Abstract
Recent reports have shown that food‐borne or commensal bacteria can function as reservoirs of antibiotic resistance. However, the antibiotic susceptibility of bacterial isolates of most milk samples or the total bacterial counts (TBC) in human milk from healthy donors, are not fully understood in Taiwan. Thus, five healthy mothers were randomly recruited each month, and totally 30 mothers without any symptoms of infection were recruited over 6 months. Milk samples were then harvested and analyzed immediately after collection. The antibiotic susceptibility was analyzed in bacteria isolated from milk samples using nine clinically relevant antibiotics, such as oxacillin, ampicillin, cephalothin, amoxicillin, ciprofloxacin, erythromycin, clindamycin, gentamicin, and oxytetracycline. The Staphylococcus strains (48 isolates) found in milk resisted to 48.6 ± 20.1% selected antibiotics. Streptococcus‐related isolates (8 isolates) exhibited resistance to 41.7 ± 26.4% selected antibiotics. Acinetobacter isolates (5 isolates) were resistant to 66.7 ± 13.6% antibiotics, and Enterococcus isolates (5 isolates) were resistant to 73.3 ± 6.1% tested antibiotics. Rothia‐related isolates (4 isolates) were resisted to 58.2 ± 31.9% of tested antibiotics. In contrast, Corynebacterium isolates (5 isolates) were sensitive to 66%–100% of selected antibiotics. Furthermore, the TBC ranged from 40 to 710,000 CFU/ml, implying a wide spectrum of bacteria in milk from healthy mothers. Despite this, all milk donors were healthy during sampling, and they did not show any symptoms related to mastitis or subclinical mastitis. According to the previously described TBC criteria for the use of donated human milk, only 73% of the current milk samples could be accepted for the milk bank. In conclusion, the majority of the isolated bacterial strains from current human milk samples are multiresistant strains. In milk samples for preterm infants or milk banks, higher TBC levels or potentially antibiotic‐resistant bacteria in some milk samples have supported people using approaches to disinfect human milk partially.
Highlights
Human milk is generally accepted to be the ideal food for babies, and it is a rich fluid that contains essential nutrients, such as various bioactive compounds, proteins, carbohydrates, immune cells, and immunoglobulins, which can provide sufficient nutritional and protective requirements for infants (Petherick, 2010; Walker, 2010)
Several recent reports have shown that food-borne or commensal bacteria can function as reservoirs of antibiotic resistance genes, which are similar to those found in pathogenic bacterial strains (Devirgiliis, Zinno, & Perozzi, 2013; Mathur & Singh, 2005; White, Zhao, Simjee, Wagner, & McDermott, 2002)
Another study demonstrated that several Enterococcus faecalis and E. faecium isolates from human milk contained virulence genes and antibiotic resistance that could serve as a reservoir of antibiotic resistance in offspring (Jimenez et al, 2013)
Summary
Human milk is generally accepted to be the ideal food for babies, and it is a rich fluid that contains essential nutrients, such as various bioactive compounds, proteins, carbohydrates, immune cells, and immunoglobulins, which can provide sufficient nutritional and protective requirements for infants (Petherick, 2010; Walker, 2010). In our pilot study in Taiwan, most bacteria isolated from human milk of 19 healthy donors displayed mild to strong antibiotic resistance. Only 19 healthy donors had been recruited in this pilot study, and the antibiotic susceptibility of bacterial isolates of most human milk samples are not fully understood in Taiwan.
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