In vitro susceptibility of Ornithobacterium rhinotracheale to several antimicrobial drugs

As part of the basic characterization of Ornithobacterium rhinotracheale, the minimal inhibitory concentrations of 10 antimicrobial drugs were determined for reference strains and Mexican isolates by a broth microdilution method. For optimal growth of the organisms, a supplemented brain-heart infusion broth was used. The susceptibility of O. rhinotracheale to amoxicillin, enrofloxacin, and oxytetracycline was variable. However, consistent higher minimal inhibitory concentrations values were obtained for gentamicin, fosfomycin, trimethoprim, sulfamethazine, sulfamerazine, sulfaquinoxaline, and sulfachloropyridazine. Obtained results among Mexican isolates indicate a marked antimicrobial drug resistance trend.     

In vitro susceptibility of canine and feline Escherichia coli to fosfomycin

Therapeutic options for multi-drug resistant (MDR) Escherichia coli in dogs or cats are limited. The objective of this study was to establish in vitro susceptibility of canine and feline E. coli to fosfomycin. Two sources of isolates were categorized based on susceptibility as to no resistance (NDR), single drug resistance (SDR), multidrug resistance (MDR) or extreme drug resistance (XDR). Clinical isolates were collected from throughout the US from dogs (n=157) or cats (n=43) with naturally occurring infection between March 2008 and January 2010. Experimental isolates were collected from fecal samples of dogs treated with no drug (NDR), amoxicillin (expressing SDR) or enrofloxacin (expressing MDR or XDR). Fosfomycin minimum inhibitory concentrations (MIC) were determined using E-Test(?). For clinical isolates, most (165/200) originated from the urinary tract, with the number of isolates per resistant category being: NDR (N=44, 22%), SDR (N=65, 32.5%), MDR (N=74, 37%), and XDR (N=17, 8.5%). Of these isolates, 99% (197/200) were susceptible to fosfomycin with the MIC(90) and MIC(50) being 2 and 1 μg/ml, respectively (range: 0.25-196 μg/ml). The number of experimental isolates in each category was NDR (3), SDR (23), MDR (38), and XDR (11) (29.3, 44, and 14.7%, respectively). Of these, 100% were susceptible to fosfomycin with MIC(90) and MIC(50) being 1.5 and 1 μg/ml (range: 0.38-4 μg/ml), respectively. The susceptibility of canine and feline MDR and XDR E. coli to fosfomycin at concentrations well below the susceptible breakpoint supports further investigation for its use when treating E. coli resistant to alternative antimicrobials.     

Phenotypic and molecular characterization of isolates of Ornithobacterium rhinotracheale from chickens and pigeons in Taiwan

Forty Ornithobacterium rhinotracheale (ORT) strains were isolated from 28 chickens and 12 pigeons for the first time in Taiwan. All isolates reacted positively in the p-nitrophenyl-beta-D-galactopyranoside (PNPG) and oxidase tests, showing an API 20NE identification system biocode 0-0-2-0-0-0-4. All the pigeon isolates and 85.7% (24 of 28) of the chicken isolates belonged to serotype A. Compared to the ORT ATCC 51464 strain, 14.3% (4 of 28) of chicken isolates and 58.3% (7 of 12) of pigeon isolates showed smaller colonies after 72 hr incubation. Most of the chicken isolates (22 of 28), but none of the pigeon isolates, could agglutinate chicken and pigeon red blood cells. There appears to be a correlation that ORT isolates with a larger colony size tend to be more able to agglutinate red blood cells than the ORT isolates with a smaller colony size. A majority of isolates was sensitive to amoxicillin, ampicillin, ceftiofur, penicillin, and oxytetracycline. The 16S ribosomal RNA (rRNA) sequences of 23 Taiwanese ORT isolates showed high identity (98%-100%) to sequences in GenBank. Phylogenetic analysis of these sequences showed that pigeon isolates formed a distinctive cluster, while chicken isolates and all other 16S rRNA sequences obtained from GenBank belonged to another two clusters. The results indicate that pigeon ORT isolates are different from most chicken isolates in regard to a number of phenotypic and molecular traits.     

