clinicalbacteriolog handout to teach

Clinical bacteriology:Bacterial Skin Infection: 

Clinical bacteriology: Bacterial Skin Infection Sasima Eimpunth, MD. Faculty of Medicine Naresuan University February 2nd, 2007

Clinical bacteriology: 

Clinical bacteriology กายวิภาคและกลไกการป้องกันของระบบผิวหนัง ปัจจัยชักนำที่ทำให้เกิดการติดเชื้อ โรคติดเชื้อแบคทีเรียต่างๆ ที่พบได้บ่อยในผิวหนัง/ แบคทีเรียที่เป็นสาเหตุ/ อาการของโรค การแปลผลทางห้องปฏิบัติการที่สำคัญ การรักษาโรค

Anatomy of the skin: 

Anatomy of the skin

Pathogenesis of bacterial infection of the skin: 

Pathogenesis of bacterial infection of the skin Bacterial infection of the skin Host defense mechanism Pathogen Portal of entry

ปัจจัยชักนำที่ทำให้เกิดการติดเชื้อ (Pathogenesis of bacterial infection of the skin): 

The host-bacterial relationship in infection of the skin, as in infectious disease in general, involves three major elements the pathogenic properties of the organism the portal of entry the host factors ปัจจัยชักนำที่ทำให้เกิดการติดเชื้อ (Pathogenesis of bacterial infection of the skin)

Pathogenicity of the microorganism: 

Pathogenicity of the microorganism The disease-producing capacity The invasive potential (often based on antiphagocytic surface components) The toxigenic properties of the organism Exotoxin : S.aureus (TSST-1) Endotoxin : gram-negative (lipopolysaccharide-LPS) TNF, IL-1

The Shwartzman reaction: 

The Shwartzman reaction An intensified response in experimental animals to bacteria containing LPS or to purified LPS itself Systemic LPS injected intravenously twice, 24h apart Disseminated intravascular coagulation in rabbits Localized LPS intradermally + a second (intravenous) injection Hemorrhagic necrosis of the skin at the site of intradermal introduction Poor tissue perfusion from capillary blockage by neutrophils + plateles + local fibrin formation TNF is the major mediator Purpura fulminans (10-20% of cases of meningococcal sepsis)

Portal of entry: 

Portal of entry Vascular wall is often the primary site of skin involvement during bacteremic infection Skin

Defense mechanism of the skin: 

Defense mechanism of the skin Intact skin Immunologic mechanism Local resistance Low pH Natural antibacterial substances in the sebaceous secretions Circulating immunoglobulins Moisture content The indigenous cutaneous microflora Bacterial interference the “normal cutaneous flora”

Intact skin: 

Intact skin ผิวหนังปกติของคนที่สุขภาพดีมีความทนทานสูงต่อการบุกรุกของแบคทีเรียหลายชนิดที่ต้องเผชิญอยู่ตลอดเวลา เป็นการยากที่จะทำให้มีการติดเชื้อเช่น impetigo, furunculosis, หรือ cellulitis ในสัตว์ทดลองหรืออาสาสมัครมนุษย์ที่ผิวหนังปกติ เชื้อก่อโรคเช่น Streptococcus pyogenes (group A streptococcus) และ S. aureus จะทำให้เกิด cellulitis และ furunculosis ผ่านผิวหนังที่มีการแยก (disruption) เช่น จากแมลงกัด รอยถลอก หรือได้รับสิ่งแปลกปลอมเข้าไป Elek พบว่าการมีเส้นไหมในร่างกาย ทำให้ปริมาณของเชื้อ S.aureus ที่ต้องการในการทำให้เกิดฝีในผิวหนังมนุษย์ ลดลงถึง 10,000 เท่า

Immunologic mechanism: 

Immunologic mechanism การรักษาด้วยยากดภูมิคุ้มกันทำให้ผู้ป่วยเสี่ยงต่อการติดเชื้อที่มี lower intrinsic pathogenicity Enhanced susceptibity of the compromised host is not understood but undoubtedly involves specific and nonspecific factors Immunocompetence nutritional state integrity of the cutaneous barrier Innate immunity Adaptive immunity

Local resistance: 

