12 Other Gram Negative Bacteria (17) Flashcards
Case
A 65-year-old man with chronic obstructive pulmonary disease (COPD) presents with a cough with copious purulent sputum, shortness of breath, and a 3-day history of a low-grade fever. Gram stain of the sputum shows a high predominance of Gram-negative diplococci among many polymorphs. Intracellular Gram-negative diplococci are also observed. Culture of the sputum on blood agar yields a predominant growth of opaque, non-hemolytic, grayish-white colonies of Gram-negative diplococci after overnight aerobic incubation at 37°C. The colonies remain intact when pushed across the surface of the agar. The cocci are oxidase-positive, DNAse-positive, fail to ferment carbohydrates, reduce nitrate to nitrite, and grow on nutrient agar at 22°C. An antibiotic susceptibility test shows sensitivity to tetracycline, ciprofloxacin, amoxicillin/clavulanic acid, extended-spectrum cephalosporins, and aminoglycosides. The organism is resistant to penicillin, ampicillin, vancomycin, clindamycin, and methicillin.
What bacterium is most likely causing the patient’s symptoms?
1 Neisseria meningitidis
2 Acinetobacter baumannii
3 Neisseria lactamica
4 Neisseria sicca
5 Moraxella catarrhalis
Moraxella catarrhalis
Moraxella (Branhamella) catarrhalis is a Gram-negative, aerobic diplococcus previously known as Neisseria catarrhalis; it is considered to be a harmless commensal of the upper respiratory tract. This organism has emerged as a pathogen in the last 2 decades. It is particularly associated with lower respiratory infections in patients with COPD, causing an exacerbation of the condition. It also causes opportunistic infections (e.g. meningitis, septicemia, pneumonia, and endocarditis) and nosocomial infections in immunocompromised hosts. It is one of the leading causes of community-acquired pneumonia in immunocompetent individuals. It causes acute sinusitis, lower respiratory tract infections, and acute otitis media in children. The organism isolated from the sputum has typical characteristics of Moraxella catarrhalis.
Positive DNAse and reduction of nitrate are valuable differentiating features. Ability to grow at 22°C on nutrient agar also helps to differentiate from the well-known pathogenic Neisseria (N. meningitidis and N. gonorrheae). β-lactamase-producing strains of M. catarrhalis are very common. These enzymes are encoded by chromosomal genes and can be transferred from cell to cell by conjugation. β-lactamase activity is inhibited by clavulanic acid and sulbactum; therefore, amoxicillin/clavulanate is one of the drugs used for treatment of M. catarrhalis infections. The bacterium possesses inherent resistance to trimethoprim. Positive reaction for tributyrin hydrolysis is a characteristic of M. catarrhalis. Rapid fluorometric tests based on the ability of the organism to produce butyrate esterase are available for identification. PCR-based tests have been designed and used for direct detection of M. catarrhalis in clinical samples, although they are not available for routine use. Neutrophil defensin-mediated adherence of the bacterium to the host cells is suggested as a contributing factor to the persistence of the infection, as found in COPD patients. Complement resistance is also considered a virulence feature of the organism.
Neisseria meningitidis, the etiological agent of meningococcal meningitis, is a Gram-negative diplococcus (often encapsulated), oxidase-positive, and DNAse-negative; it ferments glucose and maltose and does not grow at 22°C. The organism requires 5-10% carbon dioxide for primary isolation from clinical specimens.
Acinetobacter baumannii is taxonomically closely related to Moraxella. It is an obligate aerobe, nonmotile, Gram-negative, and appears as coccobacilli and cocci in pairs resembling Neisseria. It occurs as a saprophyte and also as commensal on human skin. It causes nosocomial infections (e.g. urinary tract infections, ventilator-associated pneumonia, device-associated infections, and iatrogenic meningitis). The organism can cause opportunistic infections in immunocompromised persons. Multidrug-resistant strains are often encountered. Acinetobacter baumannii is oxidase-negative and DNAse-negative.
Neisseria lactamica is closely related to N. meningitidis; it is DNAse-negative and ferments glucose, maltose, and lactose. It grows on a modified Thayer-Martin medium used as a selective medium for N. meningitidis and N. gonorrheae.
Neisseria sicca is a commensal Neisseria, DNAse-negative, and ferments carbohydrates, glucose, maltose, and sucrose.
