Antibiotic resistance is widespread in clinical settings, indicating a serious problem with infectious disease treatment. Novel strategies such as using natural products derived from microbes are being explored, generating increased research interest to address this issue. Here, the antimicrobial property of gut-associated Bacillus species against multidrug-resistant (MDR) strains; methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli producing extended-spectrum beta-lactamase (EsβL E. coli), and Pseudomonas aeruginosa producing metallo beta-lactamase (MβL P.aeruginosa) was evaluated using a cross-streak method and agar diffusion assay. The Bacillus isolates inhibited MRSA and ESβL E. coli with an average zone of inhibition of 9.57 ± 33.40 mm and 5.07 ± 32.69 mm, respectively, in the cross-streak method. The cell-free supernatant (CFS) of ten Bacillus species demonstrated anti-MRSA activity but was ineffective against ESβL E. coli and MβL P. aeruginosa. The relative enzyme activities of ten Bacillus isolates were determined in vitro, and amylase, caseinase, cellulase, lipase, and gelatinase production were confirmed. Isolates were identified as Bacillus siamensis, Bacillus velezensis, and Bacillus subtilis through biochemical tests and 16s rRNA sequence analysis. Minimum inhibitory concentrations (MICs) of the CFSs against MRSA range is between 12.5 and 25%. Bacillus species isolated from fish and snail guts exhibited antibacterial activity against MRSA. Therefore, it is imperative to confirm the presence of anti-MRSA active compounds in Bacillus CFS and characterize them further to determine their suitability for antimicrobial drug development.

• Ahmad, B., Nigar, S., Shah, S. S. A., Bashir, S. J., Ali, J., Yousaf, S., & Bangash, J. A. (2013). Isolation and identification of cellulose degrading bacteria from municipal waste and their screening for potential antimicrobial activity. World Applied Science Journal, 27(11), 1420-1426. https://doi.org/10.5829/idosi.wasj.2013.27.11.81162

• Alikhani, A., Babamahmoodi, F., Alizadegan, L. F., Shojaeefar, A., & Babamahmoodi, A. (2015). Minimal inhibitory concentration of microorganisms causing surgical site infection in referral hospitals in North of Iran, 2011-2012. Caspian Journal of Internal Medicine, 6(1), 34-39.

• Altschul, S. F., Madden, T. L., Schäffer, A. A., Zhang, J., Zhang, Z., Miller, W., & Lipman, D. J. (1997). Gapped BLAST and PSI-BLAST: A new generation of protein database search programs. Nucleic Acids Research, 25(17), 3389-3402. https://doi.org/10.1093/nar/25.17.3389

• Aminnezhad, S., Kermanshahi, R. K., & Ranjbar, R. (2015). Evaluation of synergistic interactions between cell-free supernatant of Lactobacillus strains and Amikacin and Genetamicin against Pseudomonas aeruginosa. Jundishapur Journal of Microbiology, 8(4), Article e16592. https://doi.org/10.5812/jjm.8(4)2015.16592

• Aslim, B., & Saglam, N., & Beyatli, Y. (2002). Determination of some properties of Bacillus isolated from soil. Turkish Journal of Biology, 26(1), 41-48.

• Aunpad, R., & Na-Bangchang, K. (2007). Pumilicin 4, a novel Bacteriocin with anti-MRSA and anti-VRE activity produced by newly isolated bacteria Bacillus pumilus strain WAPB4. Current Microbiology, 55(4), 308-313. https://doi.org/10.1007/s00284-006-0632-2

• Bartholomew, J. W., & Mittwer, T. (1952). The gram stain. Bacteriological Reviews, 16(1), 1-29. https://doi.org/10.1128/br.16.1.1-29.1952

• Bäumler, A. J., & Sperandio, V. (2016). Interactions between the microbiota and pathogenic bacteria in the gut. Nature, 535(7610), 85-93. http://doi.org/10.1038/nature18849

• Bell, S. C., & Grundy, W. E. (1968). Preparation of agar wells for antibiotic assay. Applied Microbiology, 16(10), 1611-1612. https://doi.org/10.1128/am.16.10.1611-1612.1968

• Bergen, P. J., Bulitta, J. B., Forrest, A., Tsuji, B. T., Li, J., & Nation, R. L. (2010). Pharmacokinetic/Pharmacodynamic investigation of colistin against Pseudomonas aeruginosa using an in vitro model. Antimicrobial Agents and Chemotherapy, 54(9), 3783-3789. https://doi.org/10.1128/aac.00903-09

• Bernard, K. A. (2015). General approaches to the identification of aerobic gram-positive rods. In Manual of Clinical Microbiology (pp. 437-440). ASM Press. https://doi.org/10.1128/9781555817381.ch25

