Identification of Emerging Human Mastitis Pathogens by MALDI-TOF and Assessment of Their Antibiotic Resistance Patterns

Abstract

Lactational mastitis constitutes one of the main causes of undesired weaning, depriving the mother–infant pair from the benefits of breastfeeding; therefore, this condition should be considered a relevant public health issue. The role of specific microorganisms remains unclear since human milk cultures and antibiotic susceptibility testing (AST) are not routinely performed, despite the fact that this would be key to ensure an early and effective diagnosis and treatment. The objective of this study was to describe the culturable microbial diversity in 647 milk samples from breastfeeding women with clinical symptoms of mastitis by Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF) VITEK MS technology and to analyze the antimicrobial susceptibility profiles of a collection of isolates from these samples by the VITEK 2 AST system. Staphylococcus epidermidis was the most common species isolated from mastitis samples (87.6%), while Staphylococcus aureus was detected in 22.1%. Streptococci constituted the second (68.6%) most prevalent bacterial group, with Streptococcus mitis/oralis, Streptococcus salivarius, and Streptococcus parasanguinis detected with frequencies of 40.8, 36.8, and 14.4%, respectively. The antibiotic susceptibility profiles of 642 staphylococcal isolates indicated a remarkable resistance to benzylpenicillin (88.3%) and erythromycin (67.3%) with differences between species. A high percentage of Staphylococcus isolates were resistant to at least one antibiotic (Staphylococcus hominis, 100%; S. epidermidis, 98.2%; S. aureus, 92.9%; Staphylococcus lugdunensis, 90.5%) and the percentage of multidrug-resistance (MDR) isolates was noticeable (S. hominis, 81%; S. epidermidis, 64.4%; S. aureus, 11.5%; S. lugdunensis, 10.5%). In relation to streptococcal isolates (n = 524), AST revealed high or moderate percentages of resistance to erythromycin (68.7%), benzylpenicillin (63.7%), ampicillin (51.5%), and tetracycline (30.8%). Antibiotic resistance to at least one antibiotic was detected in 97.6% of S. parasanguinis, 92.6% of S. salivarius, 83.3% of S. mitis/oralis, and 72.4% of Streptococcus vestibularis isolates. A significant number of MDR streptococcal isolates was also found (S. parasanguinis, 51.2%; S. salivarius, 39.3%; S. mitis/oralis, 34.6%; and S. vestibularis, 19%). The results highlight the important role of coagulase-negative staphylococci and streptococci as human mastitis-causing agents. Moreover, the high rates of antimicrobial resistance among these microorganisms must be contemplated as an issue of clinical relevance in relation to treatment options.

Bovine mastitis bacteria resolved by MALDI-TOF mass spectrometry

“…The MALDI-TOF technique is also gaining ground for bacteria of veterinary importance, originating from bovine, ovine, porcine, and avian sources and, to a lesser extent, of canine, caprine, and equine provenance (Randall et al, 2015). Several researchers have applied the technique to bacterial groups causing bovine mastitis, such as group B streptococci (Barreiro et al, 2010), group D streptococci (Werner et al, 2012), non-aureus staphylococci (Barreiro et al, 2010;Cameron et al, 2017;Mahmmod et al, 2018), Enterobacteriaceae (Rodrigues et al, 2017;Savage et al, 2017), and even lactational mastitis in humans (Marín et al, 2017). Classical phenotypical and biochemical tests have limitations-they typically take from one to several days to perform and read, and misidentification of bacteria is not uncommon (Bes et al, 2000;Taponen et al, 2006).…”

Bovine milk transcriptome analysis reveals microRNAs and RNU2 involved in mastitis

“…Mastitis can be classified as either noninfectious or infectious. Infectious mastitis is caused by bacterial invasion through the teat cistern or a fissure in the nipple , and Staphylococcus and Streptococcus are common mastitis pathogens in both humans and cows , suggesting that infectious mastitis shares some biological similarities among mammalian species.…”

<p>Abscess Drainage with or Without Antibiotics in Lactational Breast Abscess: Study Protocol for a Randomized Controlled Trial</p>

“…To the best of our knowledge, very few well-powered studies have so far focused explicitly on the impact of routine antibiotic usage for lactational breast abscess. 20 Previous studies have showed that Staphylococcus aureus, a frequent causative pathogen, is diversely resistant to antibiotics, 26,27 while in clinical practice, antibiotics are empirically administrated in many cases without definite etiology of infection, or even without the report of antibiotic sensitivity test. 26,27 This might worsen the condition of drug resistance and repeated courses might even increase the risk for opportunistic infection, such as Candida.…”

“…20 Previous studies have showed that Staphylococcus aureus, a frequent causative pathogen, is diversely resistant to antibiotics, 26,27 while in clinical practice, antibiotics are empirically administrated in many cases without definite etiology of infection, or even without the report of antibiotic sensitivity test. 26,27 This might worsen the condition of drug resistance and repeated courses might even increase the risk for opportunistic infection, such as Candida. [28][29][30] On account of inherent limitations of the studies available in the literature, well-designed studies on a larger scale are thus warranted to properly assess the role of antibiotics for the treatment of breast abscess in breastfeeding women.…”