Open AccessMechanisms of Ampicillin Resistance in Haemophilus influenzae Type B
Author(s) -
Rocío de la Vega,
H. L. Sadoff,
Maria J. Patterson
Publication year - 1976
Publication title -
antimicrobial agents and chemotherapy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.07
H-Index - 259
eISSN - 1070-6283
pISSN - 0066-4804
DOI - 10.1128/aac.9.1.164
Subject(s) - microbiology and biotechnology , haemophilus influenzae , ethidium bromide , amp resistance , ampicillin , subculture (biology) , plasmid , biology , extrachromosomal dna , nalidixic acid , dna , antibiotics , genetics
The genetic mechanisms associated with ampicillin resistance in strains ofHaemophilus influenzae type b were investigated. In experiments concerned with transfer of total deoxyribonucleic acid in vitro, expression of resistance by wild-type strains occurred at a frequency of about 10%. The minimum inhibitory concentration of ampicillin for the transformed strains was similar to that of the resistant donor strains, and resistance in transformants was associated with acquisition of the ability to produce beta-lactamase. Exposure to 39 μg of acridine per ml for 18 h cured resistance at a frequency of 80%, and there was spontaneous loss of resistance after repeated subculture of some strains. Analysis by cesium chloride-ethidium bromide density gradient centrifugation demonstrated the presence of extrachromosomal deoxyribonucleic acid in the resistant strains, providing further evidence that the resistance factor is plasmid mediated.