A novel, selective synthetic acetamide containing culture medium for isolating Pseudomonas aeruginosa from milk

A selective synthetic medium has been developed both in liquid (Z-broth) and solid (Z-agar) forms for selective isolation of Pseudomonas aeruginosa from foods. The simple, easy to prepare peptone-free synthetic medium contained acetamide that is metabolized to ammonia and acetic acid providing nitrogen and carbon supply. The medium contained no inhibitors. Selectivity of the liquid medium was tested by inoculation of pure cultures of different bacteria belonging to the groups Bacillus, Pseudomonas, Enterobacteriaceae and Staphylococcus. It was found that the selectivity of the medium was complete for the examined range of bacteria. However, a similar result was obtained when nitrofurantoin broth was used. Applicability of the synthetic agar medium was also tested by a nation-wide inter-laboratory test using two milk samples containing 10(3)/ml (sample I) and 10(5)/ml (sample II) Pseudomonas aeruginosa. According to this test, no microbiologically relevant differences were found between the results obtained by Z-agar and cetrimide-agar a frequently used selective agar in case of sample II. However, a relevant and statistically significant difference was found in the results of sample I in favour of the Z-agar, that could indicate the presence of a low number of bacteria. Concerning repeatability and reproducibility, Z-agar proved to be superior to cetrimide agar.

Staphylococcus hominis subsp. novobiosepticus subsp. nov., a novel trehalose- and N-acetyl-D-glucosamine-negative, novobiocin- and multiple-antibiotic-resistant subspecies isolated from human blood cultures

A new subspecies, Staphylococcus hominis subsp. novobiosepticus, isolated from human blood cultures, a wound, a breast abscess and a catheter tip, is described on the basis of a study of 26 strains isolated between 1989 and 1996. DNA-DNA reassociation reactions, conducted under stringent conditions, and macrorestriction pattern analysis demonstrated that these strains are closely related to previously characterized S. hominis strains isolated from human skin and clinical specimens, but are significantly divergent. S. hominis subsp. novobiosepticus can be distinguished from S. hominis (now named S. hominis subsp. hominis) by its combined characteristics of novobiocin resistance and failure to produce acid aerobically from D-trehalose and N-acetyl-D-glucosamine. Furthermore, all 26 strains of the new subspecies are resistant to nalidixic acid, penicillin G, oxacillin, kanamycin and streptomycin, and were either resistant or had intermediate resistance to methicillin and gentamicin. Most strains were also resistant to erythromycin, clindamycin, chloramphenicol, trimethoprim/sulfamethoxazole and ciprofloxacin. Based on a comparison of the sequences of a 1001 bp mecA amplification product from reference methicillin-resistant staphylococci, the mecA gene present in S. hominis subsp. novobiosepticus was identified as homologue A, commonly found in S. aureus and many coagulase-negative staphylococcal species. The type strain of S. hominis subsp. novobiosepticus is ATCC 700236T. Descriptions of S. hominis subsp. novobiosepticus subsp. nov and S. hominis subsp. hominis are given and the description of S. hominis is emended.

Identification and characterization of the Staphylococcus carnosus nitrate reductase operon

Physiological and genetic characterization of Staphylococcus carnosus nitrate reductase-negative mutants led to the identification of the nitrate reductase operon, narGHJI. Transcription from the nar promoter was stimulated by anaerobiosis, nitrate, and nitrite. This is in accordance with the nitrate reductase activities determined with benzyl viologen as electron donor. However, in the presence of oxygen and nitrate, high transcriptional initiation but low nitrate reductase activity was observed. Since the alphabeta complex of the nitrate reductase formed during anaerobic growth was insensitive to oxygen, other oxygen-sensitive steps (e.g., post-transcriptional mechanisms, molybdenum cofactor biosynthesis) must be involved. The nitrate-reducing system in S. carnosus displays similarities to the dissimilatory nitrate reductases of Escherichia coli. However, in the S. carnosus nar promoter, no obvious Fnr and integration host factor recognition sites are present; only one site that is related to the E. coli NarL consensus sequence was found. Studies to determine whether the E. coli proteins NarL and Fnr are functional at the S. carnosus narGHJI promoter indicated that the promoter is not functional in E. coli.

