Mechanisms of fluoroquinolone resistance in Pseudomonas aeruginosa isolates from canine infections

Chronic otitis externa in dogs is often associated with Pseudomonas aeruginosa infection. Fluoroquinolones are often used for treating such infections. Fluoroquinolone resistance mechanisms were characterized in 10 strains of P. aeruginosa isolated from chronic canine otitis externa. Nine out of ten strains harbored a mutation in the gyrA gene and presented an overexpression of efflux pump(s). There was a good correlation between the lipophilicity of the fluoroquinolone being tested and the effect of the efflux pump inhibitor in the final MIC. Therefore, both mechanisms, mutation in the gyrA gene and increased efflux pump(s), seem to play an important role in the acquisition of fluoroquinolone resistance in veterinary clinical isolates of P. aeruginosa. Levels of resistance to fluoroquinolones suggest that they could not be a good choice for systemic therapy of Pseudomonas otitis.     

Antimicrobial testing of selected fluoroquinolones against Pseudomonas aeruginosa isolated from canine otitis

A total of 100 Pseudomonas aeruginosa (P. aeruginosa) isolates were collected over a 1.5-year period from cases of canine otitis. Sensitivities to enrofloxacin, marbofloxacin, and orbifloxacin were determined using minimum inhibitory concentration testing (MICT). Isolates were also tested for sensitivities to enrofloxacin and marbofloxacin using disk-diffusion susceptibility testing (DDST). Isolates were significantly more sensitive to marbofloxacin than to enrofloxacin (z = -4.57; P<0.05) or orbifloxacin (z = -5.02; P<0.05). Agreement was 87% between MICT and DDST for marbofloxacin, with approximately equal numbers of overestimation and underestimation errors. Agreement was 74% between MICT and DDST for enrofloxacin, but DDST tended to overestimate the number of enrofloxacin-susceptible strains. These results suggest that marbofloxacin is more effective against P. aeruginosa than either enrofloxacin or orbifloxacin and that relying on DDST may lead to ineffective enrofloxacin treatment.     

Trends in fluoroquinolone resistance of bacteria isolated from canine urinary tracts.

Fluoroquinolone (FQ) antimicrobial agents are used extensively in human and veterinary medicine. Widespread use of any antimicrobial agent can apply selective pressure on populations of bacteria, which may result in an increase in the prevalence of antimicrobial-resistant isolates. Antimicrobial-susceptibility data on bacteria isolated from the canine urinary tract by the University of Missouri-Columbia Veterinary Medical Diagnostic Laboratory, Columbia, MO, were used to determine whether there has been an increase in the prevalence of FQ-resistant bacteria over time. Between January 1992 and December 2001, minimum inhibitory concentrations of either ciprofloxacin (1992-1998) or enrofloxacin (1998-2001) were determined for 1,478 bacterial isolates from the canine urinary tract. The predominant bacterial species isolated were Escherichia coli (547 isolates), Proteus mirabilis (156), and Staphylococcus intermedius (147). In all, there were 13 bacterial species with more than 25 isolates each. A significant increase in the overall proportion of resistant bacterial isolates was documented from 1992 to 2001 (Cochran-Armitage test for trend, P < 0.0001). The same increase in resistant isolates was documented when either ciprofloxacin or enrofloxacin was analyzed separately (P < 0.0001 and P < 0.0002, respectively). No difference was detected in rates of bacterial FQ resistance with regard to the sex of the dog from which the bacteria were isolated. The frequency with which some bacterial species were isolated differed with the sex of the infected dog. Proteus mirabilis was found more often in females (P < 0.0001), whereas beta hemolytic Streptococcus spp., were found more often in males (P = 0.0003). Although the overall efficacy of FQ antimicrobials remained high with greater than 80% of isolates being susceptible, the data demonstrated an increase in the proportion of resistant bacteria isolated from the urinary tract of the dog.     