Case
A 25-year-old woman who handled rodents in a pet shop was admitted to the hospital with a 4-day history of fever, headache, and polyarthralgia followed by maculopapular cutaneous rashes on her extremities. She did not recall any specific instance of an animal bite.
After 72 hours of incubation, blood cultures taken on admission showed flocculent puff ball-like growth of long chains of Gram-negative bacilli. Subcultures on sheep blood agar grew smooth gray colonies 1-2 mm diameter, of pleomorphic Gram-negative bacilli appearing as chains and non-branching filaments with bead-like swellings. The organism was catalase, oxidase, urease, and indole negative.
What is the most likely isolate?
1 Borrelia burgdorferi
2 Fransicella tularensis
3 Pasteurella multocida
4 Spirillum minus
5 Streptobacillus moniliformis
Streptobacillus moniliformis
Among the listed bacteria, Streptobacillus moniliformis is the only one that possesses the characteristics of the isolate. As the name indicates, the bacilli are arranged in chains, and the filaments with bead-like swellings give a necklace-like (moniliformis) appearance. Streptobacillus moniliformis is one of the 2 causative agents of rat bite fever (RBF), the other being Spirillum minus. The patient had the risk of occupational exposure to rats and other rodents and presented with typical clinical manifestations of RBF. While handling animals in the pet shop, minor scratches and bites may be commonplace and may not be recalled.
Streptobacillus moniliformis is a natural parasite of rodents. It is found in the nasopharynx and oropharynx of small rodents, especially rats. Rats are carriers; they do not show any symptoms. RBF may result after a bite or scratch from a carrier animal. Infections due to ingestion of water or food contaminated with rat excreta have also been reported. Epidemics of water and milk-borne infections have been documented. This form of RBF is known as Haverhill fever.
S. moniliformis infection can cause clinical illness without the classic signs and symptoms of RBF. The bacterium may produce septic arthritis or polyarthritis, mimicking rheumatoid arthritis. Fever and rashes may be absent. Manifestations such as pericarditis, endocarditis, myocarditis, meningitis, pneumonia, and focal metastatic abscesses have been reported. Immunocompromised persons are more susceptible to such complications. Rare cases of fatal fulminant sepsis caused by S. moniliformis have been reported in previously healthy adults.
Laboratory diagnosis includes direct microscopic detection of pleomorphic Gram-negative bacilli in smears of blood or joint fluid or skin lesions stained by Giemsa, Wayson, or Gram’s method, and cultural isolation of S. moniliformis from the clinical specimens. The organism is fastidious and isolation is not always easy. Sodium polyanethol sulfonate, an additive used in many commercial blood culture bottles for inhibiting the antibacterial activity of human blood, may impede the growth of S. moniliformis. It has been observed that non-specific initial clinical presentation and difficulties in culturing may sometimes lead to misdiagnosis of RBF.
The bacterium is a non-motile highly pleomorphic Gram-negative rod, growing as tangled chains with beaded or fusiform swellings. It readily develops into cell wall-deficient L-forms. S. moniliformis is susceptible to a variety of antibiotics, including penicillin. Treatment with penicillin G is recommended for streptobacillary RBF. For those allergic to penicillin, tetracycline and streptomycin are alternatives. Mortality of untreated RBF is reported as 10-13%.
Borrelia burgdorferi is a spirochete 20-30 microns x 2-3 microns in size. It causes Lyme borreliosis, which is transmitted from infected animals by ticks. Early manifestations include a local lesion at the site of tick bite called erythema migrans associated with flu-like symptoms; the most common late manifestations are arthralgia and arthritis.
Francisella tularensis is a minute capsulated fastidious Gram-negative bacillus 0.3-0.7microns x 0.2microns in size. The bacterium causes a serious and occasionally fatal zoonotic disease called tularemia. It is considered a bioterrorism agent. Infection may be transmitted directly from the reservoir hosts or by arthropod vectors. Clinical presentation depends on the route of infection. Ulceroglandular, typhoidal, oropharyngeal or gastrointestinal, and pneumonic forms can occur. Pneumonic form results from inhalation of the bacteria and is rare, but this is the likely form if F. tularensis is used as a bioterrorism agent. A live attenuated vaccine is available for immunization of persons at high risk.
Pasteurella multocida is a Gram-negative, non-motile bacillus that is catalase, oxidase, and indole positive. This bacterium is carried in the upper respiratory tract of a variety of animals, including dogs, cats, rats, cattle, and sheep. Human infections are rare. Infection may occur following animal bites and may cause local suppuration, meningitis, respiratory tract infections, appendicitis, appendicular abscess, or endocarditis.
