In vitro evaluation of activities of nitazoxanide and tizoxanide against anaerobes and aerobic organisms

The antibacterial activities of nitazoxanide and its main metabolite, tizoxanide, were tested against a broad range of bacteria, including anaerobes. Metronidazole, amoxicillin, amoxicillin-clavulanic acid, piperacillin, cefoxitin, imipenem, and clindamycin were used as positive controls. MICs were determined by reference agar dilution methods. The 241 anaerobes were all inhibited by nitazoxanide, with the MICs at which 90% of isolates are inhibited (MIC90S) being between 0.06 and 4 mg/liter with the exception of those for Propionibacterium species, for which the MIC90 was 16 mg/liter. The MIC90s of nitazoxanide were 0.5 mg/liter for the Bacteroides fragilis group (80 strains), 0.06 mg/liter for Clostridium difficile (21 strains), and 0.5 mg/liter for Clostridium perfringens (16 strains). Metronidazole showed a level of activity comparable to that of nitazoxanide except against Bifidobacterium species, against which it was poorly active, and Propionibacterium species, which were resistant to metronidazole. The other antibiotics showed various levels of activity against anaerobes, with imipenem along with nitazoxanide being the most active agents tested. Tizoxanide was less effective than nitazoxanide except against the B. fragilis group, against which its activity was similar to that of nitazoxanide. Under aerobic conditions, nitazoxanide demonstrated poor activity against members of the family Enterobacteriacae and Pseudomonas, Staphylococcus, and Enterococcus species. The same results were obtained when culture was performed under anaerobic conditions with the notable exception of the results against Staphylococcus aureus. The MICs of nitazoxanide were in the range of 2 to 4 mg/liter for 34 clinical isolates of S. aureus, 12 of which were methicillin resistant, while tizoxanide was not effective.     

Metronidazole and clarithromycin resistance in Helicobacter pylori determined by measuring MICs of antimicrobial agents in color indicator egg yolk agar in a miniwell format. The Gastrointestinal Physiology Working Group of Universidad Peruana Cayetano Heredia and the Johns Hopkins University

Resistance of Helicobacter pylori to metronidazole often causes failure of commonly used combination drug treatment regimens. We determined the MICs of metronidazole and clarithromycin against 18 H. pylori strains from Peru using tetrazolium egg yolk (TEY) agar. The MIC results obtained by agar dilution with petri dishes were compared with the results found through a miniwell format. The results of the two protocols for measuring drug susceptibility differed by no more than 1 dilution in all cases. On TEY agar, bright-red H. pylori colonies were easy to identify against a yellow background. Sixty-one percent (11 of 18) of the strains were resistant to metronidazole (MIC, > or = 4 micrograms/ml) and 50% (9 of 18) were resistant to clarithromycin (MIC, > or = 0.125 micrograms/ml), whereas none (0 of 5) of the strains tested were resistant to tetracycline (MIC, > or = 1 micrograms/ml). Thus, the prevalence of metronidazole and clarithromycin resistance in Peru is higher than that in developed regions of the world. The miniwell plate with TEY agar allows easy H. pylori colony identification, requires about one-third less of the costly medium necessary for petri dish assaying, conserves space, and yields MICs equivalent to those with agar dilution in petri dishes.     

Effect of ring size on conformations of aromatic amine-DNA adducts: the aniline-C8 guanine adduct resides in the B-DNA major groove

We isolated strains of Helicobacter pylori from gastric mucosa of patients with peptic ulcer before and after eradication therapy, and studied their sensitivity to amoxicillin (AMPC) and clarythromycin (CAM). Of 85 strains of H. pylori isolated before therapy, MIC90 was 0.025 microgram/ml and no strains were resistant to AMPC. On the other hand, MIC90 of CAM was 0.05 microgram/ml and seven (8.2%) were already resistant to CAM. The H. pylori strains from eight cases of failed eradication therapy with lansoprazole + AMPC remained AMPC sensitive. However H. pylori strains from nineteen cases (82.6%) out of 23 of failed eradication therapy with lansoprazole + CAM became CAM resistant. The situation was similar for the cases of failed eradication therapy with lansoprazole + AMPC + CAM. Drug sensitivity tests prior to eradication therapy are to be recommended. A disc method may be used as a simple alternative to MIC measurement.     

