Staphylococcus aureus, a supposed normal flora of the skin, anterior nares and axilla has been transformed to a first class superbug

1. STAPHYLOCOCCUS
Prof. S. S. Taiwo
Department of Medical Microbiology
& Parasitology, College of Health
Sciences, LAUTECH, Osogbo
https://sites.google.com/a/lautech.edu.ng/dr-s-s-
taiwo/

2. INTRODUCTION
• Gram positive cocci (0.5-1.5μm in diameter), singly, or
in pairs, tetrads, short chains and irregular grape-like
clusters
• The name staphylococcus (Greek Staphyle – a bunch of
grapes) was first introduced by Ogston in 1884
• Are non-motile, non-spore forming, catalase positive,
non-encapsulated (or with limited capsule)
• Most are facultative anaerobes

3. Genus Staphylococcus…..
• Staphylococci are members of the family
Micrococcaceae that also includes genus
Micrococcus, genus Stomatococcus (Rothia) and
genus Planococcus
• The genus currently composed over 40 described
species and subspecies
• In clinical microbiology laboratory, staphylococci
are typically categorized as coagulase positive
and coagulase negative

4. Differences between Staphylococci &
Micrococci
• Staphylococci were formerly classified in a
common genus with Micrococci but there are
major differences between them
Genus Staphylococcus Genus Micrococcus
1. Has peptidoglycan-bound teichoic acid Has no teichoic acid
G+C content of DNA is high (63-
73%)
Not close to the Bacillus spp. or
Streptococci

5. Species of Staphylococci
• Currently there are over 40 Staphylococcus
species & subspecies, and about 16 are found in
humans
• Coagulase positive species (CoPS)
– S. aureus sub sp. aureus (primarily human pathogen)
– S. schleiferi sub sp. coagulans (rare human pathogen)
– S. intermedius (primarily animal pathogen)
– S. hyicus (primarily animal pathogen)
• Coagulase negative staphylococci (CoNS)

6. CoNS species
Human Animal
Species frequently associated with
diseases
1. S. epidermidis
2. S. haemolyticus
3. S. lugdunensis
4. S. saprophyticus
Species rarely associated with diseases
5. S. auricularis
6. S. capitis
7. S. caprae
8. S. carnosus
9. S. cohnii
10. S. hominis
11. S. pasteuri
12. S. pettenkoferi
13. S. pulvereri
14. S. saccharolyticus
15. S. simulans
16. S. schleiferi+
17. S. warneri
18. S. xylosus
1. S. arlettae
2. S. caseolyticus
3. S. chromogenes
4. S. condimenti
5. S. delphini
6. S. equorum
7. S. felis
8. S. fleurettii
9. S. gallinarum
10. S. hyicus+
11. S. intermedius+
12. S. kloosii
13. S. lentus
14. S. lutrae
15. S. muscae
16. S. nepalensis
17. S. piscifermentans
18. S. pseudintermedius
19. S. sciuri
20. S. simiae
21. S. succinus
22. S. vitulinus
+ some strains are coagulase
positive

7. Habitat of staphylococci
• Ubiquitous colonizers of skin & mucosa of
virtually all animals including mammals & birds
• Preferential niches by some species;
– S. epidermidis – skin
– S. capitis – scalp
– S. aureus in humans- anterior nares, axilla, perineum
– S. auricularis – human ear canal
– S. saprophyticus – human GIT & genito-urinary tract

8. Culture characteristics of
staphylococci
• Culture media
• Grow well on 5% sheep blood & chocolate agars
• Broth-Blood culture system
• Nutrient broth – (Thioglycollate & Brain-heart infusion)
• Selective culture media
• Mannitol salt agar (10% salt)

9. Incubation condition & duration
• Growth occur on incubating blood & chocolate
agars in CO2 or ambient air @ 35oC within 24
hours
• Growth on MSA may require incubation for 48
– 72 hours

10. Colonial appearance
• Size
• small, medium, large
• Shape
• convex, butyrous, circular, entire
• Consistency
• translucent, opaque, glossy, glistering, smooth

11. Colonial appearance…….
• Colour/pigment
• golden-yellow, creamy-yellow, white, tan, orange, pink
• Haemolysis
• β- haemolysis
• non-haemolytic
• Small colony variants (SCV)
• recovered from difficult-to-treat infection
• tolerant or resistant to antibiotics
• cause persistent infection

