Detection of capsular antigen production in unencapsulated strains of Staphylococcus aureus

Type 5 and 8 capsular polysaccharides are expressed by Staphylococcus aureus isolates from rabbits, poultry, pigs, and horses

A total of 103 Staphylococcus aureus isolates from rabbits (n = 37), poultry (n = 33), pigs (n = 27), and horses (n = 6) and 14 Staphylococcus intermedius isolates from wild animals were serotyped for capsular polysaccharide types 5 and 8 by an enzyme-linked immunosorbent assay using polyclonal rabbit antibodies. About 98% of the S. aureus isolates were typeable. Type 5 was predominant in the poultry (75.8%) and pig (66.7%) isolates, whereas type 8 was more frequent among the isolates from rabbits (59.5%) and horses (83.3%). By contrast, none of the 14 S. intermedius isolates was typeable.

The continuing importance of staphylococci as major hospital pathogens

Rates of hospital-acquired staphylococcal infection have risen substantially in the United States over the last decade. Moreover, it has been shown that bloodstream infections caused by these organisms account for significant morbidity and mortality. It is likely that the changes in medical practice and in types of patient account for these changes, and current antibiotic therapy has helped select more resistant organisms. The increasing use of implantable and temporary medical devices and the increased use of immunosuppressive therapies correlate strongly with the rising incidence of these organisms. Likewise, more patients are predisposed to these infections because of poor immune status and factors favouring colonization. Intrinsic microbiological factors such as glycocalyx production and the presence of bacterial surface proteins allow these organisms to adhere to protein coated foreign bodies and basement membranes thus enabling them to initiate infection and cause disease. Moreover, virulence factors such as encapsulation, slime production and elaboration of extracellular enzymes aid their resistance to host defences. As a group, staphylococci are a leading cause of hospital-acquired infection, and species identification is required for both treatment and control.

Demonstration of alpha and beta components of group B streptococcal protein antigen c in serum-soft agar

Among 85 group B streptococcal cultures with protein type antigen c 56 cultures demonstrated a diffuse type of colony morphology in plain soft agar. The addition of monospecific antibodies against the protein antigen c components c alpha and c beta converted specifically the colony morphology from diffuse to compact. According to this results the serum-soft agar technique could also be used to further characterize individual cultures of group B streptococci with protein antigen c.

Induction of resistance with heat-killed unencapsulated strains of Staphylococcus epidermidis against challenge with encapsulated strains of Staphylococcus epidermidis

Active immunization of mice with high doses of heat-killed unencapsulated strains of Staphylococcus epidermidis, which were grown in brain heart infusion media, protected mice against challenge with encapsulated strains of S. epidermidis. The unencapsulated strains were capable of absorbing the protective antibody in rabbit hyperimmune sera prepared with the encapsulated strains. Also, mice treated with rabbit hyperimmune sera prepared with the unencapsulated strains were protected against challenge with the encapsulated strains. The protective activities of these rabbit hyperimmune sera were assumed to be essentially identical to those of the protective antibody induced by the encapsulated strains.

Outermost-cell-surface changes in an encapsulated strain of Staphylococcus aureus after preservation by freeze-drying

The effects of drying time during freeze-drying on the outermost cell surface of an encapsulated strain of Staphylococcus aureus S-7 (Smith, diffuse) were investigated, with special attention paid to capsule and slime production. To quantify capsule and slime production, capsule antigen production and cellular characteristics such as growth type in serum-soft agar, cell volume index, and clumping factor reaction were examined. After freeze-drying the colonial morphology of strain S-7 was altered from a diffuse to a compact type in serum-soft agar. In accordance with these changes, the titer of the clumping factor reaction increased while the cell volume index, capsule and slime production, and capsule antigen production were markedly decreased in parallel with the period of freeze-drying. The ability of the strain to adhere to collagen, fibrinogen, and soybean lectin was also compared before and after freeze-drying. Fibrinogen levels slightly increased when 10% skim milk and 2% honey were used as cryoprotective agents and showed a remarkable increase when 0.05 M phosphate buffer was used as a control. Also, the ability of strain S-7 to adhere to soybean lectin declined, whereas no changes were observed for collagen under any conditions. Strain S-7 was phage nontypable before freeze-drying but the number of typable cells increased after freeze-drying; phage-typable cells reacted to phage 52 alone after 5 h of freeze-drying, but additional cells also proved to be phage typable to phage 42E after 10 h. Electron micrographs indicated that strain S-7, an encapsulated strain, was converted to an unencapsulated state after freeze-drying.(ABSTRACT TRUNCATED AT 250 WORDS)