• Besednova, N. N., Andryukov, B. G., Zaporozhets, T. S., Kryzhanovsky, S. P., Kuznetsova, T. A., Fedyanina, L. N., Makarenkova, I. D., & Zvyagintseva, T. N. (2020). Algae polyphenolic compounds and modern antibacterial strategies: Current achievements and immediate prospects. In Biomedicines (Vol. 8, Issue 9, p. 342). MDPI AG. https://doi.org/10.3390/biomedicines8090342

• Bonnet, R. (2003). Growing group of extended-spectrum -lactamases: The CTX-M enzymes. Antimicrobial Agents and Chemotherapy, 48(1), 1-14. https://doi.org/10.1128/aac.48.1.1-14.2004

• Branda, S. S., González-Pastor, J. E., Ben-Yehuda, S., Losick, R., & Kolter, R. (2001). Fruiting body formation by Bacillus subtilis. Proceedings of the National Academy of Sciences of the United States of America, 98(20), 11621-11626. http://doi.org/10.1073/pnas.191384198.

• Cantarel, B. L., Coutinho, P. M., Rancurel, C., Bernard, T., Lombard, V., & Henrissat, B. (2009). The carbohydrate-active enzymes database (CAZy): An expert resource for glycogenomics. In Nucleic Acids Research (Vol. 37, pp. D233-D238). Oxford University Press (OUP). https://doi.org/10.1093/nar/gkn663

• Carlsson, N. O., & Lacoursière, J. O. (2005). Herbivory on aquatic vascular plants by the introduced golden apple snail (Pomacea canaliculata) in Lao PDR. Biological Invasions, 7(2), 233-241. https://doi.org/10.1007/s10530-004-0741-4

• Caulier, S., Nannan, C., Gillis, A., Licciardi, F., Bragard, C., & Mahillon, J. (2019). Overview of the antimicrobial compounds produced by members of the Bacillus subtilis group. In Frontiers in Microbiology (Vol. 10). Frontiers Media SA. https://doi.org/10.3389/fmicb.2019.00302

• Chada, V. G. R., Sanstad, E. A., Wang, R., & Driks, A. (2003). Morphogenesis of Bacillus spore surfaces. Journal of Bacteriology, 185(21), 6255-6261. http://doi.org/10.1128/JB.185.21.6255-6261.2003

• Chalasani, A. G., Dhanarajan, G., Nema, S., Sen, R., & Roy, U. (2015). An antimicrobial metabolite from Bacillus sp.: Significant activity against pathogenic bacteria including multidrug-resistant clinical strains. Frontiers in Microbiology, 6, Article 1335. https://doi.org/10.3389/fmicb.2015.01335

• CLSI. (2009). M100: Performance standards for antimicrobial susceptibility testing (32 Ed.). Clinical and Laboratory Standards Institute. https://clsi.org/standards/products/microbiology/documents/m100

• CLSI. (2012). Performance standards for antimicrobial disk susceptibility tests; Approved standard - 11th edition (Vol. 32, No. 1). Clinical and Laboratory Standards Institute.

• Cowie, R. H. (2002). Apple snails (Ampullariidae) as agricultural pests: Their biology, impacts and management. In Molluscs as Crop Pests (pp. 145-192). CABI. https://doi.org/10.1079/9780851993201.0145

• Culligan, E. P., Sleator, R. D., Marchesi, J. R., & Hill, C. (2013). Metagenomics and novel gene discovery. Virulence, 5(3), 399-412. https://doi.org/10.4161/viru.27208

• Davies, J., & Davies, D. (2010). Origins and evolution of antibiotic resistance. Microbiology and Molecular Biology Reviews, 74(3), 417-433. https://doi.org/10.1128/mmbr.00016-10

• de Jesus, E. C., Arpini, C. M., Martins, J. D. L., da Silva, C. B. B., Castheloge, V. D., Clemente-Carvalho, R. B. G., & Gomes, L. C. (2016). Isolation and evaluation of autochthonous Bacillus subtilis strains as probiotics for fat snook (Centropomus parallelus Poey, 1860). Journal of Applied Ichthyology, 32(4), 682-686. https://doi.org/10.1111/jai.13080

• Dias, D. A., Urban, S., & Roessner, U. (2012). A historical overview of natural products in drug discovery. Metabolites, 2(2), 303-336. https://doi.org/10.3390/metabo2020303

• Doron, S., & Davidson, L. E. (2011). Antimicrobial stewardship. In Mayo Clinic Proceedings (Vol. 86, Issue 11, pp. 1113-1123). Elsevier. https://doi.org/10.4065/mcp.2011.0358

• Driks, A. (2002). Maximum shields: The assembly and function of the bacterial spore coat. Trends in Microbiology, 10(6), 251-254. https://doi.org/10.1016/s0966-842x(02)02373-9