Local resistance เมื่อนำแบคทีเรียไปทาที่ผิวหนัง พบว่า ไม่สามารถทะลุชั้นขี้ไคลของผิวหนังปกติได้ มีการลดจำนวนลงอย่างรวดเร็ว ปัจจัยที่มีผลต่อการปกป้องเฉพาะที่ (local resistance) ต่อการแบ่งตัวและการติดเชื้อแบคทีเรียนี้ ยังไม่ทราบชัดเจน

ปัจจัยที่มีผลต่อการปกป้องเฉพาะที่ (local resistance): 

ปัจจัยที่มีผลต่อการปกป้องเฉพาะที่ (local resistance) Low pH Natural antibacterial substances in the sebaceous secretions unsaturated long-chain fatty acids Linoleic and linolenic acids Inhibit S.aureus > coagulase-negative staphylococci (the normal skin flora) Circulating immunoglobulins Moisture content the indigenous cutaneous microflora Bacterial interference the “normal cutaneous flora”

Pathogenesis of bacterial infection of the skin: 

Pathogenesis of bacterial infection of the skin Bacterial infection of the skin Host defense mechanism Pathogen Portal of entry

Fever + cutaneous lesions: 

Fever + cutaneous lesions Problem in medicine Treatable etiology (bacterial, fungal, herpes group viruses) should always be raised initially

Slide16: 

The timely recognition of the cutaneous clues of bacteremia may probide the early warning to consider life-threatening infections due to organisms such as Pseudomonas aeruginosa Vibrio vulnificus Salmonella typhi Staphylococcus aureus Neisseria meningitides

โรคติดเชื้อแบคทีเรียต่างๆ ที่พบได้บ่อยในผิวหนัง/ แบคทีเรียที่เป็นสาเหตุ/ อาการของโรค: 

Bacterial infections involving the skin Primary pyodermas Secondary bacterial infections Cutaneous involvement in systemic bacterial infections (exclusive of venereal diseases and mycobacterial infections) Infections due to unusual organisms โรคติดเชื้อแบคทีเรียต่างๆ ที่พบได้บ่อยในผิวหนัง/ แบคทีเรียที่เป็นสาเหตุ/ อาการของโรค

Primary bacterial infections (Pyodermas): 

Primary bacterial infections (Pyodermas) The invasion of normal skin by a single species of pathogenic bacteria Treatment aimed at the bacterial pathogen almost universally results in cure of the lesion

Secondary bacterial infections: 

Secondary bacterial infections Develop in areas of already damaged skin the bacteria may aggravate and prolong the disease broken or bruised skin often show a mixture of organisms on culture The appearance of these lesions is not characteristic The result of antibacterial treatment is much less clear-cut, because it has no effect on the underlying process

Primary pyodermas: 

Primary pyodermas Impetigo Folliculitis Furuncles and carbuncles Paronychia Ecthyma Erysipelas Cellulitis Lymphangitis Erythrasma Bacillary angiomatosis

Impetigo : 

Impetigo Group A streptococci Staphylococcus aureus

Folliculitis : 

Folliculitis S.aureus Lowered host resistance Opportunistic organisms Gram-negative bacilli Associated with water exposure Pseudomonas aeruginosa

Furuncles and carbuncles : 

Furuncles and carbuncles S.aureus (almost always)

Paronychia : 

Paronychia S.aureus Group A streptococci Chronic form P.aeruginosa Hand trauma Chronic moisture

Ecthyma : 

Ecthyma Group A streptococci S.aureus Usually a consequence of neglected impetigo From a 1° pyoderma Preexisting dermatoses Site of trauma

Erysipelas : 

Erysipelas Group A streptococci (most common) Face or lower extremities

Cellulitis : 

Cellulitis S.aureus Group A streptococci Compromised hosts: a variety of other organisms

Lymphangitis : 

Lymphangitis Group A streptococci S.aureus (occasionally) other organisms

Erythrasma : 

Erythrasma Corynebacterium minutissimum Wood’s lamp: coral red fluorescence

Bacillary angiomatosis: 

Bacillary angiomatosis Bartonella henselae

Secondary bacterial infection: 

