Medical Microbiology I - Lecture8

MEDICAL MICROBIOLOGY I

Lesson 8Lesson 8

Staphylococci and Diseases

Staphylococcus

Staphylococcaceae contains 4 genera, the

most important of which is the genus

Staphylococcus

Staphylococcus (from Greek: staphyl, bunch

Staphylococcus (from Greek: staphyl, bunch

of grapes and KKKO, kkkos, granule) is a

genus of Gram positive bacteria

Under microscope they appear round (cocci)

and form in grape-like clusters

Staphylococcus

Staphylococcus

The Staphylococcus genus includes 32 species

and 8 sub-species

Members of this genus are facultatively

anaerobic, non-motile, Gram positive cocci anaerobic, non-motile, Gram positive cocci

that usually form irregular clusters

They are catalase positive, oxidase negative,

ferment glucose, and have teichoic acid in

their cell walls

Staphylococcus

Organisms in clinical material may also appear

as single cells, pairs, or short chains

Most staphylococci are 0.5 - 1 m in diameter

Grow in medium containing 10% NaCl and at a Grow in medium containing 10% NaCl and at a

temperature ranging from 18 - 40C

Staphylococcus

Staphylococci are normally associated with the skin, skin glands, and mucous membranes of warm-blooded animals

Staphylococcus can cause a wide variety of Staphylococcus can cause a wide variety of diseases in humans and other animals through either toxin production or penetration

Staphylococcal toxins are a common cause of food poisoning, as it can grow in improperly stored food

Staphylococcus

Staphylococcus are responsible for many

human diseases

Staphylococcus cause a wide spectrum of life

threatening systemic diseases; infections of threatening systemic diseases; infections of

the skin, soft tissues, bones, and urinary tract;

and opportunistic infections

Staphylococcus

Sometimes responsible for endocarditis and

infections of patients with lowered resistance

(e.g. wound infections, surgical infections,

urinary tract infections, body piercing)urinary tract infections, body piercing)

S. aureus is the most important human

staphylococcal pathogen and cause boils,

abscesses, wound infections, pneumonia,

toxic shock syndrome, and other diseases

Physiology and Structure

Capsule

A loose-fitting, polysaccharide layer (slime layer)

The capsule protects the bacteria by inhibiting The capsule protects the bacteria by inhibiting the chemotaxis and phagocytosis of the organisms by polymorphonuclear leukocytes , as well as by inhibiting the proliferation of mononuclear cells after mitogen exposure

It also facilitates the adherence of bacteria to catheter and other synthetic material


Peptidoglycan

Half of the cell wall by weight is peptidoglycan

The peptidoglycan consists of layers of glycan chains built with 10 - 12 alternating subunits of N-acetylmuramic acid and N-acetylglucosamineN-acetylmuramic acid and N-acetylglucosamine

The peptidoglycan has endotoxin-like activity, stimulating the production of endogenous pyrogens, activation of complement and the production of interleukin-1 monocytes, and aggregation of polymorphonuclear leukocytes ( a process responsible for abscess formation)


Teichoic acid

Species-specific, phosphate-containing

polymers that are bound covalently to the

peptidoglycan layer or through lipophilic peptidoglycan layer or through lipophilic

linkage to the cytoplasmic membrane

Mediate the attachment of staphylococci to

mucosal surfaces through their specific

binding to fibronectin


Teichoic acid

Although the teichoic acids are poor immunogens, a specific antibody response is stimulated when they are bound to stimulated when they are bound to peptidoglycan

The monitoring of this antibody response has been used to detect systemic staphylococcal disease although this is less sensitive than are other diagnostic tests


Protein A

The surface of most S. aureus (but not the

coagulase-negative staphylococci) is uniformly

coated with protein Acoated with protein A

Extracellular protein A can also bind to

antibodies, thereby forming immune

complexes with the subsequent consumption

of the complement


Coagulase and other surface proteins

The outer surface of most strains of S. aureus

contains clumping factor (or bound coagulase)

This protein binds fibrinogen, converts it to This protein binds fibrinogen, converts it to

insoluble fibrin, causing the staphylococci to

clump or aggregate

Detection of this protein is the primary test for

identifying S. aureus


Cytoplasmic membrane

Made up of a complex of proteins, lipids, and

a small amount of carbohydrates

Serves as an osmotic barrier for the cell and Serves as an osmotic barrier for the cell and

provides an anchorage for the cellular

biosynthesis and respiratory enzymes

Classification

The main classification of staphylococci is

based on their ability to produce coagulase,

an enzyme that causes blood clot formation

2 classification: 2 classification:

Coagulase positive

Coagulase negative

Classification

Coagulase Positive

S. aureus - can produce coagulase

Some may be atypical in that they do not produce coagulaseproduce coagulase

S. aureus is also catalase-positive, able to convert hydrogen peroxide (H2O2) to water and oxygen, which makes the catalase test useful to distinguish staphylococci from enterococci and streptococci.

