Ann-Marie Bergholm

Properties of high and low density subpopulations of group B streptococci: enhanced virulence of the low density variant☆☆☆

From the group B streptococcus (GBS) reference strain 090 la Colindale two subpopulations, which differed markedly regarding their capacities for biosynthesis of type-specific polysaccharide, were obtained by separation on a hypotonic Percoll density gradient. In the original strain and the high and low density variants, there was a negative correlation between buoyant density and bio-synthesis of type-specific polysaccharide as determined by ultrastructure and quantitative assays. The invasiveness of these variants was investigated by infecting rabbits via subcutaneously implanted tissue cages. In the animals infected with highly encapsulated bacteria, heavy bacteremia was detected 8 h post-infection, whereas in the animals which received high density bacteria with small amount of capsule, heavy bacteremia was not detected until after five days. All isolates recovered from the blood or organs of these rabbits were of the capsule rich phenotype, indicating a phenotypic shift in the subpopulation of high density bacteria. An apparently similar phenotypic shift was noted in an isolate from a baby with early onset septicemia. There was a dominance of low density bacteria in the isolate obtained from the baby as compared with the colonizing population of bacteria isolated from the cervix of the mother. From these type III isolates, subpopulations with different density maxima were obtained. A reversed shifting towards dominance of less encapsulated, high density bacteria was observed during in vitro passage of these subpopulations.

A streptococcal plasminogen activator in the focus of infection and in the kidneys during the initial phase of experimental streptococcal glomerulonephritis

Strains of group A streptococci known to secrete the nephritis strain‐associated protein (NSAP), a plasminogen activator, were studied for their ability to produce APSGN in rabbits. A tissue cage model was used to monitor the secretion of NSAP at the focus of infection and histopathological examination of kidney tissue was used to determine glomerular pathology. Animals infected with NSAP positive strains exhibited NSAP deposits in the glomerular tissue by day 7 in the absence of antibody to this molecule with progressive pathology indicative of APSGN three weeks later. Animals infected with the NSAP negative streptococcal strain exhibited no abnormal pathology. The ability of NSAP to bind to kidney tissue suggested that it has unique nephrotropic properties; and its ability to activate plasminogen to plasmin, possibly in situ, suggests that much of the pathological events associated with APSGN may be initiated by plasmin activity.

Static and dynamic properties of tissue cage fluid in rabbits

The properties of tissue cage fluid in a steel net tissue cage model in rabbits were compared to those of serum by determination of the protein profile, the cell contents, and the pharmacokinetics of125I albumin,3H sucrose and3H fusidic acid. The dominating serum proteins demonstrated by crossed immunoelectrophoresis were also detected in tissue cage fluid but at lower levels and at various ratios. The cell pattern gradually changed from an initial dominance of polymorphonuclear cells to lymphocytes during the five weeks following the subcutaneous implantation of the cages. The distribution of the highly protein-bound fusidic acid was markedly slower and the maximal tissue cage fluid level significantly lower than that of sucrose. Equilibrium of125I albumin between serum and tissue cage fluid was slowly achieved during the following two weeks. The advantages and disadvantages of tissue cage models for studies of drug pharmacokinetics are discussed. The properties of tissue cage fluid and the possibility of repeated sampling make the model suitable for studies of experimental local infections. The influence of therapeutic agents and the hosts response to the infectious process may also be elucidated.

A sialic-acid-specific lectin from Cepaea hortensis that promotes phagocytosis of a group-B, type-Ia, streptococcal strain.

Group-B streptococci that possess a type-specific surface polysaccharide undergo phagocytosis only in the presence of antibodies to this, and complement. The snail Cepaea hortensis forms a lectin that is specific for sialic acid; treatment with this promoted the phagocytosis of a group-B streptococcus of serotype Ia (strain O90) in the absence of opsonic antibodies. The effect of the lectin was dose-dependent and required the presence of complement. The specificity of the lectin reaction for sialic acid was proved by the inhibition of phagocytosis by bovine submaxillary mucin. The participation of complement in the reaction was confirmed by demonstrating that C3 was bound to the surface of lectin-treated cells.

Active Phenoxymethylpenicillin (Pcv) in the Mucous Membranes of the Oral Bucca and Maxillary Sinus and in Diffusion Chambers Implanted in Rabbits: A Methodological Study

The intention of prescribing antibiotic treatment must be to achieve a concentration of the agent within the infected tissue well above th MIC or the bacteria causing the infection. As a basis for further clinical studies on antibiotic concentrations in maxillary sinus mucosa in humans, determinations of biologically active penicillin V in the mucous membranes of the maxillary sinus and the buccal mucose as well as in tissue fluids and tissue from subcutaneously implanted tissue cages in rabbits were made. Several experimental conditions were studied, with the purpose of establishing optimal conditions with regard to tissue sampling, blood contamination, prediffusion time, etc. Penicillin V was shown to have a good penetration into mucosal tissue in the rabbit, even at low perfusion pressure.

