In vitro action of combinations of antimicrobial agents and EDTA-tromethamine on Pseudomonas aeruginosa

Combinations of EDTA-tromethamine and 7 antimicrobial agents (chloramphenicol, nalidixic acid, oxytetracycline, penicillin, polymyxin-B, streptomycin, and triple sulfa) were tested for synergistic activities against Pseudomonas aeruginosa. Three in vitro tests were used, including minimal inhibitory concentrations of the drugs, a 2-dimensional Microtiter checkerboard technique, and bacterial inhibition studies. A synergistic inhibitory action was observed with combinations of EDTA-tromethamine plus penicillin and EDTA-tromethamine plus oxytetracycline. When chloramphenicol, streptomycin, nalidixic acid, polymyxin-B, or triple sulfa was mixed with EDTA-tromethamine, synergistic action did not occur.     

Potentiation of thein vitro activity of some antimicrobial agents against selected Gram-negative bacteria by EDTA-tromethamine

Thein vitro synergistic effects of combinations of EDTA-tromethamine and six antimicrobial agents (ampicillin, chloramphenicol, oxytetracycline, streptomycin, nalidixic acid and sulphadimethoxine) on clinically isolated strains ofPseudomonas aeruginosa, Proteus mirabilis andEscherichia coli were investigated. The antibacterial activity was assessed from the minimal inhibitory concentration for the antibiotics alone or in combination with EDTA-tromethamine. EDTA-tromethamine potentiated the antibacterial activity of ampicillin, chloramphenicol, oxytetracycline and streptomycin up to four-fold. There were no significant or consistent synergistic effects with nalidixic acid or sulphadimethoxine.Abbreviations cfu colony-forming units - EDTA ethylenediaminetetraacetic acid - MIC minimal inhibitory concentration - tromethamine tris(hydroxymethyl)aminomethane Part of this paper was communicated at the XLV Congress of the Italian Society of Veterinary Sciences, Palermo, 25–28 September 1991     

In vitro susceptibilities of canine urinary bacteria to selected antimicrobial agents

Antimicrobial susceptibility tests were conducted on bacteria that were isolated from urine specimens collected by antepubic cystocentesis from dogs with urinary tract infections. Antimicrobics to which greater than or equal to 90% of these urinary bacteria were susceptible in vitro included trimethoprim-sulfamethoxazole (TMP-SMZ), nitrofurantoin, cephalexin, nalidixic acid, and gentamicin for isolates of Escherichia coli; ampicillin, TMP-SMZ, cephalexin, nalidixic acid, and gentamicin for isolates of Proteus mirabilis; ampicillin chloramphenicol, TMP-SMZ, nitrofurantoin, cephalexin, kanamycin, and gentamicin for isolates of coagulase-positive staphylococci; cephalexin, nalidixic acid, and gentamicin for isolates of Klebsiella pneumoniae; ampicillin, TMP-SMZ, and gentamicin for isolates of Streptococcus faecalis, Str faecium, and Str zymogenes; ampicillin, chloramphenicol, TMP-SMZ, and gentamicin for isolates of Str viridans; and ampicillin, chloramphenicol, TMP-SMZ, nitrofurantoin, cephalexin, kanamycin, and gentamicin for isolates of Str canis. No antimicrobial agent tested was effective in vitro at the 90% level for isolates of Pseudomonas aeruginosa, but gentamicin was closest, at 89%.     

In vitro activity of 10 antimicrobial agents against bacteria isolated from cows with clinical mastitis

The susceptibility of 495 strains of bacteria, recently isolated in France from cows with clinical mastitis, to 10 antimicrobial agents--penicillin G, cloxacillin, oxacillin, cephalexin, cefazolin, cephapirin, cefquinome, neomycin, ampicillin and colistin--was determined by measuring their minimum inhibitory concentrations (MICS). Overall, the levels of resistance were very low except for staphylococci and penicillin G. The 167 streptococcal strains were susceptible to all of the beta-lactams tested, but six (3-6 per cent) were highly resistant to neomycin. Of the 171 staphylococcal isolates, 36.2 per cent were resistant to penicillin G, one strain of Staphylococcus sciuri was classified as methicillin-resistant, but they were all susceptible to neomycin. None of the 122 strains of Escherichia coli was resistant to colistin, but 12 had high MIC values for one or more of the cephalosporins.     