Possible common biological and immunological properties for detecting encapsulated strains of Staphylococcus epidermidis

Twenty strains of capsular type II Staphylococcus epidermidis, determined by the method of Ichiman, were obtained from clinical specimens. Among them, 5, 5, and 10 strains were 4+, 3+, and 2+ in the intensities of their reactions against fluorescent antibody, respectively. Strains exhibiting 4+ and 3+ intensities were mouse virulent and phage nontypable, while 2+ strains were mouse avirulent and phage typable. When three strains randomly selected from each of the mouse-virulent and mouse-avirulent strains were compared in terms of their cell volume indices, all mouse-virulent strains had significantly higher indices (average, 1.86 times) than the mouse-avirulent strains. With intraperitoneal injection of the strains into mice, strains with higher cell volume indices resisted ingestion by peritoneal cells, while strains with low cell volume indices were sensitive to phagocytosis. When the capacity to absorb a definite amount of passive protective activity in rabbit antiserum prepared with capsular type II strains was compared among these strains, 10 to 20 mg of mouse-virulent strains was capable of completely absorbing the passive protective activity, whereas more than 80 mg of the cells was required for similar absorption by mouse-avirulent strains. In ultra-thin sections of three mouse-virulent strains stained with ferritin-conjugated rabbit antiserum, well-defined capsules were detected around cell walls; however, no capsule was seen around the walls of three mouse-avirulent strains.

Comparison of compact colony-forming activity and paracoagulation activity of strains of Staphylococcus aureus in serum and plasmas of various animals

Using 20 strains of Staphylococcus aureus isolated from clinical specimens, the compact colony-forming activity (CCFA) in serum-soft agar (SSA) in sera from various animals and the paracoagulation (PC) activity of the compact colony-forming active substance (CCFAS) extracted from these strains were investigated. The results of this comparative study revealed that the CCFA and PC of S. aureus for sera from various animals in SSA were different, not only among different strains but also in the same strains. In addition, the effect of galactose and calcium ions on the PC activity of these strains in experiments employing human fibrinogen permitted the recognition of these groups of S. aureus strains. In one group, PC activity was decreased by galactose but unaffected by calcium ions, in the second group PC activity was unaffected by galactose but increased by calcium ions, while in the third group it was unaffected by both. These results suggest the possibility of heterogeneity of CCFA among different strains of S. aureus.

The growth of compact and diffuse variants of Staphylococcus aureus in bovine mastitic and normal whey

Strains of Staphylococcus aureus producing either diffuse or compact colonies in serum-soft agar were grown in bovine normal and mastitic whey. Bacterial growth was followed by automated turbidometry. Compact strains multiplied faster and to higher final numbers in mastitic whey than diffuse strains, whereas diffuse strains grew to higher numbers in normal whey. Nutrients (hemolysed bovine blood, bovine serum, proteose-peptone) were added to normal whey to enhance bacterial growth as in mastitic whey. The growth-promoting effect of these nutrients was dose-dependent for compact strains but not for diffuse strains. The difference in the growth characteristics of diffuse and compact strains in bovine whey explains some aspects of the pathogenesis of bovine mastitis.

Human specific immunoglobulin protects against infection with common Staphylococcus in mice

Mice infected with non-capsulated Staphylococcus aureus strains highly resistant to methicillin survived after the administration of specific immunoglobulin extracted from pooled human sera by using homologous capsular type strains, but no protective effect was shown with a conventional immunoglobulin preparation and methicillin, even with high doses.

