title: Loss of plasmid DNA coding for beta-lactamase during experimental infection with Haemophilus influenzae type b.
abstract: Apparent R factor-negative segregation was documented during infection of infant monkeys with two of three strains of ampicillin-resistant Haemophilus influenzae type b. In vitro the bacterial population of one strain (A-Sm) uniformly produced beta-lactamase. All bacteria isolated from blood or cerebrospinal fluid from both animals inoculated with strain A-Sm produced the enzyme. In contrast, 98% and 96% of bacteria from two other strains produced beta-lactamase in vitro. After intranasal inoculation of infant Macacca mulatta with these two strains, bacteria isolated from blood and cerebrospinal fluid uniformly did not produce beta-lactamase. Loss of the beta-lactamase-producing phenotype was associated with loss of plasmid DNA. Strains containing a mixed population of bacteria may undergo spontaneous loss of plasmid DNA during experimental infection. It is suggested that in these strains the bacteria carrying plasmids are less virulent.
mesh_terms: D000667:Ampicillin / Q000627:therapeutic use; D000818:Animals; D004269:DNA, Bacterial / Q000235:genetics*; D004587:Electrophoresis, Agar Gel; D005815:Genetic Code; D006192:Haemophilus Infections / Q000188:drug therapy / Q000235:genetics*; D006193:Haemophilus influenzae / Q000235:genetics; D008251:Macaca / Q000235:genetics*; D008253:Macaca mulatta / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D010957:Plasmids; D001618:beta-Lactamases / Q000235:genetics*
chemical_list: D004269:DNA, Bacterial; D000667:Ampicillin; D001618:beta-Lactamases