In vitro susceptibility of Pseudomonas mallei to antimicrobial agents

Pseudomonas mallei was isolated from pus samples obtained from 34 mallein-positive horses. The isolates were subjected to in vitro sensitivity test using 16 different antimicrobial discs. All isolates (34) were sensitive to sulfamethizole, gentamycin, tetracycline, sulfathiazole, kanamycin, tobramycin, streptomycin and a combination of trimethoprim and sulfamethoxazole while none of them were sensitive to cephalothin, colistin, ampicillin, penicillin and nitrofurantoin. Rifapicin, chloramphenicol and carbenicillin were effective against 32, 26 and 18 isolates respectively. The minimum inhibitory concentrations (MICs) of gentamycin, tetracycline, tobramycin, sulfamethizole, streptomycin, rifampicin and a combination of trimethoprim and sulfamethoxazole were 0.28, 0.38, 0.67, 1.40, 3.40, 5.86 and 5.30 micrograms/ml, respectively.     

大环内酯类抗生素对畜禽病原菌体外抗菌敏感性试验研究

针对兽医临床的细菌耐药现象,为指导临床合理用药,采用微量肉汤稀释法研究了三代大环内酯类抗生素泰乐菌素、替米考星和泰地罗新对兽医临床常见的15种共74株病原菌的体外抑菌效果。结果显示:对于革兰阳性菌,泰乐菌素和替米考星对乳房炎常见的金黄色葡萄球菌、猪链球菌、无乳链球菌、停乳链球菌均有较强的抑菌活性,优于泰地罗新;泰地罗新对肺炎链球菌抑菌效果较强。对于革兰阴性菌,如支气管败血波氏杆菌、溶血性曼氏杆菌、胸膜肺炎放线杆菌、副猪嗜血杆菌等致病菌,替米考星的抑菌效果比泰乐菌素强1～64倍,泰地罗新比替米考星强2～32倍。对引起肠道感染的大肠杆菌,泰地罗新亦表现出很好的抑菌活性,效果优于泰乐菌素和替米考星。本试验为畜禽细菌性疾病的防控以及大环内酯类抗菌药物的合理使用提供了基础数据。     

Action of EDTA-Tris and antimicrobial agent combinations on selected pathogenic bacteria

The concentration of EDTA-Tris (3.22 mM EDTA and 0.05 M Tris) used as a lavage to treat otitis externa, cystitis or other persistent infections in dogs and cats, was found to prevent the growth of Pseudomonas aeruginosa, Staphylococcus aureus and beta streptococci when present in growth media. Pseudomonas aeruginosa was rapidly lysed in this solution. Escherichia coli and Proteus vulgaris grew in the presence of EDTA-Tris, but to a lesser extent than the controls without these compounds. Minimal inhibitory concentrations (MIC) for 8 antimicrobial agents with and without EDTA-Tris were determined for E. coli and P. vulgaris. A potentiation effect on E. coli (greater than 50% decrease MIC) was observed when EDTA-Tris was combined with penicillin, oxytetracycline or chloramphenicol. A similar effect was observed with P. vulgaris when combinations of EDTA-Tris plus gentamicin, oxytetracycline, polymyxin-B or triple sulfa were used. The results of this study indicate that EDTA-Tris appears to have merit in selected cases of otitis externa, cystitis or other persistent infections where lavage might be used.     

In vitro antimicrobial susceptibility of anaerobic bacteria isolated from caprine footrot

The in vitro antimicrobial susceptibility of Gram-negative anaerobic bacilli commonly isolated from footrot in goats was studied. A total of 97 isolates belonging to the genera Dichelobacter, Fusobacterium, Prevotella, Porphyromonas and Bacteroides, obtained from clinical cases of footrot in south-western Spain between March 2000 and May 2001, were tested against 25 antimicrobial agents comprising beta-lactams, aminoglycosides, macrolides, chloramphenicol, quinolones, lincosamides, sulphonamides and tetracyclines in order to optimise antibiotic treatment of this disease in goats. beta-lactams, tetracyclines and metronidazole displayed the highest in vitro efficacy against the species involved in the pathogenesis of footrot.     

