关于 Cronobacter

The genus Cronobacter consists of a group of opportunistic Gram-negative pathogens associated with severe and potentially life-threatening medical diseases^[1]. Cronobacter spp. are ubiquitous in the environment and have been isolated from various food and environmental samples, including cereals, milk powder, vegetables, fruits, plants, feces, and river water^[2].

The Cronobacter genus consists of seven species: C. sakazakii, C. malonaticus, C. universalis, C. turicensis, C. muytjensii, C. dublinensis, and C. condiment^[3,4]. Among these, C. sakazakii, C. malonaticus, and C. turicencis are of serious clinical significance, while the other four species of the genus primarily exist as environmental commensals with low clinical significance^[5,6]. Notably, C. sakazakii and C. malonaticus have been associated with outbreaks in powdered infant formula (PIF)^[7,8]. Despite the low incidence of infection, the mortality of Cronobacter infection in neonates can be as high as 27%–80%. Therefore, neonates and low-birth-weight infants are the most susceptible population group since they could become infected through the consumption of PIF, or through contaminated bottles and appliances used for PIF preparation. The clinical profiles are mainly severe infantile septicemia, necrotizing enterocolitis, meningitis, and serious neurological sequelae^[3,4,9].

The pathogenicity and development of disease caused by Cronobacter depend on several key aspects such as virulence factors, which may be encoded by plasmids^[8]. Various virulence traits have been identified so far, such as cell adhesion and invasion in cellular lines such as HEp-2 and Caco-2, flagellar motility, survival in macrophages, sialic acid utilization, capsule and endotoxin production, and the presence of virulence genes such as ompA, cpa, fliC, hly, sip, aut, plas, and inv^{[3, 8,10]}. In addition, antibiotic resistance is another aspect to be considered since Cronobacter resistance toward ß-lactam antibiotics such as the first and second generations of cephalosporins and ampicillin and the presence of resistance genes such as marA, glpT, ampH, blaCSA, and mcr in Cronobacter have been well documented^[8,11]. The antibiotic resistance profile of Cronobacter spp. has paramount importance since rapid treatment of infected newborns is generally accomplished through antibiotic therapy.

Cronobacter spp. has good environmental stress tolerance, associated with the presence of a transmissible locus of stress tolerance (tLST), previously termed the locus of heat resistance (LHR), which confers resistance to heat^[12]. The tolerance to heat is not very high in many strains, but it is increased in strains possessing tLST. The tLST is composed of some heat shock-encoding genes, including those encoding the small heat shock protein sHSP20, heat resistance protein PsiE-GI, and heat resistance proteins YfdX1 and YfdX2, which can be mobilized by horizontal gene transfer in some Enterobacteriaceae^[13]. In addition, biofilm formation also helps bacteria to resist various environmental stressors. Bacteria are capable of forming biofilms on the surface of materials, increasing the possibility of environmental persistence of this pathogen^[14].

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