Immune-mediated pyogranulomatous panniculitis with hypercalcemia in a dog.

An 11-year-old neutered male large crossbreed dog was presented for investigation because of a 10-day history of progressive lethargy, hyporexia, and pyrexia. Physical and dermatological examinations were unremarkable. Blood biochemical analysis identified a marked total and ionized hypercalcemia and increased C-reactive protein concentration. Bicavitary computed tomography screening for causes of the dog's clinical and biochemical abnormalities identified a diffuse panniculitis. Histopathological examination of full-thickness skin biopsies was consistent with pyogranulomatous inflammation. Extensive histochemical staining revealed no infectious etiology. Complete clinical and biochemical remissions were observed after starting immunosuppressive, followed by tapering, doses of prednisolone, supporting an immune-mediated etiology. Key clinical message: Sterile, immune-mediated pyogranulomatous inflammation should remain a differential diagnosis for hypercalcemia in dogs. Significant dermatological disease may occur without visible abnormalities.

Panniculite pyogranulomateuse à médiation immunitaire avec hypercalcémie chez un chienUn grand chien croisé mâle castré de 11 ans a été présenté pour examen en raison d'antécédents de léthargie progressive, d'hyporexie et de pyrexie depuis 10 jours. Les examens physiques et dermatologiques étaient sans particularité. L'analyse biochimique du sang présentait une hypercalcémie totale et ionisée marquée et une concentration accrue de protéine C-réactive. Le dépistage par tomodensitométrie bicavitaire des causes des anomalies cliniques et biochimiques du chien a identifié une panniculite diffuse. L'examen histopathologique des biopsies cutanées de pleine épaisseur était compatible avec une inflammation pyogranulomateuse. Un examen par coloration histochimique extensive n'a révélé aucune étiologie infectieuse. Les rémissions cliniques et biochimiques complètes ont été observées après le début du traitement immunosuppresseur, suivies d'une diminution progressive des doses de prednisolone, confirmant une étiologie à médiation immunitaire.Message clinique clé:L'inflammation pyogranulomateuse stérile à médiation immunitaire doit rester un diagnostic différentiel de l'hypercalcémie chez le chien. Une maladie dermatologique importante peut survenir sans anomalies visibles.(Traduit par Dr Serge Messier).

Longitudinal study of ESBL/AmpC-producing Enterobacterales strains sharing between cohabiting healthy companion animals and humans in Portugal and in the United Kingdom.

Extended-spectrum beta-lactamase (ESBL)- and plasmid-mediated cephalosporinase (AmpC)-producing Enterobacterales (ESBL/AmpC-E) are an increasing healthcare problem in both human and veterinary medicine. The aim of this study was to investigate the possible sharing of ESBL/AmpC-E strains between healthy companion animals and humans of the same household in Portugal (PT) and the United Kingdom (UK). In a prospective longitudinal study, between 2018 and 2020, faecal samples were collected from healthy dogs (n=90), cats (n=20) and their cohabiting humans (n=119) belonging to 41 PT and 44 UK households. Samples were screened for the presence of ESBL/AmpC-E and carbapenemase-producing bacteria. Clonal relatedness between animal and human strains was established by using REP-PCR fingerprinting method, followed by whole-genome sequencing (WGS) of selected strains. ESBL/AmpC-E strains were detected in companion animals (PT=12.7%, n=8/63; UK=8.5%, n=4/47) and humans (PT=20.7%, n=12/58; UK=6.6%, n=4/61) in at least one timepoint. REP-PCR identified paired multidrug-resistant ESBL/AmpC-producing Escherichia coli strains from companion animals and owners in two Portuguese households (4.8%) and one UK household (2.3%). WGS analysis of nine E. coli strains from these three households confirmed that interhost sharing occurred only between the two animal-human pairs from Portugal. Three shared strains were identified: one CTX-M-15-producing E. coli strain in a cat-human pair (O15-H33-ST93) and two CTX-M-15- and CTX-M-55/CMY-2-producing E. coli strains, in a dog-human pair (O8:H9-ST410 and O11:H25-ST457, respectively) at different timepoints. These E. coli clonal lineages are human pandemic, highlighting the role of companion animals living in close contact with humans in the dissemination and persistence of antimicrobial resistance in the household environment.

mcr-1 colistin resistance gene sharing between Escherichia coli from cohabiting dogs and humans, Lisbon, Portugal, 2018 to 2020.

