Antimicrobial Resistance of Escherichia coli O157 Isolated from Humans, Cattle, Swine, and Food

A total of 361 Escherichia coli O157 isolates, recovered from humans, cattle, swine, and food during the years 1985 to 2000, were examined to better understand the prevalence of antimicrobial resistance among these organisms. Based on broth microdilution results, 220 (61%) of the isolates were susceptible to all 13 antimicrobials tested. Ninety-nine (27%) of the isolates, however, were resistant to tetracycline, 93 (26%) were resistant to sulfamethoxazole, 61 (17%) were resistant to cephalothin, and 48 (13%) were resistant to ampicillin. Highest frequencies of resistance occurred among swine isolates (n = 70), where 52 (74%) were resistant to sulfamethoxazole, 50 (71%) were resistant to tetracycline, 38 (54%) were resistant to cephalothin, and 17 (24%) were resistant to ampicillin. Based on the presence of Shiga toxin genes as determined by PCR, 210 (58%) of the isolates were identified as Shiga toxin-producing E. coli (STEC). Among these, resistance was generally low, yet 21 (10%) were resistant to sulfamethoxazole and 19 (9%) were resistant to tetracycline. Based on latex agglutination, 189 (52%) of the isolates were identified as E. coli O157:H7, among which 19 (10%) were resistant to sulfamethoxazole and 16 (8%) were resistant to tetracycline. The data suggest that selection pressure imposed by the use of tetracycline derivatives, sulfa drugs, cephalosporins, and penicillins, whether therapeutically in human and veterinary medicine or as prophylaxis in the animal production environment, is a key driving force in the selection of antimicrobial resistance in STEC and non-STEC O157.     

Antimicrobial resistance of Escherichia coli O157 isolated from humans, cattle, swine, and food

A total of 361 Escherichia coli O157 isolates, recovered from humans, cattle, swine, and food during the years 1985 to 2000, were examined to better understand the prevalence of antimicrobial resistance among these organisms. Based on broth microdilution results, 220 (61%) of the isolates were susceptible to all 13 antimicrobials tested. Ninety-nine (27%) of the isolates, however, were resistant to tetracycline, 93 (26%) were resistant to sulfamethoxazole, 61 (17%) were resistant to cephalothin, and 48 (13%) were resistant to ampicillin. Highest frequencies of resistance occurred among swine isolates (n = 70), where 52 (74%) were resistant to sulfamethoxazole, 50 (71%) were resistant to tetracycline, 38 (54%) were resistant to cephalothin, and 17 (24%) were resistant to ampicillin. Based on the presence of Shiga toxin genes as determined by PCR, 210 (58%) of the isolates were identified as Shiga toxin-producing E. coli (STEC). Among these, resistance was generally low, yet 21 (10%) were resistant to sulfamethoxazole and 19 (9%) were resistant to tetracycline. Based on latex agglutination, 189 (52%) of the isolates were identified as E. coli O157:H7, among which 19 (10%) were resistant to sulfamethoxazole and 16 (8%) were resistant to tetracycline. The data suggest that selection pressure imposed by the use of tetracycline derivatives, sulfa drugs, cephalosporins, and penicillins, whether therapeutically in human and veterinary medicine or as prophylaxis in the animal production environment, is a key driving force in the selection of antimicrobial resistance in STEC and non-STEC O157.     

Serovar distribution and antimicrobial susceptibility of swine Salmonella isolates from clinically ill pigs in diagnostic submissions from Indiana in the United States

