Cronobacter sakazakiiSusan Joseph and Stephen J.ForsytheAbstract.Half (20/41) of the C.sakazakii strains were sequence type (ST) 4, and 9/12 meningitis isolates were ST4.C.sakazakiiEnterobacteriaceae.It is closely related to the genera Enterobacter and Citrobacter.Cronobacter spp.have been frequently isolated from the environment, plant material (wheat, rice, herbs, and spices), and various food products, including powdered infant formula (PIF).Cronobacter spp.have come to prominence because of their a*sociation with severe neonatal infections, which can be fatal (13). Our current knowledge of the virulence and epidemiology of this organism is limited.However, because neonates are frequently fed reconstituted PIF, this product has been the focus of attention for reducing infection risk to neonates because the number of exposure routes is limited (1,2).Infections with Cronobacter spp.occur across all age groups, and most infections, albeit less severe, are in the adult population. However, neonates, particularly those of low birthweight, are the major identified group at risk, because the organism can cause meningitis, necrotizing enterocolitis (NEC), and sepsis in patients in neonatal intensive care units and has a high mortality rate (13). Bowen and Braden (4) reviewed 46 cases of invasive (non-NEC) infant Cronobacter infections to define risk factors and provide guidance for prevention and treatment.Although these infections have been a*sociated with intrinsically and extrinsically contaminated PIF, other environmental sources are possible and several noninfant formulaa*sociated cases have been reported (5).Cronobacter spp.have been shown to invade human intestinal cells, replicate in macrophages, and invade the bloodbrain barrier (6).Kucerova et al.(CronobacterRecently, Baldwin et al.(9) constructed a comprehensive multilocus sequence typing (MLST) scheme for Cronobacter spp.based on 7 housekeeping genes (atpD, fusA, glnS, gltB, gyrB, infB, ppsA; 3,036 nt concatenated length).The MLST scheme currently has 66 defined sequence types covering all Cronobacter spp.(www.pubMLST.org/cronobacter). However, the scheme has not been applied for any epidemiologic purposes. Therefore, we investigated whether severity of infection by Cronobacter spp.is a*sociated with particular genotype(s) by compiling patient details, isolation site, and clinical signs for clinical C.sakazakiiThe StudyC.sakazakii strains were included in the study.These strains were from 7 countries and had been isolated during 19532008. The strains included those of recent (13,1012) and those of more historic interest (>25 years; 1315).Strains used in this study, along with patient details and clinical signs, are shown in Table 1.Details of clinical signs were collated from information in the a*sociated publication or supplied by the strain provider (Centers for Disease Control and Prevention, Atlanta, GA, USA).Primers and conditions for amplification and sequencing of the 7 MLST genes ppsA).All sequences are available for download and independent analysis through open access at www.pubMLST.org/cronobacter.CronobacterC.sakazakii spp.However, the clinical strains were not evenly distributed across the STs.Of particular interest was that half (20/41) of the strains were ST4 (Table 2).The remaining strains were ST8 (7), ST1 (4), ST12 (3), ST3 (2), ST13, ST15, ST18, ST31, and ST41 (1 each). Of the 20 ST4 strains, 10 were from neonates, 7 from infants, and 1 from a child; 2 had no patient details.Similarly, most (9/12) isolates from meningitis cases were ST4 strains; 7 were isolated from cerebrospinal fluid and the others from blood and the trachea.The remaining ST4 strains were from bacteremia cases (1), NEC (2), and undefined infection (1), with 6 from unknown sources.ST4 was the main ST a*sociated with neonates (10/18); this ST has been reported by Baldwin et al.(9) for the high incidence of PIF isolates.
The ST4 clinical strains were from 6 countries (the Netherlands, France, United States, New Zealand, Czech Republic, and Canada) and had been isolated during 19772008 (Table 1).Of the 30 strains with known patient details, only 1 isolate (ST1) was from an adult patient.To date, all other isolates from adults have been identified as C.malonaticus (S.Joseph, unpub.data).The 7 housekeeping genes for MLST analysis are not virulence related, but a large proportion of severe neonatal infections were caused by a single sequence type.Whether this is caused by survival characteristics increasing persistence under desiccated conditions, and hence neonatal exposure or particular virulence capabilities, is uncertain.It is plausible that different age groups are exposed to different genotypes of C.sakazakii according to their diet and lifestyle.C.sakazakii ST4 appears to be a stable clone because strains have been isolated from 7 countries for >50 years.The earliest (1951) nonclinical isolate was from a can of dried milk (13). Whether this clonal nature occurs in other Cronobacter spp.awaits future investigation.AcknowledgmentsMs Joseph is a research student at Nottingham Trent University.She is currently investigating the genomic diversity of Cronobacter spp.
Dr Forsythe is professor of microbiology at Nottingham Trent University.His research interests are foodborne pathogens, especially emergent bacterial pathogens and the origin of their virulence.Himelright I, Harris E, Lorch V, Anderson M.Enterobacter sakazakii infections a*sociated with the use of powdered infant formulaTennessee, 2001.JAMA.2002;287:22045.PubMed DOI
