Quinolones are broad-spectrum antibacterial agents, commonly used in both clinical and veterinary medicine. Their extensive use has resulted in bacteria rapidly developing resistance to these agents. Two mechanisms of quinolone resistance have been established to date: alterations in the targets of quinolones, and decreased accumulation due to impermeability of the membrane and/or an overexpression of efflux pump systems. Recently, mobile elements have also been described, carrying the qnr gene, which confers resistance to quinolones.

Seventeen multiple-antibiotic-resistant nonpathogenic Escherichia coli strains of human, animal, and food origins showed a wide variety of antibiotic resistance genes, many of them carried by class 1 and class 2 integrons. Amino acid changes in MarR and mutations in marO were identified for 15 and 14 E. coli strains, respectively.

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,

The prevalence of hemolysin, type 1 fimbriae, P fimbriae, cytotoxic necrotizing factor-1 (CNF-1), aerobactin, and autotransporter toxin (sat) was analyzed by polymerase chain reaction and phenotypic assays of 42 epidemiologically unrelated Escherichia coli strains causing acute pyelonephritis in women (21 nalidixic acid-susceptible and 21 nalidixic acid-resistant strains) and 58 E. coli strains causing cystitis in women (29 nalidixic acid-susceptible and 29 nalidixic acid-resistant strains). Hemolysin and CNF-1 were less prevalent (P<.05) in nalidixic acid-resistant than in nalidixic acid-susceptible E. coli strains from patients with either pyelonephritis (14.3% vs. 52.4%) or cystitis (0% vs. 31.0%). Among E. coli strains causing cystitis, type 1 fimbriae expression was less prevalent (P<.05) in the nalidixic acid-resistant group (55.2%) than in the nalidixic acid-susceptible group (86.2%). None of the nalidixic acid-resistant and 20.7% of the nalidixic acid-susceptible strains causing cystitis showed the proteolytic toxin Sat (P<.05). These results suggest that resistance to quinolones may be associated with a decrease in the presence or the expression of some virulence factors in uropathogenic E. coli.

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.

BackgroundDiarrheal disease remains a leading cause of illness and death, particularly in low-income countries. Its burden, microbiological causes and risk factors were examined in children aged 0–59 months living in Manhiça, rural southern Mozambique.MethodsTrends of diarrhea-related burden of disease were estimated during the period 2001–2012. A prospective, age-stratified and matched (by age, gender and geographical origin), case-control study was conducted during 2007–2011. Clinical, epidemiology, anthropometric measurement and fecal samples obtained from recruited children were used to estimate moderate-to-severe diarrhea (MSD) weighted attributable fractions.ResultsOver the last decade the incidence of acute diarrhea has dropped by about 80%. Incidence of MSD per 100 child years at risk for the period 2007–2011 was 9.85, 7.73 and 2.10 for children aged 0–11, 12–23 and 24–59 months respectively. By adjusted population attributable fractions, most cases of MSD were due to rotavirus, Cryptosporidium, ETEC ST (ST only or ST/LT), Shigella and Adenovirus 40/41. Washing hands and having facilities to dispose child’s stools were associated with a reduced risk of MSD, while giving stored water to the child was associated with an increased risk of MSD.ConclusionsDespite the predominantly decreasing trends observed throughout the last decade, diarrheal diseases remain today a major cause of morbidity among children aged 0–59 months living in this rural Mozambican area. Rotavirus, cryptosporidium, Shigella, ETEC ST and Adenovirus 40/41 were the most important aetiologies of MSD. Thus, well-known preventive strategies such as washing hands, improving the treatment of stored water, having facilities to dispose children stools, and accelerating the introduction of the rotavirus vaccine should be promoted on a wider scale to reduce the current burden of diarrheal diseases.

Differences in the presence of nine urovirulence factors among clinical isolates of Escherichia coli causing cystitis and pyelonephritis in women and prostatitis in men have been studied. Hemolysin and necrotizing factor type 1 occur significantly more frequently among isolates causing prostatitis than among those causing cystitis (P < 0.0001) or pyelonephritis (P < 0.005). Moreover, the papGIII gene occurred more frequently in E. coli isolates associated with prostatitis (27%) than in those associated with pyelonephritis (9%) (P < 0.05). Genes encoding aerobactin and PapC occurred significantly less frequently in isolates causing cystitis than in those causing prostatitis (P < 0.01 and P < 0.0001, respectively) and pyelonephritis (P < 0.01 and P < 0.0001, respectively). No differences in the presence of Sat or type 1 fimbriae were found. Finally, AAFII and Bfp fimbriae are no longer considered uropathogenic virulence factors since they were not found in any of the strains analyzed. Overall, the results showed that clinical isolates producing prostatitis need greater virulence than isolates producing pyelonephritis in women or, in particular, cystitis in women (P < 0.05). Overall, the results suggest that clinical isolates producing prostatitis are more virulent that those producing pyelonephritis or cystitis in women.Urinary tract infections (UTIs) are one of the most common infectious diseases encountered in the clinical practice, mainly being associated with different members of the family Enterobacteriaceae. In fact, Escherichia coli is by far the most predominant pathogen causing UTIs (4,18,19,21).In general, rates of UTIs are higher among women than among men (15), with cystitis being the most prevalent UTI in women. It is noteworthy that the prevalence of quinolone resistance among E. coli strains causing cystitis is significantly higher than the prevalence of quinolone resistance among strains causing urinary parenchymatous infections such as prostatitis and pyelonephritis (2, 23). Velasco et al. (23) found that 20% of the isolates causing cystitis were resistant to ciprofloxacin, while only 8% of the invasive isolates causing UTIs had a resistant phenotype. Some studies suggest that resistance to the quinolones may be associated with a diminished virulence of the uropathogenic strains (16). Moreover, in a recent work (25), the prevalence of different genes encoding certain virulence factors among quinolone-resistant E. coli isolates causing cystitis and pyelonephritis in women was found to be lower than that among quinolone-susceptible strains.Both host and bacterial factors have been associated with the pathogenesis of these infections (9, 21). Thus, uropathogenic strains of E. coli are believed to display a variety of virulence properties that help them colonize host mucosal surfaces and circumvent host defenses to allow invasion of the normally sterile urinary tract (15,18,21). A number of virulence determinants have been related to the acquisition or development of UTIs. Among these factors, sidero...