13. Pathogenic factors of
staphylococci
• S. aureus
– Surface proteins
– Capsular polysaccharides
• cap5 – polysaccharide capsule type 5
• cap8 – polysaccharide capsule type 8
– Membrane active proteins & cytotoxins
– Super-antigens
– Enzymes

14. Pathogenic factors of
staphylococci…
• CoNS
– Biofilm ESS
• S. epidermidis - adherence, maturation & dispersal
– Peptidoglycan
– Lipotechoic acid
– Phenol-soluble modulin
– Poly-D-glutamate
– Delta toxin
– Exo-enzymes e.g. fatty acid-modifying enzyme
(FAME), lipases, proteases, elastase
– Lantibiotics
• epidermin, epilancin, epicidin, pep5, k7

15. STAPHYLOCOCCUS AUREUS
• Gram positive cocci in clusters
• Coagulase positive
• Highly successful opportunistic pathogen with
extra ordinary capacity to adapt and survive in
a variety of environment esp with development
of antibiotic resistance

16. HABITAT OF S. AUREUS
• Ubiquitous colonizer of skin & mucosa of humans,
animals and birds
• In humans, S. aureus has a preferential niche for
anterior nares (esp. adults) and on skin of axilla &
perineum. Exists as resident or transient member of
normal flora
• Nasal carrier (10-40%) may be transient, persistent or chronic
• Can produce a wide variety of diseases - local invasive
or distant toxigenic disease

17. GENOMIC STRUCTURE OF S. AUREUS
• During the last 2 decades, molecular and genetic
dissection of S. aureus has revealed a great number of
surface adhesins, secreted enzymes and toxins
responsible for local & distant disease.
• Development of genomics and availability of complete
genome sequences of ≥ 10 S. aureus have helped
(http://www.ncbi.nlm.nih.gov/genomes/lproks.cgi)
• Genetic plasticity due to horizontal gene transfer with
acquisition of foreign genetic materials has contributed
to success of S. aureus as a pathogen

18. Whole genome of S. aureus - MRSA 252
versus CoNS - MSSA 476

19. Mobile genetic islands in S.
aureus
• Pathogenicity islands (SaPIs)
– relatively short (≤ 15kb),
– mobile by inverted repeats as attachment (att) site
– contains various types of virulence genes
• SaPI1 & SaPI2 – harbors TSS genes
• SaPI3 & SaPI4 – harbors several ET genes
• SaPIbov – encodes bovine version of TSST
• SaPIbap – encodes bovine adherence protein
• Genomic islands
– more stable & larger genetic element
– designated as vSaα & vSa
– harbors exotoxin genes (set) hence called exotoxin gene cluster (egc) or
virulence gene nursery
– mechanism of its mobilization unclear

20. Mobile genetic islands in S.
aureus…
• Resistance island
• staphylococcal chromosome cassette (SCC) mec
• exogenous piece of DNA 15 – 60kb in size
• boundaries demarcated by direct & inverted repeats which
allows integration at homologous site into the chromosome
• mec A gene of the SCCmec confers resistance to methicillin
& related β-lactam antibiotics
• ccr genes (ccrA & ccrB) encodes recombinases for
mobilization of the island
• rest of SCCmec – Junkyard (J) region contain various
determinants

21. ccrA3
ccrB3
Tn554 mecI
mecR1
mecA
IS431mec
pT181
IS431 IS431
mer
Tn554
orfX
ccr complexmec complex (class A)
ccr complex (type3)
Type III SCCmec (67kb)
ccrA1 ccrB1R-I
IS1272
mecR1
mecA
IS431mec
orfX
Type I SCCmec
(34kb)
mec complex (class B)ccr complex (type1)
ccrA2 ccrB2 Tn554 mecImecR1
Type II SCCmec (53kb) mec complex (class A)
orfX
IS431mec
pUB110
IS431mec
ccr complex (type 2)
ccr complex (type2)
mec complex (class B)
orfX
IS 1272
mecR1
mecA IS431mec
Type IV SCCmec
(24kb)
mecA
Resistance island in S. aureus (SCCmec)

22. PATHOGENESIS OF S. AUREUS INFECTIONS
• Colonization (precedes infection)
• Invasion
– direct through break in natural barriers
– indirect (e.g. toxins)
• Dissemination
– contiguous extension
– haematogenous (blood stream) to distant sites
• Toxinoses

