Antibiotic resistance and molecular characterization of ophthalmic Staphylococcus pseudintermedius isolates from dogs

Pathogenic Potential of Coagulase-Positive Staphylococcus Strains Isolated from Aviary Capercaillies and Free-Living Birds in Southeastern Poland

The aim of the study was to determine the occurrence and characteristics of coagulase-positive Staphylococcus strains in the carcasses of wild birds and aviary capercaillies in Southeastern Poland. In total, samples taken from 333 birds were examined. The material consisted of swabs from the internal organs of dead birds (heart, liver, and spleen), the tarsal joints, and mucous membranes (conjunctiva and palatine fissure), as well as from unhatched embryos. The isolated Staphylococcus strains were tested for sensitivity to nine antimicrobial agents and the presence of selected virulence genes. An analysis of the similarity of isolates within species was performed using pulsed-field gel electrophoresis (PFGE). The result indicates that coagulase-positive strains accounted for 5.7% and belonged to the species: Staphylococcus aureus, Staphylococcus pseudintermedius, and Staphylococcus delphini. Among isolated strains, 15.8% were multidrug resistant. The most frequently detected virulence genes were hla in 58% of isolates and hlb and hld in 47.4% of isolates. The results of multiplex PCR showed the presence of genes responsible for the production of enterotoxins C, B, E, and J, in single isolates. It can be concluded that coagulase-positive Staphylococcus strains accounted for a small percentage of staphylococci isolated from free-living birds in the study area. The occurrence of multidrug-resistant coagulase-positive Staphylococcus strains in aviary capercaillies suggests that they play a role in the transmission and spread of resistant strains into the environment. Free-living birds may also be a reservoir of enterotoxigenic Staphylococcus strains.

Argon cold atmospheric plasma eradicates pathogens in vitro that are commonly associated with canine bacterial keratitis

Purpose

To investigate the antimicrobial effect of cold atmospheric plasma (CAP) on pathogens associated with canine bacterial keratitis.

Materials and methods

Pseudomonas aeruginosa, Staphylococcus pseudintermedius, and Streptococcus canis strains, which were obtained from dogs with infectious keratitis, were subjected to testing. For each species, four isolates and a reference strain were cultivated on Columbia sheep blood agar and treated with the kiNPen Vet® plasma pen from Neoplas GmbH, Greifswald, Germany. Various continuous treatment durations (0.5, 2, and 5 min) were applied, along with a 0.5-min treatment repeated four times at short intervals. These treatments were conducted at distances of 3 and 18 mm between the agar surface and the pen.

Results

CAP treatment reduced bacterial growth in all three species. The most effective treatment duration was 5 min at 3 mm distance, resulting in inhibition zones ranging from 19 to 22 mm for P. aeruginosa, 26-45 mm for S. pseudintermedius and an overall reduction of bacterial growth for Str. canis. Inhibition zones were smaller with decreasing treatment duration and larger distance. Treatment times of 30 s repeated four times and 2 min showed comparable results. Treatment with argon alone did not lead to visible reduction of bacterial growth.

Conclusion

Argon cold atmospheric plasma demonstrated a potent in vitro antimicrobial effect on P. aeruginosa, S. pseudintermedius and Str. canis strains with the latter showing the highest sensitivity.

Genomic Features of Antimicrobial Resistance in Staphylococcus pseudintermedius Isolated from Dogs with Pyoderma in Argentina and the United States: A Comparative Study

