Acta pathologica, microbiologica, et immunologica Scandinavica. Section B, Microbiology最新文献

Group A streptococcal strains (three T-type 1, two T-type 2 and three T-type 4), freshly isolated from throat cultures, were subjected to 25 serial passages on blood agar. All strains changed their M protein production and/or opacity factor (OF)-activity during the passages. The capacity of each strain to adhere to a pool of buccal cells from six healthy individuals was studied both before and after passage. Five of six strains with decreased OF-activity/M protein production diminished significantly in adherence capacity, whereas one of two strains with increasing OF-activity adhered better to the epithelial cells. The results are discussed in relation to the clinical view of asymptomatic carriers of group A streptococci.

The coagglutination test, which uses staphylococcal protein A for typing strains of Streptococcus pneumoniae was extended to include typing within 13 groups. Typing was performed using the factors remaining in group antisera after absorption with a strain of a type within the group. 93 of 99 strains of S. pneumoniae, which belonged to one of the 13 groups included in the 23 valent vaccine formulation were correctly identified when compared to the capsular reaction test.

One hundred and twelve beta-lactamase producing strains of Staphylococcus aureus with known quantitative production were investigated together with 45 non-beta-lactamase producing derivatives by three qualitative beta-lactamase tests: the microbiological clover leaf test, the iodometric tube test and a chromogenic cephalosporin disc test. For the beta-lactamase producing strains strong positive reactions in the qualitative tests were not correlated with high beta-lactamase production, large degree of extracellularity or high induction ratio in any of the tests. Low beta-lactamase production was not correlated to weak reactions. Best results in identifying beta-lactamase production were obtained using the iodometric test in which 109 of 112 beta-lactamase producing strains were positive and no false positive reactions were observed. Some strains had only weak positive reactions but they were easily read. The clover leaf test and the chromogenic cephalosporin test detected 105 and 107 of 112 strains, respectively. The chromogenic cephalosporin disc test had more weakly reacting strains, which were difficult to read, especially among strains of phage type 95. Three non-beta-lactamase producing strains of phage type 95 were positive in the clover leaf test. It is concluded that the iodometric tube test is the most useful one for qualitative determination of beta-lactamase production in S. aureus. It is recommended as control when normal susceptibility testing for penicillin has shown susceptibility or doubtful susceptibility. Furthermore, it is useful when no susceptibility testing has been carried out and a rapid result is needed.

The distribution among mammalian species of non-immune F(ab')2- and Fc-mediated immunoglobulin interactions with surface proteins of S. aureus (protein A) and of group C and G streptococci was studied. Serum samples from 48 mammalian species representing 15 orders were first tested for their capacity to inhibit streptococcal F(ab')2-mediated binding; 26 of these sera were also tested for streptococcal IgG Fc-mediated binding. Analogous inhibition experiments were then carried out with staphylococci. All mammalian species studied inhibited both types of immunoglobulin binding to streptococci, viz the serum samples contained both F(ab')2- and Fc-reactive immunoglobulins. The reactivity was equal to that of human serum in 26 out of 47 mammalian sera. Seven sera showed a low degree of inhibition compared to human serum. The inhibiting capacities of the two streptococcal non-immune interactions showed a direct correlation (r = 0.91, p less than 0.0001 for the r-value) for individual species. The inhibition patterns observed with S. aureus differed from the profiles recorded with the streptococcal strains, suggesting that these organisms interact with separate sites on the immunoglobulin molecules. Isolated F(ab')2-binding was recorded in 5 out of 24 sera, and Fc-binding alone was noted in 7 sera. Taken together, the present studies demonstrate that mammalian immunoglobulins possess F(ab')2- and Fc-binding sites for protein A and for receptors on group C and G streptococci. The F(ab')2-mediated binding to streptococci is associated with Fc-reactivity, in contrast to protein A which may interact exclusively with a complementary structure in either the F(ab')2- or the Fc-portion of the immunoglobulins.

A two-dimensional thin-layer chromatographic method was developed which allowed separation of the different mycobacterial mycolic acids as methyl esters. Dichloromethane (once) and petroleum ether:acetone (95:5, v/v twice or three times) were used as solvents. Alkaline saponification of freeze-dried cells followed by methylation of the mycolic acids using iodomethane gave satisfactory results, whereas methylation using boron trichloride-methanol complex or trans-esterification through direct acid methanolysis was found to degrade epoxy-mycolates. The chromatographic method developed here is rapid and informative, and should prove valuable in routine mycobacterial differentiation.

