DERMAL AND MUSCULAR INFECTIONS MSC TID 1 28 TH APRIL 2010 Nyakundi BM

DERMAL AND MUSCULAR INFECTIONS Infections of the skin can be primary eg primary pyodermas or secondary eg to burns or surgical wounds.Primary pyodermas include;- impetigo,furuncles,carbuncles,chancriform lesions,cellulitis.There are many possible pathogens that can be found in abcesses,burns, wounds and draining sinuses.

PATHOGENS Bacterial-Gram positive- Staphylococcus aureus,Streptococcus pyogenes,Enterococcus species,Anaerobic Streptococcus,Clostridium perfringens,Actinomyces Israeli Bcterial Gram Negative- Proteus species,Pseudomonas aeruginosa,Escherichia coli,Bacteroides,Klebsiella and Pasteurella species. Also Mycobacterium leprae,ulcerans,tuberculosis and marinum.

Dermal Infections These can be primary Or secondary infections eg on burns,wounds. Also secondary infections can occur as a result of bacteraemia eg in staph aureus,Group A streptococci and Neisseria meningitidis

Sumary of predisposing factors Minor injuries,insect bites,friction blisters,superficial fungal infections,burns,use of indwelling catheters in children and minor surgical procedures.

Overview of the various Bacterial Pathogens Staph aureus is the commonest pathogen isolated from subcutaneus abscesses and skin wounds.Penicillin and methicillin resistant strains are common causes of hospital acquired wound infections. P.aeruginosa is associated with infected burns and hospital acquired infections. Chronic leg ulceration is common in those with sickle cell disease.The commonest patogens isolated-S aureus,P aeruginosa,S pyogenes and bacteriodes speceies. Mycobacterium tuberculosis is associated with “cold” abcsesses

Overview of the various bacterial pathogens Yersinia pestis causes plague.It is called bubonic plague when the organisms infects a lymph gland and produces a painful swelling called a bubo.The organism can be found in the fluid aspirated from the bubo Bacillus anthracis causes anthrax with the cutaneous form of the disease producing a pustule on the hand or arm with highly contagious fluid.

Overview of the various bacterial pathogens E coli,Proteus species,P aeruginosa and Bacteroides species are the pathogens most frequently isolated from abdominal abscesses and wounds. C perfringens is found mainly in deep wounds where anaerobic conditions exist. A Israeli and other species of Actinomyces cause Actinomycosis-small yellow granules can be found in pus from a draining sinus.

Overview of the various bacterial pathogens M leprae can be found in skin smears of lepromatous leprosy and occassionally in borderline forms of the disease. T carateum causes pinta-central america,colombia,T pertenue causes yaws esp in west africa Vincents organisms (Borrelia vincenti with gram neg anaerobic fusiform organisms) are associated with tropical ulcers. Esp in malnourished childrens legs.Staphylococci and streptococci are secondary invaders.

SKELETAL MUSCLE INFECTIONS Classification of infectious myositis; This can be by the type of process involved ; 1.Pyogenic and predominantly localized- (spreading by contiguity) 2.Non pyogenic and predominantly generalized

Pyogenic,localized infections Bacteria invade muscle either from contigous sites ( eg skin and subcutaneous abscesses,penetrating wounds, decubitus ulcers,osteomyelitis) or by haematogenous spread from a distant focus. Clinical pattern includes pyomyositis,gas gangrene,non clostridial (crepitant)myositis,psoas abscess.

Clinical patterns and principal aetiological agents 1.Pyomyositis- staph aureus 2.Gas gangrene- clostridium perfringens 3.Non clostridial (crepitant) myositis; a)anaerobic streptococcal gangrene-caused by peptostreptococcus,group A streptococci/S aureus b)Group A streptococcal necrotizing myositis c)synergistic non clostridial anaerobic myonecrosis- caused by mixed infections-Bacteroides and other anaerobic gram neg non spore forming bacilli ; peptostreptococci and various streptococci;E coli,klebsiella,Enterobacter. d)Infected vascular gangrene-same as (c) above. e)Aeromonas hydrophila myonecrosis