Characterization of moeB--part of the molybdenum cofactor biosynthesis gene cluster in Staphylococcus carnosus

Transposon mutagenesis of Staphylococcus carnosus led to the identification of a gene cluster comprising nine genes that are important for molybdenum cofactor biosynthesis. Two nitrate-reductase-negative Tn917-insertion mutants were defective in MoeB. In cell-free extracts of an moeB mutant, the molybdenum-cofactor-deficient nitrate reductase could be reconstituted with a low-molecular-mass component (most likely free molybdenum cofactor) from an S. carnosus mutant that is defective in the nitrate reductase structural genes. The expression of moeB was studied in response to oxygen and nitrate. Primer-extension studies indicated that anaerobiosis and nitrate each enhance transcription of moeB.

Differentiation and distribution of three types of exfoliative toxin produced by Staphylococcus hyicus from pigs with exudative epidermitis

Exfoliative toxins of approximately 30 kDa produced by Staphylococcus hyicus strains NCTC 10350, 1289D-88 and 842A-88 were purified and specific polyclonal antisera were raised against each of the toxins. It was shown by immunoblot analysis and ELISA that three exfoliative toxins from S. hyicus were antigenically distinct. The three toxins were designated ExhA, ExhB and ExhC. From 60 diseased pigs, each representing an outbreak of exudative epidermitis, a total of 584 isolates of S. hyicus were phage typed and tested for production of exfoliative toxin. ExhA-, ExhB- and ExhC-producing S. hyicus isolates were found in 12 (20%), 20 (33%) and 11 (18%), respectively, of the 60 pig herds investigated. Production of the different types of exfoliative toxin was predominantly associated with certain phage groups. However, toxin production was found in all of the six phage groups defined by the phage typing system. Some changes in the distribution of isolates between phage groups were observed when the results of this study were compared to previous investigations. In this study two new antigenically distinct exfoliative toxins were isolated and tools for in vitro detection of toxin producing S. hyicus isolates and for further studies on the exfoliative toxins from S. hyicus have been provided.

Self-assembled alpha-hemolysin pores in an S-layer-supported lipid bilayer

The effects of a supporting proteinaceous surface-layer (S-layer) from Bacillus coagulans E38-66 on a 1,2-diphytanoyl-sn-glycero-3-phosphatidylcholine (DPhPC) bilayer were investigated. Comparative voltage clamp studies on plain and S-layer supported DPhPC bilayers revealed no significant difference in the capacitance. The conductance of the composite membrane decreased slightly upon recrystallization of the S-layer. Thus, the attached S-layer lattice did not interpenetrate or rupture the DPhPC bilayer. The self-assembly of a pore-forming protein into the S-layer supported lipid bilayer was examined. Staphylococcal alpha-hemolysin formed lytic pores when added to the lipid-exposed side. The assembly was slow compared to unsupported membranes, perhaps due to an altered fluidity of the lipid bilayer. No assembly could be detected upon adding alpha-hemolysin monomers to the S-layer-faced side of the composite membrane. Therefore, the intrinsic molecular sieving properties of the S-layer lattice do not allow passage of alpha-hemolysin monomers through the S-layer pores to the lipid bilayer. In comparison to plain lipid bilayers, the S-layer supported lipid membrane had a decreased tendency to rupture in the presence of alpha-hemolysin.

In vivo presence of capsular polysaccharide in coagulase-negative staphylococci of ovine origin

Three strains of coagulase-negative staphylococci identified as Staphilococcus warnery, Staphylococcus simulans and Staphylococcus haemolyticus were examine for evidence of capsular polysaccharide, in vitro by negative staining with India ink, and in vivo by transmission electron microscopy. In vitro, unstained materials surrounded clusters or single cocci. In vivo, capsula materials were surrounding phagocytosed bacteria cells. These capsular materials were either closely or loosely bound to bacterial cells, or projecting like "pili" from the surface of the cell wall. The evidence suggests that capsular polysaccharide is a common characteristic of coagulase-negative staphylococci causing prolonged intramammary infection of sheep.