• Duary, R. K., Rajput, Y. S., Batish, V. K., & Grover, S. (2011). Assessing the adhesion of putative indigenous probiotic lactobacilli to human colonic epithelial cells. The Indian Journal of Medical Research, 134(5), 664-671. http://doi.org/10.4103/0971-5916.90992

• Eckburg, P. B., Bik, E. M., Bernstein, C. N., Purdom, E., Dethlefsen, L., Sargent, M., Gill, S. R., Nelson, K. E., & Relman, D. A. (2005). Diversity of the human intestinal microbial flora. Science, 308(5728), 1635-1638. http://doi.org/10.1126/science.1110591

• Epand, R. M., Walker, C., Epand, R. F., & Magarvey, N. A. (2016). Molecular mechanisms of membrane targeting antibiotics. In Biochimica et Biophysica Acta (BBA) - Biomembranes (Vol. 1858, Issue 5, pp. 980-987). Elsevier. https://doi.org/10.1016/j.bbamem.2015.10.018

• Fuego, B. N., Romano, K. G., Pinlac, C. D., & Lirio, G. A. C. (2021). Evaluation of the antimicrobial activity of endophytic fungus isolated from Cocos nucifera (L.) cotyledon against medically-important pathogens. Journal of Biosciences and Medicines, 9(01), 86-97. https://doi.org/10.4236/jbm.2021.91007

• Ghosh, K., Banerjee, S., Moon, U. M., Khan, H. A., & Dutta, D. (2017). Evaluation of gut associated extracellular enzyme-producing and pathogen inhibitory microbial community as potential probiotics in Nile Tilapia, Oreochromis niloticus. International Journal of Aquaculture, 7(23), 143-158. https://doi.org/10.5376/ija.2017.07.0023

• Giatsis, C., Sipkema, D., Smidt, H., Verreth, J., & Verdegem, M. (2014). The colonization dynamics of the gut microbiota in Tilapia larvae. PLoS ONE, 9(7), Article e103641. http://doi.org/10.1371/journal.pone.0103641

• Godoy, M. S., Castro-Vasquez, A., & Vega, I. A. (2013). Endosymbiotic and host proteases in the digestive tract of the invasive snail Pomacea canaliculata: Diversity, origin and characterization. PLoS ONE, 8(6), Article e66689. https://doi.org/10.1371/journal.pone.0066689

• Gorbach, S. L. (1996). Microbiology of the gastrointestinal tract. In S. Baron (Ed.), Medical Microbiology (4th Ed., pp. 33-45). University of Texas Medical Branch at Galveston.

• Hao, H., Cheng, G., Iqbal, Z., Ai, X., Hussain, H. I., Huang, L., Dai, M., Wang, Y., Liu, Z., & Yuan, Z. (2014). Benefits and risks of antimicrobial use in food-producing animals. Frontiers in Microbiology, 5, Article 288. https://doi.org/10.3389/fmicb.2014.00288

• Hassan, M. A., Haroun, B. M., Amara, A. A., & Serour, E. A. (2013). Production and characterization of keratinolytic protease from new wool-degrading Bacillus species isolated from Egyptian ecosystem. BioMed Research International, 2013, Article 175012. https://doi.org/10.1155/2013/175012

• Hengstmann, U., Chin, K., Janssen, P. H., & Liesack, W. (1999). Comparative phylogenetic assignment of environmental sequences of genes encoding 16S rRNA and numerically abundant culturable bacteria from anoxic rice paddy soil. Applied and Environmental Microbiology, 5(11), 5050-5058. https://doi.org/10.1128/AEM.65.11.5050-5058.1999

• Hiergeist, A., Gläsner, J., Reischl, U., & Gessner, A. (2015). Analyses of intestinal microbiota: Culture versus sequencing. ILAR Journal, 56(2), 228-240. https://doi.org/10.1093/ilar/ilv017

• Hooper, L. V., & Macpherson, A. J. (2010). Immune adaptations that maintain homeostasis with the intestinal microbiota. Nature Reviews Immunology, 10(3), 159-169. https://doi.org/10.1038/nri2710

• Horng, Y. B., Yu, Y. H., Dybus, A., Hsiao, F. S. H., & Cheng, Y. H. (2019). Antibacterial activity of Bacillus species-derived surfactin on Brachyspira hyodysenteriae and Clostridium perfringens. AMB Express, 9, Article 188. https://doi.org/10.1186/s13568-019-0914-2

• Hu, Y., Liu, A., Vaudrey, J., Vaiciunaite, B., Moigboi, C., McTavish, S. M., Kearns, A., & Coates, A. (2015). Combinations of β-lactam or aminoglycoside antibiotics with plectasin are synergistic against methicillin-sensitive and methicillin-resistant Staphylococcus aureus. PLOS ONE, 10(2), Article e0117664. https://doi.org/10.1371/journal.pone.0117664

