Background Tests to determine serum antibody levels—the 2-tier sonicate immunoglobulin M (IgM) and immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) and Western blot method or the IgG of the variable major protein-like sequence-expressed (VlsE) sixth invariant region (C6) peptide ELISA method—are the major tests available for support of the diagnosis of Lyme disease. However, these tests have not been assessed prospectively. Methods We used these tests prospectively to determine serologic responses in 134 patients with various manifestations of Lyme disease, 89 patients with other illnesses (with or without a history of Lyme disease), and 136 healthy subjects from areas of endemicity and areas in which the infection was not endemic. Results With 2-tier tests and the C6 peptide ELISA, only approximately one-third of 76 patients with erythema migrans had results that were positive for IgM or IgG seroreactivity with Borrelia burgdorferi in acute-phase samples. During convalescence, 3–4 weeks later, almost two-thirds of patients had seroreactivity with the spirochete B. burgdorferi. The frequencies of seroreactivity were significantly greater among patients with spirochetal dissemination than they were among those who lacked evidence of disseminated disease. Of the 44 patients with Lyme disease who had neurologic, heart, or joint involvement, all had positive C6 peptide ELISA results, 42 had IgG responses with 2-tier tests, and 2 patients with facial palsy had only IgM responses. However, among the control groups, the IgG Western blot was slightly more specific than the C6 peptide ELISA. The differences between the 2 test systems (2-tier testing and C6 peptide ELISA) with respect to sensitivity and specificity were not statistically significant. Conclusions Except in patients with erythema migrans, both test systems were sensitive for support of the diagnosis of Lyme disease. However, with current methods, 2-tier testing was associated with slightly better specificity.

The interpretation of serological results for patients who had Lyme disease many years ago is not well defined. We studied the serological status of 79 patients who had had Lyme disease 10-20 years ago and did not currently have signs or symptoms of active Lyme disease. Of the 40 patients who had had early Lyme disease alone, 4 (10%) currently had IgM responses to Borrelia burgdorferi, and 10 (25%) still had IgG reactivity to the spirochete, as determined by a 2-test approach (enzyme-linked immunosorbent assay and Western blot). Of the 39 patients who had had Lyme arthritis, 6 (15%) currently had IgM responses and 24 (62%) still had IgG reactivity to the spirochete. IgM or IgG antibody responses to B. burgdorferi may persist for 10-20 years, but these responses are not indicative of active infection.

In Escherichia coli the frequency of spontaneous single-step mutation to high levels of resistance to the newer 4-quinolone agent norfloxacin was confirmed to be over 300-fold lower than that to the older agent nalidixic acid. Serial passage on incremental concentrations of drug was necessary to produce mutants highly resistant to norfloxacin. Genetic analysis of one such highly resistant strain identified two mutations conferring drug resistance. One mutation, nfxA, mapped around 48 min on the E. coli genetic map and was shown to be an allele of gyrA by studies demonstrating an increased drug resistance of DNA gyrase reconstituted with the gyrase A subunit isolated from the mutant strain. These findings also identified the DNA gyrase A subunit as a target of norfloxacin. The second mutation, nfxB, mapped between 20 and 22 min and was associated with additional resistances to tetracycline, chloramphenicol, and cefoxitin and with decreases in outer membrane porin protein OmpF. The nfxA and nfxB mutations together accounted for most, but not all, of the norfloxacin resistance phenotype of this strain.The newer 4-quinolone antimicrobial agents such as norfloxacin (NFX) are structurally related to nalidixic acid (NAL) but have substantially increased potency and are broader in spectrum. The newer agents, therefore, show promise for use in treatment of a variety of bacterial infections. A potentially serious limitation to this usefulness, however, might be the development of bacterial resistance, a problem that occurred with NAL in certain settings (28).Resistance of bacteria to NAL and the 4-quinolones results from chromosomal mutations, but has not been found to be carried on plasmids or transposons (1). A target of NAL action is the essential bacterial enzyme DNA gyrase (9). The structure and functions of DNA gyrase have been the subject of several reviews (3, 9, 35). Mutations in the gene [gyrA (nalA)] encoding the A subunit of the enzyme DNA gyrase confer on the bacterium and the enzyme high-level resistance to NAL. In addition to two A subunits, this enzyme contains two B subunits, the products of the gyrB (cou) gene. Purified DNA gyrase has a variety of activities in vitro that are inhibited by NAL, including the introduction of negative superhelical twists into duplex circular DNA and the reversible interlocking of DNA circles like links in a chain. In the growing bacterium DNA gyrase is required for DNA replication, transcription of certain operons, DNA repair, and other processes, all of which are antagonized by NAL. The level of superhelical twisting of intracellular DNA is controlled at least in part by the activities of DNA gyrase and topoisomerase I, the product of the topA gene. Other genes in which mutations may cause altered levels of resistance to NAL include nalB (12), nalC (gyrB) (37), nalD (31, 37), icd (18), cya (18), and crp (17).Less is known about the mechanisms of resistance of bacteria to NFX and other newer 4-quinolones. The frequency with which bacteria spontaneously become resistant to h...