Molecular analysis of community-acquired methicillin-susceptible and resistant Staphylococcus aureus isolates recovered from bacteraemic and osteomyelitis infections in children from Tunisia

Thirty-six children (27 boys, nine girls) that fulfilled CDC criteria for community-acquired infections were diagnosed with bacteraemia and/or osteomyelitis caused by Staphylococcus aureus during an 18-month period (2006–2008). Antibiotic susceptibility was determined by an agar dilution method. SCCmec type, carriage of pvl genes, agr type and spa-typing were determined using specific PCR protocols. Clonal relatedness was examined by pulsed field gel electrophoresis-SmaI and mutilocus sequence typing techniques. From the 36 isolates, eight (22%) corresponded to methicillin-resistant Staphylococcus aureus (MRSA) -t044/042-CC80/CC5-IVc-pvl⁺-agrIII/II. The highest genetic diversity was observed among the 28 community-acquired methicillin-susceptible S. aureus (CA-MSSA) isolates: 22 spa-variants that also grouped by multilocus sequence typing in CC1, CC5, CC6, CC8, CC30, CC80, CC97 and the singletons ST464, ST1467, ST1468 and ST1469. The pvl genes were detected in all eight CA-MRSA isolates and in eight CA-MSSA isolates (28%), being significantly more frequent among isolates causing osteoarticular infection (11 of 12, 92%) than in the bacteraemic isolates (six of 24, 25%). Based on patients’ age, three groups were considered: newborns, infants and children. Bacteraemia was diagnosed in all newborns and infants, whereas in 42% of the children group osteomyelitis was the unique presentation. In most cases, the portal of entry was either the skin or unknown. In general, favourable outcome was observed, except in four cases—three of whom had severe complications and one died. In summary, we analysed the epidemiological and genetic background of community-acquired staphylococcal strains causing bacteraemic and/or osteomyelitis infections in children from Tunisia, describing three new sequence types and one novel spa type.