Residual concentrations of antimicrobial growth promoters in poultry litter favour plasmid conjugation among Escherichia coli

Considering that plasmid conjugation is a major driver for the dissemination of antimicrobial resistance in bacteria, this study aimed to investigate the effects of residual concentrations of antimicrobial growth promoters (AGPs) in poultry litter on the frequencies of IncFII-FIB plasmid conjugation among Escherichia coli organisms. A 2x5 factorial trial was performed in vitro, using two types of litter materials (sugarcane bagasse and wood shavings) and five treatments of litter: non-treated (CON), herbal alkaloid sanguinarine (SANG), and AGPs monensin (MON), lincomycin (LCM), and virginiamycin (VIR). E. coli H2332 and E. coli J62 were used as donor and recipient strains, respectively.The presence of residues of monensin, lincomycin and virginiamycin increased the frequency of plasmid conjugation among E. coli in both types of litter materials. On the contrary, sanguinarine significantly reduced the frequency of conjugation among E. coli in sugarcane bagasse litter. The conjugation frequencies were significantly higher in wood shavings compared to sugarcane bagasse only in the presence of AGPs. Considering that the presence of AGPs in the litter can increase the conjugation of IncFII-FIB plasmids carrying antimicrobial resistance genes, the real impact of this phenomenon on the dissemination of antimicrobial resistant bacteria in the poultry production chain must be investigated.

Swine as reservoirs of zoonotic borderline oxacillin-resistant Staphylococcus aureus ST398

Methicillin resistance mediated by the mecA gene in Staphylococcus aureus, also known as "true MRSA", is typically associated with high oxacillin MIC values (≥8 mg/L). Because non-mecA-mediated oxacillin resistant S. aureus phenotypes can also cause hard-to-treat diseases in humans, their misidentification as methicillin-susceptible S. aureus strains (MSSA) can compromise the efficiency of the antimicrobial therapy. These strains have been refereed as Borderline Oxacillin-Resistant S. aureus (BORSA) but their characterization and role in clinical microbiology have been neglected. Considering the increasing importance of livestock-associated methicillin-resistant S. aureus ST398 (LA-MRSA) as an emerging zoonotic pathogen worldwide, this study aimed to report the genomic context of oxacillin resistance in porcine S. aureus ST398 strains. S. aureus isolates were recovered from asymptomatic pigs from three herds. Oxacillin MIC values ranged from 4 to 32 mg/L. MALDI-TOF-confirmed isolates were screened for mecA and mecC by PCR and genotyped by means of PFGE and Rep-PCR. Seven isolates were whole genome sequenced. None of the isolates harbored the mecA gene or its variants. Although all seven sequenced isolates belonged to one sequence type (ST398), two different spa types (t571 and t1471) were identified. All isolates harbored conserved blaZ gene operon and no mutations on genes encoding for penicillin-binding-proteins were detected. Genes conferring resistance against other drugs such as aminoglycosides, chloramphenicol, macrolide, lincosamide and streptogramin (MLS), tetracycline and trimethoprim were also detected. Isolates also harbored virulence genes encoding for adhesins (icaA; icaB; icaC; icaD; icaR), toxins (hlgA; hlgB; hlgC; luk-PV) and protease (aur). Pigs can serve as reservoirs of non-mecA-mediated oxacillin-resistant ST398 strains potentially pathogenic to humans. Considering that mecA has been the main target to screen methicillin-resistant staphylococci, the occurrence of BORSA phenotypes is probably underestimated in livestock.

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.