Staphylococcus pseudintermedius is the most common opportunistic pathogen in dogs and methicillin resistance (MRSP) has been identified as an emerging problem in canine pyoderma. Here, we evaluated the antimicrobial resistance (AMR) features and phylogeny of S. pseudintermedius isolated from canine pyoderma cases in Argentina (n = 29) and the United States (n = 29). 62% of isolates showed multi-drug resistance. The AMR genes found: mecA, blaZ, ermB, dfrG, catA, tetM, aac(6')-aph(2″), in addition to tetK and lnuA (only found in U.S. isolates). Two point mutations were detected: grlA(S80I)-gyrA(S84L), and grlA(D84N)-gyrA(S84L) in one U.S. isolate. A mutation in rpoB (H481N) was found in two isolates from Argentina. SCCmec type III, SCCmec type V, ΨSCCmec₅₇₃₉₅ were identified in the Argentinian isolates; and SCCmec type III, SCCmec type IVg, SCCmec type V, and SCCmec type VII variant in the U.S. cohort. Sequence type (ST) ST71 belonging to a dominant clone was found in isolates from both countries, and ST45 only in Argentinian isolates. This is the first study to comparatively analyze the population structure of canine pyoderma-associated S. pseudintermedius isolates in Argentina and in the U.S. It is important to maintain surveillance on S. pseudintermedius populations to monitor AMR and gain further understanding of its evolution and dissemination.

Otitis Externa in Dogs: Distribution and Antimicrobial Susceptibility Patterns of Staphylococcus Spp. Isolates

The study aimed to investigate the Staphylococcus species from dogs with chronic otitis externa in Istanbul and to determine their antibiotic susceptibility patterns. Ear swab samples were collected from 100 dogs suspected of otitis externa admitted at the clinics of Istanbul University - Cerrahpaşa, Faculty of Veterinary Medicine. The dogs were of different age, gender, and breed. The bacterial isolation was performed by conventional methods. BD Phoenix Automated Microbiology System was used to confirm bacterial identification by conventional methods and to test antimicrobial susceptibility. Staphylococcus spp. were isolated from 36% of the samples collected from the dogs. S. pseudintermedius, S. aureus, S. epidermidis, S. hyicus and S. chromogenes were identified in 41.6%, 22.2%, 11.1%, 5.5%, and 5.5%. In Staphylococcus spp. isolates, enrofloxacin, penicillin, and ampicillin-sulbactam resistance was 8.3%, marbofloxacin resistance was 11.1%, doxycycline resistance was 16.6%, amoxicillin-clavulanic acid, erythromycin, and gentamicin resistance was 19.4%, tetracycline, clindamycin, and sulphonamide resistance was 25%. Methicillin resistance was not observed in any of the isolates. However, multiple drug resistance (MDR) was detected in 11 (30.5%) of 36 isolates. In conclusion, the early detection and antimicrobial sensitivity testing of Staphylococcus spp in dog otitis externa cases that do not respond to empiric therapy could be beneficial for appropriate antibiotic selection and treatment thus preventing MDR.

Inhibition potential of Caryocar brasiliense on methicillin-resistant Staphylococcus pseudintermedius isolated from the ocular surface of dogs with ophthalmopathies

ABSTRACT The indiscriminate use of antibiotics has contributed to the emergence of multiresistant bacteria. Faced with this, the search for antibiotics from plants has proven to be a promising alternative. The objective of this work was to isolate and identify Staphylococcus sp. resistant to methicillin of the ocular surface of dogs with ophthalmopathies and to evaluate its susceptibility to alcoholic extract of the bark and hexane extract of the pulp of Caryocar brasiliense. Biological material was collected from the ocular surface of 21 dogs presenting ophthalmopathies. We isolated 64 S. pseudintermedius, among these, 4 isolates were identified as methicillin-resistant S. pseudintermedius (MRSP). The alcoholic extract of C. brasiliense peel was able to inhibit the bacterial growth of MRSP isolates at a concentration of 2.2%. Thus, the extract from the C. brasiliense peel has antimicrobial potential and represents an alternative in the control of MRSP.