Flow cytometric quantification of surface-displayed recombinant receptors on staphylococci

Surface display of recombinant proteins on bacteria and phages has become an important tool in bioscience. To evaluate the various host systems, a great need exists for quantitative methods to determine the densities of displayed proteins and peptides on the bacteria and phage surfaces. Here we describe how a method previously applied for quantification of surface proteins on mammalian cells has been adapted for quantification of chimeric receptors surface-displayed on bacteria; in this study, the bacteria being recombinant staphylococci. The presented method takes advantage of fluorescence-activated cell sorting (FACS) technology and a new type of nonfluorescent plastic beads, similar in size (2 microns in diameter) to bacterial cells, and thus suitable for generation of calibration curves from which the number of chimeric receptors can be obtained. The method was used to estimate the number of antigenic sites on two types of recombinant staphylococci, both carrying heterologous chimeric receptors, and it was found that the recombinant Staphylococcus carnosus cells carried approximately 10(4) surface-displayed antigenic sites, while recombinant Staphylococcus xylosus exposed approximately 3 x 10(3) sites per cell. The use of the deviced method for different applications is discussed.

epr, which encodes glycylglycine endopeptidase resistance, is homologous to femAB and affects serine content of peptidoglycan cross bridges in Staphylococcus capitis and Staphylococcus aureus

Staphylococcus capitis EPK1 produces a glycylglycine endopeptidase, ALE-1 (M. Sugai, T. Fujiwara, T. Akiyama, M. Ohara, H. Komatsuzawa, S. Inoue, and H. Suginaka, J. Bacteriol. 179:1193-1202, 1997), which hydrolyzes interpeptide pentaglycine chains of cell wall peptidoglycan of S. aureus. Characterizations of the enzyme activity and cloning of ale-1 revealed that ALE-1 is very similar to prolysostaphin produced by S. simulans bv. staphylolyticus. Strain EPK1 is resistant to lysis by ALE-1 and by lysostaphin. A gene that renders the cells resistant to glycylglycine endopeptidase (epr) was found 322 bp upstream of and in the opposite orientation to ale-1. The deduced amino acid sequence of epr showed similarities to FemA and FemB, which have been characterized as factors essential for methicillin resistance of S. aureus. Inactivation of either femA or femB causes decreased resistance to methicillin, increased resistance to lysostaphin, and decreased glycine content in the interpeptide chains of peptidoglycan. Therefore, femAB is suggested to be involved in the addition of glycine to pentapeptide peptidoglycan precursor. S. aureus with epr on a multicopy plasmid had phenotypes similar to those of femAB mutants except that it did not alter resistance level to methicillin. These results suggest that epr and femAB belong to the protein family involved in adding amino acids to the pentapeptide peptidoglycan precursor and that epr is involved in the addition of serine to the pentapeptide.

Structure of an enzyme required for aminoglycoside antibiotic resistance reveals homology to eukaryotic protein kinases

Bacterial resistance to aminoglycoside antibiotics is almost exclusively accomplished through either phosphorylation, adenylylation, or acetylation of the antibacterial agent. The aminoglycoside kinase, APH(3')-IIIa, catalyzes the phosphorylation of a broad spectrum of aminoglycoside antibiotics. The crystal structure of this enzyme complexed with ADP was determined at 2.2 A. resolution. The three-dimensional fold of APH(3')-IIIa reveals a striking similarity to eukaryotic protein kinases despite a virtually complete lack of sequence homology. Nearly half of the APH(3')-IIIa sequence adopts a conformation identical to that seen in these kinases. Substantial differences are found in the location and conformation of residues presumably responsible for second-substrate specificity. These results indicate that APH(3') enzymes and eukaryotic-type protein kinases share a common ancestor.

