Medically Important Bacteria + Images

Streptococcus Pyogenes

• Gram +ve
• Beta hemolytic
• Carbohydrate capsule
• C5a peptidase
• Streptolysin-O
• Streptolysin-S
• M-protein (more than 80 types exist)
• F-protein
  
• Streptolysin
  
• Streptokinase
• Hyaluronidase
• DNAase
• Erythrogenic pyogenic factor (A, B, and C)
  
• Toxic shock syndrome toxin (TSST)
  
• Causes Group A streptococcal infections
  
• Diseases: Acute Pharyngitis - Impetigo - Erysipelas - Scarlet Fever - Toxic Shock Syndrome - Cellulitis - Rheumatic Fever - Acute Post Streptococcal Glomerulonephritis - Necrotizing Fasciitis
  
• Diagnosis: a throat swab is taken to the laboratory for testing. A Gram stain is performed to show Gram positive, cocci, in chains. Then, culture the organism on blood agar with added bacitracin antibiotic disk to show beta-haemolytic colonies. Then, perform catalase test, which should show a negative reaction for all Streptococci. Antigenic detection ELISA. PCR.
  
• Treatment of choice: penicillin
  

Enterococci

• Gram positive diplococci
• Non hemolytic
• Short chains or pairs
• Commensal in GIT
• E. faecalis and E. faecium are the most commonly associated with disease
  
• Diseases: Subacute bacterial endocarditis - Billiary tract infection - UTI - Peritonitis - Wound infection - Puerperal sepsis
  
• Diagnosis: Specimen - Direct film Gram Stain - Culture non hemolytic - Mac Conkey agar small pink colonies, they have the ability to survive in the presence of bile - Catalase -ve - Ferment mannite - rapid reduction litmus milk, changes from violet to white color (decolorization)
  
• Some new enterococci emerged in the US that is resistant to vancomycin
  

Streptococcus Viridans

• Gram +ve
• Viridans = Green
  
• Either Alpha hemolytic and produce a green color in culture or non hemolytic
• Commensal of Upper respiratory tract and buccal cavity
  
• Diseases: Subacute bacterial endocarditis - Dental Caries -Brain and liver abscesses
• Diagnosis: Specimen ... - Gram stain ... - Culture ... -Viridans streptococci can be differentiated from Streptococcus pneumoniae using an optochin test, as Viridans streptococci are optochin resistant.
  

Streptococcus Pneumoniae

• Gram +ve in pairs
  
• Lancet diplococcus
• Alpha Hemolytic
• Found in nasopharyx of 30% of healthy individuals
• Virulence factors: polysaccharide capsule, pneumolysin, Autolysin, Hydrogen peroxide, Pili, IgA1 protease,
  
• Disease: Lobar Pneumonia - Pneumococcal Meningitis - Sepsis - otitis media(in children)
• Diagnosis: Specimen - Direct smear Gram stain - Culture alpha hemolysis - Positive Quellung test capsule swelling - Latex agglutination or coagulation using type specific antiserum - Gram Stained film - Highly pathogenic to mice - Inulin fermentation +ve - Raffinose fermentation -ve - sensitive to optochin
  

Staphylococcus Aureus

• Gram +ve
  
• Golden staph
  
• Catalase positive
• Coagulase positive
• Yellow endopigment
• Present on nasal mucosa of ~50% of people
  
• Capsular polysaccharide
  
• Protein A
• Hemolysin
• Fibrinolysin
  
• Leukocidins
• Penicillinase
• Phosphatase
  
• Beta Lactamase
  
• Hyaluronidase
• Staphylokinase
• Lipase
• Liquefy gelatin
  
• Exfoliatin
• Enterotoxin
• Mannite fermentation +ve
  
• Toxic shock syndrome toxin
• Diseases: Gastroenteritis - Toxic Shock Syndrome - Scalded Skin Syndrome - Pneumonia - Meningitis - Osteomyelitis - Acute Bacterial Endocarditis - Septic Arthritis Skin Infection - Sepsis - Urinary Tract Infection - Abscess - Boils - Carbuncles - Impetigo - Osteomyelitis - Wound Sepsis - Food Poisoning
  
