Susceptibility patterns of clinical and fish isolates of Laribacter hongkongensis: comparison of the Etest, disc diffusion and broth microdilution methods.
OBJECTIVE
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.


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 beta-lactams, MICs obtained with Etest were in good correlation with broth microdilution for all drugs except ampicillin/sulbactam, with >90% agreement within 2 log(2) 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 beta-lactams.
Lau
Susanna K P
SK
State Key Laboratory of Emerging Infectious Diseases, The University of Hong Kong, Hong Kong.
Wong
Gilman K M
GK
Poon
Rosana W S
RW
Lee
Leo C K
LC
Leung
Kit-Wah
KW
Tse
Cindy W S
CW
Ho
Pak-Leung
PL
Que
Tak-Lun
TL
Woo
Patrick C Y
PC
Yuen
Kwok-Yung
KY
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001431:Bacteriological Techniques / Q000379:methods*; D005393:Fish Diseases / Q000382:microbiology*; D005399:Fishes; D005759:Gastroenteritis / Q000382:microbiology*; D016908:Gram-Positive Bacterial Infections / Q000382:microbiology* / Q000662:veterinary*; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D009346:Neisseriaceae / Q000302:isolation & purification*
D000900:Anti-Bacterial Agents