Pathogenic potential and antimicrobial resistance of Staphylococcus pseudintermedius isolated from human and animals

Crossing of interspecies barriers by microorganisms is observed. In recent years, Staphylococcus pseudintermedius-a species formerly thought to be animal-has also been isolated from human clinical materials. Many virulence factors are responsible for the colonization, which is the first step an infection, of the new host organism. We analyzed the factors influencing this colonization as well as susceptibility to antibiotics in fourteen S. pseudintermedius strains isolated from clinical cases from humans and animals. The occurrence of genes responsible for binding elastin, fibronectin, and fibrinogen and some phenotypic features, although different between strains, is comparable in both groups. However, the animal isolates had more genes coding for virulence factors. All isolates tested had the exfoliating toxin gene and the leukotoxin determining genes, but only the human strains had enterotoxin genes. The assessment of antibiotic resistance of strains of both groups indicates their broad resistance to antibiotics commonly used in veterinary medicine. Antibiotic resistance was more common among animal isolates. The multilocus sequence typing analysis of the studied strains was performed. The results indicated a large diversity of the S. pseudintermedius population in both studied groups of strains. Equipped with important virulence factors, they showed the ability to infect animals and humans. The clonal differentiation of the methicillin-susceptible strains and the multidrug resistance of the strains of both studied groups should be emphasized. The considerable genetic diversity of strains from a limited geographical area indicates the processes of change taking place within this species. Thus, careful observation of the ongoing process of variation is necessary, as they may lead to the selection of S. pseudintermedius, which will pose a significant threat to humans.

Antibiotic resistance, biofilm formation, and virulence factors of isolates of staphylococcus pseudintermedius from healthy dogs and dogs with keratitis

Canine bacterial keratitis is a common infection that can potentially threaten vision. Staphylococcus pseudintermedius (S. pseudintermedius) is an opportunistic pathogen that has been isolated from the canine conjunctival sac but there are only a few reports on the role of this bacterium in canine keratitis. This study focused on the distribution rate of S. pseudintermedius in the canine conjunctival sac, and the antibiotic resistance, biofilm-producing ability, and dissemination of virulence factors in strains of S. pseudintermedius isolated from healthy dogs and dogs with keratitis. The study included 35 healthy dogs and 40 dogs with keratitis. Bacterial species were confirmed by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI–TOF MS). Strains of S. pseudintermedius were screened for resistance against nine different antibiotics by the Kirby–Bauer assay. The ability to produce biofilm was investigated by microtiter plate assay (MtP) and amplification of icaA and icaD genes. Virulence factors in the strains were also evaluated. A total of 132 aerobic bacteria were isolated from the 119 samples in the study. Among them, 67 bacterial strains were isolated from 70 eyes of healthy dogs, and 65 bacterial strains were isolated from 49 eyes of dogs with keratitis. The prevalence of S. pseudintermedius, which was the most frequent bacterial isolate in both the groups, was 20.9% in the healthy group and 23.08% in the keratitis group. Most of the isolates of S. pseudintermedius were sensitive to rifampin (96.6%), oxacillin (100%), and neomycin (96.6%), and resistant to tetracycline (96.6%). Virulence factors such as lip (96.6%), hlgB (96.6%), and hlgA (96.6%) were found in most of the isolates, and 89.66% of isolates were classed as biofilm producers. In conclusion, S. pseudintermedius was the common bacterium in the conjunctivital sac of the healthy dogs and dogs with keratitis in Yangzhou, China, and the presence of virulence factors and biofilm-formation ability were high in the strains isolated from the dogs with keratitis.

Case Report: The First Report on Moraxella canis Isolation From Corneal Ulcer in a Bulldog

A 5-year-old castrated male bulldog was diagnosed with a corneal ulcer accompanied by edema and conjunctival hyperemia. Ophthalmic examination and microbiological analysis were performed, and the bacteria were found to be gram-negative and globular. The isolated clone was identified as Moraxella canis (MZ579539) via MALDI-TOF MS and 16S rDNA sequencing. Antimicrobial susceptibility testing showed that the bacteria were sensitive to tetracycline and chloramphenicol, but resistant to levofloxacin and ciprofloxacin. After a conjunctival flap was placed, tobramycin ophthalmic solution and 5% sodium hyaluronate were administered. Following surgery, the ulcer was effectively controlled, and after 3 weeks, the cornea healed. This is the first case report of a canine corneal ulcer associated with M. canis, which should be considered when corneal ulceration or keratitis were suspected.