Antibacterial activity of teicoplanin against Clostridium difficile

The in vitro inhibitory action of teicoplanin, vancomycin, metronidazole and clindamycin against clinical isolates of Clostridium difficile was investigated. Minimum inhibitory concentrations (MICs) were determined using E test. Teicoplanin (MIC range 0.023-0.75 microgram/ml), vancomycin (MIC range 0.5-3 micrograms/ml) and metronidazole (MIC range 0.19-1 microgram/ml) were all very active against the isolates examined. No resistant strains of C. difficile to those three antimicrobial agents were observed, whereas resistance to clindamycin was found in 39.5% of the tested strains. Teicoplanin was about 4-times more potent than vancomycin. It appears to be a more promising antimicrobial for treatment of C. difficile enteric disease.     

Drug resistance of Helicobacter pylori strains isolated from patients with inflammation of stomach mucous membrane and peptic ulcer of stomach and duodenum

Twelve strains of H. pylori were tested. They were isolated from biosamples from 23 patients with stomach inflammation (16 persons) and stomach (3) and duodenum peptic ulcer. By application of solid medium dilution of MIC50 and MIC90-16 antibiotics and antimicrobials were tested. Values of MIC50 and MIC90 for antibiotics from the tetracycline group were, respectively 0.25-0.5 microgram/ml and 0.12-1.0 microgram/ml. Similar results were obtained with macrolide antibiotics. All strains were sensitive to penicillin (MIC 0.03-0.12 microgram/ml, ampicillin (MIC 0.06-0.5 microgram/ml) and amoxicillin and rifampicin (MIC 0.07-0.3 microgram/ml). Ten out of 12 investigated strains were resistant to metronidazole (MIC90 = 30 micrograms/ml). Results of this study may be important for etiotropic treatment of infections with H. pylori.     

Unsuccessful deflation of a bifoil balloon during percutaneous mitral valvuloplasty

Triple therapy (bismuth and two antibiotics) will eradicate Helicobacter pylori infection in 70-90% of subjects. Treatment failure has been attributed to patient compliance and antimicrobial drug resistance. The aim of this study was to examine factors influencing the eradication of H. pylori following triple therapy. Thirty seven subjects with H. pylori cultured from antral biopsies were treated with colloidal bismuth subcitrate (120 mg qid for 2 weeks), metronidazole (400 mg tid for 1 week) and amoxycillin (500 mg tid for 1 week). Pretreatment isolates of H. pylori were tested for metronidazole susceptibility by agar dilution according to the National Committee for Clinical Laboratory Standards guidelines. Factors including age, sex, clinical diagnosis and metronidazole resistance were evaluated in relation to H. pylori. The overall metronidazole resistance was 32%. Metronidazole resistant strains were more frequent in females, with a resistance rate of 54%. Helicobacter pylori eradication occurred in 68% of patients with a metronidazole susceptible stain and only 17% of patients with a metronidazole resistant strain (P < 0.03). Helicobacter pylori eradication is dependent upon susceptibility to metronidazole. This data would support the role for routine metronidazole susceptibility testing using appropriate standardized methods when triple therapy is to be considered.     

Susceptibilities of penicillin- and erythromycin-susceptible and -resistant pneumococci to HMR 3647 (RU 66647), a new ketolide, compared with susceptibilities to 17 other agents

Susceptibility of 230 penicillin- and erythromycin-susceptible and -resistant pneumococci to HMR 3647 (RU 66647), a new ketolide, was tested by agar dilution, and results were compared with those of erythromycin, azithromycin, clarithromycin, roxithromycin, rokitamycin, clindamycin, pristinamycin, ciprofloxacin, sparfloxacin, trimethoprim-sulfamethoxazole, doxycycline, chloramphenicol, cefuroxime, ceftriaxone, imipenem, and vancomycin. HMR 3647 was very active against all strains tested, with MICs at which 90% of the strains were inhibited (MIC90s) of 0.03 microg/ml for erythromycin-susceptible strains (MICs, < or =0.25 microg/ml) and 0.25 microg/ml for erythromycin-resistant strains (MICs, > or =1.0 microg/ml). All other macrolides yielded MIC90s of 0.03 to 0.25 and >64.0 microg/ml for erythromycin-susceptible and -resistant strains, respectively. The MICs of clindamycin for 51 of 100 (51%) erythromycin-resistant strains were < or =0.125 microg/ml. The MICs of pristinamycin for all strains were < or =1.0 microg/ml. The MIC90s of ciprofloxacin and sparfloxacin were 4.0 and 0.5 microg/ml, respectively, and were unaffected by penicillin or erythromycin susceptibility. Vancomycin and imipenem inhibited all strains at < or =1.0 microg/ml. The MICs of cefuroxime and cefotaxime rose with those of penicillin G. The MICs of trimethoprim-sulfamethoxazole, doxycycline, and chloramphenicol were variable but were generally higher in penicillin- and erythromycin-resistant strains. HMR 3647 had the best kill kinetics of all macrolides tested against 11 erythromycin-susceptible and -resistant strains, with uniform bactericidal activity (99.9% killing) after 24 h at two times the MIC and 99% killing of all strains at two times the MIC after 12 h for all strains. Pristinamycin showed more rapid killing at 2 to 6 h, with 99.9% killing of 10 of 11 strains after 24 h at two times the MIC. Other macrolides showed significant activity, relative to the MIC, against erythromycin-susceptible strains only.     