23. 1. Host factors predisposing to S.
aureus infection
• Age
• very young & elderly
• Gender
• male > female (population studies)
• Necessity for dialysis
• RR, 150-204 for peritoneal dialysis and RR, 257-291 for haemodialysis
• Underlying disease conditions
• DM (RR, 7)
• Cancer (RR, 7.1-12.9)
• HIV infection (RR, 23.7)
• IVDU (RR, 10.1)
• Alcohol abuse (RR, 8.2)

24. Host factors ………..
• Defects of host chemotaxis, opsonin &
phagocytosis
• Inherited defects
– Job syndrome
– Chediak-Higashi syndrome
– Wiskott Aldrich syndrome
– Down’s syndrome
• Acquired defects
– RA
– decompensated acidotic DM
• Chronic S. aureus nasal carriage

25. 2. Pathogenic factors of S. aureus
– Surface adhesins/proteins
• collectively called Microbial Surface Component Reacting with
Adherence Matrix Molecules (MSCRAMM) bound covalently
to peptidoglycan
• Anchorage to cell wall is mediated by the membrane-bound
enzyme called sortase that recognizes a conserved amino acid
motif (LPXTG) at the C-terminal end of the wall attached
proteins.
• MSCRAMM mediates adherence of bacteria to host matrix
proteins (11 well characterized & 10 putative MSCRAMM)
– spa – Protein A
– clfA &clfB – Clumping factor A & Clumping factor B
– fnbA & fnbB – Fibronectin BPA & Fibronectin BPB
– cna – Collagen BP

26. Pathogenic factors ……….
– Capsular polysaccharides
– cap5 – polysaccharide capsule type 5
– cap8 – polysaccharide capsule type 8
– Teichoic acids (TAs) & Lipotechoic acids (LTAs)
– TAs are polyribitol-phosphate polymers crossed linked to
NAMA residue of peptidoglycan cell wall
– LTAs are plasma-membrane counterparts of TAs
– Peptidoglycan
– Major scaffold for anchoring most MSCRAMMs

27. Pathogenic factors …….……
– Membrane active proteins & cytotoxins
• hla – α - haemolysin
• hlb – β - haemolysin
• hld – δ - haemolysin
• hlg – γ - haemolysin
– lukS/F – Panton Valentine Leucocidin (PVL)
– Super-antigens
• sea – Enterotoxin A
• seb – Enterotoxin B
• sec – Enterotoxin C
• sed – Enterotoxin D
• eta – Exfoliatin A
• etb – Exfoliatin B
• tst – Toxic shock toxin-1

28. Pathogenic factors …….……
• Enzymes
• coa – Coagulase
• sak – Staphylokinase
• hys – Hyaluronidase
• nuc – Nuclease
• lip – Lipase (butyryl esterase)
• geh - Glycerol ester hydrolase
• SplA-F – Serine protease-like
• ssp – V8 protease
• sspB – Cysteine protease
• aur – Metalloprotease (aureolysin)
• plc – Phospholipase C
• scp – Staphopain (protease II)
• fme - FAME (fatty acid-modifying enzyme)

29. 3. Regulation of virulence genes
expression of S. aureus
• Regulation of virulence determinants is
accomplished by 3 families of regulatory
elements intertwining to adjust gene expression to
specific environmental conditions;
– Two component regulatory system (TCRS) e.g. agr
(accessory gene regulator) – quorum sensing control
– DNA binding protein e.g. sar (staphylococcal
accessory regulator) family of protein – regulates agr
– Small regulatory RNAs e.g. RAP/TRAP (RNAIII-
activating proteins/target of RNAIII-activating
proteins) activates agr.

