Bacteria of Ophthalmic Importance Diane Hendrix, DVM, DACVO Professor of Ophthalmology
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Bacteria of Ophthalmic Importance Diane Hendrix, DVM, DACVO Professor of Ophthalmology THE UNIVERSITY OF TENNESSEE COLLEGE OF VETERINARY MEDICINE DEPARTMENT OF <<INSERT DEPARTMENT NAME HERE ON MASTER SLIDE>> 1 Bacteria Prokaryotic organisms – cell membrane – cytoplasm – RNA – DNA – often a cell wall – +/- specialized surface structures such as capsules or pili. –lack a nuclear membrane or mitotic apparatus – the DNA is organized into a single circular chromosome www.norcalblogs.com/.../GeneralBacteria.jpg 2 Bacteria +/- smaller molecules of DNA termed plasmids that carry information for drug resistance or code for toxins that can affect host cellular functions www.fairscience.org 3 Variable physical characteristics • Mycoplasma lacks a rigid cell wall • Borrelia and Leptospira have flexible thin walls. • Pili are short, hair-like extensions at the cell membrane that mediate adhesion to specific surfaces. http://www.stopcattlepinkeye.com/about-cattle-pinkeye.asp 4 Bacteria reproduction • Asexual binary fission • The bacterial growth cycle includes: – the lag phase – the logarithmic growth phase – the stationary growth phase – the decline phase • Iron is essential for bacteria 5 Opportunistic bacteria • Staphylococcus epidermidis • Bacillus sp. • Corynebacterium sp. • Escherichia coli • Klebsiella sp. • Enterobacter sp. • Serratia sp. • Pseudomonas sp. (other than P aeruginosa). 6 Infectivity • Adhesins are protein determinates of adherence. Some are expressed in bacterial pili or fimbriae. • Flagella • Proteases, elastases, hemolysins, cytoxins degrade BM and extracellular matrix. • Secretomes and lipopolysaccharide core biosynthetic genes inhibit corneal epithelial cell migration 7 8 Normal bacterial and fungal flora Bacteria can be cultured from 50 to 90% of normal dogs. – Gram + aerobes are most common. – Gram - bacteria have been recovered from 8% of normal dogs. – Anaerobes are rarely isolated. Normal flora varies with the season and the breed of dog. Fungi have been isolated from 22% of dogs in one study. 9 Conjunctival flora in dogs with ulcerative keratitis. • Bacteria are more commonly isolated. • Malassezia pachydermatitis is present in 23% of eyes with corneal ulceration 10 Equine flora Normal bacterial flora Corynebacterium spp., beta-hemolytic Streptococcus, Staphylococcus spp., Klebsiella spp., Bacillus cereus and Moraxella spp. Fungal flora Unidentifiable molds, dematiaceous molds, Chrysosporuim spp., Cladosporium spp., Aspergillus spp. and Penicillium spp. 11 Bovine flora • Cladosporium spp. and Penicillium spp. • No seasonal or housing difference. • May represent transient seeding from the environment, including the hay, as suspected in other species. 12 Normal flora •Bats • Alpacas • Chelonians 13 www.biology4kids.com Staphylococcus spp. • Ubiquitous and are part of the microflora of the skin and mucous membranes. • Gram + organisms that appear cytologically as individuals, pairs, small groups or grapelike clusters. • Facultative anaerobes and fermentative. • Isolates commonly recovered from ocular sources are coagulase-positive species. 14 Infectious Keratitis – S aureus is isolated from about 5% of horses – S intermedius is isolated from 2% of horses and 29% of dogs – Coagulase-negative species include S epidermidis (isolated from 6% of affected horses). 15 Resistance • Canine isolates are sensitive to cefazolin, ciprofloxacin, and chloramphenicol. • Of 4 equine isolates all were sensitive to bacitracin, chloramphenicol, neomycin, and enrofloxacin. upload.wikimedia.org 16 Streptococcus spp. and related cocci • Ubiquitous, suppurative bacteria • Enterococci are opportunists • Streptococcal keratitis is relatively common 17 • β-hemolytic Strep spp - 17% of dogs • S. equi subsp zoo - 12% and 22% of the isolates from horses. 18 Streptococcus spp. UT – Equine and canine • all isolates were susceptible to ciprofloxacin, cephalothin and chloramphenicol • > 80% resistance to neomycin, polymixin B and tobramycin UF - Equine • All susceptible to chloramphenicol, bacitracin • An increase in resistance of S.equi subsp zooepidemicus to gentamicin was found over time Australia >80% of isolates were resistant to ciprofloxacin but remained susceptible to chloramphenicol and cephalexin 19 Streptococcus spp. Strangles • Streptococcus equi subsp. equi • Transmission via direct contact and fomites • Colonizes within the pharyngeal and nasal mucosa Signs – Lymphadenopathy –Pyrexia – Malaise – Purulent discharge – Pharyngitis – Abscessed lymph nodes 20 Streptococcus spp. Bastard strangles • Cases involving any area other than the pharyngeal area. • Ocular abnormalities – Serous then mucopurulent discharge – Panophthalmitis – Chorioretinitis – Central blindness • Dx via culture or PCR 21 Corynebacterium spp. • Gram + rods • Appear singly or in pairs • +/- clubbed ends • Flora of normal skin and mucous membranes 22 Bacillus spp. • Gram + rods found singly, in pairs or chains. • May have a single endospore • More pathogenic organisms usually present as co-infections. • Most common organism isolated from endophthalmitis in humans. http://content.answers.com/main/content/wp/en-commons/thumb/4/42/260px-Bacillus_subtilis_Spore.jpg 23 Listeriosis • Rod-shaped, Gram + bacterium • L monocytogenes most common in animals • Spoiled or incompletely fermented corn or hay silage is the main source of infection in outbreaks. VCNA Food AnimPract. 