Antimicrobial Resistance in Coagulase-Positive Staphylococci Isolated from Various Animals in Bosnia and Herzegovina

The objective of this study was to determine and compare the antimicrobial resistance profiles of clinical Staphylococcus pseudintermedius (n = 90) and Staphylococcus aureus (n = 61) isolates from different animal species in Bosnia and Herzegovina. Among S. pseudintermedius isolates from dogs (n = 86), resistance to penicillin (87.2%) was most common followed by amoxicillin (76.7%) and amoxicillin/clavulanic acid (67.4%). A total of 25 isolates were found to be resistant to oxacillin of which 21 were mecA-positive and multidrug resistant (MDR). The most frequent MDR pattern was penicillins-lincosamides-cephalosporins-macrolides-fluoroquinolones. Among the 61 methicillin-susceptible S. pseudintermedius isolates, 18 were MDR (penicillins-lincosamides-macrolides). Most of S. aureus isolates were resistant to penicillin (50.8%), followed by amoxicillin (41%) and amoxicillin/clavulanic acid (31%). Resistance to cefoxitin was detected in only two isolates. All S. aureus isolates were mecA and mecC-negative. MDR was observed in six S. aureus isolates of which five were from cattle (penicillins-lincosamides-fluoroquinolones). Isolates from red foxes (Vulpes vulpes) were sensitive to most of the antimicrobials tested. The high number of methicillin-resistant S. pseudintermedius and MDR isolates in dogs exposed in this study underlines the urgent need for establishment of national antimicrobial resistance surveillance program in animals in the country, as well as for the surveillance of veterinary antimicrobial consumption.

Antibiotic resistance in the pathogenic foodborne bacteria isolated from raw kebab and hamburger: phenotypic and genotypic study

Background

In recent years, interest in the consumption of ready-to-eat (RTE) food products has been increased in many countries. However, RTE products particularly those prepared by meat may be potential vehicles of antibiotic-resistance foodborne pathogens. Considering kebab and hamburger are the most popular RTE meat products in Iran, this study aimed to investigate the prevalence and antimicrobial resistance of common foodborne pathogens (Escherichia coli, Salmonella spp., Staphylococcus aureus, and Listeria monocytogenes) in raw kebab and hamburger samples collected from fast-food centers and restaurants. Therefore, total bacterial count (TBC), as well as the prevalence rates and antibiogram patterns of foodborne pathogens in the samples were investigated. Also, the presence of antibiotic-resistance genes (bla_SHV, bla_TEM,bla_Z, and mecA) was studied in the isolates by PCR.

Results

The mean value of TBC in raw kebab and hamburger samples was 6.72 ± 0.68 log CFU/g and 6.64 ± 0.66 log CFU/g, respectively. E. coli had the highest prevalence rate among the investigated pathogenic bacteria in kebab (70%) and hamburger samples (48%). Salmonella spp., L. monocytogenes, and S. aureus were also recovered from 58, 50, and 36% of kebab samples, respectively. The contamination of hamburger samples was detected to S. aureus (22%), L. monocytogenes (22%), and Salmonella spp. (10%). In the antimicrobial susceptibility tests, all isolates exhibited high rates of antibiotic resistance, particularly against amoxicillin, penicillin, and cefalexin (79.66–100%). The bla_TEM was the most common resistant gene in the isolates of E. coli (52.54%) and Salmonella spp. (44.11%). Fourteen isolates (23.72%) of E. coli and 10 isolates (29.41%) of Salmonella spp. were positive for bla_SHV. Also, 16 isolates (55.17%) of S. aureus and 10 isolates (27.27%) of L. monocytogenes were positive for mecA gene.