Phenotypic and Genotypic Characterization of Salmonella enterica in Captive Wildlife and Exotic Animal Species in Ohio, USA

The purpose of this study was to investigate the occurrence, antimicrobial resistance patterns, phenotypic and genotypic relatedness of Salmonella enterica recovered from captive wildlife host species and in the environment in Ohio, USA. A total of 319 samples including faecal (n = 225), feed (n = 38) and environmental (n = 56) were collected from 32 different wild and exotic animal species in captivity and their environment in Ohio. Salmonellae were isolated using conventional culture methods and tested for antimicrobial susceptibility with the Kirby-Bauer disc diffusion method. Salmonella isolates were serotyped, and genotyping was performed using the pulsed-field gel electrophoresis (PFGE). Salmonella was detected in 56 of 225 (24.9%) faecal samples; six of 56 (10.7%) environmental samples and six of 38 (15.8%) feed samples. Salmonella was more commonly isolated in faecal samples from giraffes (78.2%; 36/46), cranes (75%; 3/4) and raccoons (75%; 3/4). Salmonella enterica serotypes of known public health significance including S. Typhimurium (64.3%), S. Newport (32.1%) and S. Heidelberg (5.3%) were identified. While the majority of the Salmonella isolates were pan-susceptible (88.2%; 60 of 68), multidrug-resistant strains including penta-resistant type, AmStTeKmGm (8.8%; six of 68) were detected. Genotypic diversity was found among S. Typhimurium isolates. The identification of clonally related Salmonella isolates from environment and faeces suggests that indirect transmission of Salmonella among hosts via environmental contamination is an important concern to workers, visitors and other wildlife. Results of this study show the diversity of Salmonella serovars and public health implications of human exposure from wildlife reservoirs.

Comparative phenotypic and genotypic analyses of Salmonella Rissen that originated from food animals in Thailand and United States

Salmonella enterica serovar Rissen has been recognized as one of the most common serovar among humans and pork production systems in different parts of the world, especially Asia. In the United States, this serovar caused outbreaks but its epidemiologic significance remains unknown. The objectives of this study were to compare the phenotypic (antimicrobial susceptibility) and genotypic attributes of Salmonella Rissen isolated in Thailand (Thai) and the United States (US). All the Thai isolates (n = 30) were recovered from swine faecal samples. The US isolates (n = 35) were recovered from swine faecal samples (n = 29), cattle (n = 2), chicken (n = 2), dog (n = 1) and a ready-to-eat product (n = 1). The antimicrobial susceptibility of isolates was determined using the Kirby-Bauer disk diffusion method with a panel of 12 antimicrobials. Pulse-field gel electrophoresis (PFGE) was used to determine the genotypic diversity of isolates. All Thai isolates showed multidrug resistance (MDR) with the most frequent antibiotic resistance shown against ampicillin (100%), sulfisoxazole (96.7%), tetracycline (93.3%), streptomycin (90%) and chloramphenicol (30%). About half of the isolates of USA origin were pan-susceptible and roughly 30% were resistant to only tetracycline (R-type: Te). Salmonella Rissen isolated from Thailand and the USA in this study were found to be clonally unrelated. Genotypic analyses indicated that isolates were clustered primarily based on the geographic origin implying the limited clonality among the strains. Clonal relatedness among different host species within the same geography (USA) was found. We found genotypic similarity in Thai and US isolates in few instances but with no epidemiological link. Further studies to assess propensity for increased inter-regional transmission and dissemination is warranted.

Effect of mannan oligosaccharides (Bio-Mos) and outdoor access housing on pig growth, feed efficiency and carcass composition

