Development of a highly sensitive and specific assay to detect Staphylococcus aureus in bovine mastitic milk

Diagnosis of udder infections with Staphylococcus aureus by bacteriological milk testing of quarter milk samples is often not satisfactory. To get reliable results, repeated sampling is necessary, which is normally too expensive. Therefore, we developed a test that allows the highly specific detection of Staph. aureus in bovine milk samples at very low concentrations. It is based on a fast procedure to prepare bacteria from milk, followed by DNA extraction and quantitative PCR. The whole analysis is done within 5 h. For clinical milk samples, the analytical sensitivity of the assay was 50.7 times and 507 times higher than conventional bacteriology with 100 and 10 microL, respectively. The diagnostic specificity was 100%. The test is further characterized by a low intra- and interassay variability as well as by a good recovery of Staph. aureus from raw milk. Furthermore, a high correlation (R = 0.925) between the agar plate counts and the quantitative PCR methodology over the whole range of measurement was found. In addition, our test revealed considerably more positive results than bacteriology. Due to its favorable properties, the assay might become an important diagnostic tool in the context of bovine mastitis caused by Staph. aureus.

Inflammation and NO(X)-induced nitration: assay for 3-nitrotyrosine by HPLC with electrochemical detection

The identification of 15N-labeled 3-nitrotyrosine (NTyr) by gas chromatography/mass spectroscopy in protein hydrolyzates from activated RAW 264.7 macrophages incubated with 15N-L-arginine confirms that nitric oxide synthase (NOS) is involved in the nitration of protein-bound tyrosine (Tyr). An assay is presented for NTyr that employs HPLC with tandem electrochemical and UV detection. The assay involves enzymatic hydrolysis of protein, acetylation, solvent extraction, O-deacetylation, and dithionite reduction to produce an analyte containing N-acetyl-3-aminotyrosine, an electrochemically active derivative of NTyr. We estimate the level of protein-bound NTyr in normal rat plasma to be approximately 0-1 residues per 10(6) Tyr with a detection limit of 0.5 per 10(7) Tyr when > 100 nmol of Tyr is analyzed and when precautions are taken to limit nitration artifacts. Zymosan-treated RAW 264.7 cells were shown to have an approximately 6-fold higher level of protein-bound NTyr compared with control cells and cells treated with N(G)-monomethyl-L-arginine, an inhibitor of NOS. Intraperitoneal injection of F344 rats with zymosan led to a marked elevation in protein-bound NTyr to approximately 13 residues per 10(6) Tyr, an approximately 40-fold elevation compared with plasma protein of untreated rats; cotreatment with N(G)-monomethyl-L-arginine inhibited the formation of NTyr in plasma protein from blood and peritoneal exudate by 69% and 53%, respectively. This assay offers a highly sensitive and quantitative approach for investigating the role of reactive byproducts of nitric oxide in the many pathological conditions and disease states associated with NO(X) exposure such as inflammation and smoking.

A multiplex real-time PCR assay for rapid detection and differentiation of 25 bacterial and fungal pathogens from whole blood samples

Early detection of bloodstream infections (BSI) is crucial in the clinical setting. Blood culture remains the gold standard for diagnosing BSI. Molecular diagnostic tools can contribute to a more rapid diagnosis in septic patients. Here, a multiplex real-time PCR-based assay for rapid detection of 25 clinically important pathogens directly from whole blood in <6 h is presented. Minimal analytical sensitivity was determined by hit rate analysis from 20 independent experiments. At a concentration of 3 CFU/ml a hit rate of 50% was obtained for E. aerogenes and 100% for S. marcescens, E. coli, P. mirabilis, P. aeruginosa, and A. fumigatus. The hit rate for C. glabrata was 75% at 30 CFU/ml. Comparing PCR identification results with conventional microbiology for 1,548 clinical isolates yielded an overall specificity of 98.8%. The analytical specificity in 102 healthy blood donors was 100%. Although further evaluation is warranted, our assay holds promise for more rapid pathogen identification in clinical sepsis.

Comparison of interferon-gamma release assay versus tuberculin skin test for tuberculosis screening in inflammatory bowel disease

OBJECTIVES: Reactivation of latent tuberculosis (TB) in inflammatory bowel disease (IBD) patients treated with antitumor necrosis factor-alpha medication is a serious problem. Currently, TB screening includes chest x-rays and a tuberculin skin test (TST). The interferon-gamma release assay (IGRA) QuantiFERON-TB Gold In-Tube (QFT-G-IT) shows better specificity for diagnosing TB than the skin test. This study evaluates the two test methods among IBD patients. METHODS: Both TST and IGRA were performed on 212 subjects (114 Crohn's disease, 44 ulcerative colitis, 10 indeterminate colitis, 44 controls). RESULTS: Eighty-one percent of IBD patients were under immunosuppressive therapy; 71% of all subjects were vaccinated with Bacille Calmette Guérin; 18% of IBD patients and 43% of controls tested positive with the skin test (P < 0.0001). Vaccinated controls tested positive more often with the skin test (52%) than did vaccinated IBD patients (23%) (P = 0.011). Significantly fewer immunosuppressed patients tested positive with the skin test than did patients not receiving therapy (P = 0.007); 8% of patients tested positive with the QFT-G-IT test (14/168) compared to 9% (4/44) of controls. Test agreement was significantly higher in the controls (P = 0.044) compared to the IBD group. CONCLUSIONS: Agreement between the two test methods is poor in IBD patients. In contrast to the QFT-G-IT test, the TST is negatively influenced by immunosuppressive medication and vaccination status, and should thus be replaced by the IGRA for TB screening in immunosuppressed patients having IBD.

