An approach towards public health and foodborne human listeriosis--the Austrian Listeria monitoring

The Institute for Milk Hygiene, Milk Technology and Food Science has launched a Listeria monitoring for Austrian cheese factories in 1988 which is nowadays a valuable tool to control the safety of cheese production. It is a means to qualify the proper hygienic conditions in the participating cheese plants. Proper hygiene protects cheese plants from getting contaminated by L. monocytogenes. The preventive elimination of foodborne pathogens facilitates a thriving economical development of the domestic cheese industry as contamination by L. monocytogenes may lead to a stop of delivery, product recall and other costly measures. This report comprehensively describes the principle of the monitoring including a description of the microbiological and molecular tools. It summarizes data on the detection frequency of Listeria contamination with respect to the different matrices under investigation. Furthermore an overview is given on the course of 17 contamination periods in 10 cheese plants and the outcome of the decontamination endeavours is described. Apart from epidemiological investigations, this report summarizes data regarding molecular species confirmation in the genus Listeria as the species assignment was comparatively examined by both conventional microbiology and molecular tools. Genotyping by Pulsed Field Gel Electrophoresis was applied in three plants which were confronted with a long term contamination period. The data presented in this paper rely on results which were collected through a decade of investigation (1990-2000).

Unique signaling properties of B cell antigen receptor in mature and immature B cells: implications for tolerance and activation

Immature B cells display increased sensitivity to tolerance induction compared with their mature counterparts. The molecular mechanisms underlying these differences are poorly defined. In this study, we demonstrate unique maturation stage-dependent differences in B cell Ag receptor (BCR) signaling, including BCR-mediated calcium mobilization responses. Immature B cells display greater increases in intracellular calcium concentrations following Ag stimulation. This has consequences for the induction of biologically relevant responses: immature B cells require lower Ag concentrations for activation than mature B cells, as measured by induction of receptor editing and CD86 expression, respectively. BCR-induced tyrosine phosphorylation of CD79a, Lyn, B cell linker protein, and phospholipase Cgamma2 is enhanced in immature B cells and they exhibit greater capacitative calcium entry in response to Ag. Moreover, B cell linker protein, Bruton's tyrosine kinase, and phospholipase Cgamma2, which are crucial for the induction of calcium mobilization responses, are present at approximately 3-fold higher levels in immature B cells, potentially contributing to increased mobilization of calcium. Consistent with this possibility, we found that the previously reported lack of inositol-1,4,5-triphosphate production in immature B cells may be explained by enhanced inositol-1,4,5-triphosphate breakdown. These data demonstrate that multiple mechanisms guarantee increased Ag-induced mobilization of calcium in immature B cells and presumably ensure elimination of autoreactive B cells from the repertoire.

Prevalence and characterization of Listeria monocytogenes in the feces of healthy Austrians

The aims of the study were to determine the prevalence of Listeria monocytogenes in the feces of healthy Austrians and to characterize the isolates by various typing methods. Stool specimens from 505 healthy volunteers from the Tyrol were tested for the presence of L. monocytogenes using cold enrichment for 6 months and five different detection methods: conventional plating onto Palcam and Rapid'L.MONO agar, immunomagnetic separation (IMS) followed by conventional plating, enzyme-linked fluorescent immunoassay (ELFA), ELISA, and PCR. L. monocytogenes was isolated by conventional plating from one specimen (0.2%), and a further three were positive on immunomagnetic separation (0.8%). Only one specimen tested positive with ELFA and EIA, although it tested negative by conventional culture, IMS, and PCR. Eighteen of 505 samples were positive by PCR (3.6%), and this included three of the four culture-confirmed specimens. Serotyping, phage-typing, arsenic cadmium, antimicrobial-resistance typing and pulsed-field gel electrophoresis showed that multiple L. monocytogenes isolates from three of the four carriers were indistinguishable. Our data indicate that the Austrian fecal carriage rate is at least 0.8%. In view of a listeriosis incidence of 0.16/100,000 per year, the chances of fecal carriage developing into listeriosis appear to be very low.