• Janda, J. M., & Abbott, S. L. (2007). 16S rRNA gene sequencing for bacterial identification in the diagnostic laboratory: Pluses, perils, and pitfalls. Journal of Clinical Microbiology, 45(9), 2761-2764. https://doi.org/10.1128/JCM.01228-07

• Jeyanthi, V., & Velusamy, P. (2016). Anti-methicillin Resistant Staphylococcus aureus compound isolation from halophilic Bacillus amyloliquefaciens MHB1 and determination of its mode of action using electron microscope and flow cytometry analysis. Indian Journal of Microbiology, 56(2), 148-157. https://doi.org/10.1007/s12088-016-0566-8

• Jochumsen, N., Marvig, R. L., Damkiær, S., Jensen, R. L., Paulander, W., Molin, S., Jelsbak, L., & Folkesson, A. (2016). The evolution of antimicrobial peptide resistance in Pseudomonas aeruginosa is shaped by strong epistatic interactions. Nature Communications, 7, Article 13002. https://doi.org/10.1038/ncomms13002

• Johansen, H. K., Moskowitz, S. M., Ciofu, O., Pressler, T., & Høiby, N. (2008). Spread of colistin resistant non-mucoid Pseudomonas aeruginosa among chronically infected Danish cystic fibrosis patients. Journal of Cystic Fibrosis, 7(5), 391-397. https://doi.org/10.1016/j.jcf.2008.02.003

• Kabir, S. M. L. (2009). The role of probiotics in the poultry industry. International Journal of Molecular Sciences, 10(8), 3531-3546. https://doi.org/10.3390/ijms10083531

• Kıvanç, S. A., Takım, M., Kıvanç, M., & Güllülü, G. (2014). Bacillus spp. isolated from the conjunctiva and their potential antimicrobial activity against other eye pathogens. African Health Sciences, 14(2), 364-371. http://doi.org/10.4314/ahs.v14i2.11

• Klančnik, A., Piskernik, S., Jeršek, B., & Možina, S. S. (2010). Evaluation of diffusion and dilution methods to determine the antibacterial activity of plant extracts. Journal of Microbiological Methods, 81(2), 121-126. https://doi.org/10.1016/j.mimet.2010.02.004

• Koleva, Z., Dedov, I., Kizheva, J., Lipovanska, R., Moncheva, P., & Hristova, P. (2014). Lactic acid microflora of the gut of snail Cornu aspersum. Biotechnology & Biotechnological Equipment, 28(4), 627-634. https://doi.org/10.1080/13102818.2014.947071

• Kong, W., Huang, C., Tang, Y., Zhang, D., Wu, Z., & Chen, X. (2017). Effect of Bacillus subtilis on Aeromonas hydrophila-induced intestinal mucosal barrier function damage and inflammation in grass carp (Ctenopharyngodon idella). Scientific Reports, 7, Article 1588. https://doi.org/10.1038/s41598-017-01336-9

• Kumar, V. M., Thippeswamy, B., & Shivakumar, C. (2013). Evaluation of antimicrobial activity of Bacillus cereus and Bacillus pumillus metabolites against human pathogens. International Journal of Current Pharmaceutical Review and Research, 4, 47-60.

• Lach, L., Britton, D. K., Rundell, R. J., & Cowie, R. H. (2000). Biological Invasions, 2(4), 279-288. https://doi.org/10.1023/a:1011461029986

• Lagier, J. C., Million, M., Hugon, P., Armougom, F., & Raoult, D. (2012). Human gut microbiota: Repertoire and variations. Frontiers in Cellular and Infection Microbiology, 2, Article 136. http://doi.org/10.3389/fcimb.2012.00136

• Lane, D. J. (1991). 16S/23S rRNA sequencing. In E. Stackebrandt & M. Goodfellow (Ed.), Nucleic acid techniques in bacterial systematics (pp. 115-175). John Wiley & Sons.

• Latorre, J. D., Hernandez-Velasco, X., Wolfenden, R. E., Vicente, J. L., Wolfenden, A. D., Menconi, A., Bielke, L. R., Hargis, B. M., & Tellez, G. (2016). Evaluation and selection of Bacillus species based on enzyme production, antimicrobial activity, and biofilm synthesis as direct-fed microbial candidates for poultry. Frontiers in Veterinary Science, 3, Article 95. https://doi.org/10.3389/fvets.2016.00095

• Lee, P. Y., Costumbrado, J., Hsu, C. Y., & Kim, Y. H. (2012). Agarose gel electrophoresis for the separation of DNA fragments. Journal of Visualized Experiments, (62), Article e3923. https://doi.org/10.3791/3923.