In vitro fluoroquinolone susceptibility of Pseudomonas aeruginosa isolates from dogs with ulcerative keratitis

OBJECTIVE: To determine the in vitro fluoroquinolone susceptibility profiles of Pseudomonas aeruginosa isolates from dogs with ulcerative keratitis. Animals-27 dogs with P. aeruginosa-associated ulcerative keratitis. PROCEDURES: P. aeruginosa isolates from dogs with ulcerative keratitis were collected during a 3-year period. Isolates were tested by use of the disk diffusion method for their susceptibility to 7 fluoroquinolones that are available as commercial ophthalmic preparations. The antimicrobials included second- (ciprofloxacin, ofloxacin, norfloxacin, and lomefloxacin), third- (levofloxacin), and fourth-generation (gatifloxacin and moxifloxacin) fluoroquinolones. Isolates were designated as susceptible, intermediate, or resistant to the various antimicrobials. The percentage of susceptible isolates was compared among individual fluoroquinolones and among fluoroquinolone generations. RESULTS: None of the dogs had received topical or systemic fluoroquinolone treatment prior to referral. Twenty-seven P. aeruginosa isolates were collected during the study period. In vitro, bacterial resistance to the tested fluoroquinolones was infrequently identified (24/ 27 isolates were susceptible to all fluoroquinolones evaluated); susceptibility percentages ranged from 88.9% to 100% for individual antimicrobials. There were no significant differences among isolate susceptibilities to the individual antimicrobials or among generations of fluoroquinolones. CONCLUSIONS AND CLINICAL RELEVANCE: On the basis of these in vitro data, none of the 7 evaluated fluoroquinolones (individually or collectively by generation) appeared to offer a clinically important advantage in the treatment of P. aeruginosa-associated ulcerative keratitis in dogs. Among the P. aeruginosa isolates collected from dogs with ulcerative keratitis in this study, the likelihood of susceptibility to the fluoroquinolones evaluated was high.     

Antimicrobial susceptibility of Pseudomonas aeruginosa isolates from dogs with otitis externa

Pseudomonas aeruginosa is a common cause of otitis externa in dogs, and treatment of these infections is becoming problematic because of the increasing number of multiresistant strains. The aim of the present study was to compare the in vitro activities of cefepime, ceftazidime, enrofloxacin, ciprofloxacin, gentamicin and ticarcillin/clavulanic acid against 104 strains of P aeruginosa isolated from dogs with otitis externa. Antimicrobial susceptibility and minimum inhibitory concentrations, in μg/ml, were evaluated by the E test (bioMérieux). The most active compound was ceftazidime, with 100 per cent efficiency. The majority of tested strains were susceptible to ticarcillin/clavulanic acid (89.4 per cent), followed by ciprofloxacin (88.5 per cent) and cefepime (60.6 per cent). The highest resistance was observed to enrofloxacin (51.9 per cent) and gentamicin (43.3 per cent). Large numbers of strains were intermediately susceptible to antibiotics registered for use in veterinary medicine in Croatia--enrofloxacin (47.1 per cent) and gentamicin (41.3 per cent).     

Antimicrobial resistance of Escherichia coli isolates from canine urinary tract infections

This study determined the antimicrobial resistance profiles of Escherichia coli isolates from dogs with a presumptive diagnosis of urinary tract infection (UTI). Urine samples from 201 dogs with UTI diagnosed through clinical examination and urinalysis were processed for isolation of Escherichia coli. Colonies from pure cultures were identified by biochemical reactions (n=114) and were tested for susceptibility to 18 antimicrobials. The two most frequent antimicrobials showing resistance in Urinary E. coli isolates were oxytetracycline and ampicillin. Among the resistant isolates, 17 resistance patterns were observed, with 12 patterns involving multidrug resistance (MDR). Of the 69 tetracycline-resistant E. coli isolates, tet(B) was the predominant resistance determinant and was detected in 50.9% of the isolates, whereas the remaining 25.5% isolates carried the tet(A) determinant. Most ampicillin and/or amoxicillin-resistant E. coli isolates carried bla_TEM-1 genes. Class 1 integrons were prevalent (28.9%) and contained previously described gene cassettes that are implicated primarily in resistance to aminoglycosides and trimethoprim (dfrA1, dfrA17-aadA5). Of the 44 quinolone-resistant E. coli isolates, 38 were resistant to nalidixic acid, and 6 were resistant to nalidixic acid, ciprofloxacin and enrofloxacin. Chromosomal point mutations were found in the GyrA (Ser83Leu) and ParC (Ser80Ile) genes. Furthermore, the aminoglycoside resistance gene aacC2, the chloramphenicol resistant gene cmlA and the florfenicol resistant gene floR were also identified. This study revealed an alarming rate of antimicrobial resistance among E. coli isolates from dogs with UTIs.     

