Gram reaction & characteristics: Gram +ve cocci arrange in clusters (grape-like), non-motile. Habitat: Flora in the anterior nares (10-60% of population), nasopharynx, perineal area, skin & mucosa. Virulence factor: Protein A (binds Fc portion of IgG), coagulase (forms fibrin coat around organism) hemolysins, leukocidins (destroy RBCs and WBCs), hyaluronidase (breaks down connective tissue), staphylokinase (lyses formed clots), lipase (breaks down fat), Toxic shock syndrome toxin. Disease: Causes food poisoning (via enterotoxin), pneumonia, meningitis, osteomyelitis, septic arthritis bacteremia, endocarditis, wounds, abscesses, suppurative cutaneous infections, staphylococcal scalded skin syndrome, boils (carbuncles), furuncles, sinusitis, otitis media, folliculitis, impetigo, scalded skin syndrome (SSS), Tricuspid valve endocarditis (TVIE)> affects IV drug users. Produces six types of enterotoxin and toxic shock syndrome toxin-1 (TSST-1)> TSS (fever, diarrhea, kidney failure, fever, headache). Ritter’s disease in newborn (severe form of scalded skin syndrome in neonates). S. aureus is a leading cause of osteomyelitis in children and adults.

1. Medical Microbiology
(Bacteriology)

2. Gram positive cocci
Staphylococci & micrococci

3. Staphylococcus spp
aerobic & facultative anaerobic

4. Staphylococcus aureus
• Gram reaction & characteristics:
• Gram +ve cocci arrange in clusters (grape-like), non-motile.
• Habitat:
• Flora in the anterior nares (10-60% of population), nasopharynx, perineal area, skin &
mucosa.
• Virulence factor:
• Protein A (binds Fc portion of IgG), coagulase (forms fibrin coat around organism)
hemolysins, leukocidins (destroy RBCs and WBCs), hyaluronidase (breaks down connective
tissue), staphylokinase (lyses formed clots), lipase (breaks down fat), Toxic shock syndrome
toxin.
• Disease:
• Causes food poisoning (via enterotoxin), pneumonia, meningitis, osteomyelitis, septic
arthritis bacteremia, endocarditis, wounds, abscesses, suppurative cutaneous infections,
staphylococcal scalded skin syndrome, boils (carbuncles), furuncles, sinusitis, otitis media,
folliculitis, impetigo, scalded skin syndrome (SSS), Tricuspid valve endocarditis (TVIE)>
affects IV drug users.
• Produces six types of enterotoxin and toxic shock syndrome toxin-1 (TSST-1)> TSS (fever,
diarrhea, kidney failure, fever, headache). Ritter’s disease in newborn (severe form of
scalded skin syndrome in neonates).
• S. aureus is a leading cause of osteomyelitis in children and adults.

5. • Mode of transmission:
• Traumatic introduction (surgical wounds or microabrasions), person to person
(with lesions), fomites, aerosolized, food.
• Treatment:
• Penicillin, if not sensitive, penicillinase-resistant penicillins (methicillin, oxacillin,
dicloxacillin, cloxacillin, flucloxacillin, nafcillin).
• MRSA (methicillin-resistant S. aureus) presence of mecA gene: vancomycin or
Linezolid.
• Predisposing factor for MRSA, hospitalization, indiscriminate use of antibiotics, IV
drug abuse, indwelling medical devices.

6. Methicillin resistant S. aureus (MRSA)
• Resistance of S. aureus to penicillin & all other beta-lactam antibiotics including the third-
generation cephalosporins and carbapenems.
• MRSA is mediated by the mecA gene; which is chromosomally coded. It alters penicillin-binding
protein (PBP) present on S. aureus cell membrane to PBP-2a.
• Colonizes the broken skin and can cause a wide range of local and systemic staphylococcal
infections. Hospital staffs harboring MRSA are the chief source of infection for the patients.
• Cause a wide range of infections including bacteremia, endocarditis, and pneumonia.
• Community-associated MRSA (CA-MRSA):
• More virulent.
• Cause necrotizing fasciitis.
• Hospital associated MRSA (HA-MRSA):
• Low virulent.
• Cause perioperative wound infections.
• Recognized as important agents of hospital-acquired infection (HA-MRSA) in hospitalized patients
undergoing prosthetic heart valve surgery.
• Methicillin-resistant Staphylococcus epidermidis (MRSE), treated by vancomycin.
• Vancomycin-intermediate S. aureus (VISA), have developed resistance to the usual dosages of
vancomycin, lead to the use of higher doses to treat infections caused by these organisms. VISA
strains are sometimes referred to as glycopeptide-intermediate S. aureus (GISA).
• Vancomycin-resistant S. aureus (VRSA) strains have also been recovered from patient specimens.

