established as a common cause of infection although occasional cases in
adults and infants not exposed to powdered infant formula indicate that
this is not invariably the vehicle.
Pasteurisation is an effective control measure; conventional pasteuri-
sation conditions of 72oC for 15 seconds would produce more than a 10
log reduction in the number of survivors, assuming a D 60 of 2.5 minutes
and z¼5.8oC. It seems that the organism is most likely to enter the
product as a result of post pasteurisation contamination.
Surveys of powdered infant formulae have shown contamination rates
ranging between 0 and 14% but generally, when it occurs, levels of
contamination are low ranging from 0.36 cfu/100g to 66 cfu/100g. It may
be that the infectious dose is very low in the very vulnerable patients
affected, but poor hygienic practices during reconstitution and prolonged
storage of the reconstituted product allowing bacterial multiplication
have been identified as significant risk factors.
7.8 Escherichia coli
7.8.1 Introduction
Since 1885, when it was first isolated from childrens’ faeces and described
by the German bacteriologist Theodor Escherich, scientific attention has
been lavished on Escherichia coli to such an extent that it is today
probably the best understood free-living organism.
E. coliis an almost universal inhabitant of the gut of humans and
other warm-blooded animals where it is the predominant facultative
anaerobe though only a minor component of the total microflora.
Generally a harmless commensal, it can be an opportunistic pathogen
causing a number of infections such as Gram-negative sepsis, urinary
tract infections, pneumonia in immunosuppressed patients, and menin-
gitis in neonates. Its common occurrence in faeces, ready culturability,
generally non-pathogenic character, and survival characteristics in water
led to the adoption ofE. colias an indicator of faecal contamination and
the possible presence of enteric pathogens such asS. Typhi in water. This
usage has been transferred to foods where greater circumspection is
required in interpreting the significance of positive results.
Strains ofE. coliwere first recognized as a cause of gastroenteritis by
workers in England investigating summer diarrhoea in infants in the early
1940s. Until 1982, strains producing diarrhoea were classified into three
types based on their virulence properties: enteropathogenicE. coli(EPEC),
enteroinvasiveE. coli(EIEC), and enterotoxigenicE. coli(ETEC). They
are not very common causes of foodborne illness in developed countries,
but an important cause of childhood diarrhoea in less developed countries.
216 Bacterial Agents of Foodborne Illness