Antibiotic resistance among Listeria, including Listeria monocytogenes, inretail food

Aims: In the past eight to 10 years, reports of antibiotic resistance in fo od-borne isolates in many countries have increased, and this work examined the susceptibility of 1001 food isolates of Listeria species. Methods and Results: Susceptibility/resistance to eight antibiotics was det ermined using the Bauer-Kirby disc diffusion assay, and 10.9% of the isolat es examined displayed resistance to one or more antibiotics. Resistance to one or more antibiotics was exhibited in 0.6% of Listeria monocytogenes iso lates compared with 19.5% of Listeria innocua isolates. Resistance was not observed in Listeria seeligeri or Listeria welshimeri. Resistance to tetrac ycline (6.7%) and penicillin (3.7%) was the most frequently observed, and w hile resistance to one antibiotic was most common (9.1%), isolates resistan t to two or more antibiotics (1.8%) were also observed. Conclusions: While resistance to the antibiotics most commonly used to trea t human listeriosis was not observed in L. monocytogenes, the presence of s uch resistance in other Listeria species raises the possibility of future a cquisition of resistance by L. monocytogenes. Significance and Impact of the Study: The higher level of resistance in L. innocua compared with L. monocytogenes suggests that a species-related abil ity to acquire resistance to antibiotics exists.