The expression of capsule in serum-soft agar by Staphylococcus aureus isolated from bovine mastitis

Strains of Staphylococcus aureus were isolated from bovine mastitis, subcultured and maintained in the laboratory for up to 3 years. Encapsulation was assessed by production of a diffuse colony in serum-soft agar. Eight (4%) of 200 strains were encapsulated. Three rapid passages of the remaining 192 strains through either brain-heart infusion broth containing 30% serum or modified 110 medium retrieved the capsule in 75%, but this was rapidly lost after subculture on blood agar. The stimulation of capsule production was studied in 18 of these strains by addition of various components to the passaging medium. Heat-labile factors in serum, milk and mastitic milk enhanced capsule production while bovine serum albumin, an extract of polymorphonuclear leucocytes, NaCl and immunoglobulins had minimal effect. The results indicate that encapsulation is common in bovine staphylococci and while it is lost on subculture, may be retrieved under appropriate conditions.

Antiserum agar method for identification of Smith type exopolysaccharides in clinical isolates of Staphylococcus aureus

We used an antiserum agar method to identify clinical Staphylococcus aureus strains producing an exopolysaccharide antigenically identical to the S. aureus Smith diffuse strain. S. aureus blood isolates were obtained from 137 patients, and three additional isolates were obtained from bone debridement. The 140 patients were clinically divided into the following groups: endocarditis (7 patients); pneumonia, empyema, or both (33 patients); intravascular device (34 patients); superficial or wound infection or both (35 patients); deep tissue infections (18 patients); and 6, unknown bacteremias (13 patients). Ninety (64.3%) of the total 140 S. aureus isolates were found to produce precipitin halos on the antiserum agar. The percentage was greatest in the isolates from the endocarditis group (100%) and least in deep tissue infections (55.5%). The presence of clinical S. aureus strains producing exopolysaccharides antigenically identical to the Smith diffuse strain exopolysaccharide appears to be a common phenomenon.

Applications of fluorescent antibody for detecting capsular substances in Staphylococcus epidermidis

A fluorescent antibody technique was developed for the determination of the type of capsule of strains of Staphylococcus epidermidis. Many mouse virulent and avirulent strain populations were investigated. Of 300 fresh isolates of Staph. epidermidis, 27 were mouse virulent strains and of these 74.1% and 25.9% were mono- and polyvalent, respectively. The frequency of capsular type antigens I, II and III, produced by the 27 virulent strains was found to be 18.5%, 88.9% and 18.5%, the majority being capsular type II. In the mouse avirulent strains, capsular type antigen production was demonstrated in 263 out of 273 strains examined and mono- and polyvalent capsular types comprised 52.3% and 44.0%, respectively. Capsular type I, II, III strains and non-typable strains occurred at frequencies of 15.0%, 95.2%, 34.9% and 3.7% respectively, the majority of mouse avirulent strains also being capsular type II. These results indicate that a majority of ordinary Staph. epidermidis produced capsular type antigens although the capability is quantitatively different according to strain.

Staphylococcal capsular vaccine for preventing mastitis in two herds in Georgia

An encapsulated staphylococcal vaccine, consisting of heat-killed capsular-type A and B Staphylococcus aureus strains and capsular polysaccharide extracted from strain ATCC 31432 of Staphylococcus epidermidis, was used to control bovine mastitis in two herds in Georgia. The vaccine was administered intramuscularly into 97 and 125 cows in the herds, and equal numbers of animals were controls. Two weeks after primary vaccination a booster injection was given. No side effects were observed. In one herd, leucocyte content of milk samples decreased remarkably 1 wk after the booster injection. Significant resistance to infection was maintained for 4 mo after vaccination. Estimation of the total loss of milk yield showed less loss compared to that in the control group for 4 mo after vaccination. In the other herd, remarkable improvements of milk samples were observed as early as 1 wk after primary vaccination and resistance to infection continued for 6 mo after vaccination, when experiments were terminated. At 3 mo after vaccination, loss of milk yield was approximately one-third of that in the control group, and this reduction of loss was maintained for 6 mo after vaccination.

