Factors associated with antimicrobial-resistant Escherichia coli in zoo animals

Factors associated with the carriage of antimicrobial-resistant Escherichia coli isolates were analysed among zoo animals. An association was observed between selection of amoxicillin as the first-line therapy and a significantly higher percentage of resistance to ampicillin (54.5%) from 11 animals treated with antimicrobials, compared with isolates from 32 untreated animals (9.4%). In addition, the percentage resistance to kanamycin (36.4%), gentamicin (27.3%), trimethoprim (27.3%) and tetracycline (63.6%) from 11 treated animals was significantly higher than those from 32 untreated animals (3.1%, 3.1%, 3.1% and 25%, respectively), although these antimicrobials were rarely used. All kanamycin-, gentamicin- and trimethoprim-resistant isolates and more than half of the tetracycline-resistant isolates from treated animals were also resistant to ampicillin. Co-resistance to other antimicrobials with ampicillin was suggested to contribute to an increasing of resistance towards antimicrobials that were rarely administered. The present investigation revealed an association of antimicrobial treatment with the spread of antimicrobial-resistant bacteria among zoo animals.     

Carriage of potentially pathogenic Escherichia coli in chickens

DNA-DNA hybridization, cultured cell lines, and transmission electron microscopy were used to study pathogenicity traits of 64 Escherichia coli isolated from apparently healthy chickens from 18 small-scale farms in Thika District, Kenya. A total of 39 (60.9%) isolates hybridized with the eae gene probe for enteropathogenic E. coli (EPEC) whereas another 16 (25%) hybridized with the lt and st gene probes and were categorized as enterotoxigenic E. coli. Electron microscopic examination of the eae probe-positive E. coli cultures with the HT-2919A cell line confirmed that they were able to attach intimately and produced effacement typical of EPEC. In addition, negative stain electron microscopy showed that the EPEC strains produced pili that have previously been associated with increased virulence of E. coli infections in chickens. This study has also demonstrated that apparently healthy chickens may carry enteropathogenic E. coli strains.     

Risk behaviors for disease transmission among petting zoo attendees

OBJECTIVE: To evaluate risk behaviors for transmission of zoonotic diseases at petting zoos during a period without a recognized disease outbreak. DESIGN: Observational survey with environmental microbiologic sampling. SAMPLE POPULATION: 6 petting zoos in Tennessee. PROCEDURES: Attendees were observed for animal and environmental contact, eating or drinking, hand-to-face contact, and use of a hand sanitizer. Hands were examined via bacteriologic culture on some attendees. Environmental samples were collected at three petting zoos. RESULTS: 991 attendees were observed; of these, 74% had direct contact with animals, 87% had contact with potentially contaminated surfaces in animal contact areas, 49% had hand-to-face contact, and 22% ate or drank in animal contact areas. Thirty-eight percent used hand sanitizer; children had better compliance than adults. Results of bacteriologic cultures of hands were negative for Salmonella spp and Escherichia coli O157; Salmonella spp were isolated from 63% and E coli O157 from 6% of the environmental samples. CONCLUSIONS AND CLINICAL RELEVANCE: High risk behaviors were common among petting zoo visitors, and disease prevention guidelines were inconsistently followed. This is an example of the importance of one-medicine, one-health initiatives in protecting the public health. Veterinarians, venue operators, and public health authorities must work together on targeted education to improve implementation of existing disease prevention guidelines.     

Sheep-associated malignant catarrhal fever in a petting zoo.

In a privately owned petting zoo in Arizona, 17 deer from five different species, white-tailed deer (Odocoileus virginianus), Reeve's muntjac (Muntiacus reevesi), mule deer (Odocoileus hemionus), reindeer (Rangifer tarandus), and axis deer (Axis axis), died of suspected malignant catarrhal fever (MCF) over a period from late 1992 to early 1995. A PCR assay specific for ovine herpesvirus 2, the putative causative agent of sheep-associated MCF, and a competitive-inhibition enzyme-linked immunosorbent assay based on a monoclonal antibody specific to an epitope conserved among all known MCF viral isolates were used to investigate the outbreak. Ovine herpesvirus 2 DNA sequences were detected by PCR from fresh-frozen and/or formalin-fixed, paraffin-embedded tissue samples in seven deer out of eight available animals previously suspected as cases by histopathology. A high seroprevalence to the virus was found among mouflon (Ovis musimon, 80%) and pygmy goats (Capra hircus, 61%), both of which were present on the farm during the outbreak. Sixteen percent of fallow deer (Dama dama) were also seropositive to the virus. After removal of the mouflon and positive pygmy goats, no further MCF cases occurred on the farm, confirming the importance of careful management to avoid mixing clinically susceptible species with carrier species. Until better control measures are available, adherence to this practice is necessary if MCF is to be prevented in intense exposure environments such as zoos and densely populated animal parks.     

