Diagnosis of Renibacterium salmoninarum infection in harvested Atlantic salmon (Salmo salar L.) on the east coast of Canada: Clinical findings, sample collection methods and laboratory diagnostic tests

Chronic subclinical infection with the aetiological agent of bacterial kidney disease (BKD), Renibacterium salmoninarum, presents challenges for the clinical management of disease in farmed salmonids and for prevalence estimation. Harvested salmon sampled at processing plants provide the opportunity to describe subclinical outcomes of BKD using gross necropsy observations and diagnostic test results in farmed Atlantic salmon (Salmo salar L.) populations that are apparently healthy (i.e. alive at harvest) but naturally exposed to R. salmoninarum infection. Sampling of farmed salmon (Population A, n = 124 and Population B, n = 160) was performed immediately post-slaughter as fish were being processed at a plant in New Brunswick, Canada. Populations were selected based on planned harvests from sites with histories of recent exposure events related to clinical BKD as evidenced by the site veterinarian's diagnosis of mortality attributable to BKD: One site (Pop A) had recently increasing mortalities attributed to BKD, and the other site (Pop B) had ongoing low-level mortalities with BKD pathology. As expected with the different exposure histories, Pop A had a higher percentage (57.2%) of R. salmoninarum culture-positive kidney samples compared with similar fish samples in Pop B (17.5%). Diagnosis of R. salmoninarum by gross granulomatous lesions in internal visceral organs, bacterial culture and identification by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) using different swab transport methods, and molecular detection methods (quantitative PCR, qPCR) were compared. Agreement of culture-positive percentages at the sample level was moderate (kappa: 0.61-0.75) among specimens collected using different kidney sampling methods in Pop A and Pop B. The highest proportion of R. salmoninarum-positive cultures occurred when kidney tissues were transported to the laboratory and inoculated directly onto agar using a swab (94% of cultures from Pop A and 82% from Pop B when fish were positive by any culture method). Fish with cumulative lesion scores (severity of granulomatous lesions in 3 different visceral organs) of >4 were all culture positive, and when compared with non-lesioned fish, had substantially higher odds of being culture positive: Pop A: odds ratio (OR) = 73, 95% confidence interval (CI) (7.91, 680.8); Pop B: OR = 66, 95% CI (6.12, 720.7). Our study found that onsite postmortem examinations with severity scores of gross granulomatous lesions were predictive of positive culture results for R. salmoninarum, and they were a useful proxy for assessing prevalence in apparently healthy populations with subclinical infection.

Comparative Study of Different Diagnostic Routine Methods for the Identification of Acinetobacter radioresistens

Recent publications indicate that A. radioresistens can cause infections in humans, even though it is rarely reported in routine diagnostics. However, the fact that it is infrequently detected may be explained by the misidentification of the species by conventional methods. It is also likely that A. radioresistens is not considered clinically relevant and therefore not consistently included in diagnostic results. To elucidate the medical significance of this probably clinically underestimated bacterial species, we created a well-documented reference strain collection of 21 strains collected in routine diagnostics. For further analysis of A. radioresistens, it is essential to know which methods can be used to achieve a trustworthy identification. We, therefore, compared three methods widely used in routine diagnostics (MALDI-TOF MS, VITEK 2, and sequencing of housekeeping genes) in terms of secure and reliable identification of A. radioresistens. As reference methods, whole genome-based approaches were applied. VITEK 2 led to misidentification for four strains. However, MALDI-TOF MS and sequencing of housekeeping genes led to reliable and robust identifications.

Propionibacterium/Cutibacterium species-related positive samples, identification, clinical and resistance features: a 10-year survey in a French hospital

A 10-year retrospective study of Propionibacterium/Cutibacterium-positive samples gathered from hospitalized patients was conducted at Nantes University hospital. A total of 2728 Propionibacterium/Cutibacterium-positive samples analyzed between 2007 and 2016 were included. Due to the implementation of MALDI-TOF identification in 2013, most non-Cutibacterium acnes isolates were identified a second time using this technology. Over that period, Cutibacterium acnes remained the most predominant species accounting for 91.5% (2497/2728) of the isolates, followed by Cutibacterium avidum (4.2%, 115/2728) and Cutibacterium granulosum (2.4%, 64/2728). Regarding the origin of samples, the orthopaedic department was the main Cutibacterium sample provider representing 51.9% (1415/2728) of all samples followed by the dermatology department (11.5%, 315/2728). Samples were recovered from various tissue locations: 31.5% (858/2728) from surgery-related samples such as shoulder, spine or hip replacement devices and 19.1% (520/2728) from skin samples. MALDI-TOF method revealed misidentification before 2013. Cutibacterium avidum was falsely identified as C. granulosum (n = 33). Consequently, MALDI-TOF technology using up-to-date databases should be preferred to biochemical identification in order to avoid biased species identification. Regarding antibiotic resistance, 14.7% (20/136) of C. acnes was resistant to erythromycin. 4.1% (41/1005) of C. acnes strains, 17.9% (12/67) of C. avidum strains and 3.6% (1/28) of C. granulosum strains were found resistant to clindamycin.

