Comparison of methods to detect resistance of Penicillium expansum to thiabendazole

Aims:  Because of the lack of a standard method, the aim of this work is to evaluate the suitability of the broth microdilution method CLSI M38-A in determining the resistance level of some Penicillium expansum isolates to thiabendazole (TBZ). The ability of the isolates to produce patulin (PAT) and citrinin (CIT) has been also assessed.
Methods and Results:  Penicillium expansum isolates (128) were assayed (apples, pears, grapes and five reference strains). It was observed that 69·4% of the strains isolated from apples and pears were resistant to TBZ. Sensitive isolates were inhibited at 0·25–0·5 μg ml⁻¹ whilst resistant isolates still grew at 512 μg ml⁻¹. PAT was produced by all P. expansum isolates. CIT was detected in 98·8% of TBZ-resistant isolates and in 89·1% of the TBZ-sensitive isolates.
Conclusions:  The preliminary screening method combined with the adaptation of the method CLSI M38-A, can be a good strategy to be used in assessing the in vitro activity of TBZ against a large number of isolates.
Significance and Impact of the Study:  The proposed methodology can be a contribution to the standardization of susceptibility tests to fungicides against P. expansum.     

In vitro efficacy of nisin Z against Candida albicans adhesion and transition following contact with normal human gingival cells

Aim:  To investigate the nisin Z innocuity using normal human gingival fibroblast and epithelial cell cultures, and its synergistic effect with these gingival cells against Candida albicans adhesion and transition from blastospore to hyphal form.
Methods and Results:  Cells were cultured to 80% confluence and infected with C. albicans in the absence or presence of various concentrations of nisin Z. Our results indicate that only high concentrations of nisin Z promoted gingival cell detachment and differentiation. Determination of the LD₅₀ showed that the fibroblasts were able to tolerate up to 80  μ g ml⁻¹ for 24 h, dropping thereafter to 62  μ g ml⁻¹ after 72 h of contact, compared to 160  μ g ml⁻¹ after 24 h, and 80  μ g ml⁻¹ after 72 h recorded by the gingival epithelial cells which displayed a greater resistance to nisin Z. The use of nisin Z even at low concentration (25  μ g ml⁻¹) at appropriate concentrations with gingival cells significantly reduced C. albicans adhesion to gingival monolayer cultures and inhibited the yeast's transition.
Conclusion:  These findings show that when used at non-toxic levels for human cells, nisin Z can be effective against C. albicans adhesion and transition and may synergistically interact with gingival cells for an efficient resistance against C. albicans .
Significance and Impact of the Study:  This study suggests the potential usefulness of nisin Z as an antifungal agent, when used in an appropriate range.     

Effects of the high pressure of homogenization on some spoiling micro-organisms, representative of fruit juice microflora, inoculated in saline solution

Aims:  This study was aimed to investigate the effects of a high-pressure homogenization (HPH) treatment on some micro-organisms, involved in the spoilage of fruit juices.
Methods and Results:  Lactobacillus plantarum , Lactobacillus brevis , Bacillus coagulans cells, Saccharomyces bayanus , Pichia membranaefaciens and Rhodotorula bacarum were separately inoculated in a saline solution (0·9% NaCl); the initial inoculum was ca. 5 log CFU ml⁻¹. Then, the samples were processed through a homogenizer at 10–150 MPa for 1, 2 or 3 times. Yeasts were completely inactivated at 50–110 MPa with a single pass treatment, while lactic acid bacteria counts were reduced to approximately 1 log CFU ml⁻¹ after a three-steps HPH processing.
Conclusions:  Yeasts were the most sensitive micro-organisms, followed by B. coagulans . On the other hand, lactic acid bacteria appeared resistant to HPH.
Significance and Impact of the Study:  The results of this study provided some useful information on the susceptibility of microflora of juices to homogenization; moreover, they suggested that HPH could be used successfully to inactivate yeasts.     

