Gram positive cocci - Weebly · Gram positive cocci Streptococcus Facultative anaerobics Catalase...
Transcript of Gram positive cocci - Weebly · Gram positive cocci Streptococcus Facultative anaerobics Catalase...
Gram positive cocci Streptococcus and enterococcus
ILOs
• Classification: categories and principles
• Understand basic characteristics and distinctive features
• Virulence factors and roles in pathogenesis
• Associated infections
• Diagnosis:
• Understand general lines of treatment and prevention
Group A streptococcus (Streptococcus pyogenes )
Virulence factors:
• F-protein: attachment to cell fibronectin, iternalization
• M proteins : antiphagocytic, more than 100 serotypes of M protein.
• Hyaluronic capsule: antiphagocytic, resembles connective tissue haluronic acid
• Hyaluronidase and DNAse:
Degrade hyalyronic acid of the connective tissue < spread
• Streptokinase: fibrinolysis < cellulitis rather than abscess
Group A streptococcus (Streptococcus pyogenes )
Virulence factors cont’d:
Streptolysin O and S:
Lyse erythrocytes, polymorphonuclear leucocytes and platelets by forming pores in their cell membrane.
Streptolysin S is responsible for the β-haemolysis
Streptolysin O :Intravenous injection into experimental animals causes death within seconds, as the result of an acute toxic action on the heart.
Pyrogenic toxins A, B, C:
• Super antigens
• Tissue destruction, toxic shock – like syndrom
Group A streptococcus (Streptococcus pyogenes )
Clinically:
Non invasive infections
Pharyngitis: pustular
Skin impetigo
Scarlet fever
Invasive infections such as
Necrotizing fascitis : fat and fascia
Toxic shock syndrome
meningitis
Immune sequale:
Rheumatic fever following pharyngitis?
Glomerulonephritis following skin infections
Group B streptococcus (Streptococcus Agalactiae )
• Characteristics:
• Facultative anaerobic , encapsulated gram-positive
• Produces a narrow zone of -hemolysis on blood agar
• Normal flora of throat, colon, urethra and, importantly, in 10-40% of women vagina.
• Positive CAMP test (Christine, Atkins, Munch-Peterson): enhanced -haemolysis when streaked with S. aureus on blood agar
Group B streptococcus (Streptococcus Agalactiae )
• Major virulence factors:
• Haemolysin (including CAMP factor)
• Polysaccharide capsule
• Peptidase and hyaluronidase enzymes
Group B streptococcus
Clinically:
1. Non pregnancy associated:
• Pneumonia, UTIs, meningitis, infective endocarditis and soft tissue infection (multisystem involvement)
• Sepsis and septic shock
usually in unhealthy people e.g chronic illnesses,
immunocompromised and elderly
Clinical picture / Cont’d
2. Pregnancy associated:
MOT (mode of transmission):
1. Vertical (Ascending from vagina to placenta)
2. During delivery and birth canal passage of the baby (intrapartum)
3. After birth
Clinically:
1. Chorioamnionitis
2. Abortion
3. Neonatal sepsis: early and late sepsis
Diagnosis:
Antibiotic treatment of group A and B:
Usually penicillins , if patient is allergic use erythromycin or clindamycins
Streptococcus pneumonia
45 years old man, smoker.
Sudden onset fever and chills
Shortness of breath and pleuritic chest pain
Productive rusty coloured sputum (blood stained)
Examination:
Vitals: RR 24, PR 110, T 39, B.P normal, O2 Saturation 90%
Chest: decreased air entry, dull on percussion, decreased chest expansion
CXR: Right upper lobe consolidation
WBC 16 mainly neutrophils
Streptococcus pneumonia
• > member of the oropharyngeal flora of 5-70% of the population, with the highest isolation rate in children during
• the winter months.
• Diplococci , catalase negative:
Streptococcus pneumonia
> An important pathogen:
* It primarily causes disease of the upper and lower
respiratory tract
* May spread to other sites, such as the joints, peritoneum, endocardium, biliary tract and, in particular, the meninges.
Streptococcus pneumonia
• Virulence factors
1. Capsule
• The capsular polysaccharide is a crucial virulence factor.
