Characterisation of virulence genes in methicillin susceptible and resistant Staphylococcus aureus isolates from a paediatric population in a university hospital of Medellín, Colombia

Virulence and antibiotic resistance are significant determinants of the types of infections caused by Staphylococcus aureus and paediatric groups remain among the most commonly affected populations. The goal of this study was to characterise virulence genes of methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) strains isolated from a paediatric population of a Colombian University Hospital during 2009. Sixty MSSA and MRSA isolates were obtained from paediatric patients between zero-14 years. We identified the genes encoding virulence factors, which included Panton-Valentine leucocidine (PVL), staphylococcal enterotoxins A-E, exfoliative toxins A and B and toxic shock syndrome toxin 1. Typing of the staphylococcal chromosome cassette mec (SCCmec) was performed in MRSA strains. The virulence genes were more diverse and frequent in MSSA than in MRSA isolates (83% vs. 73%). MRSA strains harboured SCCmec types IVc (60%), I (30%), IVa (7%) and V (3%). SCCmec type IVc isolates frequently carried the PVL encoding genes and harboured virulence determinants resembling susceptible strains while SCCmec type I isolates were often negative. PVL was not exclusive to skin and soft tissue infections. As previously suggested, these differences in the distribution of virulence factor genes may be due to the fitness cost associated with methicillin resistance.

Slow clearance of Plasmodium vivax with chloroquine amongst children younger than six months of age in the Brazilian Amazon

Plasmodium vivax is the most widespread parasite causing malaria, being especially prevalent in the Americas and Southeast Asia. Children are one of the most affected populations, especially in highly endemic areas. However, there are few studies evaluating the therapeutic response of infants with vivax malaria. This study retrospectively evaluated the parasitaemia clearance in children diagnosed with vivax malaria during the first five days of exclusive treatment with chloroquine (CQ). Infants aged less than six months old had a significantly slower parasitaemia clearance time compared to the group of infants and children between six months and 12 years old (Kaplan-Meier survival analysis; Wilcoxon test; p = 0.004). The impaired clearance of parasitaemia in younger children with vivax malaria is shown for the first time in Latin America. It is speculated that CQ pharmacokinetics in young children with vivax malaria is distinct, but this specific population may also allow the detection of CQ-resistant parasites during follow-up, due to the lack of previous immunity.