In vitro activity of gemifloxacin (SB-265805) compared with 14 other antimicrobials against intestinal pathogens

R. Fernández-Roblas, F. Cabria, J. Esteban, J. C. López, I. Gadea and F. Soriano*

Department of Medical Microbiology, Fundación Jiménez Díaz, Avenida Reyes Católicos 2, 28040 Madrid, Spain


    Abstract
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
We studied the in vitro activity of gemifloxacin (SB-265805) and 14 comparator antimicrobials against 288 recent isolates of enteropathogenic bacteria (106 Salmonella spp., 32 Hafnia alvei, 22 Yersinia enterocolitica, 21 Shigella spp., 16 Aeromonas spp. and 91 Campylobacter jejuni). Gemifloxacin, the other fluoroquinolones and cefotaxime were very active against all microorganisms tested except for C. jejuni. Seventy-seven per cent of isolates of C. jejuni were inhibited by erythromycin <=0.5 mg/L. Only one strain of C. jejuni was highly resistant to this antimicrobial agent. Of the compounds tested, gentamicin was the most active in vitro. The in vitro activity of the other antibiotics tested was variable. A quinolone could be a good choice for treating gastrointestinal infections when antimicrobial therapy is indicated. For C. jejuni, another antibiotic such as erythromycin should be considered.


    Introduction
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Gemifloxacin (SB-265805) is a novel quinolone agent with a broad spectrum of antibacterial activity, including against both Gram-negative and Gram-positive microorganisms. Classical oral antimicrobial agents used against enteropathogenic bacterial isolates have recently demonstrated poor in vitro activity;14 this prompted us to test a range of antimicrobial agents against these organisms. Here, the in vitro activity of gemifloxacin and 14 other antimicrobials against recognized bacterial enteric pathogens and Hafnia alvei—a bacterium with possible enteric pathogenic capacity5—is compared.


    Materials and methods
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Bacterial strains

Two hundred and eighty-eight recent isolates of enteropathogenic bacterial isolates from patients with acute gastroenteritis were studied, including 106 Salmonella spp. (75 Salmonella enteritidis, 19 Salmonella typhimurium, five Salmonella virchow, two Salmonella hadar, two Salmonella tshiongwe, one Salmonella newport, one Salmonella ohio and one Salmonella georgia), 32 H. alvei, 22 Yersinia enterocolitica, 21 Shigella spp., (15 Shigella sonnei, five Shigella flexneri and one Shigella boydii), 16 Aeromonas spp. (12 Aeromonas hydrophila and four Aeromonas sobria) and 91 Campylobacter jejuni. The strains were stored in skimmed milk at –80°C until studied. All infections were community acquired in Spain. None of the isolates was known to have been obtained from cases of travellers' diarrhoea.

Antimicrobials

The antibiotics tested were gemifloxacin, trovafloxacin, grepafloxacin, ciprofloxacin, ofloxacin, norfloxacin, levofloxacin, nalidixic acid, amoxycillin, cefotaxime, gentamicin, doxycycline, colistin, co-trimoxazole and, for C. jejuni, erythromycin. Each was provided as a powder of known potency by SmithKline Beecham Pharmaceuticals, Harlow, UK.

Antimicrobial susceptibility tests

MICs were determined by an agar dilution method6 on Mueller–Hinton agar (Difco Laboratories, Detroit, MI, USA) supplemented with 5% sheep blood for C. jejuni isolates. The plates were incubated aerobically at 35°C for 24 h, except for C. jejuni, where a microaerophilic atmosphere was obtained by using Campy Pack (Becton Dickinson, Cockeysville, MD, USA). Incubation was for 48 h. All organisms were tested with an inoculum of c. 104 cfu/spot. Dilutions tested ranged from 0.015 to 128 mg/L. MICs were defined as the lowest antimicrobial concentration at which there was no visible growth. Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 29213 and Pseudomonas aeruginosa ATCC 27853 were used as controls. The antimicrobial susceptibility breakpoints3,6 used to define the percentage of susceptible isolates were as follows: erythromycin, 0.5 mg/L; grepafloxacin and ciprofloxacin, 1 mg/L; colistin, co-trimoxazole, ofloxacin and levofloxacin, 2 mg/L; norfloxacin, gentamicin and doxycycline, 4 mg/L; amoxycillin and cefotaxime, 8 mg/L; and nalidixic acid, 16 mg/L. For comparison purposes the chosen breakpoint for susceptibility of gemifloxacin and trovafloxacin was 1 mg/L.


