Streptococci and enterococci

Streptococci and enterococci

Streps are nasty ….

• Pneumococcus kills a million patients a year (mostly under 5 years old)

• Streptococcus pyogenes used to cause hospital epidemics with 90% mortality

• Bacterial endocarditis pre-antibiotics had 100% mortality

Streptococci and enterococci

• GPC, chains or pairs, catalase negative

• Alpha, beta or non-haemolytic

• Mouth, pharynx, gut, vagina

Bacteriology of the

streptococci

A - G

Betahaemolysis

Alpha

Pneumococci oftengrow as “draughtsman”colonies

Oral streptococci (1)

• 50% of population of tongue and saliva• 25% of population of supragingival & gingival

plaque• Most are alpha haemolytic (“viridans

streptococci”)

Oral streptococci (2)

Samaranayake 3rd ed. Chapter 11

Oral streptococci (3)

• Major part of oral flora• Access to bloodstream: bacteraemia• Roles in disease

• Infective endocarditis• Caries (especially S. mutans)• Abscesses–Oral (dentoalveolar, periodontal)– Extra-oral: Anginosus group

Mutans streptococci

• Group name for 7 different species

• S. mutans: important role in caries– Associated with initiation & progression – Animal studies

Streptococcus mutans and caries: why?

• Sugar transport mechanisms• Multiple

• Acid production (acidogenic)• Rapid production, including lactic acid

• Acid tolerant (aciduric)• Extracellular polysaccharides

• Part of plaque matrix

• Intracellular polysaccharides

Active immunisation

• Antigens from mutans streps successfully used as vaccines to prevent caries in animal models

• Potential to induce autoimmune damage?• Purified antigens which do not cross react

now used in research• ?? Further development – economic

constraints etc

Passive immunisation: experimental studies

• Suppress mutans streps with chlorhexidine• Administer monoclonal antibodies to mutans antigen • Recolonisation by mutans streps inhibited• Use transgenic plants to make dimeric MAbs

Replacement therapies

• Use engineered strains of S. mutans• Hillman’s work

– Developed a strain with LDH knocked out– This strain also produces an antibiotic which gets rid of other

strains of S. mutans (mutacin 1140)– Aiming for clinical trial …

• More info: see Marsh & Martin, pages 142-3

Beta-haemolytic streps

• Lancefield types A,B,C,D,F,G• Type A usually = Streptococcus pyogenes• Type B = S. agalactiae

Rebecca Lancefield

S. pyogenes

• Virulence factors: M proteins; erythrogenic toxins; streptolysins; hyaluronidase

• Pharyngitis and local complications• Scarlet fever• Skin and soft tissue infections• Streptococcal toxic shock syndrome• Bacteraemia and septicaemia

Pharyngitis: about a third of cases are caused by beta-haemolytic streptococci

Scarlet fever

“Circumoral pallor”

Streptococcal pyrogenic exotoxins; Spe A associated with scarlet fever (previously “erythrogenic toxin”)

Impetigo:

Streptococcus pyogenes

and/or

Staphylococcus aureus

Erysipelas:limb

Distinctborder

Cellulitis:often streptococcal

Cellulitis caused by Staphylococcus aureus

Skin and soft tissue infections: different planes involved

UvulitisCauses include Haemophilus influenzae type b,S. pyogenesMay progress to respiratory obstruction

Acute streptococcal gingivitis“This condition affects the gingivae which can result in severe

illness. The gingivae become red, swollen and full of fluid (oedematous), the temperature is raised and the regional lymph nodes are also enlarged.

Lancefield Group A streptococci (S. pyogenes) canbe isolated from the affected gingivae. This disease is usually preceded by a sore throat and hence it is possible that there is a direct spread of S. pyogenes from throat to gingivae.”

Oral Microbiology 5th ed. 2009

S. pyogenes

• Non-suppurative complications: acute rheumatic fever (ARF), acute glomerulonephritis (AGN)

• ARF: heart tissues, joints and other tissues• AGN: kidneys

Group B strep neonatal sepsis:septicaemia, pneumonia, meningitis

How about a vaccine?

Prophylactic penicillin can be givento the mothers before birth in selected cases

Group C and group G streps

• Pharyngitis • Skin and soft tissue infections• Toxic and post-streptococcal complications

rare

Group D cocci

• Enterococcus species and certain streptococci• Enterococci: nosocomial infections; UTI• Increasing isolations of vancomycin-resistant

enterococci (VRE)• “S. bovis”: isolation from blood

(bacteraemia, endocarditis) strongly associated with early colon cancer

“S. bovis”

• “S. bovis” has now been split into several new, named species/subspecies.

• These include S. gallolyticus,S. infantarius & S. pasteurianus

Alpha haemolytic streptococci

• S. pneumoniae – the pneumococcus; capsulated

• “Viridans streptococci”

Viridans streptococci …

Collectively, commensal streptococci are often called ‘viridans streptococci’ which refers to their -haemolytic property (viridis = green). Not quite logically, this term also includes the few streptococci, such as those of the salivarius and mutans groups, that induce neither not haemolysis. Moreover, in common usage, the term excludes Str. pneumoniae …

Medical Microbiology 17th ed, 2007Greenwood D et al

S. pneumoniae (pneumococcus)

• Pneumonia• Meningitis• Bacteraemia/septicaemia• Upper respiratory tract infections• Etc etc

Pneumococcal infections: some risk factors

Pneumococcal vaccines

• Polyvalent polysaccharide

• Conjugate vaccine is newer and better (routine childhood vaccine in USA)

Oral streptococciare a commoncause of native valveendocarditis

Vegetation

Prevention of Infective Endocarditis

• Clinical teachers will discuss current thinking & FoD practice

– Involve cardiologist caring for patient

– Stay up to date: read your dental journals

But don’t forget …

Recommendation 1.1.5

Any episodes of infection in people at risk of IE should be investigated and treated promptly to reduce the risk of endocarditis developing

NICE Clinical Guideline 64 (UK, 2008)

… and …

Healthcare professionals should offer people at risk of IE … information about prevention, including …

• the importance of maintaining good oral health

NICE Clinical Guideline 64 (UK, 2008)

Joint prostheses

• Infection usually leads to pain, loss of function … removal/?replacement

• Need for dental prophylaxis contentious

Treatment

• Resistance problems especially in– Pneumococci– Enterococci

• Need bactericidal regimen if bacterial endocarditis

• E.g. benzylpenicillin + gentamicin