Conclusions

The findings of this study showed that raw kebab and hamburger are potential carriers of antibiotic-resistance pathogenic bacteria, which can be a serious threat to public health.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02326-8.

Prevalence of Antimicrobial Resistant Bacteria from Conjunctival Flora in an Eye Infection Prone Breed (Saint Bernard)

The conjunctival bacterial resident and opportunistic flora of dogs may represent a major source of dissemination of pathogens throughout the environment or to other animals and humans. Nevertheless, contamination with bacteria from external sources is common. In this context, the study of the antimicrobial resistance (AMR) pattern may represent an indicator of multidrug resistant (MDR) strains exchange. The present study was focused on a single predisposed breed-Saint Bernard. The evaluated animals were healthy, but about half had a history of ocular disease/treatment. The swabs collected from conjunctival sacs were evaluated by conventional microbiological cultivation and antimicrobial susceptibility testing (AST). The most prevalent Gram-positive was Staphylococcus spp.; regardless of the history, while Gram-negative was Pseudomonas spp.; exclusively from dogs with a history of ocular disease/treatment. Other identified genera were represented by Bacillus, Streptococcus, Trueperella, Aeromonas and Neisseria. The obtained results suggest a possible association between the presence of mixed flora and a history of ocular disease/treatment. A high AMR was generally observed (90%) in all isolates, especially for kanamycin, doxycycline, chloramphenicol and penicillin. MDR was recorded in Staphylococcus spp. and Pseudomonas spp. This result together with a well-known zoonotic potential may suggest an exchange of these strains within animal human populations and the environment.

Virulence factors in coagulase-positive staphylococci of veterinary interest other than Staphylococcus aureus

Coagulase-positive Staphylococci (CoPS) can exist as commensals in humans, companion and food-producing animals, but can cause severe or even lethal diseases. Exchange of these bacteria between humans and animals has been described. Special attention has been focused on Methicillin-Resistant Staphylococcus aureus, but other CoPS can also represent an important threat. In addition to significant antimicrobial resistance, these bacteria may carry a plethora of virulence factors - molecules that allow bacteria to establish on or within a host and increase their ability to cause disease. These virulence factors have been widely described in S. aureus but information about other species of CoPS is scarce. The aim of this paper is to review the recent literature about the virulence factors of non-aureus CoPS of animal origin. Their possible effects on human health are also described. The role and prevalence of different virulence factors including leukocidins, hemolysins, adhesins, enterotoxins, exfoliative and toxic shock syndrome toxins as well as superantigen-like proteins are addressed. The effect of these virulence factors on human health is also described. The possibility of misdiagnosis of species of CoPS has been demonstrated in human clinical samples. Prevalence of zoonotic infections could be higher than thought and medical laboratories should be aware of these other staphylococcal species. In keeping with the ‘One Health’ approach to animal and human disease, medical professionals, veterinarians and health workers should be aware of the risks derived from exposure to these bacteria in people in close contact with animals, including pet owners, farmers and veterinarians themselves.

Staphylococcus pseudintermedius: an undocumented, emerging pathogen in humans

The first infections of methicillin-resistant Staphylococcus pseudintermedius in humans were recorded in 2006, and is now becoming a concern because of its close similarities to human pathogens in the Staphylococcusintermedius group (SIG). These bacteria have all the properties which a multidrug-resistant Staphylococcus aureus possesses.

The literature was searched using the term “Staphylococcus pseudintermedius” in PubMed and other reference databases. The virulence factor and the pathogenicity are under investigation, but reports have suggested that this commensal of animals is transmitted easily via close contact to animals by owners, veterinarians and staff.