Antimicrobial resistance of Actinobacillus pleuropneumoniae isolated from swine

The aim of this retrospective study was to evaluate the antimicrobial resistance rates and the trend in resistance of Actinobacillus pleuropneumoniae isolated from pigs in Italy from 1994 to 2009. A total of 992 A. pleuropneumoniae isolates were tested for their susceptibility to a panel of antimicrobial agents in a disk diffusion method. Resistance to 7 drugs (amoxicillin, amoxicillin/clavulanic acid, ampicillin, cefquinome, cotrimoxazole, penicillin G and tilmicosin) showed a significant increasing trend over the time, while for 2 drugs (gentamycin and marbofloxacin) a significant decrease was observed. Resistance to the remaining 14 antimicrobial agents tested did not change significantly over the study period. Most of the isolates retained high susceptibility to antimicrobials usually effective against A. pleuropneumoniae such as amphenicols, fluoroquinolones and ceftiofur. However, high rates of resistance were observed for potentiated sulfa drugs, tetracyclines and penicillins which are currently recommended antimicrobials for pig pleuropneumonia therapy. Our results suggest the importance of continued monitoring of A. pleuropneumoniae clinical isolates in order to choose the most appropriate treatment of infections and to control the increase of resistance to currently used antimicrobials.     

Antimicrobial resistance of Escherichia coli isolated from chickens

Faecal Escherichia coli isolated from healthy farm chickens, from farm chickens with avian influenza, and from chickens with diarrhoea were more resistant to antimicrobial agents (94-100%) than those isolated from healthy domestic chickens (20%). Transfer of drug resistance was readily achieved from strains isolated from both healthy and sick farm chickens, and from diarrhoeic chickens; it was more difficult to demonstrate in strains from domestic chickens. Resistant E. coli showing serotypes suspected to be enteropathogenic for man, i.e 0126:K71(B16), 044:K74 (L) and 0119:K69(B14), were isolated from faecal samples of healthy and sick farm chickens, but not from healthy domestic birds.     

水貂绿脓杆菌分离株的生物学特性和血清型分析

为了解国内水貂出血性肺炎病原绿脓杆菌的生物学特性和血清型分布,2002—2010年间从国内5个省水貂养殖场暴发出血性肺炎的水貂肺中分离获得45株绿脓杆菌,测定了分离株的生化特性、血清型、抗生素敏感性和对小鼠和水貂的半数致死量(LD50)。结果表明:分离菌株的主要生化指标除甘露醇和ONPG与人医临床分离株的不同外,其余均与绿脓杆菌的生理生化特性相同。45株菌共分为3种血清型:G型(42/45),B型(2/45)和I型(1/45),此结果与国外近几十年流行的水貂出血性肺炎和人医临床分离的绿脓杆菌主要流行血清型相同。45株菌对5种抗生素均较敏感,敏感性与分离的年份和菌株的血清型无关系。经动物试验证明,所选的4株菌毒力均不同,2株B型菌株毒力均较G型弱,4菌株对水貂的毒力均强于对小鼠的毒力,说明菌株对水貂较易感。     

Antimicrobial susceptibility of Prototheca zopfii isolated from bovine intramammary infections

In vitro antimicrobial susceptibility tests were carried out on 48 strains of Prototheca zopfii, an achlorophyllous algae causing refractory mastitis in dairy cows; 27 antimicrobials were evaluated. All strains were susceptible to both myxin and nystatin. In addition, 22 strains were susceptible to amphotericin B, 21 to polymyxin B, and 18 to gentamicin. Only 1 strain was susceptible to kanamycin. All strains were resistant to ampicillin, bacitracin, carbenicillin, cephalothin, chloramphenicol, clotrimazole, cloxacillin, erythromycin, flucytosine, ketoconazole, lincomycin, miconazole, neomycin, nitrofurazone, novobiocin, oleandomycin, penicillin, rifampin, streptomycin, tetracycline, and vancomycin.     

Serotypes and antimicrobial susceptibility of Pseudomonas aeruginosa strains isolated from diseased dogs

Strains of Pseudomonas aeruginosa isolated from diseased dogs in Tokyo area during 1983 through 1986 were serotyped and assayed for antimicrobial susceptibility to obtain an epizootiological aspect of canine P. aeruginosa infection. Major sources of specimens were ear and nasal discharges and urine. The results of O-antigen typing using a monoclonal antibody kit showed that the most predominant serotype was type M. Types G and B were also major serotypes. In a yearly distribution of serotypes, type I was almost limited in 1986, and was isolated mainly from surgical wounds, which showed an episode of nosocomial infection, whereas that of type M or B was dispersed during 4 years from 1983 to 1986. As a result of antimicrobial susceptibility test, most canine strains were considered to be susceptible to 4 drugs, which were commonly used in both human and veterinary clinics, in contrast to human isolates.     