Inhibitory effects of sucrose fatty acid esters on survival of Yersinia enterocolitica on eggshell surface and use of blue lake as indicator of bacterial penetration into eggs

Aims:  To determine the effectiveness of sucrose monolaurate (SML) and sucrose monocaprate (SMC), alone and in combination with ethylenediaminetetraacetic acid (EDTA), propionic acid (PA) or citric acid (CA) in reducing mesophilic aerobic bacteria (MAB) and Yersinia enterocolitica O:9 populations on eggshells and their damage potential on the microstructure of shell cuticle.
Methods and Results:  Uninoculated eggs and eggs submerged in a solution of Y. enterocolitica were immersed in solutions of the various treatments. MAB and Y. enterocolitica counts on the surface of the eggs were carried out before and after treatment. MAB counts decreased less than 2 logs on uninoculated eggshells irrespective of treatment and reductions of 3·2 and 3·0 logs of Y. enterocolitica were obtained with 1000 μg ml⁻¹ SML plus 0·1% CA or 1000 μg ml⁻¹ SML plus 600 μg ml⁻¹ EDTA solutions, respectively. Y. enterocolitica 2/O:9 was recovered from natural microflora. Use of blue lake staining revealed minimal damage to the shells from the washing treatments.
Conclusions:  SML and SMC at 1000 μg ml⁻¹ combined with CA or EDTA could be effective in reducing Y. enterocolitica on eggshells with a minimal risk of later bacterial recontamination.
Significance and Impact of the Study:  Eggs are a recognized vehicle for transmission of Y enterocolitica although a prevalence of only 2·7% was detected in this study. Washing eggs in solutions containing SML or SMC could eliminate Y. enterocolitica contamination of egg shells.     

A potent anti-oxidant property: fluorescent recombinant α-phycocyanin of Spirulina

Aims:  To express and product a fluorescent antioxidant holo-α-phycocyanin (PC) of Spirulina platensis ( Sp ) with His-tag (rHHPC; recombinant holo-α-phycocyaninof Spirulina platensis with His-tag) in 5-l bench scale.
Methods and Results:  A vector harbouring two cassettes was constructed: cpcA along with cpcE - cpcF in one cassette; ho1 - pcyA in the other cassette. Lyases CpcE/F of Synechocystis sp. PCC6803 ( S6 ) could catalyse the 82 site Cys in apo-α-PC of Sp linking with bilin chromophores, and rHHPC was biosynthesized in Escherichia coli BL21. The constant feeding mode was adopted, and transformant reached the biomass of rHHPC up to 0·55 g l⁻¹ broth in 5-litre bench scale. rHHPC was purified by Ni²⁺ affinity column conveniently. The absorbance and the fluorescence emission spectra of rHHPC had λ_max at 621 and 650 nm, respectively. The IC₅₀ values of rHHPC were 277·5 ± 25·8 μ g ml⁻¹ against hydroxyl radicals and 20·8 ± 2·2  μ g ml⁻¹ against peroxyl radicals.
Conclusions:  Combinational biosynthesis of rHHPC was feasible, and the constant feeding mode was adopted to produce good yields of rHHPC. Fluorescent rHHPC with several unique qualitative and quantitative features was effective on scavenging hydroxyl and peroxyl radicals.
Significance and impact of the study:  A potent antioxidant rHHPC was co-expressed, produced and characterized for nutritional and pharmacological values, which would help to develop phycobiliproteins' applications in their fluorescent and biological activities.     

