Micro Ch 33 Bacterial Skin Diseases

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skin infxns occur when a

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microbe directly infects skin or gains entry into host via some portal, resp/genital etc and spreads to skin

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wound infxns imply

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that skin or mucous membrane barrier is broken so that infectious agents may enter tissue where they are normally precluded

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leprosy bacillus, hpv, and ringworm result from

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direct infection of skin. other agents normally do so by access thru a wound or break in skin

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type of wound infected is imp to

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the types of disease that may result

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puncture

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results in crushed tissue with dead tissue debris and destroyed arterioles and venues. Anaerobic conditions develop and anaerobic and bacteria are often found at such sites, esp when the puncture was d/t something in the soil where anaerobes are abundant conditions

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a wound that perforates intestinal tract will

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allow intestinal organism that may be perfectly harmless in GI tract to flourish in peritoneal cavity

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if a wound contains foreign material

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microbial growth is protected around it which is why foreign objects such as rocks and sticks must be removed from the wound site

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burns are a serious form of damage to skin because

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the tissue, along with vasculature is destroyed which prevents delivery of O2 and phagocytic cells to site. the dead seared tissue is a rich environment for bacterial growth

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Tetanus characteristics

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bact skin disease; gram+ bacillus; spore forming; anaerobic

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organism of tetanus

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clostridium tetani is muscular in effect it is considered skin/wound disease because mechanism of infxn via skin wound.

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Tetanus is d/t

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the tetanus toxin or tetanospasmin which causes muscle spasms. or tetany, causes the jaw muscles to contract intesnsely = lockjaw

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prevention of tetanus

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easy with the tetanus toxoid vaccine

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C. tetani survives

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many years in the soil because of its spore forming ability and easily acquired by wounds, such as those that result from stepping on a rusty nail.

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tetanus booster

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Q10y

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tetanus death rate

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80-90% fatal

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Staphlococcal Diseases characteristics

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bact skin diseases; gram+, catalase+; staphlococci ( grape cluster like bunches of spherical cells); aureus (gold, most patient isolates produce yellow colonies

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Staph aureus must be distinguished from

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staph epidermidis, which is a commensal on skin or everyone

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S. epidermidis is

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nonpathogenic tho it has caused infection (rarely) in the severly immunodeficient pt.

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Coagulase test

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differentiates S. epidermidis and S. aureus. only S. aureaus can coagulate the clotting factors in plasma.

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S. aureus is normally

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mannitol+ (can use mannitol as a carbo source), while S. epidermitidis is not

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Inapparent infxns common:

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30-50% of people carry S. aureau in the anterior nares at any given time

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most imp virulence factor of staph aureus

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(a substance produced by the infecting organism to resist the host immune system) is protein A

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protein A

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a surface protein that binds human Abs by the Fc end which result in a bacterium that appears on the surface to be the host; (the immune sys only sees FAB arms of the host's own Abs. this phenomenon prevents acquired immumity from developing and has so far prevented the development of a vaccine

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S. aureus also produces

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hemolysins and leukocidin that destroy RBCs and WBCs respectively

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secreted coagulase

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clots in blood near the infected site to form an abscess and effectively walls off the area from the immune system

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catalase

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protects the bacteria from lysosomal reactive oxygen compounds

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S. aureus causes

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impetigo and boils and is highly pyogenic (pus producing). pus must be drained to effect recovery

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rarely S. aureus causes

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pneumonia with an 80% fatality rate. and osteomyelitis (bone infxns) infrequently which is often missed in DX

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some strains of S. aureaus produce

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an exfoliatin that causes desquamation or denuding often seen in newborns. this disease is called scalded skin syndrome

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scalded skin syndrome in a newborn unit

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all babies are removed and the carrier of the exfoliatin bearing strain is identified for tx to prevent further spread

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hospital acquired S. aureus

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are usually resistant to most penicillins. Methicillin, a penicillinase-resistant PCN, has been our bacup tx; however, now many isolates are methicillin resistant S. aureus called MRSA.

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Vancomycin

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has been our RX of last resort; however, since 1995 we have seen vanco resistant infections that are higlky disconcerting d/t the lack of appropriate ABTs. Infected pts are dying today because of lack of good tx

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A. aureus is probably the

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hardiest non spore forming bacterial pathogen, strict handwashing and other asseptic techniques are essential. Neither freezing nor cafeteria tray temps will kill it.

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Anthrax characteristics:

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bacterial skin; gram+ bacillus; spore former; anaerobe

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organism of anthrax

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Bacillus anthracis is known to form spores that survive in soil for at least 100y

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US incidence

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a few anthrax cases are seen each year in US when spread from cattle to humans

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Anthrax prevention

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by vaccination and tx of cattle

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Anthrax is considered to be

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a primary candidate for biological warfare because of its survival in nature; its potential for spread of billions of spores easily; the severity of the blood infxn that includes hemorrhaging, boils, and bloody diarrhea, and an 80% mortality rate when untx

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Leprosy characteristics

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bact skin disease; rod shaped; doesn't stain by Gram's stain; slowest advancing of all bacterial diseases known

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organism of leprosy:

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mycobacterium leprae is the cause of Hansen's disease (leprosy), a disease of the skin and neurons

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in hypersensitivity, __________develops in most infected people

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hypersensitivity- immune rxn holds growth in check & slowly destroys neurons, bone, and skin. loss of fingers/toes/nose tissue common

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when hypersensitivity doesn't develop?

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resulting disease is called lepromatous leprosy- organisms multiply greatly in the mucus and tissues. billions of bact spread from mucus of nose/throat

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nonlepromatous leprosy is

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not highly contagious, many cases of spouses not contracting disease after decades of life w/infected partner

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M. leprae growth on media?

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can't be grown in bacteriological media. The only way to culture it today is to sue the nine-banded armadillo as a host

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The nine banded armadillo

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found in Texas may lead to transmission to humans

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leprosy is DX by:

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appearance of skin lesions that have lost sensation. in underdeveloped countries - brush feather on lesion to test tickling sensation is absent d/t neuronal damage

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M. leprae grows

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very slowly in pts and may have incubation period of 2-10y before s/s appear

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tx of leprosy:

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ABT dapsone for 2+years. dapsone is reserved for leprosy only. some drug resistance noted and multiple ABTs must be used in those cases.

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Gas Gangrene characteristics:

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bact skin disease; gram+ bacillus; anaerobe; spore former

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organism of gas gangrene:

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C. perfringens causes gas gangrene

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gas gangrene gets its name from the fact that

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bacteria are prolific producers of gas, lesions become green then black as organism produces extracellular enzymes that putrefy the tissues and block blood flow

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tx of gas gangrene:

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amputation of necrotic limb

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gas gangrene occurs mainly in

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neglected wounds left w/o tx or debridement (removal of dead tissue and foreign material

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Enterococcus faecalis characteristics:

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bact disease of skin; beta-hemolytic; Group D strep; normal flora of the gut

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enterococcus faecalis was formerly called

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streptococcus faecalis and these organisms reside as normal flora in intestinal tract and are frighteningly resistant to antibiotics.(which caused them to be placed into new genus)

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While E. faecalis can cause _______

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subacute endocarditis, most common infxns occur from perforation of bowel via knife/GSW/nosocomial diseases by the immunoincompetent

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many isolates of E. faecalis are

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resistant to methicillin and even vancomycin. vanco resistance is so common today that resistant E. faecalis organisms have been given their own name: VRE vancomycin-resistant enterococcus)

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the most common bact for which we don't have adequate ABT tx is

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VRE. often in hosp physically separate VRE pts and nursing staff from those without VRE