Oxidative and nitrosative responses of the chicken macrophage cell line MQ-NCSU to experimentalSalmonellainfection

Phagocytes limit replication or kill ingested organisms by producing toxic reactive oxygen and nitrogen species via NADPH oxidase and inducible nitric oxide synthase (iNOS). The present experiments were to investigate the production and the possible roles of superoxide, hydrogen peroxide (H2O2) and nitric oxide (NO) in the MQ-NCSU chicken macrophage cell line infected with Salmonella in vitro. After infection, intracellular Salmonella viable counts remained constant until 24 h post infection (PI) and started to decline from 48 h PI. Infection of cells with S. Typhimurium, S. Enteritidis and S. Gallinarum, as well as exposure to S. Enteritidis LPS induced low, but significant concentrations of superoxide 1 to 2 h PI, as determined by reduction of ferricytochrome c. There was no difference in superoxide production in infected cells and control cells after 4 h. Increased H2O2 was observed from cells infected with all the different Salmonella species between 2 and 3 h of infection. Nitrite was always greater in infected cells compared to uninfected cells at all times. However, Salmonella was not completely eliminated from the cells though these cells are capable of eliciting a noticeable oxidative burst response and great nitrosative responses, indicating that a strong oxidative burst (and other mechanism/s) is essential for the elimination of intracellular Salmonella.

A dimer of the Toll-like receptor 4 cytoplasmic domain provides a specific scaffold for the recruitment of signalling adaptor proteins

The Toll-like receptor 4 (TLR4) is a class I transmembrane receptor expressed on the surface of immune system cells. TLR4 is activated by exposure to lipopolysaccharides derived from the outer membrane of Gram negative bacteria and forms part of the innate immune response in mammals. Like other class 1 receptors, TLR4 is activated by ligand induced dimerization, and recent studies suggest that this causes concerted conformational changes in the receptor leading to self association of the cytoplasmic Toll/Interleukin 1 receptor (TIR) signalling domain. This homodimerization event is proposed to provide a new scaffold that is able to bind downstream signalling adaptor proteins. TLR4 uses two different sets of adaptors; TRAM and TRIF, and Mal and MyD88. These adaptor pairs couple two distinct signalling pathways leading to the activation of interferon response factor 3 (IRF-3) and nuclear factor κB (NFκB) respectively. In this paper we have generated a structural model of the TLR4 TIR dimer and used molecular docking to probe for potential sites of interaction between the receptor homodimer and the adaptor molecules. Remarkably, both the Mal and TRAM adaptors are strongly predicted to bind at two symmetry-related sites at the homodimer interface. This model of TLR4 activation is supported by extensive functional studies involving site directed mutagenesis, inhibition by cell permeable peptides and stable protein phosphorylation of receptor and adaptor TIR domains. Our results also suggest a molecular mechanism for two recent findings, the caspase 1 dependence of Mal signalling and the protective effects conferred by the Mal polymorphism Ser180Leu.

Occurrence and virulence factors of non-O157 Shiga toxin-producing Escherichia coli in retail meat in Dunedin, New Zealand

Retail raw meat was sampled for the presence of Shiga toxin-producing Escherichia coli (STEC) using enrichment culture and Vero cell assay. The STEC obtained were serotyped and tested for enterohaemolysin (Ehly) production and the eae gene. The presence of Shiga toxin genes (stx) was confirmed by polymerase chain reaction. A total of 18 STEC were isolated accounting for 12% of beef, 17% of lamb and 4% of pork samples. Five isolates produced Ehly but none possessed the eae gene. Five isolates were identified which possessed the stx2 gene and belonged to serotypes associated with severe infection.