Aims:  To determine serovar distribution and levels of antimicrobial susceptibility of Salmonella isolated from clinically ill pigs in diagnostic submissions.
Methods and Results:  A total of 197 Salmonella isolates were obtained by the Indiana Animal Disease Diagnostic Laboratory from 2003 to 2005. Minimal inhibitory concentrations (MICs) were determined using the standard microbroth dilution method. The top four serovars identified were Salm. enterica serovar Typhimurium variant Copenhagen, Salm . Derby, Salm . Choleraesuis var. Kunzendorf and Salm . Typhimurium. All isolates were susceptible to the fluoroquinolones tested except that eight isolates were intermediate to difloxacin. The isolates showed a low prevalence of resistance to trimethoprim/sulphadiazine (Sxt), gentamicin (G), ceftiofur (Cf) and cephalothin (Cp) with low MIC₅₀ value of ≤0·5, 0·5, 1 and 4  μ g ml⁻¹, respectively. They showed a high prevalence of resistance to tetracycline (T; 83·8%), and a moderate prevalence to ampicillin (55·8%), spectinomycin (42·6%), ticarcillin (41·6%) and florfenicol (41·1%). There were more isolates of Salm . Typhimurium, including var. Copenhagen and Salm . Agona, that possessed multiple antimicrobial resistance to amoxicillin/clavulanic acid, ampicillin, ceftiofur and cephalothin (AxApCfCp) than the other serovars.
Conclusions:  The swine Salmonella isolates were susceptible to the fluoroquinolones, Sxt, G, Cf and Cp, but resistant to T.
Significance and Impact of the Study:  These findings provided useful information regarding antimicrobial susceptibility and resistance in dealing with clinical salmonellosis in pig herds.     

Antimicrobial resistance and in vitro gene transfer in bacteria isolated from the ulcers of EUS-affected fish in India

Aims:  The occurrence of drug resistance and plasmid-mediated transferability was investigated in 15 Aeromonas isolates collected from the ulcers of epizootic ulcerative syndrome (EUS)-affected fishes Katla ( Catla catla ), Mrigel ( Cirrhinus mrigala ) and Punti ( Puntius sp.).
Methods and Results:  Disc diffusion assay showed that all the strains were resistant to ampicillin and sensitive to streptomycin. Of the 15 isolates examined, 93·3% isolates were resistant to erythromycin, sulfadiazine and novobiocin, while 66% were resistant to rifampin and 20% to chloramphenicol. All isolates harboured plasmids with sizes ranging from 64 to 23 kbp with a 23-kbp plasmid in common. Plasmids from 11 Aeromonas strains were transferred to Escherichia coli DH5α recipient strain along with the transfer of ampicillin, erythromycin and chloramphenicol resistance determinants with frequencies ranging from 7·0 × 10⁻⁶ to 1·8 × 10⁻⁵ transconjugants per recipient cell.
Conclusions:  The resistance to ampicillin, erythromycin, sulfadiazine, novobiocin and chloramphenicol is prevalent among the bacteria isolated from EUS-affected fish, and resistant determinants of some of these antibiotics have been transferred to the bacteria of other origin.
Significance and Impact of the Study:  The emergence of antibiotic resistance bacteria and gene transfer in vitr o suggests that antibiotics should be used more cautiously to treat Aeromonas infections in aquaculture.     

Comparison of antimicrobial resistance patterns between clinical and sewage isolates in a regional hospital in Taiwan

Aims:  To compare bacterial populations and antimicrobial resistance patterns between clinical and sewage isolates from a regional hospital in northern Taiwan. The dissemination of antibiotic-resistant bacteria from hospital compartments to the hospital sewage treatment plant was examined.
Methods and Results:  A total of 1020 clinical isolates and 435 sewage isolates were collected between July and September 2005. The percentages of Gram-negative bacteria from the clinical and sewage isolates were 87·2% and 91·0%, respectively ( P  =   0·033). Escherichia coli were the leading bacterial isolates in both groups. Antimicrobial susceptibility testing showed a significant difference ( P  <   0·001) in resistance to ampicillin (85·6% vs 94·1%), ampicillin/sulbactam (31·7% vs 55·4%), cefazolin (29·2% vs 71·5%) and cefuroxime (20·7% vs 61·9%) between clinical and sewage coliform isolates, respectively.
Conclusions:  The sewage isolates had higher antimicrobial resistance rates than the clinical isolates from the same hospital.
Significance and Impact of the Study:  The low efficacy of the hospital sewage treatment may contribute to the dissemination of multidrug resistant bacteria from this hospital compartments to the environment. Practices which limit the disposal of antimicrobial agents into the wastewater system may be the possible measure to prevent the selection of multidrug-resistant bacteria from sewage treatment plants.     

