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The Gram stain, developed in the late 1800s by Hans Christian Gram, is used to distinguish 2 major categories of bacteria. Gram-positive bacteria retain the purple hue of the initial crystal violet stain, whereas Gram-negative bacteria are decolorized and subsequently stain red by safranin or carbol fuchsin. While Gram-positive bacteria have thick walls of peptidoglycan and secondary polymers that are relatively impermeable and resist decolorization, Gram-negative bacteria have a thin peptidoglycan layer with an outer lipid membrane bilayer that is readily disrupted by this process.1
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Gram-negative bacteria may be further categorized by their morphology and metabolic capabilities. Gram-negative cocci found in clinical isolates typically represent Neisseria spp., which may be identified as Neisseria meningitidis or Neisseria gonorrhoeae depending on maltose fermenting activity. On the other hand, Gram-negative bacilli may be subdivided based on morphology, including coccobacilli, comma-shaped bacilli, fusiform bacilli, and rods. Gram-negative rods, for example, can be further subdivided by lactose fermenting activity, oxidase positivity, and so on.2 This chapter focuses on cutaneous manifestations of Gram-negative infections not already covered in other chapters. Many manifestations occur from direct invasion of the skin or subcutaneous tissues, and may be accompanied by signs such as fever or hypotension attributable to the patient’s immune response.
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INFECTIONS CAUSED BY NEISSERIA MENINGITIDIS
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AT-A-GLANCE
Worldwide, Neisseria meningitidis is responsible for 1.2 million cases of infection and 135,000 deaths annually.
Disseminated meningococcal infection may present as (a) meningitis alone, (b) acute meningococcemia with or without meningitis, or (c) chronic meningococcemia.
In acute meningococcemia, a classic petechial rash is present in approximately 60% of patients, most commonly on the extremities. In severe cases, necrosis of the skin and underlying tissue may necessitate amputation.
The rash of chronic meningococcemia more commonly consists of rose-colored macules and papules, although petechiae, nodules, vesicles, and pustules may be present. The rash may wax and wane with periodic fevers.
Mortality rates for meningococcal infection in the United States are 10% to 15% with 11% to 19% of survivors suffering from long-term sequelae.
The gold standard for diagnosis is culture isolation of N. meningitidis from blood, cerebrospinal fluid, other bodily fluids, or skin biopsy tissues. Polymerase chain reaction is useful when cultures are negative.
The single most important factor in the treatment of acute meningococcal infection is early initiation of antibiotics.
In the United States, vaccination with a capsular polysaccharide conjugate vaccine against serogroups A, C, W135, and Y is recommended for all patients at 11 or 12 years of age with a booster at age 16 years.
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INTRODUCTION AND BACTERIOLOGY
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N. meningitidis is a maltose-fermenting aerobic Gram-negative diplococcus. It is a fastidious organism, meaning it has complex nutritional requirements and will die within hours on nonliving surfaces. It grows on blood agar, trypticase soy agar, chocolate agar, and modified Thayer-Martin agar, which consists of a chocolate agar base with growth factors and ...