Spirillum minus causes a type of RBF called Sodoku, seen mostly outside the U.S. The bacterium is short, with 2 or 3 regular spirals, is actively motile with amphitrichous flagella, and does not grow on laboratory media. It is Gram-negative but better visualized by Giemsa or silver stains. RBF cause is associated with suppuration of rat bite wound, regional lymphadenopathy, and fever of relapsing type.
Veillonella species are:
1 Aerobic gram positive rods
2 Anaerobic gram positive rods
3 Aerobic gram positive cocci
4 Anaerobic gram positive cocci
5 Anaerobic gram negative cocci
Anaerobic gram negative cocci
Anaerobic gram negative cocci
Associated with human infections.
Normal flora of oral cavity
Nitrate positive
Sensitive to penicillin, cephalosporins, clindamycin, metronidazole, and chloramphenicol.
A study on the bacterial etiology of acute otitis media (AOM) in children was conducted in the otorhinolaryngology department of a university hospital. About 20% of the isolates from the middle ear fluid samples were oxidase positive Gram-negative diplococci. These isolates were identified by conventional methods and were found to belong to a bacterial species that is accepted as one of the 3 most common agents of acute otitis media in children. What is an important characteristic of this bacterial species?
1 Shows inherent resistance to penicillin
2 Ferments a variety of carbohydrates with production of acid
3 Grows only on blood containing media
4 Frequently colonizes in the upper respiratory tract of children
5 Has a polysaccharide capsule
6 Is an obligate anaerobe
Frequently colonizes in the upper respiratory tract of children
Acute otitis media (AOM) is one of the most common infections in young children and a major cause of morbidity in children < 3 years. Streptococcus pneumoniae, Haemophilus influenzae (untypeable), and Moraxella catarrhalis are the 3 major bacterial agents of AOM. Of these, Moraxella catarrhalis is the only oxidase positive diplococcus. M.catarrhalis is a commensal and a potential mucosal pathogen.
Frequently M.catarrhalis colonizes in the upper respiratory tract of children. Adhesion to the mucosal surface is the initial event in the colonization process in which bacterial surface proteins attach to the host cell carbohydrate receptors.
Other childhood diseases caused by M.catarrhalis include sinusitis, tracheitis, bronchitis, pneumonia, and less commonly ocular infections.
In children, nasopharyngeal colonization often precedes M.catarrhalis-mediated disease.
In Otitis media, colonization is followed by retrograde ascension of the pathogen up the eustachian tube into the middle ear.
Generally colonization occurs by the age of 1 year. Carriage rates of M.catarrhalis are found to increase during childhood, reaching peak by 2-3 years, decrease by 15-16 years, and again increases after 65 years. Nasopharyngeal carriage rates as high as 75% have been reported in young children. Age-dependent development of secretory immunoglobulinA (IgA) is considered to be a probable cause for the difference in the rates of colonization between children and adults.
Increased carriage rates have been observed in adults with chronic respiratory diseases.
Nasopharyngeal colonization by antibiotic resistant strains is associated with increased incidence of unresolved Otitis Media (OM). There is ongoing research in the field of vaccine for OM. One of the strategies for development of OM vaccine is aimed at reducing nasopharyngeal carriage of the bacterial pathogens by mucosal vaccination, thereby diminishing the chance of developing AOM. Conjugate vaccines based on Moraxella catarrhalis lipooligosaccharide (LOS) are in early experimental stage in animal models.
M.catarrhalis does not possess the other characteristics listed. Resistance to penicillin is acquired and is due to beta-lac tamase production. The bacterium does not ferment carbohydrates and can grow in the absence of blood on nutrient agar medium. M.catarrhalis is not known to express a capsule and is not an obligate anaerobe.
Case
A 10-year-old boy was diagnosed with a zoonotic infection endemic in the U.S. that is recognized as a frequent cause of benign lymphadenopathy in children and is caused by a small pleomorphic Gram-negative bacillus. Following a scratch from his pet cat, the boy developed an erythematous papule on his arm and a few weeks later, regional lymphadenitis.
The etiological agent of the boy’s infection most likely belongs to what genera?