BackgroundThe emergence of colistin resistance is a One Health antimicrobial resistance challenge worldwide. The close contact between companion animals and humans creates opportunities for transmission and dissemination of colistin-resistant bacteria.AimTo detect potential animal reservoirs of colistin-resistant Escherichia coli and investigate the possible sharing of these bacteria between dogs, cats and their cohabiting humans in the community in Lisbon, Portugal.MethodsA prospective longitudinal study was performed from 2018 to 2020. Faecal samples from dogs and cats either healthy or diagnosed with a skin and soft tissue or urinary tract infection, and their cohabiting humans were screened for the presence of colistin-resistant E. coli. All isolates were tested by broth microdilution against colistin and 12 other antimicrobials. Colistin-resistant isolates were screened for 30 resistance genes, including plasmid-mediated colistin resistance genes (mcr-1 to mcr-9), and typed by multilocus sequence typing. Genetic relatedness between animal and human isolates was analysed by whole genome sequencing.ResultsColistin-resistant E. coli strains harbouring the mcr-1 gene were recovered from faecal samples of companion animals (8/102; 7.8%) and humans (4/125; 3.2%). No difference between control and infection group was detected. Indistinguishable multidrug-resistant E. coli ST744 strains harbouring the mcr-1 gene were found in humans and their dogs in two households.ConclusionsThe identification of identical E. coli strains containing the plasmid-mediated mcr-1 gene in companion animals and humans in daily close contact is of concern. These results demonstrate the importance of the animal-human unit as possible disseminators of clinically important resistance genes in the community setting.

The nose is not enough: Multi-site sampling is best for MRSP detection in dogs and households.

BACKGROUND: Following recovery from meticillin-resistant Staphylococcus pseudintermedius (MRSP) infection of any type, dogs may continue to carry MRSP asymptomatically on skin and mucosae, contributing to the spread of this multidrug-resistant, veterinary hospital-associated pathogen with zoonotic potential to others and into the environment. OBJECTIVES: This study determined which canine anatomic and household environmental sites are most sensitive for sampling to identify carriage and contamination. METHODS AND MATERIALS: Fifty-one dogs and 22 households, MRSP-positive on at least one tested site, were sampled on 132 and 40 occasions over time, respectively. Dogs were swabbed at six sites (mouth, nose, conjunctiva, skin, prepuce/vulva, perianal area); household environments were sampled using contact plates (mannitol salt agar [MSA] and MSA + 6 mg/L oxacillin [MS+]) on five sites. MRSP was isolated after enrichment, grown on MSA/MS+ and was confirmed by PCR. Generalized estimating equations were used for calculation of sensitivity (95% confidence interval) for each site/combination. RESULTS: Each anatomical and environmental site yielded MRSP at least once. MRSP was isolated from only a single site in 27.3% of dogs, with the buccal mucosa showing the highest sensitivity (63.8%). Multi-site sampling of a minimum of four canine anatomical or four environmental sites, respectively, was needed to achieve >95% sensitivity. CONCLUSIONS AND CLINICAL RELEVANCE: The canine buccal mucosa should be included in MRSP sampling protocols, ideally in addition to at least three other anatomical sites. Likewise, environment sampling should be of multiple household sites in cases where it is used as a part of clinical case management.

Malassezia otitis unresponsive to primary care: outcome in 59 dogs.

BACKGROUND: Otitis externa (OE) is a common disorder in dogs. Infection by the commensal yeast, Malassezia pachydermatis, may result in chronic disease that does not respond to standard primary care. Chronic infectious OE may be associated with otitis media (OM). HYPOTHESIS/OBJECTIVE: To report medical management, clinical outcomes and frequency of middle ear involvement, in dogs with Malassezia otitis unresponsive to primary care. ANIMALS: Fifty-nine dogs from one referral veterinary hospital from January 2007 to September 2018. METHODS AND MATERIALS: Retrospective analysis of medical records of dogs referred with chronic otitis and treated for Malassezia otitis at a referral veterinary hospital. RESULTS: Chronic Malassezia OE was treated successfully in 91% of ears, in 87% of these cases with one ear flush intervention. Median time-to-resolution was 27 days after ear flush intervention. Neither duration of otitis, presence of neutrophils in aural discharge nor administration of oral itraconazole affected clinical outcome. Malassezia OM occurred concurrently in 17% of ears. CONCLUSIONS AND CLINICAL RELEVANCE: These findings assist clinicians and carers of affected dogs in decision-making, by documenting that most cases of canine Malassezia otitis that have not resolved with standard primary care, can be treated successfully with a well-staged and intense medical treatment plan. Malassezia OM should be suspected to occur concurrently in around a fifth of affected ears.