Eradication of Helicobacter pylori with lansoprazole, roxithromycin and metronidazole--an open pilot study

BACKGROUND: The most extensively studied Helicobacter pylori eradication regimen comprises omeprazole, clarithromycin and metronidazole. Macrolide antibiotics other than clarithromycin should achieve similar efficacy, but they have not yet been thoroughly tested. AIM: To determine the efficacy and safety of a triple therapy regimen using lansoprazole, roxithromycin, and metronidazole on the basis of multicentre outpatient care in an open pilot study. METHODS: 163 patients with duodenal ulcer and proven H. pylori infection received lansoprazole 30 mg b.d., roxithromycin 300 mg b.d. and metronidazole 500 mg b.d. for 7 days followed by another 7 days of lansoprazole 30 mg once daily. H. pylori status was determined by urease quick test, histology, microbiology and 13C-urea breath test before starting and at least 4 weeks after completing treatment. RESULTS: 150 patients were available for evaluation; H. pylori was successfully eradicated in 84.7% (127/ 150) as determined by urease quick test, 78.0% (117/150) by histology, 81.3% (109/134) by 13C-urea breath test; and in 75.3% (113/150), at least two tests were negative. Side-effects were reported in 34 patients (most commonly diarrhoea and changes in liver function tests), in two cases the study medication was interrupted. Prior to treatment, 23% of the H. pylori isolates were resistant against metronidazole and 3.4% against roxithromycin. After unsuccessful treatment, 84% of the isolates were resistant against metronidazole and 21% against roxithromycin. Primary resistance to metronidazole increased the chance of treatment failure approximately sevenfold (7% vs. 53%). CONCLUSIONS: For H. pylori eradication, the combination of lansoprazole, roxithromycin and metronidazole proved to be as safe as other current triple therapy regimens, while a comparison of efficacy rates yet remains to be assessed in prospective controlled trials. The metronidazole-resistant H. pylori is not rare in Germany and, in the present study, has strongly influenced treatment success.     

Non-alcoholic steatohepatitis (NASH): a disease of emerging identity and importance

The agar dilution MIC method was used to test the activity of cefminox, a beta-lactamase-stable cephamycin, compared with those of cefoxitin, cefotetan, moxalactam, ceftizoxime, cefotiam, cefamandole, cefoperazone, clindamycin, and metronidazole against 357 anaerobes. Overall, cefminox was the most active beta-lactam, with an MIC at which 50% of isolates are inhibited (MIC50) of 1.0 microg/ml and an MIC90 of 16.0 microg/ml. Other beta-lactams were less active, with respective MIC50s and MIC90s of 2.0 and 64.0 microg/ml for cefoxitin, 2.0 and 128.0 microg/ml for cefotetan, 2.0 and 64.0 microg/ml for moxalactam, 4.0 and > 128.0 microg/ml for ceftizoxime, 16.0 and > 128.0 microg/ml for cefotiam, 8.0 and >128.0 microg/ml for cefamandole, and 4.0 and 128.0 microg/ml for cefoperazone. The clindamycin MIC50 and MIC90 were 0.5 and 8.0 microg/ml, respectively, and the metronidazole MIC50 and MIC90 were 1.0 and 4.0 microg/ml, respectively. Cefminox was especially active against Bacteroides fragilis (MIC90, 2.0 microg/ml), Bacteroides thetaiotaomicron (MIC90, 4.0 microg/ml), fusobacteria (MIC90, 1.0 microg/ml), peptostreptococci (MIC90, 2.0 microg/ml), and clostridia, including Clostridium difficile (MIC90, 2.0 microg/ml). Time-kill studies performed with six representative anaerobic species revealed that at the MIC all compounds except ceftizoxime were bactericidal (99.9% killing) against all strains after 48 h. At 24 h, only cefminox and cefoxitin at 4x the MIC and cefoperazone at 8x the MIC were bactericidal against all strains. After 12 h, at the MIC all compounds except moxalactam, ceftizoxime, cefotiam, cefamandole, clindamycin, and metronidazole gave 90% killing of all strains. After 3 h, cefminox at 2 x the MIC produced the most rapid effect, with 90% killing of all strains.     

