Gram‐Positive Bacteria Contamination in a Brazilian Mangrove: An Imminent Risk

Mangroves, essential for ecological stability, are increasingly threatened by anthropogenic activities. This study assessed water quality in the mangroves of Itamaracá Island (Brazil), focusing on multidrug‐resistant (MDR) microorganisms, biofilm formation, and metal contamination. Trace elements were quantified by inductively coupled plasma optical emission spectrometry (ICP‐OES) and bacterial isolates identified via matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS). All analyses were performed in triplicate to ensure analytical reliability. Results revealed critical sulfide levels, exceeding legal limits by approximately 270 000‐fold, along with aluminum (up to 160% above limit) and boron (up to 540% above limit) contamination. Copper (Cu) also exceeded standard limits at point P1 (0.021 mg L − 1 ), remaining near the threshold at P2 and P7. Thirty‐seven Gram‐positive isolates were identified, predominantly Bacillus pumilus (48.6%) and Staphylococcus ureilyticus (24.3%). Notably, 100% of the isolates were classified as MDR, displaying high resistance to penicillin and oxacillin. Furthermore, 91.9% exhibited biofilm‐forming capacity, with 48.6% categorized as strong formers. Seven Gram‐positive bacterial species were identified: B. pumilus , Bacillus altitudinis , S. ureilyticus , Staphylococcus cohnii , Staphylococcus hominis , Priestia megaterium , and Priestia endophytica . All isolates (100%) were MDR, and 48.6% demonstrated strong biofilm‐forming capacity. This pioneering study reveals, for the first time in Itamaracá Island, that mangrove ecosystems serve as reservoirs of MDR Gram‐positive bacteria. This co‐occurrence of metal contamination and resistant pathogens suggests heavy metals may drive antimicrobial resistance in coastal ecosystems, posing significant risks to vulnerable human populations and highlighting the urgent need for integrated (One Health) surveillance.