N-1-tert-butyl-substituted quinolones: in vitro anti-Mycobacterium avium activities and structure-activity relationship studies

We determined the MICs of 63 quinolones against 14 selected reference and clinical strains of the Mycobacterium avium-Mycobacterium intracellulare complex. Sixty-one of the compounds were selected from the quinolone library at Parke-Davis, Ann Arbor, Mich., including N-1-tert-butyl-substituted agents. T 3761 and tosufloxacin were also tested. The activities of all 63 compounds were compared with those of ciprofloxacin and sparfloxacin. The results showed 45 of the quinolones to be active against the M. avium-M. intracellulare complex, with MICs at which 50% of the strains were inhibited (MIC50s) of less than 32 micrograms/ml. Twenty-four of these quinolones had activities equivalent to or greater than that of ciprofloxacin, and nine of them had activities equivalent to or greater than that of sparfloxacin. The most active compounds were the N-1-tert-butyl-substituted quinolones, PD 161315 and PD 161314, with MIC50s of 0.25 microgram/ml and MIC90s of 1 microgram/ml; comparable values for ciprofloxacin were 2 and 4 micrograms/ml, respectively, while for sparfloxacin they were 1 and 2 micrograms/ml, respectively. The next most active compounds, with MIC50s of 0.5 microgram/ml and MIC90s of 1 microgram/ml, were the N-1-cyclopropyl-substituted quinolones, PD 138926 and PD 158804. These values show that the tert-butyl substituent is at least as good as cyclopropyl in rendering high levels of antimycobacterial activity. However, none of the quinolones showed activity against ciprofloxacin-resistant laboratory-derived M. avium-M. intracellulare complex strains. A MULTICASE program-based structure-activity relationship analysis of the inhibitory activities of these 63 quinolones and 109 quinolones previously studied against the most resistant clinical strain of M. avium was also performed and led to the identification of two major biophores and two biophobes.     

Antimicrobial susceptibility of Shigella from a rural community in Bangladesh

Of the 63 Shigella strains isolated from stool cultures from 200 patients who attended a district hospital in Bangladesh with bloody diarrhoea, 37 (59%) were S. dysenteriae type 1, 25 (39%) were S. flexneri and only one (2%) was S. sonnei. Over half (54%) of the Shigella isolates came from children aged < 10 years. Most (89%) of the isolates of S. dysenteriae type 1 were resistant to ampicillin, cotrimoxazole, nalidixic acid, tetracycline and chloramphenicol. Although many (60%) of the isolates of S. flexneri were resistant to ampicillin and cotrimoxazole, only 4% of them were resistant to nalidixic acid. However, all of the S. dysenteriae and S. flexneri were sensitive to ciprofloxacin. The need for periodic monitoring to determine the resistance pattern in remote areas is emphasised.     

Resistance to fluoroquinolones in Escherichia coli isolated from poultry

Quinolone-resistant Escherichia coli strains were isolated from poultry clinical samples in Saudi Arabia. The poultry flocks had been treated with oxolinic acid or flumequine prophylaxis. The measure of the uptake of fluoroquinolones showed that none of the strains had a reduced accumulation of quinolones. The result of complementation with the wild-type E. coli gyrA gene, which restored fluoroquinolone susceptibility, and the isolation of DNA gyrase from six isolates indicated that the resistant strains had an altered DNA gyrase. The minimum effective dose of ciprofloxacin for inhibition of supercoiling catalyzed by the isolated gyrases varied from 0.085 microgram/ml for a susceptible isolate (MIC < 4 micrograms/ml) up to 96 micrograms/ml for the more resistant one (strain 215, MIC > 64 micrograms/ml). For the same two isolates, the minimum effective doses of sparfloxacin varied from 0.17 up to 380 micrograms/ml. The in vitro selection of spontaneous single-step fluoroquinolone-resistant mutants using ciprofloxacin suggested that the more resistant mutants are likely the result of several mutations. These results also show that, as in human medicine, cross-resistance between older quinolones and fluoroquinolones can exist in veterinary isolates and reiterate the need for the prudent use of these drugs.     

