Microbiology lec5

1. Medical MicrobiologyMedical Microbiology
Lecture 6Lecture 6
Dr. Saleh M Y OTHDr. Saleh M Y OTH
PhDPhD
Medical Molecular Biotechnology and Infectious DiseasesMedical Molecular Biotechnology and Infectious Diseases
11/10/201011/10/2010
IMS - MSUIMS - MSU
Systemic bactreiology

2. Streptococci and its DiseasesStreptococci and its Diseases
Systemic bactreiology

3. 3
Staphylococci
-Coagulase-negative staphylococcus; frequently
involved in nosocomial and opportunistic infections
-S. epidermidis – lives on skin and mucous
membranes; endocarditis, bacteremia, UTI
- S. saprophyticus – infrequently lives on skin,
intestine, vagina; UTI

4. Staphylococci are gram positive cocci arranged in
grape like clusters.
The genus Staphylococcus includes 3 species of
medical importance;
Staph. aureus,
Staph. epidermidis and
Staph. saprophyticus.

5. 5
General Characteristics of the Staphylococci
-Common inhabitant of the skin and mucous membranesCommon inhabitant of the skin and mucous membranes
-Spherical cells arranged in irregular clustersSpherical cells arranged in irregular clusters
-Gram-positive Gram-positive
-Lack spores and flagellaLack spores and flagella
-May have capsuleMay have capsule

6. Staphylococcus aureus morphology
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7. 7
S. aureus
- Grows in large, round, opaque colonies
- Optimum temperature of 37
o
C
- Facultative anaerobe
- Withstands high salt, extremes in pH,
and high temperatures
- Produces many virulence factors

8. S. aureus
Major human pathogenMajor human pathogen
Habitat - part of normal flora in some humans Habitat - part of normal flora in some humans
and animalsand animals
Source of organism - can be infected human Source of organism - can be infected human
host, carrier, fomite or environmenthost, carrier, fomite or environment

9. Natural history of disease
-Many neonates, children, adults -intermittently
colonised by S. aureus
-Usual sites; skin, nasopharynx, perineum
-Breach in mucosal barriers; can enter
underlying tissue
- Characteristic abscesses; Disease due to toxin
production

10. Grouping for Clinical Purposes
1. Coagulase positive Staphylococci
- Staphylococcus aureus
2. Coagulase negative Staphylococci
- Staphylococcus epidermidis
- Staphylococcus saprophyticus

11. Diseases
- Due to direct effect of organism
- Local lesions of skin
- Deep abscesses
- Systemic infections
- Toxin mediated
- Food poisoning
- toxic shock syndrome
- Scalded skin syndrome

12. Factors predisposing to S. aureus infections
Host factors
- Breach in skin
- Chemotaxis defects
- Opsonisation defects
- Neutrophil functional defects
- Diabetes mellitus
- Presence of foreign bodies
Pathogen Factors
- Catalase (counteracts
host defences)
- Coagulase
- Hyaluronidase
- Lipases (Imp. in
disseminating infection)
- B lactasamase(ass. With
antibiotic resistance)

13. Skin Lesions
- Boils جارخو حرقت
- Styes لمامد
- Furuncles (infection of hair follicle)
- Carbancles (infection of several hair follicles)
- Wound infections (progressive appearance
of swelling and pain in a surgical wound after
about 2 days from the surgery)
- Impetigo (skin lesion with blisters that break
and become covered with crusting exudate)

15. Deep abscessses
- Can be single or multiple
- Breast abscess can occur in 1-3% of
nursing mothers in puerperiem
- Can produce mild to severe disease
- Other sites - kidney, brain from septic
foci in blood

16. Systemic Infections
1. With obvious focus ةحرقتم ةرؤب
-Osteomyelitis, septic arthritis
2. No obvious focus
- heart (infective endocarditis)
- Brain (brain abscesses)
3. Ass. With predisposing factors
- multiple abscesses, septicaemia(IV drug users)
- Staphylococcal pneumonia (Post viral)

17. Toxin Mediated Diseases
1. Staphylococcal food poisoning
- Due to production of entero toxins
- heat stable entero toxin acts on gut
- produces severe vomiting following a very
short incubation period
- Resolves on its own within about 24 hours

18. Toxic shock syndrome
- High fever, diarrhoea, shock and
erythematous skin rash which
desquamate
- Mediated via ‘toxic shock syndrome toxin’
- 10% mortality rate
- Described in two groups of patients
- Ass. With young women using tampones
during menstruation
- Described in young children and men

20. Scalded skin syndrome
- Disease of young children
- Mediated through minor Staphylococcal
infection by ‘epidermolytic toxin’ producing
strains
- Mild erythema and blistering of skin
followed by shedding of sheets of
epidermis
- Children are otherwise healthy and most
eventually recover

