1. Summary, 678
2. Introduction
2.1. Chemical and biological stress agents affecting enterobacteria, 678
2.2. Sensing of chemical and biological stress stimuli, 678
2.3. Intracellular sensors detect intracellularly‐produced chemical stressing agents, 679
2.4. Intracellular sensors and intracellular induction components could delay response induction by extracellular chemical or biological stress agents, 680
2.5. Extracellular sensors and EICs give early warning of stress, 681
2.6. Disadvantages of extracellular components being needed for stress response induction, 682
2.7. Extracellular sensors and EICs allow stressed cells to warn unstressed ones, 682
2.8. A second role for some extracellular stress sensors, 683
3. Responses switched on by extracellular sensors and EICs
3.1. Involvement of EICs and ESCs in acid tolerance induction at pH 5·0 and at other mildly acidic pH values, 683
3.2. Further evidence for the obligate involvement of extracellular sensors and EICs in acid tolerance induction at pH 5·0, 684
3.3. On the nature of the acid pH tolerance‐inducing ESC and EIC, 686
3.4. The acid tolerance ECs and their relation to other extracellular response‐inducing components, 686
3.5. Extracellular components are needed for other inducible acid tolerance responses, 687
3.6. Involvement of EICs and extracellular sensors in acid tolerance in E. coli O157, 687
3.7. EICs involved in acid tolerance induction are diffusible, 687
4. Acid sensitization at alkaline pH and the role of extracellular sensor and EIC(s), 688
5. Responses affecting tolerance to alkali
5.1. Alkali sensitization at acidic pH, 688
5.2. Induced alkali tolerance at pH 9·0 and role of extracellular components, 688
6. Inducible tolerance to alkylhydroperoxides, 689
7. Are extracellular sensors and extracellular induction components needed for all stress responses?, 689
8. Altered responsiveness of extracellular sensors depending on growth conditions, 691
9. Protection of living cells from chemical stress by dead cultures, 691
10. How can intracellular levels of stress be detected?, 692
11. Are Nikolaev’s extracellular ‘protectants’ and similar components related to EICs?, 693
12. Conclusions, 693
13. References, 694