AFA and F17 adhesins produced by pathogenic Escherichia coli strains in domestic animals.

AFA and F17 are afimbrial and fimbrial adhesins, respectively, produced by pathogenic Escherichia coli strains in domestic animals. F17-related fimbriae are mainly detected on bovine and ovine E. coli associated with diarrhoea or septicaemia. The F17-G adhesin subunits recognize N-acetyl-D-glucosamine (GlcNAc) receptors present on bovine intestinal cells. Some F17 subtypes also bind to GlcNAc receptors present on human uroepithelial and intestinal Caco-2 cells or to the laminin contained in the basement of mammalian membranes. F17 is often associated with other virulence factors (aerobactin, serum resistance, CNF2 toxin, K99, CS31A or AFA adhesins) on pathogenic E. coli. A cluster of only four genes is required to synthesize functional F17-related fimbrial structures. The hypothesis of multifunctional F17 fimbrial subunits is supported by the fact that: i) the N-terminal part of the adhesin subunit participates in receptor recognition, whereas the C-terminal part is required for biogenesis of the fimbrial filament; and ii) the interaction between structural and adhesin subunits seems to be crucial for the initiation of monomer polymerization. Recently, determinants related to the afa gene clusters from human pathogenic E. coli associated with intestinal and extra-intestinal infections were identified in strains isolated from calves and piglets with diarrhoea and septicaemia. Two afa-related gene clusters, designated afa-7 and afa-8, that encode afimbrial adhesins were cloned and characterized from bovine pathogenic E. coli. These animal afa gene clusters were plasmid and chromosome borne and were expressed by strains that produced other virulence factors such as CNF toxins, F17, PAP and CS31A adhesins. A high frequency of afa-8 and a low prevalence of afa-7 among bovine E. coli isolates were suggested by preliminary epidemiological studies. As with the human afa gene clusters, the animal ones encode an adhesive structure composed of two proteins: AfaE which mediates adhesion to epithelial cells and AfaD which is an invasin.     

Multidrug-resistant extraintestinal pathogenic Escherichia coli of sequence type ST131 in animals and foods

Multidrug-resistant Escherichia coli sequence type 131 (ST131) has recently emerged as a globally distributed cause of extraintestinal infections in humans. Diverse factors have been investigated as explanations for ST131's rapid and successful dissemination, including transmission through animal contact and consumption of food, as suggested by the detection of ST131 in a number of nonhuman species. For example, ST131 has recently been identified as a cause of clinical infection in companion animals and poultry, and both host groups have been confirmed as faecal carriers of ST131. Moreover, a high degree of similarity has been shown among certain ST131 isolates from humans, companion animals, and poultry based on resistance characteristics and genomic background and human and companion animal ST131 isolates tend to exhibit similar virulence genotypes. However, most ST131 isolates from poultry appear to possess specific virulence genes that are typically absent from human and companion animal isolates, including genes associated with avian pathogenic E. coli. Since the number of reported animal and food-associated ST131 isolates is quite small, the role of nonhuman host species in the emergence, dissemination, and transmission of ST131 to humans remains unclear. Nevertheless, given the profound public health importance of the emergent ST131 clonal group, even the limited available evidence indicates a pressing need for further careful study of this significant question.     

Virulence gene regulation in pathogenic Escherichia coli.