• Antiphagocytic and anticomplement.
• A total of nearly 100 different capsular serotypes have been identified.
• About 90% of cases of bacteraemic pneumococcal pneumonia and meningitis are caused by some 23 serotypes.
Streptococcus pneumonia
2. Lipotechoic acid and coline binding proteins:
Adhesion molecule
3. IgA1 protease
• Pneumococci produce an extracellular protease that specifically cleaves human IgA1 in the hinge region.
• This protease enables these pathogens to evade the protective functions of the principal immunoglobulin isotype of the upper respiratory tract.
Streptococcus pneumonia
4. Pneumolysin (pore forming toxin)
• Pneumococci produce an intracellular membrane-damaging toxin known as pneumolysin, which is released by autolysis.
• Pneumolysin also suppresses organism-targeted immunity (Neutrophils, lymphocyte proliferation and immunoglobulin synthesis).
• Pneumolysin is immunogenic and might be suitable for a new pneumococcal vaccine.
Streptococcus pneumonia
5. Autolysin
• When this enzyme activated, the pneumococcal autolysin breaks the peptide cross-linking of the cell wall peptidoglycan, leading to lysis of the bacteria.
• Autolysis:
Enables the release of pneumolysin
Release of peptidoglycans from cell wall leading to massive inflammatory response and sepsis to these peptidoglycan fragments.
Streptococcus pneumonia
• EPIDEMIOLOGY
• Source:
• Humans are the reservoir of pneumococci, which are commonly found in the upper respiratory tract of healthy persons throughout the world.
• Occurrence:
• Pneumococcal infections are among the leading causes worldwide of illness and death for young children, persons who have underlying debilitating medical conditions and the elderly.
Streptococcus pneumonia
• 1 million deaths yearly worldwide
• 6 million cases of otitis media in USA
• The estimated global annual incidence is 1-3 per 1000 of the population, with a > 5% case fatality rate.
• Mode of Transmission:
• Pneumococci are transmitted by aspiration or from person-to-person by droplet spread and indirectly through articles freshly soiled with respiratory discharges.
Streptococcus pneumonia
• Cultivation and identification :
• blood agar.
• Colonies of pneumococci are α-haemolytic and smooth dome shaped.
• During prolonged incubation, autolysis of bacteria within the flat pneumococcal colonies results in a typical subsidence of the centre ('draughtsman colonies').
• Optochin sensitive and bile (10% sodium desoxycholate) soluble
Streptococcus pneumonia
• Capsule:
• Mixing a suspension of pneumococci with type-specific antisera increases the visibility of the capsule in the microscope, and is the basis of the quellung reaction or capsular swelling test.
• The addition of India ink to a suspension of pneumococci shows the presence of the capsule as a clear halo around the organisms.
Streptococcus pneumonia
Typing :
• Pneumococci are typed on the basis of the differences in capsular polysaccharides, of which 90 have been described (in reference lab.)
Streptococcus pneumonia
• TREATMENT
• I.V benzylpenicillin (penicillin G) or oral phenoxymethylpenicillin (penicillin V). / resistance increasing and mediated by PBP alteration.
• In cases of hypersensitivity to penicillin, erythromycin or clindamycin is usually the second choice, but resistance to erythromycin occurs and is common in some countries.
• If penicillin resistant: Ceftriaxone, vancomycin/clindamycin.
Streptococcus pneumonia
• Vaccines:
• Protein Conjugated: protection for 7-11 types < 2 years
• Non-conjugated: 23 polyvalent vaccine > 2 years
• Enterococcus:
• As indicated by the name, members of the genus Enterococcus have their natural habitat in the human
• intestines. The species most commonly associated with human disease are E. faecalis and E. faecium.
• The diseases with which they are associated are:
• urinary tract infection, infective endocarditis, biliary tract infections, suppurative abdominal lesions, peritonitis.
• E. faecalis and E. faecium are important causes of wound and urinary tract infection in hospital
• Bacteraemia carries a poor prognosis as it often occurs in patients with major underlying pathology and in those who are immunocompromised.