Antimicrobial drug resistance in Staphylococcus aureus isolated from cattle in Brazil

Methicillin-Resistant Staphylococcus aureus from Brazilian Dairy Farms and Identification of Novel Sequence Types

The aim of this study was to investigate the phenotypic and genotypic diversity and anti-microbial resistance among staphylococci of dairy herds that originated from Paraiba State, north-eastern Brazil, a region where such studies are rare. Milk samples (n = 552) were collected from 15 dairy farms. Isolates were evaluated for anti-microbial susceptibility by Kirby-Bauer disc diffusion method. Confirmation of methicillin-resistant Staphylococcus aureus (MRSA) was performed using multiplex PCR targeting mecA and nuc genes in addition to phenotypic assay based on PBP-2a latex agglutination. Clonal relatedness of isolates was determined by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) genotyping. Staphylococci were detected in 269 (49%) of the samples. Among these, 65 (24%) were S. aureus. The remaining 204 isolates were either coagulase-negative staphylococci (n = 188; 70%) or coagulase positive other than S. aureus (n = 16; 6%). Staphylococci were cultured in seven (35%) of the 20 hand swab samples, from which five isolates were S. aureus. The isolates were most commonly resistant against penicillin (43%), ampicillin (38%) and oxacillin (27%). The gene mecA was detected in 21 S. aureus from milk and in one isolate from a milker's hand. None of the isolates were resistant to vancomycin. PFGE findings showed high clonal diversity among the isolates. Based on MLST, we identified a total of 11 different sequence types (STs 1, 5, 6, 83, 97, 126, 1583, 1622, 1623, 1624 and 1625) with four novel STs (ST1622-ST1625). The findings show that MRSA is prevalent in milk from semi-extensive dairy cows in north-eastern Brazil, and further investigation on its extent in various types of milk production systems and the farm-to-table continuum is warranted.

Antimicrobial Efficacy of Gatifloxacin and Moxifloxacin with and without Benzalkonium Chloride Compared with Ciprofloxacin and Levofloxacin Against Methicillin- ResistantStaphylococcus aureus

We compared the antimicrobial activity of gatifloxacin and moxifloxacin with and without benzalkonium chloride (BAK) against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA). Minimum inhibitory concentrations (MICs) against clinical isolates of MRSA were evaluated. Approximately 10(5 )CFU/ml of methicillinresistant S. aureus was added to Mueller-Hinton broth containing two-fold concentration increments of drug. For the evaluation of gatifloxacin with BAK, 50 microg/ml of BAK were added to the first well of the plate with gatifloxacin or moxifloxacin and then serially diluted. The combination of gatifloxacin or moxifloxacin with BAK was more active than either fluoroquinolone without BAK. The MICs ranged from <or=0.008 microg/ml to 0.125 microg/ml for gatifloxacin plus BAK, from 0.063 microg/ml to (3)8 microg/ml with unpreserved gatifloxacin from <0.004 to 0.25 for moxifloxacin plus BAK, and from <or=0.016 microg/ml to 16.0 microg/ml with unpreserved moxifloxacin. The combinations of gatifloxacin or moxifloxacin and BAK were highly active against MRSA in vitro, providing MICs that were approximately 2- to 500-fold lower than the MICs provided by either gatifloxacin or moxifloxacin without BAK.

Dihydrostreptomycin or streptomycin in combination with penicillin G in dairy cattle therapeutics: A review and re-analysis of published data Part 2: Resistance and residues

Combination formulations of penicillin G salts and dihydrostreptomycin were developed during the 1960s and are currently marketed in New Zealand for parenteral and intramammary use in dairy cattle. In this paper, the second part of a two paper series, the mechanisms by which bacteria develop resistance to each of these drugs independently is reviewed and the impact of this resistance on potential for synergy is discussed. Further, the considerable potential for tissue drug residues with dihydrostreptomycin or streptomycin from these formulations is examined by re-analysis of literature data, demonstrating an urgent need to reassess the place for aminoglycoside-containing formulations in dairy cattle therapeutics.

Airborne antibiotic resistant and nonresistant bacteria and fungi recovered from two swine herd confined animal feeding operations

Inhalation of microorganisms could be a health concern for workers inside and downwind of animal confinement units. Using the Andersen two-stage viable microbial particle sizing sampler, air samples were collected from locations upwind, inside, and downwind during two visits to two swine herd confined animal feeding operations. Six samples were taken at each location on each site. Bacteria isolated from each site were then tested for antibiotic resistance using the Kirby-Bauer disc diffusion method. Resistant bacterial forms were found inside and downwind of the swine confinement facilities, indicating that resistant organisms were being produced in and released from these facilities. Resistance to a battery of antibiotics including ampicillin, erythromycin, oxytetracycline, penicillin, tetracycline, and tylosin was found in the following bioaerosols: Staphylococcus aureus, Salmonella spp., and fecal coliforms. The major conclusion reached by this study was that bacteria were recovered inside and downwind of these facilities in levels that previous studies had stated could cause a potential human health hazard.

Eliminação de resistência a drogas por fluorquinolonas em Staphylococcus aureus de origem bovina

Cepas de Staphylococcus aureus de origem bovina foram submetidas ao tratamento com quatro fluoquinolonas na concentração subinibitória (1/2 x CMI), para avaliar a influência desses agentes sobre plasmídios. A ciprofloxacina mostrou ser a fluorquinolona mais eficiente, eliminando marcas de resistência para estreptomicina, tetraciclina, penicilina e cádmio. A norfloxacina e a pefloxacina eliminaram resistência para penicilina e tetraciclina, respectivamente; no entanto, não foi evidenciada a eliminação de plasmídio com ofloxacina. Os resultados confirmam a eficácia das fluor-quinolonas em eliminar plasmídios de resistência mostrando a importância desses estudos como contribuição para o entendimento da prevenção de linhagens multiresistentes, uma vez que as quinolonas em concentrações subinibitórias podem aumentar a sensibilidade das linhagens a outros agentes antimicrobianos.