• Leelavatch, V., Chantharas, K., Warong, T., & Mapatsa, P. (2011). High potential probiotic Bacillus species from gastro-intestinal tract of Nile Tilapia (Oreochromis niloticus). Biotechnology, 10(6), 498-505. https://doi.org/10.3923/biotech.2011.498.505.

• Lertcanawanichakul, M., & Sawangnop, S. (2011). A comparison of two methods used for measuring the antagonistic activity of Bacillus species. Walailak Journal of Science and Technology (WJST), 5(2), 161-171.

• Ley, R. E., Peterson, D. A., & Gordon, J. I. (2006). Ecological and evolutionary forces shaping microbial diversity in the human intestine. Cell, 124(4), 837-848. https://doi.org/10.1016/j.cell.2006.02.017

• Lirio, G. A. C., De Leon, J. A. A., & Villafuerte, A. G. (2018). Antimicrobial activity of epidermal mucus from top aquaculture fish species against medically-important pathogens. Walailak Journal of Science and Technology (WJST), 16(5), 329-340. https://doi.org/10.48048/wjst.2019.6287

• Lirio, G. A. C., Suavengco, A. B. A., Antonio, K. C. C., Aggarao, J. E. P., & Mamansag, J. G. (2020). Evaluation of the biocontrol potential of endophytic bacteria isolated from Coffea liberica (w. Bull ex hiern) against brown eyespot-causing fungal phytopathogen. Malaysian Society for Microbiology. https://doi.org/10.21161/mjm.200778

• Lodge, D. M., Cronin, G., Van Donk, E., & Froelich, A. J. (1998). Impact of herbivory on plant standing crop: Comparisons among biomes between vascular and nonvascular plants, and among freshwater herbivore taxa. In E. Jeppesen (Ed.), The Structuring Role of Submerged Macrophytes in Lakes (pp. 149-174). Springer.

• Löffler, B., Hussain, M., Grundmeier, M., Brück, M., Holzinger, D., Varga, G., Roth, J., Kahl, B. C., Proctor, R. A., & Peters, G. (2010). Staphylococcus aureus Panton-Valentine Leukocidin is a very potent cytotoxic factor for human neutrophils. PLoS Pathogens, 6(1), Article e1000715. https://doi.org/10.1371/journal.ppat.1000715

• Malanovic, N., & Lohner, K. (2016). Antimicrobial peptides targeting gram-positive bacteria. Pharmaceuticals, 9(3), Article 59. https://doi.org/10.3390/ph9030059

• Mariottini, G. L., & Grice, I. D. (2016). Antimicrobials from Cnidarians. A new perspective for anti-infective therapy? Marine Drugs, 14(3), Article 48. https://doi.org/10.3390/md14030048

• McKenney, P. T., Driks, A., & Eichenberger, P. (2012). The Bacillus subtilis endospore: Assembly and functions of the multilayered coat. Nature Reviews Microbiology, 11(1), 33-44. https://doi.org/10.1038/nrmicro2921

• Meidong, R., Doolgindachbaporn, S., Jamjan, W., Sakai, K., Tashiro, Y., Okugawa, Y., & Tongpim, S. (2017). A novel probiotic Bacillus siamensis B44v isolated from Thai pickled vegetables (Phak-dong) for potential use as a feed supplement in aquaculture. The Journal of General and Applied Microbiology, 63(4), 246-253. https://doi.org/10.2323/jgam.2016.12.002

• Mingeot-Leclercq, M. P., & Tulkens, P. M. (1999). Aminoglycosides: Nephrotoxicity. Antimicrobial Agents and Chemotherapy, 43(5), 1003-1012. https://doi.org/10.1128/AAC.43.5.1003

• Miranda, C. A. C., Martins, O. B., & Clementino, M. M. (2007). Species-level identification of Bacillus strains isolates from marine sediments by conventional biochemical, 16S rRNA gene sequencing and inter-tRNA gene sequence lengths analysis. Antonie van Leeuwenhoek, 93(3), 297-304. https://doi.org/10.1007/s10482-007-9204-0

• Monisha, R., Uma, M. V., & Murthy, V. K. (2009). Partial purification and characterization of Bacillus pumilus xylanase from soil source. Kathmandu University Journal of Science, Engineering and Technology, 5(2), 137-148.

• Nicas, T. I., & Hancock, R. E. (1983). Pseudomonas aeruginosa outer membrane permeability: Isolation of a porin protein F-deficient mutant. Journal of Bacteriology, 153(1), 281-285. https://doi.org/10.1128/jb.153.1.281-285.1983

• Olaitan, A. O., Morand, S., & Rolain, J. M. (2014). Mechanisms of polymyxin resistance: Acquired and intrinsic resistance in bacteria. Front Microbiol, 5, Article 643. https://doi.org/10.3389/fmicb.2014.00643.