The ability to regulate gene expression throughout the course of an infection is important for the survival of a pathogen in the host. Thus, virulence gene expression responds to environmental signals in many complex ways. Frequently, global regulatory factors associated with specific regulators co-ordinate expression of virulence genes. In this review, we present well-described regulatory mechanisms used to co-ordinate the expression of virulence factors by pathogenic Escherichia coli with a relative emphasis on diseases caused by E. coli in animals. Many of the virulence-associated genes of pathogenic E. coli respond to environmental conditions. The involvement of global regulators, including housekeeping regulons and virulence regulons, specific regulators and then sensor regulatory systems involved in virulence, is described. Specific regulation mechanisms are illustrated using the regulation of genes encoding for fimbriae, curli, haemolysin and capsules as examples.     

Characteristics of conjugative R-plasmids from pathogenic avian Escherichia coli.

Three of four virulent avian Escherichia coli isolates transferred a single large molecular-weight R-plasmid to two recipient E. coli strains. Antibiotic resistances transferred included streptomycin (two isolates) and streptomycin-tetracycline-sulfa (one isolate). Production of colicin and siderophores, complement resistance, and embryo lethality present in the virulent isolates were not transferred to recipient organisms. From the results, it appears that the R-plasmids of these virulent avian E. coli are not associated with virulence.     

合肥地区动物源致病性大肠杆菌ESBLs和PMQR基因流行分布

从安徽省合肥地区多个养殖厂分离鉴定了65株致病性大肠杆菌,用PCR方法检测ESBLs和PMQR基因的流行分布情况,用微量肉汤稀释法测定30株ESBLs和/或PMQR阳性菌对16种抗菌药物的最小抑菌浓度.PCR结果显示:ESBLs阳性率为24.6％(16/65),分别为blaOXA(16株)、blaTEM(15株)和blaCTX-M(14株),未检出blaSHV; PMQR的阳性率为46.2％(30/65),分别为qnrA(9株)、qnrS(18株)、aac(6')-Ib～cr(28株),未检出qnrB、qnrC、qnrD和qepA;且携带ESBLs基因的阳性菌株均携带PMQR基因.首次检测出有7株大肠杆菌同时携带ES-BLs基因型(blaOXA、blaTEM、blaCTX-M)和PMQR基因型(qnrA、qnrS、aac(6')-Ib-cr).药物敏感性测定结果显示:30株携带ESBLs和/或PMQR基因的阳性大肠杆菌对16种抗菌药物的耐药率为16.7％～100％,耐药谱较广,耐药性较严重.16株同时携带ESBLs和PMQR基因的阳性菌株对11种及11种以上药物耐药的菌株占87.5％,14株仅携带PMQR基因的阳性菌株对11种及11种以上药物耐药的菌株占28.5％,表明携带PMQR基因的同时携带ESBLs基因大大增强了菌株的耐药性,携带耐药基因的数量和种类与菌株的多重耐药性相关.     

papA gene of avian pathogenic Escherichia coli

P fimbrial adhesins may be associated with the virulence of avian pathogenic Escherichia coli (APEC). However, most APECs are unable to express P fimbriae even when they are grown under conditions that favor P fimbrial expression. This failure can be explained by the complete absence of the pap operon or the presence of an incomplete pap operon in Pap-negative APEC strains. In the present study, we analyzed the pap operon, specifically the papA gene that encodes the major fimbrial shaft, to better understand the pap gene cluster at the genetic level. First, by PCR, we examined a collection of 500 APEC strains for the presence of 11 genes comprising the pap operon. Except for papA, all the other genes of the operon were present in 38% to 41.2% of APEC, whereas the papA was present only in 10.4% of the APEC tested. Using multiplex PCR to probe for allelic variants of papA, we sought to determine if the low prevalence of papA among APEC was related to genetic heterogeneity of the gene itself. It was determined that the papA of APEC always belongs to the F11 allelic variant. Finally, we sequenced the 'papA region' from two papA-negative strains, both of which contain all the other genes of the pap operon. Interestingly, both strains had an 11,104-bp contig interruptingpapA at the 281-bp position. This contig harbored a streptomycin resistance gene and a classic Tn10 transposon containing the genes that confer tetracycline resistance. However, we noted that the papA gene of every papA-negative APEC strain was not interrupted by an 11,104-bp contig. It is likely that transposons bearing antibiotic resistance genes have inserted within pap gene cluster of some APEC strains, and such genetic events may have been selected for by antibiotic use.     