In vitro activity of the new fluoroquinolone CP-99,219

The in vitro activity of the new fluoroquinolone CP-99,219 [7-(3-azabicyclo[3.1.0]hexyl)naphthyridone] was compared with those of four other quinolones against 541 gram-negative, 283 gram-positive, and 70 anaerobic bacterial isolates. CP-99,219 inhibited 90% of many isolates in the family Enterobacteriaceae at a concentration of < or = 0.25 micrograms/ml (range, < 0.008 to 1 microgram/ml), an activity comparable to those of tosufloxacin and sparfloxacin and two times greater than that of temafloxacin. Ninety percent of the Proteus vulgaris, Providencia rettgeri, Providencia stuartii, and Serratia marcescens isolates were inhibited by 0.5 to 2 micrograms of CP-99,219 per ml. CP-99,219 inhibited 90% of the Pseudomonas aeruginosa and Haemophilus influenzae isolates at 1 and 0.015 micrograms/ml, respectively. The compound inhibited methicillin-susceptible Staphylococcus aureus at 0.06 micrograms/ml, whereas a ciprofloxacin concentration of 1 microgram/ml was required to inhibit these organisms. CP-99,219 inhibited 90% of methicillin-resistant S. aureus isolates at a concentration of < or = 4 micrograms/ml, while ciprofloxacin and temafloxacin had MICs against these isolates of > 16 micrograms/ml. Streptococci were inhibited by < or = 0.25 micrograms/ml, an activity comparable to that of tosufloxacin. CP-99,219 was eight times more active than ciprofloxacin against Streptococcus pneumoniae. Bacteroides species were inhibited by CP-99,219 at a concentration of 2 micrograms/ml, whereas inhibition of these species required 4- and 16-microgram/ml concentrations of tosufloxacin and ciprofloxacin, respectively. The MBCs of CP-99,219 ranged from two to four times the MICs, and inoculum size had a minimal effect on MIC. CP-99,219 was active against P. aeruginosa at pH 5.5, with only a fourfold increase in MIC compared with values obtained at pH 7.5. The addition of up to 9 mM Mg(2+) increased the MIC range from 0.03 to 0.06 microgram/ml to 0.12 to 0.5 microgram/ml. In view of its excellent in vitro activity against both gram-positive and gram-negative bacteria, CP-99,219 merits further study to determine it's clinical pharmacologic properties and potential for therapeutic use.     

Comparative in vitro activities of new quinolones against coryneform bacteria

The in vitro activities of eight quinolones against 115 coryneform bacteria (20 Corynebacterium jeikeium, 15 Corynebacterium minutissimum, 15 Corynebacterium striatum, 25 Corynebacterium urealyticum, 10 Corynebacterium xerosis, 10 Corynebacterium group ANF-1, 10 Corynebacterium group 12, and 10 Listeria monocytogenes) were determined. The MICs of ciprofloxacin, ofloxacin, and sparfloxacin for 90% of C. jeikeium, C. urealyticum, and C. xerosis isolates tested were > 16 micrograms/ml. Those of BAY Y 3118 and clinafloxacin against these species were 0.5 and 1 to 2 micrograms/ml, respectively. The MICs for 90% of all 115 strains tested were 0.5 microgram/ml for BAY Y 3118, 1 microgram/ml for clinafloxacin, 2 micrograms/ml for E-5068, 4 micrograms/ml for E-5065, and > 16 micrograms/ml for ciprofloxacin, ofloxacin, sparfloxacin, and E-4868.     

Inactivation of beta-lactamase from Shigella flexneri UCSF-129 by BRL 42715, a potent inhibitor

The effect of a powerful inhibitor, BRL 42715, on beta-lactamase from Shigella flexneri UCSF-129, to overcome the problem of shigellosis and its resistance to ampicillin, was studied. The I50 was determined for BRL 42715 [C6-(N1-methyl-1,2,3 triazolylmethylene)penem] as 0.0049 microgram/ml being 20-fold lower than the best inhibitor, 6-beta-iodopenicillanic acid, previously reported. The MIC fell from 2,048 to 2 micrograms/ml in the presence of 1 microgram/ml of BRL 42715. The synergism of the ampicillin plus this inhibitor lasted for 9 h. BRL 42715 is an irreversible inhibitor, according to the dialysis results, and a substrate analogue.     

