Effects of the natural antimicrobial peptide aureocin A53 on cells of Staphylococcus aureus and Streptococcus agalactiae involved in bovine mastitis in the excised teat model

Aureocin A53 is an N-formylated antimicrobial peptide (AMP) produced by Staphylococcus aureus. Aureocin A53 has a broad spectrum of antimicrobial activity against human and animal pathogens. In the present study, its antagonistic activity was investigated towards 30 strains of S. aureus and 30 strains of Streptococcus spp. isolated from bovine mastitis cases in Brazil. Bovine mastitis is a disease that causes a major economic impact worldwide. Aureocin A53 inhibited the growth of all 60 strains tested, including multidrug-resistant streptococcal isolates and strains of S. aureus belonging to different pulsotypes. This AMP proved to be bactericidal against the six target strains randomly selected among staphylococci and streptococci, also exhibiting a lytic mode of action against the staphylococcal cells. Furthermore, it was determined that 2,048 AU/mL of the AMP were required to inhibit 99.99% of the cell growth of the strain less sensitive to aureocin A53. Aureocin A53 was not toxic to bovine mammary gland epithelial cells after a 24-h exposure and maintained its antimicrobial activity when tested in the excised-teat model against strains of S. aureus and Streptococcus agalactiae, the species responsible for most intramammary infections, not only in Brazil but in other countries as well. Therefore, the use of aureocin A53 in the development of new pharmacological products for the prophylaxis and/or treatment of bovine mastitis was considered promising.

Cloxacillin benzathine-loaded polymeric nanocapsules: Physicochemical characterization, cell uptake, and intramammary antimicrobial effect

The present work shows the development and evaluation of the veterinary antibiotic cloxacillin benzathine (CLOXB) loaded into poly-ε-caprolactone (PCL) nanocapsules (NC), as a potential new treatment strategy to manage bovine intramammary infections, such as mastitis. Staphylococcus aureus-induced mastitis is often a recurrent disease due to the persistence of bacteria within infected cells. CLOXB-PCL NC were prepared by interfacial deposition of preformed biodegradable polymer followed by solvent displacement method. The mean diameter of NC varied from 241 to 428 nm and from 326 to 375 nm, when determined by dynamic light scattering and by atomic force microscopy, respectively. The zeta potential of NC was negative and varied from -28 to -51 mV. In vitro release studies from the NC were performed in two media under sink conditions: PBS with 1% polyethylene glycol or milk. A reversed-phase HPLC method was developed to determine the NC entrapment efficiency and kinetics of CLOXB release from the NC. Free CLOXB dissolution occurred very fast in both media, while drug release from the NC was slower and incomplete (below 50%) after 9 h. CLOXB release kinetics from polymeric NC was fitted with the Korsmeyer-Peppas model indicating that CLOXB release is governed by diffusion following Fick's law. The fluorescence confocal microscopy images of macrophage-like J774A.1 cells reveal NC uptake and internalization in vitro. In addition, antimicrobial effect of the intramammary administration of CLOXB-PCL NC in cows with mastitis resulted in no clinical signs of toxicity and allowed complete pathogen elimination after treatment. The in vivo results obtained in this work suggest that CLOXB-PCL NC could be a promising formulation for the treatment of intramammary infections in cattle, considering their physicochemical properties, release profiles and effects on bovine mastitis control.

Presence of mecA-positive multidrug-resistant Staphylococcus epidermidis in bovine milk samples in Brazil

Bacteria of the genus Staphylococcus are one of the major pathogens causing bovine mastitis. In recent decades, resistance of this genus to oxacillin (methicillin) has been a matter of concern due to the possibility of reducing the effectiveness of mastitis treatments and the transfer of resistance determinants to other bacteria. Oxacillin resistance was studied in 170 staphylococci from bovine milk samples, including 79 Staphylococcus aureus and 91 coagulase-negative staphylococci (CNS). The susceptibility profile of 10 antimicrobial agents used in veterinary practice was determined by the Etest method. In addition to the Etest, the phenotypic characterization of oxacillin resistance was tested using the cefoxitin disk diffusion test. All isolates were screened by PCR to detect the mecA gene in 2 different regions of the gene. The isolates with an oxacillin minimum inhibitory concentration ≥0.5 µg/mL or resistant to cefoxitin were identified by sequencing a 536-bp fragment of the 16S rRNA gene. This group of isolates was also evaluated for the presence of blaZ and mecC genes. Molecular analysis of the mecA gene was carried out by typing of the staphylococcal cassette chromosome mec (SCCmec). The relatedness of the mecA-positive isolates was evaluated by macrorestriction of chromosomal DNA followed by pulsed-field gel electrophoresis. With the exception of penicillin and oxacillin, 86% of the isolates showed susceptibility to cephalothin, gentamicin, erythromycin, sulfonamide, trimethoprim-sulfamethoxazole, and tetracycline. All S. aureus isolates were susceptible to oxacillin, whereas 47% (n=43) of the CNS isolates were resistant. The CNS isolates showed a higher resistance to cephalothin, erythromycin, tetracycline, and gentamicin in comparison with S. aureus. The mecA gene was only detected in 10 CNS isolates, identified as Staphylococcus epidermidis, and classified into 3 pulsotypes (A, B, and C) and 4 subtypes (A1, B1, B2, and B3). Among the isolates with an oxacillin resistance phenotype, 12 were positive for the blaZ gene, and 9 of them were mecA-positive. Two of the oxacillin-resistant isolates amplified the mecA homolog gene of Staphylococcus sciuri and none amplified mecC. Three SCCmec types, I, IV, and V, were found. Our results suggest that Staphylococcus epidermidis can be a reservoir for mecA for other Staphylococcus species. Studies investigating the molecular and phenotypic profile of antimicrobial resistance in staphylococcal species should be performed for controlling the spread of resistance and the selection of appropriate therapeutic measures.

