Beta-lactamase gene expression in a penicillin-resistant Bacillus anthracis strain

Abstract

Expression of the bla1 and bla2 genes in an archetypal Bacillus anthracis strain is insufficient for penicillin resistance. In a penicillin-resistant clinical isolate, both genes are highly transcribed, but bla1 is the major contributor to high-level resistance to ampicillin. Differential expression of the bla genes is dependent upon strain background.

FIG. 1.

bla gene transcription in penicillin-resistant (Pen^r) and penicillin-susceptible (Pen^s) B. anthracis strains. Total RNA was extracted from B. anthracis strains during exponential growth in Luria-Bertani medium. (A) Reverse transcription-PCR analysis of bla transcripts. Lane M, molecular size markers. (B) Northern blot analysis of bla transcripts. Internal DNA probes for bla1 and bla2 were generated by using primers listed in Table 2. Sizes of transcripts are indicated.

FIG. 2.

Promoter activity of bla genes in Pen^r and Pen^s B. anthracis strains. (A) Schematic representation of sequence differences in bla genes. Cloned DNA regions for lacZ fusions are indicated. Loci of nucleotide differences are shown as asterisks. (B) Promoter activities of bla genes in Pen^r (UT223) (filled symbols) and Pen^s (UM44) (open symbols) strains. Isolates harbored pUTE546 (vector), pUTE547 (P_bla1), or pUTE548 (P_bla2) as indicated. β-Galactosidase activity was determined following growth in Luria-Bertani medium at 37°C with shaking at 200 rpm. Data shown are representative of at least three experiments.

FIG. 3.

β-Lactamase production by B. anthracis strains. β-Lactamase activity was determined following incubation for 7 h at 37°C with shaking at 200 rpm, when the cultures were in late log phase. The strains used were UT223 (Pen^r), UT247 (bla1), UT248 (bla2), UT249 (bla1 bla2), and UM44 (Pen^s).