Determination of the Susceptibility In Vitro of 54 Isolates of Mycobacterium fortuitum against Three Fluoroquinolones Using Two Methods

Abstract

The In Vitro susceptibility to ofloxacin, norfloxacin and ciprofloxacin or 54 Mycobacterium fortuitum isolates originating from clinical samples (7) of patients attending the Hospital Universitario de Canarias and Hospital del Tórax, and from environmental (47) sources, were determined. For this, two methods were used: dilution in agar with Middlebrook 7H10 Agar as a base medium culture, and broth microdilution, with Mueller-Hinton Broth without supplement.

The different isolates under study revealed a uniform susceptibility by both methods against ciprofloxacin.

100% inhibition was obtained from a Minimum Inhibitory Concentration (MIC) of 0.25 μg/ml, and 2 μg/ml of ciprofloxacin, for broth microdilution and dilution in agar, respectively.

For ofloxacin and norfloxacin, all the isolates were inhibited at an MIC of 0.5 μ/ml, by the broth microdilution method, which contrasted sharply with an MIC of 32 μ/ml, in the case of dilution in agar.

In this study, we have observed the existence of differences in the In Vitro susceptibility of the isolates of M. fortuitum against the three fluoroquinolones assayed, mainly for ofloxacin and norfloxacin, by both methods. We, therefore, consider it necessary to establish a standardized, reproducible assay method, for the study of sensitivity to atypical mycobacteria.     

Comparative Evaluation of the In Vitro Antimycobacterial Activities of Six Aminoglycoside Antibiotics Using an Agar Dilution Method

Abstract

Given the increasing prevalence of mycobacterial resistance to aminoglycoside antibiotics, we examined the susceptibility of 76 clinical isolates of mycobacteria to arbekacin, amikacin, gentamicin, kanamycin, tobramycin and streptomycin using an agar dilution method. Only arbekacin and amikacin showed excellent therapeutic potential (minimum inhibitory concentrationis (MICs) ≤0.25-4 μg/ml) against 30 isolates of rapidly growing mycobacteria, including Mycobacterium fortuitum M. chelonae and a related organismNocardia asteroides. The MIC₉₀ of tobramycin against 23 isolates of M. avium complex was 8 μg/ml, while that of the other 5 aminoglycosides ranged from 64-256 μg/ml. Of the 23 M. tuberculosis isolates tested, 5 showed aminoglycoside resistance (MICs 128 to ≥1,024 μg/ml), while the others were variably susceptible (MICs ≤0.25-32 μg/ml) to all 6 aminoglycosides. The chemotherapeutic potential of arbekacin, amikacin and streptomycin as treatment of tuberculosis was apparent; however, proper patient management would be required to control against the emergence of the drug-resistant strains during prolonged treatment.     

Promising New Drugs in the Treatment of Tuberculosis and Mycobacteriosis

Summary

The aims of this work were to investigate the possible effect of several antimicrobial agents alone and in combinations against 190 clinical isolates of Mycobacterium tuberculosis and 30 isolates of Mycobacterium avium, 30 Mycobacterium fortuitum and 30 Mycobacterium chelonei. The susceptibility was determined in Müller-Hinton agar and Middlebrook 7H 10 agar. For interpretation of the results the minimum inhibitory concentration (MIC) was determined and for the combinations of antimicrobials we used the Fractional Inhibitory Concentration Index (FIC). The possible clinical efficacy was determined by the Inhibitory Quotient. The synergistic effect of several combinations of these compounds was demonstrated.     