• Diagnosis: Depending upon the type of infection present, an appropriate specimen is obtained accordingly and sent to the laboratory. A Gram stain is first performed to guide the way, which should show typical gram-positive bacteria, cocci, in clusters. Secondly, culture the organism in Mannitol Salt Agar, which is a selective medium with 7–9% NaCl that allows S. aureus to grow producing yellow-colored colonies as a result of salt utilization and subsequent drop in the medium's pH. Furthermore, for differentiation on the species level, catalase (positive for all species), coagulase (fibrin clot formation), DNAse (zone of clearance on nutrient agar), lipase (a yellow color and rancid odor smell), and phosphatase (a pink color) tests are all done. For staphylococcal food poisoning, phage typing can be performed to determine if the staphylococci recovered from the food to determine the source of infection.
• Treatment: Depending on the case DOC may be, Penicillin G, methocillin, oxacillin, or vancomycin.
  

Staphylococcus epidermidis

• Gram +ve cocci in clusters
  
• Catalase positive
• Coagulase Negative
• Non hemolytic
• Commensal on skin, in mouth, GIT, ...
  
• Polysaccharide capsule
• Highly resistant to antibiotics
• Diseases: nosocomail infection: prosthetic joints, prosthetic heart valves, sepsis from intravenous lines, urinary tract infections - frequent skin contaminant from blood cultures
• Treatment: Vancomycin!
• Diagnosis: Gram stain - Culture, white colonies - Metabolic, coagulase negative, no hemolysis, -ve litmus milk clotting, -ve gelatin liquefaction, -ve mannite fermentation - novobiocin sensitive
  

Corynebacterium Diphtheria

• Catalase positive
• Exotoxin: A subunit and B subunit
• Disease: diphtheria: sore throat, pseudomembrane in pharynx, myocarditis, neural involvemnnt
• Diagnosis: gramstain-culture

Neisseria Gonorrhoeae

• Kidney Bean Shaped
• Gram Negative Diplococci
• Ferments only glucose not maltose (remember there is only a "G" in gonorrhoeae and no "M")
• Pili
• IgA1 protease
• Protein I
• Protein II
• Endotoxin no exotoxin
• Diseases: Men,urithritis-Women, cervial gonorrhoeae-Both men and women, gonococcal bacterimia, septic arthritis-Neonates, neonatorum, conjunctivitis
• Diagnosis: Gram stain of urethral pus-Culture
• No immunity after infection, a person can be reinfected many times

Neisseria Meningitidis

• Gram Negative
• Kidney Bean shaped diplococci
  
• 5-10% of of normal healthy individuals are are carriers for meningococci in the nasopharynx
• Oxidase +ve
  
• Polysaccharide capsule
• 90% of cases are caused by serogroups A, B, and C
• Capsular polysaccharide Ag
• Lipopolysaccharide
• IgA prtease enzyme
• Transferrin
  
• Ferments maltose and glucose (remember there are both a G and an M in meningitidis)
• Endotoxin, no Exotoxin
• Diseases: Meningitis - Septicemia
• Diagnosis of case: Specimen - Check CSF turbidity, neutrophils, protein, glucose, - centrifuge - Supernatant capsular Ag - Deposit - Culture on chocolate blood or Thayer Martin - Oxidase +ve
  
• Diagnosis of carrier: Specimen - Culture chocolate blood or Thayer Martin Medium
• Treatment: 3rd generation cephalosporins
• Prophylaxis: Vaccine, capsular polysaccharide antigen A, C, Y, W135 - Rifampin for children - Ciprofloxacin for adults
  

Bonus notes:

1. The most common cause of infective endocarditis is skin infection with staphylococci as a result of intravenous drug abuse followed by Streptococcus viridan.
2. Amoxicillin is givin before any dental procedures in patients with rheumatic fever or with prosthetic heart valves.
3. 
   

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All images are in the public domain or licensed under a creative commons. Thanks to cdc.gov and wikipedia.org

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