CASE HISTORY
In San Francisco, a 3-year-old boy named Luke was admitted to the hospital after an abrupt onset of fever and a generalized seizure. The boy's cerebrospinal fluid was normal, and he had a normal chest radiograph, but his white blood cell count was 20,000/mm3 (normal is 5,000-10,000), with 85% polymorphonuclear leukocytes (PMns). Luke's blood culture revealed bacteremia (bacteria in the blood). The bacteria were identified as "nontypeable" Haemophilus influenzae bacteria. The nontypeable H. influenzae strain was beta-lactamase-positive (expressed an enzyme to inactivate penicillin G, ampicillin, and amoxicillin) but proved sensitive to cefixime, a third-generation cephalosporin.
The diagnosis surprised the boy's two fathers. They showed the doctor Luke's full record of immunizations and booster shots, including the standard DTaP (diphtheria, tetanus, and pertussis), hepatitis B, pneumococcus, and Haemophilus influenzae b (Hib). Why was Luke not protected by the Hib vaccine? The doctor explained that the Hib vaccine protected only from H. influenzae type b, the most common virulent strain-but not the only virulent strain. Six strains, or serotypes, a through f, are "typed" based on the type of polysaccharide capsule surrounding the cell envelope. The Hib vaccine targets capsule type b. But some variant strains of H. influenzae, called "nontypeable," lack a capsule. These strains can be identified on the basis of other properties, such as enzyme activities, but they are unaffected by the vaccine. Fortunately, after seven days of intravenous antibiotic, Luke recovered fully.
The H. influenzae strain infecting Luke was beta-lactamase positive. Would the cell be likely to express the gene for this enzyme at all times? Describe one mechanism by which the cell could regulate the expression of this enzyme.

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The Answer of CASE HISTORY
In San Francisco, a 3-year-old boy named Luke was admitted to the hospital after an abrupt onset of fever and a generalized seizure. The boy's cerebrospinal fluid was normal, and he had a normal chest radiograph, but his white blood cell count was 20,000/mm3 (normal is 5,000-10,000), with 85% polymorphonuclear leukocytes (PMns). Luke's blood culture revealed bacteremia (bacteria in the blood). The bacteria were identified as "nontypeable" Haemophilus influenzae bacteria. The nontypeable H. influenzae strain was beta-lactamase-positive (expressed an enzyme to inactivate penicillin G, ampicillin, and amoxicillin) but proved sensitive to cefixime, a third-generation cephalosporin.
The diagnosis surprised the boy's two fathers. They showed the doctor Luke's full record of immunizations and booster shots, including the standard DTaP (diphtheria, tetanus, and pertussis), hepatitis B, pneumococcus, and Haemophilus influenzae b (Hib). Why was Luke not protected by the Hib vaccine? The doctor explained that the Hib vaccine protected only from H. influenzae type b, the most common virulent strain-but not the only virulent strain. Six strains, or serotypes, a through f, are "typed" based on the type of polysaccharide capsule surrounding the cell envelope. The Hib vaccine targets capsule type b. But some variant strains of H. influenzae, called "nontypeable," lack a capsule. These strains can be identified on the basis of other properties, such as enzyme activities, but they are unaffected by the vaccine. Fortunately, after seven days of intravenous antibiotic, Luke recovered fully.
The H. influenzae strain infecting Luke was beta-lactamase positive. Would the cell be likely to express the gene for this enzyme at all times? Describe one mechanism by which the cell could regulate the expression of this enzyme.

CASE HISTORY In San Francisco, a 3-Year-Old Boy Named Luke Was Admitted