Comparison of synovial fluid culture and 16S rRNA PCR in dogs with suspected septic arthritis

Detection of bacterial DNA in synovial fluid in dogs with arthritis: a comparison between bacterial culture and 16S rRNA polymerase chain reaction

Background

Septic arthritis (SA) is a serious condition in dogs that requires a prompt diagnosis and treatment to minimize long-term joint pathology. Although bacterial detection in synovial fluid (SF) through culture or cytology is often performed to confirm diagnosis, the sensitivity of these tests is low. The need for a reliable diagnostic tool to confirm the presence of bacteria in SF in humans has led to the increased use of 16S rRNA (i.e., ribosomal RNA) gene sequencing by polymerase chain reaction (16S rRNA PCR). The aim of this prospective clinical study was to compare the sensitivity and specificity of 16S rRNA PCR with bacterial culture on blood agar plates after pre-incubation of SF in paediatric blood bacterial culture bottles to identify bacteria in dogs with clinical signs of SA and to investigate the usefulness of these methods as diagnostic tools.

Results

Ten dogs with clinical signs of SA, nine with osteoarthritis (OA, control group) and nine with clinical signs of immune-mediated polyarthritis (IMPA, second control group) were examined. Bacterial culture was positive in seven of 10 dogs with clinical SA, of which only two were positive by 16S rRNA PCR. The sensitivity of 16S rRNA PCR and bacterial culture analysis for dogs with clinical SA were 20% and 70%, respectively. All SF samples collected from control group (n = 9) and second control group (n = 14) animals were negative on culture, and 16S rRNA PCR rendered a specificity of 100%.

Conclusions

Our study showed a lower sensitivity of 16S rRNA PCR than bacterial culture for dogs with clinical SA. Our findings suggest that there is currently no advantage in using 16S rRNA PCR as a diagnostic tool for dogs with clinical SA. Furthermore, our study indicates that pre-incubation in paediatric blood bacterial culture bottles before bacterial cultivation on blood agar plates might enhance bacterial culture sensitivity compared to other culture methods.

Comparison of the effects of cefazolin and ceftriaxone on canine chondrocyte culture

Cephalosporins (CEFs) are antibiotics frequently used to treat bone infections and septic arthritis. The effects of CEFs on chondrocytes have not been studied until now. Cefazolin (cef1) and ceftriaxone (cef3), first-and third-generation CEFs, were selected to investigate their direct effects on normal and osteoarthritic (OA) primary canine chondrocytes, which were either nonstimulated or stimulated with the pro-inflammatory cytokine IL-1β. In our results, treatment with CEFs increased the negative effects on both conditioned normal and OA chondrocytes, especially when applied to IL-1β-stimulated cells (inflammatory stimulus). CEFs significantly decreased cell viability and induced apoptotic cell death in both normal and OA chondrocytes; moreover, treatment with cef1 caused necrotic cell death in OA chondrocytes. Cef3 treatment could increase s-GAG synthesis in normal cells preincubated with IL-1β, while cef1 had no significant effect. The expression of TNF was clearly downregulated after cef3 treatments, whereas it was upregulated after cef1 treatments. However, cef3 induced stronger downregulation of TIMP1 and the extracellular matrix component genes COL2A1 and ACAN. In conclusion, these results suggest both the cytotoxic effects of CEFs and their adverse effects on chondrogenic marker genes at the transcriptional level, which provide additional insight into the clinical application of cef1 and cef3.

Retrospective evaluation of the efficacy of isolating bacteria from synovial fluid in dogs with suspected septic arthritis

OBJECTIVE

To evaluate the efficacy of synovial fluid culture in obtaining the causative organism from dogs with suspected septic arthritis.

METHODS

In this retrospective evaluation, synovial fluid cytology and microbiology submissions from dogs with suspected septic arthritis from March 2007 to August 2011 were reviewed. Synovial fluid cytology consistent with joint sepsis was identified. Cultures of synovial fluid from dogs with clinical histories and abnormalities consistent with septic arthritis were used to evaluate the efficacy of bacterial isolation.

RESULTS

In total, 36 dogs met the inclusion criteria. Initial aerobic cultures of joint fluid yielded bacterial growth in 44% of these dogs. All anaerobic cultures were negative. In 19% of the dogs with positive cultures, antibiotics had been administered prior to arthrocentesis compared with 10% of dogs with negative cultures. There was no association between culture efficacy and the administration of antimicrobial treatment prior to synovial fluid culture or recent surgery involving the affected joint (P=0.637 and P=0.106, respectively).

CONCLUSION

Culture of synovial fluid from dogs with suspected septic arthritis has a low yield, necessitating a more effective means of identifying bacteria from suspected septic joints in dogs.

Comparison of synovial fluid culture and 16S rRNA PCR in dogs with suspected septic arthritis

OBJECTIVE

To prospectively compare the sensitivity and specificity of 16S rRNA PCR with culture for identifying the causative organism in synovial fluid obtained from dogs with suspected septic arthritis.

METHODS

Synovial fluid cytology, PCR analysis and aerobic, anaerobic and Mycoplasma culture of samples from the affected joints of 18 dogs presenting with suspected septic arthritis were performed. Synovial fluid samples from the corresponding contralateral joints of 7 dogs were also analysed as negative controls.

RESULTS

There was no significant difference between the sensitivity of bacterial detection via culture (63.2%) versus PCR (73.7%) of synovial fluid (P=0.728) or between culture and combined PCR and culture (89.5%) of synovial fluid (P=0.124). The specificity of PCR (42.9%) was significantly lower than culture specificity (100%) (P=0.07).

CONCLUSION

Although 16S PCR may hold potential as an ancillary diagnostic test for identifying the causative organism in dogs with septic arthritis, our study failed to demonstrate improved accuracy compared with traditional synovial fluid culture.