F. Namavar

Differences in virulence within the species Bacteroides gingivalis

In order to gain insight into the relative importance of several virulence factors of Bacteroides gingivalis, 8 strains with a varying virulence were studied. The virulence of B. gingivalis was determined in a mouse model. Strains HG 66, HG 76 and HG 184 were very virulent causing phlegmonos abscesses with lesions and necrosis. The strains HG 405 and HG 462 caused phlegmonous abscesses with pus. Strains HG 91, HG 94 and HG 185 were less virulent and induced gravity abscesses. In vitro strains HG 66, HG 76 and HG 184 induced low amounts of chemiluminescence by polymorphonuclear leucocytes. All other strains including HG 405 and HG 462 caused a relatively high chemiluminescence. Most strains displayed a high sensitivity to the bactericidal activity of fresh serum except for the highly virulent strains HG 66, HG 76 and HG 184. No differences in extracellular proteolytic activity on Azocoll, production of volatile fatty acids and ammonia were found between the B. gingivalis strains studied. In conclusion, differences in virulence were shown within the species B. gingivalis; the relative importance of several virulence factors was investigated.

Epidemiology of the Bacteroides fragilis group in the colonic flora in 10 patients with colonic cancer.

We report the relative frequencies of members of the Bacteroides fragilis group in the faeces, in colon lavage fluid obtained pre-operatively, and in colonic tissue specimens obtained at operation from 10 patients with colonic cancer. B. vulgatus was the most and B. fragilis and B. ovatus were the least frequently isolated Bacteroides spp. in the faeces of the 10 subjects. B. uniformis and B. thetaiotaomicron ranked second and third in the faeces. The relative frequencies of all species except B. fragilis were lower in the lavage fluid and in cultures of mucosa. The relative frequency of B. fragilis increased from 4% in faeces to 39% in the final lavage fluid and to 42% in the colonic mucosa culture. Our results suggest that B. fragilis has a more intimate association with the gut mucosa than other members of the B. fragilis group, which might be one explanation for the high incidence of this species in gut-associated intra-abdominal infections.

In vitro susceptibility of Helicobacter pylori to several antimicrobial combinations.

Synergy between metronidazole and its hydroxymetabolite and between each compound and amoxicillin or tetracycline-HCl was determined against Helicobacter pylori. Metronidazole plus its hydroxymetabolite and either compound combined with amoxicillin showed synergism against all 10 strains of H. pylori tested. Metronidazole plus tetracycline-HCl or the hydroxymetabolite plus tetracycline-HCl acted synergistically against seven and six strains, respectively, acted additively against three strains, and had no additional effect against one strain. These results may help to explain the in vivo efficacies of metronidazole combinations in the treatment of H. pylori-associated gastritis.

KILLING CAPACITY OF HUMAN POLYMORPHONUCLEAR LEUKOCYTES IN AEROBIC AND ANAEROBIC CONDITIONS

The killing by human polymorphonuclear leukocytes of several species of bacteria, some of which were catalase positive, was examined in vitro in aerobic and anaerobic conditions. When all conditions other than the oxygen tension were identical, killing after 30 min was slightly greater in aerobic than in anaerobic conditions. However, after 60 and 120 min the difference between aerobic and anaerobic killing was smaller, and killing was nearly complete for all strains tested. These results conflict with the common opinion that oxygen is essential for efficient killing. Minor differences in experimental conditions can greatly influence results, and may be responsible for the discrepancy between this study and some previous studies on this subject.

POLYMORPHONUCLEAR LEUKOCYTE CHEMOTAXIS BY MIXED ANAEROBIC AND AEROBIC BACTERIA

The induction of chemotactic activity of polymorphonuclear leukocytes (PMNL) by anaerobic and aerobic bacteria alone or in combination was evaluated. Washed cells as well as the supernate of Proteus mirabilis were chemotactic for leukocytes. The supernate of cultures of two strains of Bacteroides fragilis contained small amounts of chemotactic factors. No chemotactic factors were released from the non-fragilis Bacteroides strains. The supernates of cultures of anaerobic bacteria were capable of inhibiting chemotaxis of leukocytes to the chemotactic factors of P. mirabilis. P. mirabilis and two strains of B. fragilis generated chemotactic factors in serum but none of the other Bacteroides spp. tested were able to induce serum chemotactic factors.

