Aureocin A53 is an antimicrobial peptide produced by Staphylococcus aureus A53. The genetic determinants involved in aureocin A53 production and immunity to its action are organized in at least four transcriptional units encoded by the 10.4-kb plasmid pRJ9. One transcriptional unit carries only the bacteriocin structural gene, aucA. No immunity gene is found downstream of aucA, as part of the same transcriptional unit. Further downstream of aucA is found an operon which contains the three genes aucEFG, whose products seem to associate to form a dedicated ABC transporter. When aucEFG were expressed in RN4220, an aureocin A53-sensitive S. aureus strain, this strain became partially resistant to the bacteriocin. A gene disruption mutant in aucE was defective in aureocin A53 externalization and more sensitive to aureocin A53 than the wild-type strain, showing that aucEFG are involved in immunity to aureocin A53 by active extrusion of the bacteriocin. Full resistance to aureocin A53 was exhibited by transformants carrying, besides aucEFG, the operon formed by two genes, aucIB and aucIA, located between aucA and aucEFG and carried in the opposite strand. AucIA and AucIB share similarities with hypothetical proteins not found in the gene clusters of other bacteriocins. A gene disruption mutant in orf8, located upstream of aucA and whose product exhibits about 50% similarity to a number of hypothetical membrane proteins found in many Gram-positive bacteria, was strongly affected in aureocin A53 externalization but resistant to aureocin A53, suggesting that Orf8 is also involved in aureocin A53 secretion.
In the present study, 31 coliform strains were isolated from salad, cheese, and meat products sold in commercial establishments in Rio de Janeiro city, and were tested for antibiotic resistance and antimicrobial substance production. Thirteen strains (41.9%) were resistant to at least one antibiotic tested, among which one presented resistance to nine different antibiotics. Two strains (6.4%) exhibited inhibitory activity against the indicator strains, Escherichia coli LMIFRJ and Salmonella enterica I. The antimicrobial substances that they produced were sensitive to proteolytic enzymes, suggesting that they might be bacteriocins. The producer strains were identified as Klebsiella ozaenae and Raoultella terrigena. Although they had similar spectrums of action, the bacteriocins were shown to be different. Both of them were able to inhibit E. coli, Klebsiella, Enterobacter, and Salmonella strains, including antibiotic-resistant ones. Our results suggest that these bacteriocins, named klebicin K and raoultellin L, could have potential use against some foodborne pathogens.
ANTIMICROBIAL SUBSTANCES PRODUCED BY Bacillus spp. ISOLATED FROM FRUITSThe present work aimed to investigate the production of a new antimicrobial substances by Bacillus sp. isolated from fruit, and verify its potential as a pathogen inhibitor associated to deterioration and food disease transmission, such as fungus and Gram-positive and Gram-negative bacteria. Ten strains were submitted to Gram stain and showed to be bacilli. These strains were tested for production of antimicrobial substances, using as indicators different Gram-positive bacteria. Three strains, named Ame3, Mam1 and Pes1 presented the largest spectrum of action against Gram-positive bacteria, suggesting that the substances produced by these strains may have some potential application as food biopreservative.
KEY-WORDS: Bacillus sp.; FOOD BIOPRESERVATIVE; ANTIMICROBIAL SUBSTANCES.
A salada é um dos alimentos mais consumidos em restaurantes “self service”, entretanto, pode atuar como um importante veículo de transmissão de bactérias do grupo dos coliformes. Neste trabalho, foi realizada a quantificação de coliformes totais e termotolerantes presentes em saladas cruas e cozidas comercializadas em restaurantes do tipo “self-service” da cidade do Rio de Janeiro. Dentre as 37 amostras analisadas, 32 (83,8%) apresentaram contagens de coliformes termotolerantes superiores ao máximo permitido pela legislação vigente. Escherichia coli foi o coliforme mais isolado, sendo encontrado em 29% das amostras analisadas, seguido por Serratia sp., e Enterobacter aerogenes. Dezenove estirpes isoladas foram submetidas à avaliação do perfil de resistência a antibióticos, onde 12 delas (63,1%) apresentaram resistência a pelo menos três antibióticos diferentes. Os resultados obtidos apontam para uma deficiência nas práticas de higiene no manuseio e/ou acondicionamento das saladas analisadas, tornando este alimento um possível risco à saúde dos consumidores, inclusive pelo potencial de transmissão de estirpes resistentes a drogas.
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