Acid-induced autoagglutination found in chicken pathogenic Escherichia coli strain.

Chicken pathogenic Escherichia coli strains were found to autoagglutinate in a static culture of trypticase soy broth (TSB). One strain, designated PDI-386, was further studied for its autoagglutinating property. Acidity in the cultured medium caused by glucose degradation induced the autoagglutination. The bacterial cells grown in a glucose-free L-broth could be aggregated by adding acid, which suggests a potentiality of autoagglutination of the strain grown in the L-broth. The autoagglutinating parent (Agg) formed small colonies with irregular edges like rough colonies on the TS agar, whereas its non-autoagglutinating variant (Nag) formed larger smooth colonies with a perfectly round edge. The Nag colony was easily generated from the Agg colony on the TS agar. The autoagglutinating property was very unstable when the bacteria was passed in the TSB, but rather stable in the L-broth. Under electron microscope, the Agg were found to possess pili of more than 20 microns in length. However, the phenotypic expression of autoagglutination did not correlate with that of mannose-sensitive hemagglutination against guinea pig erythrocytes. Incubation of the Nag in the L-broth at room temperature for more than 10 days provoked the reversion of the autoagglutination. There was no difference between the Agg and the Nag in terms of surface hydrophobicity, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns of membrane proteins and LPS, and plasmid profiles. The virulence of the Agg was higher than that of the Nag. The autoagglutination property is, however, so unstable that the pathogenicity of E. coli isolates from chickens should be carefully evaluated.     

Avian pathogenic Escherichia coli (APEC).

Avian pathogenic Escherichia coli (APEC) cause aerosacculitis, polyserositis, septicemia and other mainly extraintestinal diseases in chickens, turkeys and other avian species. APEC are found in the intestinal microflora of healthy birds and most of the diseases associated with them are secondary to environmental and host predisposing factors. APEC isolates commonly belong to certain serogroups, O1, O2 and O78, and to a restricted number of clones. Several experimental models have been developed, permitting a more reliable evaluation of the pathogenicity of E. coli for chickens and turkeys. Hence, virulence factors identified on APEC are adhesins such as the F1 and P fimbriae, and curli, the aerobactin iron sequestering system, K1 capsule, temperature-sensitive hemagglutinin (Tsh), resistance to the bactericidal effects of serum and cytotoxic effects. Experimental infection studies have shown that the air-exchange regions of the lung and the airsacs are important sites of entry of E. coli into the bloodstream of birds during the initial stages of infection and that resistance to phagocytosis may be an important mechanism in the development of the disease. They have also demonstrated that F1 fimbriae are expressed in the respiratory tract, whereas P fimbriae are expressed in the internal organs of infected chickens. The role of these fimbrial adhesins in the development of disease is not yet, however, fully understood. The more recent use of genetic approaches for the identification of new virulence factors will greatly enhance our knowledge of APEC pathogenic mechanisms. Diagnosis of APEC infections is based on the clinical picture, lesions and isolation of E. coli. This may be strengthened by serotyping and identification of virulence factors using immunological or molecular methods such as DNA probes and PCR. Approaches for the prevention and control of APEC infections include the control of environmental contamination and environmental parameters such as humidity and ventilation. Antibiotherapy is widely used, although APEC are frequently resistant to a wide range of antibiotics. Vaccines containing killed or attenuated virulent bacteria protect against infection with the homologous strain but are less efficient against heterologous strains. Hence, vaccination for colibacillosis is not widely practised because of the large variety of serogroups involved in field outbreaks.     

Avian pathogenic Escherichia coli (APEC)

