Multilocus enzyme electrophoretic (MEE) analysis of Australian isolates of Salmonella enteritidis.

Seventy-three Australian isolates of Salmonella Enteritidis (SE) were analysed by multilocus enzyme electrophoresis (MEE) using a polyacrylamide gel system. Analysis of 11 enzyme loci identified eight electrophoretic types (ETs), with 61 of the isolates assigned to ET1, and 72 isolates considered to represent a clonal lineage. Representative isolates of each of the Australian ETs were then compared with isolates from England, Germany and the United States, using a starch gel system and 13 enzyme loci. The overseas isolates formed a single ET with representatives of the major Australian ET. It is concluded that Australian isolates of SE are closely related genetically to those from countries in which egg-borne transmission is common.

Experimental infection of mice with Rhodococcus equi: differences in virulence between strains.

The growth kinetics in outbred mice of clinical and environmental isolates of Rhodococcus equi were followed by serial bacterial enumeration of organ homogenates. Clinical isolates multiplied until Day 4 before being progressively cleared, but could still be recovered from the liver at 3-4 weeks post-infection. Intravenous inoculation of clinical strains was associated with histopathological responses very similar to those elicited by intravenous infection with various facultative intracellular parasites. Whereas lesions in mice and foals at 7-9 days following respiratory infection are those of severe bronchopneumonia with massive consolidation, a week later the patterns of host response have diverged as the murine lesions resolve. The type strain, NCTC 1621 and 4-6 environmental isolates were eliminated without prior multiplication and these strains caused negligible lesions. The two environmental strains which behaved as the clinical strains were recovered from a stud with an R. equi problem. No association of colonial morphology of R. equi with virulence was apparent.

The immunological response of foals to Rhodococcus equi: a review.

Normal horses of all ages regularly show evidence of having responded immunologically to R. equi, thus adding serological support to epidemiological evidence that this organism is a normal intestinal inhabitant. More animals from "diseased" farms show a stronger antibody response when compared with foals from "healthy" farms. Various serological tests have been used to detect evidence of infection and to relate antibody level to severity of disease. Anti-R. equi IgG antibody levels, as measured by ELISA, are raised significantly during natural infection. Clinical severity of pneumonia can be correlated with lower specific antibody responses. Following experimental infection, immunological responses can be detected by complement fixation, indirect immunofluorescence, ELISA, lymphocyte blastogenesis and skin testing. Very little work has been carried out to evaluate vaccines against R. equi infection and results have not been encouraging. Success in treatment has been reported following passive immunisation. Administration of immune leucocyte extracts has had no effect on morbidity or mortality rates. The widespread distribution of this organism, together with the relative infrequency of disease caused by it, suggest that R. equi may initiate infection only in such circumstances as a very high infectious challenge, immunological immaturity or deficiency in the host and genetic predisposition.

Sensitivity of Australian isolates of Salmonella enteritidis to nitrofurantoin and furazolidone.

Susceptibility of 66 and 62 Australian isolates of Salmonella enteritidis to nitrofurantoin and furazolidone, respectively, was determined. Most isolates were susceptible to both antibiotics. Cross-resistance was low among all isolates, but higher among the subset of phage type 4 isolates. These results contrast directly with those of a previous study (Rampling, A., Upson, R. and Brown, D.F.J. (1990) J. Antimicrob. Chemother., 25: 285-290). Sensitivity among Australian isolates of S. enteritidis does to some extent, support the contention that furans may have played a role in the selection and enhanced colonisation of poultry by Salmonella enteritidis in Britain. Furthermore, nitrofurantoin should not be used as a selective agent in the isolation of Salmonella enteritidis.

The effect of immunosuppression on resistance to Rhodococcus equi in mice.