The present study was conducted as a 3 × 2 factorial experiment in 7 pen replications conducted using progeny (n = 360) of successive farrowings of 1 Landrace breeding female population. Grower-finisher dietary treatments included the addition of Bio-Mos (BM; at 0.2, 0.1 and 0.05% inclusion rates for phase 1 (30.2 to 63.5 kg), 2 (63.5 to 90.5 kg), and 3 (90.5 to 113.6 kg), respectively), the inclusion of a subtherapeutic antibiotic (AB; tetracycline; at 0.0055% inclusion rate in all dietary phases) and a no additive control (CON) diet. Housing systems were a conventional, indoor (IN) facility providing 1.0 m(2)/pig solid concrete and 0.3 m(2)/pig slatted floor with 12 pigs per pen and an outdoor access (OUT) system providing 1.1 m(2)/pig indoor, bedded concrete, and 1.9 m(2)/pig outdoor solid concrete with 6 pigs per pen. Housing systems analyses acknowledge confounding of space with number of pigs per pen. Daily growth rate (ADG), feed intake (ADFI), feed conversion (G:F), ultrasonic carcass composition, blood hematocrit (1 group), and observed illnesses were measured. Dietary × housing treatment interactions were not observed. Pigs reared in OUT had greater ADFI (0.1 kg/d; P = 0.01) resulting in greater ADG (0.04 kg/d; P < 0.0005) and required fewer days to reach a standard 113.6 kg endpoint (4.0 d; P < 0.0005) but had reduced (poorer) G:F (0.01 kg gain/kg feed; P = 0.05) when compared to IN. Pigs fed BM and CON diets had greater ADG (0.02 kg/d; P < 0.05) and required 3 fewer days to 113.6 kg (P < 0.05) when compared with pigs fed AB. Carcass composition measures were not different across dietary or housing treatments. Hematocrit was 2 units greater (P < 0.05) at the end of the trial (d 84) for OUT housed pigs but not different at the start, d 28, or d 56 of the trial. In the present study, the addition of a subtherapeutic antibiotic in swine finisher diets did not improve pig growth, efficiency, or health whereas the addition of BM did not increase growth performance compared to the CON diet in both housing systems, a finding suggesting the potential for improved gut health and or improved appetite in pigs not fed an antibiotic. Whereas pigs reared OUT had greater growth rate and a more desirable hematocrit level, the observed differences may be attributed to stocking density, number of pigs per pen, or outdoor access, effects that are not able to be fully described under the experimental design.

Salmonella serovars and antimicrobial resistance profiles in beef cattle, slaughterhouse personnel and slaughterhouse environment in ethiopia

The present study was undertaken to determine the occurrence, distribution and antimicrobial resistance profiles of Salmonella serovars in slaughter beef cattle, slaughterhouse environment and personnel engaged in flaying and evisceration during slaughtering process. A total of 800 samples (each sample type, n = 100) consisting of swabs from hides, slaughterhouse personnel hands at flaying and evisceration, rumen and caecal contents, mesenteric lymph nodes, carcasses and holding pens were collected. Of the total 100 beef cattle examined, 14% were Salmonella positive in caecal content and/or mesenteric lymph nodes. Of the various samples analysed, Salmonella was detected in 31% of hides, 19% of rumen contents, 8% of mesenteric lymph nodes, 6% of caecal contents, 2% of carcass swabs, 9% of palm swabs taken from the hands of personnel in the slaughterhouse during flaying (7%) and evisceration (2%), and in 12% of holding pen swabs. The Salmonella isolates (n = 87) belonged to eight different serovars of which S. Anatum (n = 54) and S. Newport (19) were the major serovars and both serovars were detected in all sample sources except in carcass swabs. Eighteen of the 87 (20.7%) Salmonella serovars consisting of Newport (n = 14), Anatum (n = 3) and Eastbourne (n = 1) were resistant to one or more antimicrobials. Among the antimicrobial resistant Salmonella serovars, S. Newport was multidrug resistant (15.6%) and exhibited resistance to streptomycin, sulphisoxazole and tetracycline.

