Comparative in vitro activity of faropenem and 11 other antimicrobial agents against 405 aerobic and anaerobic pathogens isolated from skin and soft tissue infections from animal and human bites

Ellie J. C. Goldstein*, Diane M. Citron, C. Vreni Merriam, Yumi A. Warren, Kerin L. Tyrrell and Helen T. Fernandez

R. M. Alden Research Laboratory, Santa Monica-UCLA Medical Center, Santa Monica, CA 90404 and the UCLA School of Medicine, Los Angeles, CA 90073, USA

Received 1 May 2002; returned 28 May 2002; revised 6 June 2002; accepted 7 June 2002


    Abstract
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Faropenem, a new oral ß-lactam agent with a penem structure, was very active against 405 aerobic and anaerobic bite isolates. It inhibited 232 of 236 (98%) aerobic isolates, including all Pasteurella spp. and Eikenella corrodens at <=0.25 mg/L, and 164/169 (97%) anaerobic isolates, at <=1 mg/L. The 10 isolates that required >=2 mg/L for inhibition were one strain each of Acinetobacter lwoffi, Corynebacterium minutissimum, Bacteroides ovatus, Lactobacillus delbrueckii and Peptostreptococcus tetradius, plus Corynebacteriumaquaticum (two strains) and Veillonella sp. (three strains).

Keywords: faropenem, bite wounds, Pasteurella, anaerobes, cellulitis


    Introduction
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Of the 4.5 million American and 200 000 British persons bitten by animals or humans each year, many will require either therapeutic or prophylactic antimicrobial therapy; most will be treated as outpatients with oral antimicrobial therapy directed against a complex polymicrobial flora.1 Since many laboratories do not isolate or identify these potential pathogens, nor, if isolated, perform susceptibility testing on these fastidious organisms, the clinician is usually required to rely on the published literature for both empirical and specific antimicrobial selection.

Faropenem is a new oral penem antibiotic that is a unique structural hybrid of the penicillin and cephalosporin nuclei and distinct from all current ß-lactam classes. Faropenem is characterized by potent penicillin-binding protein activity and ß-lactamase stability. It has exhibited activity against Gram-positive, Gram-negative and some anaerobic bacteria.24 It is bactericidal, has a slight inoculum effect, is stable against many ß-lactamases including ‘group 2be’, and also has a significant post-antibiotic effect.2,3 Faropenem is reported to enhance superoxide anion production by human neutrophils in vitro,5 and may, therefore, have an added benefit of enhancing neutrophil function.

Previous in vitro studies of faropenem have focused primarily on typical respiratory pathogens and staphylococci.3,6,7 They have not evaluated the activity of faropenem against the specific range of bacteria commonly found in human and animal bite wound infections, which are unique in that the pathogen source is the oral flora of the biting animal, such as Pasteurella spp., Eikenella corrodens, Prevotella heparinolytica1 and some skin pathogens. Therefore, we determined the activity of faropenem against 407 aerobic and anaerobic strains recently isolated from such infections in humans.


    Materials and methods
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
The specific sources were: dog bites, 99; cat bites, 108; human bites, 191; and other animal bites, seven. All isolates were identified by standard criteria;8 the numbers and species tested are given in Table 1. Control strains included Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922, Bacteroides fragilis ATCC 25285 and Bacteroides thetaiotaomicron ATCC 29741.


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Table 1.  In vitro activity of faropenem and 11 other antimicrobials against aerobic and anaerobic pathogens isolated from human and animal bite wound infections in humans
 
Standard laboratory powders were supplied as follows: faropenem, ciprofloxacin and moxifloxacin, Bayer Corp. (West Haven, CT, USA); imipenem and ertapenem, Merck & Co. (West Point, PA, USA); meropenem, AstraZeneca Pharmaceuticals (Wilmington, DE, USA); co-amoxiclav, GlaxoSmithKline Pharmaceuticals (Philadelphia, PA, USA); ampicillin–sulbactam, Pfizer Inc. (New York, NY, USA); levofloxacin, Ortho-McNeil Pharmaceuticals (Raritan, NJ, USA); erythromycin, Eli Lilly & Co. (Indianapolis, IN, USA); and doxycycline and penicillin G, Sigma Chemical Co. (St Louis, MO, USA). Antimicrobial agents were reconstituted according to the manufacturers’ instructions. Serial two-fold dilutions were added to the media on the day of testing.

Frozen cultures were transferred twice on Trypticase soy agar (TSA) blood or chocolate agars (Hardy Diagnostics, Santa Maria, CA, USA) for the aerobes, and Brucella agar supplemented with haemin, vitamin K1 and 5% sheep blood (Anaerobe Systems, Morgan Hill, CA, USA) for the anaerobes, to ensure purity and good growth. Susceptibility testing was performed according to NCCLS standards.8 Supplemented brucella agar was the basal medium used for anaerobic species and for E. corrodens and Bergeyella zoohelcum. Mueller–Hinton agar was used for staphylococci, and Mueller–Hinton agar supplemented with 5% sheep blood was used for the remainder of the organisms.