Antimicrobial activity of novel furanonaphthoquinone analogs

Analogs of furanonaphthoquinone (FNQ) from Tecoma ipe Mart had MICs ranging from 1.56 to 25 microg/ml against gram-positive bacteria. FNQ showed significantly lower MICs against methicillin-resistant Staphylococcus aureus than against methicillin-sensitive S. aureus. FNQ inhibited Helicobacter pylori with an MIC of 0.1 microg/ml. Fungi, including pathogenic species, were sensitive to FNQ with MICs similar to those of amphotericin B.     

In vitro selection of resistance to four beta-lactams and azithromycin in Streptococcus pneumoniae

Selection of resistance to amoxicillin (with or without clavulanate), cefaclor, cefuroxime, and azithromycin among six penicillin G- and azithromycin-susceptible pneumococcal strains and among four strains with intermediate penicillin sensitivities (azithromycin MICs, 0.125 to 4 microg/ml) was studied by performing 50 sequential subcultures in medium with sub-MICs of these antimicrobial agents. For only one of the six penicillin-susceptible strains did subculturing in medium with amoxicillin (with or without clavulanate) lead to an increased MIC, with the MIC rising from 0.008 to 0.125 microg/ml. Five of the six penicillin-susceptible strains showed increased azithromycin MICs (0.5 to >256.0 microg/ml) after 17 to 45 subcultures. Subculturing in medium with cefaclor did not affect the cefaclor MICs of three strains but and led to increased cefaclor MICs (from 0.5 to 2.0 to 4.0 microg/ml) for three of the six strains, with MICs of other beta-lactams rising 1 to 3 twofold dilutions. Subculturing in cefuroxime led to increased cefuroxime MICs (from 0.03 to 0.06 microg/ml to 0.125 to 0.5 microg/ml) for all six strains without significantly altering the MICs of other beta-lactams, except for one strain, which developed an increased cefaclor MIC. Subculturing in azithromycin did not affect beta-lactam MICs. Subculturing of the four strains with decreased penicillin susceptibility in amoxicillin (with or without clavulanate) or cefuroxime did not select for beta-lactam resistance. Subculturing of one strain in cefaclor led to an increase in MIC from 0.5 to 2.0 microg/ml after 19 passages. In contrast to strains that were initially azithromycin susceptible, which required >10 subcultures for resistance selection, three of four strains with azithromycin MICs of 0.125 to 4.0 microg/ml showed increased MICs after 7 to 13 passages, with the MICs increasing to 16 to 32 microg/ml. All azithromycin-resistant strains were clarithromycin resistant. With the exception of strains that contained mefE at the onset, no strains that developed resistance to azithromycin contained ermB or mefE, genes that have been found in macrolide-resistant pneumococci obtained from clinic patients.     

In vitro activity of RP59500, an injectable streptogramin antibiotic, against vancomycin-resistant gram-positive organisms

The in vitro activity of RP59500, a streptogramin antibiotic, against 146 clinical isolates of vancomycin-resistant gram-positive bacteria was examined. Five strains of the species Enterococcus casseliflavus and Enterococcus gallinarum, for which the MIC of vancomycin was 8 micrograms/ml, were also studied. Twenty-eight vancomycin-susceptible strains of Enterococcus faecalis and Enterococcus faecium were included for comparison. The drug was highly active against Leuconostoc spp., Lactobacillus spp., and Pediococcus spp. (MICs, < or = 2 micrograms/ml). RP59500 was more active against vancomycin-susceptible strains of E. faecium than E. faecalis (MICs for 90% of the strains [MIC90s], 1.0 versus 32 micrograms/ml). Vancomycin-resistant strains of E. faecalis were as resistant to RP59500 as vancomycin-susceptible strains (MIC90, 32 micrograms/ml), but some vancomycin-resistant E. faecium strains were relatively more resistant to the new agent (MIC90, 16; MIC range, 0.5 to 32 micrograms/ml) than were vancomycin-susceptible organisms of this species.     

