Biological attributes of staphylococcal cell walls

Generation of bi-transgenic pigs overexpressing human lactoferrin and lysozyme in milk

Intensive swine production industry uses antibiotics to treat diseases and improve pig growth. This can not only cause antibiotic resistance, but can also pollute the environment or eventually affect human public health. To date, human lactoferrin (hLF) and human lysozyme (hLZ) have been known as non-adaptive but interactive antimicrobial members and could act in concert against bacteria, which contribute to host defense. Therefore, their expression in pigs might be an alternative strategy for replacing antibiotics in the pig production industry. In our study, we produced hLF and hLZ bi-transgenic pigs and assessed the milk's antibacterial ability. Integration of both transgenes was confirmed by PCR and southern blot. Both the hLF and hLZ were expressed in the mammary gland of bi-transgenic pigs, as detected by western blotting. The expression amounts were 6.5 g/L for hLF and 1.1 mg/L for hLZ using ELISA. Interestingly, pig milk containing hLF and hLZ had synergistic antimicrobial activity. Our results suggest an alternative approach for avoiding the use of antibiotics in the pig industry, which would be of great benefit to the commercial swine production.

High surface hydrophobicity of autoaggregating Staphylococcus aureus strains isolated from human infections studied with the salt aggregation test

A total of 209 strains of Staphylococcus aureus isolated from infections and 23 strains from nose cultures of healthy laboratory personnel were compared for relative surface hydrophobicity in the salt aggregation test (Lindahl et al., Biochim. Biophys. Acta 677:471-476, 1981). In the standard method, bacterial cell suspensions from blood agar-grown cultures were tested for visible aggregation by "salting out" in serial dilutions of ammonium sulfate (0.1 to 1.6 M [final concentration]). Bacteria were defined as extremely hydrophobic when showing autoaggregation in saline or in 0.002 M sodium phosphate buffer (pH 6.8). Using this definition, we found a large number of strains isolated from various infections to be very hydrophobic: 123 of 135 strains from patients with septicemia (91%), 54 of 60 strains from wound infections (90%), and 12 of 14 strains from urinary tract infections (86%). In contrast, only 9 of 23 strains from nose cultures of healthy carriers (39%) were autoaggregating. A total of 12 autoaggregating strains were grown on various solid and liquid media. Only growth on hematin agar was found to completely suppress surface hydrophobicity as revealed by our salt aggregation test method, and growth in liquid media prevented the expression of hydrophobicity in most strains. Growth at 20 or 42 degrees C or under anaerobic conditions did not affect hydrophobicity. Cells harvested from various phases of growth did not differ significantly in surface hydrophobicity. Heating washed cell suspensions at 56 degrees C did not affect the salt aggregation test values, whereas heating the cell suspensions at 80 and 100 degrees C caused a significant decline in hydrophobicity. The addition of ethylene glycol (25% [vol/vol] final concentration) prevented the autoaggregation of 10 of the 12 strains. Likewise, treating the cell suspensions with proteolytic enzymes decreased the surface hydrophobicity, indicating that surface proteins contribute to high surface hydrophobicity of autoaggregating strains.

Reduced degradability by lysozyme of staphylococcal cell walls after chloramphenicol treatment

The effectiveness of host defence against staphylococcal infections depends on the capability of phagocytes to degrade the bacterial cell walls. Treatment with bacteriostatic agents like chloramphenicol could cause problems since under these drugs staphylococcal walls will be substantially thickened. This study presents evidence that the additional wall material built in the presence of chloramphenicol could moreover be rendered more resistant to lysosomal enzymes: In vitro at pH 5.6, lysozyme from hen egg-white proved to degrade the chloramphenicol-wall material at a velocity reduced to 20% of that of the normal wall. Thus, during the degradation of chloramphenicol-treated staphylococcal cell walls the phagocytes have to deal not only with a quantitative but also with a qualitative problem. Possible reasons for the reduced degradability as to chloramphenicol-induced alterations of the wall composition as well as to activating effects of lysozyme on cell wall autolysins are discussed in view of microbiological and medical implications.

