Is ingestion of milk-associated bacteria by premature infants fed raw human milk controlled by routine bacteriologic screening?

Abstract

Expressed human milk is often used to feed premature infants. Raw milk contains bacteria which may be a source of infection. Milk banks have developed screening programs which combine periodic quantitative milk cultures with arbitrary rules specifying limits of bacterial concentration. It is unknown whether such programs succeed in preventing infants from being fed milk containing bacteria. At the Health Sciences Centre (Winnipeg, Manitoba, Canada), milk is screened once weekly. When a woman's milk is found to have excess bacteria, it is discarded only if she is an unrelated donor (as opposed to an infant's mother). To assess the effectiveness of this screening program, we determined the frequency at which infants fed raw human milk were exposed to milk-associated bacteria and compared the bacterial contents of donor and maternal milk. From February 1986 to April 1987, all human milk fed to 98 premature infants during the first 2 weeks of feeding (n = 10,128 feeds) was cultured quantitatively. Among study infants, 100% were exposed at least once to coagulase-negative staphylococci, 41% were exposed to Staphylococcus aureus, and 64% were exposed to gram-negative bacilli. The proportions of feeds containing bacteria and the quantities (log10 CFU [mean +/- standard deviation]) ingested per positive feed were: 39% and 5.9 +/- 0.5 for coagulase-negative staphylococci; 2.4% and 5.1 +/- 1.0 for S. aureus; and 5.2% and 4.8 +/- 1.1 for gram-negative bacilli. There were no adverse events attributable to ingestion of milk-associated bacteria. Milk coagulase-negative staphylococcal isolates were multiply antibiotic susceptible, whereas infant isolates were antibiotic resistant. Donor milk was significantly less likely than maternal milk to contain coagulase-negative staphylococcal species in any quantity (40 versus 93% of samples, respectively [P < 0.001]) or in concentrations exceeding 10(8) CFU/liter (3 versus 27% of samples, respectively [P < 0.0001]). There was no difference between milk from either source in terms of S. aureus or gram-negative bacterial content (4 to 6%). These results suggest that the Health Sciences Centre screening program is effective in limiting the number of harmless coagulase-negative staphylococcal species but has no impact on the quantity of potentially pathogenic bacteria ingested by premature infants. Implications for screening donor milk are discussed.

Inhibition of Staphylococcus aureus by the commensal bacteria of human milk

“…Staph. aureus, found in five milk samples, has been reported as a rare contaminant in breast milk of healthy lactating women also in previous studies (Caroll et al 1979;West et al 1979;Law et al 1989;El-Mohandes et al 1993a). Our study confirms the previous reports, that contamination of breast milk with Strep.…”

“…Coagulase-negative staphylococci, of which Staph. epidermidis was the predominant species, have been reported frequent also in previous studies (Caroll et al 1979;Eidelman and Szilagyi 1979;West et al 1979;Pittard et al 1985;Law et al 1989;El-Mohandes et al 1993b). These may have originated from the maternal skin during breastfeeding (West et al 1979).…”

“…The published studies of breast milk microbiota are focused on pathogenic bacteria, as possible sources of infection (Caroll et al 1979;Eidelman and Szilagyi 1979;Law et al 1989;Bingen et al 1992;El-Mohandes et al 1993a;Wright and Feeny 1998;Novak et al 2000;Le Thomas et al 2001).…”

Bacterial Contamination of Mechanically Extracted Breast Milk

“…Law et al found a reduced exposure to coagulase-negative staphylococci in routine screening without gaining a clinical advantage. 36 The quality of a test, in this case testing breast milk to prevent neonatal sepsis, is highly dependent on pretest probability and likelihood ratio of the test. As we could demonstrate, high bacterial concentration is frequently detected in breast milk samples of a collective that is not selected for neonatal sepsis or feeding intolerance.…”

A pilot study on nutrients, antimicrobial proteins, and bacteria in commerce‐free models for exchanging expressed human milk in the USA

“…During the study, 100% of infants were exposed to CoNS, 41% were exposed to S. aureus, and mean feeding bacteria levels for different species ranged from 4.7 log CFU/mL to 7.5 log CFU/mL. Law et al (1989) found no relationship between bacteria levels in expressed human milk and feeding intolerance or invasive infection, leading the authors to conclude that "results do not support attempts to define a safe upper limit for bacterial concentration in raw expressed milk." Similarly, Schanler et al (2011) cultured 813 human milk samples from 161 mothers of preterm infants and found that half of the samples were positive for CoNS, 5% were positive for S. aureus, and over 25% of samples had high bacteria levels defined as greater than 4.0 log CFU/ mL of gram-positive organisms or greater than 3.0 log CFU/ml of gram-negative organisms.…”