7. Treatment
• Vancomycin is the drug of choice for MRSA.
• Other drugs:
• Teicoplanin, linezolid, quinupristin-dalfopristin, tigecycline, oritavancin.
• Daptomycin (for endocarditis and complicated skin infections),
• Mupirocin 2% ointment (for nasal carriers of MRSA).
• Oxazolidinones.
• Orally effective drugs (tetracycline, erythromycin, or cotrimoxazole).
• 5th generation cephalosporins, such as Ceftobiprole, ceftaroline, ceftolozane have shown
some activity against MRSA.
• Ceftaroline (MRSA & VISA).
• telavancin (against MRSA, VRSA & VISA).
• Treatment of VISA or VRSA include daptomycin, ceftaroline, linezolid, tedizolid, dalbavancin,
telavancin, quinipristin/dalfopristine and combination therapies (ampicillin-sulbactam,
amoxicillin-clavulanate, ticarcillin-clavulanate and piperacillin-tazobactam.

8. Coagulase-negative staphylococci (GNS)
Staphylococcus epidermidis & S. saprophyticus
• Gram reaction & characteristics:
• Gram positive cocci arranged in clusters.
• Habitat:
• Staphylococcus epidermidis: common skin flora & mucous membrane.
• S. saprophyticus: female genitourinary tract, skin & mucosa.
• Virulence factor:
• S. epidermidis, polysaccharide (slim or biofilm), anti-phagocytic & for adherence. Exotoxin>
delta toxin.
• Disease: cause disease in immunosuppressed and neutropenic patients.
• Staphylococcus epidermidis:
• Nosocomial infections, Stitch abscess, infection associated with artificial implants and
prosthetics (bacteremia) such as: central venous line, intra-ocular lens, ventriculo-
peritonial shunt, CSF shunts, foley catheter, urinary catheters (UTI), artificial heart
valves (endocarditis), artificial joints.
• Most common species of coagulase negative staphylococci (50-80%).

9. • S. saprophyticus:
• Common cause of hospital acquired urinary tract infections. UTIs in young sexually
active females second to E. coli, urethritis & prostatitis in males.
• Cystitis, acute pyelonephritis, septicemia, nephrolithiasis, endocarditis.
• Mode of transmission:
• S. epidermidis: sterile sites, implantation of medical devices (shunts, prosthetic
devices) & person to person.
• S. saprophyticus: sterile urinary tract, in young sexually active females.
• Treatment:
• S. epidermidis: vancomycin.
• S. saprophyticus: TMP-SMX.
• Note:
• S. epidermidis is novobiocin susceptible, while S. saprophyticus is novobiocin resistant.
• Novobiocin only performed when CNS isolated from urine of female.
• Skin flora often contaminates blood cultures (be cautious of false-positive S.
epidermidis blood cultures).

10. Lab diagnosis
• Samples: blood, CSF, sputum, (food, vomit, faeces> food poisoning), pus (aspirate or swab), pleural fluid,
urine, ear swab. Direct gram stain (pus with gram +ve cocci).
• S. aureus:
• Blood agar: opaque (golden yellow), beta-hemolytic.
• MSA, selective & differential: yellow, mannitol fermenting vs GNS, Can tolerate the high salt
concentration (7.5%).
• MacConkey agar (pink> LF).
• Phenylethyl alcohol (PEA) or Columbia colistin-nalidixic acid (CNA) agars may be used to eliminate
contamination by gram-negative organisms in heavily contaminated specimens such as feces.
• Chocolate agar, nutrient agar, glucose broth, brain-heart infusion broth (BHI), salt milk agar
(skimmed milk), Ludlam's medium> 12-24 hours at 37C.
• Biochemical test:
• Positive: catalase, coagulase and DNase, citrate, gelatin hydrolysis, MR, VP, nitrate reduction,
urease, O-F test, Fermentative (fructose, galactose, mannose, glucose, lactose, maltose,
sucrose and mannitol).
• Latex agglutination assay detects clumping factor and protein A on the surface of S. aureus.
• GNS:
• Colonies appear white to gray on blood agar and nonhemolytic.
• Catalase positive and coagulase negative.
• Media: blood agar,
• Colonial morphology:
• On SBA: white, gamma or non-hemolytic.
• On MSA: pink or red colonies.

