Hiie Soeorg

Genetic relatedness of coagulase-negative Staphylococci from gastrointestinal tract and blood of preterm neonates with late-onset sepsis.

Background: Coagulase-negative staphylococci (CoNS) are the first colonizers of gastrointestinal tract (GIT) and the commonest cause of late-onset sepsis (LOS) in preterm neonates. Intravascular catheters are considered a major source of CoNS bacteremia. However, several cases of LOS remain without an identified source. To elucidate whether GIT could be a potential source of invasive strains, we aimed to assess the molecular similarity between CoNS from blood and GIT in preterm neonates with LOS. Methods: Altogether 22 blood and 53 GIT isolates collected from 22 neonates with LOS caused by CoNS (Staphylococcus haemolyticus in 13, Staphylococcus epidermidis in 7 and Staphylococcus hominis in 2 patients) were included. Rectal swabs were collected twice weekly from birth, but only isolates obtained before LOS were analyzed. S. epidermidis isolates were typed by multilocus variable number of tandem repeats analysis and multilocus sequence typing, S. haemolyticus by pulsed-field gel electrophoresis. Results: Eighteen of 22 neonates had the same CoNS species in GIT and bloodstream; all these isolates from them (altogether 18 blood and 28 GIT isolates) underwent typing. The genotypic similarity between bloodstream and ≥1 antecedent GIT isolates was observed in 13 of 18 patients—3 of 7 with S. epidermidis and 10 of 11 with S. haemolyticus infection. The concordant GIT isolates were collected 0–7 days before the positive blood culture. Conclusions: The similarity between CoNS from GIT and bloodstream indicates that preterm neonates harbour invasive strains in GIT before LOS. Whether there is a causal relationship between GIT colonization and LOS remains to be elucidated in further studies.

In vitro synergy of oxacillin and gentamicin against coagulase-negative staphylococci from blood cultures of neonates with late-onset sepsis.

Coagulase‐negative staphylococci (CoNS) are the leading cause of late‐onset sepsis (LOS) in neonates. Increasing resistance of CoNS to beta‐lactams and aminoglycosides has led to widespread use of vancomycin, which in turn may lead to resistance to vancomycin. Thus, combination therapy of LOS has been advocated. We aimed to determine the interaction of oxacillin and gentamicin against CoNS. In 2005, 34 isolates of oxacillin‐ and gentamicin‐resistant CoNS were obtained from blood samples of neonates with LOS. Combination effect was tested using the checkerboard method, E‐test with the other antibiotic incorporated in the medium (E‐test‐1) and two E‐test strips placed in a cross‐formation (E‐test‐2). Of 34 isolates 61.8%, 53% and 73.5% revealed synergy or an additive effect when tested by the checkerboard method, E‐test‐1 and E‐test‐2, respectively. Results of all three tests were concordant for six (17.6%) isolates, four showing synergy, and two indifference. Our in vitro results support that combination therapy with penicillinase‐resistant penicillin and aminoglycoside can be an alternative to vancomycin.

Group A rotavirus genotypes circulating prior to implementation of a National Immunization Program in Estonia

Group A rotaviruses (RVA) are a major cause of acute gastroenteritis in children ≤ 5 y worldwide which could be prevented with two recently introduced vaccines – monovalent Rotarix (live-attenuated G1P[8] strain) and pentavalent RotaTeq (human-bovine reassortant containing serotypes G1, G2, G3, G4 and P[8]). Prior to implementation of vaccines into national immunization program we aimed to describe RVA genotype distribution in hospitalized children aged < 5 y in Estonia during 2007–2008. A total of 671 children with confirmed RVA gastroenteritis from three major pediatric hospitals were prospectively enrolled. G- and P-genotypes were detected from 124 stool samples by semi-nested reverse transcription-PCR. Severity of disease was assessed using Clark scoring system. The majority of cases (65%) occurred in infants aged 7 to 24 mo and were of moderate severity (mean Clark score 12.1 (SD 3.2)). The prevailing strain was G2P[4] (34.7%), causing significantly more cases than G4P[8] (12.9%), G1P[8] or G9P[8] (both 4.0%), G3P[8] (1.6%). Yearly differences in genotype distribution occurred, as G2P[4] (52.8%) dominated in 2007, but G4P[8] (26.9%) in 2008. One third of strains remained non-typeable. The distribution of RVA genotypes in Estonia differs from that seen in other Central and Eastern European countries, although one should bear in mind the large proportion of P-untypeable strains and natural fluctuations of dominating RVA genotypes. Nevertheless, considering the high genotype-independent efficacy of the vaccines, introduction of national immunization should be considered.

Coagulase-Negative Staphylococci in Human Milk From Mothers of Preterm Compared With Term Neonates

Background: Human milk is the preferred nutrition for neonates and a source of bacteria. Research aim: The authors aimed to characterize the molecular epidemiology and genetic content of staphylococci in the human milk of mothers of preterm and term neonates. Methods: Staphylococci were isolated once per week in the 1st month postpartum from the human milk of mothers of 20 healthy term and 49 preterm neonates hospitalized in the neonatal intensive care unit. Multilocus variable-number tandem-repeats analysis and multilocus sequence typing were used. The presence of the mecA gene, icaA gene of the ica-operon, IS256, and ACME genetic elements was determined by PCR. Results: The human milk of mothers of preterm compared with term neonates had higher counts of staphylococci but lower species diversity. The human milk of mothers of preterm compared with term neonates more often contained Staphylococcus epidermidis mecA (32.7% vs. 2.6%), icaA (18.8% vs. 6%), IS256 (7.9% vs. 0.9%), and ACME (15.4% vs. 5.1%), as well as Staphylococcus haemolyticus mecA (90.5% vs. 10%) and IS256 (61.9% vs. 10%). The overall distribution of multilocus variable-number tandem-repeats analysis (MLVA) types and sequence types was similar between the human milk of mothers of preterm and term neonates, but a few mecA-IS256-positive MLVA types colonized only mothers of preterm neonates. Maternal hospitalization within 1 month postpartum and the use of an arterial catheter or antibacterial treatment in the neonate increased the odds of harboring mecA-positive staphylococci in human milk. Conclusion: Limiting exposure of mothers of preterm neonates to the hospital could prevent human milk colonization with more pathogenic staphylococci.