Clinical patterns cont. 4. Psoas abscess- caused by Gram- negative bacilli;staph aureus,M. tuberculosis

Clinical patterns Non pyogenic and predominantly generalized 1.Myalgias-caused by bacteraemia eg meningococcaemia,rickettsioses eg rocky mountain spotted fever. 2.pleurodynia-coxsakie B 3.myalgias with eosinophilia- trichinosis,cysticercosis 4.myalgia secondary to other viruses

Laboratory diagnosis Collection and transport of pus,ulcer material and skin specimens; Pus from an abscess is best collected at the time when the abscess is incised and drained,or after it has ruptured naturally. Avoid contamination of the specimen with commensal organisms from the skin. A specimen from a wound should be taken before and antiseptic dressing is applied.

Laboratory diagnosis cont. When mycetoma is suspected; Obtain a specimen from a draining sinus tract using a sterile hypodermic needle to lift up the crusty surface over the sinus opening.This ensures that the pus obtained is free from secondary organisms and the draining granules can be seen clearly and removed for microscopic examination. Transfer the pus to a sterile container.

Lab diagnosis-specimens When tuberculosis is suspected,aspirate a sample of the pus and transfer it to a sterile container When the tissue is deeply ulcerated and necrotic,aspirate a sample from the side wall of the ulcer using a sterile needle and syringe,transfer to sterile container. Fluid from pustules,buboes,blisters-use sterile needle and syringe for aspiration and transfer to sterile container

Lab diagnosis Serous fluid from skin ulcers may contain treponemes;collect a drop of exudate onto a clean cover glass and invert it onto glass slide then for dark ground microscopy. Skin smears for mycobacterium leprae. Specimens from patients with suspected plague/anthrax are highly infectious- sould be labelled HIGH RISK and handled with care

Specimen description 1.Gross examination-If patient is suspected to have mycetoma or actinomycosis, report the apperance of the specimen/granules. 2.Microscopic examination-Gram stain,ziehl- nielsen stain;also Giemsa stain is bubonic plague is suspected and polychrome loefflers methylene blue when anthrax is suspected.Also dark field microscopy when yaws, pinta suspected.

Lab diagnosis-culture 3.Culture of specimen; A)Innoculation done on blood agar to isolate staph aureus and streptococci,add a bacitracin disc if streptococci are seen in gram smear.- incubate aerobically-candle extinction jar-,35-37 C in CO2 B)on mac conkey agar to isolate gram negative rods-incubate aerobically C)Into cooked meat medium or thioglycollate broth.Cooked meat should be C for up to 72 hrs.Subculture at 24 hrs and if need be 48 and 72 hrs

Anaerobic culture When anaerobic infection is suspected( specimen foul smelling or gram smear shows mixed anaerobic flora,a second blood agar plate is innoculated and incubated anaerobically for upto 48 hrs The anaerobic blood agar may be made selective by adding neomycin-this inhibits majority of anaerobic facultative gram negative rods. To aid detection of anaerobes, a metronidazole disc can be added to the anerobic blood plates;aerobes will grow to the disc,and many anaerobes will show a zone of inhibition.

Anaerobic culture results Anaerobic blood agar and cooked meat culture; Clostridium perfrigens( hydrogen sulfide gas production,reddening but no decomposition of meat – saccharyolytic reation), on anaerobic blood agar- double zone haemolysis B fragilis-on cooked meat –decomposition,blackening of the meat- foul smelling proteolytic reaction;on anaerobic blood agar-non haemolytic grey colonies Peptostreptococcus- on cooked meat produces hydrogen sulphide gas; on anaerobic blood agar small non hemolytic colonies produced;gm positive cocci and resistant to metronidazole disc.

Other tests For mycobaterium tuberculosis and ulcerans- culture Yersinia pestis- blood or bubo aspirate culture.when plague is suspected, initial smear report should indicate if bipolar organisms were seen.

treatment Most anaerobic infections are caused by penicillin susceptible bacteria with the exception of infections originating from the intestinal tract or vagina. Such infections contain B fragilis, which produces Beta lactamase and is resistant to penicillins ampicillin and most cephalosporins. Treatment is by clindamycin,metronidazole,chloramphenicol.