False-positive Mycobacterium avium-intracellulare cultures with the Bactec 460 TB system.

Isolation of Mycobacterium avium-intracellulare from a number of specimens cultured with the Bactec 460 TB system was suspected to be due to carry-over contamination. The analysis of culture records and of the typing results confirmed this hypothesis. The problem seems to have been eliminated after replacement of the needle heater and increase of the needle temperature. We recommend that a number of precautions should be taken to reduce the risk of reporting false positive mycobacterial cultures.

Antibiotic sensitivity of bacteria associated with community-acquired urinary tract infection in Britain.

Twelve laboratories in different parts of Britain each supplied approximately 80 consecutive urinary bacterial isolates from community patients. All strains were identified by a central laboratory, where sensitivity to a variety of orally administered antimicrobials was determined by microtitre broth dilution. 65.1% of isolates were Escherichia coli, 23.4% 'coliforms' other than E. coli, 4.6% Proteus and Morganella spp., 1.8% Pseudomonas spp., 2.4% enterococci, 0.7% group B streptococci, 1.5% coagulase-negative staphylococci and 0.5% Staphylococcus aureus. Using previously published breakpoint sensitivity values, 98.9% of all isolates were found to be sensitive to norfloxacin and to ciprofloxacin, 95.7% to co-amoxiclav, 86.8% to nitrofurantoin, 77.4% to cephalexin, 75.6% to trimethoprim, 75.0% to cephradine and 51.7% to amoxycillin. There were some differences in sensitivities between centres, particularly those of the cephalosporins. Using standard breakpoints, submitting laboratories were found to overestimate sensitivity to nitrofurantoin and to underestimate sensitivity to the quinolones and to co-amoxiclav; there was considerable overestimation of sensitivity to cephalosporins.