Effects of chlorophyllin on replication of poliovirus and bovine herpesvirus in vitro

Aims:  Chlorophyllin (CHLN), a synthetic derivative of chlorophyll, was assayed in the replication of poliovirus (PV-1) and bovine herpesvirus (BoHV-1) in HEp-2 cell cultures.
Methods and Results:  Virucidal activity of CHLN was evaluated and the time-of-addition assay was performed as follows: before the infection (−1 and −2 h), at the time of the infection (0 h) and after the infection (1 and 2 h). Plaque reduction assay (PRA) showed that CHLN inhibited BoHV-1 and PV-1 infection and the 50% inhibitory concentrations (IC₅₀) against BoHV-1 and PV-1 infection were 8·6 and 19·8 μg ml⁻¹, respectively. The time-of-addition study demonstrated that the CHLN was effective inhibiting viral replication in 51% and 66·5% for PV-1 and BoHV-1, respectively, at the highest concentration of 20·0 μg ml⁻¹, when added during the infection. The directed effect of CHLN on viral strains demonstrated an inhibition of 62% and 66·4% for PV-1 and BoHV-1, respectively, by PRA.
Conclusions:  These results demonstrated that CHLN could be used as an antiviral suggesting directed activity on virus particles and on virus-receptor sites to BoHV. For poliovirus, CHLN also demonstrated virucide activity, moreover, showed to inhibit early steps of the replication cycle.
Significance and Impact of the Study:  CHLN demonstrated promising selectivity index for both virus strains; therefore, it can be used for the development of an antiviral agent.     

Acrebol, a novel toxic peptaibol produced by an Acremonium exuviarum indoor isolate

Aims:  To identify a toxin and its producer isolated from woody material in a building where the occupants experienced serious ill health symptoms.
Methods and Results:  Hyphal extracts of an indoor fungus, identified as the cycloheximide-tolerant species Acremonium exuviarum , inhibited motility of boar spermatozoa (EC₅₀ 5 ± 2 μg of crude solids ml⁻¹) and caused cytolysis of murine neuroblastoma cells (MNA) and feline fetal lung cells (FL). The responsible substances were purified and identified as two structurally similar, heat-stable, novel, toxic peptaibols, 1726 Da and 1740 Da, respectively, with amino acid sequences of Acetyl-Phe-Iva/Val-Gln-Aib-Ile-Thr-Leu-Aib-Pro-Aib-Gln-Pro-Aib-(X-X-X)-SerOH and Acetyl-Phe-Iva/Val-Gln-Aib-Ile-Thr-Leu-Val-Pro-Aib-Gln-Pro-Aib-(X-X-X)-SerOH. Purified acrebol inhibited motility of boar sperm, depleted ATP half-content in 1 day (EC₅₀ of 0·1 μg ml⁻¹, 60 nmol l⁻¹) depolarised the mitochondria after 2 days, but did not affect the cellular content in NADH. This indicates mitochondrial toxicity. Plate-grown biomass of A. exuviarum BMB4 contained 0·1–1% (w/w) of acrebol, depending on the culture medium.
Conclusions:  Acrebol paralysed the energy generation of mammalian cells suggesting that mitochondria were its target of action.
Significance and Impact of the Study:  Acremonium exuviarum, as an indoor fungus, is potentially hazardous to health because of the toxic peptaibols that it produces.     

Extrinsic control parameters for ozone inactivation of Escherichia coli using a bubble column

Aims:  To investigate the effect of extrinsic control parameters for ozone inactivation of E. coli in a bubble column.
Methods and Results:  Ozone inactivation of Escherichia coli ATCC 25922 in Tryptic Soya Broth was examined. The parameters studied included temperature (ambient, 20, 25 and 30°C), exposure time (up to 30 min), gas flow rate (0·03, 0·06, 0·12, 0·25, 0·5 and 0·75 l min⁻¹) and concentration level (five different levels). The efficacy of ozone treatment was a function of the parameters investigated and optimum control parameters of flow rate (0·12 l min⁻¹), temperature (ambient) and ozone concentration (75  μ g ml⁻¹) resulted in a t _d5 (time required to achieve 5 log reduction) of 20 min.
Conclusions:  Optimum control parameters of gas flow rate, ozone concentration and temperature are reported for E. coli inactivation within a bubble column.
Significance and Impact of the Study:  In 2001, the FDA approved use of ozone as a direct additive to food and in 2004, issued guidelines for the use of ozone in liquid systems. However, these guidelines highlighted gaps in the literature for ozonation of liquid foods. This study provides useful information regarding optimum extrinsic control parameters for E. coli inactivation in liquid media using a bubble column to ensure microbiological safety.     

