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P F Chan

Publications and source records attributed to P F Chan.

8 recordsLinked to original sources
PubMed2001

Staphylococcus aureus accessory regulators: expression within biofilms and effect on adhesion.

Many of the genes encoding the virulence factors for Staphylococcus aureus are controlled by the accessory gene regulator (agr) and staphylococcal accessory regulator (sar). This regulation may be affected by the environment in which the organisms are grown. In the majority of ecosystems, bacteria grow attached to surfaces and form biofilms. We used S. aureus strains containing mutations inactivating agr and sar to determine whether the presence of these genes influences the attachment of the bacterium to a surface. We also used strains harbouring reporter constructs of the agr and sar operons to determine their expression in biofilms. The attachment study results showed that the sarA mutant strain adhered better to glass than did the agrA mutant or the wild type. There was an increased adherence to fibronectin-coated glass for all three strains compared to glass. Thus, these adhesion studies demonstrate that agr and sar have pleiotrophic effects on the surface expression of molecules responsible for binding to different substrata. In the biofilms higher numbers of bacteria and the greatest expression were observed at the base, but there were no observable differences between the reporter constructs. Expression of the agr and sar reporter fusions was significantly higher in the deepest layers of the biofilms where the greatest numbers of bacteria were also observed, perhaps as one might expect for genes that are regulated in a cell density dependent fashion.

Bacterial Adhesion↗
PubMed1998

The Staphylococcus aureus alternative sigma factor sigmaB controls the environmental stress response but not starvation survival or pathogenicity in a mouse abscess model.

The role of sigmaB, an alternative sigma factor of Staphylococcus aureus, has been characterized in response to environmental stress, starvation-survival and recovery, and pathogenicity. sigmaB was mainly expressed during the stationary phase of growth and was repressed by 1 M sodium chloride. A sigB insertionally inactivated mutant was created. In stress resistance studies, sigmaB was shown to be involved in recovery from heat shock at 54 degreesC and in acid and hydrogen peroxide resistance but not in resistance to ethanol or osmotic shock. Interestingly, S. aureus acquired increased acid resistance when preincubated at a sublethal pH 4 prior to exposure to a lethal pH 2. This acid-adaptive response resulting in tolerance was mediated via sigB. However, sigmaB was not vital for the starvation-survival or recovery mechanisms. sigmaB does not have a major role in the expression of the global regulator of virulence determinant biosynthesis, staphylococcal accessory regulator (sarA), the production of a number of representative virulence factors, and pathogenicity in a mouse subcutaneous abscess model. However, SarA upregulates sigB expression in a growth-phase-dependent manner. Thus, sigmaB expression is linked to the processes controlling virulence determinant production. The role of sigmaB as a major regulator of the stress response, but not of starvation-survival, is discussed.

Abscess↗
PubMed1998

Role of SarA in virulence determinant production and environmental signal transduction in Staphylococcus aureus.

The staphylococcal accessory regulator (encoded by sarA) is an important global regulator of virulence factor biosynthesis in Staphylococcus aureus. To further characterize its role in virulence determinant production, an sarA knockout mutant was created by insertion of a kanamycin antibiotic resistance cassette into the sarA gene. N-terminal sequencing of exoproteins down-regulated by sarA identified several putative proteases, including a V8 serine protease and a novel metalloprotease, as the major extracellular proteins repressed by sarA. In kinetic studies, the sarA mutation delays the onset of alpha-hemolysin (encoded by hla) expression and reduces levels of hla to approximately 40% of the parent strain level. Furthermore, SarA plays a role in signal transduction in response to microaerobic growth since levels of hla were much lower in a microaerobic environment than after aerobic growth in the sarA mutant. An exoprotein exhibiting hemolysin activity on sheep blood, and up-regulated by sarA independently of the accessory gene regulator (encoded by agr), was specifically induced microaerobically. Transcriptional gene fusion and Western analysis revealed that sarA up-regulates both toxic shock syndrome toxin 1 gene (tst) expression and staphylococcal enterotoxin B production, respectively. This study demonstrates the role of sarA as a signal transduction regulatory component in response to aeration stimuli and suggests that sarA functions as a major repressor of protease activity. The possible role of proteases as regulators of virulence determinant stability is discussed.