Characterisation of some Ornithobacterium rhinotracheale strains and examination of their transmission via eggs

The biochemical characteristics and antibiotic susceptibility of 12 Ornithobacterium rhinotracheale strains isolated from chickens and turkeys suffering from respiratory clinical signs and the survival of some isolates on egg-shell and within chicken eggs during hatching were examined. All O. rhinotracheale strains showed typical biochemical characteristics. Among the 16 drugs examined, penicillin G, ampicillin (MICs ranging from < or = 0.06 microgram/ml to 1 microgram/ml), ceftazidim (with MICs from < or = 0.06 microgram/ml to 0.12 microgram/ml), erythromycin, tylosin, tilmicosin (with some exceptions MICs ranged from < or = 0.06 microgram/ml to 1 microgram/ml) and tiamulin (MICs varied from < or = 0.06 microgram/ml to 2 micrograms/ml) were the most effective. Lincomycin, oxytetracycline and enrofloxacin also gave good inhibitions, but with most strains in a higher concentration (MICs ranged in most cases from 2 micrograms/ml to 8 micrograms/ml). The other antibiotics inhibited the growth of O. rhinotracheale only in very high concentrations (colistin) or not at all (apramycin, spectinomycin, polymyxin B). At 37 degrees C, O. rhinotracheale did not survive on egg-shell for more than 24 hours, while upon inoculation into embryonated chicken eggs it killed embryos by the ninth day, and from the 14th day post-inoculation no O. rhinotracheale could be cultured from the eggs at all. These results suggest that O. rhinotracheale is not transmitted via eggs during hatching.     

Confirmation that PCR can be used to identify NAD-dependent and NAD-independent Haemophilus paragallinarum isolates.

Seventy five bacteria tentatively identified as Haemophilus paragallinarum (the causative agent of infectious coryza), eight identified as Ornithobacterium rhinotracheale and 13 identified as NAD-independent Pasteurella species were isolated from chickens with respiratory infection in various provinces in South Africa. The isolates were characterized by conventional biochemical and serological methods. A polymerase chain reaction (PCR) assay specific for H. paragallinarum was used to identify the cultures directly from colonies. The PCR assay gave positive results for all isolates that were identified by conventional methods as H. paragallinarum, irrespective of whether they were nicotinamide adenine dinucleotide (NAD)-dependent (43 isolates) or NAD-independent (32 isolates). The eight isolates that were identified by conventional methods as O. rhinotracheale and the 13 isolates identified as various Pasteurella species gave negative results in the PCR assay. This study has demonstrated that colony PCR is a rapid method for uniquely identifying both NAD-dependent and NAD-independent strains of H. paragallinarum and distinguishing them from other bacteria, such as O. rhinotracheale and Pasteurella species.     

Comparison of in vitro activity of danofloxacin, florfenicol, oxytetracycline, spectinomycin and tilmicosin against recent field isolates of Mycoplasma bovis

The minimum inhibitory concentrations (MICS) and minimum mycoplasmacidal concentrations (MMCs) of danofloxacin, florfenicol, oxytetracycline, spectinomycin and tilmicosin against 62 recent British field isolates of Mycoplasma bovis were determined in vitro by a broth microdilution method. The isolates were most susceptible todanofloxacin with MIC90 and MMC90 values of 0.5 microg/ml and 1.0 microg/ml, respectively. They were less susceptible to florfenicol with a MIC90 of 16 microg/ml and MMC90 of 32 microg/ml. Oxytetracycline and spectinomycin had only a limited effect against the majority of isolates tested with MIC50s of 32 microg/ml and 4 microg/ml, respectively and MIC90s of 64 microg/ml and more than 128 microg/ml, respectively. Nearly 20 per cent of the isolates were highly resistant to spectinomycin, and tilmicosin was ineffective, with 92 per cent of the isolates having MIC values of 128 microg/ml or greater. There was no evidence of resistance by M bovis to danofloxacin.     

