Molecular characterization of resistance plasmids in epidemiologically unrelated strains of multiresistant Haemophilus influenzae.
Thirty-three epidemiologically unrelated strains of ampicillin-chloramphenicol-resistant isolates of Haemophilus influenzae (22 type b, 11 unencapsulated), isolated over 10 years in Belgium, were compared with 53 ampicillin-resistant chloramphenicol-susceptible isolates (22 type b, 31 unencapsulated). All ampicillin-chloramphenicol-resistant and 76% of ampicillin-resistant chloramphenicol-susceptible strains were resistant to tetracycline, kanamycin, or both. Resistance to these antibiotics was specified by a 37- to 44-MDa conjugative plasmid. The genetic relatedness of these plasmids and of those in multiresistance strains from Spain was investigated. Plasmids specifying ampicillin-chloramphenicol-tetracycline-kanamycin resistance in Belgium or in Spain had highly related restriction fragment patterns. By homoduplex analysis, they had similar molecular organization and contained a structure identical to Tn10-TnCm, a transposon previously identified in chloramphenicol-tetracycline-resistant H. influenzae. Plasmids coding for different resistance phenotypes had less resemblance by restriction endonuclease analysis; however, study of heteroduplex molecules indicated they shared a high proportion of core sequences. These findings support the hypothesis of independent transposition events resulting in resistance plasmids of close molecular organization.
Levy
J
J
Department of Pediatrics, Hospital Universitaire Saint-Pierre, Brussels, Belgium.
Verhaegen
G
G
De Mol
P
P
Couturier
M
M
Dekegel
D
D
Butzler
J P
JP
D001530:Belgium / Q000453:epidemiology; D003227:Conjugation, Genetic; D004352:Drug Resistance, Microbial / Q000235:genetics; D006192:Haemophilus Infections / Q000453:epidemiology / Q000382:microbiology; D006193:Haemophilus influenzae / Q000145:classification / Q000187:drug effects / Q000235:genetics* / Q000648:ultrastructure; D008854:Microscopy, Electron; D010641:Phenotype; D012150:Polymorphism, Restriction Fragment Length; D011815:R Factors / Q000648:ultrastructure; D013030:Spain / Q000453:epidemiology