Showing papers on "Dalfopristin published in 2008"
TL;DR: The large differences found in the incidence of antibiotic resistance and virulence factors and in the genetic fingerprints determined by LH-PCR suggest a clear separation of hospital-adapted populations of enterococci from those found in open environments.
195 citations
TL;DR: The high abundance of isolates carrying virulence factors and antibiotic resistance traits suggests that the sanitary quality of foods should be improved in order to decrease the incidence of enterococci.
85 citations
TL;DR: Distinct microbiological and molecular features were detected among CF-MRSA isolates, probably due to adaptation to specific conditions in CF patients, suggesting cross-transmission or a common source.
Abstract: Objectives: Although methicillin-resistant Staphylococcus aureus (MRSA) is increasingly recognized in cystic fibrosis (CF) patients, it has not been sufficiently studied in large series. We analysed all MRSA isolates recovered from respiratory secretions of patients attending our CF unit (1994‐2006). Methods: Antibiotic susceptibilities were determined using both planktonic and sessile bacteria as inocula. Genetic relationships were determined by PFGE and multilocus sequence typing (MLST). SCCmec type and the presence of the pvl gene were also investigated. Results: A total of 93 MRSA isolates (1‐20 isolates per patient) were recovered from 18 of 77 CF patients with positive staphylococcal culture. Mean prevalence (4.4%) increased (P < 0.001) over time. All isolates were susceptible to linezolid, quinupristin/dalfopristin and co-trimoxazole but presented high resistance rates to amikacin (90%), gentamicin (85%), levofloxacin (81%) and erythromycin (69%). Except for macrolides and gentamicin, isolates were less susceptible growing in biofilms than in planktonic cultures. Fifteen different PFGE patterns were found, one of them consistently recovered for 6 years in the same patient. Identical clones were detected in several unrelated patients. MLST demonstrated that the international ST228 was the most frequent (67%) clone. The pvl gene was negative in all isolates and the SCCmec corresponded to types I (97%) and IV (3%). Strong mutators were not detected, but a considerable number were considered weak mutators. Conclusions: Distinct microbiological and molecular features were detected among CF-MRSA isolates, probably due to adaptation to specific conditions in CF patients. Prevalence of MRSA increased among these patients, most of them colonized with a multiresistant biofilm-forming clone belonging to ST228-SSCmecI, suggesting cross-transmission or a common source.
70 citations
TL;DR: Despite the development of antimicrobial agents with greater potency against VRE, a significant change in clinical outcome was not observed and suggests that vancomycin resistance does not significantly influence mortality.
Abstract: Background. The impact of antibiotic resistance on the clinical outcome of patients with vancomycin-resistant Enterococcus (VRE) bacteremia remains unclear. There are limited data comparing patient outcomes during the early era of vancomycin resistance with the period of more-potent antibiotic availability. Methods. A retrospective review was conducted of 113 patients with VRE bacteremia at a single institution from August 1993 to September 2005. Patients were assigned to a group on the basis of initial antibiotic choice for treatment of VRE (linezolid, quinupristin-dalfopristin, or combinations of other agents, before newer options were available). Outcome measurements were examined for the initial episode of VRE bacteremia, and multiple logistic regression analysis was performed to compare group outcomes. Results. Overall mortality was 37.2% (42 of 113 patients). VRE bacteremia caused or significantly contributed to death in 29 (69%) of 42 patients. Seventy-one patients were initially treated with linezolid, 20 with quinupristindalfopristin, and 22 with combinations of other agents. Univariate analysis indicated significantly more deaths in the quinupristin-dalfopristin group (odds ratio, 5.45; 95% confidence interval, 1.89‐15.9) and in the other-agents group (odds ratio, 2.94; 95% confidence interval, 1.09‐7.94) than in the linezolid group. However, after adjustment for severity of illness, treatment group was not a significant independent factor. Conclusion. Despite the development of antimicrobial agents with greater potency against VRE, a significant change in clinical outcome was not observed. This suggests that vancomycin resistance does not significantly influence mortality and points to the continued need for prospective, randomized clinical trials.