Antimicrobial susceptibility of Actinobacillus pleuropneumoniae, Escherichia coli, and Salmonella choleraesuis recovered from Taiwanese swine.

Minimum inhibition concentrations (MICs) were determined for ampicillin, ceftiofur, cephalothin, chloramphenicol, enrofloxacin, gentamicin, lincomycin, lincospectin (lincomycin/spectinomycin), neomycin, premafloxacin, spectinomycin, sulfamethoxazole/trimethoprim, and tetracycline against a total of 180 isolates of Actinobacillus pleuropneumoniae, Escherichia coli, and Salmonella choleraesuis (60 each) clinically isolated from pigs on farms in Taiwan from 1994 to 1996. No more than 3 isolates per farm were used. Ceftiofur had the highest activity in vitro against isolates of A. pleuropneumoniae, E. coli, and S. choleraesuis, with MIC90 values of 0.03, 2, and 1 microg/ml, respectively. Premafloxacin was highly active against isolates of A. pleuropneumoniae, E. coli, and S. choleraesuis, with MIC90 values of 2, 8, and 0.5 microg/ml, respectively, which were lower than those with enrofloxacin (MIC90 8, 32, and 2 microg/ml, respectively). Neomycin was moderately active against A. pleuropneumoniae and E. coli, with MIC90 values of 8 and 64 microg/ml, respectively, but was inactive with S. choleraesuis. Gentamicin showed high activity against A. pleuropneumoniae (MIC90 of 2 microg/ml) but was only moderately active with E. coli and S. choleraesuis (MIC90 of 64 and 32 microg/ml). Cephalothin was highly active against isolates of A. pleuropneumoniae (MIC90 of 1 microg/ml) but was inactive with E. coli (MIC90 of 128 microg/ml). Lincomycin had moderate activity (MIC90 of 32 microg/ml) against A. pleuropneumoniae. Chloramphenicol, lincomycin, and tetracycline were inactive with E. coli and S. choleraesuis (MIC90 > 128 microg/ml). In conclusion, ceftiofur and premafloxacin were highly active against isolates of A. pleuropneumoniae, E. coli, and S. choleraesuis, enrofloxacin and gentamicin were highly to moderately active; cephalothin was highly active against A. pleuropneumoniae and moderately active against S. cholearesuis; chloramphenicol, lincomycin, and tetracycline were active only with A. pleuropneumoniae; neomycin was moderately active against A. pleuropneumoniae and E. coli. The other antimicrobials tested were inactive.     

Seroprevalence of Borrelia burgdorferi-Specific C6 Antibody in Dogs Before and After Implementation of a Nonadjuvanted Recombinant Outer Surface Protein A Vaccine in a Rhode Island Small Animal Clinic

The in vitro activity of 10 cephalosporin antimicrobial agents against 75 isolates of methicillin-susceptible Staphylococcus pseudintermedius derived from dogs was assessed. The lowest minimal inhibitory concentration for 90% of strains (MIC90) values obtained were for cephalothin, cefovecin, and cefazolin (0.12 ug/mL), followed by ceftiofur and cefoxitin (0.25 ug/mL), cefpodoxime (0.5 ug/mL), and cefaclor and cefadroxil (1 ug/mL). The highest MIC90 values were found for cephalexin and cefixime (2 ug/mL). In this in vitro study, sensitivity to cephalothin was indicative of cephalexin susceptibility, although there were marked differences in MICs. Cephalothin susceptibility was not indicative of susceptibility to all tested cephalosporins, nor was there a clear trend in susceptibility based on cephalosporin generation.     