11. MRSA
• Optimal sample: anterior nasal & groin swabs.
• The Clinical and Laboratory Standards Institute recommends the use of a 30-mg cefoxitin
disk to screen for MRSA strains.
• Oxacillin disk (media, MHA, containing 2–4% NaCl, incubation at 30 °C for 24 hours)
• Chromogenic Media, contain cefoxitin (Brilliance MRSA agar, BBL-CHROMagar).
• PCR detecting mecA gene.
• Latex agglutination test detecting PBP-2a
mauve-colored colonies

12. Micrococcus
• Gram reaction & characteristics:
• Gram positive cocci arranged in tetrads and appear larger than Staphylococcus spp.
• Habitat:
• Normal flora of the skin, mucous membranes & oropharynx.
• Disease:
• They rarely cause infections. Of low virulence.
• Immunocompromised hosts: brain abscess, meningitis, pneumonia, endocarditis,
meningitis, bacteremia, septic arthritis.
• Lab diagnosis:
• Catalase pos. Coagulase neg. oxidase pos. bacitracin sensitive.
• Colonies often pigmented (M. luteus> yellow, M. roseus> pink). High-domed colonies and
nonhemolytic on SBA.

13. Streptococci
aerobic & facultative anaerobic

14. Group A Streptococcus (S. pyogenes):
• Gram reaction & characteristics:
• Gram positive cocci arranged chains, capsulated (hyaluronic acid).
• Habitat:
• Skin, URT, carried on nasal, pharyngeal & anal mucosa.
• Virulence factor:
• Cell wall M protein inhibits phagocytosis.
• Streptococcal pyrogenic exotoxin (Spe A, Spe B, Spe C, and Spe F)>
erythrogenic toxin, causes the rash seen in scarlet fever. These
toxins act as superantigens interacting with macrophages and T
helper cells to stimulate the massive release of cytokines and are
associated with streptococcal toxic shock syndrome (STSS).
• Streptokinase dissolves clots.
• Hyaluronic acid capsule inhibits phagocytosis.
• Streptolysin O (oxygen labile) and streptolysin S (oxygen stable)
lyse erythrocytes, platelets, and neutrophils.
• Hyaluronidase hydrolyzes hyaluronic acid, an interstitial barrier,
facilitating spread of the infection. Strains that produce a
hyaluronic acid capsule will not produce hyaluronidase. DNase.
• Ag-Ab complexes deposition in the kidney.

15. • Disease:
• Causes 90% of strep infections.
• Strep sore throat (pharyngitis), impetigo, cellulitis, erysipelas,
puerperal sepsis (genital-uterus), scarlet fever (scarlatina,
sandpaper rash, strawberry tongue), pneumonia, otitis media
(middle ear infections), and necrotizing fasciitis.
• Complication include rheumatic fever and post-streptococcal
glomerulonephritis (smoky or rust-colored urine, cola/tea-
colored urine)
• Mode of transmission:
• Person to person, aerosolized droplets from coughs or sneezes.
• Lab diagnosis:
• Specimens:
• Throat swab, sputum, urine, blood or skin.
• Susceptible to bacitracin (A disk) and PYR positive, but often
identified by serological latex agglutination test (ASO +ve).
• On blood agar: colonies are pinpoint, translucent, and will show
a large zone of beta-hemolysis.
• Treatment:
• Penicillin G.
• Clindamycin.
Desquamation seen with Scarlet Fever

16. Group B Streptococcus (S. agalactiae)
• Gram reaction & characteristics:
• Gram positive cocci, arranged in chains, capsulated (sialic acid).
• Habitat:
• Normal flora of female genital tract (25% of all females carry the bacteria as
normal vaginal flora) and lower GIT, URT.
• Virulence factor:
• Capsule.
• Disease:
• Neonates acquire infections during birth, resulting in sepsis and meningitis
(neonatal septicemia, meningitis & pneumonia). Additionally, S. agalactiae can
cause postpartum fever, osteomyelitis, arthritis, wound infections, bacteremia,
endocarditis, pneumonia, and pyelonephritis in immunosuppressed patients.
• Mode of transmission:
• Gaining access to sterile sites, person to person, from mother to fetus in uterus or
during delivery, or nosocomial transmission (unwashed hands).

17. • Lab diagnosis:
• Samples: CSF, urine, blood.
• Vaginal & rectal swabs collected from pregnant women at 35–37 wk gestation.
Inoculated in selective broth, e.g., LIM, GBS broth, StrepB Carrot Broth.
• On SBA: colonies are medium-size flat, creamy, and show small zones of beta-
hemolysis. Some strains may be nonhemolytic.
• CAMP test and Hippurate hydrolysis (sodium Hippurate) positive, PYR negative.
• Resistant to bacitracin.
• Treatment:
• penicillin G.
• Ampicillin to pregnant women testing positive for S. agalactiae.
• Polysaccharide-protein conjugate vaccines, especially in pregnancy.
• Note:
• Most common cause of meningitis in newborns.
• Most common causes of neonatal meningitis: Group B Strep, E. coli, Listeria.