In vitro activity of Bay 12-8039, a new 8-methoxyquinolone, compared to the activities of 11 other oral antimicrobial agents against 390 aerobic and anaerobic bacteria isolated from human and animal bite wound skin and soft tissue infections in humans

The in vitro activity of Bay 12-8039, a new oral 8-methoxyquinolone, was compared to the activities of 11 other oral antimicrobial agents (ciprofloxacin, levofloxacin, ofloxacin, sparfloxacin, azithromycin, clarithromycin, amoxicillin clavulanate, penicillin, cefuroxime, cefpodoxime, and doxycycline) against 250 aerobic and 140 anaerobic bacteria recently isolated from animal and human bite wound infections. Bay 12-8039 was active against all aerobic isolates, both gram-positive and gram-negative isolates, at < or = 1.0 microg/ml (MICs at which 90% of isolates are inhibited [MIC90s < or = 0.25 microg/ml) and was active against most anaerobes at < or = 0.5 microg/ml; the exceptions were Fusobacterium nucleatum and other Fusobacterium species (MIC90s, > or = 4.0 microg/ml) and one strain of Prevotella loeschii (MICs, 2.0 microg/ml). In comparison, the other quinolones tested had similar in vitro activities against the aerobic strains but were less active against the anaerobes, including peptostreptococci, Porphyromonas species, and Prevotella species. The fusobacteria were relatively resistant to all the antimicrobial agents tested except penicillin G (one penicillinase-producing strain of F. nucleatum was found) and amoxicillin clavulanate.     

One week triple therapy for Helicobacter pylori: a multicentre comparative study. Lansoprazole Helicobacter Study Group

BACKGROUND: Eradication of Helicobacter pylori cures and prevents the relapse of duodenal ulceration and also results in histological resolution of chronic active gastritis. AIM: To compare four treatment regimens lasting seven days of a proton pump inhibitor and two antibiotics in the eradication of H pylori. PATIENTS: Men or women with H pylori positive duodenal ulceration or gastritis, or both. METHODS: A single blind, prospectively randomised, parallel group, comparative, multicentre study. After a positive CLO test, patients underwent histology, H pylori culture, and a 13C urea breath test to confirm H pylori status. Treatment with one of four regimens: LAC, LAM, LCM, or OAM, where L is 30 mg of lansoprazole twice daily, A is 1 g of amoxycillin twice daily, M is 400 mg of metronidazole twice daily, C is 250 mg of clarithromycin twice daily, and O is 20 mg of omeprazole twice daily, was assigned randomly. A follow up breath test was done at least 28 days after completing treatment. RESULTS: H pylori eradication (intention to treat) was 104/121 (86.0%) with LAC, 87/131 (66.4%) with LAM, 103/118 (87.3%) with LCM, and 94/126 (74.6%) with OAM. There was a significant difference (p < 0.001) in the proportion of patients in whom eradication was successful between LAC and LCM when compared with LAM, but no significant difference (p = 0.15) between LAM and OAM. Metronidazole resistance before treatment was identified as a significant prognostic factor with regard to eradication of H pylori. The regimens which contained metronidazole were significantly less effective than those without metronidazole in the presence of pretreatment resistant H pylori. There was no difference among the treatment groups with regard to the incidence and severity of adverse events reported. CONCLUSIONS: All four treatment regimens were safe and effective in eradicating H pylori in the patient population studied. LAC was the most efficacious treatment in patients with pretreatment metronidazole resistant H pylori, and was significantly better than LAM and OAM in this group of patients.     

