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.     

Antimicrobial susceptibility of Pasteurella multocida isolated from cattle and pigs

Minimum inhibitory concentrations (MICs) of 10 antimicrobial agents were determined for Pasteurella multocida from cattle and pigs (72 and 68 isolates, respectively). Higher MICs were observed with oxytetracycline, doxycycline, tilmicosin and thiamphenicol for porcine isolates than for bovine isolates. Enrofloxacin was the most active, with an MIC for 90% of the isolates (MIC90) of 0.05 microg/ml for both bovine and porcine isolates. Aspoxicillin exhibited the same excellent activity against penicillin-susceptible isolates as ceftiofur, with MICs ranging from < or = 0.025 to 0.1 microg/ml. Aminoglycosides were less active, with an MIC90 of > 100 microg/ml for both bovine and porcine isolates.     

Antimicrobial susceptibility of Mycoplasma hyorhinis

A broth microdilution technique was used to determine the antimicrobial susceptibility of 15 field isolates of Mycoplasma hyorhinis to 10 antimicrobial agents, representative of different classes, and contrasting newer agents to existing ones. For the macrolides, the MIC(90) for tylosin and tilmicosin was 1 and 4 microg/ml, respectively, but was > or = 16 microg/ml for erythromycin. Tetracycline, lincomycin and enrofloxacin each had an MIC(90) of 2 microg/ml. The mycoplasma had similar levels of susceptibility to the aminoglycoside and aminocyclictol classes exhibiting an MIC(90) of 4 microg/ml for gentamicin and 2 microg/ml for spectinomycin. The isolates exhibited high MICs to trimethoprim/sulfamethoxazole with an MIC(90) > or = 16/304 microg/ml. In summary, M. hyorhinis isolates from the US had low MICs against a variety of antimicrobials tested, with the exception of erythromycin and trimethoprim/sulfamethoxazole.     

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.     

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.     

A 10-year survey of antimicrobial susceptibility of streptococcus suis isolates from swine in Japan

A number of 689 Streptococcus suis isolates collected nationwide from diseased and healthy pigs from 1987 to 1996 were surveyed for antibiotic susceptibilities to 11 drugs. No isolates resistant to amoxicillin, chloramphenicol, and sulfamethoxazole/trimethoprim were found. Isolates were highly susceptible to penicillins (penicillin G, ampicillin, and amoxicillin) except cloxacillin. They were not susceptible to tetracycline, streptomycin, and kanamaycin (MIC90 50 microg/ml, > or = 100 microg/ml, and > or = 100 microg/ml, respectively). Multiple-resistant isolates (> or = 3 antimicrobial agents) were found in 20.3% of all isolates tested.     

Tiamulin resistance in porcine Brachyspira pilosicoli isolates

There are few studies on antimicrobial susceptibility of Brachyspira pilosicoli, therefore this study was performed to investigate the situation among isolates from pigs. The tiamulin and tylosin susceptibility was determined by broth dilution for 93 and 86 porcine B. pilosicoli isolates, respectively. The isolates came from clinical samples taken in Swedish pig herds during the years 2002 and 2003. The tylosin minimal inhibitory concentration (MIC) was >16 microg/ml for 50% (n=43) of the isolates tested. A tiamulin MIC >2 microg/ml was obtained for 14% (n=13) of the isolates and these were also tested against doxycycline, salinomycin, valnemulin, lincomycin and aivlosin. For these isolates the susceptibility to salinomycin and doxycycline was high but the MICs for aivlosin varied. The relationship between the 13 tiamulin resistant isolates was analyzed by pulsed-field gel electrophoresis (PFGE). Among the 13 isolates 10 different PFGE patterns were identified.     

Prevalence, capsular type and antimicrobial susceptibility of Streptococcus suis isolated from slaughter pigs in Korea.

