Quinolone resistance in Escherichia coli.

Escherichia coli is an important pathogen of animals and humans that causes great financial cost in food production by causing disease in food animals. The quinolones are a class of synthetic antimicrobial agents with excellent activity against Escherichia coli and other Gram-negative bacteria used in human and veterinary medicine. Different quinolones are used to treat various conditions in animals in different parts of the world. All members of this class of drug have the same mode of action: inhibition of topoisomerase enzymes, DNA Gyrase and Topoisomerase IV. Escherichia coli can become resistant to quinolones by altering the target enzymes, reducing permeability of the cell to inhibit their entry, or by actively pumping the drug out of the cell. All these resistance mechanisms can play a role in high-level fluoroquinolone resistance, however target site mutations appear to be most important. As all quinolones act in the same way resistance to one member of the class will also confer decreased susceptibility to all members of the family. Quinolone resistant Escherichia coli in animals have increased in numbers after quinolone introduction in a number of different case studies. The resistance mechanisms in these isolates are the same as those in resistant strains found in humans. Care needs to be taken to ensure that quinolones are used sparingly and appropriately as highly resistant strains of Escherichia coli can be selected and may pass into the food chain. As these drugs are of major therapeutic importance in human medicine, this is a public health concern. More information as to the numbers of quinolone resistant Escherichia coli and the relationship between resistance and quinolone use is needed to allow us to make better informed decisions about when and when not to use quinolones in the treatment of animals.     

Escherichia coli and diarrhoea in the rabbit.

An outbreak of severe diarrhoea and death in young rabbits was associated with many nonenterotoxigenic Escherichia coli in the caecum. The severe clinical, pathological and bacteriological features of the diesase, acute diarrhoea associated with typhlitis and many E. coli in the caecum, could be reproduced either by the intraintestinal inoculation of many bacteria recovered aerobically or anaerobically from the caecum of these rabbits or by the intestinal inoculation of large numbers of a serogroup of E. coli, 0153, recovered from the caecum. Further experiments showed that this serogroup of E. coli, as well as a nonenteropathogenic serotype recovered from human faeces, would cause typhlitis and diarrhoea if inoculated in large numbers into the jejunum; pathological changes also were seen in the liver and kidney. Similar changes also could be induced by intravenous inoculation of a freeze-thaw (endotoxic) extract prepared from these strains. Any factor that allows rapid multiplication of E. coli in the rabbit caecum may be followed by absorption of endotoxin and subsequent typhlitis and so metimes by severe diarrhoea; this effect is seen in some field cases of diarrhoea in the rabbit.     

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.     

Characterization of enterotoxigenic bovine Escherichia coli.

Among 300 isolates of bovine Escherichia coli, 56 which had been found enterotoxigenic in calf gut loops were characterized on the basis of O and K antigens, colonial morphology and resistance to seven antimicrobial drugs. The 56 isolates enterotoxigenic in the calf were compared with the nonenterotoxigenic ones. Of the 56 enterotoxigenic E. coli the majority possessed the A type of K antigen and had OK groups, O9:K(PS274) or O101:K(RVC118). Fourteen of these isolates had the K99 antigen. None of 27 isolates found enterotoxigenic in the piglet but not in the calf possessed the K99 antigen or belonged to OK groups O9:K(PS274) or O101:K(RVC118). Comparison of the patterns of resistance to seven antimicrobial drugs showed that all enterotoxigenic and nonenterotoxigenic isolates were susceptible to nitrofurantoin and sulphachlorphyridiazine and that there was no significant difference in the patterns between the two groups. The majority of enterotoxigenic isolates were mucoid, whereas most of the nonenterotoxigenic isolates were nonmucoid.     

The rapid identification of Escherichia coli using Bactident E. coli

165 (93.7%) of 175 E. coli strains isolated from various materials of different animal species were correctly identified as E. coli with help of commercially available Bactident E. coli (E. Merck, D-6100 Darmstadt). Further 52 strains of the family of Enterobacteriaceae (2x Providencia sp., 2x Salmonella sp., 7 Citrobacter sp., 9 Proteus sp., 15 Klebsiella sp., 17 Enterobacter sp.) were correctly not identified as E. coli by this test. Bactident E. coli is a suitable test for rapid identification of E. coli in veterinary bacteriology.     

Ocular lesions in chickens inoculated with Escherichia coli.

Specific-pathogen-free chickens (two, four and ten weeks of age) which were inoculated via the air sac with Escherichia coli developed ocular lesions. Histologically, the main ocular lesions consisted of hyphema, hemorrhages of the iris, hypopyon, keratitis and uveitis. Hyphema was associated with hemorrhages of the iris, and hypopyon with keratitis and uveitis. Cyclophosphamide treatment enhanced the incidence and severity of hyphema and hemorrhages of the iris in the chickens.     

Bacterial adherence in mastitis caused by Escherichia coli.

