Bacterial Infections

Abstract

Pyodermitis is very common and results from bacterial invasion of the skin, near soft tissue, and its appendages. Most cutaneous infections are caused by Staphylococcus aureus and group A β-hemolytic streptococci, with various presentations and severity. Clinical manifestations can range from mild superficial lesions to life-threatening necrotizing and systemic infections. The diagnosis is essentially based on clinical evaluation. Cultural examinations may be necessary to confirm the etiologic agent when there is doubt about the diagnosis or there is suspicion of resistant bacteria. Management is determined by the severity and location of the infection and by patient comorbidities. Superficial uncomplicated pyodermitis may be treated with topical antimicrobial drugs. Solitary and small abscesses respond well to drainage and seldom require antibiotics. For deep infections the initial systemic antimicrobial treatment is empiric, and generally should cover Gram-positive cocci. Patients with necrotizing infections require prompt surgical debridement and empiric polymicrobial antibiotic coverage. The antibiotic choice depends on clinical presentation and the local burden of multiresistant bacteria, mainly methicillin-resistant S. aureus.

Glossary

Abscess:

Pus collections in dermis or deeper tissues.

Acne keloidalis nuchae:

A chronic pattern of deep folliculitis of the scalp that occurs in the lower occipital region and leads to scarring alopecia with keloid formation.

Bacteremia:

Presence of viable bacteria in the bloodstream.

β-lactams:

A class of broad-spectrum antibiotics, such as the penicillins and the cephalosporins, that chemically contain a β-lactam ring.

Carbapenems:

A class of β-lactam antibiotics highly resistant to β-lactamases.

Carbuncles:

Furuncle aggregates that form large, painful inflammatory masses.

Ceftriaxone:

A third-generation cephalosporin (antibiotic).

Cellulitis:

Deep skin infection that involves the dermis and subcutaneous tissue associated with severe pain and systemic symptoms.

Cephalexin:

A first-generation cephalosporin (antibiotic).

Cephalosporins:

A class of β-lactam antibiotics originally isolated from the fungus Cephalosporium acremonium. Successive generations have different antimicrobial spectra: the newer are more active against Gram-negative bacteria.

Clindamycin:

A semisynthetic antibiotic, derived from lincomycin and active against Gram-positive and anaerobic bacteria.

Daptomycin:

A cyclic lipopeptide parenteral antibiotic with bactericidal activity against a wide range of Gram-positive bacteria, including S. aureus resistant to methicillin and vancomycin. The mechanism of action involves disruption of the bacterial cytoplasmic membrane and inhibition of protein and nucleic acids synthesis.

Dicloxacillin:

A semisynthetic penicillinase-resistant penicillin.

Dissecting cellulitis:

Also known as perifolliculitis capitis abscedens et suffodiens, it is a clinical form of chronic folliculitis of the scalp that manifests with pus collections, sinuses, and scarring alopecia.

Ecthyma:

Bacterial skin infection that reaches the superficial dermis. The main etiologic agents are S. aureus and S. pyogenes.

Elephantiasis nostra:

Chronic lymphatic swelling of lower limbs leading to skin tightening and hyperkeratosis, induced by recurrent erysipelas that damage lymphatic vessels.

Erysipelas:

Deep skin infection considered a specific type of cellulitis that involves superficial dermal structures and is distinguished clinically by its well demarcated raised borders.

Erythromycin:

A macrolide antibiotic, obtained from the actinomycete Streptomyces erythraeus.

Fluoroquinolones:

A subgroup of quinolones, antibiotics with broad spectrum of antimicrobial activity that inhibit bacterial DNA gyrase.

Folliculitis:

Inflammation of the hair follicle, associated with multiple causes. Infectious folliculitis is most commonly caused by S. aureus. It can be classified into superficial and deep folliculitis.

Folliculitis decalvans:

Specific form of chronic deep folliculitis of the scalp usually associated with S. aureus and leading to scarring alopecia.

Fournier’s gangrene:

A clinical form of necrotizing fasciitis of the perineal, genital, or perianal regions.

Furuncle:

Also known as a “boil,” the deep form of folliculitis that manifests clinically as tender inflammatory papules or nodules.