Aerobic chromate reduction by chromium-resistant bacteria isolated from serpentine soil

A group of 34 chromium-resistant bacteria were isolated from naturally occurring chromium percolated serpentine soil of Andaman (India). These isolates displayed different degrees of chromate reduction under aerobic conditions. One of the 34 isolates identified as Bacillus sphaericus was tolerant to 800 mg l⁻¹ Cr(VI) and reduced >80% Cr(VI) during growth. In Vogel Bonner broth, B. sphaericus cells (10¹⁰ cells ml⁻¹) reduced 62% of 20 mg l⁻¹ of Cr(VI) in 48 h with concomitant discoloring of yellow medium to white one. Reduction of chromate was pronounced by the addition of glucose and yeast extract as electron donors. In the presence of 4.0 g l⁻¹ of glucose, 20 mg l⁻¹ of Cr(VI) was reduced to 2.45 mg l⁻¹ after 96 h of incubation. Optimum pH and temperature for reduction were 6.0 and 25 °C, respectively. Increase in cell density and initial Cr(VI) concentration increased chromate reduction but was inhibited by metal ions like, Ni²⁺, Co²⁺, Cd²⁺ and Pb²⁺. Experiments with cell-free extracts indicated that the soluble fraction of the cell was responsible for aerobic reduction of Cr(VI) by this organism.     

Acetylation of fluoroquinolone antimicrobial agents by an Escherichia coli strain isolated from a municipal wastewater treatment plant

Aims:  To isolate environmental bacteria capable of transforming fluoroquinolones to inactive molecules.
Methods and Results:  Bacteria were isolated from the aerobic liquor of a wastewater treatment plant on a medium containing norfloxacin (100 mg l⁻¹). Twenty-two isolates were highly resistant (minimal inhibitory concentration: 6·25−200 μg ml⁻¹) to five fluoroquinolones and six of them were positive by PCR amplification for the aminoglycoside resistance gene aac(6')-Ib. Of these, only Escherichia coli strain LR09 had the ciprofloxacin-acetylating variant gene aac(6')-Ib-cr ; HPLC and mass spectrometry showed that this strain transformed both ciprofloxacin and norfloxacin by N -acetylation. This bacterium also had mutations in the quinolone-resistance determining regions of the gyrA and parC genes.
Conclusions:  An E. coli isolate from wastewater, which possessed at least two distinct fluoroquinolone resistance mechanisms, inactivated ciprofloxacin and norfloxacin by N -acetylation.
Significance and Impact of the Study:  This is the first report of N -acetylation of fluoroquinolones by an aac(6')-Ib-cr -containing bacterium from an environmental source.     

Serovar distribution and antimicrobial susceptibility of swine Salmonella isolates from clinically ill pigs in diagnostic submissions from Indiana in the United States

