration. No interaction of transferrins with the legionella cell surface was detected by direct or indirect fluorescence assay, or by dialysis culture experiments in which transferrin was separated from the bacterial cells. The demonstration of a siderophore-like activity in supernates of iron-deficient legionella cultures may account for the ability of Legionella spp. to multiply in conditions of iron restriction.

Summary. Antibody to at least one type of streptococcal opacity factor (OF) was present in 39.0% of 235 selected subjects and, in 47.8% of these, to more than one type. Only 21.6% of children less than 4 years old had antibody to OF; these were to one type in 62.5% or to more than one in 37.5%. In the study group as a whole, the commonest antibodies were those to OF from M-serotype 25 followed, in descending order, by serotypes 4, 22, 2, 9, 48, 49, 28, 61 and 75. Patients with rheumatic fever or rheumatic heart disease most often had antibodies to OF from M-types 25, 22, 4 and 9, whereas in patients with acute glomerulonephritis, antibodies to OF from M-types 48, 49 and 61 were commonest. The limitations of the OF-inhibition test as an epidemiological marker for prevalent M-types of group A streptococci are discussed.

Clinical and Molecular Aspects of Anaerobes Edited by S. P. BORRIELLO. 1990. Blackwell Scientific Publications, Oxford. Pp. 329. £39.50.