Pathogenic synergy between Escherichia coli and Bacteroides fragilis or B. vulgatus in experimental infections: a non-specific phenomenon.

The virulence of Bacteroides fragilis and B. vulgatus for mice was compared in a skin-infection model. These strains were also tested for pathogenic synergy in mixed infections with Escherichia coli. Strains of B. fragilis were generally more virulent than strains of B. vulgatus and, with one exception, the effect of Bacteroides strains in mixed infections merely reflected their inherent virulence.

K ANTIGENS OF ESCHERICHIA COLI AND VIRULENCE IN URINARY-TRACT INFECTION: STUDIES IN A MOUSE MODEL

The importance of K antigens of Escherichia coli as virulence factors was studied by comparing groups of mice given either strains of E. coli isolated from urinary tract infection in humans or mutant strains differing only in the absence of the K antigen. K antigens proved to be of minor importance for mouse nephropathogenicity; however, with the exception of the K(A) antigen, they contributed substantially to deaths attributed to more general infection. Possible mechanisms for the virulence of strains with K antigens are discussed in terms of the bactericidal effect of serum and phagocytosis.

Pathogenic synergy between Escherichia coli and Bacteroides fragilis: studies in an experimental mouse model

An animal model is described for quantitative evaluation of pathogenic synergy between Escherichia coli and Bacteroides fragilis in which adjuvants were not required for abscess formation. Two sets of strains of E. coli and B. fragilis isolated from human wound infections were tested. Pathogenic synergy was observed in only one of the two combinations and was dependent on properties of E. coli.

Novobiocin resistance and virulence of strains of Staphylococcus saprophyticus isolated from urine and skin.

A method was developed to study virulence of coagulase-negative staphylococci. Our results showed that coagulase-negative staphylococci injected into adult mice by the intracerebral route did not give rise to lethal infections, whereas mice aged 2 days were much more susceptible. Novobiocin-resistant strains of Staphylococcus saprophyticus were more virulent than strains of Staphylococcus epidermidis. Strains of S. saprophyticus biotype 3 of Baird-Parkers classification varied in virulence according to novobiocin sensitivity. In the classification of Kloos and Schleifer, S. saprophyticus biotype 3 can be subdivided into four distinct staphylococcal species, namely S. saprophyticus , S.cohnii, S.haemolyticus and S.warneri. S. chonii and S. saprophyticus were equally virulent for mice aged 2 days, but novobiocinsensitive S. haemolyticus was less virulent. On epidemiological grounds, however, it would seem that S. saprophyticus has some undefined advantage in invading the urinary tract.

Pathogenic synergy: mixed intra-abdominal infections

In this article we review our researches into the pathogenesis of mixed infections. These may conveniently be divided into in vitro and in vivo studies.In vitro we confirmed that interference with the killing of aerobes by polymorphonuclear leucocytes (PMN’s) is a property of theBacteroides strains tested and appears to depend on competition for opsonins i.e. complement factors. Further studies are in progress to define which complement factors and which bacterial structures are involved. The influence ofB. fragilis on chemotaxis has also been studied. Our preliminary data suggest thatB. fragilis is itself poorly chemotactic and reduces the chemoattractivity ofProteus mirabilis. This observation is surprising when we consider that abscess formation is the hall-mark ofB. fragilis infections and needs clarification.In vivo we have developed a skin infection model in mice which is economical and gives reproducible and quantitative results. In this model we have demonstrated pathogenic synergy betweenEscherichia coli andB. fragilis. Further studies are planned to assess the role of complement and bacterial factors in this in vivo synergy.