Aims:  To determine serovar distribution and levels of antimicrobial susceptibility of Salmonella isolated from clinically ill pigs in diagnostic submissions.
Methods and Results:  A total of 197 Salmonella isolates were obtained by the Indiana Animal Disease Diagnostic Laboratory from 2003 to 2005. Minimal inhibitory concentrations (MICs) were determined using the standard microbroth dilution method. The top four serovars identified were Salm. enterica serovar Typhimurium variant Copenhagen, Salm . Derby, Salm . Choleraesuis var. Kunzendorf and Salm . Typhimurium. All isolates were susceptible to the fluoroquinolones tested except that eight isolates were intermediate to difloxacin. The isolates showed a low prevalence of resistance to trimethoprim/sulphadiazine (Sxt), gentamicin (G), ceftiofur (Cf) and cephalothin (Cp) with low MIC₅₀ value of ≤0·5, 0·5, 1 and 4  μ g ml⁻¹, respectively. They showed a high prevalence of resistance to tetracycline (T; 83·8%), and a moderate prevalence to ampicillin (55·8%), spectinomycin (42·6%), ticarcillin (41·6%) and florfenicol (41·1%). There were more isolates of Salm . Typhimurium, including var. Copenhagen and Salm . Agona, that possessed multiple antimicrobial resistance to amoxicillin/clavulanic acid, ampicillin, ceftiofur and cephalothin (AxApCfCp) than the other serovars.
Conclusions:  The swine Salmonella isolates were susceptible to the fluoroquinolones, Sxt, G, Cf and Cp, but resistant to T.
Significance and Impact of the Study:  These findings provided useful information regarding antimicrobial susceptibility and resistance in dealing with clinical salmonellosis in pig herds.     

The antimicrobial activity of heyneanol A extracted from the root of Taiwanese wild grape

Aims:  To search for antimicrobial compounds against pathogenic bacteria from grape vines ( Vitis spp.). To investigate the antimicrobial efficacy of active compounds towards methicillin-resistant Staphylococcus aureus (MRSA).
Methods and Results:  The root extracts of taiwanese wild grape ( Vitis thunbergii var. taiwaniana ) showed marked activities against Gram-positive bacteria using the disc diffusion method. After purification, the active compound 1 was confirmed as heyneanol A by mass spectroscopy and nuclear magnetic resonance. Heyneanol A showed an minimum inhibitory concentration (MIC) value of 2  μ g ml⁻¹ towards MRSA and a value of 2 to 4  μ g ml⁻¹ for Enterococcus faecium , S. aureus , Streptococcus agalactiae and Streptococcus pyogenes . In addition, the contents of heyneanol A were determined as 36 mg g⁻¹ in roots of taiwanese wild grape.
Conclusions:  The root extracts of grapevines have good antimicrobial activities towards some strains of Gram-positive pathogens. Heyneanol A, the major antimicrobial compound, is especially active towards MRSA. In addition, the abundances of heyneanol A and other stilbenes in the roots of grapevines make it possible to produce natural antimicrobial compounds from this plant species.
Significance and Impact of the Study:  This study reports for the first time the antimicrobial compounds in the root extracts of grapevines. The results will have clinical significance owing to their activities against MRSA.     

Antimicrobial activity of essential oils and structurally related synthetic food additives towards Clostridium perfringens

Aims:  To assess the potential of essential oils and structurally related synthetic food additives in inhibiting the growth of Clostridium perfringens for the control of necrotic enteritis in chickens.
Methods and Results:  The antimicrobial activity of essential oils/compounds was measured by determining the inhibition of bacterial growth. Thirty-three of 66 oils/compounds exhibited ≥80% inhibition. Seven with the highest potency were further studied. The oils/compounds had MIC₉₅ values between 167 and 425  μ g ml⁻¹. Most of them were tolerant to low pH (2·0) and exhibited minor or no inhibition of Lactobacillus isolates from the chicken intestine. When mixed with chicken ileal digesta, the oils/compounds retained their efficacy against C . perfringens , but had little effect on the total number of lactobacilli and anaerobic bacteria in the digesta.
Conclusions:  Some essential oils/compounds demonstrated good potential in controlling C . perfringens .
Significance and Impact of the Study:  This study has identified candidates of essential oils/compounds for in vivo studies for the control of necrotic enteritis in chickens.     

