科研之友
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摘要
The mechanisms of hyperproduction (defined as greater than or equal to 200 nmoles nitrocefin hydrolysed per minute per mg of protein) of TEM-1 beta-lactamase by 38 isolates of Escherichia coli were investigated. The copy numbers of TEM-encoding plasmids were determined for the hyperproducing isolates and for 39 TEM-l-producing isolates that did not hyperproduce the enzyme. Allele-specific PCR was used to determine if the promoter region of the TEM-1 gene was of the TEM-1 or TEM-2 type. Twenty three of the 38 hyperproducers had the TEM-l-type promoter but 15 had the more efficient TEM-2-type promoter; in contrast, 37 of the 39 isolates with lower activities had the TEM-l-type promoter and only two had the TEM-2-type promoter. Many of the TEM-l-hyperproducing isolates possessed small plasmids (less than or equal to 20 MDal) with high copy numbers, in some cases together with large, low copy number plasmids; the average total copy number of TEM-encoding plasmids was 14; if only isolates with the TEM-l-type promoter were included, average total copy number was 22. Hyperproduction was attributed to high copy number(greater than or equal to 10) plasmids in 11 isolates; another seven had plasmids with moderately high copy numbers (4-9). The average total copy number for isolates that produced relatively small amounts of TEM-I beta-lactamase (less than or equal to 100 nmoles/min/mg protein) was 2.2, and for the 12 isolates with TEM-1 activities of 101-200 nmoles/min/mg protein it was 6.8. We conclude that both high copy number plasmids and a more efficient promoter are common causes of hyperproduction of TEM-1.
- 出版日期1995-12