Comparison of different approaches to quantify Staphylococcus aureus cells by real-time quantitative PCR and application of this technique for examination of cheese

Two different real-time quantitative PCR (RTQ-PCR) approaches were applied for PCR-based quantification of Staphylococcus aureus cells by targeting the thermonuclease (nuc) gene. Purified DNA extracts from pure cultures of S. aureus were quantified in a LightCycler system using SYBR Green I. Quantification proved to be less sensitive (60 nuc gene copies/microl) than using a fluorigenic TaqMan probe (6 nuc gene copies/microl). Comparison of the LightCycler system and the well-established ABI Prism 7700 SDS with TaqMan probes revealed no statistically significant differences with respect to sensitivity and reproducibility. Application of the RTQ-PCR assay to quantify S. aureus cells in artificially contaminated cheeses of different types achieved sensitivities from 1.5 x 10(2) to 6.4 x 10(2) copies of the nuc gene/2 g, depending on the cheese matrix. The coefficients of correlation between log CFU and nuc gene copy numbers ranged from 0.979 to 0.998, thus enabling calculation of the number of CFU of S. aureus in cheese by performing RTQ-PCR.

Detection and quantification of the iap gene of Listeria monocytogenes and Listeria innocua by a new real-time quantitative PCR assay

A real-time quantitative polymerase chain reaction (PCR) assay for direct detection and enumeration of Listeria monocytogenes and Listeria innocua was developed and applied to artificially contaminated milk samples. The iap gene present in both species was used as a target for amplification of a 175-bp (L. monocytogenes) and a 309-bp (L. innocua) fragment. To ensure that L. monocytogenes and L. innocua are specifically detectable, tests were carried out using 42 L. monocytogenes strains and 33 L. innocua strains belonging to different serovars. Specificity was also confirmed using 22 bacterial strains not belonging to the genus Listeria, including closely related bacteria. In addition to specificity, the reported assay is characterized by a wide dynamic range of quantification and a high sensitivity, as we could detect as few as six copies of the iap gene per PCR using purified DNA as template. When applied to direct detection and quantification of L. monocytogenes in milk, the more rapid real-time quantitative PCR assay was as sensitive as the traditional plate count method, but real-time quantitative PCR-derived iap gene copy numbers were one to two logs higher than colony-forming units obtained by the plate count method.

Epidemiologic application of pulsed-field gel electrophoresis to an outbreak of Campylobacter jejuni in an Austrian youth centre

We report the first documented Campylobacter jejuni outbreak in an Austrian youth centre. Sixty-four children were involved of which 38 showed classical signs of campylobacter gastroenteritis. Since unpasteurized milk distributed by a local dairy was suspected to be the source of infection, stool samples were collected from 20 cows providing the milk. Five of the cows tested positive for C. jejuni. These isolates together with 37 clinical samples were compared by pulsed-field-gel electrophoresis (PFGE). The PFGE patterns, using the restriction endonucleases SmaI and SalI, were identical for the human and bovine isolates. This finding confirmed that the outbreak was caused by the consumption of unpasteurized milk contaminated with C. jejuni.

Development of a multiple primer RAPD assay as a tool for phylogenetic analysis in Listeria spp. strains isolated from milkproduct associated epidemics, sporadic cases of listeriosis and dairy environments

A total of 82 Listeria strains comprising four species were examined by amplification with a multiple primer random amplified polymorphic DNA (RAPD) assay. It was the objective of the study to set up a procedure suitable for analysis of the relationships among strains from milkproduct-associated epidemics, strains from sporadic cases of listeriosis and field strains from dairy products and dairy environments. In a preliminary study, 205 primers, each 10 bp long, were screened for suitability as primers and 44 primers showing reliable and reproducible RAPD patterns at a defined reaction condition were selected. The 82 strains were assigned to 54 RAPD groups positioned in 13 major clusters. Strains isolated during milk product-associated epidemics were found to belong to a single cluster I. Human isolates from sporadic cases of listeriosis predominantly were assigned to four separate clusters. It was found that strains of clinical origin were mainly assigned to other clusters than strains of non-clinical origin.

