Development of Similar Broth Microdilution Methods to Determine the Antimicrobial Susceptibility of Flavobacterium columnare and F. psychrophilum

Flavobacterium columnare and F. psychrophilum are major fish pathogens that cause diseases that may require antimicrobial therapy. Choice of appropriate treatment is dependent upon determining the antimicrobial susceptibility of isolates. Therefore we optimized methods for broth microdilution testing of F. columnare and F. psychrophilum to facilitate standardizing an antimicrobial susceptibility test. We developed adaptations to make reproducible broth inoculums and confirmed the proper incubation time and media composition. We tested the stability of potential quality-control bacteria and compared test results between different operators. Log phase occurred at 48 h for F. columnare and 72–96 h for F. psychrophilum, confirming the test should be incubated at 28°C for approximately 48 h and at 18°C for approximately 96 h, respectively. The most consistent susceptibility results were achieved with plain, 4-g/L, dilute Mueller–Hinton broth supplemented with dilute calcium and magnesium. Supplementing the broth with horse serum did not improve growth. The quality-control strains, Escherichia coli ATCC 25922 and Aeromonas salmonicida subsp. salmonicida ATCC 33658, yielded stable minimal inhibitory concentrations (MIC) against all seven antimicrobials tested after 30 passes at 28°C and 15 passes at 18°C. In comparison tests, most MICs of the isolates agreed 100% within one drug dilution for ampicillin, florfenicol, and oxytetracycline. The agreement was lower with the ormetoprim–sulfdimethoxine combination, but there was at least 75% agreement for all but one isolate. These experiments have provided methods to help standardize antimicrobial susceptibility testing of these nutritionally fastidious aquatic bacteria.

Received June 24, 2015; accepted October 2, 2015.     

Genetic parameter estimates and strain comparisons of egg compositional traits 1

1. Genetic parameters and responses to selection involving egg composition and allied traits were estimated, using two unselected control strains and three selected strains of White Leghorns.

2. Heritability estimate for yolk weight was 0.5 ± 0.1; for albumen percentage protein, 0.6 ± 0.1; and for yolk percentage solids, 0.5 ± 0.1.

3. Genetic correlation estimates indicated that there was no antagonistic relationship between the weight of any egg component and its composition but, because of the unreliability of the estimates of the genetic correlations involving the egg number traits, it is impossible to predict the correlated effects that selection for egg composition would have on egg number.

4. Eggs from selected strains weighed an average of 3‐. g more, contained more albumen, and greater amounts of albumen percentage solids and percentage protein than controls, whereas no differences were found for yolk weight; yolk percentage solids changed little in the selected strains.

5. Comparisons of one control strain with four commercial strains suggest that the findings may be applicable to commercial stocks.     

Investigation of bovine haemoplasmas and their association with anaemia in New Zealand cattle

CASE HISTORY AND CLINICAL FINDINGS: A dairy cow, from a herd in the Waikato region of New Zealand, was reported with regenerative anaemia on 12 September 2014. Testing of blood from the animal using PCR assays for Theileria orientalis produced a negative result for both Chitose and Ikeda types.

LABORATORY FINDINGS: Using PCR and DNA sequencing, blood from the cow was positive for Candidatus Mycoplasma haemobos. Further testing of another 12 animals from the case herd, 27 days after the affected cow was first reported, showed 11 animals were positive for Candidatus M. haemobos or Mycoplasma wenyonii in the PCR. None of these cattle were clinically anaemic or positive for T. orientalis Ikeda type using PCR.

A convenience sample of 47 blood samples from cattle throughout New Zealand, submitted to the Investigation and Diagnostic Centre (Ministry for Primary Industries) for surveillance testing for T. orientalis Ikeda, was selected for further testing for bovine haemoplasmas. Of these samples, 6/47 (13%) and 13/47(28%) were positive for M. wenyonii and Candidatus M. haemobos, respectively. There was no difference in the proportion of samples positive for the bovine haemaplasmas between cattle with anaemia that were negative for T. orientalis (6/20, 33%), or without anaemia or T. orientalis (10/18, 56%), or from cattle herds experiencing anaemia and infection with T. orientalis Ikeda type (3/9, 33%).

