BT11 Bacterial Pathogens 4 Staphylcoci RF PDF

Lecture title: Bacterial Pathogens 5: Staphylococci Lecturer: Dr J R Fitzgerald Lecture 11 Learning outcomes:  Know examples of the common infections caused by different species of staphylococci  Know the economic and clinical importance of rumina...

Lecture title: Bacterial Pathogens 5: Staphylococci Lecturer: Dr J R Fitzgerald Lecture 11 Learning outcomes:  Know examples of the common infections caused by different species of staphylococci  Know the economic and clinical importance of ruminant mastitis  Know 3 of the most common mastitis pathogens  Understand the pathogenesis of mastitis caused by S. aureus including the main virulence factors and how they work  Know the host factors which influence the outcome of intramammary infection  Understand measures used for controlling mastitis infection Wide array of staphylococcal infections of animals: Intramammary infection- mastitis ruminants- cows sheep and goats Wound infections: abscesses, pustules etc. Various species as opportunistic pathogens. Pyoderma, particularly in dogs, commonly S. pseudintermedius as a secondary factor following damage caused by parasites or allergies. Also folliculitis. Tick pyemia. Infections established after damage caused by ticks, especially Ixodes ricinus. Abscesses in joints and other tissues. Exudative epidermitis (greasy pig disease) caused by S. hyicus. Highly contagious acute and generalised infection of the skin in young animals. Dermatitis, osteomyelitis and arthritis in poultry usually S. aureus. Cystitis, particularly in dogs and cats, S. pseudintermedius, S. aureus. Septicaemia, many animals incl rabbits Infective endocarditis eg horses, cows, large breed dogs Mastitis – intra-mammary infection- usually Staphylococcus aureus Infection of the udder - udder cavity invaded by pathogenic bacteria resulting in inflammation Infection types: Subclinical mastitis. No overt symptoms of disease – white cell count increased; Somatic Cell Count (SCC) Clinical mastitis (mild or acute). Clear symptoms of disease – including inflammation, swelling, tenderness, clots in milk Peracute mastitis. Very severe – systemic inflammation, gangrenous, fever, possible death Economic implications Mastitis costs to farmers in the UK ~ £93 million per annum Mastitis costs the U.S. dairy industry about $1.7-2 billion annually or 11% of total U.S. milk production. 1960’s ~ 150 cases of clinical mastitis per 100 cows/year. Now: 30 cases/100 cows/year. Sub-clinical mastitis has decreased-predominant form of disease. Other major mastitis pathogens Contagious: Staphylococcus aureus Streptococcus agalactiae Streptococcus disgalactiae Also: Actinomyces pyogenes Corynebacterium bovis Environmental: Streptococcus uberis Streptococcus faecalis Escherichia coli Also: Coagulase-negative staphylococci Mycoplasma bovis Corynebacterium bovis Klebsiella spp. Bovine mastitis pathogenesis Clinical or sub-clinical. Can colonise the teat for prolonged periods. Then penetrate the teat duct with milk providing a good nutrient source. Adherence to epithelial cells is probably very important. S. aureus virulence factors: Adherence In order to initiate infection the pathogen must gain access to the host and attach to host cells or tissues. S aureus Adheres to Host Proteins through Microbial Surface Components Recognising Adhesive Matrix Molecules (MSCRAMMs) S aureus cells express on their surface proteins that promote attachment to host proteins such as laminin and fibronectin that form part of the extracellular matrix. Fibronectin is present on epithelial and endothelial surfaces as well as being a component of blood clots. In addition, most strains express a fibrinogen/fibrin binding protein (clumping factor A) which promotes attachment. Most strains of S aureus express fibronectin- and fibrinogen-binding proteins. Fn-binding proteins mediate cellular invasion. Avoidance of Host Defenses: S aureus expresses a number of factors that have the potential to interfere with host defense mechanisms: Capsular Polysaccharide The majority of clinical isolates of S aureus express a surface polysaccharide of either serotype 5 or 8. This has been called a microcapsule because it can be visualized only by electron microscopy after antibody labeling, unlike the copious capsules of other bacteria which are visualized by light microscopy. S aureus isolated from infections expresses high levels of polysaccharide but rapidly loses it upon laboratory subculture. The capsule is involved in resistance to phagocytosis. Capsule serotype varies in different strains. Capsule types 5 and 8 represent 41% of those encountered in the USA from mastitis isolates, 59% non-typeable. In Europe 69% (types 5 & 8) with 31% non-typeable. Staphylococcal protein A (SpA) Protein A is a surface protein of S aureus which binds immunoglobulin G molecules by the Fc region. In serum, bacteria will bind IgG molecules the wrong way round by this non-immune mechanism. In principle this will disrupt opsonization and phagocytosis. Indeed mutants of S aureus lacking protein A are more efficiently phagocytozed in vitro, and studies