[Detection of the annatto dye norbixin/bixin in cheese using derivative spectroscopy and high performance liquid chromatography (HPLC)]

A derivative spectroscopic method and a HPLC-method are described for the determination of the annatto dye-stuffs, norbixin and bixin, in cheese. Both methods enable a simple and quick sample preparation since the separation of beta-carotene and fat is not required. The sample preparation step consists of extraction with acetone, filtration, evaporation of the extract and separation of water residues by the addition of a few milliliters of absolute ethanol. This is followed by evaporation and extraction of the residual solution with chloroform/acetic acid (99.5 +/- 0.5) for the derivative spectroscopic method or with acetone for the HPLC method. The qualitative detection (detection limit greater than 0.67 mg/kg, depending on the genuine beta-carotene content) as well as the quantitative determination is possible by means of the derivative spectroscopic method. Therefore, this technique may be used within the rigorous Austrian regulations or for controlling the quantities and limits of annatto dye-stuffs in cheese, if its application is allowed. The method also has the advantage of quick detection (only 75 s) and saving of material used. The HPLC method allows for the separation and quantification of norbixin and bixin as well as the other carotenoids such as beta-carotene, beta-apo-8'-carotenal and beta-apo-8'-carotenoic acid--ethylester, which may also be found in varieties of cheese (detection limit of norbixin and bixin: 0.2 mg/kg). The time required for the separation of the above mentioned substances is 20 min and the HPLC method is proposed for the confirmation of low concentrations of these substances.

[The spectrophotometric determination of natamycin in cheese]

Derivative spectroscopy was used for quantitative determination of natamycin in cheese. When measuring a methanolic cheese extract against methanol, the second derivative of the UV-spectrum is measured between 340 and 290 nm. The natamycin concentration can be determined by measuring the vertical distance between the minimum at 318 nm and the maximum at 311 nm. Under these conditions the detection limit of natamycin in a pure methanolic solution lies at 20 ng/ml, in cheese extracts at 150 ng/ml. The latter corresponds to a natamycin concentration of 2.5 ppm in the case of a 3 g test sample or 0.03 mg/dm2 in the case of a 25 cm2 cheese surface. The introduction of derivative spectroscopy makes it possible to reduce the interference of cheese substances in the photometric measurements and to increase the sensitivity and selectivity of the detection process. Besides the advantage that work and expenses are reduced - as no pimaricin-free sample has to be extracted from the interior of the cheese - it is also possible to determine natamycin photometrically in cheese, in which it is distributed homogeneously.

[Ovulation induction by cyclofenil (author's transl)]

The ovulation-inducing action of cyclofenil was investigated in 135 sexually mature women aged 20--35 years. The patients were only included in the trial if no ovulation in 2 consecutive cycles with the following criteria: basal temperature, cervix score, ascorbic acid retention, basophil count, serum hormone levels, e. g. LH and progesterone and the estrogens in the 24-hour urine could be determined. Ovulation was only considered to have occurred when all the parameters named indicated it. The lack of ovulation was accompanied by amenorrhea in 21 of the 135 patients. The ovulation rate in the 241 cycles observed was 101, corresponding to 42%. In the 114 patients with anovulatory cycles, the ovulation rate in the 184 cycles observed was 95, corresponding to 50%. In the 21 amenorrheic patients, ovulation occurred 6 times in the 57 cycles observed. Nausea or vomiting occurred as side effects in only 2 cases.

Pleuromutilins. Fermentation, structure and biosynthesis

Derivatives of pleuromutilin, formed during the fermentation of pleuromutilin, were isolated and their structure determined. 14-Acetyl-mutilin and mutilin as well as different unsaturated fatty acid esters of pleuromutilin were identified. The proportion of each derivative formed depends to a considerable degree on the conditions of the fermentation process. The possible biosynthetic pathways are shown.