1 Brucella
2 Bartonella
3 Bordetella
4 Burkholderia
5 Borrelia
Bartonella
The boy’s history of cat scratch, typical presentation with regional lymphadenitis, and the features of the zoonotic infection described are suggestive of Cat Scratch Disease (CSD). The infection is endemic in the U.S. and about 24,000 people have CSD annually, 80% of whom are children. The main agent of CSD is Bartonella henselae. Bartonella clarridgeiae and Bartonella quintana have also been reported to be associated with a few cases of CSD; therefore, the correct answer is bartonella.
B.henselae is a zoonotic pathogen capable of causing a broad range of clinical manifestations in humans. CSD is usually a self-limited infection in immunocompetent children. Other manifestations of B.henselae infection include bacillary angiomatosis-peliosis, bacteremia, encephalitis, endocarditis, and neuroretinitis. Bacillary angiomatosis-peliosis is characterized by the formation of vasoproliferative tumors resulting from bacterial colonization and activation of human endothelial cells. Ability to induce endothelial cell proliferation is a common characteristic of Bartonella species pathogenic to humans. Systemic diseases mostly occur in immunocompromised persons.
Cats are the main reservoirs of B. henselae, though other animals like dogs and rabbits can occasionally serve as sources of infection. Arthropods, mainly fleas, transmit the infection among cats.
B.henselae is a very fastidious bacterium. Once isolated from the lymph nodes of CSD patients, it needs prolonged incubation in enriched blood media in the presence of carbon dioxide, so detection is often unsuccessful. Histological examination is helpful and the bacteria can be detected in lymph node biopsy smears and sections by Warthin-Starring silver impregnation staining. Serological tests like indirect immunofluorscence assays are very useful for diagnosis except in early stages of the disease. Detection of B.henselae DNA in the lymph node tissue samples by polymerase chain reaction (PCR) assay has high specificity and is valuable in the diagnosis of CSD.
All other genera listed also contain species that cause zoonotic infections. All species of Brucellae, Bordetella bronchiseptica, Burkholderia pseudomallei, and the spirochete Borrelia burgdorferi that causes Lyme disease are zoonotic pathogens. Cats are not common reservoirs of these bacteria and mode of transmission and typical manifestations also differ.
Case
A 33-year-old male patient presents with a wound on the left hand from a human bite during a bar fight. Examination reveals inflammation and erythema encompassing the entire hand. The wound itself has a dark peripheral border with purulent exudate. An aspirate of deep purulent material is collected for Gram stain and culture. The Gram stain is significant for many white blood cells and many Gram-negative rods. The culture is positive for growth of an organism that only grows on chocolate agar media. The colonies are approximately 1-2 mm in diameter after 48 hours at 37°C, and they have clear centers surrounded by spreading growth. The colonies form pitting of the agar surface and smell strongly of hypochlorite. Several days later, the colonies begin to assume a very light yellow hue.
The patient has a wound infection due to what organism?
1 Haemophilus influenzae
2 Pasteurella multocida
3 Moraxella catarrhalis
4 Vibrio vulnificus
5 Eikenella corrodens
Eikenella corrodens
Eikenella corrodens, which was formerly called Bacteroides ureolyticus, is a facultative anaerobic, Gram-negative bacterium; it is a normally occurring inhabitant of the oral cavity, and it is often one of the pathogens associated with infected human bite wounds. Characteristically, the organism will pit the agar and produce a strong hypochlorite odor. It is a member of the HACEK group, which includes organisms such as Haemophilus aphrophilus, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, and Kingella kingae; along with other organisms in the group, it can be a cause of infective endocarditis.
Haemophilus influenzae is a facultative anaerobic, Gram-negative coccobacillus that requires the presence of X factor (hemin) and V factor (nicotinamide adenine dinucleotide [NAD]) for growth. For this reason, the organism will only grow on chocolate agar media, which is made with blood that has been heated to induce lysing of the red blood cells and in turn releases the needed factors into the agar media. The organism has a characteristic musty smell on chocolate agar media.
Pasteurella multocida is a Gram-negative, oxidase-positive rod that will characteristically grow on blood agar plate (BAP) and chocolate agar, but not on MacConkey agar. The organism is part of the normal oral flora of dogs and cats, and it is associated with cat and dog bite wound infections. The organism is commonly mistaken for Haemophilus species, but it is easily distinguished by its ability to grow on BAP and chocolate agar media; Haemophilus species will only grow on chocolate agar media.
