Mannitol salt agar-cefoxitin combination as a screening medium for methicillin-resistant Staphylococcus aureus.

In disk diffusion tests, cefoxitin is now considered a better indicator than oxacillin for the presence of the mecA gene in Staphylococcus aureus. A logical extension of this work is the incorporation of cefoxitin into media selective for methicillin-resistant Staphylococcus aureus (MRSA). This paper describes the development and subsequent testing of mannitol salt agar containing 4 mg/liter cefoxitin with a unique collection of well-characterized MRSA strains, including low-level methicillin-resistant strains and an equal number of known mecA-negative S. aureus strains. The agar supported the growth of 96.6% of the mecA-positive strains in the collection and inhibited the growth of 100% of the mecA-negative strains. These results suggest that selective media based on cefoxitin are superior to those based on oxacillin for the detection of MRSA.

Methods for identifying methicillin resistancein Staphylococcus aureus.

Five methods for the detection of methicillin-resistant Staphylococcus aureus were used to examine a collection of 100 clinical isolates comprising both susceptible and resistant strains. The disc diffusion test with oxacillin had a sensitivity of 93.3% and a specificity of 92.0% whereas mannitol salt agar containing oxacillin had a sensitivity of 100% and specificity 80.6% with high inoculum. With a low inoculum the sensitivity was 90.7% and specificity 96.0%. The MRSA screen test (Denka Seiken Co. Ltd., Japan) and Evigene MRSA Detection Kit (State Serum Institute, Denmark) tests were in complete agreement with results obtained with polymerase chain reaction assays amplifying mecA and nuc gene sequences.

Practical problems of diagnosing trichomoniasis in women.

Analysis of eight groups of data collected at varying intervals during a period of seven years showed fluctuations in the sensitivity of tests to diagnose trichomoniasis in women. The best results were obtained from fresh, correctly prepared Diamond's medium, Feinberg-Whittington's medium, and modified Squires and McFadzean's medium (which showed 82% to 94% relative sensitivity). Poor results were identified consistently in commercially prepared Bushby medium from one source (40% relative sensitivity) and in a batch of commercially prepared Squires and McFadzean's medium from which chloramphenicol had been omitted (23% relative sensitivity). Examination of wet film, culture, and exfoliative cytology stained by Papanicolaou's method were shown to be indispensable for auditing the performance of each test and to maintain the quality of a diagnostic service.

Detection of leukocyte esterase in urine: a new screening test for nongonococcal urethritis compared with two microscopic methods.

First-catch urine samples of 130 men attending a clinic for genitourinary medicine were screened with the leukocyte esterase dipstick test. Conventional microscopy of centrifuged sediment and inverted microscopy of unspun urine samples were performed 2-4 hr later. The leukocyte esterase test had sensitivities of 100% and 96.6% and specificities of 55% and 52.8%, respectively, when compared with the two microscopic methods. The apparently low predictive value of the positive leukocyte esterase test was probably linked to its ability to detect lysed cells and the limitations of the microscopic methods, which were used as the absolute indicator of nongonococcal urethritis. Of the 42 patients with microscopic pyuria, 45.2% had positive cultures for Chlamydia trachomatis, and the leukocyte esterase test was positive in every case. Twenty-one per cent of the C. trachomatis-positive patients were asymptomatic, and 42% had fewer than five polymorphonuclear leukocytes per high-power field (X1000) of the gram-stained urethral smear. The leukocyte esterase test appears to be a simple, practical, and sensitive test that is useful in screening for nongonococcal urethritis, especially asymptomatic nongonococcal urethritis.

Bacteraemia in diabetics.

During a period of 22 months one or more episodes of bacteraemia were detected in 168 patients in hospital. Of these, 29% also had diabetes compared with 10% of the total number of patients admitted to hospital during this time (P less than 0.001). The diabetics with bacteraemia were elderly and diabetes had usually been present for many years. Most of them were not receiving insulin at the time bacteraemia was diagnosed. Escherichia coli was the commonest pathogen (33%) in the diabetics, the main source of infection being the urinary tract. This finding may be due to diabetic autonomic neuropathy, which leads to a poorly emptying, chronically infected bladder. Urinary tract infections with bacteraemia in elderly diabetics are often accompanied by vague non-specific symptoms and poor diabetic control. Fever is infrequent. Prompt antibiotic therapy and insulin injections to control the diabetes usually cure these serious infections.