Abstract
Denmark is a low prevalence country with regard to methicillin resistant Staphylococcus aureus (MRSA). In 2008 and 2014, two neonatal wards in the Copenhagen area experienced outbreaks with a typical community acquired MRSA belonging to the same spa type and sequence type (t015:ST45) and both were PVL and ACME negative. In outbreak 1, the isolates harbored SCCmec IVa and in outbreak 2 SCCmec V. The clinical presentation differed between the two outbreaks, as none of five MRSA positive mothers in outbreak 1 had mastitis vs. five of six MRSA positive mothers in outbreak 2 (p < 0.02). To investigate if whole-genome sequencing could identify virulence genes associated with mastitis, t015:ST45 isolates from Denmark (N = 101) were whole-genome sequenced. Sequence analysis confirmed two separate outbreaks with no sign of sustained spread into the community. Analysis of the accessory genome between isolates from the two outbreaks revealed a S. aureus pathogenicity island containing enterotoxin C and enterotoxin-like L only in isolates from outbreak 2. Enterotoxin C and enterotoxin-like L carrying S. aureus are associated with bovine mastitis and our findings indicate that these may also be important virulence factors for human mastitis.
Highlights
Methicillin resistant Staphylococcus aureus (MRSA) is endemic in hospitals worldwide and an increasing challenge in the community
In the Capital Region of Denmark, all MRSA isolates are whole-genome sequenced and spa-types, multilocus sequence types (MLST) plus the presence or absence of the Panton-Valentine leukocidin (PVL) genes are reported to the clinicians (Bartels et al, 2015)
The remaining 17 MRSA positive cases were colonized without infection and there were no reports of mastitis in the five MRSA positive mothers
Summary
Methicillin resistant Staphylococcus aureus (MRSA) is endemic in hospitals worldwide and an increasing challenge in the community. The index case, in most outbreaks, is typically a neonate with a minor infection such as conjunctivitis, with the MRSA most likely acquired from a parent. In the Capital Region of Denmark, all MRSA isolates are whole-genome sequenced and spa-types, multilocus sequence types (MLST) plus the presence or absence of the Panton-Valentine leukocidin (PVL) genes are reported to the clinicians (Bartels et al, 2015). We analyzed the genomes of two seemingly similar neonatal MRSA outbreaks caused by MRSA t015:ST45. Mothers in the first outbreak (O1) were only colonized with MRSA whereas most mothers in the second outbreak (O2) suffered from mastitis caused by MRSA. Outbreaks of postpartum mastitis or post-partum breast abscesses are rarely reported (Saiman et al, 2003; Manoharan et al, 2012) cohort studies show that 8–20% of breastfeeding women may suffer from mastitis (Scott et al, 2008; Cullinane et al, 2015; Khanal et al, 2015)
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