Abstract
BackgroundAlthough Staphylococcus aureus is considered the main etiological agent of infectious mastitis, recent studies have suggested that coagulase-negative staphylococci (CNS) may also play an important role in such infections. The aims of this work were to isolate staphylococci from milk of women with lactational mastitis, to select and characterize the CNS isolates, and to compare such properties with those displayed by CNS strains isolated from milk of healthy women.ResultsThe milk of 30 women was collected and bacterial growth was noted in 27 of them, of which Staphylococcus epidermidis was isolated from 26 patients and S. aureus from 8. Among the 270 staphylococcal isolates recovered from milk of women with mastitis, 200 were identified as Staphylococcus epidermidis by phenotypic assays, species-specific PCR and PCR sequencing. They were typified by pulsed field gel electrophoresis (PFGE) genotyping. The PFGE profiles of the S. epidermidis strains were compared with those of 105 isolates from milk of healthy women. A representative of the 76 different PFGE profiles was selected to study the incidence of virulence factors and antibiotic resistance. The number of strains that contained the biofilm-related icaD gene and that showed resistance to oxacillin, erythromycin, clindamycin and mupirocin was significantly higher among the strains isolated from mastitic milk.ConclusionS. epidermidis may be a frequent but largely underrated cause of infectious mastitis in lactating women. The resistance to diverse antibiotics and a higher ability to form biofilms found among the strains isolated from milk of women suffering mastitis may explain the chronic and/or recurrent nature of this infectious condition.
Highlights
Staphylococcus aureus is considered the main etiological agent of infectious mastitis, recent studies have suggested that coagulase-negative staphylococci (CNS) may play an important role in such infections
We investigated the microbial diversity of breast milk in 20 women with lactational mastitis by culture-dependent and -independent techniques [4], and observed that staphylococci, mainly Staphylococcus epidermidis, seem to be the major microorganisms present in breast milk of women with infectious mastitis
The partial 16S rDNA sequences obtained from single isolates belonging to the species Staphylococcus aureus and Staphylococcus epidermidis were deposited in the EMBL nucleotide sequence database under accession numbers [EMBL: AM697666] and [EMBL: AM697667], respectively
Summary
Staphylococcus aureus is considered the main etiological agent of infectious mastitis, recent studies have suggested that coagulase-negative staphylococci (CNS) may play an important role in such infections. Staphylococcus aureus has been considered the most common etiological agent the cases in which microbiological analyses are performed are exceptional. Treatments with antibiotic or antifungal drugs are usually prescribed without knowing the etiology or the antibiotic susceptibility of the microorganism involved. This practice may lead to a worsening of the symptoms since strains that cause mastitis may exhibit multirresistance to drugs and/or form biofilms. A better knowledge of the main features of the bacterial species involved in the mastitic process would represent a great advance for the design of new strategies for the prevention and/or treatment of this condition
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