Toxigenic status of Staphylococcus aureus isolated from bovine raw milk and Minas frescal cheese in Brazil

A group of 291 Staphylococcus aureus isolates from mastitic cow's milk (n = 125), bulk tank milk (n = 96), and Minas frescal cheese (n = 70) were screened for staphylococcal enterotoxin (SE) genes (sea, seb, sec, sed, see, seg, seh, sei, selj, and sell) and for the tst-1 gene encoding staphylococcal toxic shock syndrome toxin 1 by PCR assay. A total of 109 (37.5%) of the isolates were positive for at least one of these 11 genes, and 23 distinct genotypes of toxin genes were observed. Of the S. aureus isolates bearing SE genes, 17 (13.6%) were from mastitic cow's milk, 41 (41.7%) were from bulk tank milk, and 51 (72.9%) were from Minas frescal cheese. The occurrence of exclusively more recently described SE genes (seg through sell) was considerably higher (87 of 109 PCR-positive strains) than that of classical SE genes (sea through see, 15 strains). The SE genes most commonly detected were seg and sei; they were found alone or in different combinations with other toxin genes, but in 60.8% of the cases they were codetected. No strain possessed see. The tst-1 gene was found in eight isolates but none from mastitic cow's milk. Macrorestriction analysis of chromosomal DNA from 89 S. aureus isolates positive for SE gene(s) was conducted with the enzyme SmaI. Fifty-five distinct pulsed-field gel electrophoresis patterns were found, demonstrating a lack of predominance of any specific clone. A second enzyme, Apa I, used for some isolates was less discriminating than Sma I. The high genotype diversity of potential toxigenic S. aureus strains found in this study, especially from Minas frescal cheese, suggests various sources of contamination. Efforts from the entire production chain are required to improve consumer safety.

Expression profile of genes associated with mastitis in dairy cattle

In order to characterize the expression of genes associated with immune response mechanisms to mastitis, we quantified the relative expression of the IL-2, IL-4, IL-6, IL-8, IL-10, IFN-γ and TNF- α genes in milk cells of healthy cows and cows with clinical mastitis. Total RNA was extracted from milk cells of six Black and White Holstein (BW) cows and six Gyr cows, including three animals with and three without mastitis per breed. Gene expression was analyzed by real-time PCR. IL-10 gene expression was higher in the group of BW and Gyr cows with mastitis compared to animals free of infection from both breeds (p < 0.05). It was also higher in BW Holstein animals with clinical mastitis (p < 0.001), but it was not significant when Gyr cows with and without mastitis were compared (0.05 < p < 0.10). Among healthy cows, BW Holstein animals tended to present a higher expression of all genes studied, with a significant difference for the IL-2 and IFN- γ genes (p < 0.001). For animals with mastitis no significant difference in gene expression was observed between the two breeds. These findings suggest that animals with mastitis develop a preferentially cell-mediated immune response. Further studies including larger samples are necessary to better characterize the gene expression profile in cows with mastitis.

Engineering a recombinant Deinococcus radiodurans for organopollutant degradation in radioactive mixed waste environments

Thousands of waste sites around the world contain mixtures of toxic chlorinated solvents, hydrocarbon solvents, and radionuclides. Because of the inherent danger and expense of cleaning up such wastes by physicochemical methods, other methods are being pursued for cleanup of those sites. One alternative is to engineer radiation-resistant microbes that degrade or transform such wastes to less hazardous mixtures. We describe the construction and characterization of recombinant Deinococcus radiodurans, the most radiation-resistant organism known, expressing toluene dioxygenase (TDO). Cloning of the tod genes (which encode the multicomponent TDO) into the chromosome of this bacterium imparted to the strain the ability to oxidize toluene, chlorobenzene, 3,4-dichloro-1-butene, and indole. The recombinant strain was capable of growth and functional synthesis of TDO in the highly irradiating environment (60 Gy/h) of a 137Cs irradiator, where 5x10(8)cells/ml degraded 125 nmol/ml of chlorobenzene in 150 min. D. radiodurans strains were also tolerant to the solvent effects of toluene and trichloroethylene at levels exceeding those of many radioactive waste sites. These data support the prospective use of engineered D. radiodurans for bioremediation of mixed wastes containing both radionuclides and organic solvents.