Resistance to beta-lactams (including methicillin) is a primary concern. Drug resistance to methicillin is a considerable problem in developing countries, as antibiotic use is not regulated. Studies from Europe have reported multidrug resistant isolates from clinical specimens. Although data on drug resistance and pathogenesis of S. pseudintermedius are not sufficient, it is extremely important to identify the pathogen correctly. Only then can its pathogenesis be studied during the course of disease and appropriate measures developed to prevent it becoming a global problem.

In Vitro Efficacy of Essential Oils from Melaleuca Alternifolia and Rosmarinus Officinalis, Manuka Honey-based Gel, and Propolis as Antibacterial Agents Against Canine Staphylococcus Pseudintermedius Strains

Essential oils (EOs) and honeybee products (e.g., honey and propolis) are natural mixtures of different volatile compounds that are frequently used in traditional medicine and for pathogen eradication. The aim of this study was to evaluate the antibacterial properties of tea tree (Melaleuca alternifolia) EO (TTEO), Rosmarinus officinalis EO (ROEO), manuka-based gel, and propolis against 23 strains of Staphylococcus pseudintermedius (SP) isolated from canine pyoderma. Antimicrobial resistance screening was assessed using a panel of nine antimicrobial agents coupled with a PCR approach. An aromatogram was done for both EOs, using the disk diffusion method. The minimum inhibitory concentration (MIC) was determined for all the compounds. Among the 23 SP strains, 14 (60.9%) were multidrug-resistant (MDR), 11 strains (47.8%) were methicillin-resistant (MRSP), and 9 (39.1%) were non-MDR. The mean diameter of the inhibition zone for Melaleuca and Rosmarinus were 24.5 ± 8.8 mm and 15.2 ± 8.9 mm, respectively, resulting as statistically different (p = 0.0006). MIC values of TTEO and ROEO were similar (7.6 ± 3.2% and 8.9 ± 2.1%, respectively) and no statistical significances were found. Honeybee products showed lower MIC compared to those of EOs, 0.22 ± 0.1% for Manuka and 0.8 ± 0.5% for propolis. These findings reveal a significant antibacterial effect for all the tested products.

Investigation on Antibiotic-Resistance, Biofilm Formation and Virulence Factors in Multi Drug Resistant and Non Multi Drug Resistant Staphylococcus pseudintermedius

Staphylococcus pseudintermedius is a commensal bacterium frequently isolated from canine skin and recognized as a zoonotic agent especially for dog-owners. This study focused on (a) the antibiotic-resistance phenotypes; (b) the ability to produce biofilm (slime); and (c) the dissemination of virulence factors in S. pseudintermedius strains. Seventy-three S. pseudintermedius strains were screened for antibiotic-resistance against 22 different molecules by means of Kirby-Bauer assay. The ability to produce biofilm was investigated using the microtiter plate assay (MtP) and the amplification of icaA and icaD genes. Virulence factors such as cytotoxins (lukI), enterotoxins (seC), and exfoliative toxins (siet, expA, and expB) were evaluated. The antibiotic-resistance profiles revealed 42/73 (57%) multi-drug resistant (MDR) strains and 31/73 (43%) not-MDR. All the MDR strains and 8/31 (27%) of not-MDR resulted in biofilm producers. Leukotoxin LukI was found in 70/73 (96%) of the isolates. Moreover, the enterotoxin gene seC was detected in 47/73 (64%) of the strains. All the isolates carried the siet gene, whereas expA and expB were found in 3/73 (4%) and 5/73 (7%), respectively. In conclusion, S. pseudintermedius should be considered a potential zoonotic and human agent able to carry different virulence determinants and capable of producing biofilm which facilitates horizontal gene transfer.