Moraxella catarrhalis, which was formerly called Branhamella catarrhalis, causes acute, localized infections such as otitis media, sinusitis, and bronchopneumonia as well as life-threatening systemic diseases, including endocarditis and meningitis. The organism is a Gram-negative diplococcus; it is oxidase positive, has a slight pink pigment, is catalase-positive, and is usually positive for the production of the beta-lactamase enzyme. The organism characteristically produces butyrate esterase, and the detection of this enzyme will provide a rapid identification.
Vibrio vulnificus normally lives in warm seawater and is part of a group of vibrios that are called “halophilic” because they require salt. It is a Gram-negative rod that is oxidase positive and motile by means of polar flagella. Characteristically, it is lactose positive. Infections with the organism are generally due to ingestion of raw oysters and/or exposure of traumatic wounds to infected marine animals or contaminated water. TCBS (thiosulfate citrate bile salts sucrose) agar is the agar media of choice in isolating the organism.
Veillonella species are
1 Aerobic gram positive rods
2 Anaerobic gram positive rods
3 Aerobic gram positive cocci
4 Anaerobic gram positive cocci
5 Anaerobic gram negative cocci
Anaerobic gram negative cocci
The characteristics of Veillonella include the following:
Anaerobic gram negative cocci
Associated with human infections
Normal flora of oral cavity
Nitrate positive
Sensitive to penicillin, cephalosporins, clindamycin, metronidazole, and chloramphenicol
Aeromonads are
1 Gram Positive cocci
2 Oxidase negative rods
3 Glucose fermenters
4 Sensitive to penicillin
Glucose fermenters
The following are the characteristics of the genus aeromonas:
Gram negative rods
Oxidase positive
Glucose fermenters
Grows between 0° C to 45° C
Resistant to penicillin, ampicillin, carbenicillin, and cephalothin
Which of the following associated agents corresponds with non-encapsulated, non-motile gram negative bacillus that causes “rat bite fever”?
1 Gardnerella vaginalis
2 Eikenella corrodens
3 Bartonella bacilliformis
4 Streptobacillus moniliforms
5 Calymmatobacterium granulomatis
Streptobacillus moniliforms
Streptobacillus moniliforms and Spirillum minor are causative agent of “rat bite fever.”
These organisms are normal flora of the rat throat and are transmitted to human through rat bites. Clinical symptoms include blotchy and petechial rashes, septic fever and polyarthritis. Streptobacillus moniliforms is implicated in Haverhill fever, the infection acquired from ingestion of contaminated milk.
Clue cells are characteristics of this gram negative bacillus associated with vaginitis
1 Gardnerella vaginalis
2 Eikenella corrodens
3 Bartonella bacilliformis
4 Streptobacillus moniliforms
5 Calymmatobacterium granulomatis
Gardnerella vaginalis
Clue cells are vaginal epithelial cells covered with many bacilli found in wet smear of patients with bacterial vaginitis. Vaginitis associated with Gardnerella vaginalis is characterized by presence of clue cells in the wet smear and vaginal discharge with fishy odor.
Which of the following associated agents corresponds with gram negative rod isolated on blood agar, causing characteristic pitting of the agar, and is associated with infections caused by human bites?
1 Gardnerella vaginalis
2 Eikenella corrodens
3 Bartonella bacilliformis
4 Streptobacillus moniliforms
5 Calymmatobacterium granulomatis
Eikenella corrodens
Eikenella corrodens is resident flora of upper respiratory tract and is implicated in infection caused by human bite or in patients with disease or trauma of oral cavity. It is an opportunist pathogen that causes infections in immunocompromised patients. It is a nonmotile, gram negative, facultative anaerobe. Growth of the organism is characterized by the pitting or corroding of agar. It is a very fastidious organism that does not grow on MacConkey agar. Penicillin or ampicillin is the drug of choice for infection caused by Eikenella corrodens.
Which of the following associated agents corresponds with small, motile, gram negative bacillus that is etiological agent of Oroya fever and verruga peruana?
1 Gardnerella vaginalis
2 Eikenella corrodens
3 Bartonella bacilliformis
4 Streptobacillus moniliforms
5 Calymmatobacterium granulomatis
Bartonella bacilliformis
Oroya fever is severe infectious anemia and is initial stage of Bartonella bacilliformis.
Verruga peruana is the eruptive stage of bartonellosis that occurs 2-8 weeks following Oroya fever or can also be seen in absence of Oroya fever.
Bartonella bacilliformis invades the red cells and endothelial cells in Oroya fever. It causes destruction of red cell leading to severe anemia, which leads to hepatomegaly and splenomegaly. Proliferation of the organism in blood vessel can result in thrombosis and vascular occlusion. Blood smear and blood culture can be used for diagnosis.