63 citations
TL;DR: The increase in vancomycin use in the 1980s to treat antibiotic-associated colitis and methicillin-resistant Staphylococcus aureus is largely responsible for the appearance of vancomYcin-resistant enterococcus, which in turn spawned isolated cases of vanComycin- resistant S. auresis.
Abstract: The increase in vancomycin use in the 1980s to treat antibiotic-associated colitis and methicillin-resistant Staphylococcus aureus (MRSA) is largely responsible for the appearance of vancomycin-resistant enterococcus, which in turn spawned isolated cases of vancomycin-resistant S. aureus. Perhaps most worrisome to clinicians are strains of MRSA that are heteroresistant to vancomycin; these isolates are difficult to detect. Appropriate use of vancomycin coupled with awareness of infection control measures is paramount to abrogating the emergence of new vancomycin-resistant MRSA organisms and preserving its future efficacy. The continued reliance on vancomycin for the treatment of MRSA infections will depend on whether vancomycin resistance can be minimized. Newer antibacterial agents, particularly those with activity toward MRSA and vancomycin-resistant enterococcus, such as linezolid, quinupristin/dalfopristin, daptomycin, and tigecycline, may take a more prominent clinical role when gram-positive bacteria resistance to vancomycin further escalate.
44 citations
TL;DR: Vancomycin-resistant Enterococcus faecium from human wastewater effluents in a nonclinical semiclosed agri-food system in Texas were characterized for susceptibility to antibiotics and disinfectants.
Abstract: Vancomycin-resistant Enterococcus faecium (VRE) from human wastewater effluents in a nonclinical semiclosed agri-food system in Texas were characterized for susceptibility to antibiotics and disinfectants. The 50 VRE were resistant to eight fluoroquinolones and 10 of 17 antimicrobials typically active against Gram-positive organisms. The VRE were susceptible to quinupristin/dalfopristin and linezolid. Lack of the insertion element IS1251 correlated with VRE susceptibility to streptomycin and gentamicin at p < 0.0001 and p = 0.033, respectively. An association was observed between pulsed-field gel electrophoresis genotypes Ic and II and susceptibility to streptomycin at p = 0.0006. VRE susceptibility for nine disinfectants and five disinfectant components is shown. Ninety-two percent of the isolates had a minimum inhibitory concentration (MIC) for triclosan ≥2 ppm. Triclosan MICs for many of the VRE were well over expected product application levels. No association was observed between antibiotic resistance and disinfectant susceptibility in these VRE. Enterococci multiply-resistant to vancomycin and aminoglycosides were found in a non-hospital environment where one would not expect to find them.
43 citations
TL;DR: Tigecycline showed in vitro activity comparable with other highly active parenteral agents and represents an option for treating complicated infections caused by CA-MRSA.
43 citations
TL;DR: An almost complete association was found between phenotypes and genotypic traits of antibiotic resistance, whilst PFGE profiling showed the highly polyclonal composition of the set of strains under study, suggesting that, at the local level and at a particular site of infection, S. aureus may show great genetic variability and escape the general rule of expansion of the S.aureus pandemic clones.