Antimicrobial resistance and resistance plasmids in Salmonella from Ontario, Canada.

Collections of 589 human and 204 animal strains of Salmonella isolated in Ontario during the summer of1974 were examined for susceptibility to 12 antimicrobial agents. Many isolates were found to be resistant to both chloramphenicol (12.4% of the human and 38.2% of the animal sample) and ampicillin. The chloramphenicol resistance almost always occurred in strains which were also resistant to ampicillin and was usually due to a self-transmissible plasmid with a resistance pattern of CmKmSmTc (chloramphenicol, kanamycin, streptomycin, and tetracycline) or CmTc. Ampicillin resistance in these strains was mediated by a variety of plasmids with patterns ApSu (ampicillin and sulfa drugs) and ApSmSu, many of which were nonself-transmissible. Ampicillin resistance in chloramphenicol-sensitive strains was transferable from 21% of the strains, and it was associated with resistance patterns which were different from the self-transferable ampicillin patterns from the chloramphenicol-resistance strains.     

Prevalence and antimicrobial susceptibility of staphylococci isolated from the skin surface of clinically normal cats

Samples were collected from 148 adult cats, processed for isolation of Staphylococcus species and tested for susceptibility to penicillin G, gentamicin, oxacillin, amoxycillin, ampicillin, cephalexin and rifampin. Methicillin resistance was also determined. Ninety-eight isolates were obtained (66% of samples). Coagulase-negative species were most common, and the most frequently isolated species (37 samples) was Staph. felis . Other coagulasenegative species, such as Staph. simulans , Staph. epidermidis and Staph. Saprophyticus were also isolated. Coagulase-positive species were obtained from 40 cats; the most frequent was Staph. intermedius (26 samples), followed by Staph. aureus (14 samples). Resistance to antibiotics was frequently observed, with 58·2% of the isolates showing resistance to at least one drug. Resistance to Penicillin G was observed in 49 of the 98 isolates (50%), 22 samples were resistant to oxacillin (22·4%) and 12 to rifampin (12·2%). Resistance to amoxycillin and ampicillin was very similar to that observed to Penicillin G. Gentamicin was the most active antimicrobial agent. Three MRSA (methicillin-resistant Staphylococcus aureus ) were isolated, which represents 21·4% of the isolates of that species. Nineteen MRS (methicillin resistant staphylococci) were also observed, distributed among Staph. intermedius (eight), Staph. simulans (six) and Staph. felis (five) isolates. The role of these micro-organisms on the skin of cats is discussed.     

Characterization of multiple-antimicrobial-resistant salmonella serovars isolated from retail meats

A total of 133 Salmonella isolates recovered from retail meats purchased in the United States and the People's Republic of China were assayed for antimicrobial susceptibility, the presence of integrons and antimicrobial resistance genes, and horizontal transfer of characterized antimicrobial resistance determinants via conjugation. Seventy-three (82%) of these Salmonella isolates were resistant to at least one antimicrobial agent. Resistance to the following antibiotics was common among the United States isolates: tetracycline (68% of the isolates were resistant), streptomycin (61%), sulfamethoxazole (42%), and ampicillin (29%). Eight Salmonella isolates (6%) were resistant to ceftriaxone. Fourteen isolates (11%) from the People's Republic of China were resistant to nalidixic acid and displayed decreased susceptibility to ciprofloxacin. A total of 19 different antimicrobial resistance genes were identified in 30 multidrug-resistant Salmonella isolates. The bla(CMY-2) gene, encoding a class A AmpC beta-lactamase, was detected in all 10 Salmonella isolates resistant to extended-spectrum beta-lactams. Resistance to ampicillin was most often associated with a TEM-1 family beta-lactamase gene. Six aminoglycoside resistance genes, aadA1, aadA2, aacC2, Kn, aph(3)-IIa, and aac(3)-IVa, were commonly present in the Salmonella isolates. Sixteen (54%) of 30 Salmonella isolates tested had integrons ranging in size from 0.75 to 2.7 kb. Conjugation studies demonstrated that there was plasmid-mediated transfer of genes encoding CMY-2 and TEM-1-like beta-lactamases. These data indicate that Salmonella isolates recovered from retail raw meats are commonly resistant to multiple antimicrobials, including those used for treating salmonellosis, such as ceftriaxone. Genes conferring antimicrobial resistance in Salmonella are often carried on integrons and plasmids and could be transmitted through conjugation. These mobile DNA elements have likely played an important role in transmission and dissemination of antimicrobial resistance determinants among Salmonella strains.     

