These data show that sub-MIC concentrations of fluoroquinolone significantly increase mutation rates and these data suggest that care must be taken to ensure that bacteria are not exposed to subinhibitory concentrations when adding quinolones to a regimen used to treat mycobacterial infection.

Background: Tuberculosis notification rates for London have risen dramatically in recent years. Molecular typing of Mycobacterium tuberculosis has contributed to our understanding of the epidemiology of tuberculosis throughout the world. This study aimed to assess the degree of recent transmission of M tuberculosis in London and subpopulations of the community with high rates of recent transmission. Methods: M tuberculosis isolates from all persons from Greater London diagnosed with culture positive tuberculosis between 1 July 1995 and 31 December 1997 were genetically fingerprinted using IS6110 restriction fragment length polymorphism (RFLP) typing. A structured proforma was used during record review of cases of culture confirmed tuberculosis. Cluster analysis was performed and risk factors for clustering were examined in a univariate analysis followed by a logistic regression analysis with membership of a cluster as the outcome variable. Results: RFLP patterns were obtained for 2042 isolates with more than four copies of IS6110; 463 (22.7%) belonged to 169 molecular clusters, which ranged in size from two (65% of clusters) to 12 persons. The estimated rate of recent transmission was 14.4%. Young age (0-19 years) (odds ratio (OR) 2.65, 95% confidence interval (CI) 1.59 to 4.44), birth in the UK (OR 1.55, 95% CI 1.04 to 2.03), black Caribbean ethnic group (OR 2.19, 95% CI 1.15 to 4.16), alcohol dependence (OR 2.33, 95% CI 1.46 to 3.72), and streptomycin resistance (OR 1.82, 95% CI 1.15 to 2.88) were independently associated with an increased risk of clustering. Conclusions: Tuberculosis in London is largely caused by reactivation or importation of infection by recent immigrants. Newly acquired infection is also common among people with recognised risk factors. Preventative interventions and early diagnosis of immigrants from areas with a high incidence of tuberculosis, together with thorough contact tracing and monitoring of treatment outcome among all cases of tuberculosis (especially in groups at higher risk of recent infection), remains most important.

It is assumed that bacteria always pay a significant physiological price for the acquisition of resistance to antibiotics. To test whether this was the case for a strain of Streptococcus pneumoniae that develops resistance to fluoroquinolone antibiotics, we selected resistance to these agents in a wild-type strain and measured their fitness in comparative growth experiments. The relative growth rate of a mutant strain selected on ciprofloxacin (parC Serine 79 to Tyrosine) was compared with its susceptible isogenic parent and no significant deficit was found (relative fitness 1.15 95% C.I. +/- 0.2.). A double mutant, however, had a relative fitness of 0.81 (parC Serine 79 to Tyrosine gyrA Serine 81 to Tyrosine). Mutant strains selected on gemifloxacin had only a modest increase in minimum inhibitory concentration; thus, second-round mutants were competed with a first-round gyrA Serine 81 to Tyrosine or the susceptible isogenic parent. The growth rate of three double-mutant strains parC Serine 79 to Tyrosine gyrA Serine 81 to Phenylanine, parC Serine 79 to Tyrosine, and Asparagine 83 to Phenylalanine were similar to the isogenic susceptible parent 1.16 (95% C.I. +/- 0.17), 0.99 (95% C.I. +/- 0.05), and 0.95 (95% C.I. +/- 0.05), respectively. These data suggest that mutation in the parC and gyrA genes may, on some occasions, not be associated with a physiological deficit.

The present study was designed to evaluate the use of variable number tandem repeat (VNTR) and IS6110-restriction fragment length polymorphism (RFLP) analyses in combination as a two-step strategy for discrimination (as measured by the Hunter-Gaston Discrimination Index [HGDI]) of both high-and lowcopy-number IS6110 Mycobacterium tuberculosis isolates compared to IS6110-RFLP alone with an unselected collection of isolates. Individually, IS6110-RFLP fingerprinting produced six clusters that accounted for 69% of the low-copy-number IS6110 isolates (five clusters) and 5% of the high-copy-number IS6110 isolates (one cluster). A total of 39% of all the isolates were clustered (HGDI ‫؍‬ 0.97). VNTR analysis generated a total of 35 different VNTR allele profile sets from 93 isolates (HGDI ‫؍‬ 0.938). Combining IS6110-RFLP analysis with VNTR analysis reduced the overall percentage of clustered isolates to 29% (HGDI ‫؍‬ 0.988) and discriminated a further 27% of low-copy-number isolates that would have been clustered by IS6110-RFLP alone. The use of VNTR analysis as an initial typing strategy facilitates further analysis by IS6110-RFLP, and more importantly, VNTR analysis subdivides some IS6110-RFLP-defined clusters containing low-and single-copy IS6110 isolates.