Closed genome sequences of Staphylococcus lloydii sp. nov. and Staphylococcus durrellii sp. nov. isolated from captive fruit bats (Pteropus livingstonii).

The increasing availability of whole genome sequencing of bacteria has accelerated the discovery of novel species which may not have been easy to discriminate using standard phenotypic or single gene methods. Phylogenomic analysis of genome sequences from a collection of coagulase-negative staphylococcal species isolated from captive fruit bats revealed two clusters which were close to Staphylococcus kloosii. To assess the relatedness of the strains we used digital DNA-DNA hybridization (dDDH) and two methods for average nucleotide identity (ANI) computation which predicted two novel species having dDDH less than 70 % and ANI less than 95%. We propose these species as Staphylococcus lloydii sp. nov. (type strain 23_2_7_LYT=NCTC 14453T=DSM 111639T) and Staphylococcus durrellii sp. nov (type strain 27_4_6_LYT=NCTC 14454T=DSM 111640T).

DIVERSITY OF STAPHYLOCOCCAL SPECIES CULTURED FROM CAPTIVE LIVINGSTONE'S FRUIT BATS (PTEROPUS LIVINGSTONII) AND THEIR ENVIRONMENT.

Livingstone's fruit bats (Pteropus livingstonii) are critically endangered and a captive population has been established as part of the International Union for Conservation of Nature Species Action Plan. The largest colony, in Jersey Zoo, was sampled for staphylococcal carriage and at infection sites, as disease associated with staphylococci had previously been found. Staphylococci were cultured from swabs from 44 bats (skin, oropharynx, mouth ejecta, skin lesions) and from their enclosure. The isolates were identified by matrix-assisted laser desorption-ionization time of flight mass spectrometry; antimicrobial susceptibility testing was performed by disc diffusion and screening for mecA and mecC. Seventeen species of coagulase-negative staphylococci including Staphylococcus xylosus, S. kloosii, S. nepalensis, and S. simiae were isolated. Staphylococcus aureus was identified from both carriage and lesional sites. These findings suggest S. nepalensis may be part of the normal carriage flora of bats. Antimicrobial resistance rates were low and methicillin-resistant Staphylococcus aureus (MRSA) was not identified. Sampling of mouth ejecta for staphylococci may provide results representative for carriage sites.

Long-term management of horses with atopic dermatitis in southeastern England: a retrospective questionnaire study of owners' perceptions.

BACKGROUND: Allergic pruritus and urticaria in the horse are challenging for veterinarians and owners; little is known about their long-term management. OBJECTIVES: To summarize intradermal allergen test results (IDT), and to assess owners' perceptions of skin disease and the effects of medical treatment and management changes in their atopic horses over time. ANIMALS: Eighty two horses with atopic dermatitis in southeastern England between 2006 and 2011. METHODS AND MATERIALS: The IDT results were reviewed retrospectively. Owners completed telephone questionnaires on skin changes, medication, effect of allergen-specific immunotherapy (ASIT) and management. RESULTS: Sixty one owners (74.4%) could be contacted, an average of 5.9 years (range 28-88 months) after IDT; of those, three could not be enrolled. Of the 58 remaining horses, eleven (19%) were deceased at the time of owner interview, including four (6.9%) euthanized due to uncontrollable skin disease. The remaining 47 owners reported that the signs of skin disease had not been seen for at least two years in 18 horses (38.3%), including two that only flared with known triggers. Twenty nine horses (61.7%) still required medication to control skin disease although 25 (53.2%) required less since testing. Owners reported benefit from ASIT in nine of 14 horses (64.3%) from glucocorticoids in 33 of 35 (94.3%) and from antihistamines in 17 of 28 (60.7%). Specific management changes were implemented for 22 horses and reported as beneficial in nine of 22 (40.9%). CONCLUSIONS: Equine atopic dermatitis may not always be chronic, but severe cases appear difficult to control. IDT may help to formulate ASIT and can help to guide management changes.

Opportunities for topical antimicrobial therapy: permeation of canine skin by fusidic acid.