30. SPECTRUM OF S. AUREUS INFECTIONS
• Tissue invasive diseases
– local
– systemic
• Toxin-mediated diseases
– local e.g. SSTI by PVL toxin, SSSS by exfoliative
toxins A or B
– distant & systemic e.g. TSST-1

31. 1. Skin and soft tissue infections
• Infection of skin - primary pyoderma
• infection of epidermis - impetigo
• infection of superficial dermis – folliculitis
• infection of deep dermis (hair follicle) – furuncles (boil),
carbuncles (multiple hair follicles) & hydradenitis suppurativa
(affects apocrine sweat glands)
• mastitis
• surgical site infection (SSI)
• Soft tissue infection - infection of subcutaneous
cellular tissue
• erysipelas, cellulitis, fasciitis and pyomyositis

32. 2. Blood stream infections (BSI)
• BSI is defined as one or more positive blood
cultures associated with general symptoms
such as fever and hypotension
– Nosocomial acquired BSI
• +ve blood cultures ≥ 2days of hospital admission
– Community acquired BSI/Community-onset BSI
• +ve blood cultures < 2 days of hospital admission
– Healthcare associated BSI
– Community associated BSI

33. 3. Infective endocarditis
• One of the most severe complications of S.
aureus bacteraemia
• S. aureus endocarditis typically follows acute
course with multiple peripheral septic emboli,
valve destruction, myocarditis and mixed
cardiogenic and septic shock

34. 4. Meningitis
• S. aureus meningitis – uncommon 1-9% of cases
of BM
• 2 types of presentation:
– postoperative meningitis
• associated with neurosurgical procedures, shunt devices,
head trauma
• nosocomial in origin
– spontaneous haematogenous meningitis
• from S. aureus infection outside the CNS
• community in origin

35. 5. Pericarditis
• S. aureus pericarditis is purulent in nature
• S. aureus may be responsible for up to 22% of
pericarditis
• Infection results from;
– contiguous contamination during surgery
– local extension of paravalvular infection
– embolization of septic materials in the coronary
arteries

36. 6. Pulmonary infections
• Pneumonia
• Community acquired pneumonia (CAP)
– S. aureus is responsible for < 10% of cases of CAP
• Hospital acquired pneumonia (HAP)
– 20-30% of cases
– associated with high mortality from respiratory distress
• Pleural empyema
• S. aureus is the most common cause (1/3 of cases)
• arises from direct spread from S. aureus pneumonia or lung
abscess

37. 7. Osteomyelitis
• S. aureus is the leading cause – 50-70% of
cases
• Acute
• Chronic
• Prosthetic joint infections
• S. aureus is second most common cause after CoNS
• Biofilm formation (S. aureus also form biofilm)

38. 8. Other S. aureus invasive
infections
• Septic arthritis
• S. aureus is the most common in children and 2nd
commonest in adult after gonococcus
• Septic bursitis
• affects periarticular bursa e.g. olecranon & patella (pressure
areas)
• manifests as acute juxta-articular inflammation
• S. aureus is responsible for 80% of cases

39. Other S. aureus invasive
infections…
• Primary pyomyositis
• also called tropical myositis, infective myositis,
pyogenic myositis, myositis purulenta tropica
• rare subacute infection of skeletal muscles because of
resistance of muscle to infection
• haematogenous in origin
• usually a history of muscle trauma

40. Toxin mediated S. aureus diseases
• 1. S. aureus infection caused by haemolysins
& leukocidin
– SSTI & haemorrhagic pneumonia
• caused by S. aureus PVL toxin (a γ haemolysin)
encoded by lukS & lukF genes carried by a mobile
phage (øSLT) and regulated by agr TCRS
• PVL is found in CA-MRSA (100%) and less in HA-
MRSA or MSSA (<2%)

41. 2. S. aureus infections caused by
exfoliative toxins
• Staphylococcus scalded skin syndrome (SSSS)
– Superficial S. aureus infection affecting stratum granulosum of the epidermis
– never affects mucosa (as in Lyell’s syndrome - TEN)
• caused by S. aureus carrying exfoliative toxin A (ETA) or
exfoliative toxin B (ETB) encoded by eta (phage) & etb (plasmid)
genes respectively
• ETC & ETD isoforms described
• affects newborn & infants & known also as Ritter’s disease
• causes local blistering (bullous impetigo) to generalized scalding
(Nikolsky’s sign)

42. 3. S. aureus infections caused by
super-antigens
• Superantigens (SAgs) are large family of
pyrogenic exotoxins
• Activates immune system outside the normal
antigen binding groove between APCs & T-cells
• SAgs are made of;
– Toxic shock syndrome toxin (TSST-1)
– Staphylococcal enterotoxins (SEs).
• 15 different enterotoxins - SE (A, B, C, D, E, G, H, I, J, K, L,
M, N, O) or SET1-SET15