    Results
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Table IGo shows the activity of gemifloxacin and the other antimicrobials tested against 288 enteropathogenic bacterial strains. Fluoroquinolones were very active against all microorganisms except for C. jejuni, where only 32% of strains were susceptible. Rates of non-susceptibility (resistant plus intermediate strains) to nalidixic acid were 27, 5 and 6% for Salmonella spp., Y. enterocolitica and Aeromonas spp., respectively. Only 1% of the 106 Salmonella spp. studied were non-susceptible to grepafloxacin (MIC 2 mg/L). Cefotaxime was active against 100% of isolates, except C. jejuni isolates, only 57% of which were susceptible to this antimicrobial. The activity of amoxycillin was variable: isolates of Y. enterocolitica, H. alvei and Aeromonas spp. were non-susceptible to this ß-lactam, and 43, 77 and 69% of isolates of Shigella spp., Salmonella spp. and C. jejuni, respectively, were susceptible to this antibiotic. Table IIGo shows MICs of the quinolones studied against six isolates of Salmonella spp., for which the MICs of ciprofloxacin were >=0.25 mg/L.


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Table I. In vitro activity of gemifloxacin and 13 other antimicrobialsa against enteropathogenic bacterial strains
 

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Table II. MICs (mg/L) of quinolones tested against six isolates of Salmonella spp. in which MICs of ciprofloxacin were >=0.25 mg/L
 
Gentamicin was the most active antimicrobial tested, with only 4% of isolates of Salmonella spp. being resistant to it. Colistin was active against Y. enterocolitica, Shigella spp. and Aeromonas spp. Only 32% of Salmonella isolates were susceptible to colistin and its activity was also poor against H. alvei and C. jejuni. Cotrimoxazole was very active against all species studied, except for Shigella spp., with only 4% of Salmonella spp. and C. jejuni being resistant to this antibiotic. Doxycycline was very active against Aeromonas spp.; its activity against the other organisms tested was variable, with 40% of C. jejuni, 43% of Shigella spp., 78% of Salmonella spp., 78% of H. alvei and 95% of Y. enterocolitica isolates being susceptible to it.

Seventy-seven per cent of isolates of C. jejuni were inhibited by erythromycin <=0.5 mg/L. Only one isolate was highly resistant to this antimicrobial (MIC 128 mg/L); the other isolates were all inhibited by erythromycin <=4 mg/L.

By weight, gemifloxacin was the most active compound tested, with 100% of isolates of each species, except for C. jejuni, being inhibited by a concentration of 0.25 mg/L.


    Discussion
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Antimicrobials may be useful for treating some cases of bacterial diarrhoea and for preventing this illness and the further spread of infection.7 Since 1988, an increase in the resistance of Salmonella spp. to classical antimicrobials such as ampicillin, chloramphenicol, tetracycline and co-trimoxazole has been described, especially among S. typhimurium and S. virchow.2,3,8 Our results confirm this, with rates of non-susceptibility of Salmonella spp. to amoxycillin, doxycycline and co-trimoxazole of 23, 22 and 4%, respectively. MICs of ciprofloxacin of >=0.25 mg/L against Salmonella spp. isolates are considered by some authors as being of therapeutic relevance.8 Six isolates of S. virchow, S. hadar, S. tshiongwe and S. newport with MICs of ciprofloxacin of >=0.25 mg/L were studied. Gemifloxacin was the most active quinolone against these isolates (Table IIGo). Many Shigella spp. are resistant to aminopenicillins, co-trimoxazole and doxycycline,3 as confirmed by our results, with high rates of resistance in these species to these three antimicrobials. H. alvei, in which virulence factors similar to those found in some phenotypes of E. coli have been described,5 is usually susceptible to quinolones, newer cephalosporins, carbapenems and piperacillin. Our data suggest that a quinolone, cefotaxime, gentamicin and co-trimoxazole and, to a lesser extent, doxycycline, could be useful in the treatment of infections caused by this microorganism. Our data confirmed the good activity of quinolones, doxycycline, co-trimoxazole, gentamicin and cefotaxime and the inefficacy of aminopenicillins against Aeromonas spp.9 Y. enterocolitica produces ß-lactamases that inactivate some ß-lactams and resistance to other antibiotics has also been described.4 The antibiotics we tested, with the exception of amoxycillin, were very active against this microorganism.