BACKGROUND: Staphylococcal infection of the canine epidermis and hair follicle is amongst the commonest reasons for antimicrobial prescribing in small animal veterinary practice. Topical therapy with fusidic acid (FA) is an attractive alternative to systemic therapy based on low minimum inhibitory concentrations (MICs, commonly <0.03 mg/l) documented in canine pathogenic staphylococci, including strains of MRSA and MRSP (methicillin-resistant Staphylococcus aureus and S. pseudintermedius). However, permeation of canine skin by FA has not been evaluated in detail. This study aimed to define the degree and extent of FA permeation in canine skin in vitro from two sites with different hair follicle density following application of a licensed ophthalmic formulation that shares the same vehicle as an FA-betamethasone combination product approved for dermal application in dogs. Topical FA application was modelled using skin held in Franz-type diffusion cells. Concentrations of FA in surface swabs, receptor fluid, and transverse skin sections of defined anatomical depth were determined using high-performance liquid chromatography and ultraviolet (HPLC-UV) analysis. RESULTS: The majority of FA was recovered by surface swabs after 24 h, as expected (mean ± SEM: 76.0 ± 17.0%). FA was detected within 424/470 (90%) groups of serial sections of transversely cryotomed skin containing follicular infundibula, but never in 48/48 (100%) groups of sections containing only deeper follicular structures, nor in receptor fluid, suggesting that FA does not permeate beyond the infundibulum. The FA concentration (mean ± SEM) in the most superficial 240 µm of skin was 2000 ± 815 µg/g. CONCLUSIONS: Topically applied FA can greatly exceed MICs for canine pathogenic staphylococci at the most common sites of infection. Topical FA therapy should now be evaluated using available formulations in vivo as an alternative to systemic therapy for canine superficial bacterial folliculitis.

Bacterial resistance to antimicrobial agents and its impact on veterinary and human medicine.

BACKGROUND: Antimicrobial resistance has become a major challenge in veterinary medicine, particularly in the context of bacterial pathogens that play a role in both humans and animals. OBJECTIVES: This review serves as an update on acquired resistance mechanisms in bacterial pathogens of human and animal origin, including examples of transfer of resistant pathogens between hosts and of resistance genes between bacteria. RESULTS: Acquired resistance is based on resistance-mediating mutations or on mobile resistance genes. Although mutations are transferred vertically, mobile resistance genes are also transferred horizontally (by transformation, transduction or conjugation/mobilization), contributing to the dissemination of resistance. Mobile genes specifying any of the three major resistance mechanisms - enzymatic inactivation, reduced intracellular accumulation or modification of the cellular target sites - have been found in a variety of bacteria that may be isolated from animals. Such resistance genes are associated with plasmids, transposons, gene cassettes, integrative and conjugative elements or other mobile elements. Bacteria, including zoonotic pathogens, can be exchanged between animals and humans mainly via direct contact, but also via dust, aerosols or foods. Proof of the direction of transfer of resistant bacteria can be difficult and depends on the location of resistance genes or mutations in the chromosomal DNA or on a mobile element. CONCLUSION: The wide variety in resistance and resistance transfer mechanisms will continue to ensure the success of bacterial pathogens in the future. Our strategies to counteract resistance and preserve the efficacy of antimicrobial agents need to be equally diverse and resourceful.

Skin disease in captive bats: results of an online survey of zoos and rehabilitators in Europe, North America and Australasia.

BACKGROUND: Bats may be held captive in zoos and breeding programmes, and for rehabilitation due to illness, abandonment or injury. OBJECTIVES: To describe the frequency and characteristics of skin disease in captive bats. METHODS: Zoos (n = 164) in Europe, North America, Australia and New Zealand, Wildlife Disease Association members and rehabilitators were invited to complete online questionnaires on skin lesions and housing. Associations between lesion type and site, frequency, species, age, suspected cause and season, and their association with housing in zoos were tested using chi-squared and two-sample z-tests. RESULTS: Skin lesions were seen by 38.5% (15 of 39) of responding zoos and more frequently by rehabilitators (66.7%, 18 of 27; P = 0.024). Of the total of 153 lesions of any type reported by zoos and rehabilitators, almost two thirds occurred on the pinnae (49 of 153, 32%) or wing membranes (45 of 153, 29%). Amongst pinnal lesions, crusting (27%), swelling and redness (25%) and necrosis (20%) were most frequent. In zoos, pinnal (P = 0.001) and wing lesions (P = 0.045) were associated with "season", being more common in winter. Pruritus was rare but more often reported from rehabilitation centres (12 of 77 observed lesions) than from zoos (1 of 76) (P = 0.0015). Lesions most often affected adult and geriatric bats in zoos, and juveniles and adults in rehabilitation. Eight respondents reported that skin disease necessitated euthanasia in individual bats. There was no significant association between type of housing and lesions. CONCLUSION: Pinnal and wing lesions were common in captive bats, often with necrosis. Further research into the causes is needed to improve health and welfare of captive bats.