43. a. Toxic shock syndrome (TSS)
• Staphylococcal TSS is caused by TSST-1 toxin secreted
locally by S. aureus carrying the gene tst that is regulated
by the agr TCRS
• 2 types
– Menstrual TSS associated with high-absorbency tampons
which creates 4 conditions in the vagina necessary for
expression
• elevated protein
• relatively neutral pH
• elevated partial pressure of O2
• elevated partial pressure of CO2
– Non-menstrual TSS
• By TSST-1 and also by SEB & SEC from any site or person

44. b. Enterotoxins and food poisoning
• There are 15 staphylococcal enterotoxin SAgs
• SEA, SEB & SEC are the most common cause of food
poisoning
• Causes food poisoning from preformed toxins
swallowed in food contaminated by S. aureus carrying
sea, seb or sec genes
• Presents with gastrointestinal symptoms of vomiting
and diarrhoea in primates and humans

45. LABORATORY IDENTIFICATION OF S. AUREUS
• 1. Microscopy
– Gram positive cocci in clusters on Gram smears of
specimens
• 2. Culture on Blood agar/MSA/MH broth
– Incubate at 35-37oC for 18-24 hours in ambient air
– Typical colony
• golden yellow/white colony on Blood agar
• yellow mannitol fermenting on MSA agar
– Morphology variants takes 2-3 days
• small colony variants (scv)

46. 3. Phenotypic identification tests of S. aureus
• Catalase (slide & tube)
• Coagulase (slide & tube)
• DNase
• Agglutination test to detect surface determinants & toxins
– clumping factors, protein A, polysaccharides
• Antibiotic resistance test
– Disk and agar diffusion
– Broth dilution & E-test
– Automated methods
• measure metabolic activity, growth rates

47. 4. Molecular identification tests of S. aureus
• Molecular method offers;
– Rapid detection of S. aureus
– Identify drug resistance determinants
• DNA probes to detect 16S rRNA
– Florescence in situ hybridization (FISH)
– Peptic nucleic acid – florescence in situ hybridization (PNA-
FISH)
• DNA amplification by PCR
– Conventional PCR to detect species specific genes (coa, nuc,
sod, hsp70 etc)
– Real time PCR including multiplexing to detect antibiotic R
genes

48. 5. Molecular typing of S. aureus
• Molecular typing is used to;
– understand S. aureus evolution and population structure
– identify outbreak strain prior to infection intervention
• Typing methods
– Chromosomal restriction-fragment length analysis by
PFGE
– Single gene locus sequence analysis e.g. spa typing
– Double locus sequence typing e.g. spa-clfB typing
– Multilocus sequence typing (MLST)
• involves sequencing of seven housekeeping genes

49. DRUG TREATMENT OF S. AUREUS
INFECTIONS & ANTIBIOTIC
RESISTANCE
• Drugs for treatment of S. aureus infections include such
classes as;
– β-lactam and glycopeptides
– Ribosomal inhibitors
• MLS B, aminoglycosides, tetracycline, fusidic acid and the new
oxazolidinones
– RNA polymerase inhibitors – rifampicin
– DNA gyrase blockers – fluoroquinolones
– Antimetabolites such as sulphonamides
– Lipopeptides & lipoglycopeptides e.g. dalbavancin
• S. aureus has developed resistance to virtually all these
antibiotic classes

50. 1. S. aureus resistance to β-
lactams
• Penicillinase (β-lactamase) enzyme
– encoded by bla gene usually carried on plasmid
– inducible and preceded by blaRI and blaI regulatory
determinants
– breaks down β-lactam ring of the antibiotic thereby
conferring bacteria resistance to penicillin
• Penicillin binding protein 2a (PBP2a)
– encoded by mecA gene in resistance island (SCCmec)
– mecRI and mecI regulatory mechanism
– PBP2a has low binding affinity for penicillins & most
β-lactams including β-lactamase-stable β-lactams

51. mec A gene regulation in MRSA
SCCmec I-VI and more… variants
IV (V, VI) is most commonly found in CA-MRSA; 24 kb, mobile

52. Accessory determinant in mecA
regulation
– 14 or more of such determinants which include;
• femABC
• femhB
– Transglycosidase domain of normal PBP2 of S.
aureus is required for correct action of PBP2a (a
mono-functional enzyme with only transpeptidase
domain)