Suppression of adjuvant arthritis in rats by intraperitoneal Mycobacterium butyricum

Abstract

The In Vitro activity of fluoroquinolones, including lomefloxacin, ofloxacin, ciprofloxacin, sparfloxacin, moxifloxacin and gatifloxacin, was evaluated against 55 clinical isolates of Mycobacterium tuberculosis by absolute concentration method on Lowenstein-Jensen (L-J) and Middlebrook's 7H11 media. Both ofloxacin susceptible and ofloxacin resistant strains of M. tuberculosis isolates were tested. The in vitro activities of these fluoroquinolones on the M. tuberculosis isolates were in the order: lomefloxacin相似文献   

Comparative In- Vitro Activity of Fourteen Antibiotics Against Clinical Isolates of Enterococci

Summary

The in-vitto antibacterial activities of fourteen antimicrobial agents, including ampicillin, amikacin, Augmentin, ceftazidime, cefotaxime, ceftriaxone, ciprofloxacin, erythromycin, gentamicin, penicillin G, piperacillin, rifampicin, streptomycin and vancomycin, were compared against 195 enterococcal strains isolated from clinical specimens received at the King Abdulaziz University Hospital in Saudi Arabia. The antibacterial susceptibility was determined by the minimal inhibitory concentration (MIC) using an agar dilution method. Ampicillin, Augmentin and vancomycin exhibited the greatest activity, inhibiting 90% of the tested strains (MIC90) at 2 μg/ml, followed by penicillin G and piperacillin with MIC90 of 4 μg/ml. Erythromycin, third generation cephalosporins, aminoglycosides and rifampicin, on the other hand, had poor activity against enterococci with MIC90s well above the obtainable serum concentrations. The clinical implications of resistance to aminoglycosides and the alternative antimicrobial therapy in serious entrococcal infections are discussed in the text.     

In Vitro Efficacy of Levofloxacin Alone or in Combination Tested Against Multi-Resistant Pseudomonas aeruginosa Strains

Abstract

Levofloxacin, the S(-) isomer of ofloxacin, demonstrates In Vitro activity against Pseudomonas aeruginosa. To further characterize this activity, levofloxacin was tested against three populations of recent clinical isolates categorized by their resistance patterns to several other anti-pseudomonal agents. Results demonstrate the minimum inhibitory concentrations (MICs) for levofloxacin were generally two- to fourfold higher than for ciprofloxacin. Higher fluoroquinolone MICs were associated with MIC increases in other drugs. Levofloxacin demonstrated cross resistance against ciprofloxacin-resis-tant strains. Combinations of levofloxacin and several co-drugs revealed that the majority of evaluable interactions demonstrated indifferent action. Levofloxacin exhibited enhanced activity (additive or degrees of synergy) principally with piperacillin, aztreonam, or ceftazidime. The synergy and additive rate (21 to 30%) compared favorably with the enhanced interactions observed with gen-tamicin combined with piperacillin or ceftazidime (27 to 30%). Levofloxacin activity against P. aeruginosa was most comparable to that of ciprofloxacin, which was applicable against > 90% of strains found to be resistant to other classes of antimicrobial agents.     

In Vitro Susceptibility of Trichosporon beigelii to Antifungal Agents

Abstract

The minimum inhibitory concentrations (MICs) and minimum fungicidal concentrations (MFCs) of amphotericin B, flucytosine, miconazole, fluconazole and itraconazole against 21 isolates of Trichosporon beigelii in RPMI-1640 medium were determined using National Committee for Clinical Laboratory Standards (NCCLS) methodology in microdilution method. Most isolates were sensitive to miconazole (MIC₉₀ 0.78 μ/ml), fluconazole (MIC₉₀ 6.25 μ/ml), and itraconazole (MIC₉₀ 0.19 μ/ml), with the former being the most active agent tested (MFC₉₀ 3.12 μ/ml). Although amphotericin B inhibited most strains (MIC range, 0.78-3.12 μ/ml), poor fungicidal activity was observed (MFC range, 1.56 -12.5 μ/ml) showing a pattern of relative resistance In Vitro. Flucytosine showed generally poor activity against most isolates tested. These In Vitro findings confirm the resistance of T.beigelii to amphotericin B and suggest that azoles may be an alternative to the former for the treatment of disseminated trichosporonosis. However, in vivo studies would better validate these In Vitro findings.     