Recommendations for approaches to meticillin-resistant staphylococcal infections of small animals: diagnosis, therapeutic considerations and preventative measures.: Clinical Consensus Guidelines of the World Association for Veterinary Dermatology.

BACKGROUND: Multiple drug resistance (MDR) in staphylococci, including resistance to the semi-synthetic penicillinase-resistant penicillins such as meticillin, is a problem of global proportions that presents serious challenges to the successful treatment of staphylococcal infections of companion animals. OBJECTIVES: The objective of this document is to provide harmonized recommendations for the diagnosis, prevention and treatment of meticillin-resistant staphylococcal infections in dogs and cats. METHODS: The authors served as a Guideline Panel (GP) and reviewed the literature available prior to September 2016. The GP prepared a detailed literature review and made recommendations on selected topics. The World Association of Veterinary Dermatology (WAVD) provided guidance and oversight for this process. A draft of the document was presented at the 8th World Congress of Veterinary Dermatology (May 2016) and was then made available via the World Wide Web to the member organizations of the WAVD for a period of three months. Comments were solicited and posted to the GP electronically. Responses were incorporated by the GP into the final document. CONCLUSIONS: Adherence to guidelines for the diagnosis, laboratory reporting, judicious therapy (including restriction of use policies for certain antimicrobial drugs), personal hygiene, and environmental cleaning and disinfection may help to mitigate the progressive development and dissemination of MDR staphylococci.

Clinical features, cytology and bacterial culture results in dogs with and without cheilitis and comparison of three sampling techniques.

BACKGROUND: Cheilitis is a common presentation in dogs associated with a variety of skin diseases and often complicated by microbial infections. OBJECTIVES: To describe and compare clinical and cytological features and bacterial culture results from the lower lips of dogs with cheilitis (as compared to healthy controls), and to evaluate three cytology sampling techniques for their abilities to differentiate between the groups. ANIMALS: Fifty six dogs with cheilitis and 54 controls. METHODS: Anatomy and clinical signs of the lower lip were recorded. Cytology samples taken by tape strip, direct impression and swabs rolled over skin were scored semiquantitatively for microorganisms, inflammatory cells and keratinocytes. Cytology scores were correlated with semiquantitative bacterial culture scores. RESULTS: Pure breeds, frequency of lip folds and all cytology scores except keratinocytes were higher in dogs with cheilitis than in controls, but a substantial overlap was seen in all microorganisms between the groups. Hypersensitivity disorders were diagnosed in 40 of 56 dogs with cheilitis. The tape strip technique yielded the greatest differences between groups. Bacterial growth was reported in 100% of dogs with cheilitis and in 93% of the controls. Pathogens such as Staphylococcus pseudintermedius, Escherichia coli and Pseudomonas spp were found more frequently in dogs with cheilitis. Cytology and bacterial culture were poorly correlated. CONCLUSION: Cheilitis was associated with primary hypersensitivity disorders and the presence of a lip fold was a predisposing factor. Results of aerobic culture were similar to prior studies on pyoderma of other body sites, except for higher rates of Pseudomonas spp. isolation.

Interaction of chlorhexidine with trisEDTA or miconazole in vitro against canine meticillin-resistant and -susceptible Staphylococcus pseudintermedius isolates from two UK regions.

BACKGROUND: Topical therapy is an important alternative to systemic antibacterial therapy for treatment of canine superficial pyoderma in light of the emergence of multidrug-resistant staphylococci. Chlorhexidine is widely used in shampoo products alone or in combination with miconazole or tromethamine-ethylenediaminetetraacetic acid (trisEDTA). Comparisons of these combinations have not been made. HYPOTHESIS/OBJECTIVES: To determine minimum inhibitory concentrations (MICs) of combinations of chlorhexidine/miconazole and chlorhexidine/trisEDTA in vitro in a collection of Staphylococcus pseudintermedius (SP) from northern (NUK) and southeastern (SEUK) United Kingdom (UK) sources. METHODS: MICs of chlorhexidine, miconazole, trisEDTA and combinations of chlorhexidine/miconazole (1:1) or chlorhexidine/trisEDTA (80:16:1 and 80:5:1) were determined for 196 canine SP isolates from NUK [49 meticillin-resistant (MRSP), 50 meticillin-susceptible (MSSP)] and fom SEUK (48 MRSP, 49 MSSP) using agar dilution. RESULTS: TrisEDTA alone did not inhibit growth. Chlorhexidine/miconazole MICs (median = 0.5 mg/L) were lower than those of either drug alone (P < 0.05) and lower than chlorhexidine/trisEDTA MICs (median = 1 mg/L; P < 0.0005) in each bacterial type and from both regions, except for miconazole in NUK MSSP. An additive interaction was noted between chlorhexidine and miconazole or trisEDTA (80:16:1 ratio) in 79 and 43 isolates, respectively, whereas antagonism between chlorhexidine and trisEDTA was noted for three isolates. NUK isolates were more susceptible than SEUK isolates (P < 0.05), except MRSP exposed to chlorhexidine and the chlorhexidine/trisEDTA (80:16:1) combination. CONCLUSIONS AND CLINICAL IMPORTANCE: These low MICs are likely to be exceeded by topical therapy. Evaluation of the mechanisms by which chlorhexidine combinations interact to reduce MICs is warranted, in view of increasing concerns of biocide tolerance in staphylococci.