Using equipment in unfamiliar clinical settings: audiology screening

To develop a better and selective medium for the isolation of Shigella spp., MacConkey's Agar (MAC) was modified by adding potassium tellurite (K2TeO3) at a concentration of 1 microgram/ml. The formulation designated Teknaf Enteric Agar (TEA) was studied for the inhibitory effect of potassium tellurite on the growth of different enteric bacteria, and as a medium for isolating Shigella spp. from clinical stool samples (n = 3125). We observed that the growth of E. coli was effectively inhibited on TEA with no effect on the growth of S. dysenteriae type 1 and S. flexneri. A total of 2019 Shigellae were isolated through the combined use of TEA, MAC, and Salmonella-Shigella Agar (SS). On TEA, 1921 S. dysenteriae type 1 and S. flexneri were isolated as compared to 1765 from the combined use of MAC and SS. A total of 194 of S. dysenteriae type 1 and S. flexneri were exclusively isolated from TEA as compared to 38 which were only made from MAC and SS. We conclude that TEA significantly increased the overall isolation rate of Shigella spp. as compared to the combined use of MAC and SS (P < 0.0001), although it is not suitable for the isolation of S. sonnei.     

Detection of mutations in parC in quinolone-resistant clinical isolates of Escherichia coli

The gene parC encodes the A subunit of topoisomerase IV of Escherichia coli. Mutations in the parC region analogous to those in the quinolone resistance-determining region of gyrA were investigated in 27 clinical isolates of E. coli for which ciprofloxacin MICs were 0.0007 to 128 micrograms/ml. Of 15 isolates for which ciprofloxacin MICs were > or = 1 microgram/ml, 8 showed a change in the serine residue at position 80 (Ser-80), 4 showed a change in Glu-84, and 3 showed changes in both amino acids. No mutations were detected in 12 clinical isolates for which ciprofloxacin MICs were < or = 0.25 micrograms/ml. These findings suggest that ParC from E. coli may be another target for quinolones and that mutations at residues Ser-80 and Glu-84 may contribute to decreased fluoroquinolone susceptibility.     

Antibacterial activity of gatifloxacin (AM-1155, CG5501, BMS-206584), a newly developed fluoroquinolone, against sequentially acquired quinolone-resistant mutants and the norA transformant of Staphylococcus aureus

Alternate mutations in the grlA and gyrA genes were observed through the first- to fourth-step mutants which were obtained from four Staphylococcus aureus strains by sequential selection with several fluoroquinolones. The increases in the MICs of gatifloxacin accompanying those mutational steps suggest that primary targets of gatifloxacin in the wild type and the first-, second-, and third-step mutants are wild-type topoisomerase IV (topo IV), wild-type DNA gyrase, singly mutated topo IV, and singly mutated DNA gyrase, respectively. Gatifloxacin had activity equal to that of tosufloxacin and activity more potent than those of norfloxacin, ofloxacin, ciprofloxacin, and sparfloxacin against the second-step mutants (grlA gyrA; gatifloxacin MIC range, 1.56 to 3.13 microg/ml) and had the most potent activity against the third-step mutants (grlA gyrA grlA; gatifloxacin MIC range, 1.56 to 6.25 microg/ml), suggesting that gatifloxacin possesses the most potent inhibitory activity against singly mutated topo IV and singly mutated DNA gyrase among the quinolones tested. Moreover, gatifloxacin selected resistant mutants from wild-type and the second-step mutants at a low frequency. Gatifloxacin possessed potent activity (MIC, 0.39 microg/ml) against the NorA-overproducing strain S. aureus NY12, the norA transformant, which was slightly lower than that against the parent strain SA113. The increases in the MICs of the quinolones tested against NY12 were negatively correlated with the hydrophobicity of the quinolones (correlation coefficient, -0.93; P < 0.01). Therefore, this slight decrease in the activity of gatifloxacin is attributable to its high hydrophobicity. Those properties of gatifloxacin likely explain its good activity against quinolone-resistant clinical isolates of S. aureus harboring the grlA, gyrA, and/or norA mutations.     