Age-related changes in adenosine in rat coronary resistance vessels

The purpose of the present investigation was to determine if the efficacy of amoxicillin-clavulanate against penicillin-resistant Streptococcus pneumoniae could be improved by increasing the pediatric amoxicillin unit dose (90 versus 45 mg/kg of body weight/day) while maintaining the clavulanate unit dose at 6.4 mg/kg/day. A rat pneumonia model was used. In that model approximately 6 log10 CFU of one of four strains of S. pneumoniae (amoxicillin MICs, 2 microg/ml [one strain], 4 microg/ml [two strains], and 8 microg/ml [one strain]) were instilled into the bronchi of rats. Amoxicillin-clavulanate was given by computer-controlled intravenous infusion to approximate the concentrations achieved in the plasma of children following the administration of oral doses of 45/6.4 mg/kg/day or 90/6.4 mg/kg/g/day divided every 12 h or saline as a control for a total of 3 days. Infusions continued for 3 days, and 2 h after the cessation of infusion, bacterial numbers in the lungs were significantly reduced by the 90/6.4-mg/kg/day equivalent dosage for strains for which amoxicillin MICs were 2 or 4 microg/ml. The 45/6.4-mg/kg/day equivalent dosage was fully effective only against the strain for which the amoxicillin MIC was 2 microg/ml and had marginal efficacy against one of the two strains for which amoxicillin MICs were 4 microg/ml. The bacterial load for the strain for which the amoxicillin MIC was 8 microg/ml was not reduced with either dosage. These data demonstrate that regimens which achieved concentrations in plasma above the MIC for at least 34% of a 24-h dosing period resulted in significant reductions in the number of viable bacteria, indicating that the efficacy of amoxicillin-clavulanate can be extended to include efficacy against less susceptible strains of S. pneumoniae by increasing the amoxicillin dose.     

Fluconazole versus Candida albicans: a complex relationship

A murine model of systemic candidiasis was used to assess the virulence of serial Candida albicans strains for which fluconazole MICs were increasing. Serial isolates from five patients with 17 episodes of oropharyngeal candidiasis were evaluated. The MICs for these isolates exhibited at least an eightfold progressive increase from susceptible (MIC < 8 microg/ml; range, 0.25 to 4 microg/ml) to resistant (MIC >/= 16 microg/ml; range, 16 to >/=128 microg/ml). Virulence of the serial isolates from three of five patients showed a more than fivefold progressive decrease in the dose accounting for 50% mortality and was associated with development of fluconazole resistance. Low doses of fluconazole prolonged survival of mice infected with susceptible yeasts but failed to prolong survival following challenge with a resistant strain. In addition, a decreased burden of renal infection was noted in mice challenged with two of the three resistant strains. This was consistent with reduced virulence. Fluconazole did not further decrease the level of infection. In the isolates with a decrease in virulence, two exhibited overexpression of CDR, which encodes an ABC drug efflux pump. In contrast, serial isolates from the remaining two patients with the development of resistance did not demonstrate a change in virulence and fluconazole remained effective in prolonging survival, although significantly higher doses of fluconazole were required for efficacy. Resistant isolates from both of these patients exhibited overexpression of MDR. This study demonstrates that decreased virulence of serial C. albicans isolates is associated with increasing fluconazole MICs in some cases but not in others and shows that these low-virulence strains may not consistently cause infection.     

Antimicrobial susceptibility of Capnocytophaga

Capnocytophaga (Bacteroides ochraceus, Center for Disease Control biogroup DF-1) is associated with sepsis in granulocytopenic patients and is isolated in large numbers from the affected periodontal pockets in patients with juvenile periodontosis. The minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) of 17 antimicrobial agents for 13 strains of Capnocytophaga organisms were determined. In addition, the ratio of the MBC to the MIC for each antimicrobial agent was determined for each strain. At concentrations of 1 microgram/ml or less, penicillin, ampicillin, carbenicillin, erythromycin, and clindamycin killed 90% of the strains. At concentrations of 3.12 microgram/ml or less, tetracycline, metronidazole, cefoxitin, and chloramphenicol killed 90% of the strains. None of the aminoglycosides tested demonstrated antibacterial activity at 50 microgram/ml. Penicillin, ampicillin, carbenicillin, and cefoxitin exhibited MBC/MIC ratios of 4 or less with all strains. Erythromycin, tetracycline, and metronidazole exhibited MBC/MIC ratios of 4 or less for 12 of 13 strains. The MICs of cephalothin and cefazolin for 90% of the strains were 25 and 50 microgram/ml, respectively. The MBC/MIC ratios for these drugs were 4 or less for 12 of 13 and 7 of 13 strains, respectively. The MIC of cefamandole for 90% of the strains was 3.12 microgram/ml; however, only nine strains had an MBC/MIC ratio of 4 or less.     