In vitro activity of fifteen antimicrobial agents against methicillin-resistant and methicillin-susceptible Staphylococcus intermedius

In this study the susceptibility of 91 methicillin-resistant and -susceptible Staphylococcus intermedius strains (MRSI and MSSI, respectively) against 15 antimicrobial agents was determined. The activity of the antimicrobial agents was studied at pH 7.2 and pH 8.5. Methicillin was more active at pH7.2 (28 strains methicillin-resistant) than at pH 8.5 (55 strains methicillin-resistant). Gentamicin showed excellent activity, with only 3 strains resistant at pH 8.5. However, gentamicin would have to be administered parenterally. Oxytetracy-cline cannot be recommended for treatment of canine staphylococcal dermatitis, due to the high percentage (over 25%) of strains that were found to be resistant. Clindamycin showed little activity in inhibiting growth of the strains studied, the percent resistance at pH 7.2 was 93.4%. Rifampin behaved differently at the two pH values. However, a close relationship was noted between methicillin-resistant and rifampin-resistant strains, particularly at the lower pH. Of the fluoroquinolones, ciprofloxacin or enrofloxacin would be a good useful alternative for the treatment of methicillin-resistant strains of S. intermedius . Lastly, very high resistance to sulphamethoxypyridazine was found, as was the case with trimethoprim and a combination of trimethoprim/ sulphamethoxypyridazine, against not only MRSI but also MSSI strains.     

In vitro susceptibility of rabbit strains of Clostridium spiroforme to antimicrobial agents

Using an agar dilution method we measured the minimum inhibitory concentration (MIC) of 12 antimicrobial agents against 11 strains of iota-toxigenic strains of Clostridium spiroforme. Each strain was isolated from a separate outbreak of toxic diarrhoea of rabbits. Vancomycin and bacitracin, both agents used to treat intestinal clostridioses of humans and other animals, had a relatively high MIC (8 micrograms/ml or more). Metronidazole was uniformly active against C. spiroforme. With MIC of 8 micrograms/ml or more, both lincomycin (11 strains) and erythromycin (9 strains) were relatively inactive against C. spiroforme, conversely, penicillin G was active (MIC for 8 strains was 0.5 micrograms/ml or less). Exposure to any one of these drugs has been implicated as a predisposing factor for C. spiroforme mediated diarrhoea of rabbits. The greatest variation in MIC was seen for erythromycin (8-fold), penicillin G (8-fold) and tetracycline (16-fold).     

Potentiation of antibiotic activity by EDTA-tromethamine against three clinically isolated Gram-positive resistant bacteria. Anin vitro investigation

Thein vitro synergistic effects of combinations of EDTA-tromethamine and five antimicrobial agents (ampicillin, cephalexin, oxytetracycline, streptomycin and sulphadimethoxine) on three clinically isolated Gram-positive bacteria (Staphylococcus aureus, Staphylococcus hominis andStreptococcus faecium) were investigated. The bacteria had been isolated from three cases of canine otitis resistant to -lactam antibiotic therapy. The antimicrobial activity was evaluated by measuring the minimal inhibitory concentration for the antibiotics alone or in combination with EDTA-tromethamine. EDTA-tromethamine potentiated the activity of cefalexin againstS. aureus andS. hominis, of oxytetracycline againstS. aureus andS. faecium and of streptomycin againstS. faecium. No significant effects were noted on the activity of oxytetracycline againstS. hominis. The remaining combinations gave a slight synergistic effect. As previously shown for Gram-negative resistant bacteria, these data suggest that the association of EDTA-tromethamine and appropriate antibiotic therapy may be useful to overcome persistent infections of soft tissues in domestic animals.Abbreviations cfu colony forming units - EDTA ethylenediaminetetraacetic acid - MIC minimal inhibitory concentration - tromethamine tris(hydroxymethyl)- aminomethane Part of this paper was communicated at the XLVI Congress of the Italian Society of Veterinary Sciences, Venice, 30 September – 3 October 1992     

Inhibitory effects of combinations of oxytetracycline, dimethyl sulfoxide, and EDTA-tromethamine on Escherichia coli

Antibacterial activity against Escherichia coli was obtained with subminimal inhibitory concentrations of oxytetracycline (OTC) and EDTA-tromethamine. Inhibitory effects were not observed using combinations of dimethyl sulfoxide and OTC or dimethyl sulfoxide and EDTA-tromethamine. Neither EDTA-tromethamine nor OTC used alone was capable of the same degree of inhibition. Using a 2-dimensional Microtiter checkerboard technique, the inhibitory activity of these combinations was studied and isobolograms were plotted. A synergistic effect was seen with combinations of OTC and EDTA-tromethamine. Kinetic studies of microbial death, using subminimal inhibitory concentrations of these agents, confirmed these findings.     