21. Virulence factors of S. aureus
Enzymes:
- Coagulase; coagulates plasma and blood;
produced by 97% of human isolates; diagnostic
- Hyaluronidase; digests connective tissue
- Staphylokinase; digests blood clots
- DNase; digests DNA
- Lipases; digest oils; enhances colonization on
skin
- Penicillinase; inactivates penicillin
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Virulence factors of S. aureus
Toxins:
- Hemolysins (α, β, γ, δ); lyse red blood cells
- Leukocidin; lyses neutrophils and macrophages
- Enterotoxin; induce gastrointestinal distress
- Exfoliative toxin; separates the epidermis from
the dermis
- Toxic shock syndrome toxin (TSST); induces
fever, vomiting, shock, systemic organ damage

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Epidemiology and Pathogenesis
- Present in most environments frequented by
humans
- Readily isolated from fomites
- Carriage rate for healthy adults is 20-60%
- Carriage is mostly in anterior nares, skin,
nasopharynx, intestine
- Predisposition to infection include: poor hygiene and
nutrition, tissue injury, pre-existing primary
infection, diabetes, immunodeficiency
- Increase in community acquired methicillin
resistance - MRSA

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Staphylococcal Disease
Range from localized to systemic
Localized cutaneous infections; invade skin
through wounds, follicles, or glands
- Folliculitis; superficial inflammation of hair follicle;
usually resolved with no complications but can progress
- Furuncle; boil; inflammation of hair follicle or sebaceous
gland progresses into abscess or pustule ةرثب
- Carbuncle; larger and deeper lesion created by
aggregation and interconnection of a cluster of furuncles
- Impetigo; bubble-like swellings that can break and peel
away; most common in newborns

25. Bullous impetigo

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Cutaneous lesions of S. aureus

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Systemic infections

-Osteomyelitis; infection is established in
the metaphysis; abscess forms
- Bacteremia; primary origin is bacteria from
another infected site or medical devices;
endocarditis possible

28. Staphylococcal osteomyelitis in a long bone
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Staphylococcal Disease
Toxigenic disease
- Food intoxication – ingestion of heat
stable enterotoxins; gastrointestinal
distress
- Staphylococcal scalded skin syndrome
– toxin induces bright red flush, blisters,
then desquamation of the epidermis
- Toxic shock syndrome – toxemia leading
to shock and organ failure

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Effects of
staphylococcal
toxins on skin

31. Toxic Shock Syndrome Toxin
- Superantigen- Superantigen
- Non-specific - Non-specific
binding of toxin to binding of toxin to
receptors triggers receptors triggers
excessive excessive
immune responseimmune response

32. TSS Symptoms
- 8-12 h post infection
- Fever
- Susceptibility to Endotoxins
- Hypotension
- Diarrhea
- Multiple Organ System Failure
- Erythroderma (rash)

33. TSS Treatment
- Clean any obvious wounds and remove any - Clean any obvious wounds and remove any
foreign bodiesforeign bodies
- Prescription of appropriate antibiotics to eliminate - Prescription of appropriate antibiotics to eliminate
bacteriabacteria
- Monitor and manage all other symptoms, e.g. - Monitor and manage all other symptoms, e.g.
administer IV fluids administer IV fluids
- For severe cases, administer methylprednisone, - For severe cases, administer methylprednisone,
a corticosteriod inhibitor of TNF-a synthesisa corticosteriod inhibitor of TNF-a synthesis

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Identification of Staphylococcus in
Samples
-Frequently isolated from pus, tissue Frequently isolated from pus, tissue
exudates, sputum, urine, and bloodexudates, sputum, urine, and blood
- Cultivation, catalase, biochemical testing, - Cultivation, catalase, biochemical testing,
coagulasecoagulase

35. Catalase test
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Clinical Concerns and Treatment
- 95% have penicillinase and are resistant to
penicillin and ampicillin
- MRSA – methicillin-resistant S. aureus;
carry multiple resistance
- Some strains have resistance to all major drug
groups except vancomycin
- Abscesses have to be surgically perforated
- Systemic infections require intensive lengthy
therapy

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Prevention of Staphylococcal Infections
- Universal precautions by healthcare
providers to prevent nosocomial infections
- Hygiene and cleansing

38. Antibiotic sensitivity pattern
- Very variable and not predictable
- Very important In Patient Management
- Mechanisms
1. B lactamase production - plasmid mediated
- Has made S. aureus resistant to penicillin group of antibiotics -
90% of S. aureus (Gp A)
- β-lactamase stable penicillins (cloxacillin, oxacillin, methicillin)
used
2. Alteration of penicillin binding proteins
- (Chromosomal mediated)
- Has made S. aureus resistant to β-lactamase stable penicillins
- 10-20% S. aureus Gp (B) GH Colombo/THP resistant to all
Penicillins and Cephalasporins)
- Vancomycin is the drug of choice

39. DIAGNOSIS
1. In all pus forming lesions
- Gram stain and culture of pus
2. In all systemic infections
- Blood culture
3. In infections of other tissues
- Culture of relevant tissue or exudate

40. S. epidermidis
-Skin commensal
-Has predilection for plastic material
-Ass. With infection of IV lines, prosthetic heart
valves, shunts
-Causes urinary tract infection in cathetarised
patients
- Treatment should be aided with ABST

41. S. saprophyticus
-Skin commensal
-Imp. cause of UTI in sexually active young
women.
- Usually sensitive to wide range of
antibiotics