• Oscoz, J., Tomás, P., & Durán, C. (2010). Review and new records of non-indigenous freshwater invertebrates in the Ebro River basin (Northeast Spain). In Aquatic Invasions (Vol. 5, Issue 3, pp. 263-284). Regional Euro-Asian Biological Invasions Centre Oy (REABIC). https://doi.org/10.3391/ai.2010.5.3.04

• Oskay, M., (2009). Antifungal and antibacterial compounds from Streptomyces strains. African Journal of Biotechnology, 8(13), 3007-3017.

• Oumer, O. J., & Abate, D. (2017). Characterization of pectinase from Bacillus subtilis strain Btk 27 and its potential application in removal of mucilage from coffee beans. Enzyme Research, 2017, 1-7. https://doi.org/10.1155/2017/7686904

• Oyeleke, S. B., Egwim, E. C., Oyewole, O. A., & John, E. E. (2012). Production of cellulase and protease from microorganisms isolated from gut of Archachatina marginata (giant African snail). Science and Technology, 2(1), 15-20. https://doi.org/10.5923/j.scit.20120201.03

• Palomino, J. C., Martin, A., Camacho, M., Guerra, H., Swings, J., & Portaels, F. (2002). Resazurin microtiter assay plate: Simple and inexpensive method for detection of drug resistance in Mycobacterium tuberculosis. Antimicrobial Agents and Chemotherapy, 46(8), 2720-2722. https://doi.org/10.1128/AAC.46.8.2720-2722.2002

• Peschel, A. (2002). How do bacteria resist human antimicrobial peptides? Trends in Microbiology, 10(4), 179-186. https://doi.org/10.1016/s0966-842x(02)02333-8

• Peschel, A., & Collins, L. V. (2001). Staphylococcal resistance to antimicrobial peptides of mammalian and bacterial origin. Peptides, 22, 1651-1659. https://doi.org/10.1016/S0196-9781(01)00500-9

• Philippon, A., Labia, R., & Jacoby, G. (1989). Extended-spectrum beta-lactamases. Antimicrobial Agents and Chemotherapy, 33(8), 1131-1136. https://doi.org/10.1128/AAC.33.8.1131

• Pitout, J. D., & Laupland, K. B. (2008). Extended-spectrum β-lactamase-producing enterobacteriaceae: An emerging public-health concern. The Lancet Infectious Diseases, 8(3), 159-166. https://doi.org/10.1016/s1473-3099(08)70041-0

• Poirel, L., & Nordmann, P. (2002). Acquired carbapenem-hydrolyzing beta-lactamases and their genetic support. Current Pharmaceutical Biotechnology, 3(2), 117-127. https://doi.org/10.2174/1389201023378427

• Powthong, P., & Suntornthiticharoen, P. (2017). Antimicrobial and enzyme activity produced by Bacillus Spp. isolated from soil. International Journal of Pharmacy and Pharmaceutical Sciences, 9(3), 205-210. https://doi.org/10.22159/ijpps.2017v9i3.1389

• PSA. (2016). Fisheries statistics of the Philippines. Philippine Statistics Authority. https://bit.ly/3HCZ8vg

• Ramachandran, R., Chalasani, A. G., Lal, R., & Roy, U. (2014). A broad-spectrum antimicrobial activity of Bacillus subtilis RLID 12.1. The Scientific World Journal, 2014, Article 968487. http://doi.org/10.1155/2014/968487

• Rani, M. K., Chelladurai, G., & Jayanthi, G. (2014). Isolation and identification of bacteria from marine market fish Scomberomorus guttatus (Bloch and Schneider, 1801) from Madurai district, Tamil Nadu, India. Journal of Parasitic Diseases: Official Organ of the Indian Society for Parasitology, 40(3), 1062-1065. https://doi.org/10.1007/s12639-014-0634-0

• Raut, S. K., & Barker, G. M. (2002). Achatina fulica Bowdich and other Achatinidae as pests in tropical agriculture. In Molluscs as Crop Pests (pp. 55-114). CABI. https://doi.org/10.1079/9780851993201.0055

• Rawlings, T. A., Hayes, K. A., Cowie, R. H., & Collins, T. M. (2007). The identity, distribution, and impacts of non-native apple snails in the continental United States. BMC Evolutionary Biology, 7(1), Article 97. https://doi.org/10.1186/1471-2148-7-97

• Reuter, G. (2001). Probiotika--Möglichkeiten und Grenzen ihres Einsatzes in Lebensmitteln, im Tierfutter und in pharmazeutischen Präparaten für Mensch und Tier [Probiotics -Possibilities and limitations of their application in food, animal feed, and in pharmaceutical preparations for men and animals]. Berliner und Munchener tierarztliche Wochenschrift, 114(11-12), 410-419.