Non-O157 Vero cytotoxin producing Escherichia coli: aetiological agents of diarrhoea in children in Dunedin, New Zealand

Strains of Escherichia coli that produce Vero cytotoxin (VTEC) commonly cause diarrhoea, haemorrhagic colitis and haemolytic-uraemic syndrome in many northern hemisphere countries. In these countries, serotype O157:H7/H-predominates and has caused large food-borne outbreaks of infection. In contrast, few cases of infection with this serotype have been reported in New Zealand. Over a 3-month period, 484 stool specimens submitted to medical laboratories in Dunedin were screened for E. coli O157:H7/H-using sorbitol MacConkey agar, Y1 and Vero cell assays. Where possible, Vero cytotoxin production was confirmed by an ELISA test. Specimens from children aged 12 years or less were additionally screened for non-O157 VTEC. In the specimens of the children tested, O157:H7/H-VTEC was not isolated, but VTEC belonging to other serogroups were isolated from the children. Of interest was the detection of other species of Enterobacteriaceae, which produced a cytopathic effect on Vero cells. This study confirms the low incidence of infection with O157:H7/H- VTEC in New Zealand and suggests that non-O157 VTEC is a more important cause of diarrhoeal disease.

A fluorescent antibody staining technique to detect bacterial adherence to urinary tract epithelial cells

A fluorescent antibody technique has been devised to assess specifically the adherence of Escherichia coli in vitro to uroepithelial cells from healthy women and bacterial adherence in vivo to cells from women with symptomatic urinary tract infection. Similar values can be obtained using methylene blue as the bacterial stain, but this depends on the experience of the observer. The results indicate that E. coli adherence to uroepithelial cells is a factor in the infection process. We suggest that uroepithelial cells from patients with symptoms of a urinary tract infection whose urine has a low bacterial count (less than 10(3) cells/ml) could be examined for the presence of adherent uropathogens, which may be indicative of an infection. Although the fluorescent staining technique possibly would be expensive, the results would be specific and reliable. Other diagnostic and research applications suggest themselves as in studies of bacterial colonization of mucosal tissues or plastic catheters, where conventional light microscopy and radiolabelling methods are not effective.

In vivo attachment of E coli to human epithelial cells

There was a high incidence of a mannose sensitive adhesin and a mannose resistant and eluting adhesin among 111 Escherichia coli urinary isolates and 23 faecal isolates. Attachment of E coli to human uroepithelial and buccal cells was significantly higher for strains possessing a mannose resistant adhesin after growth on agar. Strains possessing a mannose sensitive adhesin after single or multiple subculutres in broth did not attach in large numbers and the adherence was unaffected by the presence of D-mannose. The mannose resistant adhesin was more often detected in strains with O serotypes commonly found in urinary tract infections, was produced at 37C but not at 18C and was destroyed or weakened by exposure to heat and formaldehyde treatment. Electron microscopy confirmed fimbrial presence on 67% of strains producing a mannose resistant adhesin, but non-fimbriated strains attached equally well to uroepithelial cells.

In vitro attachment of Escherichia coli to human uroepithelial cells: variation in receptivity during the menstrual cycle and pregnancy

An in vitro system was used for assay of the attachment of Escherichia coli to viable uroepithelial cells harvested from the urine of premenopausal women. A 15% level of variation from the mean attachment value was noted within given cell samples. Uroepithelial target cells with large numbers of adherent bacteria were found. The receptivity of uroepithelial cells to the attachment of certain strains of E coli varied over the menstrual cycle and during pregnancy. This finding may suggest that adult women are more susceptible to urinary tract infection at particular times during their reproductive period. Double-staining techniques were used for the detection of bacterial attachment to mucopolysaccharide-coated and non-mucopolysaccharide-coated uroepithelial cells. The level of attachment of one strain of E coli was higher when cells were mucus coated, while the attachment of a second strain was unaffected by the presence of a mucus coat. The results suggest the existence of at least two different mechanisms whereby E coli attaches to uroepithelial cells.

The use of double staining techniques for investigating bacterial attachment to mucopolysaccharide-coated epithelial cells

Double staining techniques were devised to study Escherichia coli attachment to mucopolysaccharide-coated urinary tract epithelial cells. In addition, vital stains were used to distinguish between viable and nonviable epithelial cells. Alcian blue was used to confirm the presence of glycosaminoglycans and periodic acid Schiff was used to distinguish a further group of polysaccharides, proteoglycans, neutral mucosubstances and glycolipids. The staining methods enabled investigations to be carried out concerning the possible importance of mucopolysaccharides in the attachment of bacteria to mucosal surfaces. Staining techniques were also used to investigate whether the presence of a mucopolysaccharide coat is related to epithelial cell viability. The combinations of vital and mucopolysaccharide stains were found to give reproducible results when cell preparations were evaluated by three individuals. Both in vivo and in vitro certain populations of epithelial cells have been found with a large number of bacteria preferentially attached. The double staining techniques described here may help to reveal the nature of these target cells.

