Relationship between haemagglutination and HeLa-cell adherence of Rhodococcus equi

Molecular and infection biology of the horse pathogen Rhodococcus equi

The soil actinomycete Rhodococcus equi is a pulmonary pathogen of young horses and AIDS patients. As a facultative intracellular bacterium, R. equi survives and multiplies in macrophages and establishes its specific niche inside the host cell. Recent research into chromosomal virulence factors and into the role of virulence plasmids in infection and host tropism has presented novel aspects of R. equi infection biology and pathogenicity. This review will focus on new findings in R. equi biology, the trafficking of R. equi-containing vacuoles inside host cells, factors involved in virulence and host resistance and on host-pathogen interaction on organismal and cellular levels.

Pheno- and genotyping of Rhodococcus equi isolated from faeces of healthy horses and cattle

The present study was designed to comparatively investigate 21 Rhodococcus equi isolates from the faeces of clinically healthy horses and cattle. The isolates were identified by cultural and biochemical properties and by PCR analysis. The latter, targeted to the gene coding for the 16S ribosomal RNA, revealed a species specific PCR product. The isolates were further characterised by serotyping with two typing systems, by haemagglutination tests and by plasmid and virulence protein profiling. Among the 21 cultures, four cultures contained plasmids, two of the four cultures expressed 15-17 kDa virulence proteins, no cultures contained 20 kDA virulence proteins. The 21 cultures were further analysed by DNA-fingerprinting. This was performed by macrorestriction analysis of chromosomal DNA by pulsed-field gel electrophoresis (PFGE). The DNA-restriction patterns were different for most of the isolates indicating a clone heterogeneity among isolates from single farms. Serotyping, determination of virulence marker and PFGE analysis of R equi appeared to be useful for further characterisation of this species, possibly of importance for virulence estimation of single R equi isolates and for epidemiological studies.

Cytokine induction in murine macrophages infected with virulent and avirulent Rhodococcus equi

To look for a possible correlation between the virulence of Rhodococcus equi and its cytokine-inducing capacity, we evaluated intracellular survival and measured cytokine induction by mouse macrophages infected with a virulent strain containing an 85-kb plasmid and expressing VapA (103+), its avirulent plasmid-cured derivative (103-), and heat-killed 103+ (HK). After incubation with similar numbers of bacteria, macrophages infected with 103- contained significantly more organisms than those infected with 103+ or HK. The number of bacteria in the macrophages infected with 103- and HK decreased progressively, whereas the 103+ numbers remained constant over 48 h. Interleukin 1beta (IL-1beta), IL-6, IL-10, IL-12 p40, and tumor necrosis factor alpha (TNF-alpha) mRNA induction peaked at 4 h and returned to baseline between 12 and 48 h postinfection. IL-1beta, IL-6, IL-10, and TNF-alpha concentrations assessed by enzyme-linked immunosorbent assay generally agreed well with mRNA expression; IL-12 could, however, not be detected. For all the cytokines detected, mean concentrations in the supernatants were consistently higher in the 103(-)-infected monolayers than in those infected with 103+, although, with the exception of IL-1beta, the differences were not statistically significant. R. equi HK was a poor inducer of cytokine production. In conclusion, virulent and avirulent R. equi strains induced similar levels of cytokine synthesis. The slightly greater induction of most cytokines observed following infection with 103- is likely secondary to greater uptake by macrophages rather than to a direct role of VapA or another plasmid-encoded product in downregulating cytokine induction.

Identification and epidemiological relationship of Rhodococcus equi isolated from cases of lymphadenitis in cattle

The present study was designed to comparatively investigate 10 Rhodococcus equi isolates from cases of lymphadenitis in cattle. The isolates could be identified by cultural and biochemical properties. By serotyping the R. equi isolates 9 and 1, cultures could be classified as Nakazawa's serotypes 15 and 8, respectively. The isolates did not agglutinate rabbit erythrocytes, were uniformly susceptible to most of the antibiotics tested, did not contain plasmids nor expressed virulence-associated proteins and yielded identical patterns in protein fingerprinting. To further analyze the epidemiological relationships, the isolates were additionally subjected to DNA fingerprinting. This was performed by pulsed-field gel electrophoresis (PFGE) after digestion of the chromosomal DNA with the endonuclease AsnI. PFGE analysis of the chromosomal DNA revealed 4 DNA restriction groups with DNA pattern I with 7 isolates as predominant group and DNA pattern II to IV with one isolate, respectively. The present results indicate that a single R. equi clone belonging to Nakazawa's serotype 15 and according to PFGE to DNA restriction pattern I of the present investigation seems to be responsible for most of the cases of lymphadenitis of cattle described in this study.

Studies on the rod-coccus life cycle of Rhodococcus equi

In the present study all 19 Rhodococcus equi cultures isolated from horses and 19 of 22 R. equi cultures isolated from human patients displayed a rod-coccus life cycle after cultivation under defined growth conditions. A bacillary growth could be observed after cultivation of the bacteria in fluid media for 4 h at 37 degrees C, a coccoid morphology after cultivation of the bacteria for 24 h either on sheep blood agar plates or in fluid media. The different morphological features did not significantly influence the typability of the bacteria or the expression of surface proteins including 15-17 kDa virulence proteins. Studies on further surface characteristics revealed a relation between haemagglutinating properties, the surface hydrophobicity and adherence properties of the bacteria to HeLa cells. These properties seemed to be influenced by the cultivation conditions but not by the different morphological forms of the bacteria. A haemagglutination reaction, a hydrophobic surface and an enhanced adherence to HeLa cells could be observed with coccoid bacteria after cultivation in fluid media for 24 h at 37 degrees C but not with coccoid bacteria harvested from sheep blood agar plates or with bacillary bacteria after 4 h growth in fluid media. This difference might possibly be caused by the degree of encapsulation of the bacteria after various cultivation conditions and a subsequent masking effect of the hydrophilic polysaccharide capsule of R. equi.