恩诺沙星与其他抗菌药对鸡毒支原体的体外联合抑菌试验

采用2倍稀释法测定了恩诺沙星及其他8种抗菌药对鸡毒支原体BG44T株的最小抑菌浓度（MIC）,再以棋盘法测定恩诺沙星分别与其他8种抗菌药不同联合对鸡毒支原体BG44T株的敏感性。结果显示：恩诺沙星、替米考星、泰乐菌素、吉他霉素、林可霉素、沃尼妙林、泰妙菌素、氯霉素及氟苯尼考对鸡毒支原体BG44T株的MIC分别为0．063、0．004、0．016、0．063、16、〈0．004、0．008、8、8μg／mL。在8种不同联合用药对鸡毒支原体BG44T株的药敏试验中,恩诺沙星＋替米考星、恩诺沙星＋泰乐菌素、恩诺沙星＋吉他霉素、恩诺沙星＋林可霉素、恩诺沙星＋沃尼妙林、恩诺沙星＋泰妙菌素联合表现出相加作用,恩诺沙星＋氯霉素、恩诺沙星＋氟苯尼考表现出拮抗作用。     

In vitro assessment of chloramphenicol and florfenicol as second‐line antimicrobial agents in dogs

The aim of this study was to evaluate the potential of chloramphenicol and florfenicol as second‐line antimicrobial agents for treatment of infections caused by methicillin‐resistant Staphyococcus pseudintermedius (MRSP) and extended‐spectrum β‐lactamase (ESBL)‐producing Escherichia coli in dogs, through a systematic in vitro assessment of the pharmacodynamic properties of the two drugs. Minimum inhibitory concentrations (MIC) and phenicol resistance genes were determined for 169 S. pseudintermedius and 167 E. coli isolates. Minimum bactericidal concentrations (MBC), time‐killing kinetics, and postantibiotic effect (PAE) of both agents against wild‐type isolates of each species were assessed. For S. pseudintermedius, the chloramphenicol MIC₉₀ was 32 μg/mL. No florfenicol resistance was detected in this species (MIC_90 = 4 μg/mL). The MIC₉₀ of both agents against E. coli was 8 μg/mL. Resistance genes found were cat_pC221 in S. pseudintermedius and catA1 and/or floR in E. coli. The phenicols displayed a time‐dependent, mainly, bacteriostatic effect on both species. Prolonged PAEs were observed for S. pseudintermedius, and no PAEs were detected for E. coli. More research into determination of PK/PD targets of efficacy is needed to further assess the clinical use of chloramphenicol and florfenicol as second‐line agents in dogs, optimize dosage regimens, and set up species‐specific clinical break points.     

In vitro antimicrobial susceptibilities of three Porphyromonas spp and in vivo responses in the oral cavity of cats to selected antimicrobial agents