Tuberculosis in a Swiss army training camp: contact investigation using an Interferon gamma release assay

BACKGROUND: In tuberculosis (TB), the risk of exposure is determined mainly by the proximity to and the hours of direct contact with an infectious patient. We describe the contact investigation after detection of an infectious form of TB in a military camp using an Interferon-g-Release-Assay (IGRA, QuantiFERON-TB Gold In Tube [QTF-GIT]) eight weeks after detection of the index case. INDEX PATIENT: The index patient presented with fever, cough and weight loss in the military hospital six weeks after entering the camp. TB was suspected and anti-tuberculous therapy given immediately. Subsequently, TB was microbiologically confirmed. METHODS: Four exposure groups were formed a priori based on the proximity and the hours of direct contact to the index case. 168 (95.5%) agreed to be investigated: - Group A: sharing the same dormitory (15 persons) - Group B: same platoon, but not sharing the dormitory (20 persons) - Group C: staff and patients of the military hospital (22 persons) - Group D: other three platoons and senior military staff (111 persons). RESULTS: 34 (20.2%) out of 168 contacts tested positive in the QFT-GIT assay. For the exposure groups, the respective QFT-GIT testing results were: group A, 14/15 (93%); group B, 4/20 (20%); group C, 5/22 (22.7%); and group D, 11/111 (9.9%). No secondary TB cases were identified. CONCLUSIONS: In our study, test results show a correlation with the risk of exposure, suggesting that IGRA may be useful for the assessment of TB infection in TB contacts. The high mobility of recruits reduced traceability of contacts. In this context, QFT-GIT allowed for an efficient screening of contacts at a single time point.

Value of a novel Neisseria meningitidis--specific polymerase chain reaction assay in skin biopsy specimens as a diagnostic tool in chronic meningococcemia

BACKGROUND: Chronic meningococcemia (CM) is a diagnostic challenge. Skin lesions are frequent but in most cases nonspecific. Polymerase chain reaction (PCR)-based diagnosis has been validated in blood and cerebrospinal fluid for acute Neisseria meningitidis infection, in patients in whom routine microbiologic tests have failed to isolate the bacteria. In 2 patients with CM, we established the diagnosis by a newly developed PCR-based approach performed on skin biopsy specimens. OBSERVATIONS: Two patients presented with fever together with systemic and cutaneous manifestations suggestive of CM. Although findings from blood cultures remained negative, we were able to identify N meningitidis in the skin lesions by a newly developed PCR assay. In 1 patient, an N meningitidis strain of the same serogroup was also isolated from a throat swab specimen. Both patients rapidly improved after appropriate antibiotherapy. CONCLUSIONS: To our knowledge, we report the first cases of CM diagnosed by PCR testing on skin biopsy specimens. It is noteworthy that, although N meningitidis-specific PCR is highly sensitive in blood and cerebrospinal fluid in acute infections, our observations underscore the usefulness of PCR performed on skin lesions for the diagnosis of chronic N meningitidis infections. Whenever possible, this approach should be systematically employed in patients for whom N meningitidis infection cannot be confirmed by routine microbiologic investigations.

IS711-based real-time PCR assay as a tool for detection of Brucella spp. in wild boars and comparison with bacterial isolation and serology

BACKGROUND: Control of brucellosis in livestock, wildlife and humans depends on the reliability of the methods used for detection and identification of bacteria. In the present study, we describe the evaluation of the recently established real-time PCR assay based on the Brucella-specific insertion sequence IS711 with blood samples from 199 wild boars (first group of animals) and tissue samples from 53 wild boars (second group of animals) collected in Switzerland. Results from IS711 real-time PCR were compared to those obtained by bacterial isolation, Rose Bengal Test (RBT), competitive ELISA (c-ELISA) and indirect ELISA (i-ELISA). RESULTS: In the first group of animals, IS711 real-time PCR detected infection in 11.1% (16/144) of wild boars that were serologically negative. Serological tests showed different sensitivities [RBT 15.6%, c-ELISA 7.5% and i-ELISA 5.5%] and only 2% of blood samples were positive with all three tests, which makes interpretation of the serological results very difficult. Regarding the second group of animals, the IS711 real-time PCR detected infection in 26% of animals, while Brucella spp. could be isolated from tissues of only 9.4% of the animals. CONCLUSION: The results presented here indicate that IS711 real-time PCR assay is a specific and sensitive tool for detection of Brucella spp. infections in wild boars. For this reason, we propose the employment of IS711 real-time PCR as a complementary tool in brucellosis screening programs and for confirmation of diagnosis in doubtful cases.