Natural antibiotic susceptibility of Listeria species: L. grayi, L. innocua, L. ivanovii, L. monocytogenes, L. seeligeri and L. welshimeri strains.
OBJECTIVE
To investigate the natural susceptibility to 71 antimicrobial agents of 103 Listeria strains belonging to all known Listeria species (L. monocytogenes (N = 21), L. innocua (N = 21), L. seeligeri (N = 21), L. ivanovii (N = 19), L. welshimeri (N = 11), and L. grayi (N = 10)).


METHODS
MICs were determined using a microdilution procedure in H-Medium.


RESULTS
All listeriae were naturally sensitive or intermediate to tetracyclines, aminoglycosides, penicillins (except oxacillin), loracarbef, cefazoline, cefaclor, cefotiam, cefoperazone, carbapenems, macrolides, lincosamides, glycopeptides, dalfopristin/quinupristin, chloramphenicol and rifampicin (probably except L. grayi). Listeria spp. were naturally resistant or intermediate to most 'modern' cephalosporins (cefetamet, cefixime, ceftibuten, ceftazidime, cefdinir, cefpodoxime, cefotaxime, ceftriaxone, cefuroxime), aztreonam, pipemidic acid, dalfopristin quinupristin and sulfamethoxazole. Significant differences in natural susceptibility among the species were seen with the quinolones, trimethoprim, co-trimoxazole, rifampicin, fosfomycin and fusidic acid. It seems likely that L. grayi is naturally resistant to all antifolates; the species was least susceptible to rifampicin and most susceptible to quinolones, whereas L. ivanovii was naturally resistant to most quinolones. L. ivanovii was naturally sensitive to fosfomycin, whereas L. innocua and L. monocytogenes were naturally resistant. L. ivanovii was also the most susceptible species to fusidic acid.


CONCLUSIONS
The present study describes a database on the natural susceptibility of Listeria spp. to a wide range of antibiotics, which can be used to validate susceptibility testing results of these microorganisms.
Troxler
R
R
Institut für Medizinische Mikrobiologie, Universität Zürich, Zürich, Switzerland.
von Graevenitz
A
A
Funke
G
G
Wiedemann
B
B
Stock
I
I
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003470:Culture Media; D016208:Databases, Factual; D004352:Drug Resistance, Microbial; D018432:Drug Resistance, Multiple; D008087:Listeria / Q000187:drug effects* / Q000472:pathogenicity; D008826:Microbial Sensitivity Tests
D000900:Anti-Bacterial Agents; D003470:Culture Media