No abstract

The mutations in the quinolone resistance-determining region of the gyrA and gyrB genes from 27 clinical isolates of Escherichia coli with a range of MICs of ciprofloxacin from 0.007 to 128 ,ug/ml and of nalidixic acid from 2 to >2,000 ,ug/ml were determined by DNA sequencing. All 15 isolates with ciprofloxacin MICs of .1 ,ug/ml showed a change in Ser-83 to Leu of GyrA protein, whereas in clinical isolates with a MIC of .8 ,ug/ml (11 strains), a double change in Ser-83 and Asp-87 was found. All isolates with a MIC of nalidixic acid of .128 ,ug/ml showed a mutation at amino acid codon Ser-83. Only 1 of the 27 clinical isolates of E. coli analyzed showed a change in Lys-447 of the B subunit of DNA gyrase. A change in Ser-83 is sufficient to generate a high level of resistance to nalidixic acid, whereas a second mutation at Asp-87 in the A subunit of DNA gyrase may play a complementary role in developing the strain's high levels of ciprofloxacin resistance.New fluoroquinolones are broad-spectrum antibacterial agents which inhibit DNA gyrase activity (26). DNA gyrase contains two subunits of GyrA and two subunits of GyrB (13,19). Gyrase A mediates DNA strand breakage and reunion with the Tyr residue at position 122 forming a transient phosphotyrosine linkage with a broken DNA strand. The mechanisms of quinolone resistance essentially fall into two classes: (i) mutations in gyrA (1,2,5,6,8,17,28,30) or gyrB genes (27, 29) or (ii) reduced levels of quinolone accumulation in the cells (3, 4, 9-12). The mutations in the gyrA gene involved in the resistance are clustered in a region between nucleotides 199 (Ala-67) and 318 (Gln-106), which contains nucleotide 247 (Ser-83), the most frequently changed in spontaneus gyrA mutations. In the gyrB gene, two quinolone resistance-determining sites (amino acids 426 and 447) have been found (27,29). The mutation at amino acid codon Asp-426 confers resistance to nalidixic acid and the new fluoroquinolones, whereas the change of Lys-447 results in resistance to nalidixic acid and increased susceptibility to the fluoroquinolones (29). Recently, Heisig et al. (8) identified mutations in the gyrA gene of Escherichia coli 205096, a highly fluoroquinolone-resistant strain (MIC of ciprofloxacin, 128 ,ug/ml). From 1989 to 1993, the level of resistance to ciprofloxacin in our hospital increased from 0 to 16% in E. coli isolated from urine samples. To further assess the importance of these gyrA and gyrB mutations in the acquisition of high-level quinolone resistance, we examined by DNA sequencing 27 clinical isolates of E. coli with a range of MICs of ciprofloxacin from 0.007 to 128 ,ug/ml and of nalidixic acid from 2 to >2,000 ,ug/ml.The clinical isolates of E. coli were obtained from urine samples from outpatients, who had not previously received quinolones,

Mutations in the parC gene, which encodes a subunit of topoisomerase IV, were determined in 21 epidemiologically unrelated clinical isolates of Acinetobacter baumannii. Our studies highlight the conserved sequences in the quinolone-resistance-determining region of the parC gene from A. baumannii and other bacteria. Nine of ten isolates with MICs of ciprofloxacin of > or = 32 mg/L showed a change of Ser80 to Leu and one showed a change of Glu84 to Lys. These results suggest that ParC from A. baumannii is a secondary target for quinolones and that mutations at residues Ser80 and Glu84, when combined with mutations at Ser83 of GyrA, may render A. baumannii highly resistant to quinolones.

The gyrA gene mutations associated with quinolone resistance were determined in 21 epidemiologically unrelated clinical isolates of Acinetobacter baumannii. Our studies highlight the conserved sequences in the quinolone resistance-determining region of the gyrA gene from A. baumannii and other bacteria. All 15 isolates for which the MIC of ciprofloxacin is Ն4 g/ml showed a change at Ser-83 to Leu. Six strains for which the MIC of ciprofloxacin is 1 g/ml did not show any change at Ser-83, although a strain for which the MIC of ciprofloxacin is 1 g/ml exhibited a change at Gly-81 to Val. Although it is possible that mutations in other locations of the gyrA gene, the gyrB gene, or in other genes may also contribute to the modulation of the MIC level, our results suggest that a gyrA mutation at Ser-83 is associated with quinolone resistance in A. baumannii.

Clinical manifestations of Giardia duodenalis infection vary from asymptomatic infection to chronic diarrhoea. We study the correlation between the presence of symptoms and the G. duodenalis genotype in 108 patients with giardiasis. Patient age ranged from 2 to 72 years old. We found a correlation between assemblage AII and symptomatic infections, and between assemblage B and asymptomatic infections in the overall patient group and in patients less than five years of age. Nevertheless, if only patients of more than five years of age were considered, no statistically significant relationship between assemblage and symptomatic or asymptomatic Giardia infections was found. In these patients, host factors may affect the presence of clinical manifestations more than Giardia assemblage.