The agar plates were inoculated with a Steers replicator (Craft Machine Inc., Chester, PA, USA). The inoculum used was 104 cfu/spot for aerobic bacteria, and 105 cfu/spot for E. corrodens and anaerobic bacteria. Control plates without antimicrobial agents were inoculated before and after each set of drug-containing plates. Plates with aerobic isolates were incubated at 35°C in an aerobic environment for 18–20 h and then examined; E. corrodens, B. zoohelcum and streptococci were incubated in 5% CO2 for 42–44 h. Plates with anaerobes were incubated in an anaerobic chamber (Anaerobe Systems) at 35°C for 44–48 h. The MIC was defined as the lowest concentration of an agent that yielded no growth, or a marked change in growth as compared with the control plate.


    Results
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
The full results of the study are presented in Table 1. Faropenem inhibited 395/405 (98%) of the aerobic and anaerobic isolates at <=1 mg/L. The 10 isolates that required >=2 mg/L for inhibition were Acinetobacter lwoffi (one strain, 4 mg/L), Corynebacterium aquaticum’ (two strains, 8 mg/L), Corynebacterium minutissimum (one strain, 4 mg/L), Bacteroides ovatus (one strain, 2 mg/L), Lactobacillus delbrueckii (one strain, 4 mg/L), Peptostreptococcus tetradius (one strain, 4 mg/L) and Veillonella spp. (three strains, 4–8 mg/L). Overall, the other antimicrobial agents gave results in accordance with our previous studies, with erythromycin having the poorest activity.8,9


    Discussion
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 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Our 10 isolates of Moraxella species did not include any Moraxella catarrhalis strains and these bite isolates were more susceptible to faropenem than reported by others,3,4,6,7 with all our isolates inhibited by <=0.125 mg/L. Critchley et al.3 studied 1193 isolates of M. catarrhalis and found all were inhibited by <=2 mg/L of faropenem with an MIC90 of 0.5 mg/L. Hikida et al.6 found all 53 strains of M. catarrhalis to be inhibited by <=0.78 mg/L of faropenem, while Miyazaki et al.7 and Woodcock et al.4 found MIC90s of 0.5 mg/L.

Von Eiff et al.10 found faropenem to be ‘active against a considerable number of methicillin-resistant strains of Staphylococcus aureus (MRSA) and coagulase-negative staphylococci’. They reported that 18 of 31 MRSA strains were inhibited by <=2 mg/L of faropenem but had an MIC90 of >128 mg/L. All Staphylococcus epidermidis isolates, both methicillin-susceptible and -resistant, were inhibited by 0.25 mg/L of faropenem. All our S. aureus isolates, none of which was methicillin resistant, were inhibited by <=0.5 mg/L of faropenem. All our S. epidermidis isolates and other coagulase-negative Staphylococcus species isolates, none of which was methicillin resistant, were inhibited by <=1 mg/L. However, Hikida et al.6 and Miyazaki et al.7 found faropenem to have an MIC90 of 0.2 mg/L against methicillin-susceptible S. aureus but to be inactive against MRSA with MIC50s of >100 and >128 mg/L, respectively. Their reports suggest a bimodal distribution of activity against S. epidermidis with Hikida et al.6 reporting an MIC50 of 0.1 mg/L and an MIC90 >100 mg/L, and Miyazaki et al.7 reporting an MIC50 of 2 mg/L and an MIC90 of >128 mg/L for methicillin-resistant strains. In contrast, Woodcock et al.4 found all 20 MRSA isolates tested to be inhibited by <=2 mg/L of faropenem and an MIC90 of 0.25 mg/L for methicillin-susceptible S. aureus strains. Woodcock et al.4 also noted a bimodal distribution for 20 S. epidermidis isolates with an MIC90 of 0.5 mg/L but a range of 0.06–>128 mg/L.

Faropenem has been studied against a limited number of anaerobic pathogens.2,4 Against B. fragilis isolates, Woodcock et al.4 reported an MIC90 of 4 mg/L (range 0.125–32 mg/L). However, Boswell et al.,2 who studied time–kill kinetics, noted faropenem to be bactericidal against B. fragilis but at a much less rapid rate than against the other isolates studied. Our three B. fragilis isolates were inhibited by 0.03, 0.06 and 1 mg/L of faropenem. Against peptostreptococci, our results are in accordance with the data of Woodcock et al.,4 who tested 19 strains of peptostreptococci and found an MIC90 of 0.5 mg/L, with all isolates inhibited by <=1 mg/L of faropenem. Of our 16 peptostreptococcus isolates, all were inhibited by <1 mg/L of faropenem with the exception of one strain of P. tetradius that required 4 mg/L for inhibition.