Abstract: Several characteristics were analysed in 37 Staphylococcus aureus isolates from nosocomial catheter infections: the PFGE profile after SmaI digestion of chromosomal DNA, the ability to form a biofilm on a polystyrene surface, antibiotic susceptibility patterns (penicillin, oxacillin, erythromycin, tetracycline, clindamycin, telithromycin, gentamicin, ciprofloxacin, quinupristin/dalfopristin, rifampicin, vancomycin and linezolid), and the presence of genetic determinants of antibiotic resistance and biofilm formation. All strains but three (92 %) were able to grow on a plastic surface as a biofilm. An almost complete association was found between phenotypes and genotypic traits of antibiotic resistance, whilst PFGE profiling showed the highly polyclonal composition of the set of strains under study. Sixteen isolates (43 %) were meticillin-resistant and were subjected to staphylococcal cassette chromosome mec (SCCmec) and cassette chromosome recombinase (ccr) complex type determination by multiplex PCR. Only a subgroup of six strains belonged to the archaic clone PFGE type and bore the SCCmec/ccrAB type I structure. Among the remaining strains some presented small rearrangements of the SCCmec/ccrAB genetic locus, whilst others could barely be traced back to a known structural type. These observations suggest that, at the local level and at a particular site of infection, S. aureus may show great genetic variability and escape the general rule of expansion of the S. aureus pandemic clones.
41 citations
TL;DR: The ribosome-blocking antibiotics telithromycin and quinupristin-dalfopristin, but not linezolid, inhibit the growth of Plasmodium falciparum, suggesting that their effect involves the impairment of apicoplast translation processes.
Abstract: Antibacterial agents are used in malaria therapy due to their effect on two prokaryote organelles, the mitochondrion and the apicoplast. We demonstrate here that the ribosome-blocking antibiotics telithromycin and quinupristin-dalfopristin, but not linezolid, inhibit the growth of Plasmodium falciparum. Both drugs induce delayed death in the parasite, suggesting that their effect involves the impairment of apicoplast translation processes.
34 citations
TL;DR: The detection of a considerable rate (43.5%) of iMLSB resistance among erythromycin-resistant/clindamycin-susceptible strains suggests that the true percentage of clindamyci resistance may be underestimated if testing for inducible resistance is not performed.
34 citations
TL;DR: Tigecycline, a glycylcycline, and ceftobiprole, a novel cephalosporin under investigation, have activity both against Gram-positive and Gram-negative organisms, and alternative treatment approaches that require further investigation have been introduced into clinical practice.
TL;DR: A review of literature evaluating alternative therapies, specifically linezolid, quinupristin/dalfopristin, daptomycin and tigecycline, will be presented and Interpretations of these data are offered followed by a brief presentation of future therapies, including oritavancin, telavanc in, dalbavancein, ceftobiprole and iclaprim, all of which possess potent Gram-positive activity.
Abstract: Infectious disease continues to evolve, presenting new and challenging clinical situations for practitioners. Specific to device-related and neurosurgical-related CNS infections, Gram-positive organisms are of growing concern. Current Infection Disease Society of America guidelines for the treatment of CNS infections offer little direction after conventional therapy, consisting of vancomycin, has failed or the patient has demonstrated intolerance. A review of literature evaluating alternative therapies, specifically linezolid, quinupristin/dalfopristin, daptomycin and tigecycline, will be presented. Interpretations of these data are offered followed by a brief presentation of future therapies, including ortavancin, telavancin, dalbavancin, ceftobiprole and iclaprim, all of which possess potent Gram-positive activity.
TL;DR: Treatment of VRE in pregnancy can be challenging due to the teratogenicity or unknown safety of available options, but the use of daptomycin in this patient enabted a successful outcome of multidrug-resistant E. faecium in a complicated pregnant patient without observed neonatal abnormalities.
Abstract: Objective:To report successful treatment using daptomycin for pyelonephritis associated with van cornycin-resistant Enterococcus faecium (VRE) in a 27-week pregnant woman.Case Summary:A 20-year-old 27-week pregnant patient with a history of spina bifida, neurogenic bladder, and multiple hospitalizations for recurrent urinary tract infections (UTIs) was diagnosed with pyelonephritis. She was treated with daptomycin 260 mg (4 mg/kg) daily for 14 days on the basis of a urine culture that revealed E. faecium resistant to ampicillin, nitrofurantoin, and vancomycin. All cultures following treatment revealed no growth, and the patient as well as the neonate displayed no adverse effects.Discussion:VRE UTIs can be treated safely in pregnancy with nitrofurantoin, if the organism is susceptible. Other viable options in the treatment of VRE, including linezolid, doxycycline, and quinupristin/dalfopristin, have lower urinary concentrations, teratogenic risk, or limited findings regarding their safety in pregnancy. Dap...