Secondary bacterial infection Complicating preexisting skin lesions Distinctive dermatologic clinical entities Secondary folliculitis Infectious eczematous dermatitis Intertrigo Pilonidal and sebaceous cysts Infectious gangrene Necrotizing ulcers

Intertrigo : 

Intertrigo S.aureus Group A streptococci (occasionally)

Infectious gangrene: 

Infectious gangrene Necrotizing fasciitis Mixed organisms

Necrotizing ulcers : 

Necrotizing ulcers Decubitus ulcer S.aureus Coliforms Pseudomonas Bacteroieds Clostridium perfringens

Cutaneous involvement in systemic bacterial infections (exclusive of venereal diseases and mycobacterial infections): 

Cutaneous involvement in systemic bacterial infections (exclusive of venereal diseases and mycobacterial infections) Bacteremia Pseudomonas aeruginosa Cutaneous lesions without direct microbial involvement of the skin Bacterial endocarditis Streptococcosis (group A) : purpura fulminans Chronic meningococcemia S.aureus including toxin-mediated syndromes- “scalded skin” and “toxic shock” Erythema nodosum Bacteroids Purpura (other than purpura fulminans and DIC) associated with bacteremias (S.aureus;gram-negative bacteria)

Pseudomonas aeruginosa: 

Pseudomonas aeruginosa “Ecthyma gangrenosum” A gun-metal gray, infarcted lesion with surrounding erythema evolves into a necrotic black or gray-black eschar and surrounding erythema Vesicles and bullae Gangrenous cellulitis Macular or papular nodular lesions

Bacterial endocarditis: 

Bacterial endocarditis Subacute BE Petechiae & hemorrhages Subungual “splinter hemorrhages” Osler’s nodes (painful) Pads of fingers & toes Thenar & hypothenar Arms Janeway lesions (painless) Palms or soles

Streptococcal (group A) infection : 

Streptococcal (group A) infection “Purpura fulminans” Acute DIC Localized, massive ecchymoses, often with sharp, irregular (“geographic”) borders Erythema nodosum Guttate psoriasis

Staphylococcal scalded skin syndrome: 

Staphylococcal scalded skin syndrome 4S S.aureus Exfoliative toxin A or B Clinical Generalized indistinct erythemas Flaccid bullae, large denudedareas similar to scalding Generalized desquamation with characteristic large sheets

Staphylococcal toxic shock syndrome: 

Staphylococcal toxic shock syndrome Exotoxin TSST-1 Diffuse macular erythroderma Fever, hypotension, conjunctival injection Nonpitting edema Strawberry tongue Desquamation of palms and sole occurs 1 or 2 weeks later

Infections due to unusual organisms: 

Infections due to unusual organisms Cutaneous diphtheria Listeriosis (Listeria monocytogenes) Animal-borne or associated diseases Diseases associated with particular geographic locations

Animal-borne or associated diseases: 

Animal-borne or associated diseases Bacillus anthracis: cutaneous anthrax (malignant pustule) Pasteurelloses and related organisms Francisella tularensis (Tularemia) P.multocida: produces infection at site of animal (usually cat bite) Yersinea pestis (plague) Brucellosis: skin lesions are rare in this systemic disease Rat-bite fever Streptobacillus moniliformis (Haverhill fever) Spirillum minus (sodoku) Erysipeloid (Erysipelothrix rhusiopathia) Leptospirosis (Leptospira interrogans serotypes) Sreptococcus iniae infections due to Capocytophaga canimorsus (dog bite) Rhodococcus equi infection Glanders (Burkholderia mallei; formerly Pseudomonas pseudomallei)

Anthrax : 

Anthrax “Malignant pustule” Bacillus anthracis

Erysipeloid : 

Erysipeloid Erysipelothrix rhusiopathiae

Diseases associated with particular geographic locations: 

Diseases associated with particular geographic locations Bartonellosis (Carrison’s disease) Melioidosis (Burkholderia pseudomallei) infections due to Vibrio spp. (V.vulnificus, V.cholerae non 01) Rhinoscleroma (Klebsiella rhinoscleromatis)

Vibrio vulnificus: 

