C18 
Gorbach 
mately 80% are caused by E. coli. Hospitalized 
patients are also prone to E. coli infection. In- 
deed, this organism is the leading cause of noso- 
comial infections, constituting approximately 
20% of the total. Again, the urinary tract is the 
major site of hospital-acquired disease. Indwell- 
ing urinary catheters or operative procedures are 
the predisposing causes in the majority of E. coli 
infections related to hospitalization. 
E. coli Intestinal Infections 
E. coli are important pathogens in diarrheal dis- 
eases of young animals. In the developing coun- 
tries of the world, E. coli causes serious diar- 
rhea in young children [30], This organism also 
is the leading cause of the diarrhea of travelers 
[34, 35]. In the United States and England, how- 
ever, E. coli diarrhea is relatively uncommon. 
The organisms responsible for intestinal infec- 
tions in humans fall into certain O serogroups. 
Among the toxigenic organisms, at least two 
viridence factors, genetically controlled by dif- 
ferent plasmids, are required for a fully patho- 
genic strain [26], The organism must produce an 
enterotoxin, either a heat-labile (LT) or heat- 
stable (ST) variety. In addition, the organism 
must be capable of colonizing in the small intes- 
tine, a property that is related to a pilus or pro- 
tein antigen. These K antigens are host-specific; 
thus, the K88 type is associated with diarrhea in 
piglets, the K99 in calves, and a different type, as 
yet unclassified, is specific for humans [27]. 
The invasive strains of E. coli fall within an- 
other group of serotypes and possess different 
mechanisms of pathogenicity. Behaving like shi- 
gella organisms, the invasive E. coli are capable 
of penetrating the intestinal mucosa of the large 
bowel and multiplying within the epithelial cells; 
they cause a disease similar to bacillary dysen- 
tery [31]. Again, implantation in the bowel is 
the critical first step in the pathogenic events. 
Extraintestinal Infections Caused by E. coli 
E. coli strains that are isolated from patients with 
septicemia, urinary tract infections, pneumonia, 
and wound infections possess certain character- 
istics more frequently than do strains isolated 
from the normal flora. As reported by Minshew 
et al., pathogenic strains exhibited hemolysin 
production, biosynthesis of colicin V, hemagglu- 
tination of human erythrocytes, and the ability 
to kill 13-day-old chick embryos [33]. E. coli K12 
was found to be deficient in all of these charac- 
teristics. 
Urinary tract infections caused by E. coli 
have been the subject of extensive epidemiologic 
and laboratory study. The O serotypes isolated 
from infected urine are restricted to relatively 
few groups which may show some variation in 
different parts of the world [36]. The most preva- 
lent serotypes are Ol, 02, 04, 06, 050, and 
075. These serogroups are also the most frequent 
in the intestinal microflora, although there are 
some anomalies such as 06, which is more fre- 
quently associated with infection than with bow- 
el carriage. Similarly, there is a relatively re- 
stricted group of K surface antigens associated 
with urinary tract infections: Kl, K2, K3, K5, 
K12, and K13 [23]. 
Montgomerie and his colleagues have de- 
scribed virulence factors in E. coli that promote 
the development of pyelonephritis [32], These 
features are resistance to phagocytosis and serum 
bactericidal activity, presence of K antigen, dul- 
citol fermentation, and the ability to multiply 
in urine or in minimal medium. Of this list, E. 
coli K12 possesses only dulcitol fermentation as a 
regular character. 
The pathogenesis of community-acquired uri- 
nary tract infection is fry the ascending route, 
from the urethra, to the bladder, and upward to 
the kidneys. Stamey et al. base shown that the 
initiating event is colonization of the vaginal in- 
troitus and periurethral mucosa by coliforms 
which are derived from the intestinal flora [37, 
38]. Women who have never experienced urinary 
tract infections rarely have colonization of this 
site. On die other hand, prospective studies have 
demonstrated colonization of the vaginal introi- 
tus prior to development of overt urinary tract 
infection. 
There are two schools of thought regarding the 
nature of E. coli associated with urinary tract in- 
fections. One view asserts that the pathogens, be- 
ing in the intestinal microflora, are “in the right 
place at the right time.” The other view suggests 
that the urinary tract pathogens are endowed 
with “special properties” to produce infection. 
[ 156 ] 