The possible role of bacterial adherence in the pathogenesis of experimental mastitis in the mouse was examined with four strains of Escherichia coli. Two of these strains had a known adhesion antigen (K88) and two did not. The K88 antigen did not play a significant role in the virulence or infectivity of E. coli either in the murine or bovine mammary gland. Two E. coli strains, W1 (K88+) and J2 (K88-) were virulent in the mouse but did not adhere to epithelial cells. Both these strains produced clinical mastitis in the cow. A third strain, D282 (K88-), produced mild disease in the mouse but was avirulent in the cow. The fourth strain, 233/ID (K88+), was avirulent in both the mouse and the cow. Strains D282 and 233/1D were killed rapidly by bovine serum whilst J2 and W1 were more resistant. All strains were more sensitive than the control resistant strain E. coli P4, which is known to be highly virulent for the lactating udder.     

Acute airsacculitis in untreated and cyclophosphamide-pretreated broiler chickens inoculated with Escherichia coli or Escherichia coli cell-free culture filtrate.

Ninety commercial broiler chickens were divided into three equal groups; 30 were injected with brain-heart-infusion broth into the cranial thoracic air sacs (controls), 30 were similarly inoculated with a culture of Escherichia coli, and 30 were similarly inoculated with E. coli cell-free culture filtrate. Birds were examined from 0 to 6 hours post-inoculation. E. coli-inoculated and cell-free culture filtrate-inoculated chickens reacted similarly, with exudation of heterophils into the air sac. Microscopically, heterophils were present in low numbers perivascularly 0.5 hour after inoculation and became more numerous by 3 hours post-inoculation. By 6 hours post-inoculation, there was severe swelling of air sac epithelial cells and thickening of the air sac by proteinaceous fluid and heterophils. Ultrastructurally, air sac epithelial cells were swollen and vacuolated, and interdigitating processes were separated. Histologically and ultrastructurally, all features in control chickens were normal, with only rare heterophils in the air sac interstitium. In E. coli-inoculated and cell-free culture filtrate-inoculated chickens, cell counts (predominantly heterophils) in air sac lavage fluids increased markedly at 3 and 6 hours, with only slight increases in counts from lavages of controls. Heteropenia was observed in E. coli-inoculated chickens, whereas heterophilia was observed in cell-free filtrate chickens and controls. Ninety additional chickens were pretreated with cyclophosphamide, subdivided into three equal groups, and inoculated and examined similarly as above. Cyclophosphamide pretreatment reduced inflammatory changes in air sacs, lowered cell numbers in lavage fluids, and abolished hematologic changes; however, it did not prevent epithelial cell changes. These results indicate that cell-free culture filtrate of E. coli induces changes similar to those induced by cultures of E. coli.     

Escherichia coli infection in lambs

Abstract

Extract

Published records of Escherichia coli infection in lambs have appeared with increasing frequency in recent years. Reports have come from Australia (Roberts, 1957 Roberts, D. S. 1957. Anst. vet. J., 33: 43–43.  [Google Scholar], 1958 Roberts, D. S. 1958. Anst. vet. J., 34: 152–152.  [Google Scholar]; Charles, 1957 Charles, G. 1957. Anst. vet. J., 33: 329–329.  [Google Scholar]) and from Britain (Terlecki and Shaw, 1959 Terlecki, S. and Shaw, W. G. 1959. Vet. Rec., 71: 181–181.  [Google Scholar]; Rees, 1958 Rees, T. A. 1958. J. comp. Path., 68: 399–399.  [Google Scholar]; Hughes, 1962 Hughes, L. E. 1962. Vet. Rec., 74: 350–350.  [Google Scholar]). In the Australian outbreaks, the age of affected lambs ranged from three to eight weeks, while in the British outbreaks lambs became affected within one day of birth. In both countries the illness lasted from one to three days. Characteristically, the infection localized in the central nervous system leading to purulent meningo-encephahtis, and in the joints causing fibrino-purulent arthritis.     

Secretion of virulence factors by Escherichia coli.

In order to interact with their host, pathogenic strains of E. coli need to secrete some virulence factors which can modify the metabolism of host cells, contributing to disease. Since E. coli is a Gram-negative bacteria, this secretion process involves the crossing of both the inner and the outer membranes. E. coli uses mainly four secretion mechanisms called type I, type II, type III and type IV secretion systems. In the type I secretion system, the secretion machinery is composed of three proteins forming a channel through the inner and outer membranes. It is a one-step mechanism. The secretion signal is present in the carboxyterminal region of the secreted protein but without proteolytic cleavage. In E. coli, the best studied type I secreted protein is haemolysin. In type II and type IV secretion systems, the crossing of the inner membrane involves the sec machinery with the cleavage of an aminoterminal signal sequence. The crossing of the outer membrane involves the formation of a pore either by other proteins (type II) or by the carboxyterminal region of the protein (type IV). The A-B toxins, such as heat labile enterotoxin, are secreted by the first mechanism and members of the IgA proteases are secreted by the second. The type III secretion system involves at least 20 proteins including cytoplasmic, inner membrane and outer membrane proteins. The originality of this system is the ability to inject secreted bacteria into the cytosol of the host cells. Such a system is found in attaching and effacing E. coli and in diffusely adhering E. coli.     

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.