DIAGNOSIS: Bovine haemoplasmosis.

CLINICAL RELEVANCE: The presence of bovine haemoplasmas in blood does not establish causality for anaemia in cattle. Diagnosis of anaemia associated with haemoplasmosis would require exclusion of other causes of regenerative anaemia and an association of the agent with anaemia in affected cattle herds. The data collected in this study did not provide evidence that bovine haemoplasmas were associated with a large number of outbreaks of anaemia in cattle in New Zealand.     

Keratin degradation by bacteria and fungi isolated from a poultry farm and plumage

1. Poultry processing generates a large quantity of feather waste. Feathers are a rich source of keratin and could be used as a feather meal in the feed industry if the keratin is degraded using suitable micro-organisms.

2. In this study, keratin-degrading micro-organisms were isolated from a poultry farm. The predominant organisms were identified as Bacillus subtilis, Aspergillus flavus, A. fumigatus and Trychophyton sp.

3. The isolates were inoculated into feather medium and observed for keratin degradation by measuring the protein content, free amino acids and change in pH.

4. During feather degradation by B. subtilis, the concentration of soluble protein released to the medium increased gradually and reached the maximum (433 µg/ml) during d 7 of incubation and the pH increased from the initial 6.9 to 8.4 on d 9 of incubation. Similarly, the maximum protein content of 414 µg/ml and pH of 8.5 was observed for A. fumigatus on d 21 of incubation.

5. B. subtilis and A. fumigatus showed almost the same level of keratinase activity.     

Pharmacokinetics of difloxacin in healthy and E. coli-infected broiler chickens

1. The pharmacokinetics of difloxacin were investigated in healthy and E. coli-infected broiler chickens following intravenous and oral administration of a single dose of 10 mg/kg bodyweight.

2. After intravenous injection of difloxacin, the serum concentration–time curves were best described by a two-compartment open model. The distribution and elimination half-lives (t_0.5α) and (t_0.5el), respectively, were 0.10 ± 0.016 h and 3.7 ± 0.08 h in healthy chickens compared with 0.05 ± 0.005 h and 6.42 ± 0.71 h in E. coli-infected birds. The volumes of distribution V_dss were 3.14 ± 0.11 and 9.25 ± 0.43 l/kg, with total body clearance (Cl_tot) of 0.65 ± 0.018 and 1.14 ± 0.1 ml/kg/h, respectively.

3. Following oral administration, difloxacin was absorbed with t_0.5(ab) of 0.57 ± 0.06 and 0.77 ± 0.04 h and was eliminated with t_0.5(el) of 4.7 ± 0.34 and 3.42 ± 0.19, respectively, in normal and infected chickens. The peak serum concentrations were 1.34 ± 0.09 and 1.05 ± 0.06 µg/ml and attained a T_max of 2.27 ± 0.07 and 2.43 ± 0.06 h, respectively. The systemic bioavailability of difloxacin following oral administration was 86.2% in healthy chickens and 90.6% in E. coli-infected birds. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of difloxacin against the field strain of E. coli O78 in vitro were 0.02 µg and 0.04 µg/ml, respectively.

4. These results show that administration of a therapeutic dose of difloxacin is effective in the treatment of E. coli infection in chickens. The serum concentration of the drug was much higher than the MIC of the E. coli O78 strain in both healthy and infected chickens.     

Bioprocess enhancement of feather degradation using alkaliphilic microbial mixture

1. The main aim of this work is to develop a robust method to generate a microbial mixture which can successfully degrade poultry feathers to overcome environmental problems.

2. Four different alkaliphilic microbes were isolated and shown to degrade poultry feathers.

3. Two of the isolates were phylogenetically identified as Lysinibacillus and the others were identified as Nocardiopsis and Micrococcus.

4. The best microbial co-culture for white and black feather degradation was optimised for pH, temperature and relative population of the isolates to achieve almost 96% of degradation compared with a maximum of 31% when applying each isolate individually.

5. The maximum activity of keratinase was estimated to be 1.5 U/ml after 3 d for white feathers and 0.6 U/ml after 4 d for black feathers in a basal medium containing feather as the main carbon source. Additionally, non-denaturing polyacrylamide gel electrophoresis showed 4 and 3 protease activity bands for white and black feather, respectively.