53. 2. Resistance to glycopeptides
• Glycopeptide antibiotics
– Vancomycin
– Teicoplanin
• Glycopeptide intermediate resistance (GISA or VISA)
– vancomycin MIC of 4 - 8mg/L
– genetic basis unknown
• Glycopeptide resistance (GRSA or VRSA)
– low-level resistance - vancomycin MIC ≥ 16 mg/L
– high-level resistance - vancomycin MIC ≥ 256 mg/L
– acquisition of vanA operon from Enterococcus

54. 3. Resistance to protein synthesis
inhibitors
– Ribosome modification
• erm (erythromycin methylase) with cross resistance to MLSB
detected by D-test (erythromycin & clindamycin disks)
– Drug efflux
• msrA gene codes for complex ABC transporter that export
macrolides & streptogramins (MS-resistance phenotype)
compared to mefA (S. pyogenes) or mefE (S. pneumoniae)
which are major facilitator transporter and export only
macrolide (M-resistance phenotype)
– Mutation in 23S rRNA gene of 50s ribosome
• Linezolid resistance

55. 4. Resistance to quinolones
• Chromosomal mutations of quinolone targets
• Topoisomerase IV (grlA & grlB) genes
• DNA gyrase (gyrA & gyrB) genes
• Plasmid mediated
• qnr gene (in G-ve bacteria)– protects target
• qnr-like gene in Enterococcus faecalis can be
transferred to S. aureus (not yet in clinical isolates)

56. STAPHYLOCOCCUS EPIDERMIDIS
• Of the over 40 CoNS, 4 species are frequently
associated with human disease;
• S. epidermidis, S. saprophyticus, S. lugdunensis and S.
haemolyticus
• S. epidermidis is now the most common cause of;
• primary bacteraemia
• infection associated with prosthesis & implants
• S. epidermidis pathogenic attributes;
• natural niche is the host skin, giving it access to inserted devices
• ability to adhere to biomaterials and form a biofilm

57. Virulence factors of S.
epidermidis
• 1. Biofilm
– S. epidermidis growing in biofilm have unique
transcriptional responses compared to those
outside
– Cells within shift their physiology to anaerobic or
microaerophilic metabolism to produce 4 different
cell types in the biofilm
• aerobic, anaerobic, dormant and dead cells
• leads to tolerance to antibiotics and development of
persisters and/or dormant cells
• immune system avoidance

58. Biofilm – 3 stages
• a. Adherence by S. epidermidis adhesins
• Autolysin adhesin (Aae)– binds fibrinogen, fibronectin & vitronectin
• Bap homologue protein (Bhp) – binds polystyrene
• Elastin binding protein (Ebp) – binds elastin
• Extracellular matrix binding protein (EmbP) - fibronectin
• Fibronectin binding protein (Fbe)
• Glycerol ester hydrolase (GehD) – binds collagen
• Staphylococcal conserved antigen (ScaA) – fibrinogen, fibronectin,
vitronectin
• Staphylococcal conserved antigen (ScaB) – unknown ligands
• Serine aspartate repeat protein F (SdrF) – collagen
• Serine aspartate repeat protein G (SdrG) – fibrinogen
• Staphylococcal surface protein 1 (Ssp-1) - polystyrene
• Staphylococcal surface protein 2 (Ssp-2) - polystyrene
• Teichoic acid - fibronectin

59. Biofilm – 3 stages….
• b. Maturation – intercellular adhesion of bacteria
– Mediated by polymeric molecules
• eDNA (extracellular DNA)
• polysaccharide intercellular adhesin (PIA) or poly –N-glucosamine (PNAG)
– icaADBC operon (icaA, icaD, icaB & icaC) + icaR (repressor)
• c. Dispersal
– Dispersal of biofilm and subsequent spread to other
potential sites
– Mediated by phenol soluble modulins (PSMs)
• PSM production is regulated by agr TCRS
• PSM act as surfactant – leading to loss of cellular clusters
• PSMs are proinflammatory - recruit immune cells and lyse neutrophils

60. Virulence factors of S. epidermidis….
• 2. Other virulent factors
– Poly-Gamma-DL-Glutamic Acid (PGA)
• cell surface-associated anti-phagocytic polymer (similar to that of
B. anthracis)
• inhibits innate immune system
• facilitates host skin colonization
– Lantibiotics - bacteriocins
• (Epidermin, Pep5, epilancin, epicidin)
• thio-ether amino acid containing antimicrobial peptides
• bacterial interference
• successful skin colonization
• persistence on human skin