Characterization of antimicrobial susceptibility and virulence genes of Salmonella serovars collected at a commercial turkey processing plant

Aims:  To determine the antimicrobial susceptibility profiles, distribution of class 1 integrons, virulence genes and genes encoding resistance to tetracycline ( tetA , tetC , tetD and tetE ) and streptomycin ( strA , strB and aadA1 ) in Salmonella recovered from turkeys.
Methods and Results:  The antimicrobial susceptibility of 80 isolates was determined using National Antimicrobial Resistance Monitoring System. The distribution of resistance genes, class 1 integrons and virulence genes was determined using PCR. Resistances to tetracycline (76·3%) and streptomycin (40%) were common. Sixty-two (77·5%) isolates displayed resistance against one or more antimicrobials and 33 were multi-drug resistant. tetA was detected in 72·5% of the isolates, while tetC , tetD and tetE were not detected. The strA and strB genes were detected in 73·8% of the isolates. Two isolates possessed class 1 integrons of 1 kb in size, containing the aadA1 gene conferring resistance to streptomycin and spectinomycin. Fourteen of the virulence genes were detected in over 80% of the isolates.
Conclusions:  This study shows that continuous use of tetracycline and streptomycin in poultry production selects for resistant strains. The Salmonella isolates recovered possess significant ability to cause human illness.
Significance and Impact of the Study:  Information from this study can be employed in guiding future strategies for the use of antimicrobials in poultry production.     

Antimicrobial resistance and plasmid profiles of Campylobacter jejuni and Campylobacter coli from human and animal sources

AIMS: The purpose of this study was to determine the susceptibility of Campylobacter jejuni and Campylobacter coli isolates to antimicrobial agents and to investigate the presence of plasmid DNA. METHODS AND RESULTS: A total of 15 clinical isolates from children faeces, and 29 animal isolates of Campylobacter jejuni (n=22) and Campylobacter coli (n=22) were tested for susceptibility to 9 antimicrobial agents using a disc diffusion method, and screened for the presence of plasmid DNA by agarose gel electrophoresis. Of the 44 isolates, 56.8% were resistant to sulphonamide, 25% to norfloxacin, 18.2% to erythromicin, ciprofloxacin and ampicillin, and 13.6% to tetracycline. All isolates were susceptible to gentamicin, chloramphenicol and cefotaxime. Plasmids were detected in one Camp. jejuni (4.54%) strain isolated from sheep and in six (27.27%) Camp. coli strains isolated from rhesus monkey(3), swine(2), and poultry(1) with sizes ranging from 3.4 to 50 kb. CONCLUSIONS: The majority of the human isolates were susceptible to antibiotics commonly used for the treatment of campylobacteriosis. SIGNIFICANCE AND IMPACT OF THE STUDY: The origin and spread of Campylobacter resistance to antibiotics are discussed, with particular respect to the current situation in Brazil.     