Development of a rapid assay for detecting gyrA mutations in Escherichia coli and determination of incidence of gyrA mutations in clinical strains isolated from patients with complicated urinary tract infections

The MICs of ofloxacin for 743 strains of Escherichia coli isolated from 1988 to 1994 were determined by testing. The strains were from patients with urinary tract infections complicated by functional or anatomical disorders of the urinary tract. Those determined to be ofloxacin resistant (MIC, > or =12.5 microg/ml) comprised 3 of 395 strains (1.3%) from the 1988 to 1990 group, 2 of 166 strains (1.2%) from the 1991 to 1992 group, and 7 of 182 strains (3.8%) from the 1993 to 1994 group. The incidence of resistant strains increased significantly during this period. The percentage of isolates with moderately decreased susceptibilities to ofloxacin (MIC, 0.39 to 3.13 microg/ml) also rose during the same period. To determine the incidence of gyrA mutations in urinary-tract-derived strains of E. coli, we developed a simple and rapid assay based on PCR amplification of the region of the gyrA gene containing the mutation sites followed by digestion of the PCR product with a restriction enzyme. Using this assay, we examined all 182 strains isolated in 1993 and 1994 for the presence of mutations at Ser-83 and Asp-87 in the gyrA gene. Of these strains, 33 (18.1%) had mutations in the gyrA gene. The incidences of mutations at Ser-83, at Asp-87, and at both codons were 10.4 (19 strains), 4.4 (8 strains), and 3.3% (6 strains), respectively. To determine the correlation of the mutations in the gyrA gene with susceptibilities to quinolones (nalidixic acid, ofloxacin, norfloxacin, and ciprofloxacin), we further examined 116 strains for which the MICs of ofloxacin were > or =0.2 microg/ml that were chosen from the isolates in the 1988 to 1992 group. The MICs of nalidixic acid for the strains without mutations at either Ser-83 or Asp-87 were < or =25 microg/ml, whereas those for the strains with single mutations or double mutations were from 50 to >800 microg/ml. For the fluoroquinolones, significant differences in the distributions of the MICs were observed among the strains without mutations, with single mutations, and with double mutations. The accumulation of mutations in the gyrA gene was associated with an increase in fluoroquinolone resistance. Ofloxacin MICs for the majority of the strains with single and double mutations were 0.39 to 3.13 and 6.25 to 100 microg/ml, respectively. This study demonstrates a chronological increase in the percentage of not only highly fluoroquinolone-resistant strains, corresponding to those with double mutations in the gyrA gene, but also strains with moderately decreased susceptibilities to fluoroquinolones, corresponding to those with single mutations. This increase in the incidence of strains with a single mutation in the gyrA gene portends a further increase in the incidence of strains with clinically significant resistance to fluoroquinolones.     

Susceptibilities of bacteria isolated from patients with lower respiratory infectious diseases to antibiotics (1996)