The present study demonstrates that pregnant mice seem to be more sensitive to encephalomyocarditis (EMC) infection than non-pregnant mice, and the infection results in significantly increased maternal plasma levels of insulin and pregnancy-associated murine protein-2 (PAMP-2), of placental origin, and alpha-fetoprotein (AFP), of foetal origin. Maternal plasma levels of PAMP-2 and AFP are correlated with placental and foetal growth respectively. This indicates that the EMC infection and the increased peripheral insulin levels lead to increased growth of the foetoplacental unit.

Irrespective of IgG Fc-receptor activity, earlier characterized, many group A streptococci were recently found to bind aggregated IgG Fab and/or light chains. In the present study, binding of glutaraldehyde-aggregated, radiolabelled, intact human IgG (a*IgG) to group A streptococci was tested, and strains representing several M-types were found reactive. In particular, high binding was observed among type M12 strains, earlier found devoid of Fc-receptors for monomeric IgG; accordingly, unlabelled, native IgG had little influence on the binding. The sites binding a*IgG were highly sensitive to trypsin and relatively resistant to heat treatment. The binding to M12 was inhibited by human fibrinogen and, to a lesser extent, by heat-aggregated serum albumin. Rabbit antiserum to M12 was more inhibitory than antiserum to a heterologous type of group A streptococci or normal rabbit serum. Our results indicate that streptococcal M-protein binds a*IgG by a multipoint requiring interaction of low specificity and that previously described Fc-receptors binding native IgG are not involved. For comparison, in Cowan I staphylococci and one strain of group G streptococci tested, high binding of a*IgG was also observed; however, this binding was inhibited by native IgG, indicating that protein A and group G streptococcal Fc-receptor, earlier known to bind untreated IgG, also bound a*IgG.

Susceptibility to ciprofloxacin (Cfl) and nalidixic acid (Nal) was tested in vitro by means of the population analysis technique against six strains of Staphylococcus, one strain of Pseudomonas aeruginosa, and seven strains from five genera of Enterobacteriaceae. All strains of Staphylococcus were uniformly resistant to Nal as was the Pseudomonas aeruginosa strain, all bacteria being resistant to 250- less than 500 micrograms/ml. The Enterobacteriaceae were heterogeneous as regards susceptibility to Nal. With some strains minority populations of highly-resistant bacteria could be detected with frequencies of about 10(-6.3). The MIC for Cfl for the staphylococci varied between 0.25 and 0.50 microgram/ml. There were no differences in MIC of penicillinase-producing and penicillin-susceptible strains, either in Staphylococcus aureus or in Staphylococcus epidermidis. The MIC for Cfl in the enterobacteria varied between 0.004 and 0.03 microgram/ml. The MIC for Cfl in the Pseudomonas aeruginosa was 0.25 microgram/ml. MIC for Cfl increased in all strains when the parental strains were compared to bacteria selected from the plates with the highest concentration permitting growth, indicating heterogeneity against Cfl. But while the MIC of the selected enterobacteria were lower than one fourth of the level obtainable in serum, the MIC of the selected staphylococci and Pseudomonas aeruginosa were either exceeding the level obtainable in serum or were only a little lower than this level. While Cfl thus seems to be a promising antimicrobial agent in the treatment of infections caused by enterobacteria, the suitability for infections caused by staphylococci and Pseudomonas aeruginosa should be further explored.

A simple experimental set-up, using a slit-sampler, was tried in order to measure the effect of wearing face-masks. During the experiments we discovered that when talking unmasked, the number of bacteria collected by the slit-sampler was considerably lower than the number actually spread. When speaking, the contamination spread was mainly in the form of bacterial clusters. These were not sampled on the agar plate but withheld in the sampling equipment (wall loss) or lost. The advantage of using a slit-sampler when comparing face-masks is discussed.

Two antibiotic-susceptible and two multi-resistant strains of diphtheroid rods of the group JK, obtained from clinical specimens in Denmark and from CDC in the U.S. were studied. The cells of all four strains presented an ordinary Gram-positive cell wall and an additional surface layer. Septum formation in dividing cells appeared to result in a "snapping-like" dividing mechanism, thus corroborating the relationship of the JK cells to the genus Corynebacterium. A significantly increased thickness of the surface layer of the multi-resistant strains was observed when cells were treated with ruthenium red. It is suggested that such a structural difference on the exterior of the cell-wall among JK bacteria may affect the cell-wall's permeability to antibiotics.