香港养殖海鲷弧菌致病菌药物敏感性及耐药质粒研究

从发病海鲷(Sparus sarba)中共分离到51株弧菌(\%Vibrio)\%,经API20E细菌快速鉴定系统及Alsina和Blanch关键生理生化特性分析鉴定为7个种,它们分别是：溶藻胶弧菌(\%V.alginolyticus)(24株),创伤弧菌(V.vulnificus)(12株)和副溶血弧菌(V.parahaemolyticus)(7株),火神弧菌(V.logei)(4株),远洋弧菌Ⅱ菌(V.pelagius Ⅱ)(2株),河弧菌(V.fluvialis)(1株)和地中海弧菌(V.mediterranei)(1株)\%。其中3种优势菌溶藻胶弧菌创伤弧菌和副溶血弧菌证实对海鲷有致病性。另外采用平板稀释法检测了51株菌对16种抗菌素的敏感性。发现所有菌株对ceftriaxone,链霉素,萘啶酮酸和利福霉素敏感,几乎所有菌株对ceftazidime, netilimicin,氯霉素和sulfamethoxazole敏感.大部分菌株对氨苄青霉素 (60.8%),cefuroxime(667%),丁胺卡那霉素(55%),卡那霉素(588%)和三甲氧苄氨嘧啶(765%)等具有较强的耐药性。通过对菌株中所含有的耐药质粒进行分析,发现15株菌株含有1～4个质粒,分子量范围为9～123kb之间,对12株既含有较大分子量质粒又具有耐药性的菌株进行了质粒转化试验,结果其中9株菌的质粒具有转化能力,转化率为１０－１１～１０－９,表明所分离的菌株的抗药性是由于细菌染色体相关突变造成的。     

Incidence of antimicrobial resistance among Enterobacteriaceae isolated in Riyadh

The antimicrobial resistance of 1,018 isolates of Enterobacteriaceae isolated from fecal specimens of the urban population of Riyadh, Saudi Arabia, was studied. Resistance to 1 or more of 10 antimicrobial agents was encountered in 50.2% of the isolates. Of the isolates tested,Escherichia coli (0.8%) andKlebsiella species (1.6%) were found resistant to seven antimicrobial agents simultaneously: ampicillin, chloramphenicol, kanamycin, colistin, streptomycin, tetracycline, and carbenicillin. Resistance to nalidixic acid was encountered in only 0.68% of theE. coli isolates. No isolate was found to be resistant to gentamicin. Eighty-six of the resistant strains were tested for their ability to transfer their resistance. Forty percent were able to do so withE. coli K-12.     

Effects of subtherapeutic administration of antimicrobial agents to beef cattle on the prevalence of antimicrobial resistance in Campylobacter jejuni and Campylobacter hyointestinalis

The influence of antimicrobial agents on the development of antimicrobial resistance (AMR) in Campylobacter isolates recovered from 300 beef cattle maintained in an experimental feedlot was monitored over a 315-day period (11 sample times). Groups of calves were assigned to one of the following antimicrobial treatments: chlortetracycline and sulfamethazine (CS), chlortetracycline alone (Ct), virginiamycin, monensin, tylosin phosphate, and no antimicrobial agent (i.e., control treatment). In total, 3,283 fecal samples were processed for campylobacters over the course of the experiment. Of the 2,052 bacterial isolates recovered, 92% were Campylobacter (1,518 were Campylobacter hyointestinalis and 380 were C. jejuni). None of the antimicrobial treatments decreased the isolation frequency of C. jejuni relative to the control treatment. In contrast, C. hyointestinalis was isolated less frequently from animals treated with CS and to a lesser extent from animals treated with Ct. The majority (> or =94%) of C. jejuni isolates were sensitive to ampicillin, erythromycin, and ciprofloxacin, but more isolates with resistance to tetracycline were recovered from animals fed Ct. All of the 1,500 isolates of C. hyointestinalis examined were sensitive to ciprofloxacin. In contrast, 11%, 10%, and 1% of these isolates were resistant to tetracycline, erythromycin, and ampicillin, respectively. The number of animals from which C. hyointestinalis isolates with resistance to erythromycin and tetracycline were recovered differed among the antimicrobial treatments. Only Ct administration increased the carriage rates of erythromycin-resistant isolates of C. hyointestinalis, and the inclusion of CS in the diet increased the number of animals from which tetracycline-resistant isolates were recovered. The majority of C. hyointestinalis isolates with resistance to tetracycline were obtained from cohorts within a single pen, and most of these isolates were recovered from cattle during feeding of a forage-based diet as opposed to a grain-based diet. The findings of this study show that the subtherapeutic administration of tetracycline, alone and in combination with sulfamethazine, to feedlot cattle can select for the carriage of resistant strains of Campylobacter species. Considering the widespread use of in-feed antimicrobial agents and the high frequency of beef cattle that shed campylobacters, the development of AMR should be monitored as part of an on-going surveillance program.     

