staphylococcus aureus from medical bacteriology

Medical bacteriology

1. Vivekanandha arts and science college for women . VeerachiPalayam-637303, Sankagiri , Salem dt , tamilnadu , India Affiliated to Periyar University, salem . Department of microbiology . Subject : medical bacteriology title : staphylococcus . aureus SUBJECT INCHARGE: Dr.R.MYTHILI RAVICHANDRAN, ASSISTANT PROFESSOR, HEAD OF THE DEPARTMENT, DEPARTMENT OF MICROBIOLOGY. SUBMITTED BY : Ms . M . ARTHI, lll . Bsc ., MICROBIOLOGY, DEPARTMENT OF MICROBIOLOGY.

2. Staphylococcus aureus Synopsis : Introduction Morphology History Virulence factors Pathogenesis Clinical syndrome Culture characteristics Lab diagnosis Mode of transmission Treatment Prevention reference

3. Introduction staphylococcus Gram positive cocci, belongs to Family Micrococcaceae . Aerobic , some facultative anaerobes. Arrangement in clusters ( like grapes ), pairs or tetrads, Catalase positive. S . aureus is the most important human pathogen, others human pathogens are CONS (Coagulase negative Staphylococci) which include S . saprophyticus , S . epidermidis , S . hominis etc. Staphylococcus are capable of acquiring resistance to antibiotics, Can cause serious clinical and epidemiological problems.

4. Staphylococcus aureus Morphology Non motile and non spore forming Gram positive cocci Size is 0.7 to 1.2mm in diameter Irregular clusters that resemble cluster of grapes.

5. S . Aureus morphology

6. History Robert Koch (1878)- first to see staphylococci in pus specimen Louis Pasteur (1880)- first to cultivate in liquid medium Sir Alexander Ongston (1881)- named the bacteria as “ Staphylococcus ”

7. Virulence factors Cell wall associated structures Peptidoglycan Capsule Protein A Clumping factor (bound Coagulase) Extra cellular toxins Haemolysin Leukocidin Enterotoxin TSST Exfoliatin toxin Coagulase Staphylokinase DNAase Phosphatase Lipase Phospholipase Hyaluronidase Serokinase Protease

8. Pathogenesis Cause localised lesions First multiply in tissues, produce toxins and stimulate inflammation. Adhere to damaged skin. Evade defense mechanism of host. Cause tissue damage and from abscesses, produce extra-cellular enzymes and exotoxins. Host immunity: No life long immunity. Repeated infections occur in susceptible host.

9. Clinical syndrome 2 types: inflammatory and toxin mediated staphylococcal disease. INFLAMMATORY DISEASES: Impetigo, folliculitis, furuncle, carbuncle, surgical wound infection, postpartum breast infection. Bacterimia (bacteria found in blood) and septicemia ( multiplication of bacteria produce toxins cause high rate of fever) Endocarditis. Osteomyelitis and arthritis. Deep seated abscess in any organ after bacterimia .

10. Toxin mediated staphylococcal disease: Staphylococcal food poisoning: Caused by Enterotoxin. Milk, milk products, meat fish when kept at room temperature after cooking, contaminants multiply and produce toxins. Virulent when release of interoleukins ( L-1and L-2). Sudden symptoms after 2-6 hour of ingestion Nausea, vomiting, abdominal cramps, watery or bloody diarrhea.

11. 2. Staphylococcal toxic shock syndrome (TSST): Caused by toxin shock syndrome toxin. Release of large amount of interleukin lL-1 and lL-2. Life threatening condition. Fever, vomiting, hypertension, myalgia( muscle pain) mucosal hyperemia, erythematous rash ( redness due to increased blood flow). 3. Staphylococcal scaled skin syndrome (SSSS): Caused by exfoliative toxin Common in infants and children Outer layer of skin of epidermis is separated from underlying tissue. Appears as extensive bullae ( rupture and leave behind red, tender skin ).

12. Staphylococcus aureus Culture characteristics : Grow readily on ordinary culture media. Optimum temperature -37°C Optimum pH – 7.4 – 7.6 Aerobes and facultative anaerobes.

13. Lab diagnosis: Specimens: Pus – from wound or abscess or burns Nasal Swab – from suspected carrier Food – to diagnose staphylococcal intoxication Blood- to diagnose endocarditis and bacteremia Sputum- to diagnose lower respiratory tract infection

14. 2. Gram staining : The diagnosis of staphylococcus aureus is suggested by the finding of gram positive bacteria in clumps in the sample. 3. Culture: on nutrient agar, Golden yellow and opaque colonies with smooth glistening surface, 1-2mm in diameter

15. On blood agar: Golden yellow colonies, surrounded by a clear zone of hemolysis ( beta hemolysis), esp. When incubated in sheep blood agar in atmosphere of 20% CO2 On MacConkey agar: Smaller colonies than those on NA (0.1-0.5mm) and are pink coloured due to lactose fermentation

16. On Mannitol salary agar: S . aureus ferments mannitol and appear as yellow colonies MSA is a useful selective medium for recovering S . aureus from faecal specimen, when investigating food poisoning

17. Biochemical properties Indole test – negative MR test – positive VP test – positive Urease test – positive Phosphatase – positive DNAase test – positive Coagulase test – positive Hydrolyse gelatin Reduces nitrate to nitrite

18. Mode of transmission Person with lesions Airborne droplets Asymptomatic carrier Cross infection

19. Treatment

20. Prevention

21. Reference Ananthanarayan and Paniker’s text book of Microbiology 12 th edition Google images

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