TL;DR: A 3-week-old infant who developed enterococcal bacteremia on post-operative day 10 after a surgical palliation for complex congenital heart disease that was complicated by acute renal failure is reports the first case of successful treatment of probable endocarditis due to VRE in a neonate using a daptomycin-containing regimen.
Abstract: Infections caused by vancomycin-resistant enterococci (VRE) may be difficult to treat because of the limited armamentarium of antimicrobial agents. The difficulty is compounded in pediatric patients in general and neonates in particular because many of the newer antimicrobials have not been studied or approved for children. We report a 3-week-old infant who developed enterococcal bacteremia on post-operative day 10 after a surgical palliation for complex congenital heart disease that was complicated by acute renal failure. Despite removal of vascular catheters and antimicrobial regimens that included linezolid, quinupristin/dalfopristin, ampicillin/sulbactam, rifampin, and gentamicin, bacteremia persisted. It was not cleared until daptomycin (in combination with doxycycline) was started. This is the first case of successful treatment of probable endocarditis due to VRE in a neonate using a daptomycin-containing regimen.
TL;DR: Current available data suggest that tigecycline may play an important role in the future as a monotherapy alternative to older broad-spectrum antibiotics, such as advanced generation cephalosporins, carbapenems, fluoroquinolones, piperacillin/tazobactam, and Gram-positive directed agents for which resistance is being increasingly reported from all parts of the world.
Abstract: Tigecycline is the first Food and Drug Administration (FDA) approved glycylcycline antibiotic. It has shown remarkable in vitro activity against a wide variety of gram-positive, gram-negative and anaerobic bacteria including many multidrug resistant (MDR) strains. However, it has minimal activity against Pseudomonas aeruginosa and Proteus spp. To date, little resistance to tigecycline has been reported. Clinical trials studying complicated skin and skin-structure infections (cSSSIs) demonstrated that tigecycline has equivalent efficacy and safety compared with the combination of vancomycin and aztreonam. For complicated intra-abdominal infections (cIAIs), tigecycline was found to be as effective as imipenem/cilastatin. Adverse events related to tigecycline therapy, i.e. nausea and vomiting, were tolerable. Currently available data suggest that tigecycline may play an important role in the future as a monotherapy alternative to older broad-spectrum antibiotics, such as advanced generation cephalosporins, carbapenems, fluoroquinolones, piperacillin/tazobactam, and gram-positive directed agents (e.g. daptomycin, linezolid and quinupristin/dalfopristin) for which resistance is being increasingly reported from all parts of the world.
TL;DR: Results clearly demonstrate that tigecycline has a minimal inhibitory concentration range of 0.015-0.5 mg/L both against tetracycline-susceptible and -resistant isolates carrying other resistance determinants, suggesting that this drug could play an important role in the treatment of infections caused by these multiresistant Gram-positive pathogens.
TL;DR: Among 10 hospital- and community-acquired Staphylococcus aureus strains with differing methicillin and vancomycin resistotypes, all strains were susceptible to ceftobiprole at MICs
Journal Article•
TL;DR: The mupirocin-resistant S. aureus isolates were all methicillin resistant and more resistant to the other antimicrobial agents compared with the mupiracin-susceptible strains.