6. This study provides a robust method to develop potential new mixtures of microorganisms that are able to degrade both white and black feathers by applying a Central Composite Design.     

Enrichment of conjugated linoleic acid (CLA) in hen eggs and broiler chickens meat by lactic acid bacteria

1. The aim of this work was to compare conjugated linoleic acid (CLA) concentrations in chickens supplemented with 4 American Tissue Culture Collection (ATCC) bacterial strains, Lactobacillus plantarum, Lactobacillus lactis, Lactobacillus casei and Lactobacillus fermentum, and 4 isolates of Lactobacillus reuteri from camel, cattle, sheep and goat rumen extracts.

2. Micro-organisms were grown anaerobically in MRS broth, and 10⁶ CFU/ml of bacteria were administered orally to mixed-sex, 1-d-old broiler chickens weekly for 4 weeks and to 23-week-old layer hens weekly for 6 weeks.

3. The 4 strains were evaluated for their effects on synthesis of CLA in hen eggs and broiler meat cuts.

4. Administration of pure Lactobacillus and isolated L. reuteri strains from camel, cattle, goat and sheep led to significantly increased CLA concentrations of 0.2–1.2 mg/g of fat in eggs and 0.3–1.88 mg/g of fat in broiler chicken flesh homogenates of leg, thigh and breast.

5. These data demonstrate that lactic acid bacteria of animal origin (L. reuteri) significantly enhanced CLA synthesis in both eggs and broiler meat cuts.     

Thermal panting and respiratory alkalosis in the laying hen

1. Changes in respiratory rate (f), rectal temperature (T_r ) and blood acid‐base values were measured in laying hens exposed to ambient temperatures (T_a) of 32, 35, 38 or 41 °G.

2. At T_a 32 °G there was no panting. At T_a 35 °G panting occurred without any increase in T_r but there was a slight alkalosis (pH 7.55).

3. At T_a 38 °G T_r increased and panting was accompanied by moderate alkalosis (pH 7.58).

4. At T_a 41 °G T_r increased considerably and severe alkalosis developed (pH 7.65).

5. From the relation between T_r , f and pH it is concluded that some degree of alkalosis is a normal response to panting in the laying hen.     

Identification of chromosome instability in Japanese quail (Coturnix japonica)

1. A study of the incidence of chromosome instability in the Japanese quail as assessed by sister chromatid exchange (SCE) and fragile site identification in chromosomes was conducted in two parent breeds and their F1 and F2 generations.

2. The mean incidence of SCEs was 6.02 ± 0.45 and the frequency of fragile sites was 1.17 ± 0.79.

3. There were moderately negative correlations of 0.51–0.64 between chromosome instability and fertility in the F1 and 0.10–0.23 in the F2. The hatch of fertilised eggs was negatively correlated with the number of SCE in male (0.31) and female (0.33) F1 and was lower in P (0.18 and 0.19, respectively), whereas the correlations were similar for the number of fragile sites in both generations (0.51–0.62).     

In vitro and in vivo protective effects of three mycotoxin adsorbents against ochratoxin A in broiler chickens

1. The objective of this study was to investigate in vitro and in vivo (in broiler chickens) ochratoxin A (OTA) adsorption efficiency of three different adsorbents: inorganic (modified zeolite); organic (esterified glucomannans) and mixed (inorganic and organic components plus enzymes).

2. The aim of the study was to investigate which of these adsorbents provided the best protection against the presence of residues of OTA in the pectoral muscle and liver of broilers given an OTA-contaminated diet. In addition, it was important to test and compare the results of adsorbent efficiency using two different in vitro methods.

3. The results from classical in vitro investigations carried out in the artificial intestinal fluid, showed that the inorganic adsorbent (Mz), exhibited the highest adsorption, having adsorbed 80.86 ± 1.85% of OTA, whereas average in vitro adsorption abilities of organic (30.52 ± 3.50%) and mixed (32.00 ± 2.60%) adsorbents were significantly lower.