In vitro and in vivo antibacterial activities of T-3761, a new quinolone derivative

T-3761, a new quinolone derivative, showed broad and potent antibacterial activity. Its MICs for 90% of the strains tested were 0.20 to 100 micrograms/ml against gram-positive bacteria, including members of the genera Staphylococcus, Streptococcus, and Enterococcus; 0.025 to 3.13 micrograms/ml against gram-negative bacteria, including members of the family Enterobacteriaceae and the genus Haemophilus; 0.05 to 50 micrograms/ml against glucose nonfermenters, including members of the genera Pseudomonas, Xanthomonas, Acinetobacter, Alcaligenes, and Moraxella; 0.025 micrograms/ml against Legionella spp.; and 6.25 to 25 micrograms/ml against anaerobes, including Bacteroides fragilis, Clostridium difficile, and Peptostreptococcus spp. The in vitro activity of T-3761 against these clinical isolates was comparable to or 2- to 32-fold greater than those of ofloxacin and norfloxacin and 2- to 16-fold less and 1- to 8-fold greater than those of ciprofloxacin and tosulfoxacin, respectively. When administered orally, T-3761 showed good efficacy in mice against systemic, pulmonary, and urinary tract infections with gram-positive and gram-negative bacteria, including quinolone-resistant Serratia marcescens and Pseudomonas aeruginosa. The in vivo activity of T-3761 was comparable to or greater than those of ofloxacin, ciprofloxacin, norfloxacin, and tosufloxacin against most infection models in mice. The activities of T-3761 were lower than those of tosufloxacin against gram-positive bacterial systemic and pulmonary infections in mice but not against infections with methicillin-resistant Staphylococcus aureus. The activities of T-3761 against systemic quinolone-resistant Serratia marcescens and Pseudomonas aeruginosa infections in mice were 2- to 14-fold greater than those of the reference agents.     

Ampicillin resistance mediated by the R plasmid in strains of Shigella flexneri]

Forty Shigella flexneri strains isolated from children attended to at the Children's Hospital of Camagüey during an outbreak of acute diarrheal disease were studied; the minimal inhibitory concentration of ampicillin was determined. 33 strains (82.5%) were resistant to higher concentrations: 8 to 16 micrograms/mL, and 7 were susceptible to 4 micrograms/mL concentrations. Resistance plasmid (R) extraction was carried out in all the isolated strains and a common plasmid was found this plasmid was purified and transferred to Escherichia coli HE 101. Resistance transmission was tested.     

In vitro and in vivo antibiotic susceptibility of Lyme disease Borrelia isolated from the ixodid tick in Japan

Antimicrobial susceptibility of the Lyme disease Borrelia, strain HP1 vi, isolated from the tick ixodes persulcatus in Hokkaido, Japan, was determined in vitro and in vivo. A broth dilution technique was used to determine the minimum inhibitory concentrations (MICs) and minimum borreliacidal concentrations (MBCs) of five antimicrobial agents. Strain HP1 vi was most susceptible to minocycline (MBC, 0.2 micrograms/ml). The other antimicrobial agents tested, aspoxicillin, cefmetazole sodium, imipenem cilastatin sodium, and panipenem betamipron, had higher MBCs of 12.5 micrograms/ml, 25 micrograms/ml, > 25 micrograms/ml, and > 25 micrograms/ml, respectively. In vivo antibiotic susceptibility study using a ddY mouse model demonstrated that minocycline and amoxicillin were effective; minocycline had a lower 50% effective dose (ED50) value (6.25 mg/kg) than amoxicillin (30 mg/kg).     