Abstract: Background: The topical agent mupirocin plays a crucial role in strategies designed to control outbreaks of methicillin-resistant Staphylococcus aureus. The rate of high- and low-level mupirocin resistance among S. aureus strains from Iranian hospitals is not known. Material/Methods: Two hundred twenty-two nonduplicate S. aureus strains consecutively isolated in four university hospitals in Tehran, Iran, were tested for mupirocin susceptibility by disc diffusion agar method and minimum inhibitory concentration (MIC) determination by the E-test. Susceptibility to 16 other antimicrobial agents was also determined. Results: With the disc diffusion agar method, the majority of strains (97.3%) were susceptible to mupirocin and only 2.7% were resistant. The S. aureus strains showed high resistance (>50%) to most antibiotics, including penicillin G, ampicillin-sulbactam, oxacillin, cefoxitin, ciprofloxacin, erythromycin, tetracycline, clindamycin, gentamicin, and rifampicin, but resistance to linezolid, chloramphenicol, cotrimoxazole, and quinupristin/dalfopristin was low and no isolate was resistant to vancomycin. In the E-test, six strains had MICs of >4 mg/l, i.e. five strains had MICs of 8-256 mg/l (low-level mupirocin resistance) and one strain had 1024 mg/l (high-level mupirocin resistance). One strain was resistant to mupirocin in the disc diffusion agar method but showed sensitivity in the E-test (MIC: 0.94 mg/l). The mupirocin-resistant S. aureus isolates were all methicillin resistant and more resistant to the other antimicrobial agents compared with the mupirocin-susceptible strains. Conclusions: This study is the first report about mupirocin resistance of S. aureus in Iranian hospitals.
Journal Article•
TL;DR: Since MRSA is under continuous pressure of acquiring multiple drug resistance, it is imperative to focus routine surveillance on HA and CA-MRSA strains to monitor and limit the spread of this organism.
Abstract: Methicillin-resistant Staphylococcus aureus (MRSA), an established nosocomial and emerging community pathogen associated with many fatalities due to its hyper-virulence and multiple drug resistant properties, is on the continuous rise. To update the current status on the susceptibility of local MRSA isolates to various classes of antibiotics and to identify the most potent antibiotics, thirty-two clinical isolates comprised of hospital acquired (HA) and community acquired (CA) infections were investigated by disk diffusion test. Of the 32 MRSA isolates, 14 (43.75%) and 18 (56.25%) were community and hospital acquired MRSA, respectively. All isolates were multiple drug resistant to more than 3 classes of antibiotics despite the source or specimen from which it was isolated. The oxacillin MICs for all isolates ranged from 2 to ≥ 256 μg/ml. Twenty-five of 26 erythromycin-resistant MRSA isolates exhibited an inducible MLSB resistance phenotype while one showed an MS phenotype. More than half the isolates (68.75%) were resistant to at least one of the six aminoglycosides tested, with netilmicin as the most susceptible. The most effective antistaphylococcal agents were linezolid, vancomycin, teicoplanin and quinupristin/dalfopristin exhibited 100% susceptibility. Since MRSA is under continuous pressure of acquiring multiple drug resistance, it is imperative to focus routine surveillance on HA and CA-MRSA strains to monitor and limit the spread of this organism.
TL;DR: The results show the good in vitro activity of daptomycin in MRSH strains possessing a multi-resistant phenotype, similar to that of quinoprist in/dalfopristin and lower than the values for vancomycin, linezolid and teicoplanin.
Journal Article•
TL;DR: In this article, the minimum inhibitory concentration (MIC) of vancomycin of isolates was determined by agar dilution method and E-test were used to confirm presence of resistance to vancomymycin.