The influence of penicillin on growth and morphology of streptococcus pyogenes in vivo

The influence of penicillin (pc) on the growth, phagocytosis and killing of Streptococcus pyogenes was studied for an M protein positive (M+) and an M protein negative (M-) strain in vivo as well as in vitro. In vivo studies were based on a tissue cage model and the analyses were performed by CFU determinations and electron microscopic investigations. The M- strain was easily phagocytized with and without pc, but killing only occurred after pc treatment and thus the number of viable bacteria rapidly decreased under the influence of pc. M+ streptococci were not reduced in numbers by pc-treatment in vivo, but morphological changes and at high pc concentrations, phagocytosis could be seen. When this strain (M+) was cultivated in the absence of pc, the phagocytic cells were totally destroyed - a reaction that was prevented by penicillin. Variations in surface morphology of the two strains seem to influence the differences in sensitivity to penicillin, phagocytosis and killing.

Postantibiotic effect of the penem FCE 22101 against selected gram-positive and gram-negative bacteria in vitro and in vivo by the use of a tissue cage model in rabbits.

Isolates of Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae and Klebsiella pneumoniae were tested for their bactericidal activity and postantibiotic effect (PAE) with the new penem FCE 22101. The tissue cage model in rabbits was used to study PAE in vivo. The bactericidal activity against all four species was shown to be in the range of 0.05‐4.0 mg/1. A 99.9% killing effect at MBC concentrations was reached within 2 hours with S. pneumoniae and K. pneumoniae and within 6–8 hours with S. aureus and H. influenzae. After in vitro exposure by FCE 22101 a PAE in vitro and in vivo was obtained against S. aureus, S. pneumoniae and H. influenzae strains but no PAE could be demonstrated against K. pneumoniae. FCE 22101 showed a good bactericidal activity and PAE against the strains investigated, except for K. pneumoniae.

Experimental infection with group B streptococci in tissue cages implanted in rabbits.

Using tissue cages subcutaneously implanted in rabbits an experimental group B streptococcal (GBS) infection was induced. The type Ia strain differed from the type III strain in producing a septicemic infection leading to the death of the animals on day 4 of infection. Active immunization with whole cells of the homologous strain resulted in phagocytosis and killing of the bacteria, whereas passive immunization only resulted in inhibition of the spread of the type Ia infection from the cages. Electron microscopy showed that in unprotected animals infection with either strains was followed by a lysis of erythrocytes and polymorphonuclear cells in the cage fluid. Opsonization by type-specific antibodies already present in the cage fluid preceded the phagocytosis of streptococci in the immunized animals. The tissue cage model offers a suitable way for studies of the pathogenesis of GBS infection. The different factors influencing the process of infection can also be easily monitored.

Concentration of Phenoxymethylpenicillin (Pcv) in the Mucous Membrane of Maxillary Sinus in Patients with and without Sign of Sinusitis

Maxillary sinus infections start in the mucous membrdnes. Chiefly for this reason we decided to study the concentration of penicillin-V in the maxillary sinus mucosa. 40 patients with or without maxillary sinus infections received 12.5 or 25 mg penicillin-V orally at different time intervals before operation for the removal of the sinus mucosa. The results indicate that a single oral dose of 25 mg per kg bodyweight. of the potassium salt of penicillin-V (Calciopen, Leo) gives an antibiotic concentration in the maxillary sinus mucosa in infected as well as uninfected patients which is well above the MIC for the majority of the microorganisms causing maxillary sinusitis.

Synergy and cumulated killing effect of the penems FCE 22101 and FCE 25199 in combination with gentamicin against bacteria isolated from septicaemia

Blood isolates of Enteroeoecus faecalis, Streptococcus sanguis, Staphylococcus aureus, E.coli and Klebsiella oxytoca were tested for their synergistic and cumulated killing effect (CKE) with the new penems FCE 22101 or FCE 25199 in combination with gentamicin. The tissue cage model in rabbits was used to study the CKE in vivo after antibiotic treatment of the bacteria in vitro. Synergy was observed within two to seven h with all isolates in early logarithmic phase, except with S. aureus, which was rapidly killed by the penems alone. After one h treatment with the antibiotic combinations in vitro, a CKE was demonstrated for up to six h both in vitro and in vivo. The magnitude of the CKE differed between strains and in vitro vs. in vivo.