**4.1 Period 1981–1990**

For the time period 1981–1990 the performed survey resulted in 20,739 documents and the MeSH-based co-word analysis resulted in 10 different clusters. The strategic diagram is shown in **Figure 2**. The description of the identified research topics is summarized in **Table 1**.

#### **Figure 2.**

*Strategic diagram of the period 1981–1990. Each research topic is represented by a node and labeled with the most frequent pair MeSH heading/MeSH subheading. The size of the node is proportional to the number of MeSH heading/MeSH subheading pairs in each cluster.*

*Exploring the Knowledge Landscape of* Escherichia coli *Research: A Scientometric Overview DOI: http://dx.doi.org/10.5772/intechopen.109207*


#### **Table 1.**

*Principal research topics related to* E. coli *research in the period 1981–1990.*

In the period 1981–1990 the biggest cluster was the cluster "DNA Replication/ drug effects" comprised of the MeSH headings dealing with drug or radiation effects on DNA replication and DNA repair. This cluster was found to be the basic theme in this time period. A typical representative article for this cluster is the article published by Fram et al. with the title "DNA repair mechanisms affecting cytotoxicity by streptozotocin in *E. coli*" [31]. A further important basic research time in this period was also encompassed in the cluster "Transcription, Genetic/ drug effects" consisting of the MeSH headings relating to the gene expression and regulation of gene expression and drug effects on the gene expression and regulation of this expression. A typical representative article for this cluster is the article published by Goda and Greenblatt with the title "Efficient modification of *E. coli* RNA polymerase *in vitro* by the N gene transcription antitermination protein of bacteriophage lambda" [32]. The major motor theme in this period was covered by the cluster "Bacterial Proteins/metabolism" involving MeSH headings related to metabolism and isolation and purification of different bacterial proteins, e.g., ribosomal proteins, transcription factors, repressors, and other DNA-binding proteins. A typical representative article for this cluster is the article published by Thomas et al. with the title "Amplification and purification of UvrA, UvrB, and UvrC proteins of *Escherichia coli*" [33]. Only one niche theme was detected—the cluster

"DNA, Bacterial/genetics"—covering MeSH headings dealing mostly with isolation and purification of DNA and with DNA analysis. A typical representative article for this cluster is the article published by Klaer et al. with the title "The sequence of IS*4*" [34].
