Expression of Staphylokinase Gene S. aureus Strains Isolated from Breast Milk and Clinical Outcomes in Breastfed Infants

This study aimed to look for the presence of the immune evasion gene cluster in the strains of Staphylococcus aureus isolated from breast milk of women and to estimate their possible role in development of infant’s staphylococcal infections. Strains of S. aureus are isolated by bacteriological examination of breast milk in a hospital (24 strains) and an ambulatory (11 strains) basis. Breastfed infants had staphylococcal infections (42.9 %), intestinal infections (5.7 %), and respiratory infections (20 %), and 11 (31.4 %) infants were intestinal carriers of S. aureus. PCR analysis of 35 strains S. aureus was carried out to detect genes of staphylokinase (sak), inhibitor of the system of complement (scn), inhibitor of chemotaxis of leukocytes (chp), and β-hemolysin (hlb). Sak gene was found in 20 (57 %) S. aureus isolates. Scn, chp, and hlb genes in S. aureus isolates were not detected. Infants received breast milk infected with sak positive S. aureus strains more frequently had S. aureus intestinal colonization than infants who received breast milk infected with sak negative S. aureus (OR 4.5 (1.02; 20.30)). Presence of sak gene in S. aureus strains from breast milk was not associated with development of staphylococcal infection in infant (OR 1.2 (0.3–4.7)). In conclusion, sak is an important factor in avoiding immune defense by S. aureus strains in infected breast milk. Expression of sak gene by S. aureus in infected breast milk may be an important factor for S. aureus intestinal colonization of infants, but not the development of staphylococcal infections in breastfed infants.