The role of breast milk in the colonization of neonatal gut and skin with coagulase-negative staphylococci

BackgroundWe aimed to determine the genetic relatedness between Staphylococcus epidermidis colonizing breast milk (BM) and BM-fed neonates during the first month of life.MethodsS. epidermidis was isolated from the stool and skin swabs of 20 healthy term and 49 preterm neonates hospitalized in the neonatal intensive care unit and from the BM of mothers once a week and typed by multilocus variable-number tandem-repeat analysis. Virulence-related genes were determined by PCR.ResultsThe gut (95%) and skin (100%) of term neonates were colonized with strains genetically similar to those in BM and carrying mecA and IS256 at low rate (both <6.7%). In preterm neonates, colonization with strains genetically similar to those in BM was low on the skin (34.7%) and in the gut in the first week of life (14.3%), but the prevalence of mecA (>90.6%) and IS256 (>61.7%) was high. By the fourth week, in the gut of preterm neonates the prevalence of mecA (73.8%) and IS256 (18.4%) decreased, but colonization with strains genetically similar to those in BM increased (83.7%).ConclusionDuring early life, the skin and gut of preterm neonates is colonized with S. epidermidis that is distinct from strains found in BM, but gradually the gut is enriched with strains genetically similar to those in BM, as in term neonates.

Molecular epidemiology of Staphylococcus epidermidis in neonatal intensive care units.

Late‐onset sepsis (LOS) in preterm neonates is increasingly reported to be associated with gut‐colonizing Staphylococcus epidermidis. We aimed to describe the molecular epidemiology of S. epidermidis colonizing the gut of neonates hospitalized in two neonatal intensive care units. S. epidermidis from rectal swabs were typed by multilocus variable‐number tandem‐repeat analysis (MLVA), randomly chosen isolates of predominant MLVA types additionally by multilocus sequence typing. Antimicrobial susceptibility, the presence of icaA, IS256, arginine catabolic mobile element (ACME), agr type, and SCCmec type were determined. Of 276 neonates (38.4%), 106 were colonized with S. epidermidis, yielding a total of 139 isolates (62 in one unit and 77 in another unit). Of the 55 MLVA types identified, the five predominant detected in both units corresponded to sequence type (ST) 2, ST5, and ST59 or its single locus variant ST81 and formed three major MLVA clonal complexes accounting for 74.8% of all isolates. Overall, the prevalence of mecA, icaA, IS256, and ACME was 91.4%, 28.1%, 64%, and 77%, respectively. Of the mecA‐positive isolates (n = 127), 43.9% carried SCCmec type IV. Of eight episodes of LOS, four were caused by ST2 and two by ST5. Preventing gut colonization with nosocomial epidemic S. epidermidis in hospitalized neonates could contribute to the prevention of LOS.

Higher intake of coagulase-negative staphylococci from maternal milk promotes gut colonization with mecA -negative Sta p hylococcus e p idermidis in preterm neonates

ObjectiveWe aimed to determine factors associated with gut colonization of preterm neonates with coagulase-negative staphylococci (CoNS) from maternal milk (MM).Study DesignCoNS isolated from weekly collected stool and MM of hospitalized preterm (n = 49) and healthy term neonates (n = 20) were genotyped. Colonization-related factors were determined by Cox proportional hazards regression.ResultGut colonization with mecA-negative Staphylococcus epidermidis from MM was less prevalent (40.8% vs. 95%) and delayed (median age 15.5 vs. 2 days) in preterm compared with term neonates. Enhanced colonization was associated with higher intake of CoNS from MM (hazard ratio (95% confidence interval) 1.006 (1.00–1.01) for 106 colony-forming units), lower proportion of mecA-positive predominant NICU strains in gut (0.09 (0.01–0.49) for 1%) and lower incidence of late-onset CoNS sepsis (5% vs. 34% in those without colonization).ConclusionEnteral feeding with larger proportion of unpasteurized MM and limiting spread of predominant strains may promote colonization with CoNS from MM.

Genetic relatedness of Gram-negative bacteria colonizing gut and skin of neonates and mother’s own milk

ObjectiveWe described colonization of mother’s own milk with Gram-negative bacteria and its relationship with neonatal colonization.Study DesignGram-negative bacteria isolated from weekly collected stool, skin and mother’s own milk of hospitalized preterm (n = 49) and healthy term neonates (n = 20) were genotyped. Colonization-related factors were determined by logistic regression.ResultsGram-negative bacteria were isolated from mother’s own milk of 22.4% (n = 11) and 15% (n = 3) of mothers of preterm and term neonates, respectively. According to pulsed-field gel electrophoresis genetically similar strains were present in mother’s own milk and gut of 8.2% (n = 4) of mother–preterm neonate, but none of mother–term neonate pairs. In three of four late-onset sepsis caused by Gram-negative bacteria, colonization of gut, but not mother’s own milk, with invasive species preceded late-onset sepsis.ConclusionsColonization of mother’s own milk with Gram-negative bacteria is uncommon and transmission to neonatal gut may occur in less than one-tenth of neonate–mother pairs.