This study was undertaken to determine the prevalence, capsular serotype, and antimicrobial susceptibility of Streptococcus suis isolated from slaughter pigs. Capsular serotype and antimicrobial susceptibility were determined by coagglutination test and agar dilution minimum inhibitory concentration, respectively. Streptococcus suis was isolated from 55 of the 406 palatine tonsillar samples tested (13.8%) and 14 of the 29 sampled herds (48.3%). Of the 55 isolates recovered from slaughter pigs, 26 (47.3%) were untypeable. Of the remaining 29 isolates, capsular serotypes 9 (9 isolates) and 16 (4 isolates) were the most common, followed by capsular serotypes 4 (3 isolates) and 7 (3 isolates). Every capsulated isolate was typeable and no palatine tonsillar sample yielded more than one serotype. Most of isolates were susceptible to low concentrations (MIC90) of amoxicillin (2 microg/mL), ceftiofur (1 microg/mL), and penicillin (1 microg/mL). No correlation was found between antimicrobial susceptibility and capsular serotype.     

Minimum inhibitory concentrations of 20 antimicrobial agents against Staphylococcus aureus isolated from bovine intramammary infections in Japan

Minimum inhibitory concentrations (MICs) of 20 antimicrobial agents were determined against 51 isolates of Staphylococcus aureus from bovine intramammary infections. Fourteen (27.4%) isolates were resistant to benzylpenicillin, but none of the isolates was resistant to cloxacillin, nafcillin, or cephems. Among aminoglycosides, gentamicin was the most active, with an MIC50 of 0.2 microg/ml, followed by kanamycin, with an MIC50 of 0.78 microg/ml. Five isolates (9.8%) were resistant to dihydrostreptomycin, three isolates (5.9%) to kanamycin and two isolates (3.9%) to gentamicin. Resistance to erythromycin was observed in two isolates (3.9%). Tylosin was less active than erythromycin, with MIC50s of 1.56 microg/ml versus 0.39 microg/ml, but none of the isolates was resistant to this antibiotic. Oxytetracycline MICs were situated in the range of 0.39-1.56 microg/ml for 48 susceptible isolates. Although 19 (37.3%) isolates were resistant to one or more antimicrobial agents, a single resistance pattern was most frequent: benzylpenicillin (12 isolates), dihydrostreptomycin (two isolates) and kanamycin (one isolate). There were no isolates resistant to antimicrobial agents such as methicillin, lincomycin, clindamycin, chloramphenicol, florfenicol and virginiamycin, which have not been approved for use in cattle husbandry in Japan.     

Minimum inhibitory concentrations of tulathromycin against respiratory bacterial pathogens isolated from clinical cases in European cattle and swine and variability arising from changes in in vitro methodology

The in vitro activity of tulathromycin was evaluated against common bovine and porcine respiratory pathogens collected from outbreaks of clinical disease across eight European countries from 1998 to 2001. Minimum inhibitory concentrations (MICs) for one isolate of each bacterial species from each outbreak were determined using a broth microdilution technique. The lowest concentrations inhibiting the growth of 90% of isolates (MIC90) for tulathromycin were 2 microg/ml for Mannheimia (Pasteurella) haemolytica, 1 microg/ml for Pasteurella multocida (bovine), and 2 microg/ml for Pasteurella multocida (porcine) and ranged from 0.5 to 4 microg/ml for Histophilus somni (Haemophilus somnus) and from 4 to 16 microg/ml for Actinobacillus pleuropneumoniae. Isolates were retested in the presence of serum. The activity of tulathromycin against fastidious organisms was affected by culture conditions, and MICs were reduced in the presence of serum.     

