JAC Advance Access originally published online on February 6, 2009
Journal of Antimicrobial Chemotherapy 2009 63(4):704-708; doi:10.1093/jac/dkp010
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Original research |
Susceptibility patterns of clinical and fish isolates of Laribacter hongkongensis: comparison of the Etest, disc diffusion and broth microdilution methods
1 State Key Laboratory of Emerging Infectious Diseases, The University of Hong Kong, Hong Kong 2 Research Centre of Infection and Immunology, The University of Hong Kong, Hong Kong 3 Department of Microbiology, The University of Hong Kong, Hong Kong 4 Department of Pathology, Kwong Wah Hospital, Hong Kong 5 Department of Pathology, Tuen Mun Hospital, Hong Kong
Received 27 October 2008; returned 21 November 2008; revised 23 December 2008; accepted 6 January 2009
* Corresponding author. Department of Microbiology, The University of Hong Kong, University Pathology Building, Queen Mary Hospital, Hong Kong. Tel: +852-28554892; Fax: +852-28551241; E-mail: pcywoo{at}hkucc.hku.hk
Objectives: To determine the antibiotic susceptibility patterns of 60 strains of Laribacter hongkongensis isolated from humans and fish to eight antibiotics and compare the results obtained from broth microdilution, Etest and disc diffusion susceptibility testing.
Patients and methods: The susceptibilities of 60 isolates of L. hongkongensis from humans with gastroenteritis and fish to eight antibiotics were tested by three methods [broth microdilution (reference method), Etest and disc diffusion] and their results were compared.
Results: All isolates were susceptible to imipenem and ciprofloxacin by all three methods, except for one strain which was resistant to ciprofloxacin by broth microdilution. All were susceptible to ampicillin/sulbactam by Etest and disc diffusion, but eight were resistant by broth microdilution. By broth microdilution, 90%, 100%, 46.7%, 100% and 8.3% of isolates were resistant to ampicillin, ceftriaxone, cefuroxime, erythromycin and tetracycline, respectively. Although broth microdilution generally yielded higher MICs of β-lactams, MICs obtained with Etest were in good correlation with broth microdilution for all drugs except ampicillin/sulbactam, with >90% agreement within 2 log2 dilutions for imipenem, ciprofloxacin, erythromycin and tetracycline. Comparison of susceptibilities between broth microdilution and the other two methods showed the highest (>95%) percentage agreement for imipenem, ciprofloxacin and tetracycline. The highest discrepancies were observed with erythromycin (58.3% agreement), with an apparent increase in susceptibility by disc diffusion. A higher proportion of human isolates than fish isolates were tetracycline-resistant by all three tests (P=0.022).
Conclusions: Etest and disc diffusion appear to be reliable for evaluation of susceptibilities of L. hongkongensis to imipenem, ciprofloxacin and tetracycline. However, these methods may underestimate resistance to other β-lactams.
Keywords: antibiotic susceptibility , infectious diarrhoea , community-acquired gastroenteritis
These authors contributed equally to this work.