Analysis of integrons in human isolates of Salmonella enterica serovar typhimurium isolated in the Slovak Republic

About 110 sporadic, epidemiologically unrelated Salmonella enterica serovar typhimurium strains isolated in the Slovak Republic were analyzed for the presence of integrons. Of these 110 examined strains, 47 were of definitive phage type DT104 and 63 were strains of various phage type, RDNC and untypeable, designated here as non-DT104 strains. All isolates were also tested for antimicrobial resistance to 10 antibiotics as well as for the presence of virulence plasmid. Of 63 non-DT104 strains, 15 isolates were multiple-resistant, independently from phage type, other strains were resistant to one, two or three drugs. Resistance to ampicillin, streptomycin, tetracycline and sulfisoxazole was most frequently observed. Among the DT104 isolates up 65.9% exhibited characteristic pentaresistance--ACSSuT phenotype. The integron content was studied in PCR experiments using a 5'-CS/3'-CS primer pair. Fourteen non-DT104 strains, independently from phage type, were found to carry integrons with amplicons 650-1900 bp in size. Thirty-six DT104 strains contained integrons of 1000 and 1200 bp and 31 of they exhibited the ACSSuT phenotype. No integron was found in 10 DT104 strains, which included strains mostly resistant only to streptomycin, tetracycline and sulfisoxazole. The majority of non-DT104 strains did not possess any integrons. Our findings show the widespread existence of both resistant and multiple-resistant epidemiologically unrelated Salmonella typhimurium strains and suggest that integrons contribute to this antimicrobial resistance. The presence of 90-kb virulence plasmid in the 54 non-DT104 and in the all DT104 strains was found.     

Investigation of Antimicrobial Resistance in Escherichia coli and Enterococci Isolated from Tibetan Pigs

Objectives

This study investigated the antimicrobial resistance of Escherichia coli and enterococci isolated from free-ranging Tibetan pigs in Tibet, China, and analyzed the influence of free-ranging husbandry on antimicrobial resistance.

Methods

A total of 232 fecal samples were collected from Tibetan pigs, and the disk diffusion method was used to examine their antimicrobial resistance. Broth microdilution and agar dilution methods were used to determine minimum inhibitory concentrations for antimicrobial agents for which disks were not commercially available.

Results

A total of 129 E. coli isolates and 84 Enterococcus isolates were recovered from the fecal samples. All E. coli isolates were susceptible to amoxicillin/clavulanic acid, and 40.4% were resistant to tetracycline. A small number of isolates were resistant to florfenicol (27.9%), ampicillin (27.9%), sulfamethoxazole/trimethoprim (19.4%), nalidixic acid (19.4%), streptomycin (16.2%) and ceftiofur (10.9%), and very low resistance rates to ciprofloxacin (7.8%), gentamicin (6.9%), and spectinomycin (2.3%) were observed in E. coli. All Enterococcus isolates, including E. faecium, E. faecalis, E. hirae, and E. mundtii, were susceptible to amoxicillin/clavulanic acid and vancomycin, but showed high frequencies of resistance to oxacillin (92.8%), clindamycin (82.1%), tetracycline (64.3%), and erythromycin (48.8%). Resistance rates to florfenicol (17.9%), penicillin (6.0%), ciprofloxacin (3.6%), levofloxacin (1.2%), and ampicillin (1.2%) were low. Only one high-level streptomycin resistant E. faecium isolate and one high-level gentamicin resistant E. faecium isolate were observed. Approximately 20% and 70% of E. coli and Enterococcus isolates, respectively, were defined as multidrug-resistant.

Conclusions

In this study, E. coli and Enterococcus isolated from free-ranging Tibetan pigs showed relatively lower resistance rates than those in other areas of China, where more intensive farming practices are used. These results also revealed that free-range husbandry and absence of antibiotic use could decrease the occurrence of antimicrobial resistance to some extent.     