Faropenem had similar MIC ranges and MIC90s to co-amoxiclav, which was active against most aerobic and anaerobic isolates. The carbapenems tested (imipenem, meropenem and ertapenem) had excellent activity against almost all isolates, except for the enterococci. The fluoroquinolones tested (ciprofloxacin, moxifloxacin and levofloxacin) had good activity against most aerobes but were less active than faropenem against most anaerobes. Erythromycin was the least active agent tested.

Faropenem exhibited good activity against the full spectrum of human and animal bite pathogens and merits clinical evaluation in skin and soft tissue infections due to bite wounds. The activity of faropenem, coupled with its ß-lactamase stability and the ability to be taken orally, makes it suitable for treating the outpatient bite wound population.


    Acknowledgements
 
We wish to thank Judee H. Knight and Alice E. Goldstein for assistance. This study was supported, in part, by a grant from Bayer Corporation.


    Footnotes
 
* Correspondence address. 2021 Santa Monica Blvd, Suite 740 East, Santa Monica, CA 90404, USA. Tel: +1-310-315-1511; Fax: +1-310-3153662; E-mail: EJCGMD{at}aol.com Back


    References
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
1 . Talan, D. A., Citron, D. A., Abrahamian, F. A., Moran, G. J., Goldstein, E. J. C. & the Emergency Medicine Animal Bite Infection Study Group. (1999). The bacteriology and management of dog and cat bite wound infections presenting to Emergency Departments. New England Journal of Medicine 340, 85–92.[Abstract/Free Full Text]

2 . Boswell, F. J., Andrews, J. M. & Wise, R. (1999). Pharmacodynamic properties of faropenem demonstrated by studies of time–kill kinetics and postantibiotic effect. Journal of Antimicrobial Chemotherapy 39, 415–6.[Abstract]

3 . Critchley, I. A., Karlowsky, J. A., Draghi, D. C., Jones, M. E., Thornsberry, C., Murfitt, K. et al. (2002). Activities of faropenem, an oral ß-lactam, against recent U. S. isolates of Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. Antimicrobial Agents and Chemotherapy 46, 550–5.[Abstract/Free Full Text]

4 . Woodcock, J. M., Andrews, J. M., Brenwald, N. P., Ashby, J. P. & Wise, R. (1997). The in-vitro activity of faropenem, a novel oral penem. Journal of Antimicrobial Chemotherapy 39, 35–43.[Abstract]

5 . Sato, K., Sato, N., Shimizu, H., Tsutiya, T., Takahashi, H., Kakizaki, S. et al. (1999). Faropenem enhances superoxide anion production by human neutrophils, in vitro. Journal of Antimicrobial Chemotherapy 44, 337–41.[Abstract/Free Full Text]

6 . Hikida, M., Itahashi, K., Igarashi, A., Shiba, T. & Kitamura, M. (1999). In vitro antibacterial activity of LJC 11,036, an active metabolite of L-084, a new oral carbapenem antibiotic with potent antipneumococcal activity. Antimicrobial Agents and Chemotherapy 43, 2010–6.[Abstract/Free Full Text]

7 . Miyazaki, S., Hosoyama, T., Furuya, N., Ishii, Y., Matsumoto, T., Ohno, A. et al. (2001). In vitro and in vivo antibacterial activities of L-084, a novel oral carbapenem, against causative organisms of respiratory tract infections. Antimicrobial Agents and Chemotherapy 45, 203–7.[Abstract/Free Full Text]

8 . Goldstein, E. J. C., Citron, D. M., Merriam, C. V., Warren, Y. A., Tyrell, K. & Fernandez, H. (2001). Comparative in vitro activity of ertapenem and 11 other antimicrobial agents against aerobic and anaerobic pathogens isolated from skin and soft tissue animal and human bite wound infections. Journal of Antimicrobial Chemotherapy 48, 641–51.[Abstract/Free Full Text]

9 . Goldstein, E. J. C., Citron, D. M., Hudspeth, M., Gerardo, S. H. & Merriam, C. V. (1998). Trovafloxacin compared with levofloxacin, ofloxacin, ciprofloxacin, azithromycin and clarithromycin against unusual aerobic and anaerobic human and animal bite-wound pathogens. Journal of Antimicrobial Chemotherapy 41, 391–6.[Abstract]

10 . von Eiff, C., Scheepers, S. & Peters, G. (2001). Comparative in-vitro activity of faropenem against staphylococci. In Proceedings of the Forty-first Interscience Conference on Antimicrobial Agents and Chemotherapy, Chicago, IL, 2001. Abstract 798, p. 184. American Society for Microbiology, Washington, DC, USA.