In- Vitro Susceptibility of Clinical Isolates of Pseudomonas aeruginosa to β-Lactam and Aminoglycoside Antibiotics

Summary

The in-vitro susceptibilities of 198 isolates of Pseudomonas aeruginosa from clinical human specimens were determined by an agar dilution technique against (β-lactams and aminoglycosides. These isolates were susceptible to imipenem, aztreonam and ceftazidime with the minimum inhibitory concentration (MIC) for 90% of the strains tested being 8, 16 and 8 μg/ml, respectively. Aminoglycosides, except amikacin, had low activity (MIC90 > 128 μg/ml).     

Comparative In Vitro Activity of Telithromycin and β-Lactam Antimicrobials Against Bacterial Pathogens from Community-Acquired Respiratory Tract Infections: Data from the First Year of PROTEKT (1999-2000)

Abstract

The In Vitro activity of telithromycin, a new ketolide, was compared with β-lactam antimicrobials against pathogens commonly associated with community-acquired respiratory tract infections. These pathogens were collected during 1999-2000 as part of the ongoing PROTEKT surveillance study. Globally, penicillin non-susceptibility among Streptococcus pneumoniae (n=3362) was 36.3%, ranging from 21.5% (Australasia) to 68.0% (Far East). Telithromycin showed higher potency (MIC₉₀ 0.12 mg/L) than β-lactams against S. pneumoniae; 99.9% of all and 99.6% of multi-resistant isolates were susceptible to telithromycin. Among Streptococcus pyogenes isolates (n=1485), 100% were susceptible to β-lactams, and the telithromycin MIC₅₀ and MIC₉₀ were both 0.015 mg/L. Among Haemophilus influenzae (n=2948), 16.6% produced β-lactamase, which reduced the activity of ampicillin, cefaclor and cefprozil. 99.9% of H. influenzae were susceptible to telithromycin and the MIC range for M. catarrhalis was 0.004-0.5 mg/L. The first year results of PROTEKT confirmed high potency for telithromycin against common respiratory tract pathogens, including β-lactam-resistant strains.     

Antimicrobial Susceptibility Patterns in Pseudomonas aeruginosa:Data from a Multicenter Intensive Care Unit Surveillance Study (ISS) in the United States

Abstract

The objectives of this study were to analyze susceptibility rates and patterns in Pseudomonas aeruginosa isolates from patients in intensive care units (ICU). A total of 2209 isolates in 1995/1996 and 2672 in 2001/2002 were tested at United States sites participating in the ICU Surveillance Study. In both periods, of the agents tested, amikacin was the most active and ciprofloxacin, the least. Resistance to common antipseudomonal agents tested increased from 1995/1996 to 2001/2002; the rise was least for amikacin (2%) and greatest for ciprofloxacin (16%). The proportion of isolates susceptible to all six antipseudomonal agents tested since 1996 decreased from 60.4% to 48.9% in 2001/2002. Examination of MIC distributions for the two periods showed that for some drugs, e.g. imipenem and ceftazidime, the populations of susceptible and resistant isolates remained distinct, although the resistant population increased. For other drugs, e.g. amikacin and piperacillin-tazobactam, the MIC distribution shifted upward over time. The categorical agreement between agents of the same or like classes for isolates tested in 2001/2002 was highest for ciprofloxacin and levofloxacin (93.2%, with 1.2% major errors) and lowest for the aminoglycosides (81.3%, with 10.2% major errors). We can conclude that resistance to antipseudomonal agents among ICU isolates of P. aeruginosa, especially fluoroquinolones, is increasing. The resistance rate for some antipseudomonal agents may not accurately reflect shifts in the MIC distribution curve.     