Genomic insights into the rapid emergence and evolution of MDR in Staphylococcus pseudintermedius.

OBJECTIVES: MDR methicillin-resistant Staphylococcus pseudintermedius (MRSP) strains have emerged rapidly as major canine pathogens and present serious treatment issues and concerns to public health due to their, albeit low, zoonotic potential. A further understanding of the genetics of resistance arising from a broadly susceptible background of S. pseudintermedius is needed. METHODS: We sequenced the genomes of 12 S. pseudintermedius isolates of varied STs and resistance phenotypes. RESULTS: Nine distinct clonal lineages had acquired either staphylococcal cassette chromosome (SCC) mec elements and/or Tn5405-like elements carrying up to five resistance genes [aphA3, sat, aadE, erm(B), dfrG] to generate MRSP, MDR methicillin-susceptible S. pseudintermedius and MDR MRSP populations. The most successful and clinically problematic MDR MRSP clones, ST68 SCCmecV(T) and ST71 SCCmecII-III, have further accumulated mutations in gyrA and grlA conferring resistance to fluoroquinolones. The carriage of additional mobile genetic elements (MGEs) was highly variable, suggesting that horizontal gene transfer is frequent in S. pseudintermedius populations. CONCLUSIONS: Importantly, the data suggest that MDR MRSP evolved rapidly by the acquisition of a very limited number of MGEs and mutations, and that the use of many classes of antimicrobials may co-select for the spread and emergence of MDR and XDR strains. Antimicrobial stewardship will need to be comprehensive, encompassing human medicine and veterinary disciplines to successfully preserve antimicrobial efficacy.

Oxacillin sensitization of methicillin-resistant Staphylococcus aureus and methicillin-resistant Staphylococcus pseudintermedius by antisense peptide nucleic acids in vitro.

BACKGROUND: Antibiotic resistance genes can be targeted by antisense agents, which can reduce their expression and thus restore cellular susceptibility to existing antibiotics. Antisense inhibitors can be gene and pathogen specific, or designed to inhibit a group of bacteria having conserved sequences within resistance genes. Here, we aimed to develop antisense peptide nucleic acids (PNAs) that could be used to effectively restore susceptibility to ß-lactams in methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus pseudintermedius (MRSP). RESULTS: Antisense PNAs specific for conserved regions of the mobilisable gene mecA, and the growth essential gene, ftsZ, were designed. Clinical MRSA and MRSP strains of high oxacillin resistance were treated with PNAs and assayed for reduction in colony forming units on oxacillin plates, reduction in target gene mRNA levels, and cell size. Anti-mecA PNA at 7.5 and 2.5 µM reduced mecA mRNA in MRSA and MRSP (p < 0.05). At these PNA concentrations, 66 % of MRSA and 92 % of MRSP cells were killed by oxacillin (p < 0.01). Anti-ftsZ PNA at 7.5 and 2.5 µM reduced ftsZ mRNA in MRSA and MRSP, respectively (p ≤ 0.05). At these PNA concentrations, 86 % of MRSA cells and 95 % of MRSP cells were killed by oxacillin (p < 0.05). Anti-ftsZ PNAs resulted in swelling of bacterial cells. Scrambled PNA controls did not affect MRSA but sensitized MRSP moderately to oxacillin without affecting mRNA levels. CONCLUSIONS: The antisense PNAs effects observed provide in vitro proof of concept that this approach can be used to reverse ß-lactam resistance in staphylococci. Further studies are warranted as clinical treatment alternatives are needed.