Fusidic acid:

Antibiotic derived from the fungus Fusidium coccineum that interferes with the bacterial protein synthesis by preventing translocation elongation factor G (EF-G) of the ribosome. It is only active against Gram-positive bacteria such as Staphylococcus and can be topically or systemically administered.

Impetigo:

Bacterial skin infection limited to the superficial layers of the epidermis, caused by S. aureus and S. pyogenes.

Intertrigo:

An inflammatory process in skin folds, induced or aggravated by heat, moisture, maceration, friction, and microbial proliferation.

Linezolid:

A synthetic antibiotic of the oxazolidinone class that prevents formation of essential component of bacterial protein synthesis.

Lymphedema:

Accumulation of lymphatic fluid in the interstitial tissues of the body with accompanying swelling, often of the extremities, caused by damage in lymphatic vessels or lymph nodes.

Macrolide:

A class of broad-spectrum antibiotics that chemically contain a large lactone ring and act by inhibiting protein synthesis.

Metronidazole:

A synthetic antiprotozoal and antibacterial drug that is effective against obligate anaerobes.

Mupirocin:

Topical antibiotic with bactericidal activity, derived from Pseudomonas fluorescens. Its particular mechanism of action results from inhibition of transfer RNA and is not related to any other antibacterial. It is indicated for the treatment of skin infections by Gram-positive organisms, especially S. aureus, and is often formulated in cream or ointment at 2%.

Necrotizing fasciitis:

Deep bacterial infection that extends rapidly along the superficial fascia and subcutaneous tissue planes, resulting in soft tissue necrosis and systemic toxicity.

Penicillins:

A class of β-lactam antibiotics that were originally isolated from the fungus of the genus Penicillium and later gave rise to the various semisynthetic antimicrobials.

Piperacillin-tazobactam:

A β-lactam antibiotic associated with a β-lactamase inhibitor.

Poststreptococcal glomerulonephritis (PSGN):

Acute glomerulonephritis (glomeruli inflammation) following streptococcal infection and characterized by sudden appearance of hematuria, proteinuria, edema, and hypertension.

Retapamulin:

Topical antibiotic with in vitro and in vivo activity against S. aureus (including MRSA) and S. pyogenes and poor activity against Gram-negative bacteria. It is a semisynthetic derivative of pleuromutilin compound derived from the fungus Clitopilus passeckerianus and inhibits bacterial protein synthesis, but binds at a different site on the 50S subunit of the bacterial ribosome.

Rheumatic fever:

Inflammatory systemic disease induced by toxins produced by certain strains of group A streptococci. The most characteristic findings are fever, migratory arthritis, neurologic manifestations, and permanent damage to the heart structures.

Ritter disease:

Also known as staphylococcal scalded skin syndrome, it is characterized by diffuse epidermal detachment caused by exfoliative exotoxins produced by S. aureus.

Scarlet fever:

A bacterial illness that develops in some people who have strep throat. Also known as scarlatina, scarlet fever features a bright red rash that covers most of the body. Scarlet fever is almost always accompanied by a sore throat and a high fever.

Sepsis:

Systemic inflammatory response to infection.

Staphylococcal scalded skin syndrome (SSSS):

See “Ritter disease.”

Streptolysin O:

A hemolysin produced by β-hemolytic streptococci. The laboratory titration of anti-streptolysin O antibody (ASLO) are used as a diagnostic tool of recent streptococcal infection.

Sycosis:

Etymologically the term refers to an inflammatory process in hair follicles. However, it is most commonly used to describe a chronic deep folliculitis, most commonly in the beard region, caused by staphylococcal infection.

Teicoplanin:

A glycopeptide antibiotic highly effective against Gram-positive bacteria, especially against staphylococci.

Tetracyclines:

A class of antibiotics effective against a wide variety of organisms, acting by inhibiting protein synthesis.

Tigecycline:

The first drug in the glycylcycline class of antibiotics, which acts by inhibiting protein synthesis.

Trimethoprim-sulfamethoxazole (TMP-SMX):

Also known as co-trimoxazole, it is a broad-spectrum combination antibiotic. The drug combination is synergistic as the drugs interfere with two successive steps in the formation/utilization of folic acid by microorganisms.

Vancomycin:

A glycopeptide antibiotic highly effective against Gram-positive bacteria, especially staphylococci.