• Reynolds, J., Moyes, R., & Breakwell, D. P. (2009). Differential staining of bacteria: Endospore stain. In Current Protocols in Microbiology (pp. A.3J.1-A.3J.5). John Wiley & Sons, Inc. https://doi.org/10.1002/9780471729259.mca03js15.

• Saha, S., Roy, R. N., Sen, S. K., & Ray, A. K. (2006). Characterization of cellulase-producing bacteria from the digestive tract of tilapia, Oreochromis mossambica (Peters) and grass carp, Ctenopharyngodon idella (Valenciennes). Aquaculture Research, 37(4), 380-388. https://doi.org/10.1111/j.1365-2109.2006.01442.x

• Saitou, N., & Nei, M. (1987). The neighbor-joining method: A new method for reconstructing phylogenetic trees. Molecular Biology and Evolution, 4(4), 406-425. https://doi.org/10.1093/oxfordjournals.molbev.a040454

• Salazar, O., & Asenjo, J. A. (2007). Enzymatic lysis of microbial cells. Biotechnology Letters, 29(7), 985-994. https://doi.org/10.1007/s10529-007-9345-2

• Sarkar, B., & Ghosh, K., (2014). Gastrointestinal microbiota in Oreochromis mossambicus (Peters) and Oreochromis niloticus (Linnaeus): Scanning electron microscopy and microbiological study. International Journal of Fisheries and Aquatic Studies, 2(2), 78-88.

• Sivasubramanian, K., Ravichandran, S., & Kavitha, R. (2012). Isolation and characterization of gut micro biota from some estuarine fishes. Marine Science, 2(2), 1-6. https://doi.org/10.5923/j.ms.20120202.01

• Slepecky, R. A., & Hemphill, H. E. (2006). The genus Bacillus - Nonmedical. In The Prokaryotes (pp. 530-562). Springer. https://doi.org/10.1007/0-387-30744-3_16

• Somsap, O. A., Bangrak, P., Bhoopong, P., & Lertcanawanichakul, M. (2016). Antibacterial activity and purification of bacteriocin produced by Brevibacillus laterosporus SA14. Walailak Journal of Science and Technology (WJST), 13(1), 55-65.

• Sonune, N., & Garode, A. (2018). Isolation, characterization and identification of extracellular enzyme producer Bacillus licheniformis from municipal wastewater and evaluation of their biodegradability. Biotechnology Research and Innovation, 2(1), 37-44. https://doi.org/10.1016/j.biori.2018.03.001

• Spratt, B. (1994). Resistance to antibiotics mediated by target alterations. Science, 264(5157), 388-393. https://doi.org/10.1126/science.8153626.

• Srivastava, S. (2015). Minimum inhibitory concentration, pharmacokinetics/pharmacodynamics and therapeutic drug monitoring: An integrated approach for multidrug-resistant tuberculosis. Lung India: Official Organ of Indian Chest Society, 32(4), 402-403.

• Standen, B. T., Rodiles, A., Peggs, D. L., Davies, S. J., Santos, G. A., & Merrifield, D. L. (2015). Modulation of the intestinal microbiota and morphology of tilapia, Oreochromis niloticus, following the application of a multi-species probiotic. In Applied Microbiology and Biotechnology (Vol. 99, Issue 20, pp. 8403-8417). Springer Science and Business Media LLC. https://doi.org/10.1007/s00253-015-6702-2

• Stein, T. (2005). Bacillus subtilis antibiotics: Structures, syntheses and specific functions. Molecular Microbiology, 56(4), 845-857. https://doi.org/10.1111/j.1365-2958.2005.04587.x

• Stubbendieck, R. M., Vargas-Bautista, C., & Straight, P. D. (2016). Bacterial communities: Interactions to scale. Frontiers in Microbiology, 7, Article 1234. https://doi.org/10.3389/fmicb.2016.01234

• Sumpavapol, P., Tongyonk, L., Tanasupawat, S., Chokesajjawatee, N., Luxananil, P., & Visessanguan, W. (2009). Bacillus siamensis sp. nov., isolated from salted crab (poo-khem) in Thailand. International Journal of Systematic and Evolutionary Microbiology, 60(10), 2364-2370. https://doi.org/10.1099/ijs.0.018879-0

• Tamura, K., Stecher, G., Peterson, D., Filipski, A., & Kumar, S. (2013). MEGA6: Molecular evolutionary genetics analysis version 6.0. Molecular Biology and Evolution, 30(12), 2725-2729. https://doi.org/10.1093/molbev/mst197

• Thakham, N., Thaweesak, S., Teerakulkittipong, N., Traiosot, N., Kaikaew, A., Lirio, G. A., & Jangiam, W. (2020). Structural characterization of functional ingredient levan synthesized by Bacillus siamensis isolated from traditional fermented food in Thailand. International Journal of Food Science, 2020, 1-12. https://doi.org/10.1155/2020/7352484

• Trewavas, E. (1983). Tilapiine fishes of the genera Sarotherodon, Oreochromis, and Danakilia. British Museum (Natural History). https://doi.org/10.5962/bhl.title.123198

• Ureta, R. M., Lirio, G. A., Ogbac, M. P., Cruzado, Z. I., & Muros, E. L. (2019). Antibacterial activity of the lyophilized aqueous leaf extract of the Philippine green-leafed Acalypha amentacea Roxb. (Maslakot-Ambulong) against selected human bacterial pathogens. Malaysian Journal of Microbiology, 2019, 463-470.