Rhodococcus equi, a natural pathogen of horses, produces lesions in mice following experimental infection. The effect of various immunosuppressing agents on the sequential development of these lesions has been assessed by measuring the growth of R. equi following intravenous or intranasal challenge and by histological examination. Cyclophosphamide treatment of mice, challenged intranasally, resulted in the development of lesions not unlike that seen in experimental and natural infection in foals. Cortisone acetate also impaired bacterial clearance from the lungs and affected the accumulation of mononuclear cells at infective foci. Most of the agents chosen to impair macrophage function failed to affect the resistance of mice to R. equi. Carbon, carrageenan and silica failed to alter significantly the growth kinetics of R. equi. Dextran sulphate depressed the rate of pulmonary clearance of organisms and affected the ability of animals to eliminate R. equi following rechallenge. Overall, these results support other evidence that cell mediated immunity is involved in host resistance to R. equi and that activated macrophages play a role in acquired immunity to this organism.

Early events associated with experimental infection of the murine lung with Rhodococcus equi.

Pneumonia due to Rhodococcus equi was induced in the murine lung by deposition of a known dose of organisms. From serial estimations of bacterial numbers in the lungs of inoculated mice, analysis of the cellular composition of bronchoalveolar lavage fluid and morphological examination of the lungs, events in the host-parasite interaction were followed until day 7. Early bacterial clearance from the lung was dose-dependent but was not sustained. A proportion of the inoculated R. equi was susceptible to the early nonspecific phagocytic cell response, and the contribution of neutrophils to bacterial clearance appeared largely limited to the first 24 hours. A substantial fraction of the organisms survived in the alveoli, probably within macrophages. The contribution phagocytes make to resistance against R. equi is similar to that which prevails in infection with Listeria monocytogenes.

Studies in atypical Streptococcus equi.

An atypical variety of Streptococcus equi is described. It was shown to be deficient in capsular material, to be very virulent for mice and to possess a cell-wall protein similar to the M-like protein of classical Str equi. Antiserum prepared against classical Str equi effectively opsonised the atypical strains, and induced the formation of long chains by these atypical strains. It is possible that this variant of Str equi can be used to overcome many of the current problems associated with the manufacture and use of strangles vaccines.

Epidemiology of equine streptococci.

Equine tonsillar tissue and the draining regional lymph nodes, as well as deep nasal swabs were examined bacteriologically. Group C streptococci, predominantly Streptococcus zooepidemicus, were shown to be present in all tissues. The most frequent site for isolation was the tonsil. Streptococcus equi was not located in any of the tissues sampled.

Epidemiology of Corynebacterium equi in horses.

Using a selective medium, the epidemiology of Corynebacterium equi in horses was studied. Twelve horse studs in different geographical locations were investigated. In addition, a group of horses was monitored over a period of time to determine whether faecal carriage of C equi is constant or intermittent. It was found that C equi could be recovered from every property tested and from all horse breeds. The organism was found in mares, stallions, yearlings and two year olds, and foals aged from 10 days to several months. It appears that C equi is widespread and that its occurrence is not related to any particular geographical location nor to a limited number of properties within a given area. Furthermore, it seems likely that C equi is part of the normal equine faecal flora. The results challenge the notion that C equi is primarily soil associated and do not support the concept that there are infected and non-infected areas.

Keratitis in free-ranging koalas (Phascolarctos cinereus) on Magnetic Island, Townsville.

Seventy free-ranging koalas (Phascolarctos cinereus) from Magnetic Island (Queensland, Australia) underwent an ocular examination, blood collection and serological examination for Chlamydia psittaci antibodies, and an examination of their teeth and genitalia. In 12 koalas long-standing unilateral keratitis was noted and in another 10 animals long-standing bilateral keratitis was observed. All animals were seronegative for Chlamydia psittaci and apart from some nasal discharge and a variety of assorted medical findings there was no sign of chlamydial infection. These ocular findings probably represent a new disease of unknown etiology.

Corynebacterium equi in cattle and pigs.

Summary The cervical lymph nodes of pigs, the retropharyngeal and submandibular lymph nodes of cattle and faecal samples from both animal species were examined for the presence of Corynebacterium equi. The organism was recovered from 19 (35 per cent) of 54 porcine cervical lymph nodes and from 0 of 54 bovine retropharyngeal and submandibular lymph nodes. Fifteen (50 per cent) of 30 bovine faecal and 11 (35 per cent) of 31 porcine faecal samples yielded C. equi.