Strategy for cross-protection among Shigella flexneri serotypes

Based upon the lipopolysaccharide (LPS) structure and antigenicity of Shigella group B, a strategy for broad cross-protection against 14 Shigella flexneri serotypes was designed. This strategy involves the use of two S. flexneri serotypes (2a and 3a), which together bear the all of the major antigenic group factors of this group. The novel attenuated strains used in these studies were S. flexneri 2a strain CVD 1207 (DeltaguaB-A DeltavirG Deltaset1 Deltasen) and S. flexneri 3a strain CVD 1211 (DeltaguaB-A DeltavirG Deltasen). Guinea pigs were immunized with an equal mixture of these strains and later challenged (Sereny test) with a wild-type S. flexneri serotype 1a, 1b, 2b, 4b, 5b, Y, or 6 strain of demonstrated virulence in the same model. Guinea pigs that were immunized with these two vaccine strains produced serum and mucosal antibodies that cross-reacted with all the S. flexneri serotypes tested (except of S. flexneri serotype 6) as assessed by enzyme-linked immunosorbent assay, immunoblotting, and slide agglutination. Furthermore, the combination vaccine conferred significant protection against challenge with S. flexneri serotypes 1b, 2b, 5b, and Y but not with serotypes 1a, 4b, or (as predicted) 6.     

Vocim analysis of laryngeal images: is breathiness related to the glottic area?

289 Shigella strains were isolated from children at the paediatrics department of Ankara University. 75% of the isolates were S. sonnei and 24.8% were S. flexneri. Each strain was tested for resistance to 9 antimicrobial agents. 79% of the isolates were resistant to streptomycin (S), 56% to tetracycline (T), 55.7% to trimethoprim-sulfamethoxazole (SXT), 27.7% to ampicillin (Am) and 19.7% to chloramphenicol (C). None of the isolates was resistant to ciprofloxacin, nalidixic acid, cephalothin, ampicillin-sulbactam and ceftriaxone. 56% of the isolates were resistant to 3 or more antimicrobial agents. The most frequent pattern of resistance of S. sonnei and S. flexneri strains was SXT, T, S (39.6%) and Am, SXT, T, S, C (48.6%), respectively (p < 0.0001). These results demonstrate that trimethoprim-sulfamethoxazole should not be used in the treatment of shigellosis.     

Clinical study on azithromycin in 10% fine granules and 100mg capsules in the field of pediatrics

Azithromycin (AZM), a new oral macrolide antibiotic, in 10% fine granules or 100 mg capsules was given to pediatric patients to treat various infections. The following results were obtained in our studies of AZM for its antibacterial activities against clinical isolates, its pharmacokinetics, its efficacy, and its safety. 1. MICs of AZM, erythromycin (EM) and clarithromycin (CAM) were determined against a total of 57 strains all at 10(6) cfu/ml. Among Gram-positive cocci, MICs of AZM ranged from 0.78 to > 100 micrograms/ml against Staphylococcus aureus (20 strains), from 0.05 to 0.1 microgram/ml against Streptococcus pyogenes (11 strains), and from 0.0125 to 3.13 micrograms/ml against Streptococcus pneumoniae (10 strains). These MICs were similar to those of the other macrolides. Among Gram-negative bacilli, MICs of AZM were 0.05 micrograms/ml against Moraxella subgenus Branhamella catarrhalis (1 strain), from 0.78 to 3.13 micrograms/ml against Haemophilus influenzae (9 strains), 0.78 micrograms/ml against Haemophilus parainfluenzae (1 strain) and 6.25 micrograms/ml against salmonella sp. (1 strain). These values were similar to or lower than those of the other macrolides. Against Mycoplasma pneumoniae, MICs of AZM were < or = 0.0008 micrograms/ml in three strains. One strain of M. pneumoniae showed tolerance to AZM at MIC 25 micrograms/ml. The other agents exhibited higher MIC than AZM against this organism. 2. Plasma samples were collected from five patients receiving fine granules and four patients receiving capsules for drug level determination. The patients received AZM at 10.0 approximately 16.3 mg/kg body weight once daily for 3 days. Drug concentrations in plasma at two hours after Day 3 dosing were in a range between 0.02 and 0.19 micrograms/ml for fine granules and were in a range between 0.11 and 0.42 micrograms/ml for capsules. 3. Urine samples were collected from four patients receiving fine granules and four patients receiving capsules. Drug levels were determined to be 3 micrograms/ml at post-treatment 48 hours for fine granules and post-treatment 72 hours for capsules. Urinary excretion rates of AZM in three patients on capsules lied in a range between 4.69 and 10.17%. 4. Effectiveness of AZM in fine granules was evaluated in 128 patients having a total of 19 different infections. AZM was rated "excellent" in 51 patients, "good" in 63, "fair" in 8, "poor" in 6, resulting in an efficacy rate of 89.1%. Effectiveness of AZM in capsular form was evaluated in 23 patients with five different infections. AZM was found "excellent" in 13 patients and "good" in 10, resulting in an efficacy rate of 100%. 5. AZM in fine granules eradicated 45 strains of 54 in 8 different bacteria. AZM in capsules eradicated 9 strains of 10 strains in 6 different bacteria. 6. As for adverse reactions, one patient complained of eruption, one vomiting, one loose stool, five diarrhea, when administered with fine granular form of AZM. One patient on AZM capsules experienced urticaria and vomiting. 7. As for abnormal laboratory changes, three patients were found with decreased WBC, seven with increased eosinophil, two with increased GOT and GPT, one with increased GPT. They were all on fine granular form of AZM. As far as abnormalities found in patients administered with AZM in capsular form, two showed decreased WBC, one decreased WBC along with increased eosinophil, and three increased eosinophil.     