Classification

Coagulase Positive

Inhabits and sometimes infects the skin of

domestic dogs and cats

Carry the genetic material that imparts Carry the genetic material that imparts

multiple bacterial resistance

Optical-rectalitis is caused by a coagulase-

positive organism

Classification

Coagulase Negative

S. epidermidis - a commensal of the skin, but can cause severe infections in immunosuppressed patients and those with immunosuppressed patients and those with central venous catheters

S. saprophyticus - part of the normal vaginal flora, is predominantly implicated in genitourinary tract infections in sexually-active young women

Classification

Coagulase Negative

In recent years, several other Staphylococcus

species have been implicated in human

infections, notably S. lugdunensis, and S. infections, notably S. lugdunensis, and S.

caprae

Common abbreviations for coagulase-negative

Staphylococcus species are CoNS and CNS

Pathogenesis and Immunity -

Staphylococcal Toxins

S. aureus produces many virulence factors, including at least 5 cytolytic or membrane-damaging toxins (alpha, beta, delta, gamma, and Pantovalentine [P-V] leukocidin); 2 exfoliative toxin; 8 enterotoxins (A-E, G-I), and exfoliative toxin; 8 enterotoxins (A-E, G-I), and toxic shock syndrome toxin-1 (TSST-1)

The cytolytic toxins have also been described as haemolysins, but this is misnomer because the activities of the first 4 toxins are not restricted solely to red blood cells and P-V leukocidin is unable to lyse erythrocytes



The enterotoxins and TSST-1 belong to a class of polypeptides known as superantigens

Type of toxins:

Alpha toxins Alpha toxins

Beta toxins

Delta toxins

Gamma toxins

Panton-Valentine [P-V] leukocidin

Exfoliative toxins

Enterotoxins

Toxic Shock Syndrome Toxin-1 (TSST-1)



Types:

Coagulase

Catalase

Hyaluronidase Hyaluronidase

Fibrinolysin

Lipases

Nuclease

Penicillinase

Clinical Diseases -

Staphylococcus aureus

It causes diseases through the production of toxin or through the direct invasion and destruction of tissue

The clinical manifestations of some The clinical manifestations of some staphylococcal diseases are almost exclusively the result of toxin activity, whereas other diseases result from the proliferation of the organisms, leading to abscess formation and tissue destruction

Clinical Diseases -


In the presence of a foreign body, significantly fewer staphylococci are necessary to establish disease

Patients with congenital diseases associated with an impaired chemotactic or phagocytic response (e.g. Job-Buckley syndrome, Wiskott-Aldrich syndrome, chronic granulomatous disease) are more susceptible to staphylococcal diseases

Clinical Diseases -


Staphylococcal Scalded Skin Syndrome (SSSS)

Ritters disease or SSSS - characterised by the

abrupt onset of a localised perioral erythema

(redness and inflammation around the mouth)

that covers the entire body within 2 days

Slight pressure displaces the skin and large

bullae or cutaneous desquamation of the

epithelium

Clinical Diseases -


Staphylococcal Scalded Skin Syndrome (SSSS)

The epithelium becomes intact again within 7 -10 days when the protective antibodies appear

Scarring does not occur because only the top Scarring does not occur because only the top layer of epidermis is sloughed

Low mortality; death does occur as a result of secondary bacterial infection of the denuded skin areas

Bullous impetigo - localised form of SSSS

Staphylococcal Scalded Skin Syndrome

Bullous Impetigo

Clinical Diseases -

Staphylococcal Food Poisoning

One of the most common food-borne illness, is an intoxication rather than an infection

Caused by bacterial toxin present in food, especially in processed meats (e.g. ham and salted especially in processed meats (e.g. ham and salted pork, custard-filled pastries, potato salad, and ice cream)

Staphylococcal food poisoning results from contamination of the food by a human carrier and not animal

Food preparation by individual with obvious infection or with asymptomatic nasopharyngeal colonisation

Clinical Diseases -


Heating of food will kill the bacteria but not inactivate the heat-stable toxin

After ingestion of contaminated food, the After ingestion of contaminated food, the onset of disease is abrupt and rapid, with a mean incubation period of 4 hours and symptoms generally lasting fewer than 24 hours