Identification and characterization of Ornithobacterium rhinotracheale isolates from Mexico

Ten gram-negative, pleomorphic, rod-shaped isolates from coryza-like, respiratory diseased laying and broiler chickens were identified as Ornithobacterium rhinotracheale. All O. rhinotracheale isolates showed typical biochemical and enzymatic characteristics. Also, all isolates showed hemagglutinating activity with glutaraldehyde-fixed erythrocytes. On the basis of this property, a rabbit-raised antiserum was produced for an isolate. All isolates were identified by antiserum by hemagglutination-inhibition tests. No cross-reactions were observed when O. rhinotracheale isolates were tested with Haemophilus paragallinarum antisera, and vice versa. Mild respiratory signs, including mild nasal discharge, slight rales, and sneezing, were observed in challenged chickens. At postmortem examination, multifocal pneumonia, airsacculitis, and foamy exudate in abdominal cavity were observed. Furthermore, because bacterial adherence is regarded as an essential step in the infection process, in vitro adherence of O. rhinotracheale isolates to chicken tracheal epithelial cells was tested. All isolates showed positive adherence. Obtained results indicate that O. rhinotracheale is a pathogenic agent present in the Mexican poultry.     

Studies on the bacterial etiology of airsacculitis of broilers in northern and middle Jordan with special reference to Escherichia coli,Ornithobacterium rhinotracheale,and Bordetella avium

A total of 100 poultry farms in northern and middle areas of Jordan were sampled to investigate the bacteria associated with airsacculitis in broiler chickens. Of 170 bacterial isolates, 88.2% were identified as Escherichia coli, 8.8% as Ornithobacterium rhinotracheale, and 3% as Bordetella avium. Fourteen serotypes of E. coli were identified among 66 typeable isolates and the remainder were untypeable. The most prevalent serotypes were O1, O8, and O78. The main serotype of O. rhinotracheale was serotype A. Experimental inoculation of O. rhinotracheale via intravenous, intratracheal, and intra-air sac routes resulted in growth retardation, thickening in the air sacs, arthritis, and liver necrosis. Reisolation of O. rhinotracheale from the air sacs, liver, trachea, heart, and spleen at day 7 postinoculation confirmed its role. In vitro susceptibility testing revealed that E. coli isolates were sensitive to gentamicin and colistin, O. rhinotracheale to tetracyline, and B. avium to most of the nine antibiotics examined.     

Anti-microbial susceptibility for east1 + Escherichia coli isolated from diarrheic pigs in Korea

The in vitro susceptibilities of 128 isolates of east1 + Escherichia coli from pre-weaned and post-weaned pigs with diarrhoea were tested with nine commonly used anti-microbial agents by an agar dilution minimal inhibitory concentration (MIC) procedure according to National Committee for Clinical Laboratory Standards guidelines. For the isolates from preweaned and post-weaned pigs, most of them were susceptible to low concentrations (MIC90) of tetracycline (4 and 2 microg/ml), ceftiofur (2 and 2 microg/ml), and colistin (4 and 2 microg/ml). Marked resistance was found in others.     

Antimicrobial Activity of Tulathromycin and 14 Other Antimicrobials Against Virulent Rhodococcus equi In Vitro

This study determined the antimicrobial activity of tulathromycin against Rhodococcus equi in vitro. Ninety-eight virulent isolates of R. equi from equine clinical cases were examined, of which 20 isolates were macrolide resistant. A custom 96-well antimicrobial susceptibility testing plate was used, allowing 14 additional antimicrobials to be tested against R. equi. Isolates were cultured with various concentrations of antimicrobials, and minimal inhibitory concentration (MIC) values were determined. Tulathromycin was found to have poor activity in vitro against R. equi isolates susceptible or resistant to macrolides, with MIC50 and MIC90 values >64 ug/mL for all isolates. MIC values for other macrolides tested were similar to previously published data.     

Investigation of the presence of Ornithobacterium rhinotracheale in chickens in Turkey and determination of the seroprevalance of the infection using the enzyme-linked immunosorbent assay

In this study, the presence of Ornithobacterium rhinotracheale infection in the avian population in the Marmara and the Western Black Sea region was investigated. Trachea samples were randomly obtained from 96 chickens sent to slaughterhouses. The seroprevalance of the infection was determined in 384 blood sera. Ninety-six of these 384 samples belonged to animals from which trachea samples were obtained. Eleven (11.46%) O. rhinotracheale were isolated in 96 trachea samples taken from 10 different flocks brought to the slaughterhouse. Serotype A was the predominant serotype among the 11 isolates of O. rhinotracheale. One isolate could not be serotyped. O. rhinotracheale antibodies were detected in 251 (64.4%) of the 384 sera, while 55 (14.3%) and 78 (20.3%) were suspected and negative, respectively.     