Staphylococcus hyicus exfoliative toxin: purification and demonstration of antigenic diversity among toxins from virulent strains

The exfoliative toxin produced by Staphylococcus hyicus strain 1289D-88 was purified as a single protein of approximately 30 kDa. Extracellular proteins of S. hyicus grown under small scale fermentation conditions were precipitated with ammonium sulfate. Separation of proteins was performed by hydrophobic interaction chromatography and successively anion exchange chromatography. The purified toxin was tested in a piglet skin assay. Weak epidermal lesions were macroscopically and microscopically similar to lesions caused by (NH4)2SO4-precipitated culture supernatant from the same strain. Addition of 0.5 mM CuSo4 to the purified toxin resulted in more intense skin alterations comparable to lesions caused by precipitated culture supernatant diluted 1:10. These results indicated that the activity of the exfoliative toxin was dependent on the presence of Cu2+. Polyclonal and monoclonal antibodies were prepared against the exfoliative toxin from strain 1289D-88. The in vivo activity of the exfoliative toxin could be neutralized by antibodies. It was shown that polyclonal as well as monoclonal antibodies only reacted with the toxin produced by two of nine well-defined virulent strains of S. hyicus. These results showed antigenic diversity among exfoliative toxins produced by different strains of S. hyicus.

Display of heterologous proteins on the surface of microorganisms: from the screening of combinatorial libraries to live recombinant vaccines

In recent years there has been considerable progress towards the development of expression systems for the display of heterologous polypeptides and, to a lesser extent, oligosaccharides on the surface of bacteria or yeast. The availability of protein display vectors has in turn provided the impetus for a range of exciting technologies. Polypeptide libraries can be displayed in bacteria and screened by cell sorting techniques, thus simplifying the isolation of proteins with high affinity for ligands. Expression of antigens on the surface of nonvirulent microorganisms is an attractive approach to the development of high-efficacy recombinant live vaccines. Finally, cells displaying protein receptors or antibodies are of use for analytical applications and bioseparations.

Sequence and analysis of the replication region of the Staphylococcus xylosus plasmid pSX267

The region of the 29.5-kb plasmid pSX267 from Staphylococcus xylosus DSM 20267 that is required for autonomous replication in staphylococci was isolated on a 1.8-kb DNA fragment. The sequence analysis of the fragment yielded two open reading frames, repA and orf2, encoding proteins of 37.2 and 13.2 kDa, respectively. The deduced amino acid sequence of repA showed similarity to the replication initiator protein of plasmid pAD1 from Enterococcus faecalis, to two proteins of unknown function encoded by the E. faecalis plasmid pCF10 and the lactobacillus helveticus plasmid pLJ1, and surprisingly to the mouse interferon-response element binding factor 1. The repA gene of pSX267 is indispensable for replication suggesting that it encodes the replication initiator protein of pSX267. Introduction of a frameshift mutation into repA or deletion of 26 codons at its 3'-end resulted in nonreplicative plasmids. Removal of sequences required for repA expression also abolished replication. Complementation experiments with repA in trans identified the ori of pSX267 within the repA coding region. The second orf, which is located downstream of repA, could be deleted without affecting plasmid replication. It seems to be a nonfunctional remainder of a rolling circle plasmid of the pC194/pUB110 family, since its deduced amino acid sequence resembles the pC194/pUB110-type replication proteins. The minimal replicon of pSX267 defined so far comprises 1255 bp. Besides repA, no other plasmid-encoded gene is required to mediate replication in staphylococci.

Identification of staphylococci with a self-educating system using fatty acid analysis and biochemical tests

We characterized all of the 35 aerobic taxa of the genus Staphylococcus by using an objective, self-learning system combining both whole-cell fatty acid (FA) analysis and the results of 35 biochemical tests. Isolates were compared with the type strain for each taxon to generate an FA profile library and a biochemical table of test responses. Isolates were accepted into the system if they had a similarity index of > or = 0.6 for a taxon within the FA profile library and if they were identified as the same taxon by a computer program using a probability matrix constructed from the biochemical data. These stringent criteria led to acceptance of 1,117 strains assigned to legitimate taxa. Additional FA groups were assembled from selected strains that did not meet the inclusion criteria based on the type strains and were added to the system as separate entries. Currently, 1,512 isolates have bee accepted into the system. This approach has resulted in a comprehensive table of biochemical test results and a FA profile library, which together provide a practical system for valid identifications.