Abstract: Background and Objective: Vancomycin is frequently the antibiotic of choice for the treatment of infections caused by methicillin-resistant Staphylococcus aureus (MRSA). For the last years, the incidence of vancomycin-intermediate S. aureus (VISA) and vancomycin-resistant S. aureus (VRSA) has been increased in various parts of the world. The present study was carried out to determine the presence of VISA and VRSA in Tehran. Materials and Methods: A total of 164 S. aureus strains were isolated from clinical specimens in four university-affiliated hospitals in Tehran from November 2006 to June 2007. Minimum inhibitory concentration (MIC) of vancomycin of isolates was determined by agar dilution method. Vancomycin (6 mg/l) screen agar plate method and E-test were used to confirm presence of resistance to vancomycin. Disc diffusion agar test was also used to detect resistance to other antimicrobial agents. Results: Only one VRSA (MIC 256 mg/l) was detected and three strains with MIC 4 mg/l considered VISA according to recent CLSI breakpoints for vancomycin. Only VRSA strain had shown growth on vancomycin screen agar plate and was also resistant to several antimicrobial agents but susceptible to quinupristin/dalfopristin, linezolid, chloramphenicol, mupirocin and cotrimoxazole. Isolated VISA were also multi-resistant but showed susceptibility to quinupristin/ dalfopristin, linezolid, chloramphenicol and mupirocin. Conclusion: Detection of vancomycin resistance in Iranian S. aureus isolates emphasizes the challenges confronted by the infection control specialists in hospitals in Iran as well as causing problems in the treatment of patients with S. aureus infections.
TL;DR: During 2005-2006, a total of 865 Enterococcus faecium isolated from patients from eight Greek hospitals were tested for susceptibility to quinupristin/dalfopristin (Q/D), and no strain was found to carry any of the known genes, such as vatE and vatD, involved in Q/D resistance, indicating that a non-transferable undetermined mechanism is responsible for the expression of low-level Q/ D resistance.
TL;DR: Exposure to certain concentrations of linezolid was more likely to select for stable resistance in MRSA, MSSA and enterococci than was exposure to glycopeptides and quinupristin-dalfopristin.
TL;DR: The randomaly amplified polymorphic DNA (RAPD) patterns of MRSA isolates differed significantly between clinical isolates and raw meat isolates, and new antimicrobials showed high activity against all staphylococcal isolates including methicillinresistant isolates.
Abstract: The antimicrobial susceptibilities of Staphylococcus isolated from clinical isolates and raw meats were tested for six different antimicrobial agents that are in widespread clinical use in Korea and four new antimicrobials, linezolid, quinupristin/dalfopristin, daptomycin, and tigecycline. And this study analyzed the mecA genes and genetic patterns of MRSA by performing epidemiological studies using the PCR method. 46%, 51%, and 79% of clinical isolates were identified as MRSA in 1998, 1999, and 2005, respectively, and the mecA gene was detected in 82% of these isolates. Of the 133 staphylococci isolated from raw meats, 18% of the isolates were found to be resistant to methicillin, but none of these isolates showed the presence of the mecA gene. New antimicrobials, which have rarely or not yet been used in Korean hospitals, showed high activity against all staphylococcal isolates including methicillin-resistant isolates. The randomly amplified polymorphic DNA (RAPD) patterns of MRSA isolates differed significantly between clinical isolates and raw meat isolates.
TL;DR: An independent determination of the S. cohnii Vgb crystal structure and a biochemical characterization of the enzyme are reported, and both enzymes catalyze quinupristin lactone ring opening with similar rate constants, albeit perhaps with different dependencies on divalent metal ions.
Abstract: The semisynthetic streptogramin antibiotic quinupristin/dalfopristin (trade name Synercid, Aventis Pharma) is a mixture of the A-type streptogramin dalfopristin and the B-type streptogramin quinupristin, a capped hexapeptide macrolactone. Quinupristin/dalfopristin was developed to combat multidrug resistant pathogens, but suffers from its own problems with drug resistance. Virginiamycin B lyase (Vgb) inactivates the quinupristin component of Synercid by lactone ring opening. Remarkably, the enzyme promotes this reaction by intramolecular β-elimination without the involvement of a water molecule. Recently, structures of S. aureus Vgb in the presence and absence of substrate were reported and used together with detailed mutagenesis data to suggest a catalytic mechanism. Here, we report an independent determination of the S. cohnii Vgb crystal structure and a biochemical characterization of the enzyme. As expected, the S. cohnii and S. aureus Vgb structures and active sites are very similar. Moreover, both e...