Correlation between uropathogenic properties of Escherichia coli from urinary tract infections and the antibody-coated bacteria test and comparison with faecal strains

Strains of Escherichia coli isolated from adult females with symptomatic urinary tract infection were found to possess the following properties significantly more frequently than faecal strains: (i) high K-antigen titre: (ii) haemolysin; (iii) type 1 pili; (iv) mannose-resistant haemagglutination; (v) fermentation of dulcitol and salicin; (vi) O serotype 2, 6 and 75; (vii) H serotype 1. E. coli isolated form urine specimens containing significant numbers of antibody-coated bacteria were richer in these seven properties than strains from urines without detectable antibody coated bacteria. The O and H serotypes of E. coli obtained from patients with urinary tract infection in two New Zealand cities were compared with those reported in the world literature and found to be similar.

Uropathogenic properties of Escherichia coli in recurrent urinary-tract infection

Properties of Escherichia coli considered to be important in the pathogenesis of urinary-tract infection were investigated. The following properties were more common in E. coli strains isolated from urinary infections than in periurethral strains from healthy individuals: (i) O serogroups 2, 4, 6, 8, 18ab and 75; (ii) high K-antigen titre; (iii) production of haemolysin; (iv) production of fimbriae; (v) fermentation of salicin. The correlation between isolation of a strain from the urinary tract and possession of any single property was not strong; however, strains rich in a combination of these pathogenic properties were rarely isolated from the periurethral area of healthy subjects but were common in urinary infections. Nevertheless, a significant proportion of urinary strains had few pathogenic properties. Strains rich in pathogenic properties were more commonly isolated from upper urinary-tract infections than from lower-tract infections; this indicates that the properties of the invading organism may influence the localisation of infection.

Campylobacter enteritis and Yersinia enterocolitica infection in New Zealand

A three-month survey was undertaken to determine the incidence of Campylobacter jejuni and Yersinia enterocolitica in diarrhoeal disease and acute abdominal disease in Palmerston North. C. jejuni was isolated from five domiciliary patients and one hospitalised patient with acute diarrhoea but there were no isolations from patients suffering from acute abdominal disease. The isolation rates for C. jejuni in domiciliary and hospitalised patients with acute diarrhoea were 7.8 percent and 1.7 percent respectively. Y. enterocolitica was not isolated.

The increasing isolation of Serratia species from clinical specimens

A 14-month survey was undertaken in a diagnostic bacteriology laboratory to determine the incidence of Serratia spp. in routine clinical specimens. Gram-negative organisms with enterobacteria-like colonies were tested by a simple screening procedure. Fifty-eight strains of S. marcescens and two strains of S. liquefaciens were isolated from 59 patients. The strains were usually non-pigmented and exhibited multiple antibiotic resistance. Serotyping and determination of bacteriocine sensitivity patterns revealed that the majority of infections were sporadic, although episodes of cross-infection did occur. S. marcescens was considered to contribute significantly to morbidity and mortality in 53% of patients and appears to be of increasing importance in hospital-acquired infections.

Periurethral enterobacterial carriage in pathogenesis of recurrent urinary infection

Periurethral carriage rates of enterobacteria have been studied in 20 normal women, 34 patients between episodes of bacteriuria, 34 patients with the "urethral syndrome," and 15 asymptomatic abacteriuric patients with a previous history of frequency and dysuria.Over a six-week period no difference in the Escherichia coli carriage rate was shown between these four groups. The carriage of all enterobacteria was slightly but significantly (P <0.05) lower in normal women compared with the patient groups but no difference was observed between the latter. There was no difference in the recovery rate and carriage of individual E. coli serotypes between the four groups.It is concluded that the presence of enterobacteria or E. coli on the periurethral area is not the principal determinant factor in the pathogenesis of recurrent urinary tract infection or the urethral syndrome and that definition of carriage status is of little practical value in management.