Aerobiosis↗
PubMed1995

Carbapenem antibiotic production in Erwinia carotovora is regulated by CarR, a homologue of the LuxR transcriptional activator.

Strain GS101 of Erwinia carotovora makes the carbapenem antibiotic, 1-carbapen-2-em-3-carboxylic acid. Mutants defective in antibiotic production can be assigned to two groups, group 1 and group 2. Group 2 mutants are defective in the carl gene encoding a protein responsible for synthesis of the Lux autoinducer N-(3-oxohexanoyl)-L-homoserine lactone (OHHL), which is required to induce carbapenem synthesis in strain GS101. In this paper we describe the molecular genetic analysis of the group 1 mutants which we presumed were defective in the carbapenem biosynthesis (car) genes. We isolated a cosmid (cWU142) that complemented the group 1 mutants of strain GS101. A small (1.03 kb) subclone of cWU142 complemented most of the group 1 mutants, and the sequence revealed that the relevant gene (carR) encodes a homologue of the Vibrio fischeri LuxR protein. A disproportionately high frequency of carR mutants arose in strain GS101 and this was due to carR acting as a 'hot spot' target for secondary transposition of a Tn5 element in this strain. The CarR protein joins a rapidly growing list of homologues, found in taxonomically unrelated bacteria, which act as positive transcriptional activators of genes encoding diverse metabolic functions, including bioluminescence, exoenzyme virulence factor synthesis, cell division, plasmid conjugation, rhizosphere-specific gene induction, surfactant synthesis and antibiotic production. Most of these LuxR-type regulators have been shown to depend, for their function, on N-acyl homoserine lactones, which act as chemical signals enabling co-ordination of gene expression with cell density.

Amino Acid Sequence↗
PubMed1993

A novel strategy for the isolation of luxI homologues: evidence for the widespread distribution of a LuxR:LuxI superfamily in enteric bacteria.

The pheromone N-(3-oxohexanoyl)-L-homoserine lactone (OHHL) regulates expression of bioluminescence in the marine bacterium Vibrio fischeri, the production of carbapenem antibiotic in Erwinia carotovora and exoenzymes in both E. carotovora and Pseudomonas aeruginosa. A characteristic feature of this regulatory mechanism in V. fischeri is that it is cell density-dependent, reflecting the need to accumulate sufficient pheromone to trigger the induction of gene expression. Using a lux plasmid-based bioluminescent sensor for OHHL, pheromone production by E. carotovora, Enterobacter agglomerans, Hafnia alvei, Rahnella aquatilis and Serratia marcescens has been demonstrated and shown also to be cell density-dependent. Production of OHHL implies the presence in these bacteria of a gene equivalent to luxI. Chromosomal banks from all five enteric bacteria have yielded clones capable of eliciting OHHL production when expressed in Escherichia coli. The luxI homologue from both E. carotovora (carI) and E. agglomerans (eagI) were characterized at the DNA sequence level and the deduced protein sequences have only 25% identity with the V. fischeri LuxI. Despite this, carI, eagI and luxI are shown to be biologically equivalent. An insertion mutant of eagI demonstrates that this gene is essential for OHHL production in E. agglomerans.

4-Butyrolactone↗
PubMed1992

[Transcervical resection of endometrium and submucous myomas].

Transcervical resection of the endometrium and submucous myomas using an unmodified urologic resectoscope has recently been developed as a treatment for menorrhagia and/or infertility when conservative management proves unsatisfactory but the patient desires to preserve the fertility or wishes to avoid hysterectomy. Through June 1990, 7 patients were treated with this procedure including one for endometrial ablation and six for transcervical myomectomy alone. No significant complication was seen and the results were relatively satisfactory in an average 7 1/2 months follow up. This approach seems a safe, effective surgical procedure and represents an attractive alternative to hysterectomy or abdominal myomectomy.

Adult↗