Cefadroxil in the horse: pharmacokinetics and in vitro antibacterial activity

Sodium cefadroxil was administered as a single intravenous dose (25 mg/kg) to six healthy adult mares. Plasma samples were collected over a 24-h period and cefadroxil concentrations were measured by microbiological assay. The pharmacokinetic behavior of the drug was appropriately described in terms of a one-compartment open model. Values for the major pharmacokinetic terms were: extrapolated initial plasma concentration = 59.2 +/- 15.0 micrograms/ml; half-life = 46 +/- 20 min; apparent volume of distribution = 462 +/- 191 ml/kg; and body clearance = 7.0 +/- 0.6 ml/min.kg. In a subsequent study, a suspension of cefadroxil monohydrate was administered intragastrically (25 mg/kg) to the same six horses. Plasma concentrations of the drug peaked at 1-2 h but, in general, absorption was both poor and inconsistent. The data were unsuitable for determination of cefadroxil bioavailability from this oral dosage form. Ninety-nine isolates of eleven bacterial species obtained from clinically ill horses were tested for susceptibility to cefadroxil. All strains of Streptococcus equi, Streptococcus zooepidemicus, coagulase-positive staphylococci, Corynebacterium pseudotuberculosis and five out of six strains of Actinobacillus suis were highly susceptible to the drug (MIC less than 4 micrograms/ml). Escherichia coli, Klebsiella pneumoniae and Salmonella sp. showed intermediate susceptibility (MIC 4-16 micrograms/ml), while all isolates of Corynebacterium (Rhodococcus) equi, Enterobacter cloacae and Pseudomonas aeruginosa proved to be highly resistant to cefadroxil (MIC greater than 128 micrograms/ml).     

Ornithobacterium rhinotracheale, a primary pathogen in broilers

Field strains of Ornithobacterium rhinotracheale were tested on their virulence in different chicken breeds. Ornithobacterium rhinotracheale was able to induce lesions after aerosol challenge without a previous priming with virus, and thus O. rhinotracheale was proven to be a primary pathogen. The virulence of Dutch strains, isolated between 1995 and 1998, did not increase, but the Dutch isolates and a South African strain were more pathogenic compared with an American strain of O. rhinotracheale. White specific-pathogen-free leghorns were less susceptible to O. rhinotracheale infection than broilers, whereas there was no difference in susceptibility between commercial broilers and specific-pathogen-free broilers.     

Phenotypic and molecular characterization of isolates of Ornithobacterium rhinotracheale from Peru.

Twenty-five isolates of Ornithobacterium rhinotracheale were examined by agar gel precipitation, immunoperoxidase assay, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, western blot analysis, and a polymerase chain reaction. All of the isolates were identified as serotype A. Protein profiles of whole cell extracts were similar for all the isolates, and a polypeptide with a molecular weight of 33 kD was a major component, being present in all the isolates. In the main, proteins of 33, 42, 52, and 66 kD were recognized in immunoblots with sera from chickens naturally exposed to O. rhinotracheale. A modified polymerase chain reaction assay identified O. rhinotracheale DNA from all the isolates and tracheal swabs, producing amplicons of 784 bp, and distinguished O. rhinotracheale from bacterial agents causing similar clinical signs.     