Antibiotic susceptibility testing: caeci caecos ducentes?

Antibiotic susceptibility testing is frequently conducted by diagnostic laboratories and some clinicians rely on the information which such testing provides. In this review of the procedure the rationale for interpretation of the agar diffusion test is outlined and the factors which affect determination of zone size and minimum inhibitory concentration (MIC) discussed. The relationship between zone size and MIC is considered, as well as the clinical relevance of MIC breakpoints. Against this background we assess the value of disc diffusion tests for veterinary practice.

Immunity to Streptococcus equi.

Using the long chain test, and in some cases the bactericidal test, to measure antibody, the development of the immune response in horses to Str. equi has been followed. Long chain indices in excess of 5.0, accompanied by strong bactericidal capacity, were recorded in serums after the full 3-dose immunisation course with a commercial vaccine. The full course elicited the most satisfactory antibody titres declined within the 12 month post-vaccination period, thus providing support for the recommendation that yearly booster doses should be administered. The immune response in horses during 2 strangles outbreaks was compared with the response following vaccination. Recovered animals showed declining antibody levels 9 weeks after infection, and the evidence does not support longevity of the immune response after natural infection. Reaction to vaccination was observed in those animals with high initial antibody titre.

Capsular serotypes of Rhodococcus equi.

One hundred strains of Rhodococcus equi from various animal species and sources in Australia were examined for capsular serotype. Eighty-four of the strains fell into the existing 7 serotypes, and just under half of the strains belonged to serotype 1. Isolates from the intestines and faeces of horses, cattle, pigs and other species, and from soil, were found to belong to the same serotypes as those recovered from the lungs of foals with R. equi pneumonia. There was no clear relationships between capsular serotype and source of origin of the isolates.

The isolation of antibiotic resistant coliforms from meat and sewage.

Beef and pig carcases, meat products, frozen chickens, and sewage were examined in 3 separate surveys for antibiotic resistant coliforms. Escherichia coli was isolated from 18 of 50 beef carcases; the numbers were low and resistance was found only to tetracycline. E. coli was isolated from 45 to 50 pig carcases; the numbers were high and showed a range of patterns of multiple antibiotic resistance. In meat products, the proportion of E. coli in contaminating organisms was low, and most resistance found was to tetracycline and streptomycin. E. coli was isolated from 66 of 75 chickens and these gave 23 patterns of antibiotic resistance, often multiple. Sewage from hospital or domestic origin and abattoir effluent yielded approximately 10(6) coliforms/ml, most of which were resistant to one or more antibiotics; few of those from hospital or domestic origin however, were classified as E. coli of faecal origin. Twenty-four patterns of resistance were found in coliforms from domestic sewage, 19 from hospital sewage and 11 from abattoir effluent. Transfer of resistance, often multiple, was achieved from 55% of 447 resistant strains to an E. coli K12 recipient. Much more information is required on the prevalence of R-factors in bacteria associated with food producing animals and their products.

Corynebacterium equi in the gastrointestinal tract of ruminants.

Corynebacterium equi has been recovered from the gastrointestinal tract of sheep and cattle. It can be found in all parts of the gut, and around 80% of animals have the organism in one or more intestinal sites. C. equi could be detected in the faeces of sheep which were kept caged and free from recontamination by the organism.

Corynebacterium equi in cattle and pigs.

The cervical lymph nodes of pigs, the retropharyngeal and submandibular lymph nodes of cattle and faecal samples from both animal species were examined for the presence of Corynebacterium equi. The organism was recovered from 19 (35 per cent) of 54 porcine cervical lymph nodes and from 0 of 54 bovine retropharyngeal and submandibular lymph nodes. Fifteen (50 per cent) of 30 bovine faecal and 11 (35 per cent) of 31 porcine faecal samples yielded C. equi.