Evaluation and comparison of tests to detect methicillin resistant S. aureus.

Background and Objectives: Phenotypic methods for detection of methicillin resistant Staphylococcus aureus (MRSA) have been compared with the gold standard which, as of now, is by the detection of mecA gene and femA gene by polymerase chain reaction (PCR). Discrepancies in detection have an adverse effect on patient management, thereby highlighting the importance of accuracy in detection. Our study aims to evaluate the efficacy of cefoxitin disk diffusion test to detect MRSA and compare it with other phenotypic and molecular methods. Methodology; The study was conducted from June 2006 to December 2007 and included 610 Staphylococcus aureus (S. aureus) isolates obtained from clinical samples. All isolates were tested for MRSA using oxacillin screen agar plates with 6 µg/ml of oxacillin, cefoxitin disk diffusion using 30 µg disk and MIC of oxacillin. Selected isolates (55) were tested for presence of mecA gene and Fem A gene by PCR. Results: Out of 610 isolates, MRSA was identified in 34.09% by cefoxitin disk diffusion, 34.9% by oxacillin screen agar, 34.4% by MIC and 37.3% by oxacillin disk diffusion. When selected isolates were tested with molecular methods, the cefoxitin disk diffusion and PCR tests were comparable. Discussion: Prevalence of MRSA (34.09%) is quite high as in other studies. The oxacillin disk diffusion test which was used routinely earlier is showing low specificity (56%). Among all phenotypic methods, cefoxitin disk diffusion and PCR alone have similar sensitivity and specificity. Conclusion: Results of cefoxitin disk diffusion test are in concordance with the PCR for mecA gene. Thus, the test can be an alternative to PCR for detection of MRSA in resource constraint settings.

Evaluation of various screening tests to detect asymptomatic bacteriuria in pregnant women.

To evaluate the diagnostic efficacy of various screening tests in detecting asymptomatic bacteriuria among pregnant women. Clean catch midstream urine specimens were collected from 630 consecutive pregnant women and processed. Forty-four (7.4%) of the urine samples were culture positive, with Escherichia coli as the predominant organism isolated (57.4%). The results of the four screening tests, viz., Gram's staining of uncentrifuged urine, pus cell count, nitrite test and leukocyte esterase (LE) test, were compared against urine culture. Gram's stain of the uncentrifuged urine was found to be the single most useful test with a sensitivity and negative predictive value (NPV) of 85.1% and 98.8%, respectively. Pus cell count was the least sensitive. Neither the nitrite test nor the LE test alone was sensitive enough with 74.4% and 61.7%, respectively. However, when either or both tests positive were considered, it increased the sensitivity and NPV comparable with Gram's staining results, with 82.9% and 98.8%, respectively. With the potential to be used as an office diagnostic procedure, the combined nitrite and LE dipstick test may provide an acceptable alternative.

Evaluation of an enzyme-linked immunoassay for the detection of Cryptosporidium antigen in fecal specimens of HIV/AIDS patients.

Cryptosporidium parvum, a protozoan parasite, causes severe diarrhea in immunodeficient hosts like HIV/AIDS patients, leading to significant morbidity and mortality. Diagnosis of the Cryptosporidium oocyst in the stool of these patients by conventional microscopy is labor intensive and time consuming. Therefore, we planned to evaluate the usefulness of a stool ELISA test in detecting Cryptosporidial antigen. About 89 stool specimens obtained from HIV-seropositive patients with diarrhea were subjected to an ELISA test and modified acid-fast staining (gold standard), on both direct and formol ether-concentrated specimens. The prevalence of Cryptosporidial diarrhea was found to be 12.4% (11/89). Other enteric pathogens detected were Isospora belli (3), Giardial cyst (3), Entamoeba coli cyst (2), and Entamoeba histolytica cyst (1). Dual infection with Cryptosporidium and Isospora belli was seen in two patients. Concentration technique improved identification by microscopy. The sensitivity and specificity for stool ELISA were found to be 90.9% and 98.7% respectively. The results of stool ELISA indicate that this simple, rapid, reliable, and standardized immunoassay test is sensitive and specific for routine diagnosis and may be useful for large-scale epidemiological studies of Cryptosporidiosis.