The combined effects of high pressure and nisin on germination and inactivation of Bacillus spores in milk

Aims:  The aim of this work was to investigate the germination and inactivation of spores of Bacillus species in buffer and milk subjected to high pressure (HP) and nisin.
Methods and Results:  Spores of Bacillus subtilis and Bacillus cereus suspended in milk or buffer were treated at 100 or 500 MPa at 40°C with or without 500 IU ml⁻¹ of nisin. Treatment at 500 MPa resulted in high levels of germination (4 log units) of B. subtilis spores in both milk and buffer; this increased to >6 logs by applying a second cycle of pressure. Viability of B. subtilis spores in milk and buffer was reduced by 2·5 logs by cycled HP, while the addition of nisin (500 IU ml⁻¹) prior to HP treatment resulted in log reductions of 5·7 and 5·9 in phosphate buffered saline and milk, respectively. Physical damage of spores of B. subtilis following HP was apparent using scanning electron microscopy. Treating four strains of B. cereus at 500 MPa for 5 min twice at 40°C in the presence of 500 IU ml⁻¹ nisin proved less effective at inactivating the spores of these isolates compared with B. subtilis and some strain-to-strain variability was observed.
Conclusions:  Although high levels of germination of Bacillus spores could be achieved by combining HP and nisin, complete inactivation was not achieved using the aforementioned treatments.
Significance and Impact of the Study:  Combinations of HP treatment and nisin may be an appealing alternative to heat pasteurization of milk.     

Characterization and genomic analysis of chromate resistant and reducing <Emphasis Type="Italic">Bacillus cereus</Emphasis> strain SJ1

Background  

Chromium is a toxic heavy metal, which primarily exists in two inorganic forms, Cr(VI) and Cr(III). Chromate [Cr(VI)] is carcinogenic, mutational, and teratogenic due to its strong oxidizing nature. Biotransformation of Cr(VI) to less-toxic Cr(III) by chromate-resistant and reducing bacteria has offered an ecological and economical option for chromate detoxification and bioremediation. However, knowledge of the genetic determinants for chromate resistance and reduction has been limited so far. Our main aim was to investigate chromate resistance and reduction by Bacillus cereus SJ1, and to further study the underlying mechanisms at the molecular level using the obtained genome sequence.     

Chromium resistance strategies and toxicity: what makes <Emphasis Type="Italic">Ochrobactrum tritici</Emphasis> 5bvl1 a strain highly resistant

Large-scale industrial use of chromium (Cr) resulted in widespread environmental contamination with hexavalent chromium (Cr(VI)). The ability of microorganisms to survive in these environments and detoxify chromate requires the presence of specific resistance systems. Several Cr(VI) resistant species, belonging to a variety of genera, have been isolated in recent years. Ochrobactrum tritici strain 5bvl1 is a model for a highly Cr(VI)-resistant and reducing microorganism, with different strategies to cope with chromium. The strain contains the transposon-located (TnOtChr) chromate resistance genes chrB, chrA, chrC, chrF. The chrB and chrA genes were found to be essential for the establishment of high resistance but not chrC or chrF genes. Other mechanisms involved in chromium resistance in this strain were related to strategies such as specific or unspecific Cr(VI) reduction, free-radical detoxifying activities, and repairing DNA damage. Expression of the chrB, chrC or chrF genes was related to increased resistance to superoxide-generating agents. Genetic analyses also showed that, the ruvB gene is related to chromium resistance in O. tritici 5bvl1. The RuvABC complex probably does not form when ruvB gene is interrupted, and the repair of DNA damage induced by chromium is prevented. Aerobic or anaerobic chromate reductase activity and other unspecific mechanisms for chromium reduction have been identified in different bacteria. In the strain O. tritici 5bvl1, several unspecific mechanisms were found. Dichromate and chromate have different effects on the physiology of the chromium resistant strains and dichromate seems to be more toxic. Toxicity of Cr(VI) was evaluated by following growth, reduction, respiration, glucose uptake assays and by comparing cell morphology.     