61. Host factors predisposing to S.
epidermidis infection
• 1. Transplant and neutropaenic patients
• immunosuppression
• intravascular catheterization
• mucosal or skin breach
• interleukin 2 therapy
• 2. Neonates
• very low birth weight preterm infants (<1.5kg)
• use of intravascular catheters
• total parenteral nutrition (TPN) with IV lipid emulsions
• mechanical ventilators
• umbilical catheters

62. Clinical S. epidermidis infections
- Bacteraemia (BSI)
• CoNS accounts for 30% of HCA BSI
– caused by infection of intravascular catheters or other
prosthetic medical devices
– difficulty of distinguishing CoNS true bacteraemia
from contamination
• 1-6% of blood cultures are contaminated
• CoNS is responsible for 70-80% of cases of contamination
• To differentiate CoNS contaminants from true pathogen;
– perform multiple blood cultures
– estimate serum CRP & procalcitonin
– perform molecular typing
– perform antibiogram
– detect biofilm production

63. Sources of S. epidermidis
bacteraemia
• 1. Intravascular catheter-associated BSI
• Peripheral intravascular catheters (PIC)
• Central venous catheters (CVC)
–non-tunneled
–tunneled
• CoNS enter blood stream through cutaneous
surface of the catheter in PIC & non-
tunneled CVC
• catheter hub colonization with CoNS and
passage along the lumen to the blood stream
in tunneled CVC

64. Sources of S. epidermidis …..……
• 2. Endocarditis
– Prosthetic valve endocarditis (PVE) is caused by
CoNS in 15-40% of cases of endocarditis
• usually HCA infections occurring within 12 months of
surgical placement
• usually methicillin-resistant
• presents acutely or chronically
• high mortality despite aggressive therapy (25%)
– Native valve endocarditis (NVE) caused by CoNS is
relatively rare (in 5-8% of endocarditis)
• high mortality despite aggressive medical-surgical treatment

65. Sources of S. epidermidis …..……
• 3. Infections of cardiac devices (pacemakers,
defibrillators)
• occur in 1-2% of device placement procedures
• CoNS is responsible for 50-60% of these infections
• 4. Infection of vascular grafts
• relatively rare complication of arterial reconstruction
• CoNS is responsible for 20-30% of cases

66. Sources of S. epidermidis …..……
• 5. Infections of orthopaedic prosthetic device
– CoNS most common cause responsible for 30-45%
of cases
– Bacteria inoculated usually at the time of
arthroplasty
– Infection could be;
• early (within 3 months of surgery) – S. aureus
• delayed (3 months – 2 years) - CoNS
• late (longer than 2 years) – haematogenous spread from
other sources

67. Sources of S. epidermidis …..……
• 6. Infections of CSF shunts
• most significant complication of CSF shunt implantation 1.5-
38% incidence
• S. epidermidis is responsible for 50% of cases
• usually methicillin resistant strains
• 7. Surgical site infection
• CoNS is 2nd commonest cause after S. aureus
• usually cause superficial incisional and rare in deep
incisional or organ or space infection
• usually follow clean procedures and not contaminated

68. Sources of S. epidermidis …..……
• 8. Infections of peritoneal dialysis catheters
• CoNS is the most frequent cause of peritonitis in
patients undergoing peritoneal dialysis
• accounts for 25-50% of cases & S. epidermidis accounts
for 50-80% of CoNS
• 9. Endophthalmitis
• most frequent cause of postoperative endophthalmitis
responsible for 60-70% of cases

69. Sources of S. epidermidis …..……
• 10. Urinary tract infections
• CoNS is responsible for 3% of nosocomial UTI & S.
epidermidis is responsible for 90% of cases
• usually methicillin resistant
• CoNS is responsible for 1% of community UTI
• 11. Infection of genitourinary prosthesis
• Infection rate is 2-4%
• S. epidermidis is responsible for 35-60% of infection of
synthetic urinary sphincters & penile prostheses

70. Sources of S. epidermidis …..……
• 12. Infections of breast implants
• occur in 1-2% of breast implant surgery
• often caused by CoNS
• 13. Infections of miscellaneous prosthetic
devices & implants
• coronary stents, surgical mesh, ventricular assist device
etc