4. In the investigation of absorption in everted sacs of broiler duodenal segments (Everted Duodenal Sacs Procedure), higher OTA adsorption in gut was exhibited by organic adsorbent, 74.26 ± 4.48%. Furthermore, the mean adsorption efficiency of mixed and inorganic adsorbent was 65.26 ± 4.76% and 45.75 ± 7.14%, respectively.

5. In the in vivo investigation, broilers were fed for 21 d on diets containing 2 mg/kg of OTA and supplemented with inorganic (Mz), organic (Ms) or mixed adsorbent (Mf) at the recommended concentration of 2 g/kg of feed. All three adsorbents significantly decreased OTA residue concentrations in the pectoral muscle and livers, but the order of effectiveness was mixed > organic > inorganic. The most efficient was the mixed adsorbent which decreased residue concentration by 72.50% in pectoral muscle and 94.47% in livers.

6. The Everted Duodenal Sac in vitro method provided results similar to those obtained in the in vivo study. However, further studies are required to investigate the efficiencies of adsorbents against various mycotoxins using this method.     

Selection for food conversion in broilers: Direct and correlated responses to selection for body‐weight gain,food consumption and food conversion ratio

1. Direct and correlated responses were determined after five generations in four lines of chickens selected either for increased body‐weight gain (line W), for increased food consumption (line F), for decreased food conversion ratio (line E), or at random (line C).

2. Realised heritability estimates calculated after five generations of selection were : 0–37 + 0.04 for weight gain (WG); 0.44 + 0.05 for food consumption (FC); 0.21 + 0.04 for food conversion ratio (FCR).

3. Realised genetic correlation estimates were: WG and FC, +0.71 ±006; WG and FCR, ‐0.40±0.09; FC and FCR, +0.27 + 0.09.

4. Zero‐generation heritability and genetic correlation estimates were greater than the realised estimates, and sex linkage appeared to be important in the expression of all three traits.

5. The genetic correlation between FC and FCR was asymmetrical with considerable positive response in FCR in line F (r_g = +0.79) but negligible response in FC in line E (r_g = —0.01).

6. There was an apparent plateau in response in FCR in line E from the third to the fifth selected generations.     

Electroencephalographic assessment of concussive non-penetrative captive bolt stunning of turkeys

1. The aim of this study was to evaluate the electroencephalographic (EEG) and behavioural responses of turkeys stunned with three different concussive non-penetrative captive-bolt guns prior to slaughter.

2. A total of 31 slaughter weight ex-breeding female turkeys (29 weeks of age; mean body weight 13.32 ± SD 0.65 kg) were stunned with the Cash Poultry Killer (CPK) (n = 10), Turkey Euthanasia Device (TED) (n = 10) and Zephyr EXL (n = 11).

3. Mean peak kinetic energy was highest for the CPK compared to the TED and Zephyr EXL (75.9 ± 4.5, 28.4 ± 0.4 and 24.4 ± 0.7 J, respectively).

4. A total of 29 (94%) of the turkeys were rendered unconscious following captive bolt stunning, with total power of the EEG (Ptot) significantly reduced from baseline values (reductions of 67% CPK, 84% TED and 76% Zephyr EXL, p < 0.01) and waveforms becoming isoelectric after periods of transitional EEG. However, two birds shot with the CPK and Zephyr EXL had periods of behavioural/reflexes (rhythmic respiration, nictitating membrane reflex, neck tension) and EEG activity (43–47 and 36–60 + s after the shot, respectively) indicating incomplete concussion and return of consciousness. In one bird, the shot was incorrectly positioned (Zephyr EXL), while the other appeared to be related to a defective cartridge (CPK).

5. In conclusion, all three captive bolt gun models were effective in producing unconsciousness in turkeys, provided they were positioned correctly and power loads performed according to their specifications.     

The influence of rapid growth in broilers on florfenicol pharmacokinetics – allometric modelling of the pharmacokinetic and haemodynamic parameters

1. The aim of this study was to determine if the pharmacokinetics (PK) of florfenicol (FF) undergo age-dependent changes in broilers. Since drug elimination depends on cardiovascular functions, a haemodynamic study was performed in parallel.