Development and characterization of a lux-modified 2,4-dichlorophenol-degrading Burkholderia sp. RASC

lux -marked biosensors for assessing the toxicity and bioremediation potential of polluted environments may complement traditional chemical techniques. lux CDABE genes were introduced into the chromosome of the 2,4-dichlorophenol (2,4-DCP)-mineralizing bacterium, Burkholderia sp. RASC c2, by biparental mating using the Tn 4431 system. Experiments revealed that light output was constitutive and related to cell biomass concentration during exponential growth. The transposon insertion was stable and did not interrupt 2,4-DCP-degradative genes, and expression of lux CDABE did not constitute a metabolic burden to the cell. A bioluminescence response was detectable at sublethal 2,4-DCP concentrations: at < 10.26 μg ml⁻¹, bioluminescence was stimulated (e.g. 218% of control), but at concentrations > 60 μg ml⁻¹ it declined to < 1%. Investigating the effect of [14C]-2,4-DCP concentration on the evolution of ¹⁴CO₂ revealed that, for initial concentrations of 2.5–25 μg ml⁻¹, ≈55% of the added ¹⁴C was mineralized after 24 h compared with < 1% at 50 and 100 μg ml⁻¹. Inhibition of 2,4-DCP mineralization between 25 and 50 μg ml⁻¹ corresponded well to the EC₅₀ value (33.83 μg ml⁻¹) obtained from bioluminescence inhibition studies. lux -marked RASC c2 may therefore be used as a functionally (i.e. 2,4-DCP degrader) and environmentally relevant biosensor of toxicity and biodegradation inhibition.     

Isolation, characterization and expression of a plasmid encoding chromate resistance in Pseudomonas putida KT2441

The chromium resistance properties encoded by a natural plasmid recovered from the environment were investigated. A 200 kb plasmid was isolated by the exogenous plasmid isolation method. The plasmid conferred a chromate resistance phenotype (MIC 8 mmol l⁻¹) to a chromate susceptible strain of Pseudomonas putida KT 2441 (MIC 0·5 mmol l⁻¹). The resistant strain took up 50% less ⁵¹Cr than the isogenic susceptible strain of Ps. putida KT2441. In addition, the resistant strain expressed two new membrane proteins encoded by the plasmid, an outer membrane protein (molecular weight 60 000) and an inner membrane protein (molecular weight 35 000). The physiological significance of these proteins is under current investigation.     

Antimicrobial resistance and in vitro gene transfer in bacteria isolated from the ulcers of EUS-affected fish in India

Aims:  The occurrence of drug resistance and plasmid-mediated transferability was investigated in 15 Aeromonas isolates collected from the ulcers of epizootic ulcerative syndrome (EUS)-affected fishes Katla ( Catla catla ), Mrigel ( Cirrhinus mrigala ) and Punti ( Puntius sp.).
Methods and Results:  Disc diffusion assay showed that all the strains were resistant to ampicillin and sensitive to streptomycin. Of the 15 isolates examined, 93·3% isolates were resistant to erythromycin, sulfadiazine and novobiocin, while 66% were resistant to rifampin and 20% to chloramphenicol. All isolates harboured plasmids with sizes ranging from 64 to 23 kbp with a 23-kbp plasmid in common. Plasmids from 11 Aeromonas strains were transferred to Escherichia coli DH5α recipient strain along with the transfer of ampicillin, erythromycin and chloramphenicol resistance determinants with frequencies ranging from 7·0 × 10⁻⁶ to 1·8 × 10⁻⁵ transconjugants per recipient cell.
Conclusions:  The resistance to ampicillin, erythromycin, sulfadiazine, novobiocin and chloramphenicol is prevalent among the bacteria isolated from EUS-affected fish, and resistant determinants of some of these antibiotics have been transferred to the bacteria of other origin.
Significance and Impact of the Study:  The emergence of antibiotic resistance bacteria and gene transfer in vitr o suggests that antibiotics should be used more cautiously to treat Aeromonas infections in aquaculture.