Genetic relatedness of high-level aminoglycoside-resistant enterococci isolated from poultry carcasses

Approximately 46% (75/162) or poultry enterococci collected between 1999 and 2000 exhibited high-level resistance to gentamicin (minimum inhibitory concentration [MIC] > or = 500 microg/ml), kanamycin (MIC > or = 500 microg/ml), or streptomycin (MIC > or = 1000 microg/ml). Forty-one percent of the isolates were resistant to kanamycin (n = 67), whereas 23% and 19% were resistant to genramicin (n = 37) and streptomycin (n = 31), respectively. The predominant species identified was Enterococcus faecium (n = 105), followed by Enterococcus faecalis (n = 40) and Enterococcus durans (n = 8). Using polymerase chain reaction, the isolates were examined for the presence of 10 aminoglycoside resistance genes [ant(6)-Ia, ant(9)-Ia, ant(4')-Ia, aph(3')-IIIa, aph(2")-Ib, aph(2")-Ic, aph(2")-Id, aac(6')-Ie-aph(2")-Ia, and aac(6')-Ii]. Five aminoglycoside resistance genes were detected, most frequently aac(6')-Ii and ant(6)-Ia from E. faecium. Seven E. faecalis isolates resistant to gentamicin, kanamycin, or streptomycin were negative for all genes tested, indicating that additional resistance genes may exist. Phylogenetic analysis revealed that the isolates were genetically different with little clonality. These data indicate that enterococci from poultry are diverse and contain potentially unidentified aminoglycoside resistance genes.     

Antimicrobial susceptibility of Brachyspira hyodysenteriae isolated from 21 Polish farms

Swine dysentery (SD) is a common disease among pigs worldwide, which contributes to major production losses. Antimicrobial susceptibility testing of B. hyodysenteriae, the etiological agent of SD, is mainly performed by the agar dilution method. This method has certain limitations due to difficulties in interpretation of results. The aim of this study was the analysis of antimicrobial susceptibility of Brachyspira hyodysenteriae (B. hyodysenteriae) Polish field isolates by broth microdilution procedure. The study was performed on 21 isolates of B. hyodysenteriae, collected between January 2006 to December 2010 from cases of swine dysentery. VetMIC Brachyspira panels with antimicrobial agents (tiamulin, valnemulin, doxycycline, lincomycin, tylosin and ampicillin) were used for susceptibility testing of B. hyodysenteriae. The minimal inhibitory concentration (MIC) was determined by the broth dilution procedure. The lowest antimicrobial activity was demonstrated for tylosin and lincomycin, with inhibition of bacterial growth using concentrations > 128 microg/ml and 32 microg/ml, respectively. In the case of doxycycline, the MIC values were < or = 2.0 microg/ml. No decreased susceptibility to tiamulin was found among the Polish isolates and MIC values for this antibiotic did not exceed 1.0 microg/ml. The results of the present study confirmed that Polish B. hyodysenteriae isolates were susceptible to the main antibiotics (tiamulin and valnemulin) used in treatment of swine dysentery. Further studies are necessary to evaluate a possible slow decrease in susceptibility to tiamulin and valnemulin of B. hyodysenteriae strains in Poland.     

Evaluation of the antimicrobial activity of florfenicol against bacteria isolated from bovine and porcine respiratory disease

Antimicrobial susceptibility of florfenicol (FFC) against 243 bacterial agents isolated in Korea from cattle and pigs with respiratory disease were investigated by agar diffusion and microdilution broth methods following the recommendations provided by the National Committee for Clinical Laboratory Standards. All Actinobacillus pleuropnemoniae, Pasteurella multocida, Mannheimia haemolytica and 98.6% of the Bordetella bronchiseptica isolates were susceptible to FFC, which as significantly more effective than the other antibiotics used in this study. FFC also showed high in vitro antimicrobial activities (MIC(90) < or = 1 microg/ml) against all strains tested with a minimal inhibitory concentration (MIC) determination ranging from 0.12 to 4 microg/ml. No resistant strains of A. pleuropneumoniae, P. multocida and M. haemolytica to FFC have apparently developed since the first introduction of this antibiotics for veterinary use in Korea. The results suggest that FFC is therapeutically valuable in the treatment of primary or complicating bacterial pathogens causing of the bovine and swine respiratory tract.     