In Vitro Testing of Aspergillus fumigatus Clinical Isolates for Susceptibility to Voriconazole,Amphotericin B and Itraconazole: Comparison of Sensititre versus NCCLS M38-A Using Two Different Inocula

Abstract

Voriconazole, amphotericin B and itraconazole were tested In Vitro against 18 strains of Aspergillus fumigatus isolated from cystic fibrosis patients. Susceptibility was tested with the broth microdilution method (M38-A protocol- NCCLS). Results of this reference method were compared with those of an experimental commercial microdilution broth method (Sensititre). Two different inocula, prepared from 2- and 7-day cultures, were used. Minimum inhibitory concentrations (MICs) of the reference method ranged from 0.25 to 2 μg/ml for voriconazole, 0.06 to 1 μg/ml for amphotericin B, 0.016 to >16 μg/ml for itraconazole. There were no significant differences in the MIC ranges or MIC₉₀ values obtained with the two testing methods or with the two types of inocula. These findings confirm the good In Vitro activity of voriconazole, itraconazole and amphotericin B against A. fumigatus. They also indicate that reliable susceptibility data can be generated more rapidly by commercial systems and use of 2-day cultures for inoculum preparation.     

In-Vitro Susceptibility of Clinical Isolates of Serratia Species to Antimicrobial Agents

Summary

The in-vitro activities of 12 antimicrobial agents against a total of 80 clinical isolates of Serratia marcescens and Serratia liquefaciens were determined by a broth microdilution method. Ampicillin and cefazolin were totally inactive against these organisms. The other β-lactam antibiotics such as piperacillin, cefotaxime, ceftazidime, and the aminoglycosides such as gentamicin, tobramycin and netilmicin showed poor or moderate activity against Serratia isolates. Aztreonam and amikacin inhibited most of the strains tested. Imipenem and ciprofloxacin were very active in inhibiting all strains. Within the genus, S. liquefaciens was more resistant to aztreonam, ceftazidime and amikacin than S. marcescens.     

The Minimum Inhibitory Concentration of Seventeen Antimicrobials for Salmonella Isolates from Septic Patients

Abstract

Herein we are reporting, for the first time in Kuwait, the minimum inhibitory concentrations (MICs) of Salmonella blood culture isolates vs. 17 clinically relevant antimicrobial agents. The screening of blood culture specimens was performed with the most advanced Bactec 9240 (Becton Dickinson). From over 20,000 blood cultures, 112 Salmonella isolates were obtained from 67 patients. Their MICs were determined using the automated Vitek microdilution technique (Biomerieux Vitek Inc.). During the whole 1991-1995 study period, the MICs for cefotaxime, ceftazidime, aztreonam, amikacin, gentamicin, ciprofloxacin and imipenem were below their respective susceptibility breakpoints. Resistance to chloramphenicol, ampicillin and cotrimoxazole varied from year to year, from 18% to 50%, except in 1991 when it was nil (1991 was the first year after the Gulf War, with very few newcomers from the Indian subcontinent). All ampicillin-susceptible S. typhi isolates had extremely low MIC values (≤0.25 μg/ml).     

In Vitro Activity of Ampicillin-Sulbactam Against Clinical Multiresistant Acinetobacter baumannii Isolates

Abstract

We evaluated the in vitroactivity of ampicillin-sul-bactam in comparison with that of broad-spectrum antimicrobial agents against Acinetobacter baumannii isolates. Two hundred and twelve clinical isolates collected between January 1993 and March 1995 from two tertiary hospitals located in São Paulo, Brazil were tested for susceptibility by the disk diffusion method against several broad-spectrum antimicrobial agents, including imipenem, ciprofloxacin, ceftazidime, aztreonam, amikacin, and polymyxin B. All strains were susceptible to polymyxin B. The second most active compound was the combination ampicillin-sulbactam (88% susceptibility). Only 79% of the isolates were susceptible to imipenem. Ciprofloxacin was active against 60 (28%) and amikacin against 34 (16%) isolates. Ceftazidime was the most active cephalosporin; however, only 9% of the isolates were susceptible to this compound. Both aztreonam and ampicillin alone showed very poor activity against this species (1% susceptibility). The prevalence of severe infections due to A. baumannii is increasing very rapidly in the tertiary hospitals of São Paulo and there are very few options for the treatment of these infections. Polymyxin B is invariably in vitro active against this species; however, this compound can cause severe side effects and is not commercially available for intravenous use in Brazil and in several other countries. Our results indicated that the combination ampicillin-sulbactam may be an alternative drug for the treatment of infections due to multiresistant A. baumannii; however, further studies are necessary to evaluate the clinical role of this compound for the treatment of severe infections.     