Antimicrobial resistance and genotypic characterization of coagulase-negative staphylococci over the dry period

Coagulase-negative staphylococci (CNS) have become the most frequently isolated organisms from bovine intramammary infections in recent years. While antimicrobial resistance (AR) is not considered a major problem among mastitis pathogens, concerns over emerging AR in general are increasing worldwide. Little information exists about the association between AR and one of the most common mastitis control measures, antibiotic dry cow therapy. The primary objective of the current study was to determine the prevalence of AR in CNS isolated before and after antimicrobial dry cow therapy. An additional objective was to genotypically characterize selected CNS isolates using pulsed-field gel electrophoresis (PFGE), to assess diversity and persistence of organisms over the dry period. Resistance against 10 antimicrobials was determined using a broth microdilution method and compared between CNS isolates collected at dry-off and at calving and from cows treated or not treated with intramammary antimicrobial products at dry-off (752 cows in total). Results suggested that increasing age of a cow and dry cow treatment when combined with high milk somatic cell count at dry-off and positive clinical mastitis history, were associated with increased AR to most beta-lactam antimicrobials and sulfadimethoxine. PFGE results suggested considerable diversity among the tested isolates as well as some clusters within cows and herds. PFGE would be useful in distinguishing between potentially persisting infections and cures and reinfections with different CNS strains.

Phylogenetic analysis of spring virema of carp virus reveals distinct subgroups with common origins for recent isolates in North America and the UK

Genetic relationships between 35 spring viremia of carp virus (SVCV) genogroup Ia isolates were determined based on the nucleotide sequences of the phosphoprotein (P) gene and glycoprotein (G) genes. Phylogenetic analysis based on P gene sequences revealed 2 distinct subgroups within SVCV genogroup Ia, designated SVCV Iai and Iaii, and suggests at least 2 independent introductions of the virus into the USA in 2002. Combined P- and G-sequence data support the emergence of SVCV in Illinois, USA, and in Lake Ontario, Canada, from the initial outbreak in Wisconsin, USA, and demonstrate a close genetic link to viruses isolated during routine import checks on fish brought into the UK from Asia. The data also showed a genetic link between SVCV isolations made in Missouri and Washington, USA, in 2004 and the earlier isolation made in North Carolina, USA, in 2002. However, based on the close relationship to a 2004 UK isolate, the data suggest than the Washington isolate represents a third introduction into the US from a common source, rather than a reemergence from the 2002 isolate. There was strong phylogenetic support for an Asian origin for 9 of 16 UK viruses isolated either from imported fish, or shown to have been in direct contact with fish imported from Asia. In one case, there was 100% nucleotide identity in the G-gene with a virus isolated in China.

Molecular epidemiology and diversity of Salmonella serovar Typhimurium in pigs using phenotypic and genotypic approaches

For epidemiological investigations of the most common and non-host-adapted Salmonella serotypes, such as Typhimurium, highly discriminatory approaches are essential. In the present study, we evaluated three genotyping methods; amplified fragment length polymorphism (AFLP), pulsed-field gel electrophoresis (PFGE) and repetitive palindromic extragenic-PCR (Rep-PCR) using 40 isolates. AFLP showed the highest discriminatory index (0.939), resolution and throughput. To determine clonality of Salmonella Typhimurium isolates and epidemiological relatedness in different commercial pig production units, we employed AFLP in combination with antimicrobial resistance pattern and phage typing. Salmonella serovar Typhimurium isolates (n=196) obtained from a longitudinal study of 18 pig farms over a 3-year period were studied. Using this approach, 16 distinct clonal types were identified. We found two common multidrug- resistant patterns including AmCmStSuTe and AmKmStSuTe. Two commonly multidrug- resistant phage types that are of known public health importance, DT104 and DT193, were also common. AFLP differentiated distinct clones within DT104, a phage type previously reported to be clonal. Fourteen of the clonal types were unique to one of the two production systems, showing diversity between independent commercial pig production systems located in the same geographical area. Clonal types obtained from nursery farms and corresponding finishing units were, however, similar.

Antimicrobial resistance of Salmonella isolates from swine

We examined the antimicrobial resistance of 1,257 isolates of 30 serovars of Salmonella enterica subsp. enterica isolated from swine. Serovars Typhimurium and Typhimurium var. Copenhagen were widespread and were frequently multidrug resistant, with distinct resistance to ampicillin, kanamycin, streptomycin, sulfamethoxazole, and tetracycline and to ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, and tetracycline, respectively.