Airborne Staphylococcus aureus in different environments-a review

The aim of the literature review was to describe the environments where the presence of airborne Staphylococcus aureus was confirmed and to catalogue the most often used methods and conditions of bioaerosol sampling to identify the bacteria. The basis for searching of studies on S. aureus in the bioaerosol in different environments was PubMed database resources from the years 1990-2019 (May). The review included studies which were carried on in selected environments: hospitals and other health care facilities, large-scale animal breeding, wastewater treatment plants, residential areas, educational institutions, and other public places. The highest concentrations and genetic diversity of identified S. aureus strains, including MRSA (methicillin-resistant S. aureus), have been shown in large-scale animal breeding. The role of the airborne transmission in dissemination of infection caused by these pathogens is empirically confirmed in environmental studies. Commonly available, well-described, and relatively inexpensive methods of sampling, identification, and subtyping guarantee a high reliability of results and allow to obtain fast and verifiable outcomes in environmental studies on air transmission routes of S. aureus strains.

How MALDI-TOF mass spectrometry can aid the diagnosis of hard-to-identify pathogenic bacteria - the rare and the unknown

Introduction: Ten years after its introduction into clinical microbiology, MALDI-TOF mass spectrometry has become the standard routine identification tool for bacteria in most laboratories. The technology has accelerated analyses and improved the quality of results. The greatest significance has been observed for bacteria that were challenging to be identified by traditional methods. Areas covered: We searched in existing literature (Pubmed) for reports how MALDI-TOF MS has contributed to identification of rare and unknown bacteria from different groups. We describe how this has improved the diagnostics in different groups of bacteria. Reference patterns for strains which yet cannot be assigned to a known species even enable the search for related bacteria in studies as well as in routine diagnostics. MALDI-TOF MS can help to discover and investigate new species and their clinical relevance. It is a powerful tool in the elucidation of the bacterial composition of complex microbiota in culturomics studies. Expert opinion: MALDI-TOF MS has improved the diagnosis of bacterial infections. It also enables knowledge generation for prospective diagnostics. The term 'hard-to-identify' might only be rarely attributed to bacteria in the future. Novel applications are being developed, e.g. subspecies differentiation, typing, and antibiotic resistance testing which may further contribute to improved microbial diagnostics.

Matrix-assisted laser desorption-ionization-time-of-flight mass spectrometry as a reliable proteomic method for characterization of Escherichia coli and Salmonella isolates

Aim:

Identification of pathogenic clinical bacterial isolates is mainly dependent on phenotypic and genotypic characteristics of the microorganisms. These conventional methods are costive, time-consuming, and need special skills and training. An alternative, mass spectral (proteomics) analysis method for identification of clinical bacterial isolates has been recognized as a rapid, reliable, and economical method for identification. This study was aimed to evaluate and compare the performance, sensitivity and reliability of traditional bacteriology, phenotypic methods and matrix-assisted laser desorption-ionization-time-of-flight mass spectrometry (MALDI-TOF MS) in the identification of clinical Escherichia coli and Salmonella isolates recovered from chickens.

Materials and Methods:

A total of 110 samples (cloacal, liver, spleen, and/or gall bladder) were collected from apparently healthy and diseased chickens showing clinical signs as white chalky diarrhea, pasty vent, and decrease egg production as well as freshly dead chickens which showing postmortem lesions as enlarged liver with congestion and enlarged gall bladder from different poultry farms.

Results:

Depending on colonial characteristics and morphological characteristics, E. coli and Salmonella isolates were recovered and detected in only 42 and 35 samples, respectively. Biochemical identification using API 20E identification system revealed that the suspected E. coli isolates were 33 out of 42 of colonial and morphological identified E. coli isolates where Salmonella isolates were represented by 26 out of 35 of colonial and morphological identified Salmonella isolates. Serological identification of isolates revealed that the most predominant E. coli serotypes were O1 and O78 while the most predominant Salmonella serotype of Salmonella was Salmonella Pullorum. All E. coli and Salmonella isolates were examined using MALDI-TOF MS. In agreement with traditional identification, MADI-TOF MS identified all clinical bacterial samples with valid scores as E. coli and Salmonella isolates except two E. coli isolates recovered from apparently healthy and diseased birds, respectively, with recovery rate of 93.9% and 2 Salmonella isolates recovered from apparently healthy and dead birds, respectively, with recovery rate of 92.3%.

Conclusion:

Our study demonstrated that Bruker MALDI-TOF MS Biotyper is a reliable rapid and economic tool for the identification of Gram-negative bacteria especially E. coli and Salmonella which could be used as an alternative diagnostic tool for routine identification and differentiation of clinical isolates in the bacteriological laboratory. MALDI-TOF MS need more validation and verification and more study on the performance of direct colony and extraction methods to detect the most sensitive one and also need using more samples to detect sensitivity, reliability, and performance of this type of bacterial identification.

Quantification analysis of protein and mycelium contents upon inhibition of melanin for Aspergillus niger: a study of matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS)

Mass spectrometry (MS) provides a simple discrimination method for microorganisms.