Oxidation of aliphatic olefins by toluene dioxygenase: enzyme rates and product identification

Toluene dioxygenase from Pseudomonas putida F1 has been studied extensively with aromatic substrates. The present work examined the toluene dioxygenase-catalyzed oxidation of various halogenated ethenes, propenes, butenes and nonhalogenated cis-2-pentene, an isomeric mix of 2-hexenes, cis-2-heptene, and cis-2-octene as substrates for toluene dioxygenase. Enzyme specific activities were determined for the more water-soluble C2 to C5 compounds and ranged from <4 to 52 nmol per min per mg of protein. Trichloroethene was oxidized at a rate of 33 nmol per min per mg of protein. Products from enzyme reactions were identified by gas chromatography-mass spectrometry. Proton and carbon nuclear magnetic resonance spectroscopy of compounds from whole-cell incubation confirmed the identity of products. Substrates lacking a halogen substituent on sp2 carbon atoms were dioxygenated, while those with halogen and one or more unsubstituted allylic methyl groups were monooxygenated to yield allylic alcohols. 2,3-Dichloro-1-propene, containing both a halogenated double bond and a halogenated allylic methyl group, underwent monooxygenation with allylic rearrangement to yield an isomeric mixture of cis- and trans-2,3-dichloro-2-propene-1-ol.

Verification of the role of PCP 4-monooxygenase in chlorine elimination from pentachlorophenol by Flavobacterium sp. strain ATCC 39723

The bacterial enzyme PCP 4-monooxygenase from Flavobacterium sp. strain ATCC 39723 catalyzes the oxygenolytic removal of the first chlorine from pentachlorophenol. PCP 4-monooxygenase is an FAD binding, NADPH requiring oxygenase, with similar functional domains as other bacterial flavoprotein monooxygenases specific for phenolic substrates. However, the definitive proof for the singular role of an oxygenolytic elimination of the primary chlorine from pentachlorophenol by Flavobacterium sp. has awaited the development of a genetic system whereby targeted mutagenesis via allelic exchange could be carried out with the corresponding gene from PCP 4-monooxygenase, pcpB. We report the development of a genetic system for Flavobacterium sp. strain ATCC 39723, and its application in targeted mutagenesis of the pcpB allele for elimination of PCP 4-monooxygenase activity.

Molecular analysis of pentachlorophenol degradation

A limited number of microorganisms have been described for their ability to partially degrade pentachlorophenol (PCP), or to completely mineralize it. Several years ago we chose one of these microorganisms, Flavobacterium sp. strain ATCC 39723, for use in a detailed molecular analysis of the catabolism of PCP. This strain was chosen because it had previously been studied in great detail for its growth characteristics in relation to degradation of PCP. In this paper we provide an overview of the degradation pathway of PCP to 2,6-dichloro-p-hydroquinone by Flavobacterium. The specific biochemical reactions and the genes encoding the enzymes are reviewed. The successful transformation and site specific mutagenesis of Flavobacterium, as well as the discovery of two new pcp alleles is also presented.

Cloning, sequence analysis, and expression of the Flavobacterium pentachlorophenol-4-monooxygenase gene in Escherichia coli

The pcpB gene of Flavobacterium sp. strain ATCC 39723 was cloned by using a degenerate primer designed from the N-terminal sequence of the purified enzyme. The nucleotide sequence of pcpB was determined and found to encode an open reading frame of 1,614 nucleotides, yielding a predicted translation product of 538 amino acids, in agreement with the estimated size of the purified protein analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The transcriptional start of pcpB was found to be 80 bp upstream of the translational start, and the transcript was found to be induced in Flavobacterium sp. strain ATCC 39723 by the presence of pentachlorophenol but to be constitutive in the Escherichia coli pcpB clone. DNA hybridizations with genomic DNAs from Arthrobacter sp. strain ATCC 33790 and Pseudomonas sp. strain SR3 revealed a similar-size 3.0-kb EcoRI fragment, whereas there was no positive hybridization with genomic DNA from Rhodococcus chlorophenolicus. Cell extracts from an E. coli pcpB overexpression strain, as well as the whole cells, were proficient in the dechlorination of pentachlorophenol to tetrachlorohydroquinone. Protein data base comparisons of the predicted translation products revealed regions of homology with other microbial monooxygenases, including phenol-2-monooxygenase and tryptophan-2-monooxygenase.