2010 Nov;26(3):487-503 24 • CNS disease is most likely to be associated with ocular signs in food animal species. – vestibular ataxia – cranial nerve deficits – brain stem involvement • facial nerve paralysis •KCS • Keratitis • Anterior uveitis w/hypopyon • Purulent endophthalmitis VCNA Food AnimPract. 2010 Nov;26(3):487-503 25 Other species •Dog • Conjunctivitis, neurologic signs, and pancytopenia with generalized infection. • Sheep & goats – Scleral hyperemia – Unilateral keratitis +/- ulceration – CNS signs en.wikipedia.org/wiki/Listeriosis_in_animals 26 Pseudomonas spp. • Gram - rods • Widely distributed. • Found in the skin and mucous membranes. • Cytologically indistinguishable from other rods • Antibiotic susceptibility testing is especially important 27 Pseudomonas aeruginosa • Isolated from about 15% of horses with bacterial keratitis • Isolated from 21% of dogs 28 Innate resistance Evans 2013 29 Pathogenic mechanisms sciencephoto.com www.cdc.gov www.asylumresearch.co.uk/.../Bacteria/Cell!.jpg 30 Pathogenic mechanisms of Pseudomonas aeruginosa Major matrix metalloproteinases Alkaline protease – attacks the helical structure of native type I, III, IV collagen – interferes with host defense systems by degrading complement components, IG, IFN, IL 1 and 2, and tumor necrosis factor. Elastase • As above • Activates proMMPs MucD 31 Pathogenic mechanisms of Pseudomonas aeruginosa Cytotoxic and invasive strains • Cytotoxic strains remain mostly extracellular • Invasive strains enter cells and replicate within them. • Tobramycin vs ofloxacin •Steroids? • Both antibiotics hastened disease resolution infections caused by either strain. 32 IOVS 2011 March; 52(3): 1368–1377 33 Pseudomonas aeruginosa Resistance • Almost all isolates are sensitive to gentamicin, tobramycin, and ciprofloxacin • Study with 7 fluoroquinolones • 24/ 27 isolates were susceptible to all fluoroquinolones evaluated • Susceptibility ranged from 88.9% to 100% • No significant differences among isolate susceptibilities to the individual antimicrobials or among generations of fluoroquinolones 34 Multi-drug resistant, extensively drug resistant, and pan-drug resistant strains of P aeruginosa • Risk factors: bandage contact lens, topical steroids, previous therapeutic graft, preservative-free lubricant ointment and ocular surface disorders. • Of 15 isolates, one isolate was resistant to all antibiotics. • Success with medical therapy alone was not common. These cases are more likely to require the use of tissue adhesives and keratoplasty and are likely to have treatment failure. • Another study compared the efficacy of topical 1.5% and 0.5% levofloxacin. 35 Bacteriophages/ Pseudomonas aeruginosa Predatory Prokaryotes AJVR 2011 Aug;72(8):1079-86 36 • 6 year old Quarter horse gelding • Tearing couple days previously • RDVM started neo/poly/dex 37 38 39 • Cytology – many PMNs • Treatment: – Lavage – Serum q2h – Tobramycin q2h – Cefazolin q2h – Miconazole q2h – Atropine QID – Flunixin 500 mg PO BID 40 • 4 colonies of P. aeruginosa 41 Day 4 42 Discharged on day 7 • Serum and antibiotics 5x/day • Atropine BID • Flunixin 500 mg PO QD • Day 10 - Discontinued miconazole • Day 14 – Discontinued serum, atropine to SID 43 Day 20 44 Day 30 45 Day 45 46 Moraxella spp. • A large, plump, Gram - coccobacillus • Primary cause of infectious bovine keratoconjunctivitis (IBK) “pinkeye” • Highly contagious ocular infection of cattle Monetary losses caused by: – decreased weight gain – decreased milk production – devaluation because of eye disfigurement – cost of treatment 47 Moraxella bovis Transmission • Opportunistic pathogen • Environmental factors – Exposure to UV light – Irritants- face fly • Host factors – Genetic – Nutritional – Immune status – Current infections 48 Transmission of Moraxella bovis Nonpiliated, nonpathogenic forms can exist in a carrier state in the host. • Carrier animals are asymptomatic, but shed the organism. • Harbored in nasal, ocular, and vaginal secretions Transmitted by direct contact, aerosol, or fomites. Cattle are the primary natural reservoir for M bovis and have a high nasal carrier rate. 49 Transmission of Moraxella