The hemagglutinating activity of Pseudomonas aeruginosa strains isolated from humans and animals

The presence and type of adhesins occurring in Pseudomonas aeruginosa strains were determined by hemagglutination test with a 3% suspension of normal and trypsin-treated human group A erythrocytes, with or without the addition of sugar inhibitors (D-mannose, D-glucose, L-fucose, D-galactose, D-fructose, lactose, N-acetylneuraminic acid, N-acetylglucosamine and N-acetylgalactosamine). This study showed that a low percentage of Pseudomonas aeruginosa strains caused the agglutination of normal erythrocytes. Trypsin treatment of erythrocytes did not affect the hemagglutinating properties, indicating that hemagglutination was not dependent upon a trypsin-sensitive protein on the erythrocytes surface. Most of the studied strains agglutinated RBCs at 37 degrees C. A great variability in the inhibiting activity on studied strains was observed among the carbohydrates tested. These results demonstrated the predominant role of N-acetylglucosamine, N-acetylgalactosamine and N-acetylneuraminic acid for Pseudomonas aeruginosa adhesion to RBCs.     

Antimicrobial susceptibilities and bacteriological characteristics of bovine Pseudomonas aeruginosa and Serratia marcescens isolates from mastitis

The presence of metallo-β-lactamase (MBL)-producing and multidrug-resistant Pseudomonas aeruginosa (MDRP) strains among bovine isolates of Gram-negative bacilli, and O-serotypes of bovine Serratia marcescens and P. aeruginosa isolates have been reported rarely. The aims of this study were to (1) elucidate antimicrobial susceptibilities and O-serotypes of P. aeruginosa and S. marcescens isolates from bovine mastitis and the presence of MBL-producers and MDRP strains among them and (2) evaluate their relationships to human isolates. We investigated the MICs of 24 antimicrobials and O-serotypes for 116 P. aeruginosa and 55 S. marcescens isolates in Japan, primarily in 2006. A total of 171 isolates exhibited high antimicrobial susceptibilities with the exception of a partial drug. P. aeruginosa isolates exhibited high susceptibilities of ≥ 95.7% to ciprofloxacin, imipenem, meropenem, piperacillin, ceftazidime, cefepime, cefoperazone/sulbactam, amikacin, tobramycin, and gentamicin; however, they exhibited a susceptibility of only 69.8% to aztreonam. They exhibited substantial resistances to ceftriaxone, enrofloxacin, cefotaxime, and moxalactam. S. marcescens isolates exhibited high susceptibilities of ≥ 90.9% to kanamycin, ceftiofur, sulfamethoxazole-trimethoprim, and the 15 aforementioned drugs, but exhibited resistance to minocycline. Neither MBL-producers nor MDRP strains were detected among the 171 strains. The dominant serotypes of P. aeruginosa isolates were OG, OA, OB, OI, OF, OE, and OK; those of S. marcescens isolates were O6 and O5. Every S. marcescens isolate was pigmented. These findings suggest that bovine P. aeruginosa and S. marcescens isolates differ from human isolates from both antibiogram and phenotypic perspectives, and could help to evaluate differences in bacteriological characteristics between bovine and human isolates.     

Antimicrobial resistance determinants among anaerobic bacteria isolated from footrot

Antibiotic resistance has been evaluated among 36 Gram negative and anaerobic bacilli (10 Bacteroides, 11 Prevotella, 7 Porphyromonas and 8 Fusobacterium strains) isolated from clinical cases of caprine and ovine footrot (necrotic pododermatitis). The initial analysis on this bacterial consortium evaluates the relationships existing among antimicrobial resistance determinants, phenotype expression and mobilization potential. The Bacteroides strains were generally resistant to penicillins, first-generation cephalosporins, tetracycline and erythromycin, and expressed low level of β-lactamase activity. The main determinants found among the Bacteroides strains were cepA and tetQ genes, conferring resistance to β-lactams and tetracycline, respectively. A general susceptibility to β-lactams was shown for most Prevotella, Porphyromonas and Fusobacterium strains, where none of the β-lactamase genes described in Bacteroides was detected. Resistance to tetracycline and/or erythromycin was found among the three bacterial groups. Although tetQ genes were detected for several Prevotella and Porphyromonas strains, a unique ermF positive was revealed among Prevotella strains. The expression of resistance markers was not related with the polymorphism of their coding sequences. However, the finding of sequence signatures for conjugative transposons in the vicinities of tetQ and ermF suggests a mobilization potential that might have contributed to the spread of antimicrobial resistance genes.