2. Broilers of 0.68, 1.27, 2.45 and 5.13 kg were administered FF in a single intravenous dose of 30 mg/kg body weight. Plasma drug concentrations were determined using high-performance liquid chromatography and PK parameters were calculated using a non-compartmental model. Echocardiography was used to measure haemodynamic functions.

3. During growth, the area under the drug concentration-time curve (AUC_inf) increased from 25.7 ± 2.9 to 39.0 ± 8.0 mg h/l. Total body clearance (Cl_B) gradually decreased from 1.19 ± 0.14 to 0.80 ± 0.15 l/h/kg. Elimination half-life increased from 0.73 ± 0.08 to 1.07 ± 0.07 h, whereas volume of distribution (V_ss) remained unchanged. Haemodynamic measurements revealed an increase in cardiac output, from 495 ± 65 to 1303 ± 306 ml/min, in the respective body weight groups.

4. Allometric models for PK and haemodynamic parameters were developed and validated. All models proved to be statistically significant; however, only models for Cl_B and V_ss met stringent validation criteria. Model for Cl_B was used to calculate an optimal dose for a given age group that provides uniform AUC_inf.

5. Age-dependent change in FF kinetics may cause variability in therapeutic response under clinical conditions. A novel approach to the dosing protocol was proposed as a means of optimising therapeutic efficacy.     

Bioavailability and pharmacokinetic profile of levofloxacin following intravenous,intramuscular and oral administration in turkeys

1. The pharmacokinetics and bioavailability of levofloxacin in turkeys were investigated after a single intravenous (IV), intramuscular (IM) and oral (PO) administration of 10 mg/kg body weight.

2. The concentrations of levofloxacin in plasma samples were assayed using a microbiological assay method and pharmacokinetic parameters were calculated by non-compartmental analysis.

3. Following IV administration, the elimination half-life (t_0.5(β)), volume of distribution at steady state (Vd_ss) and total body clearance (Cl) were 4.49 h, 1.31 l/kg and 0.23 l/h/kg, respectively.

4. After single IM and PO administrations at the same dose, levofloxacin was rapidly absorbed as indicated by an absorption half-life (t_0.5ab) of 1.02 and 0.76 h, respectively; maximum plasma concentrations (C_max) of 5.59 and 5.15 μg/ml were obtained at a maximum time (T_max) of 2 h for both routes and levofloxacin bioavailability (F) was 96.5 h and 79.9% respectively after IM and PO administration. In vitro plasma protein binding of levofloxacin was 24.3%.

5. Based on these pharmacokinetic parameters, a dose of 10 mg/kg body weight given intramuscularly or orally every 24 h in turkeys can maintain effective plasma concentrations with bacterial infections with (minimum inhibitory concentration) MIC₉₀ > 0.1 μg/ml.     

Toxicokinetics of the broad-spectrum pyrethroid insecticide deltamethrin in broiler chickens

1. The aim of this study was to examine single-dose toxicokinetics of deltamethrin, a broad-spectrum pyrethroid insecticide, for treatment of broiler chickens.

2. Twenty male broiler chickens were used. Animals were divided into two groups, each comprising 10 animals. An intravenous dose of 0.75 mg of deltamethrin/kg body weight was given intravenously to the first group and the same dose (0.75 mg/kg body weight) was administered by intracrop by gavage to the second group. Blood samples were also collected at specified intervals.

3. Serum deltamethrin levels were measured via micro-electron capture detection with gas chromatography equipment. According to the serum deltamethrin level-time curve, deltamethrin tended to distribute according to a two-compartment open model.

4. The half-life at β phase (t_1/2β), mean residence time (MRT) and area under the concentration time curve in 0-∞ (AUC_0→∞) values after intravenous application of deltamethrin were 4.00 ± 0.76 h, 4.65 ± 0.75 h and 702.27 ± 236.07 ng h/ml, respectively. Furthermore, the absorption half-life (t_1/2a), maximal concentration in serum after intracrop administration (C_max), time needed to reach C_max (t_max), t_1/2β, MRT and AUC_0→∞ values after intracrop application of deltamethrin were determined to be 0.18 ± 0.06 h, 19.65 ± 4.58 ng/ml, 0.70 ± 0.10 h, 7.27 ± 1.36 h, 10.46 ± 1.84 h and 153.33 ± 30.83 ng h/ml, respectively. The bioavailability of deltamethrin was 21.83%.