Coincident plasmids and antimicrobial resistance in marine bacteria isolated from polluted and unpolluted Atlantic Ocean samples.

Sewage effluent and outfall confluence samples were collected at the Barceloneta Regional Treatment Plant in Barceloneta, Puerto Rico; outfall confluence samples at Ocean City, Md., were also collected. Samples from uncontaminated open ocean areas served as clean-water controls. Bacteria were enriched in marine broth 2216 amended with 1 microgram of one of a set of chemicals selected for study per ml: nitrobenzene, dibutyl phthalate, m-cresol, o-cresol, 4-nitroaniline, bis(tributyltin) oxide, and quinone. MICs of the chemicals were determined individually for all isolates. Bacterial isolates were evaluated for resistance to nine different antibiotics and for the presence of plasmid DNA. Treated sewage was found to contain large numbers of bacteria simultaneously possessing antibiotic resistance, chemical resistance, and multiple bands of plasmid DNA. Bacteria resistant to penicillin, erythromycin, nalidixic acid, ampicillin, m-cresol, quinone, and bis(tributyltin) oxide were detected in nearly all samples, but only sewage outfall confluence samples yielded bacterial isolates that were resistant to streptomycin. Bacteria resistant to a combination of antibiotics, including kanamycin, chloramphenicol, gentamicin, and tetracycline, were isolated only from sewage effluent samples. It is concluded that bacterial isolates derived from toxic chemical wastes more frequently contain plasmid DNA and demonstrate antimicrobial resistance than do bacterial isolates from domestic sewage-impacted waters or from uncontaminated open ocean sites.     

Coincident plasmids and antimicrobial resistance in marine bacteria isolated from polluted and unpolluted Atlantic Ocean samples

Sewage effluent and outfall confluence samples were collected at the Barceloneta Regional Treatment Plant in Barceloneta, Puerto Rico; outfall confluence samples at Ocean City, Md., were also collected. Samples from uncontaminated open ocean areas served as clean-water controls. Bacteria were enriched in marine broth 2216 amended with 1 microgram of one of a set of chemicals selected for study per ml: nitrobenzene, dibutyl phthalate, m-cresol, o-cresol, 4-nitroaniline, bis(tributyltin) oxide, and quinone. MICs of the chemicals were determined individually for all isolates. Bacterial isolates were evaluated for resistance to nine different antibiotics and for the presence of plasmid DNA. Treated sewage was found to contain large numbers of bacteria simultaneously possessing antibiotic resistance, chemical resistance, and multiple bands of plasmid DNA. Bacteria resistant to penicillin, erythromycin, nalidixic acid, ampicillin, m-cresol, quinone, and bis(tributyltin) oxide were detected in nearly all samples, but only sewage outfall confluence samples yielded bacterial isolates that were resistant to streptomycin. Bacteria resistant to a combination of antibiotics, including kanamycin, chloramphenicol, gentamicin, and tetracycline, were isolated only from sewage effluent samples. It is concluded that bacterial isolates derived from toxic chemical wastes more frequently contain plasmid DNA and demonstrate antimicrobial resistance than do bacterial isolates from domestic sewage-impacted waters or from uncontaminated open ocean sites.     

Effects of Subtherapeutic Administration of Antimicrobial Agents to Beef Cattle on the Prevalence of Antimicrobial Resistance in Campylobacter jejuni and Campylobacter hyointestinalis