CD14 is a cell-activating receptor for bacterial peptidoglycan

The hypothesis that CD14 (an endotoxin receptor present on macrophages and neutrophils) acts as a cell-activating receptor for bacterial peptidoglycan was tested using mouse 70Z/3 cells transfected with human CD14. 70Z/3 cells transfected with an empty vector were unresponsive to insoluble and soluble peptidoglycan, as well as to low concentrations of endotoxin. 70Z/3-CD14 cells were responsive to both insoluble and soluble peptidoglycan, as well as to low concentrations of endotoxin, as measured by the expression of surface IgM, activation of NF-kappaB, and degradation of IkappaB-alpha. Peptidoglycan also induced activation of NF-kappaB and degradation of IkappaB-alpha in macrophage RAW264.7 cells. These peptidoglycan-induced effects (in contrast to endotoxin-induced effects) were not inhibited by polymyxin B. Both peptidoglycan- and endotoxin-induced activation of NF-kappaB were inhibited by anti-CD14 mAb. The N-terminal 151 amino acids of CD14 were sufficient for acquisition of full responsiveness to both peptidoglycan and endotoxin, but CD14 deletion mutants lacking four small regions within the N-terminal 65 amino acids showed differentially diminished responses to peptidoglycan and endotoxin. These results identify CD14 as the functional receptor for peptidoglycan and demonstrate that similar, but not identical sequences in the N-terminal 65-amino acid region of CD14 are critical for the NF-kappaB and IgM responses to both peptidoglycan and endotoxin.

Staphylococcus saprophyticus subsp. bovis subsp. nov., isolated from bovine nostrils

A new coagulase-negative subspecies, Staphylococcus saprophyticus subsp. bovis, is described on the basis of a study of five strains isolated from the anterior nares of cows. This subspecies is differentiated from the other novobiocin-resistant staphylococci by its phenotypic properties, cell wall composition, and levels of genetic relatedness. The type strain of the new subspecies is KV 12 (=CCM 4410).

[Immunoenzyme assay of staphylococcal toxin using polyamide micropore membranes]

The optimum conditions for extraction of catalytic active conjugates of alpha-amylase and antibodies for staphylococcal toxin (ST) have been created. The optimum correlation of antibodies and enzyme for the effective use of the extracted conjugate during enzyme immunoassay for ST has been established. The covalent immobilization of antibodies on the micropore polyamide membranes has been carried out. Apart from this, the extracted conjugated were purified by TSK-gel HN-55 chromatography. The optimum concentration of the conjugates has been defined.

Lethal synergy between toxins of staphylococci and enterobacteria: implications for sudden infant death syndrome

AIM

To test the hypothesis that lethal synergy occurs between toxin preparations of nasopharyngeal staphylococci and enterobacteria from sudden infant death syndrome (SIDS) victims and matched healthy infants.

METHODS

SIDS and matched healthy babies were studied if both staphylococcal and enterobacterial strains were isolated from the nasopharynx. The lethality of toxin preparations from each bacterial isolate (separately and combined) was assessed over a range of dilutions using the chick embryo assay system.

RESULTS

Staphylococci and enterobacteria were isolated together from the nasopharynx of seven SIDS babies but from only one normal healthy infant. Enterobacterial toxins were lethal at high dilutions. Staphylococcal toxins were less toxic. Simultaneous testing in the chick assay of staphylococcal and enterobacterial toxins, from each baby, at non-lethal concentrations enhanced lethality levels by 177 to 1011% compared with lethality expected by an additive effect alone.

CONCLUSIONS

Synergy occurs between the toxins of nasopharyngeal staphylococci and enterobacteria. This combination of strains is more likely to occur in the nasopharynx of SIDS victims than that of healthy infants.