18. Enterococcus (Lancefield group D)
80% are E. faecalis, 15% E. faecium
• Gram reaction & characteristics:
• Gram positive, arranged in chains, aerobic.
• Habitat:
• Normal flora, GIT, & female genitourinary tract.
• Virulence factor:
• Adhesion, cytolysins, MDR (immunocompromised patients).
• Disease:
• Health-care associated, nosocomial UTI, biliary tract infections, bacteremia,
subacute bacterial endocarditis (SBE), wound infections, ocular infection, abdomen
& pelvis infections, rare CNS & respiratory infections.
• Mode of transmission:
• Gain access to sterile sites, person to person, contaminated medical equipment.

19. • Lab diagnosis:
• Samples: urine, blood, stool. Perirectal or stool swab for VRE.
• On SBA: can be alpha-, beta-, or most commonly nonhemolytic.
• Biochemical test:
• Bile-esculin positive, positive for growth in 6.5% NaCl, 40% bile, PYR positive.
• Vancomycin-resistant enterococci (VRE), the vast majority of VRE are E. faecium.
• Treatment:
• Ampicillin or vancomycin aminoglycosides (synergistic).
• VRE (vancomycin-resistant enterococci): linezolid, daptomycin.
• Note:
• SBE: Enterococci as well as Viridans Streptococci colonize valves previously
damaged by group A Streptococci (Rheumatic fever).

20. Group D Streptococcus-nonenterococci
S. gallolyticus (formerly S. bovis)
• Gram reaction & characteristics:
• Gram positive cocci arranged in chains, aerobic.
• Habitat:
• Normal fecal and oral flora.
• Virulence factor:
• Of low virulence.
• Disease:
• Cause of nosocomial UTls, subacute bacterial endocarditis (SBE), wound infections,
bacteremia and abdominal abscesses. Isolation of group D streptococci in blood
cultures is an indicator of colon cancer.
• Inflammatory bowel disease.
• Mode of transmission:
• Endogenous, penetrates epithelium via lesions in colon.

21. • Lab diagnosis:
• Samples: urine, blood, stool.
• On SBA: colonies are gray to white, translucent, round, and convex, alpha-hemolytic
or nonhemolytic, rarely beta-hemolytic
• Biochemical test:
• Bile-esculin hydrolysis positive, negative for growth in 6.5% NaCl, PYR
negative.
• Treatment:
• Penicillin.

22. Streptococcus pneumoniae
• Gram reaction:
• Gram positive cocci, arranged in pairs (diplococci), encapsulated, lancet-football or
bullet shaped.
• Habitat:
• Upper respiratory tract flora, nasopharynx.
• Aeration:
• Aerobic (need 5-10% CO2).
• Virulence factor:
• Polysaccharide capsule, pneumolysin, IgA protease.
• Disease:
• Leading cause of meningitis & pneumonia (Lobar pneumonia), also causes sinusitis,
eyes infection & otitis media. Osteomyelitis, septic arthritis, and endocarditis.
• Mode of transmission:
• Person to person with contaminated respiratory secretions.

23. • Lab diagnosis:
• Samples: sputum, blood, throat swab, ear swab, CSF.
• Sputum samples are often rust-colored from blood.
• On SBA with 5-10% CO2, mucoid strains produce a large polysaccharide capsule.
umbilicated, depressed centers caused by autolytic enzymes, draughtsman or carom
coin shape, dome shaped (young), alpha hemolytic.
• Biochemical test:
• Bile solubility (10% sodium deoxycholate) positive.
• Quellung or Neufeld test +ve.
• Optochin: S.
• Treatment:
• Penicillin or cephalosporins, except vancomycin for meningitis.
• Pneumovax: vaccine with capsular polysaccharides.

24. Viridans streptococci
Streptococcus mutans,
Streptococcus intermedius
• Gram reaction & characteristics:
• Gram positive, arranged in chains.
• Habitat:
• Normal flora, oral cavity, GIT, respiratory tract, female genital tract.
• Aeration:
• Aerobic.
• Virulence factor:
• Extracellular polysaccharides (glucans, dextrans)> enhance attachment to host cell
surfaces, such as cardiac endothelial cells or tooth surfaces in the case of dental caries.
• Disease:
• Subacute bacterial endocarditis, in patient with damaged heart valves, bacteremia,
meningitis, S. mutans> dental caries, gingivitis, tooth decay, (cavities). Wound
infections and brain, abdominal abscesses (S. intermedius).
• Mode of transmission:
• Endogenous: from dental manipulations.

25. • Lab diagnosis:
• Samples: sputum, blood, throat swab, ear swab, CSF.
• On SBA: alpha-hemolytic, some strains nonhemolytic.
• Optochin resistant and insoluble in bile; does not grow on bile-esculin medium.
• Treatment:
• Penicillin G.

27. Alyazeed Hussein, BSc, SUST
This has been a presentation of Alyazeed Hussein
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