with mutants in infection models suggest that protein A enhances virulence. Superantigens: Superantigens stimulate T cells non-specifically without normal antigenic recognition. Up to one in five T cells may be activated, whereas only 1 in 10,000 are stimulated during antigen presentation. Cytokines are released in large amounts which is detrimental to the host and contributes to modulation of the host immune response. Superantigens bind directly to class II major histocompatibility complexes of antigen- presenting cells outside the conventional antigen-binding grove. This complex recognizes only the Vb element of the T cell receptor. Thus any T cell with the appropriate Vb element can be stimulated, whereas normally antigen specificity is also required in binding Membrane Damaging Toxins (a) -toxin The best characterized and most potent membrane-damaging toxin of S aureus is a- toxin. It is expressed as a monomer that binds to the membrane of susceptible cells. Subunits then oligomerize to form hexameric rings with a central pore through which cellular contents leak. (b) ß-toxin ß-toxin is a sphingomyelinase which damages membranes rich in this lipid. The classical test for ß-toxin is lysis of sheep erythrocytes. The majority of human isolates of S aureus do not express ß-toxin. In contrast the majority of isolates from bovine mastitis express ß-toxin, suggesting that the toxin is important in the pathogenesis of mastitis. This is supported by the fact that ß-toxin-deficient mutants have reduced virulence in a mouse model for mastitis. (c) -toxin The -toxin is a very small peptide toxin produced by most strains of S aureus. It is also produced by S epidermidis and S lugdunensis- has cytolytic activity. (d) -toxin and leukocidins The -toxin and the leukocidins are two-component protein toxins that damage membranes of susceptible cells, particularly PMNs. Enzymes S aureus can express proteases, a lipase, a deoxyribonuclease (DNase) and a fatty acid modifying enzyme (FAME). The first three probably provide nutrients for the bacteria, and it is unlikely that they have anything but a minor role in pathogenesis. However, the FAME enzyme may be important in abscesses, where it could modify anti-bacterial lipids and prolong bacterial survival. The thermostable DNase is an important diagnostic test for identification of S aureus. Host genetic factors affect susceptibility to bovine mastitis SCC and clinical mastitis varies with host variation in in vitro phagocytosis between animals Possible variable host determinants lactoferrin, lysozyme Major histocompatibility complex Udder depth milking speed milk production traits Control & treatment of mastitis hygiene is fundamental for effective control udder and teats washed prior to milking  disinfected after milking milking equipment sterilised and regularly serviced Antibiotic therapy in vitro efficacy not good predictor antibiotic residues must be cleared before milk consumption Use of interleukins in therapy ? Antibiotic resistance increasing Poultry infections- S. aureus causes joint infections such as septic arthritis and ‘bacterial chondronecrosis with osteomyelitis’ (BCO) Canine pyoderma- Staphylococcus pseudintermedius Very common skin disease of dogs, often secondary to atopic dermatitis –usually commensal. Symptoms include pruritus, alopecia, erythema, swelling, Treatment: systemic antibiotics and topical shampoo and no effective vaccine. Used to be called Staph. Intermedius until we discovered that 3 different species were indistinguishable phenotypically including Staph intermedius, Staph pseudintermedius and Staph delphini. S. delphini is associated with pyoderma of horses and S. intermedius is associated with pigeons. Emergence of methicillin-resistance in late 1990s- now a major veterinary health challenge worldwide Exudative epidermitis (greasy pig syndrome) Staphylococcus hyicus Classical symptoms- ozing of fluid from the inflamed skin. Normally commensal but causes disease after skin damage/abrasions etc The Staphylococci produce exfoliative toxins resulting in the skin lesion symptoms and also damage the liver and kidneys. It has been shown recently that during the days immediately preceding farrowing the bacterium multiples profusely in the sows vagina. Piglets are frequently infected during the birth process or soon after. In severe cases where the liver becomes damaged the piglet will die. Often only 50% of piglets affected during suckling will survive. Treatment. Determine the antibiotic sensitivity and inject affected piglets daily for 5 days, or on alternate days with a long-acting antibiotic to which the organism is sensitive to. Antibiotics include; amoxycillin, OTC, ceftiofur, cephalexin, gentamycin, lincomycin or penicillin. In severe outbreaks an autogenous vaccine can be prepared from the organism and has proved effective on some farms. Antibiotic resistance This is a major issue affecting the treatment of staphylococcal infections- in particular methicillin resistant S. aureus (MRSA) are a major cause of human infections. Recently animal MRSA strains have emerged in companion and livestock animals.