Antimicrobial susceptibility and minimal inhibitory concentration of bacteria isolated from the eyes of dogs with keratoconjunctivitis sicca

ABSTRACT: The objective of this study was to evaluate the antimicrobial susceptibility profile of bacteria isolated from the eyes of dogs with keratoconjunctivitis sicca (KCS). We evaluated 65 dogs diagnosed with KCS and 30 healthy dogs (Control Group). Conjunctival swab samples were collected after KCS was diagnosed. Microbiological examinations were performed, including aerobic culture, antimicrobial susceptibility testing and minimum inhibitory concentration (MIC) determination for chloramphenicol, tobramycin, ofloxacin and moxifloxacin. MICs of the fifteen most resistant strains of Staphylococcus pseudintermedius (Staphylococcus intermedius Group, SIG) and the fifteen most resistant strains of gram-negative bacteria were determined. By percentage, the microorganisms exhibited the highest susceptibility to polymyxin B, tobramycin and chloramphenicol and the lowest to tetracycline. Three multi-drug-resistant strains of SIG were detected: one displayed isolated susceptibility to cefazolin, another to vancomycin, and another to polymyxin B and amikacin. The species of bacteria isolated from the eyes of dogs with KCS presented variable susceptibility to the antibiotics tested. We found evidence of the emergence of quinolone-resistant strains of SIG and further evidence of increased ocular prevalence. These findings reinforce the need to identify the bacteria involved and their antimicrobial susceptibility profile, as secondary infections can serve as exacerbating and perpetuating factors in KCS.

Molecular detection of antibiotic resistance genes in multidrug-resistant Staphylococcus aureus isolates from dog dental plaque

Multidrug resistant Staphylococcus aureus strains are a major health care problem both in humans and animals. In this work we described three multiplex PCR assays for detection of clinically relevant antibiotic resistance genes in S. aureus isolated from dog dental plaques. Thirty dental plaque samples were collected; then cultural, biochemical and molecular tests performed for isolation and identification of S. aureus from samples. The antibiotic susceptibility of the isolates were checked by Kirby Bauer disc diffusion method and the prevalence of antibiotic resistance genes determined using multiplex PCR assay. As a result S. aureus was isolated from 18 dog plaque samples. Fifteen of these isolates were resistant to penicillin. The mecA gene was more prevalent than blaZ among penicillin-resistant bacteria. Ten of the isolates were resistant to tetracycline. The percentage of tetM was higher than tetK among them. Also, 10 of the isolates were resistant to cefazolin among them bla TEM detected in higher rate than blaSHV and blaOXA-1. Hence multiplex PCR assay is a suitable method for detection of antibiotic resistance patterns of S. aureus isolates.

An evaluation of matrix-assisted laser desorption ionization time-of-flight mass spectrometry for the identification of Staphylococcus pseudintermedius isolates from canine infections

It has been proposed, based on taxonomic and molecular studies, that all canine isolates belonging to Staphylococcus intermedius group (SIG) should be renamed Staphylococcus pseudintermedius. However, isolates of SIG and other coagulase-positive staphylococci share many phenotypic characteristics, which could lead to misidentification. The accuracy of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) for identifying S. pseudintermedius isolates obtained from canine infections was evaluated, using a polymerase chain reaction (PCR)-based identification as the gold standard. In addition, MALDI-TOF MS was compared with conventional biochemical tests. A central problem was the incorrect identification of S. pseudintermedius isolates as S. intermedius by either MALDI-TOF MS or biochemical identification. From the 49 S. pseudintermedius isolates identified by the molecular method, only 21 could be assigned to this species by the biochemical approach and only 12 by MALDI-TOF MS. The 6 S. aureus isolates were correctly identified by all 3 techniques. However, using biochemical tests, 9 S. pseudintermedius were mistakenly classified as S. aureus, indicating a reduced specificity relative to the MALDI-TOF MS system. Analysis with the MALDI-TOF MS platform allowed rapid and accurate identification of the 49 isolates to the S. intermedius group but the approach was very limited in identifying S. pseudintermedius isolates, as only 12 of 49 isolates were correctly identified, a sensitivity of 0.24 (95% confidence interval: 0.13-0.39).