Inhibitors and Inactivators of Beta-Lactamase from Mycobacterium fortuitum

Summary

The inhibiting or inactivating effects of some beta-lactam antibiotics on beta-lactamase from Mycobacterium fortuitum were studied. Among all substrates tested, clavulanic acid and sulbactam were the strongest competitive inhibitors of the enzyme although the latter was slightly hydrolyzed. Imipenem and cefoxitin scarcely inhibited the beta-lactamase yet expressed good activity against the microorganism in vitro, suggesting that the effectiveness of these drugs on M. fortuitum might be due to high permeation through the cell wall. All the isoxazolylpenicillins tested and methicillin inactivated the enzyme of M. fortuitum by a first rapid phase of acylation followed by a steady-state process of enzyme reactivation (deacylation). Clavulanic acid and sulbactam showed Ki values for the enzyme inactivation closely corresponding to hematic concentrations achievable in vivo during antibiotic treatment.     

Tom Bergan, 1939-2001

Abstract

A strain of Trichomonas vaginalis, isolated from a patient complaining of vaginal discharge, was incubated and cultivated to compare the In Vitro effects of ornidazole, metronidazole and ciprofloxacin on T. vaginalis trophozoites in terms of minimal inhibition concentrations (MICs) and minimal lethal concentrations (MLCs). MIC levels at 24 hours for ornidazole, metronidazole and ciprofloxacin were 50 mg/mL, 50 mg/mL, and 750 mg/mL. Corresponding MLC levels were the same. In this In Vitro study, ornidazole was found to be the most effective drug among 3 drugs tested against T. vaginalis trophozoites in terms of MIC and MLC levels. It is interesting to note that ciprofloxacin, although not as effective as the others, also had some cytotoxic effect on T. vaginalis trophozoites.     

Bacteremia Due to Pseudomonas aeruginosa: Results from a 3-Year National Study in the Slovak Republic

Abstract

Risk factors, mortality and antimicrobial susceptibility of Pseudomonas aeruginosa bacteremias isolated from 148 patients from all University Hospitals in Slovakia were analyzed. Only 1.2% of 169 strains of P. aeruginosa were resistant to meropenem, 4.1% to piperacillin/tazobactam, 7.7% to ceftazidime as well as cefepime and 12% to amikacin. More than 30% of P. aeruginosa were resistant to ciprofloxacin.

Our analysis of risk factors for antimicrobial resistance to the particular antimicrobials, indicated no difference in risk factors and outcome in cases infected with P. aeruginosa bacteremias resistant to amikacin, piperacillin/tazobactam or ceftazidime in comparison to episodes caused by P. aeruginosa due to susceptible isolates. When comparing risk factors for P. aeruginosa bacteremia in children vs. adults, cancer vs. non-cancer patients, several differences in risk factors were observed.

Neither antimicrobial resistance to amikacin, ceftazidime or piperacillin/tazobactam, nor appropriateness of therapy according to two separate analyses were associated with better outcome.     