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 pre‐weaned and post‐weaned pigs, most of them were susceptible to low concentrations (MIC₉₀) of tetracycline (4 and 2 μg/ml), ceftiofur (2 and 2 μg/ml), and colistin (4 and 2 μg/ml). Marked resistance was found in others.     

Assessment of antibiotic resistance phenotype and integrons in Salmonella enterica serovar Typhimurium isolated from swine

Salmonella enterica serovar Typhimurium (S. Typhimurium) isolated and identified from swine were subjected for the analysis of antibiotic resistance pattern and clinically important class 1 and 2 integrons. In addition, S. Typhimurium isolates exhibiting ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, tetracycline and florfenicol (ACSSuTF) resistance pattern as described in most Salmonella enterica serotype Typhimurium definitive type 104 (DT104) were characterized by polymerase chain reaction. All the isolates were resistant to more than four antibiotics and showed the highest resistance to streptomycin (94.1%), followed by tetracycline (90.1%), ampicillin (64.7%), chloramphenicol (56.8%) and gentamicin (54.9%). MIC value for the ten isolates ranged between 0.125-2 mug/ml for ciprofloxacin. Among the beta-lactams used, only one of the isolate exhibited resistance to ceftiofur (MIC 8 microg/ml). Sixty eight percent of these multi drug resistance (MDR) S. Typhimurium isolates carried clinically important class 1 integron with 1kb (aadA) and/or 2kb (dhfrXII-orfF-aadA2) resistance gene cassettes. This study reports the increasing trend of multi drug resistance (MDR) S. Typhimurium with clinically important class 1 integron in pigs. In addition, emergence of the ACSSuTF-type resistance in S. Typhimurium PT other than DT104 may limit the use of resistance gene markers in its detection methods by PCR.     

In vitro antimicrobial activity against 10 North American and European Lawsonia intracellularis isolates

The objective of this study was to determine the in vitro minimum inhibitory concentration (MIC) of antimicrobials against 10 isolates of Lawsonia intracellularis, the etiological agent of proliferative enteropathy (PE). Antimicrobials tested included carbadox, chlortetracycline, lincomycin, tiamulin, tylosin and valnemulin. The MIC of each antimicrobial against L. intracellularis was determined using a tissue culture system and was identified as the lowest concentration that inhibited 99% of L. intracellularis growth, as compared to the antimicrobial-free control. Each antimicrobial concentration was evaluated for both intracellular and extracellular activity against L. intracellularis, an obligately intracellular bacterium. When tested for intracellular activity, carbadox, tiamulin, and valnemulin were the most active antimicrobials with MICs of < or =0.5microg/ml. Tylosin (MICs ranging from 0.25 to 32microg/ml) and chlortetracycline (MICs ranging from 0.125 to 64microg/ml) showed intermediate activities and lincomycin (MICs ranging from 8 to >128mIcog/ml) showed the least activity. When tested for extracellular activity, valnemulin (MICs ranging from 0.125 to 4microg/ml) was the most active against most L. intracellularis isolates. Chlortetracycline (MICs ranging from 16 to 64microg/ml), tylosin (MICs ranging from 1 to >128microg/ml), and tiamulin (MICs ranging from 1 to 32microg/ml) showed intermediate activities. Lincomycin (MICs ranging from 32 to >128microg/ml) showed the least activity. Our in vitro results showed that each L. intracellularis isolate had a different antimicrobial sensitivity pattern and these data can be utilized as an in vitro guideline for the further antimicrobial evaluation of field L. intracellularis isolates.     

