Escherichia, Klebsiella, Enterobacter, Serratia, Citrobacter, and Proteus

Abstract

The Gram-negative bacilli of the genera Escherichia, Klebsiella, Enterobacter, Serratia, Citrobacter,and Proteus(Table 26- 1) are members of the normal intestinal flora of humans and animals and may be isolated from a variety of environmental sources. With the exception of Proteus, they are sometimes collectively referred to as the coliform bacilli because of shared properties, particularly the ability of most species to ferment the sugar lactose.Many of these microorganisms used to be dismissed as harmless commensals. Today, they are known to be responsible for major health problems worldwide. A limited number of species, including E coli, K pneumoniae, Enterobacter aerogenes, Enterobacter cloacae, S marcescens,and P mirabilis, are responsible for most infections produced by this group of organisms. The increasing incidence of the coliforms, Proteus, and other Gram-negative organisms in diseases reflects in part a better understanding of their pathogenic potential but more importantly the changing ecology of bacterial disease. The widespread and often indiscriminate use of antibiotics has created drug-resistant Gram-negative bacilli that readily acquire multiple resistance through transmission of drug resistance plasmids (R factors). Also, development of new surgical procedures, health support technology, and therapeutic regimens has provided new portals of entry and compromised many host defenses.