5. It was concluded that deltamethrin was rapidly but incompletely absorbed after intracrop administration and bioavailability was at a low level. The t_1/2β and MRT of the deltamethrin were short for both intracrop and intravenous applications, and the risk of toxic and residual effects of deltamethrin is therefore limited.     

Isolation,identification and antibiotic resistance of Campylobacter strains isolated from domestic and free-living pigeons

1. The aim of this study was to evaluate the occurrence of Campylobacter spp. in domestic and free-living pigeons and to evaluate the antibiotic resistance profiles.

2. The material consisted of cloacal swabs obtained from 108 homing pigeons and fresh faeces from 72 wild birds from Lublin and its vicinity. The identification of strains isolated on differential/selective media for Campylobacter spp. was carried out by MALDI-TOF and PCR. The susceptibility to antibiotics was evaluated by minimum inhibitory concentration (MIC) in Mueller-Hinton broth.

3. A total of 35 strains of Campylobacter spp. were isolated; 27 were identified as Campylobacter jejuni and 8 as Campylobacter coli. Over half of the isolates were resistant to erythromycin and streptomycin, 40% of strains were resistant to tetracycline and ampicillin and 37% isolates were resistant to amoxicillin. Resistance to two or more antibiotics was observed in all strains tested.

4. The results indicate that both domestic and free-living pigeons are reservoirs for bacteria of the genus Campylobacter, which are characterised by varied and growing resistance to commonly used antibiotics.     

Prevalence and spatial distribution of cattle herds infected with Theileria orientalis in New Zealand between 2012 and 2013

AIM: To describe the prevalence and spatial distribution of cattle herds infected with Ikeda and non-Ikeda types of Theileria orientalis in New Zealand between November 2012 and June 2013.

METHODS: Pooled serum samples collected historically between November 2012 and June 2013 were obtained from cattle herds throughout New Zealand. Each pooled sample consisted of approximately 20 individual cattle samples from that herd, and was provided with details of the spatial location of the herd (n=722). DNA from all samples was tested using two quantitative PCR assays for the detection of T. orientalis (all types) and the Ikeda type. The proportion of herds that were positive for T. orientalis and Ikeda type, or that were positive for T. orientalis but negative for Ikeda type (non-Ikeda positive) was determined for different regions of New Zealand.

RESULTS: The highest prevalence of herds infected with Ikeda type was detected in the Northland (33/35; 94%) and Auckland and the Waikato (63/191; 33%) regions. Only 2/204 (1%) herds were positive for the Ikeda type in the South Island. A high percentage of herds that were positive for non-Ikeda types was detected in the Gisborne and Hawkes Bay (23 (95%CI=13–37)%), Auckland and Waikato (22 (95%CI=16–29)%) and Bay of Plenty (24 (95%CI=10–44)%) regions.

CONCLUSIONS AND CLINICAL RELEVANCE: The high prevalence of Ikeda type detected in cattle herds in the Northland, Auckland and Waikato regions represents a risk to naive cattle being introduced into these regions. There is also the potential for resident cattle herds in the Gisborne and Hawkes Bay, Auckland, Waikato and Bay of Plenty regions to experience increased infection with the Ikeda type.

The overall impact experienced by regions will depend on other factors such as the number of herds present and the predominant type of farming, as well as the interplay between tick ecology, cattle immunity and movement patterns of cattle.     

Prevalence and antimicrobial resistance of Arcobacter species isolated from poultry meat in Iran

1. The objective of this study was to determine the prevalence and antimicrobial resistance of Arcobacter spp. isolated from different species of retail poultry meat in Iran.

2. From August 2012 to April 2013, a total of 540 raw poultry meat samples from chicken (n = 100), turkey (n = 100), quail (n = 100), partridge (n = 80), duck (n = 50), ostrich (n = 60) and geese (n = 50) were purchased from randomly selected retail outlets in Shahrekord, Isfahan, Sari and Rasht, Iran.