Antibiotic Resistance Among Gram-Negative Non-Fermentative Bacteria at a Teaching Hospital in Saudi Arabia

Abstract

The incidence and antimicrobial resistance of Gram-negative non-fermentative bacteria isolated over 1 year at King Abdulaziz University Hospital, Jeddah, Saudi Arabia were investigated. A total of 499 of these microorganisms were collected and account for 16% of all Gram-negative bacteria isolated. The most common species were Pseudomonas aeruginosa 291 (56%), Acinetobacter baumannii 170 (34%), and Stenotrophomonas maltophilia 35 (7%). 168 (34%) of these microorganisms were isolated from Intensive Care Unit (ICU), 147 (30%) from General Medicine, and 24 (25%) from Surgery wards. ICU was the main site of isolation of P. aeruginosa and S. maltophilia, while A. baumannii was more frequently isolated from medicine and surgery units. The vast majority of the isolates were resistant to many antibiotics tested. The antimicrobial resistance patterns of P. aeruginosa showed lowest resistance to imipenem (13%), amikacin (17%), and ciprofloxacin (18%). Imipenem was also the most active antimicrobial agent against A. baumannii (15%) resistance. S. maltophilia exhibited multi-drug resistance, and was susceptible only to sulfonamide (6%).     

Activity of Antimicrobial Drugs Evaluated by Agar Dilution and Radiometric Methods against Strains of Nocardia asteroides Isolated in Italy from Immunocompromised Patients

Summary

Benzylpenicillin, amoxicillin, amoxicillin plus clavulanic acid, cephalothin, cephaloridine, cefotaxime, imipenem, erythromycin, clarithromycin, azithromycin, amikacin, ciprofloxacin and trimethoprim-sulfamethoxazole were tested in vitro by the agar dilution method against eleven strains of Nocardia asteroides isolated both from AIDS and other immunocompromised patients. Imipenem, amikacin and trimethoprim-sulfamethoxazole were shown to be the most active drugs with minimum inhibitory concentrations (MIC) values nearly always lower than concentrations achievable in blood. Ciprofloxacin, cephaloridine and cefotaxime were moderately active, while the remaining drugs were totally ineffective.

When susceptibility was assessed by the radiometric method the MIC₉₀ values were uniformly lower than those in the agar method, possibly due to lower inactivation of the drugs during incubation. The two methods showed a good correlation only for imipenem, amikacin and ciprofloxacin. The results obtained by the radiometric method seem to indicate that, as for mycobacteria, this method may also give a more accurate evaluation of the antimicrobial susceptibility of Nocardiae.     

In Vitro Activity of Cefdinir against Respiratory Pathogens Isolated in Sicily with Reference to Beta-Lactamase Production

Abstract

The In Vitro activity of cefdinir (CI-983, FK-482), an orally absorbed aminothiazolyl cephalosporin, was evaluated against all 287 strains of Haemophilus influenzae, Haemophilus parainfluenzae, Moraxella catarrhalis, Streptococcus pneumoniae and Streptococcus pyogenes in comparison with cefaclor, cefuroxime, amoxicillin, amoxicillin-clavulanic acid, erythromycin and cotrimoxazole.

The bactericidal activity of cefdinir, cotrimoxazole, amoxicillin-clavulanic acid and erythromycin was determined against H. influenzae, M. catarrhalis and S. pneumoniae. With the exception of one beta-lactamase negative ampicillin-resistant strain of H. influenzae (resistant to all antibiotics tested), no resistance to cefdinir was observed (MIC≤1 mg/l). Cefdinir was active against H. influenzae, H. parainfluenzae and M. catarrhalis regardless of whether or not they produced beta-lactamase. In general, the inhibitory concentrations of cefdinir against H. influenzae, H. parainfluenzae and M. catarrhalis were similar to those of amoxicillin/clavulanic acid, one or two dilutions lower than those of cefuroxime and four dilu tions lower than those of cefaclor and cotrimoxazole. Against S. pneumoniae and S. pyogenes cefdinir had the same activity as cefuroxime and amoxicillin but was more effective than the other antibiotics tested.

Kinetic studies showed that cefdinir was rapidly bactericidal at concentrations 2 and 4 times the minimum inhibitory concentration (MIC): a reduction of 99.9% in CFU values was generally observed after 6-8 h.