Quinolone antibiotics in therapy of experimental pneumococcal meningitis in rabbits

Using a rabbit model of pneumococcal meningitis, we compared the pharmacokinetics and bactericidal activities in cerebrospinal fluid (CSF) of older (ciprofloxacin, ofloxacin) and newer (levofloxacin, temafloxacin, CP-116,517, and Win 57273) quinolones with those of the beta-lactam ceftriaxone. All quinolones penetrated into the inflamed CSF better than ceftriaxone, and the speed of entry into CSF was closely related to their degrees of lipophilicity. At a dose of 10 mg/kg.h, which in the case of the quinolones already in use in clinical practice produced concentrations attainable in the sera and CSF of humans, ciprofloxacin had no antipneumococcal activity (delta log10 CFU/ml.h, +0.20 +/- 0.14). Ofloxacin (delta log10 CFU/ml.h, -0.13 +/- 0.12), temafloxacin (delta log10 CFU/ml.h, -0.19 +/- 0.18), and levofloxacin (delta log10 CFU/ml.h, -0.24 +/- 0.16) showed slow bactericidal activity (not significantly different from each other), while CP-116,517 (delta log10 CFU/ml.h, -0.59 +/- 0.21) and Win 57273 (delta log10 CFU/ml.h, -0.72 +/- 0.20) showed increased bactericidal activities in CSF that was comparable to that of ceftriaxone at 10 mg/kg.h (delta log10 CFU/ml.h, -0.80 +/- 0.17). These improved in vivo activities of the newer quinolones reflected their increased in vitro activities. All quinolones and ceftriaxone showed positive correlations between bactericidal rates in CSF and concentrations in CSF relative to their MBCs. Only when this ratio exceeded 10 did the antibiotics exhibit rapid bactericidal activities in CSF. In conclusion, in experimental pneumococcal meningitis the activities of new quinolones with improved antipneumococcal activities were comparable to that of ceftriaxone.     

Skin smears in leprosy: is reduction in number of sites justified?

BACKGROUND: Infections caused by Streptococcus pneumoniae continue to be a significant cause of mortality and morbidity in humans. Diseases caused by multi-resistant pneumococci are increasing rapidly worldwide. The fluoroquinolones have been widely used clinically to treat infectious diseases. The results of a study here on the five fluoroquinolones susceptibilities of S. pneumoniae are reported from the Taichung Veterans General Hospital. METHODS: Minimum inhibitory concentrations (MICs) of five quinolones (enoxacin, norfloxacin, ofloxacin, levofloxacin and ciprofloxacin) were determined for 106 strains of S. pneumoniae. All MICs were determined by the agar dilution method utilizing Mueller-Hinton agar supplemented with 5% sheep blood. RESULTS: MIC90 of levofloxacin was 1 microgram/ ml, and was unaffected by penicillin-susceptibility. MIC90 of ofloxacin and that of ciprofloxacin were 2 and 4 micrograms/ml, respectively, with 90.6% sensitive to ofloxacin. MIC90 of enoxacin and that of norfloxacin were higher than other compounds. CONCLUSIONS: The in vitro activity of levofloxacin is twice that of ofloxacin, 4-fold of ciprofloxacin, 16-fold of norfloxacin, and 64-fold of enoxacin. MICs of these five quinolones were unaffected by penicillin-susceptibility. The antibacterial activity of levofloxacin was better than that of ofloxacin and ciprofloxacin, norfloxacin, or enoxacin against S. pneumoniae.     