3. Using culture techniques, 71 of 540 poultry meat samples (13.1%) were positive for Arcobacter spp. The highest prevalence of Arcobacter spp. was found in chicken meat (28.0%), followed by quail (12.0%), duck (11.4%), turkey (11.0%), geese (8.0%), partridge (7.5%) and ostrich (3.3%) meat. The number of A. butzleri isolated from poultry meat samples (90.1%) was significantly higher than A. cryaerophilus (7.1%) and A. skirrowii (2.8%). Significantly more poultry meat samples were found to contain Arcobacter spp. by the PCR assay than by the culture method.

4. Susceptibilities of Arcobacter isolates were determined for 14 antimicrobial drugs using the disk diffusion method. All of the 71 Arcobacter isolates tested were resistant to one or more antimicrobial agents. Resistance to cephalothin and vancomycin (95.8%) was the most common finding, followed by resistance to methicillin, azithromycin and ampicillin. All Arcobacter isolates were susceptible to gentamicin, streptomycin, tetracyclin and kanamycin.

5. The results of this study indicated the importance of poultry meat, especially chicken meat, as potential sources of Arcobacter spp. infection in people. Furthermore, the strains indicated resistance to a broad spectrum of antibiotics.     

Crossbreeding effects on reproductive traits in two strains of duck (Anas platyrhynchos): Brown Tsaiya and Pekin

1. The reproductive performances of 211 domestic duck females (Anas platyrhynchos) from the pure breeds Brown Tsaiya (Ts) and Pekin (Pk) and their two reciprocal crossbreds were analysed.

2. Differences in the 4 genotypes, additive direct and maternal crossbreeding effects and heterosis were estimated on the following traits: age at first egg, egg production to the ages of 30, 35, 40 and 52 weeks of age, egg weight at 30 weeks of age, and (egg) fertility by artificial insemination with Muscovy drakes’ pooled semen.

3. Egg production up to 52 weeks of age was higher in Ts than in Pk (respectively 214 ± 7 and 150 ± 8 eggs), but not statistically different from that of the reciprocal crossbreds. The ratio of settable eggs to total eggs was nearly 90%, without any difference between genotypes.

4. Average egg weight at the age of 30 weeks was 75 ± 0.9 g for Pk, which was higher than the corresponding values for Ts (62 ± 0.8 g), but not significantly different from the crossbreds.

5. An effect of genotype was found on egg fertility: the Pk strain exhibited the lowest value, 71.3 ±3.1% compared with 75.9 ±2.1% for Ts, 80.6 ± 2.6% for Ts × Pk and 74.6 ± 1.9% for Pk × Ts.

6. Crossbreeding genetic variables showed favourable direct genetic effects for egg production and (egg) fertility in Ts, while Pk had favourable direct genetic effects on egg weight. The Pk genotype had a favourable maternal effect on fertility. Direct heterosis was 34% and 10% for egg production up to 30 and 52 weeks of age respectively, 8.8% for egg weight and 5.4% for (egg) fertility.

7. Crossing Ts with Pk seems profitable for the production of mule ducklings.     

Prevalence of tetracycline resistance determinants in broiler isolated Escherichia coli in Iran

1. Tetracycline resistance determinants are widespread among bacterial species. Resistance to tetracycline occurs by different mechanisms regulated by various genes.

2. The study was conducted to determine the tetracycline resistance and prevalence of tetracycline resistance determinants among Escherichia coli strains isolated from broilers in northern Iran.

3. Minimum inhibitory concentration (MIC) of tetracycline and susceptibility pattern of the isolates were screened using micro-dilution and disk diffusion methods, respectively. The presence of 7 tetracycline resistance genes including tetA, tetB, tetC, tetD, tetE, tetG and tetM was tested using the polymerase chain reaction.

4. Among 100 strains isolated from broilers, 73% were identified as tetracycline resistant. All isolates showed the presence of tetracycline-associated genes. The most prevalent genes were tetA (46%) and tetB (41%) and totally, 17 different genotypes were recognised according to the presence of tetracycline resistance genes. Statistical analysis revealed that concomitant presence of the resistance genes significantly increased the tetracycline MIC and effectiveness of phenotypic characterisation.

5. The results demonstrated a high occurrence of tetracycline-resistant E. coli and related genes among broilers which presents a risk of increasing these strains in human infections associated with food animals.