The bacteria isolated from the patients with lower respiratory tract infections were collected by institutions located throughout Japan, since 1981. Ikemoto et al. have been investigating susceptibilities of these isolates to various antibacterial agents and antibiotics, and characteristics of the patients and isolates from them each year. Results obtained from these investigations are discussed. In 16 institutions around the entire Japan, 557 strains of presumably etiological bacteria were isolated mainly from the sputa of 449 patients with lower respiratory tract infections during the period from October 1996 to September 1997. MICs of various antibacterial agents and antibiotics were determined against 98 strains of Staphylococcus aureus, 93 strains of Streptococcus pneumoniae, 84 strains of Haemophilus influenzae, 84 strains of Pseudomonas aeruginosa (non-mucoid strains), 17 strains of Pseudomonas aeruginosa (mucoid strains), 31 strains of Moraxella subgenus Branhamella catarrhalis, 21 strains of Klebsiella pneumoniae etc., and the drug susceptibilities of these strains were assessed except for those strains that died during transportation. 1) S. aureus S. aureus strains for which MICs of oxacillin (MPIPC) were higher than 4 micrograms/ml (methicillin-resistant S. aureus) accounted for 67.3%. The frequency of the drug resistant bacteria increased comparing to the previous year's 52.7%. Arbekacin (ABK) and vancomycin (VCM) showed the highest activities against both S. aureus and MRSA with MIC80s of 1 microgram/ml. 2) S. pneumoniae Imipenem (IPM) and panipenem (PAPM) of carbapenems showed the most potent activities with MIC80s of 0.063 microgram/ml. Faropenem (FRPM) showed the next potent activity with MIC80 of 0.125 microgram/ml. The other drugs except erythromycin (EM), clindamycin (CLDM) and tetracycline (TC) were active against S. pneumoniae tested with MIC80s of 8 micrograms/ml or below. 3) H. influenzae The activities of all drugs were potent against H. influenzae tested with MIC80s of 4 micrograms/ml or below. Cefotiam (CTM), cefmenoxime (CMX), cefditoren (CDTR) and ofloxacin (OFLX) showed the most potent activities with MIC80s of 0.063 microgram/ml. 4) P. aeruginosa (mucoid strains) Tobramycin (TOB) showed the most potent activity against P. aeruginosa (mucoid strains) with MIC80 of 1 microgram/ml. Ceftazidime (CAZ), cefsulodin (CFS), IPM, gentamicin (GM), ABK and ciprofloxacin (CPFX) showed the next potent activities, with MIC80s of 2 micrograms/ml. The MIC80s of the other drugs ranged from 4 micrograms/ml to 16 micrograms/ml. 5) P. aeruginosa (non-mucoid strains) TOB and CPFX showed the most potent activities against P. aeruginosa (non-mucoid strains) with MIC80s of 1 microgram/ml. The MIC80s of piperacillin (PIPC) and cefoperazone (CPZ) were 16 micrograms/ml in 1995, and they were 64 micrograms/ml in 1996. 6) K. pneumoniae All drugs except ampicillin (ABPC) were active against K. pneumoniae. CMX, cefpirome (CPR), cefozopran (CZOP) and carumonam (CRMN) showed the most potent activities against K. pneumoniae with MIC80s of 0.125 microgram/ml. The MIC80s of the other drugs ranged from 0.25 microgram/ml to 2 micrograms/ml. 7) M.(B) catarrhalis Against M.(B.) catarrhalis, all drugs showed good activities with MICs of 4 micrograms/ml or below. IPM and minocycline (MINO) showed the most potent activities with MICs of 0.063 microgram/ml. Also, we investigated year to year changes in the characteristics of patients, their respiratory infectious diseases, and the etiology. Patients' backgrounds were examined for 557 isolates from 449 cases. The examination of age distribution indicated that the proportion of patients with ages over 60 years was 71.0% of all the patients showing a slight increase over that in 1994. Proportions of diagnosed diseases were as follows: Bacterial pneumonia and chronic bronchitis were the most frequent with 35.9% and 30.3% respectively. They were followed by bronchiectasis with a proportion of 10.     

Are clinical laboratories in California accurately reporting vancomycin-resistant enterococci?

In order to determine whether hospital-based clinical laboratories conducting active surveillance for vancomycin-resistant enterococci in three San Francisco Bay area counties (San Francisco, Alameda, and Contra Costa counties) were accurately reporting vancomycin resistance, five vancomycin-resistant enterococcal strains and one vancomycin-susceptible beta-lactamase-producing enterococcus were sent to 31 of 32 (97%) laboratories conducting surveillance. Each strain was tested by the laboratory's routine antimicrobial susceptibility testing method. An Enterococcus faecium strain with high-level resistance to vancomycin (MIC, 512 microg/ml) was correctly reported as resistant by 100% of laboratories; an E. faecium strain with moderate-level resistance (MIC, 64 microg/ml) was correctly reported as resistant by 91% of laboratories; two Enterococcus faecalis strains with low-level resistance (MICs, 32 microg/ml) were correctly reported as resistant by 97 and 56% of laboratories, respectively. An Enterococcus gallinarum strain with intrinsic low-level resistance (MIC, 8 microg/ml) was correctly reported as intermediate by 50% of laboratories. A beta-lactamase-producing E. faecalis isolate was correctly identified as susceptible to vancomycin by 100% of laboratories and as resistant to penicillin and ampicillin by 68 and 44% of laboratories, respectively; all 23 (74%) laboratories that tested for beta-lactamase recognized that it was a beta-lactamase producer. This survey indicated that for clinically significant enterococcal isolates, laboratories in the San Francisco Bay area have problems in detecting low- to moderate-level but not high-level vancomycin resistance. Increasing accuracy of detection and prompt reporting of these isolates and investigation of cases are the next steps in the battle for control of the spread of vancomycin resistance.