Role of mutations in DNA gyrase genes in ciprofloxacin resistance of Pseudomonas aeruginosa susceptible or resistant to imipenem

In Pseudomonas aeruginosa, resistance to imipenem is mainly related to a lack of protein OprD and resistance to fluoroquinolones is mainly related to alterations in DNA gyrase. However, strains cross resistant to fluoroquinolones and imipenem have been selected in vitro and in vivo with fluoroquinolones. We investigated the mechanisms of resistance to fluoroquinolones in 30 clinical strains of P. aeruginosa resistant to ciprofloxacin (mean MIC, >8 micrograms/ml), 20 of which were also resistant to imipenem (mean MIC, >16 micrograms/ml). By immunoblotting, OprD levels were markedly decreased in all of the imipenem-resistant strains. Plasmids carrying the wild-type gyrA gene (pPAW207) or gyrB gene (pPBW801) of Escherichia coli were introduced into each strain by transformation. MICs of imipenem did not change after transformation, whereas those of ciprofloxacin and sparfloxacin dramatically decreased (25- to 70-fold) for all of the strains. For 28 of them (8 susceptible and 20 resistant to imipenem), complementation was obtained with pPAW207 but not with pPBW801. After complementation, the geometric mean MICs of ciprofloxacin and sparfloxacin (MICs of 0.3 microgram/ml and 0.5 microgram/ml, respectively) were as low as those for wild-type strains. Complementation was obtained only with pPBW801 for one strain and with pPAW207 and pPBW801 for one strain highly resistant to fluoroquinolones. These results demonstrate that in clinical practice, gyrA mutations are the major mechanism of resistance to fluoroquinolones even in the strains of P. aeruginosa resistant to imipenem and lacking OprD, concomitant resistance to these drugs being the result of the addition of at least two independent mechanisms.     

Activity of quinolones in the Ames Salmonella TA102 mutagenicity test and other bacterial genotoxicity assays

Eight quinolones were examined for their bacterial mutagenicity in the Ames Salmonella TA102 assay and for their effects in other bacterial genotoxicity assays. In the quantitative Ames plate incorporation assay, all eight quinolones induced His+ deletion reversion in Salmonella tester strain TA102, with maximum reversion observed at about two to eight times the MIC. The quinolones also induced the SOS response. At quinolone concentrations close to the MIC, SOS cell filamentation gene sulA was induced in sulA::lacZ fusion strain Escherichia coli PQ37. RecA-mediated cleavage of lambda repressor in lambda::lacZ fusion strain E. coli BR513 was measurable at about 10 times the MIC, though no induction occurred at 20 micrograms of nalidixic or oxolinic acid per ml. Genotoxicity of quinolones also was observed in the Bacillus subtilis DNA repair assay, in which the mutant strain M45 (recA) was more susceptible to quinolones than its parent strain, H17 (rec+). The results from these analyses indicate that quinolones induce SOS functions and are mutagenic in bacteria; these properties correspond to their antimicrobial activities.     

New provisional serovar of Shigella boydii

Ten bacterial strains are described that give biochemical reactions characteristic of the genus Shigella but do not belong to any of the established or provisional serovars. The strains ferment mannitol and are antigenically indistinguishable. They do not possess any of the group antigens of Shigella flexneri, and it is therefore proposed that they be regarded as members of a new provisional serovar of Shigella boydii. Strain E16553 is designated as the test strain for the new serovar.