High rates of resistance among C. jejuni strains are being described to quinolones,1,3 but erythromycin and other macrolides are active against this microorganism. The quinolone resistance in C. jejuni found in our study is higher than that reported in 1996.3 In contrast, only one isolate (1.1%) of C. jejuni showed high resistance to erythromycin. The high rates of quinolone-resistant C. jejuni in Spain seem to be associated with the massive use of these antibiotics, especially in animals.10

In conclusion, quinolones can be good choices for treating gastrointestinal infection when indicated. For C. jejuni, different antibiotics, such as erythromycin, must be considered. Gemifloxacin is a new quinolone with good in vitro activity against important gastrointestinal pathogens and could be a good choice in these infections. The present results must be assessed in the context of in vivo trials before the clinical role of this new fluoroquinolone can be determined for these infections.


    Acknowledgments
 
We thank M. J. Giménez for critical review of the manuscript. This study was supported by a grant from SmithKline Beecham Pharmaceuticals. The results of this study were presented in part at the Thirty-Ninth Interscience Conference on Antimicrobial Agents and Chemotherapy, San Francisco, CA, 26–29 September 1999.


    Notes
 
* Corresponding author. Tel: +34-91-544-73-87; Fax: +34-91-549-47-64; E-mail: fsoriano{at}fjd.es Back


    References
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
1 . Aarestrup, F. M., Nielsen, E. M., Madsen, M. & Engberg, J. (1997). Antimicrobial susceptibility patterns of thermophilic Campylobacter spp. from humans, pigs, cattle, and broilers in Denmark. Antimicrobial Agents and Chemotherapy 41, 2244–50.[Abstract]

2 . Ramos, J. M., Alés, J. M., Cuenca-Estrella, M., FernándezRoblas, R. & Soriano, F. (1996). Changes in susceptibility of Salmonella enteritidis, Salmonella typhimurium, and Salmonella virchow, to six antimicrobial agents in a Spanish hospital, 1980–1994. European Journal of Clinical Microbiology and Infectious Diseases 15, 85–8.[ISI][Medline]

3 . Soriano, F., Fernández-Roblas, R., López, J. C., García-Corbeira, P. & Aguilar, L. (1994). Comparative in-vitro activity of rufloxacin with five other antimicrobial agents against bacterial enteric pathogens. Journal of Antimicrobial Chemotherapy 34, 157–60.[ISI][Medline]

4 . Stock, I. & Wiedemann, B. (1999). An in-vitro study of the antimicrobial susceptibilities of Yersinia enterocolitica and the definition of a database. Journal of Antimicrobial Chemotherapy 43, 37–45.[Abstract/Free Full Text]

5 . Ismaili, A., Bouske, B., de Azavedo, I. C., Ratnam, S., Karmali, M. A. & Sherman, P. M. (1996). Heterogeneity in phenotypic and genotypic characteristics among strains of Hafnia alvei. Journal of Clinical Microbiology 34, 2973–9.[Abstract]

6 . National Committee for Clinical Laboratory Standards. (1997). Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobically—Fourth Edition: Approved Standard M7-A4. NCCLS, Villanova, PA.

7 . Guerrant, R. L. (1995). Principles and syndromes of enteric infection. In Principles and Practice of Infectious Diseases, 4th edn (Mandell, G. L., Douglas, R. G., Bennett, J. E. & Dolin, R., Eds), pp. 945–62. Churchill Livingstone, New York, NY.

8 . Threlfall, E. J., Ward, L. R. & Rowe, B. (1999). Resistance to ciprofloxacin in non-typhoidal salmonellas from humans in England and Wales—the current situation. Clinical Microbiology and Infection 5, 130–4.[Medline]

9 . Burgos, A., Quindos, G., Martinez, R., Rojo, P. & Cisterna, R. (1990). In vitro susceptibility of Aeromonas caviae, Aeromonas hydrophila and Aeromonas sobria to fifteen antibacterial agents. European Journal of Clinical Microbiology and Infectious Diseases 9, 413–7.[ISI][Medline]

10 . Garau, J., Xercavins, M., Rodriguez-Carballeira, M., Gómez-Vera, J. R., Coll, I., Vidal, D. et al. (1999). Emergence and dissemination of quinolone-resistant Escherichia coli in the community. Antimicrobial Agents and Chemotherapy 43, 2736–41.[Abstract/Free Full Text]

Received 6 March 2000; returned 9 June 2000; revised 3 July 2000; accepted 29 August 2000