Staphylococcus epidermidis strains isolated from breast milk of women suffering infectious mastitis: Potential virulence traits and resistance to antibiotics

Dpt. Nutrición, Bromatología y Tecnología de Alimentos, Universidad Complutense de Madrid, 28040 Madrid, Spain.
BMC Microbiology (Impact Factor: 2.73). 02/2009; 9(1):82. DOI: 10.1186/1471-2180-9-82
Source: PubMed


Although 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.
The 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.
S. 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.

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    • "As indicated in the introduction section, some isolates of Staphylococcus or Enterococcus in milk from healthy donors exert resistance to various antibiotics[3,7,11]. In this study, a total of 22 bacterial isolates of StaphylococcusTable 3) were also evaluated for their susceptibility to several antibiotics. "
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    ABSTRACT: Recent studies have focused on foodborne or commensal bacteria as vehicles of antibiotic resistance. However, the antibiotic resistance of milk bacteria from healthy donors is still vague in Taiwan. For this purpose, human milk samples were obtained from randomly recruited 19 healthy women between 3 and 360 days post-partum. Antibiotic susceptibility profile of bacteria from milk samples was determined. About 20 bacterial species were isolated from milk samples including Staphylococcus (6 species), Streptococcus (4 species), Enterococcus (2 species), Lactobacillus (1 species), and bacteria belonging to other genera (7 species). Some opportunistic or potentially pathogenic bacteria including Kluyvera ascorbata, Klebsiella oxytoca, Klebsiella pneumoniae, Acinetobacter baumannii, Actinomyces bovis, and Staphylococcus aureus were also isolated. Intriguingly, Staphylococcus isolates (22 strains) were resistant to 2–8 of 8 antibiotics, while Streptococcus isolates (3 strains) were resistant to 3–7 of 9 antibiotics, and members of the genus Enterococcus (5 strains) were resistant to 3–8 of 9 antibiotics. Notably, Staphylococcus lugdunensis, S. aureus, Streptococcus parasanguinis, Streptococcus pneumonia, and Enterococcus faecalis were resistant to vancomycin, which is considered as the last-resort antibiotic. Therefore, this study shows that most bacterial strains in human milk demonstrate mild to strong antibiotic resistance. Whether commensal bacteria in milk could serve as vehicles of antibiotic resistance should be further investigated.
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    • "Isolates were coded according to their origin (the prefix M for milk and H for hand swabs). S. aureus Sa9, isolated from mastitis milk (García et al. 2007), and S. aureus ATCC 14458 were used as positive controls; Staphylococcus epidermidis F12 was used as a negative control (Delgado et al. 2009). All isolates were routinely cultured in tryptic soy broth (TSB, Scharlab) or in tryptic soy agar (TSA). "
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    ABSTRACT: Staphylococcus aureus is involved in human and animal infections. Because of mastitis in dairy cows, milk can be contaminated by enterotoxin-producing strains, which constitutes a food poisoning risk. Animal handlers can be asymptomatic carriers, becoming an additional source of contamination. This research aims to improve our understanding of Staphylococcus aureus in small-scale dairy systems in central Mexico. Samples were taken in 12 dairy farms and included composite milk (from the four teats) and hand swabs from each farmer. Of 149 presumptive S. aureus isolates, 102 (84 from cows; 18 from farmers) were accurately identified by molecular methods. The genetic variability of 43 randomly selected isolates was determined by RAPD-PCR, and of these, 38 were genetically distinct (≤90% similarity). Of the 38 distinct isolates, 78.9% harboured at least one enterotoxin-encoding gene (staphylococcal enterotoxin a (sea)-sed, seg, and/or sei), whereas 100% carried icaA-icaD genes and 28% carried the bap gene. The latter three genes are all involved in biofilm formation. Susceptibility to antibiotics, bacteriocins, and bacteriophages, was also assayed; 36.8% of isolates were resistant to penicillin G. Only five isolates were resistant to bacteriocins nisin A and AS-48, and phiPLA-RODI was the most effective bacteriophage, infecting all of the isolates. These results support the need to adopt management strategies to improve hygiene and milking practices in order to enhance herd health and diminish the risk of food poisoning associated with the consumption of raw milk cheese.
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    • "In this sense, a negative association between Caesarean delivery and breastfeeding exists because postoperative care routines delay the onset of lactation, disrupt mother-infant interaction and inhibit infant suckling [20]. Peripartum antibiotherapy has emerged as a strong risk factor for human mastitis because it induces the selection for antibiotic-resistant bacteria in the mammary gland and the elimination of potential competitors [21,22]. Antibiotics also affect vaginal and intestinal microbiota of the mother [22] and the development of intestinal microbiota in the infant [23]. "
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    ABSTRACT: Background The purpose of this study was to identify potential predisposing factors associated with human infectious mastitis. Methods We conducted a case–control study among breastfeeding women, with 368 cases (women with mastitis) and 148 controls. Data were collected by a questionnaire designed to obtain retrospective information about several factors related to medical history of mother and infant, different aspects of pregnancy, delivery and postpartum, and breastfeeding practices that could be involved in mastitis. Bivariate analyses and multivariate logistic regression model were used to examine the relationship between mastitis and these factors. Results The variables significantly- and independently-associated with mastitis were cracked nipples (P < 0.0001), oral antibiotics during breastfeeding (P < 0.0001), breast pumps (P < 0.0001), topical antifungal medication during breastfeeding (P = 0.0009), mastitis in previous lactations (P = 0.0014), breast milk coming in later than 24 h postpartum (P = 0.0016), history of mastitis in the family (P = 0.0028), mother-infant separation longer than 24 h (P = 0.0027), cream on nipples (P = 0.0228) and throat infection (P = 0.0224). Conclusions Valuable factors related to an increased risk of infectious mastitis have been identified. This knowledge will allow practitioners to provide appropriate management advice about modifiable risk factors, such as the use of pumps or inappropriate medication. They also could identify before delivery those women at an increased risk of developing mastitis, such as those having a familial history of mastitis, and thus develop strategies to prevent this condition.
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