OBJECTIVES: To determine in vitro susceptibility of Porphyromonas gingivalis, P salivosa and P circumdentaria to seven antimicrobial agents by agar dilution and Epsilometer test methods and to assess the effectiveness of these antimicrobial agents in reducing the numbers of each Porphyromonas spp in the oral cavity of 16 domestic cats. DESIGN: A two-part prospective study involving in vitro antimicro-bial studies using Porphyromonas spp obtained from naturally occurring feline infections and in vivo antimicrobial response studies using client-owned cats with naturally occurring periodontal disease. PROCEDURE: Isolates (n = 25) of three feline Porphyromonas spp from the oral cavity and oral-associated disease were tested for their in vitro susceptibility to amoxycillin, amoxycillin-clavulanate, benzylpenicillin, clindamycin, doxycycline, erythromycin and metronidazole, using agar dilution and Epsilometer test methods. Digoxigenin-labelled whole chromosomal DNA probes directed against P gingivalis VPB 3492, P circumdentaria NCTC 12469T and P salivosa VPB 3313 were used to quantify organisms taken from two sample sites at the gingival margins of these cats prior to, and 5 days after, treatment with one of four commonly used antimicrobial products (amoxycillin-clavulanate, clindamycin, doxycycline or spiramycin-metronidazole). The response to treatment was assessed clinically for each cat. RESULTS: All isolates were susceptible in vitro to all seven antimicrobial agents using both methods. The numbers of P gingivalis were not reduced at the gingival sample sites by administration of amoxycillin-clavulanate for 5 days, although this treatment reduced the numbers of P salivosa and P circumdentaria to below detection levels in six of eight and two of three of sample sites, respectively; clinical improvement was not observed in cats treated with amoxycillin-clavulanate. Treatment with clindamycin, doxycycline or spiramycin-metronidazole resulted in clinical improvement and a marked reduction of all Porphyromonas isolates at the sample sites. CONCLUSION: The Epsilometer test is a simple and accurate method for determining the minimum inhibitory concentration for P gingivalis, P salivosa and P circumdentaria. All strains were susceptible in vitro to all the antimicrobial agents tested although clinical improvement of gingival disease was not noted with amoxycillin-clavulanate when given for 5 days at usual doses. This appears to be the first report of the disparity between the in vivo and in vitro susceptibility of oral bacterial strains to amoxycillin-clavulanate in the veterinary dental literature. This also appears to be the first report in which clinical and microbiological responses to commonly used antimicrobial agents for periodontal disease in cats has been documented and quantified. It was shown that treatment with clindamycin, spiramycin-metronidazole or doxycycline not only produced a substantial reduction in the number of Porphyromonas spp (in the majority of cases to below detection levels), but also resulted in substantial clinical improvement. This would indicate that these antimicrobial agents are useful adjunctive therapy to mechanical debridement in domestic cats.     

In vitro activity of five tetracyclines and some other antimicrobial agents against four porcine respiratory tract pathogens

The minimal inhibitory concentrations (MIC) of five tetracyclines and ten other antimicrobial agents were determined for four porcine bacterial respiratory tract pathogens by the agar dilution method. For the following oxytetracycline-susceptible strains, the MIC50 ranges of the tetracyclines were: P. multocida (n = 17) 0.25-0.5 micrograms/ml; B. bronchiseptica (n = 20) 0.25-1.0 micrograms/ml; H. pleuropneumoniae (n = 20) 0.25-0.5 micrograms/ml; S. suis Type 2 (n = 20) 0.06-0.25 micrograms/ml. For 19 oxytetracycline-resistant P. multocida strains the MIC50 of the tetracyclines varied from 64 micrograms/ml for oxytetracycline to 0.5 micrograms/ml for minocycline. Strikingly, minocycline showed no cross-resistance with oxytetracycline, tetracycline, chlortetracycline and doxycycline in P. multocida and in H. pleuropneumoniae. Moreover, in susceptible strains minocycline showed the highest in vitro activity followed by doxycycline. Low MIC50 values were observed for chloramphenicol, ampicillin, flumequine, ofloxacin and ciprofloxacin against P. multocida and H. pleuropneumoniae. B. bronchiseptica was moderately susceptible or resistant to these compounds. As expected tiamulin, lincomycin, tylosin and spiramycin were not active against H. pleuropneumoniae. Except for flumequine, the MIC50 values of nine antimicrobial agents were low for S. suis Type 2. Six strains of this species showed resistance to the macrolides and lincomycin.     

In vitro activity of 24 antimicrobial agents against Staphylococcus and Streptococcus isolated from diseased animals in Japan

A total of 88 Staphylococcus and 61 Streptococcus isolates from diseased animals throughout Japan were examined in 2000 for the minimum inhibitory concentrations of 24 different antimicrobials by the agar dilution method standardized by the Japanese Society of Chemotherapy. The resistance rates to aminobenzylpenicillin (36.4%) and benzylpenicillin (35.2%) were high in Staphylococcus isolates, and those to oxytetracycline (45.9%) and kanamycin (21.3%) were high in Streptococcus isolates. Two isolates resistant to oxacillin harbored the mecA gene. One was Staphylococcus epidermidis derived from a pig with arthritis, and the other Staphylococcus cohnii from a head of cattle with mastitis.