Vibrio vulnificus Large hemorrhagic bullae on the extremities or trunk Raw oysters

Slide47: 

Gram-negative curved bacilli

การแปลผลทางห้องปฏิบัติการที่สำคัญ: 

การแปลผลทางห้องปฏิบัติการที่สำคัญ Direct examination of aspirates and biopsies Methods of culture of skin material Other diagnostic procedures Fluorescent antibody Other immunologic methods Polymerase chain reaction (PCR)

Direct examination of aspirates and biopsies: 

Direct examination of aspirates and biopsies Appropriate sampling Interpretation of Gram-stained smears Use of selective growth media for culturing

Appropriate sampling: 

Appropriate sampling Avoid contamination The “normal skin flora” can confuse the interpretation The finding of a potential pathogen (e.g., S.aureus or P.aeruginosa) is usually equated with the presence of disease The proper decision concerning the presence of a bacterial disease Correlate The clinical appearance of the lesion The bacteriologic data can one reach

Gram staining: 

Gram staining Guide decisions on early antibiotic therapy before a culture result a very rapid method Number of bacteria Type of bacteria The character of the inflammatory exudate Skin contaminants present in low concentration often clumped in characteristic microcolonies (growth in skin crypts) usually not associated with polymorphonuclear leukocytes

Gram positive cocci: 

Gram positive cocci Streptococcus spp. Staphylococcus spp. www.uphs.upenn.edu

Gram negative rod: 

Gram negative rod Enterobacteriaceae E.coli Vibrio spp. (curved) www.uphs.upenn.edu

Gram negative diplococci: 

Gram negative diplococci Neisseria spp. Neisseria gonorrhea www.uphs.upenn.edu

Needle aspiration: 

Needle aspiration Superficial erysipelas lesions - generally unrewarding Slightly better-aspiration culture of cellulitis Hook et al Aspirates from the advancing edge - positive cultures only 10% of patients Culture of skin punch biopsy specimens from the leading edge - positive only 20% of patients In another study Needle aspiration cultures of the leading edge of erythema in cellulitis - the yield of pathogenic bacteria was low ( 15%)

Slide56: 

Other studies Patients with underlying conditions (such as diabetes mellitus and neoplastic disease) Needle aspiration of the leading edge of cellulitis The point of maximal inflammation - a higher yield (~50%) positive cultures In children (5%) Sampling deeper cellulitic lesions and bullae associated with acute infections

Slide57: 

Sterile saline injection (a lesion that initially yields no aspirate) - bacteriostatic agent-free solutions In circumstances where no data are available from needle aspiration, a surgical biopsy may yield information that is life-saving. Local lesions of the skin and subcutaneous tissues in immunocompromised patients should always be biopsied if aspiration fails to define a pathogen.

การรักษาโรค: 

การรักษาโรค Antibiotic therapy Systemic antibacterial agents Topical antibacterial agents Local wound care Underlying skin disease General medical condition

Topical antibacterial agents: 

Topical antibacterial agents Prevent, suppress, bacterial growth in burns and other open lesions May precipitate contact dermatitis Can be absorbed toxic levels Very little evidence that they add a great deal therapeutically An exception Burn patients- Sulfamylon (mafenide) acetate cream or of 0.5% silver nitrate solution

Slide60: 

The useful topical antibacterial agents Acetic acid (1-5%) Pseudonomas nail and toe web infections bacitracin (500 units per milliliter or gram) selected superficial S.aureus and streptococcal lesions may be associated with a cutaneous hypersensitiviy reaction Neomycin (0.5% ointment) and gentamicin (0.17% cream) mixed gram-negative bacteria Mupirocin (2% ointment) various streptococci and S.aureus a safe and effective treatment of impetigo Fucidic acid cream or ointment

Broad-spectrum antiseptics: 

Broad-spectrum antiseptics antibacterial with nonirritating properties Povidone-iodine (Betadine) most gram-positive and gram-negative bacteria but does not persist in the skin to provide a residual action Chlorhexidine gluconate (4% solution) combines broad antibacterial properties with prolonged action due to local accumulation An alcoholic preparation can be used prophylactically or to treat local wounds and superficially infected dermatoses

Thank you: 

Thank you