Cell wall degradation of Staphylococcus aureus by lysozyme

In contrast to former findings lysozyme was able to attack the cell walls of Staphylococcus aureus under acid conditions. However, experiments with 14C-labelled cell walls and ribonuclease indicated that, under these conditions, lysozyme acted less as an muralytic enzyme but more as an activator of pre-existing autolytic wall enzymes. Electron microscopic studies showed that under these acid conditions the cell walls were degraded by a new mechanism (i.e. "attack from the inside"). This attack on the cell wall started asymmetrically within the region of the cross wall and induced the formation of periodically arranged lytic sites between the cytoplasmic membrane and the cell wall proper. Subsequently, a gap between the cell wall and the cytoplasmic membrane resulted and large cell wall segments became detached and suspended in the medium. The sequence of lytic events corresponded to processes known to take place during wall regeneration and wall formation. In the final stage of lysozyme action at pH 5 no cell debris but "stabilized protoplasts" were to be seen without detectable alterations of the primary shape of the cells. At the same time long extended ribbon-like structures appeared outside the bacteria. The origin as well as the chemical nature of this material is discussed. Furthermore, immunological implications are considered.

Immunological properties of teichoic acids

Images

Use of bacteriophage-resistant mutants to study the nature of the bacteriophage receptor site of Staphylococcus aureus

Bacteriophage-resistant strains of Staphylococcus aureus H were isolated after mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine. Cell walls isolated from about half of these resistant strains were incapable of inactivating phages and were shown to lack N-acetyl-d-glucosamine (GlcNAc) in their cell wall teichoic acid. Apart from the lack of GlcNAc, two of these mutant strains were deficient in cell wall phosphorus and ester-linked d-alanine. These two strains were also found to be resistant to both phage K and a host-range mutant isolated from the parent phage. These two phages could lyse the other phage-resistant mutants which lacked GlcNAc in their teichoic acid. Cell walls from the remaining phage-resistant mutant strains did inactivate phages and were found to have normal cell wall teichoic acid. Although GlcNAc in teichoic acid was required for phage inactivation, no difference in phage inactivation ability was detected with cell walls isolated from strains of S. aureus having exclusively alpha- or exclusively beta-linked GlcNAc in their cell wall teichoic acid.

Infection in mouse peritoneal cavity with a pyrimidine-requiring mutant and naturally occurring Staphylococcus aureus strains

The lethal activity of a thymineless mutant of Staphylococcus aureus Wood 46 strain has been compared with that of three naturally occurring strains: parent Wood 46, Smith, and coagulase-negative SA-13. The thymineless mutant and the parent Wood 46 strain showed a sharp decline in culturable units from the peritoneal cavity in the first 4 hr after their injection. After 6 hr, that is, 2 hr before the mice began to die, the number of culturable units of the thymineless mutant was still declining, whereas that of the parent strain increased; for both strains, the number of units was still lower than that of the inoculum. Although the thymineless mutant, unlike the parent strain, was apparently unable to multiply in mouse peritoneal cavity, it killed mice at a similar rate. The highly virulent Smith strain known to multiply rapidly and the avirulent coagulase-negative SA-13 strain were used as additional controls. Under our experimental conditions, death of mice after the injection of the thymineless mutant in the peritoneal cavity did not seem to be due to bacterial multiplication but to toxicity, death being delayed by antitoxin. The pyrimidine-requiring auxotroph we used could be better material than killed bacteria to study some aspects of the lethal activity of S. aureus.

Serological activity of staphylococcal polysaccharide

The polysaccharide from cell walls of coagulase-positive staphylococci coated both latex particles and tanned red cells for agglutination by human sera and by specific staphylococcal antisera. Treatment with trypsin or autoclaving destroyed the capacity of polysaccharide to coat particles but did not affect precipitation of antibody. Periodic acid destroyed both properties. The teichoic acid portion of the staphylococcal polysaccharide displayed precipitin activity similar to polysaccharide, but it did not coat either latex particles or tanned red cells. Teichoic acid did, however, inhibit specific agglutination of polysaccharide-coated particles or cells.