Infections with avian pathogenic Escherichia coli (APEC) cause colibacillosis, an acute and mostly systemic disease resulting in significant economic losses in poultry industry worldwide. Avian colibacillosis is a complex syndrome characterized by multiple organ lesions with airsacculitis and associated pericarditis, perihepatitis and peritonitis being most typical. Environmental factors as well as the constitution of poultry or initial viral infections influence the outcome of APEC-infections. However, several challenge experiments in chickens proofed the role of virulent APEC strains as the single aetiological agent. Currently serotypes O1:K1, O2:K1 and O78:K80 are recognized as the most prevalent, however the number of published serotypes is increasing. In addition, single APEC isolates vary profoundly in virulence, and knowledge about the molecular basis of this variability is still scarce. Known virulence factors of APEC are adhesins (F1- and P-fimbriae), iron acquisition systems (aerobactin and yersiniabactin), hemolysins (hemolysinE and temperaturesensitive hemagglutinin), resistance to the bactericidal effects of serum and phagocytosis (outer membrane protein, iss protein, lipopolysaccharide, K/1)-capsule and colilcin production) as well as toxins and cytotoxins (heat stable toxin, cyto-/verotoxin and flagella toxin). Esperimental studies have shown that the respiratory tract, principally the gas-exchange region of the lung and the interstitium of the air sacs are the most important sites of entry for avian pathogenic E. coli. APEC strains adhere to the epithelial cells of air sacs presumably through F1-fimbriae. After colonization and multiplication the bacteria enter the bloodstream, and the temperature-sensitive hemagglutinin (tsh) seems to be important int his step. After invading the bloodstream APEC cause a septicemia resulting in massive lesins in multiple internal organs and in sudden death of the birds. The ability of the bacteria to acquire iron and the resistance to the bactericidal effects of serum, predominantly conferred by the increased serum survival (iss)--protein, enables APEC to multiply quickly in their hosts. Iss is regarded a specific genetic marker for avian pathogenic E. colistrains. A critical review of the literature published so far on APEC reveals, that these pathotypes are not defined appropriately. This findings urge investigations on the population structure of APEC, enabling the establishment of appropriate diagnostic tools and avoiding the obsolete use of serotyping for APEC diagnosis. So far more than 20 APEC strains have been investigated in animal experiments, explaining contrary published results. Thus, the lack of knowledge in pathogenicity and in immunity of APEC infections urges further experimental studies. As APEC share not only identical serotypes with human pathogens but also specific virulence factors, their zoonotic potential is under consideration.     

Avian pathogenic Escherichia coli (APEC)

Escherichia coli infections are being increasingly detected among poultry flocks, indicating the growing importance of this pathogen to the industry. The infection begins as a respiratory infection of the trachea, followed by colonization of the air sacs and lungs, from where it invades the blood-stream, leading to infection of the deeper organs (liver, heart, oviduct, and peritoneum). A number of factors play a crucial role in the virulence and pathogenesis of infection. The F1 and P pili are particularly important in establishing the infection at the level of the tracheal epithelium cell. Other important factors are aerobactin, capsule, and serum resistance. Treatment is with antibiotics, but the growing bacterial resistance of avian E. coli and stricter regulations mean that attention is turning to prophylactic, preventative, measures, such as vaccination. Current vaccines provide limited homologous protection against the pathogen. Research is needed to develop a good, broad-spectrum vaccine.     

Enterotoxigenic Escherichia coli (ETEC) in farm animals.

Animal diseases due to enterotoxigenic Escherichia coli (ETEC) typically appear as severe watery diarrhoea during the first few days of life (also a few days after weaning in pigs). ETEC adhere to the small intestinal microvilli without inducing morphological lesions and produce enterotoxins acting locally on enterocytes. This action results in the hypersecretion (of water and electrolytes) and reduced absorption. Adhesins and toxins are the two prominent virulence attributes of ETEC and the level of knowledge of these factors determines the chances for successful prevention and therapy of the disease. For animal ETEC the most common adhesins are the fimbriae (pili) on the surface: F4(K88), F5(K99), F6(987P), F41, F42, F165, F17 and F18. Enterotoxins (extracellular proteins or peptides) of animal ETEC are classified as heat-labile (LT) and heat-stable (ST) enterotoxins with further subdivisions (LTh-I, LTp-I, LTIIa, LTIIb, STaH, STaP, STb) according to antigenic and biological differences. Fimbriae and LT enterotoxins are made up of large molecular weight proteins which facilitate their utilisation in vaccines and their detection using immunodiagnostic systems. The adhesive fimbriae and enterotoxins of animal ETEC are plasmid determined (except F41 and F17). Virulence gene probes (DNA hybridisation, PCR) are specific and sensitive diagnostic and epidemiologic tools for the detection of ETEC. Based on genetic typing, the ETEC, in spite of limited serogroups, seem to represent a population of E. coli with a diverse genetic background.