Effect of bile acid derivatives on taurine biosynthesis and extracellular slime production in encapsulated Staphylococcus aureus S-7

Various bile acids were added to cultures of encapsulated strains of Staphylococcus aureus growing in serum-soft agar medium of brain heart infusion broth. We examined effects of these compounds on cellular characteristics such as growth type, cell volume index, clumping factor reaction, slime yield, taurine content, and L-(--)-cysteic acid decarboxylase activity. Upon addition to the medium of either taurochenodeoxycholic acid, taurocholic acid (25 to 50 microgram/ml), or cholic acid (10 to 25 microgram/ml), the colonial morphology of taurine-positive cells (strain S-7) was altered from the diffuse to the compact type in serum-soft agar. Also, the titer of the clumping factor reaction increased, while the cell volume index and slime yield were markedly decreased. Tauro-bile acids, including taurocholic acid, taurochenodeoxycholic acid, taurodehydrocholic acid, and taurodeoxycholic acid (50 microgram/ml) inhibited the synthesis of taurine and resulted in decreased L-(--)-cysteic acid decarboxylase activity. Among all of the derivatives cholic acid itself was found to inhibit slime production and L-(--)-cysteic acid decarboxylase activity to the greatest extent. Glyco-bile acid derivatives and taurolicholic acid (50 to 100 microgram/ml) had no effect on L-(--)-cysteic acid decarboxylase activity. Compounds such as glycodeoxycholic acid (50 to 100 microgram/ml) had no effect upon any of the cellular characteristics tested. No effect was observed upon addition of any of these compounds to cultures of the taurine-negative strain (T-26-B). We did find a correlation between the inhibition of taurine biosynthesis and decreased slime production. Electron micrographs indicated that this encapsulated strain was converted to an unencapsulated state in the presence of bile acids.

Influence of encapsulation on staphylococcal opsonization and phagocytosis by human polymorphonuclear leukocytes

In previous studies, encapsulated Staphylococcus aureus strains have been shown to resist phagocytosis. In this investigation, the nature of the interference with phagocytosis by human polymorphonuclear leukocytes was examined by studying the opsonization of two pairs of unencapsulated (Smith compact and M variant) and encapsulated (Smith diffuse and M) S. aureus strains. The uptake of [3H]glycine-labeled bacteria by normal leukocytes was quantitatively measured after incubation of bacteria in pooled serum, C2-deficient serum, immunoglobulin-deficient serum, and serum from a rabbit immunized with S. aureus M. The presence of a capsule was found to interfere with opsonization by both the classical and alternative pathways of complement as well as by heat-stable opsonic factors in nonimmune human serum. This interference was significantly greater in the case of the S. aureus M strain than in the case of the Smith diffuse strain. The only effective opsonic source for S. aureus M was immune rabbit serum. It is proposed that encapsulation of S. aureus strains interferes with phagocytosis by preventing effective bacterial opsonization.

Relationship of capsular type to biochemical and immunological properties of teichoic acid preparations from unencapsulated strains of Staphylococcus aureus

We investigated the biochemical and immunological characteristics of teichoic acid preparations (TAP) obtained from four unencapsulated strains of Staphylococcus aureus which nonetheless, according to the serum-soft agar technique, produced capsular type antigen and were representative of the four types A, B, C, and D. In the agar diffusion test, TAP of each strain produced a single precipitin line only against rabbit antisera corresponding to the homologous capsular type; no lines were observed against antisera to the heterologous capsular type. All TAP were ribitol type except one, glycerol, prepared from a capsular type D strain. Major acetylglucosaminyl residues of TAP from strains having capsular type A and C antigens were attached to the polyribitol phosphate by beta-linkage, whereas TAP from a type B antigen strain had an alpha-linkage; type D antigen was attached to the polyglycerol phosphate by the beta-linkage. Chemical analyses and infrared spectrograms of these TAP further confirmed their heterogeneous nature.

Induction of resistance with heat-killed compact-type strains of Staphylococcus aureus against challenge with the diffuse variant of the Smith strain of Staphylococcus aureus

Active immunization of mice with high doses of heat-killed and autoclaved vaccine of unencapsulated strains of Staphylococcus aureus, which was grown in brain heart infusion media, protected against challenge with the Smith diffuse strain of Staphylococcus aureus. These organisms were capable of absorbing the protective antibody in rabbit hyperimmune sera prepared with the Smith diffuse strain. Also, mice treated with rabbit hyperimmune sera prepared with these strains (four out of six strains) protected against challenge with the Smith diffuse strain. Protective activities of these rabbit hyperimmune sera were assumed to be essentially identical to the protective antibody induced by the Smith diffuse strain.