71. STAPHYLOCOCCUS SAPROPHYTICUS
• S. saprophyticus colonizes rectum or urogenital tracts
of about 5-10% of women
• Possess adhesion protein, UafA, which allows
adherence to human uroepithelium & mediates
haemagglutination
• Encodes several transport proteins that enables it to
rapidly adjust to osmotic and pH changes
• Produces abundant urease that allows it to proliferate in
urine

72. S. saprophyticus infections
• 1. UTI
– S. saprophyticus is second only to E. coli as the
causative agent of uncomplicated UTI in young
sexually active women
• UTI often follow sexual intercourse or menstruation
• may occur with vaginal candidiasis
• 90% of S. saprophyticus UTI are symptomatic with
dysuria, frequency or urgency
• 80% of patients with S. saprophyticus UTI have pyuria
or haematuria

73. S. saprophyticus infections…….
• 2. Other infections (rare)
• Native valve endocarditis, endophthalmitis &
septicaemia
• S. saprophyticus can be differentiated from
other CoNS by its resistance to novobiocin
• Infection is usually easily treated with urinary
antimicrobials

74. STAPHYLOCOCCUS LUGDUNENSIS
• First described in 1988 as constituent of
normal human skin
• Infrequent but not rare human pathogen
• Behaves clinically in a manner similar to S.
aureus

75. Pathogenic factors of S.
lugdunensis
• More virulent than other CoNS due to
production of several virulent factors such as;
• delta toxin-like haemolytic peptide
• adhesins that binds to collagen, fibronectin, laminin &
vitronectin
• enzymes – DNAse, lipase
• lysozyme resistance
• biofilm formation
• von-Willebrand factor-binding protein enabling it to
bind to endothelial cells – NVE
• agr locus similar to S. aureus

76. S. lugdunensis infections
• S. lugdunensis has been described to cause;
– fulminant cases of NVE &PVE
– SSTI
– UTI
– CNS infection
– bone & joint infections
– peritonitis

77. S. lugdunensis identification
• may be confused with S. aureus if latex agglutination is
used because S. lugdunensis also produce clumping
factor
• β-lactamase production in only 25% isolates &
methicillin resistance very uncommon
• Gives positive pyrrolidonyl aminopeptidase (PYR) &
ornithine decarboxylase tests – rapid identification
• generally susceptible to most anti-staphylococcal
antibiotics

78. STAPHYLOCOCCUS HAEMOLYTICUS
• Typically the 2nd or 3rd most common CoNS
incriminated as cause of infection
• Usually cause nosocomial BSI related to intravascular
catheters
• Other infection types are UTI, SSTI, meningitis,
endocarditis and many device-associated infections
• Causes many outbreaks in neonatal intensive care units

79. S. haemolyticus pathogenic attributes
• Several putative virulence genes –
• lipases, proteases, lyases
• Resistance to multiple antibiotics including
glycopeptides
• R strain possess highly cross-linked peptidoglycans
with serine instead of glycine in their cross bridge

80. Laboratory identification tests for
CoNS
• Difficult to correctly identify CoNS to species
level in clinical microbiology laboratory as
wide number of biochemical tests are needed
• Simplified biochemical scheme can correctly
identify S. aureus and the 4 most common
CoNS human pathogen- S. epidermidis, S.
saprophyticus, S. haemolyticus & S.
lugdunensis

81. Laboratory
identification…………
• Molecular identification methods now available
• Mass spectrometry (MALDI-TOF)
• Typing methods
• PFGE of restriction fragment analysis gold standard for short
term CoNS epidemiology
• MLST for long term CoNS epidemiology
• MLVA (multiple locus variable-number tandem repeat
analysis)
• Sequence analysis of repeat regions of sdrG/aap genes

82. Bibliography
• Forbes BA, Sahm DF, Weissfeld AS. (2007). Bailey &
Scott’s Diagnostic Microbiology. 12th edn, Missouri,
Mosby Elsevier
• Mandell DL, Bennett JE, Dolin R. (2010). Mandell,
Douglas and Bennett’s Principle and Practice of
Infectious Diseases. 7th edn, Vol.1, Philadelphia, Churchill
Livingstone Elsevier
• Taiwo SS. (2009). Methicillin resistance in Staphylococcus
aureus: a review of the molecular epidemiology,
clinical significance and laboratory detection
methods.West African Journal of Medicine. 28(5): 281 -
290