TL;DR: In this article, the efficacy of quinupristin/dalfopristin versus vancomycin, alone or in combination with rifampicin, in a rabbit model of methicillin-resistant Staphylococcus aureus-induced arthritis was compared.
TL;DR: Comparison of the in vitro activity of dalfopristin and quinupristin combined with five intravenous antibiotics in a 3-dimensional model shows a very synergistic activity against all the strains and a synergy was even better against erythromycin-resistant strains.
Abstract: We compared the in vitro activity of dalfopristin and quinupristin combined with five intravenous antibiotics in a 3-dimensional model. We tested six strains of Staphylococcus aureus selected with different patterns of resistance to methicillin and erythromycin. Dalfopristin and quinupristin displayed a very synergistic activity against all the strains with a mean 16- or 32-fold decrease of inhibitory concentrations in combination. That synergy was even better against erythromycin-resistant strains. In combination with tigecycline or fosfomycin, the antibacterial activity could be consistently enhanced with the same decrease of inhibitory concentrations. A synergy was also observed, less regularly and at a lower level, with rifampin, gentamicin or vancomycin. Combinations of dalfopristin and quinupristin with tigecycline or fosfomycin could be very interesting in clinical practice because the inhibitory effect could be achieved with very low concentrations of each component, even when erythromycin-resistant strains are concerned.
TL;DR: This is the first report of quinupristin/dalfopristin-resistant S. agalactiae, and there was no clonal relationship among the MDR isolates.
Abstract: Seven Streptococcus agalactiae isolates were obtained from the vagina of 80 asymptomatic women. Three of these isolates showed multi-drug resistant (MDR) phenotypes: two isolates were resistant to clarithromycin, clindamycin, erythromycin, and tetracycline; and one isolate was resistant to clarithromycin, clindamycin, erythromycin, tetracycline, and quinupristin/dalfopristin. There was no clonal relationship among the MDR isolates. This is the first report of quinupristin/dalfopristin-resistant S. agalactiae.
TL;DR: Daptomycin displayed significant potency and a wide spectrum of activity against problematic clinical isolates of Gram-positive cocci causing nosocomial infections in European hospitals, including MDR subsets.
Dissertation•
09 Oct 2008
TL;DR: In this article, the authors investigated the relationship between intramammary treatment and the antimicrobial resistance of the bacteria from the intestinal tract and found that DCT increased significantly the ceftiofur resistance of E. coli and Enterococcus.
Abstract: The objective of the project was to detennine if the intramammary dry cow treatment (DCT) can increase the antimicrobial resistance of the intestinal bacteria Escherichia coli and Enterococcus spp. and also the mammary pathogens. The presence of the antibiotic from DCT in plasma was confirmed by tandem mass spectrometry. This presence is required to address the relationship between the intramammary treatment and the antimicrobial resistance of the bacteria from the intestinal tract. Milk and fecal samples were taken before dry-off and after calving to observe the antimicrobial resistance effect in E. coli and Enterococcus as well as mammary pathogens. These bacteria were isolated and identified as per protocols from the National Mastitis Council. These isolated bacteria were separated in two groups: dry treated cows and non-dry treated cows. Escherichia coli and Enterococcus spp. were submitted to the antimicrobial susceptibility microdilution protocol to determine the minimal inhibitory concentration (MIC) white bacterial isolates recovered from milk samples were examined with the disk diffusion test. Statistical analysis revealed that DCT increased significantly the ceftiofur resistance of the E. coli from the intestinal tract. However, the quinupristin / dalfopristin and the lincomycin resistances found in the enterococci isolates were decreased when cows were treated at dry-off. A non statistically significant increase in resistance was also observed in Staphylococcus aureus and Staphylococcus spp., recovered from milk, against penicillin / novobiocin and sulfisoxazole respectively in the dry treated group.