Food Biochemistry and Food Processing (2 edition)

BLBS102-c44 BLBS102-Simpson March 21, 2012 14:34 Trim: 276mm X 219mm Printer Name: Yet to Come

44 Emerging Bacterial Food-Borne Pathogens and Methods of Detection 839

concern warrants further attention into the epidemiology of this

pathogen and its relationship with human food-borne illness.

Cronobacter sakazakii(Enterobacter sakazakii)

Originally discovered in the early 1960s, this organism has pri-

marily been associated with neonatal meningitis of newborns

(Chenu and Cox 2009). Since then, the organism has gained in-

creased attention as a pathogen of infants and newborns and was

namedE. sakazakiiin the 1980s; as a consequence of genetic

diversity, a new genus for the species was proposed in 2008 and

namedCronobacter. This emerging pathogen has gained con-

siderable attention in the past 10 years or so with much still to

be learned about its epidemiology and pathogenesis.

Studies to date have implicated powdered infant formula

(dried milk powder or a modified version) as the vehicle of

transmission of the organism in some cases of neonatal menin-

gitis (Simmons et al. 1989, Van Acker et al. 2001, Himelright

et al. 2002, Caubilla-Barron et al. 2007, Hunter et al. 2008).

Cronobacteris a gram-negative rod, motile by peritrichous

flagella and a member of the family Enterobacteriaceae. The

genus consists of six species (Iversen et al. 2008). The organism

has a growth range of 6–45◦C with an optimum temperature

of 37–43◦C;Cronobacteris capable of growth at refrigeration

temperatures, which may be a significant health risk (Iversen

et al. 2004).

Clinical manifestations of illness have previously been asso-

ciated with neonates and present as life-threatening meningitis,

necrotizing enterocolitis, bacteremia, and septicemia (Muytjens

et al. 1983, Van Acker et al. 2001, Lai 2001, Himelright et al.

2002). Case fatality rates as high as 80% have been reported; the

survivors often suffer severe neurological disorders (Lehner and

Stephan 2004) and long-term complications.Cronobacterill-

ness has also been recognized in adults primarily among adults

with underlying disease, the immunocompromised, stroke pa-

tients, and the elderly (See et al. 2007, Healey et al. 2010).

The pathogenesis ofCronobacteris not well understood but

studies suggest that enterotoxins and the outer membrane pro-

tein OmpA may play a role in virulence and the ability of the

organism to cross the blood–brain barrier (Iversen and Forsythe

2004, Townsend et al. 2007, Singamsetty et al. 2008, Mittal et al.

2009, Mohan Nair et al. 2009).

Cronobacterappears to have an environmental association; it

has been postulated that plant material may be a source of con-

tamination (Healey et al. 2010); new reservoirs ofCronobacter

are being reported on a regular basis. Although the association

between the gut of animals andCronobacteris questionable,

the organism has been found in water, soils, and plant materials

(Iversen and Forsythe 2003).Cronobacterhas also been recov-

ered from a range of foods including meats, poultry, rice and

other grains, vegetables, herbs and spices, dry food ingredients,

breads, ultra-high temperature processed milk, cheese, sausage,

tofu, keifir, and sour tea (Iversen and Forsythe 2004, Kandhai

et al. 2004, Gurtler et al. 2005, Mullane et al. 2007, Friede-

mann 2007). Baumgartner et al. (2009) identifiedCronobacter

in ready-to-eat foods with 61% of sprout or fresh herbs and 27%

of dried herbs or spices being positive for the organism. O’Brien

et al. (2009) detectedCronobacterin follow-on infant formula

but not in powdered milk products suggesting that the risk of

illness is low but monitoring of raw ingredients is necessary to

establish sources of contamination.

One of the primary sources of illness in neonates appears

to be associated with powdered infant formula. As the powder

is nonsterile, it may become contaminated during production

or reconstitution (Simmons et al. 1989, Van Acker et al. 2001,

Caubilla-Barron et al. 2007). Also of concern is the ability of

Cronobacterto produce biofilms, which may enhance its abili-

ties to resist the killing action of disinfectants (Kim et al. 2007a).

Regardless of the narrow scope and sources ofCronobacter, its

recognition as an emerging pathogen warrants attention in light

of its epidemiology and pathogenesis being poorly understood.

Clostridium difficile

Clostridium difficileis a gram-positive anaerobic spore former

that has gained increased attention as a pathogen of human con-

cern (Weese 2010). Originally, this organism was recognized as

a pathogen associated with diarrhea as a result of antimicrobial

treatment of patients. Now, however, there is concern that this

organism may also be an agent of zoonoses (Songer 2010). Indra

et al. (2009) reported thatC. difficileis primarily considered a

nosocomial pathogen causing diarrhea and pseudomembranous

colitis, yet others have found thatC. difficileis found in food

production animals suggesting a potential relationship between

humans and animals (Songer 2004, Weese 2009a).

The pathogenesis ofC. difficileis usually associated with

overgrowth of the organism in the gut resulting in mild to life-

threatening pseudomembranous colitis, toxic megacolon, and/or

intestinal perforation (Borriello 1998); changes in the gut mi-

croflora also appear to be linked to the overgrowth ofC. difficile

(Bartlett and Perl 2005). Two toxins are also recognized as con-

tributing to pathogenesis—tox A and tox B and a third toxin

CDT is also a contributing factor (Rupnik et al. 2005). In human

disease, there has been an increase in the incidence ofC. difficile

associated with ribotype 027, which has been recognized as an

epidemic strain worldwide (Goorhuis et al. 2008).

Recently, concern forC. difficilehas escalated due to studies

demonstrating the prevalence of the organism in animals and

foods of animal sources, suggesting that community acquired

C. difficilemay contribute to human outbreaks. Studies to date

are, however, limited and have used varying approaches to de-

tect the pathogen. Indra et al. (2009) assessed the prevalence of

C. difficilein cattle, pigs, and broilers demonstrating that 4.5%

of cattle, 3.3% of pigs, and 5% of broilers were positive for the

organism. A similar assessment of retail meat samples (ground

beef, pork, and chicken) failed to detect the pathogen. In con-

trast, Songer et al. (2009) reported the prevalence ofC. difficile

in ready-to-eat meats and raw meats ranging from 14% to 50%.

Of significance in the study was the detection of ribotype 027,

a strain type that is almost exclusively associated with human

disease worldwide and has been identified as an epidemic strain

(Goorhuis et al. 2008). This ribotype has also been identified

as possessing resistance to the fluoroquinolone class of antimi-

crobials (Razavi et al. 2007).C. difficilehas also been found in