Antimicrobial susceptibilities of Staphylococcus aureus isolated from commercial broilers in northeastern Georgia

Staphylococcus aureus is an important opportunist that can cause superficial to life-threatening illnesses in a variety of animal species. In poultry, this organism has been implicated in osteomyelitis, synovitis, and cellulitis. Whereas most infections can be treated with antibiotics, because of the organism's propensity to acquire antimicrobial resistance, it is important to continually monitor antibiotic susceptibilities of clinical isolates. We surveyed 77 clinical poultry S. aureus isolates, collected from 1998 to 2000, for susceptibilities to a panel of 18 antimicrobial agents. Thirty-six percent of isolates were susceptible to all antibiotics. Forty-three and 16% of avian S. aureus were resistant to one and two antibiotics respectively. Staphylococcus aureus isolates were commonly resistant to tetracycline (40%; minimal inhibitory concentration [MIC]90 > 32 microg/ml), lincomycin (19%; MIC90 > 32 microg/ml), erythromycin (12%; MIC90 > 8 microg/ml), and kanamycin (8%; MIC90 < 128 microg/ml). All S. aureus isolates were susceptible to chloramphenicol, gentamicin, streptomycin, nitrofurantion, linezolid, quinupristin/dalfopristin, vancomycin, and the production antimicrobials virginiamycin, salinomycin, and flavomycin. A periodic assessment of antimicrobial susceptibilities of important avian pathogens like S. aureus will be important in helping the clinician's choice of antibiotic to control infection.     

Susceptibility of Bacteroides from swine abscesses to 13 antibiotics

The minimal inhibitory concentrations (MIC) of 129 strains of genus Bacteroides, isolated from abscesses in pigs, for 13 different antimicrobial agents were determined by an agar-dilution method under anaerobic conditions. Clindamycin, the most active antibiotic tested, had a median MIC of 0.8 micrograms/ml. Penicillin G, talampicillin, minocycline, chloramphenicol, and cefoxitin also inhibited all isolates at lower concentrations. Some isolates of B pyogenes were susceptible to gentamicin (MIC, 0.4 micrograms/ml), erythromycin (MIC, 0.8 micrograms/ml), cephalexin (MIC, 0.8 micrograms/ml), and cefoxitin (MIC, 3.2 micrograms/ml). Erythromycin, at a concentration of 3.2 micrograms/ml, was active against 70% of B suis tested, but it was less active against the other Bacteroides species. Some strains tested were resistant to streptomycin and neomycin.     

Antimicrobial susceptibility of pathogenic Escherichia coli isolated from pigs in Korea

The in vitro susceptibilities of 285 isolates of Escherichia coli from preweaned and postweaned pigs with diarrhea and edema disease were tested with the 15 commonly used antimicrobial drugs by an agar dilution minimal inhibitory concentration procedure according to National Committee for Clinical Laboratory Standards (NCCLS) guidelines. All E. coli isolates tested in this study belonged to enterotoxigenic E. coli, attaching and effacing E. coli, or Shiga toxin-producing E. coli. Field isolates had low MIC90 for ceftiofur (1 microg/ml). No correlation in antimicrobial resistance was found in three types of E. coli.     

In vitro susceptibility of porcine respiratory pathogens to tilmicosin.

Bacterial isolates obtained from swine with various clinical diseases were tested for susceptibility to tilmicosin by minimum inhibitory concentration (MIC) and Kirby-Bauer disk diffusion tests using National Committee on Clinical Laboratory Standards methodology. The tilmicosin MIC90 was < or =0.125 microg/ml for Erysiopelothrix rhusiopathiae, < or = 1 microg/ml for Haemophilus parasuis isolates, 8 microg/ml for Actinobacillus suis and Pasteurella multocida type A, 16 microg/ml for toxigenic and nontoxigenic P. multocida type D, 64 microg/ml for Bordetella bronchiseptica, and >128 microg/ml for Staphylococcus hyicus and Streptococcus suis. The results of disk diffusion testing matched well with the MIC results for each pathogen. This in vitro survey of tilmicosin activity against various swine isolates suggests that further clinical evaluation of tilmicosin in swine may be warranted for disease associated with E. rhusiopathiae, H. parasuis, and A. suis but not B. bronchiseptica, S. suis, or S. hyicus.