Symptoms: severe vomiting, diarrhoea, and abdominal pain or nausea

Clinical Diseases -


Contaminated food can be tested for toxins at

a public health facility

Treatment is for the relief of the abdominal

cramping and diarrhoea and for the

replacement of fluids

Antibiotic therapy is not indicated because the

disease is mediated by preformed toxin and

not by replicating organisms

Clinical Diseases -


Certain strains of S. aureus can also cause

enterocolitis, which is manifested clinically by

watery diarrhoea, abdominal cramps, and

feverfever

Enterocolitis occurs primarily in patients who

have received broad-spectrum antibiotics,

which suppress the normal colonic flora and

permit the growth of S. aureus

Clinical Diseases -

Toxic Shock Syndrome

The disease is initiated with the localised

growth of toxin-producing strains of S. aureus

in the vagina or a wound, followed by release in the vagina or a wound, followed by release

of the toxin into the bloodstream

Clinical manifestations starts abruptly and

include fever, hypotension, and a diffuse

macular erythematous rash

Clinical Diseases -


Multiple organ systems are also involved, and

the entire skin including the palms and soles

desquamatesdesquamates

The risk of recurrent disease is as high as 65%

50% of patients with TSS fail to develop

protective antibodies after their disease

dissolves

Clinical Diseases -

Cutaneous Infections

Localised, pyogenic staphylococcal infections

include impetigo, folliculitis, furuncles, and

carbuncles

Impetigo, a superficial infection affecting Impetigo, a superficial infection affecting

mostly young children, occurs primarily on the

face and limbs

Folliculitis is a pyrogenic infection in the hair

follicles

Folliculitis and Impetigo

Clinical Diseases -

Cutaneous Infections

Furuncles (boils) - an extension of folliculitis,

are large, painful, raised nodules with an

underlying collection of dead and necrotic

tissuetissue

Carbuncles occur when furuncles coalesce

and extend to the deeper subcutaneous

tissue. Multiple sinus tracts are usually

present. Patients presented with chills and

fevers, indicating the systematic spread of

staphylococci via bacteremia to other tissues

Furuncles and Carbuncles

Clinical Diseases -

Bacteremia and Endocarditis

Although bacteremias caused by most other organisms originate from an identifiable focus of infection, such as an infection of the lungs, urinary tract or GI tract, the initial foci of urinary tract or GI tract, the initial foci of infection in approximately of patients with S. aureus bacteremias are not known

Hospital acquired through surgical procedure or result from the continued use of a contaminated IV catheter

Clinical Diseases -

Bacteremia and Endocarditis

S. aureus bacteremias, particularly prolonged episodes are associated with dissemination to other body sites, including the heart

Acute endocarditis caused by S. aureus is a Acute endocarditis caused by S. aureus is a serious disease with a mortality rate approaching 50%

Initial symptoms: non-specific influenza-like symptoms. Patients condition can deteriorate rapidly and include disruption of cardiac output and peripheral evidence of septic embolisation

Endocarditis

Clinical Diseases -

Pneumonia and Empyema

S. aureus respiratory disease can develop after the aspiration of oral secretions or from the haematogenous spread of the organism from a distant sitea distant site

Aspiration pneumonia is seen primarily in the very young, the aged, and patients with cystic fibrosis, influenza, chronic obstructive pulmonary disease, and bronchiectasis

Clinical Diseases -

Pneumonia and Empyema

Haematogenous pneumonia is common for

patients with bacteremia or endocarditis

Empyema occurs in 10% of patients with Empyema occurs in 10% of patients with

pneumonia, and S. aureus is responsible for

of all cases

Empyema and Pneumonia

Clinical Diseases -

Osteomyelitis and Septic Arthritis

Osteomyelitis can result from the

haematogenous dissemination to bone, or it

can be a secondary infection resulting from

trauma or the extension of disease from an trauma or the extension of disease from an

adjacent area

The haematogenous osteomyelitis that is

seen in adults commonly occurs in the form of

vertebral osteomyelitis and rarely in the form

of infection of the long bones

Clinical Diseases -


Brodies abscess is a sequestered focus of

staphylococcal osteomyelitis that arises in the

metaphyseal area of a long bone and occurs

only in adultsonly in adults

S. aureus is the primary cause of septic

arthritis in young children and in adults who

are receiving intra-articular injections or who

have mechanical abnormal joints

Clinical Diseases

Staphylococcus epidermidis and other

coagulase-negative staphylococci

Endocarditis Endocarditis

Catheter and shunt infections

Prosthetic joint infections

Urinary tract infections

Laboratory Diagnosis

Microscopy - Gram positive cocci (clusters on

agar media and appear as single cells or small

groups in clinical specimens)

Culture - blood agar (haemolysis cause by Culture - blood agar (haemolysis cause by

cytotoxins, particularly toxins)

Serology - antibodies to cell wall teichoic acids

Identification - biochemical tests (positive

reactions for coagulase [clumping factor],

heat-stable nuclease, alkaline phosphatase

and mannitol fermentation)

Question

What are the special characteristics of

Staphylococcus?

What are the virulence factors of What are the virulence factors of

Staphylococcus?

What are the diseases that can be caused by

Staphylococcus?

Medical Microbiology I - Lecture8

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