Agglutination of Staphylococcus saprophyticus: a structural and cytochemical study

Staphylococcus saprophyticus was shown to be agglutinated by wheat germ agglutinin, wheat germ agglutinin-biotin and bovine serum albumin-p-aminophenyl-N-acetyl-beta-D-glucosaminide (GlcNAc-BSA), and sheep red blood cells. In these agglutinations, filamentous or amorphous structures radiating from the surface of S. saprophyticus were demonstrated by electron microscope observation. Cytochemical analyses of the agglutination revealed the binding sites of wheat germ agglutinin in S. saprophyticus and the binding sites of GlcNAc in the sheep red blood cells and S. saprophyticus. Since GlcNAc-BSA contains N-acetylglucosamine to which wheat germ agglutinin can bind, it is most likely that an interaction between a wheat germ agglutinin-bindable substance in S. saprophyticus and an N-acetylglucosamine-bindable substance in sheep red blood cells is involved in the agglutination.

Development of a chitin assay for the quantification of fungus

Chitin, a unique structural polysaccharide found in fungi and arthropods, is not produced by vertebrates. Thus, the potential applications of a specific and sensitive assay for chitin are numerous, including the evaluation of the extent of fungal keratitis. Chitin is a homopolymer of beta (1, 4) linked D-N-acetylglucosamine. We have developed a simple and reproducible assay for chitin and applied it to Candida albicans cultures. The assay involves homogenization of the culture and treatment with 21.1 M KOH to remove soluble materials, including proteins. This base treatment also deacetylates the chitin to the glucosamine polymer, chitosan. Chitosan is hydrolyzed by 0.5 M H2SO4 to glucosamine monomers which are then deaminated by the addition of NaNO2 to the acid solution. The resulting 2,5-anhydromannose is reduced by NaB[3H]4 to 1-[3H] 2,5-anhydromannitol. This radiolabelled sugar is isolated by paper chromatography and quantified via liquid scintillation. The sensitivity of this assay is assessed by comparison of colony forming units (CFU's) with a glucosamine standard. A typical run of the assay detects 53.1 CFU/c.p.m., and 356,000 c.p.m. per nanomole of N-acetylglucosamine. The specificity of the assay is very high because of the unique nature of chitin. This method of chitin determination may be a useful alternative method for future investigations involving the study of fungal infections in mammalian tissues.

Expression of Staphylococcus saprophyticus surface properties is modulated by composition of the atmosphere

Expression of two major surface proteins of Staphylococcus saprophyticus, the haemagglutinin and the Staphylococcus saprophyticus surface-associated protein (Ssp), required carefully defined culture conditions. The Ssp is produced when bacteria are grown on agar, whereas expression of the haemagglutinin requires growth in broth. We sought to identify the environmental signals that are responsible for this modulation. Varying the pH, the osmolarity of the growth medium or the temperature did not influence expression of the proteins. In contrast, growth in an anaerobic atmosphere increased haemagglutination titres and fibronectin binding (both mediated by the haemagglutinin) but suppressed production of the Ssp. As the influence of the CO2 level could be excluded, we conclude that expression of these surface proteins is probably modulated by the O2 content of the atmosphere.

Polar lipids of Staphylococcus strains analysed by fast atom bombardment mass spectrometry

This study used fast atom bombardment mass spectrometry (FAB MS) to obtain detailed information on polar lipids of Staphylococcus by examining 23 isolates. Eighteen major anions were found in the range m/z 199-297, consistent with the presence of carboxylate anions. A further 21 major anions were found in the higher mass regions of m/z 609-805, consistent with the presence of phospholipid anions. In Staph. aureus, Staph. epidermidis, Staph. haemolyticus and Staph. hominis, the most intense peaks putatively assigned as carboxylate ions were consistent with presence of C15:0, followed by C17:0 except in the case of Staph. epidermidis. The major phospholipid anions were consistent with the presence of PG(30:0), PG(32:0) and PG(33:0). It is concluded that Staphylococcus has a characteristic polar lipid profile and that qualitative and quantitative differences may be seen between Staph. aureus and Staph. epidermidis.