• USGS. (2013). Integrated taxonomic information system (ITIS). Smithsonian Institution. https://doi.org/10.5066/F7KH0KBK

• Valle, D. L., Cabrera, E. C., Puzon, J. J. M., & Rivera, W. L. (2016). Antimicrobial activities of methanol, ethanol and supercritical CO2 xxtracts of Philippine Piper betle L. on clinical isolates of gram positive and gram negative bacteria with transferable multiple drug resistance. PLOS ONE, 11(1), Article e0146349. https://doi.org/10.1371/journal.pone.0146349

• Van Horn, D. J., Garcia, J. R., Loker, E. S., Mitchell, K. R., Mkoji, G. M., Adema, C. M., & Takacs-Vesbach, C. D. (2011). Complex intestinal bacterial communities in three species of planorbid snails. Journal of Molluscan Studies, 78(1), 74-80. https://doi.org/10.1093/mollus/eyr038

• Verschuere, L., Rombaut, G., Sorgeloos, P., & Verstraete, W. (2000). Probiotic bacteria as biological control agents in aquaculture. Microbiology and Molecular Biology Reviews: MMBR, 64(4), 655-671. https://doi.org/10.1128/MMBR.64.4.655-671.2000

• Waksman, S. (1962). The Actinomycetes (Vol. 3). The Williams and Wilkins Company. https://doi.org/10.1002/jps.2600510829

• Whitman, W. B. (Ed.). (2009). Systematic bacteriology. Springer. https://doi.org/10.1007/978-0-387-68489-5

• Williston, E. H., Zia-Walrath, P., & Youmans, G. P. (1947). Plate methods for testing antibiotic activity of actinomycetes against virulent human type tubercle Bacilli. Journal of Bacteriology, 54(5), 563-568. https://doi.org/10.1128/jb.54.5.563-568.1947

• Wilson, J. M., Bunte, R. M., & Carty, A. J. (2009). Evaluation of rapid cooling and tricaine methanesulfonate (MS222) as methods of euthanasia in zebrafish (Danio rerio). Journal of the American Association for Laboratory Animal Science, 48(6), 785-789.

• Wimley, W. C., & Hristova, K. (2011). Antimicrobial peptides: Successes, challenges and unanswered questions. The Journal of Membrane Biology, 239(1-2), 27-34. https://doi.org/10.1007/s00232-011-9343-0

• Woiwode, J. G., Juliano, R. O., Agbayani, R. F., Corre, U. L., Hatch, U., Deutsch, W. G., Gonzales, G., Sunaz, F., & Perkins, B. (1993). Philippine prawn industry policy study. International Center for Aquaculture and Aquatic Environments.

• Xu, G., Zhao, Y., Du, L., Qian, G., & Liu, F. (2015). Hfq regulates antibacterial antibiotic biosynthesis and extracellular lytic-enzyme production in Lysobacter enzymogenes OH11. Microbial Biotechnology, 8(3), 499-509. http://doi.org/10.1111/1751-7915.12246

• Yang, L., Cheng, T., & Zhao, F. (2017). Comparative profiling of hepatopancreas transcriptomes in satiated and starving Pomacea canaliculata. BMC Genetics, 18, Article 18. http://doi.org/10.1186/s12863-017-0485-7

• Yi, Y., Zhang, Z., Zhao, F., Liu, H., Yu, L., Zha, J., & Wang, G. (2018). Probiotic potential of Bacillus velezensis JW: Antimicrobial activity against fish pathogenic bacteria and immune enhancement effects on Carassius auratus. Fish & Shellfish Immunology, 78, 322-330. https://doi.org/10.1016/j.fsi.2018.04.055

• Yilmaz, M., Soran, H., & Beyatli, Y. (2006). Antimicrobial activities of some Bacillus spp. strains isolated from the soil. In Microbiological Research (Vol. 161, Issue 2, pp. 127-131). Elsevier. https://doi.org/10.1016/j.micres.2005.07.001

• Zhou, S., Xia, Y., Zhu, C., & Chu, W. (2018). Isolation of marine Bacillus sp. with antagonistic and organic-substances-degrading activities and its potential application as a fish probiotic. Marine drugs, 16(6), Article 196. https://doi.org/10.3390/md16060196