Typing of human and bovine Staphylococcus aureus by RAPD-PCR and ribotyping-PCR

AIMS

To investigate genetic diversity among Staphylococcus aureus and to delineate the geographical distribution of the strains found.

METHODS AND RESULTS

RAPD-PCR and ribotyping-PCR were employed for the characterization of Staph. aureus isolates from bovine and nosocomial origin. Among the strains, five to nine groups were distinguished by RAPD-PCR, depending on which primer was used, while ribotyping-PCR distinguished seven ribotypes.

CONCLUSIONS, AND SIGNIFICANCE AND IMPACT OF THE STUDY

These results demonstrate the genetic heterogeneity of the strains studied, and the large dissemination of some clones throughout different regions and hosts, findings that may allow the monitoring of Staph. aureus infections.

Development of penicillin resistance among Staphylococcus aureus isolated from bovine mastitis in Denmark and other countries

This review gathers the published information regarding penicillin resistance among Staphylococcus aureus isolated from bovine mastitis from 43 different countries worldwide. For selected countries, trends over time are shown. The occurrence of resistance in the different countries is discussed in relation to the potential value of penicillin for therapy.

Resistance to gentamicin and related aminoglycosides in Staphylococcus aureus isolated in Brazil

Isolates of Staphylococcus aureus obtained from a Brazilian university hospital were characterized in relation to resistance to gentamicin and related aminoglycosides. Thirty-six isolates were susceptible to methicillin (MSSA) and 14 were resistant (MRSA). All isolates were sensitive to nucleic acid-binding compounds. All MRSA isolates and one MSSA isolate were demonstrated to be resistant to gentamicin and were coincidentally resistant to amikacin, kanamycin, neomycin and tobramycin. Among the gentamicin sensitive MSSA isolates, five isolates were found to be resistant only to kanamycin/neomycin. The resistance to gentamicin (and related aminoglycosides: kanamycin and tobramycin) must be due to AAC(6')-APH(2") activity. As these isolates also showed resistance to neomycin, they must carry an additional genetic element, probably the one responsible for APH(3')III activity, which accounts for the high level of resistance to kanamycin and to amikacin. The resistance to kanamycin/neomycin in the gentamicin sensitive isolates could not be attributed to the AAD(4')(4") activity because of the tobramycin sensitivity, and so could be ascribed to the APH(3')III activity. Curing and transfer experiments, as well as electrophoresis procedures, indicate that gentamicin resistance in Staph. aureus strains here studied has, characteristically, chromosomal localization.

Molecular subtyping of Staphylococcus aureus isolates from cases of bovine mastitis in Brazil

Sixty-six isolates of Staphylococcus aureus obtained from milk samples of dairy cows suffering from subclinical mastitis in southern Brazil were analysed by five different molecular typing methods. These included the analysis of plasmid profiles, the analysis of coagulase (coa) gene polymorphisms by PCR amplification of the 3' terminal region of the coa gene, the PCR-based detection of polymorphisms in the X region of the protein A gene (spa), the PCR-directed analysis of variations in the spacer region between 16S and 23S rRNA, and the comparison of pulsed-field gel electrophoretically separated genomic SmaI fragment patterns. The molecular typing methods were supplemented with the biochemical characterization of the isolates and the determination of their in-vitro susceptibility to 14 different antibiotics. All genotypic and phenotypic typing methods were analyzed for their ability to discriminate between the isolates. Macrorestriction analysis proved to be the most discriminatory single method (D = 0.96) followed by rRNA spacer typing (D = 0.85), coa PCR (D = 0.82), and spa PCR (D = 0.80).

Resistance to antimicrobial agents used for animal therapy in pathogenic-, zoonotic- and indicator bacteria isolated from different food animals in Denmark: a baseline study for the Danish Integrated Antimicrobial Resistance Monitoring Programme (DANMAP)

This study describes the establishment and first results of a continuous surveillance system of antimicrobial resistance among bacteria isolated from pigs, cattle and broilers in Denmark. The three categories of bacteria tested were: 1) indicator bacteria (Escherichia coli, Enterococcus faecalis, Enterococcus faecium), 2) zoonotic bacteria (Campylobacter coli/jejuni, Salmonella enterica, Yersinia enterocolitica), and 3) animal pathogens (E. coli, Staphylococcus aureus, coagulase-negative staphylococci (CNS), Staphylococcus hyicus, Actinobacillus pleuropneumoniae). A total of 3304 bacterial isolates collected from October 1995 through December 1996 were tested for susceptibility to all major classes of antimicrobial agents used for therapy in Denmark. Bacterial species intrinsically resistant to an antimicrobial were not tested towards that antimicrobial. Acquired resistance to all antimicrobials was found. The occurrence of resistance varied by animal origin and bacterial species. In general, resistance was observed more frequently among isolates from pigs than from cattle and broilers. The association between the occurrence of resistance and the consumption of the antimicrobial is discussed, as is the occurrence of resistance in other countries. The results of this study show the present level of resistance to antimicrobial agents among a number of bacterial species isolated from food animals in Denmark. Thus, the baseline for comparison with future prospective studies has been established, enabling the determination of trends over time.