The influence of antimicrobial agents on the development of antimicrobial resistance (AMR) in Campylobacter isolates recovered from 300 beef cattle maintained in an experimental feedlot was monitored over a 315-day period (11 sample times). Groups of calves were assigned to one of the following antimicrobial treatments: chlortetracycline and sulfamethazine (CS), chlortetracycline alone (Ct), virginiamycin, monensin, tylosin phosphate, and no antimicrobial agent (i.e., control treatment). In total, 3,283 fecal samples were processed for campylobacters over the course of the experiment. Of the 2,052 bacterial isolates recovered, 92% were Campylobacter (1,518 were Campylobacter hyointestinalis and 380 were C. jejuni). None of the antimicrobial treatments decreased the isolation frequency of C. jejuni relative to the control treatment. In contrast, C. hyointestinalis was isolated less frequently from animals treated with CS and to a lesser extent from animals treated with Ct. The majority (≥94%) of C. jejuni isolates were sensitive to ampicillin, erythromycin, and ciprofloxacin, but more isolates with resistance to tetracycline were recovered from animals fed Ct. All of the 1,500 isolates of C. hyointestinalis examined were sensitive to ciprofloxacin. In contrast, 11%, 10%, and 1% of these isolates were resistant to tetracycline, erythromycin, and ampicillin, respectively. The number of animals from which C. hyointestinalis isolates with resistance to erythromycin and tetracycline were recovered differed among the antimicrobial treatments. Only Ct administration increased the carriage rates of erythromycin-resistant isolates of C. hyointestinalis, and the inclusion of CS in the diet increased the number of animals from which tetracycline-resistant isolates were recovered. The majority of C. hyointestinalis isolates with resistance to tetracycline were obtained from cohorts within a single pen, and most of these isolates were recovered from cattle during feeding of a forage-based diet as opposed to a grain-based diet. The findings of this study show that the subtherapeutic administration of tetracycline, alone and in combination with sulfamethazine, to feedlot cattle can select for the carriage of resistant strains of Campylobacter species. Considering the widespread use of in-feed antimicrobial agents and the high frequency of beef cattle that shed campylobacters, the development of AMR should be monitored as part of an on-going surveillance program.     

Effect of conventional and organic production practices on the prevalence and antimicrobial resistance of Campylobacter spp. in poultry

Intestinal tracts of broilers and turkeys from 10 conventional broiler farms and 10 conventional turkey farms, where antimicrobials were routinely used, and from 5 organic broiler farms and 5 organic turkey farms, where antimicrobials had never been used, were collected and cultured for Campylobacter species. A total of 694 Campylobacter isolates from the conventional and organic poultry operations were tested for antimicrobial resistance to nine antimicrobial agents by the agar dilution method. Although Campylobacter species were highly prevalent in both the conventional and organic poultry operations, the antimicrobial resistance rates were significantly different between the organic operations and the conventional operations. Less than 2% of Campylobacter strains isolated from organically raised poultry were resistant to fluoroquinolones, while 46% and 67% of Campylobacter isolates from conventionally raised broilers and conventionally raised turkeys, respectively, were resistant to these antimicrobials. In addition, a high frequency of resistance to erythromycin (80%), clindamycin (64%), kanamycin (76%), and ampicillin (31%) was observed among Campylobacter isolates from conventionally raised turkeys. None of the Campylobacter isolates obtained in this study was resistant to gentamicin, while a large number of the isolates from both conventional and organic poultry operations were resistant to tetracycline. Multidrug resistance was observed mainly among Campylobacter strains isolated from the conventional turkey operation (81%). Findings from this study clearly indicate the influence of conventional and organic poultry production practices on antimicrobial resistance of Campylobacter on poultry farms.     

Survey of plasmids and resistance factors among veterinary isolates of Salmonella enteritidis in Malaysia

Thirty-five veterinary isolates of Salmonella enteritidis were characterized by their susceptibility to 10 antimicrobial agents and by their plasmid profiles on agarose gel electrophoresis. All were susceptible to carbenicillin, chloramphenicol and nalidixic acid but 89% were resistant to tetracycline. When examined, 91% of the isolates harboured plasmids, with sizes ranging from 9.8 to 60 MDa. However, it was only possible to associate the presence of plasmids with tetracycline resistance; plasmids occurring in 90% of the tetracycline-resistant isolates. In conjugation experiments, with Escherichia coli K12 Nal^r as recipient, the tetracycline resistance in three selected S. enteritidis isolates was observed to transfer at frequencies of 3.0×10^-3 to 1.0×10^-2/donor cell. The concomitant transfer of a 56-MDa or 60-MDa plasmid in these three S. enteritidis isolates was also detected.R. Son. A. Ansary and I. Salmah are with the Department of Genetics and Cellular Biology. University of Malaya, 59100 Kuala Lumpur, Malaysia