Aeromonas hydrophila-related septicemia in the Nile tilapia Oreochromis niloticus

From diseased wild and cultured Oreochromis niloticus in Lower Egypt, 17 Aeromonas hydrophila isolates were recovered. The mortality was between 10% and 70% in among cultured fish. The course of the disease ran in an acute manner. For cultured fish, the disease outbreaks were found mainly in winter and for the wild Nile fish, mortalities were observed in late spring and summer. Additionally wild fish were affected with ectoparasites. The LD50 values of the isolates ranged between 10(3) and 10(7). Isolates of high virulence were resistant to 1 hr boiling and to the bactericidal effect of fresh normal guinea pig serum. Moreover, they did not agglutinate in acriflavin. Only the virulent isolates could agglutinate tilapia erythrocytes. The above effects were reversed for avirulent isolates while moderately virulent isolates showed no consistency in their reactions. Tube agglutination test using O and WC antisera prepared against 6 isolates versus O and WC antigens of 17 isolates indicated an antigenic heterogenicity of different isolates. While some isolates were identical, 4 antigens out of 17 did not react with any of the sera.     

两种恩诺沙星盐对人工感染鸡杆菌及沙门氏菌的疗效

采用试管两倍稀释法,测得烟酸恩诺沙星、盐酸恩诺沙星对鸡大肠杆菌(O_1、O_2、O_(78))、副鸡嗜血杆菌的MIC均为0.125、0.125、0.06、0.25μg/mL、对沙门氏菌敏感性略差,MIC均为16μg/ml。对人工混合感染大肠杆菌、沙门氏菌、副鸡嗜血杆菌的治疗效果显示:按50mg/L(以恩诺沙星计)饮水,一日2次,连用5d,两种药物的有效率、保护率均达100％,治愈率分别达89.3％、85.7％(P>0.05),无显著性差异。     

In vitro susceptibilities of field isolates of Mycoplasma agalactiae to oxytetracycline,tylosin, enrofloxacin,spiramycin and lincomycin-spectinomycin

The minimum inhibitory concentrations (MICs) of tetracycline, enrofloxacin, tylosin, spiramycin and a lincomycin:spectinomycin 1:2 combination, against 24 Sicilian isolates of Mycoplasma agalactiae, the causative organism of contagious agalactia were determined in vitro by a broth dilution method. Enrofloxacin was the most effective antimicrobial in vitro with a range of MIC values from 0.125 to 0.500 microg/ml and an MIC(50) of 0.203 and MIC(90) of 0.365 microg/ml. Using the MIC(50) and MIC(90) values the remaining four antimicrobials are ranked in order of in vitro effectiveness as follows: tylosin (MIC(50)0.292; MIC(90)0.525 microg/ml) was slightly more effective than tetracycline (MIC(50)0.296; MIC(90)0.533 microg/ml), followed by lincomycin:spectinomycin (MIC(50)0.521; MIC(90)0.938 microg/ml) and spiramycin (MIC(50)1.583; MIC(90)2.850 microg/ml). MIC values above 1.000 microg/ml were obtained using tetracycline, tylosin and spiramycin for some M. agalactiae isolates.     

In vitro susceptibility of avian Escherichia coli and Pasteurella multocida to danofloxacin and five other antimicrobials.

The in vitro susceptibility of Escherichia coli and Pasteurella multocida isolated from poultry was determined to danofloxacin, a novel fluoroquinolone, and five other commonly used antimicrobials. A total of 1737 E. coli field isolates and 107 P. multocida isolates were tested by veterinary diagnostic laboratories in Europe, Japan, South Africa, and North America during the period 1989-91. The antimicrobial susceptibility of these isolates was determined using the Sensititre broth microdilution technique. The minimum inhibitory concentrations (MIC) of danofloxacin, furaltadone, lincomycin, oxytetracycline, spectinomycin, and trimethoprim:sulfamethoxazole that prevented growth of 90% of the bacteria were 0.25 > 64, > 64, > 64, > 128, and > 16 micrograms/ml, respectively, against E. coli isolates and 0.25, 64, 64, 16, 128, and 8 micrograms/ml, respectively, against P. multocida isolates. Danofloxacin demonstrated considerable in vitro potency against these important poultry pathogens, many of which showed extensive resistance to the other antimicrobials tested.