Verruga peruana is characterized by vascular skin lesions, which persist for extended period of time.
Which of the following associated agents corresponds with short gram negative bacillus that causes granuloma inguinale and is characterized by presence of Donovan bodies in endothelial cells?
1 Gardnerella vaginalis
2 Eikenella corrodens
3 Bartonella bacilliformis
4 Streptobacillus moniliforms
5 Calymmatobacterium granulomatis
Calymmatobacterium granulomatis
Granuloma inguinale is a sexually transmitted disease caused by Calymmatobacterium granulomatis. It is granulomatous disease characterized by presence of nodule on the genitalia or inguinal area. Staining of the granulomatous lesion reveals Donovan bodies within the phagocytes which is indicative of granuloma inguinale.
The most effective method of establishing a diagnosis is direct visualization of the organisms within the macrophages. Tissue should be obtained from the ulcer edge or base via punch biopsy, curettage, or a thin wedge. A Wright-Giemsa or Warthin-Starry stain may be used to demonstrate the Donovan bodies (intracellular bacteria) as bipolar staining, safety pin-shaped intracytoplasmic inclusions.
Afipia is
1 Catalase positive
2 Oxidase positive
3 Non motile
4 Gram positive bacilli
Oxidase positive
Afipia was isolated from the lesions of cat scratch disease however recent finding indicates the association of Rochalimaea henselae with cat scratch disease.
The characteristics of Afipia include the following:
Gram negative bacilli
Motile by means of a single flagellum
Oxidase positive
Catalase negative
Grows at 30° C and can be isolated from blood cultures and cell culture
Case
An 18-year-old man presents to the emergency department with pain and swelling to the jaw. He had been in a fight approximately 1-week prior and had obtained an injury to the jaw that produced a small laceration. Physical examination of the jaw was remarkable for swelling and erythema. There was also the presence of lymphadenopathy below the jaw. The patient had a temperature of 36.8° C, and a CBC was significant for an elevated WBC with a left shift. Drainage of the infected areas produced a purulent material that was sent to the laboratory for culture and gram stain. The gram stain had large numbers of neutrophils present but no organisms were seen. On the second day, the cultures were positive for gram-negative anaerobic cocci.
What is the most likely organism causing this infection?
1 Clostridium perfringens
2 Bacteroides fragilis
3 Fusobacterium spp
4 Veillonella spp
5 Propionibacterium acnes
Veillonella spp
Veillonella spp. is anaerobic gram-negative cocci that are found as part of the normal flora in the oral cavity, upper respiratory tract, intestine, and vagina. They have a generally low virulence but can cause serious infections given the right circumstances, such as steroid therapy, previous injury, foreign bodies, and IV drug abuse. They are generally susceptible to most of the antibiotics used to treat other anaerobic infections.
Bacteroides fragilis are anaerobic, gram-negative bacilli that grow in 20% bile; they are resistant to kanamycin, vancomycin, and colistin and are catalase and indole positive. It is the most common anaerobic isolate from intra-abdominal abscesses. The organism is part of the normal gastrointestinal flora. Anaerobic infections are usually polymicrobial with a mixture of aerobes and anaerobes. Metronidazole, clindamycin, and cefoxitin are some of the antibiotics used to treat Bacteroides fragilis.
Clostridium perfringens is an anaerobic, gram-positive, spore-forming bacillus. The organism is nonmotile and has a distinctive “box car” appearance on gram stain. It produces oval central spores, but they are rarely seen in clinical or cultures. All types produce lecithinase, which is lytic to neutrophils. Because of the action of lecithinase on neutrophils, gram stains of blister aspirates and other drainage characteristically contain gram-positive rods but little or no neutrophils. Clostridium perfringens is the main causative agent of gas gangrene, and diagnosis is made by microbiological findings, clinical findings, and the demonstration of myonecrosis at surgery. Surgical, antibiotic, and hyperbaric oxygen treatments are used in treating gas gangrene.
Fusobacterium spp. are long, thin anaerobic gram-negative rods with pointed ends. They are usually arranged in end-to-end pairs. The organism is indole variable, catalase negative, grows in 20% bile, and is sensitive to kanamycin and colistin but resistant to vancomycin. The organism is a cause of brain abscesses, sinusitis, odontogenic infections, pleuropulmonary infections, bacteremia, and endocarditis. Most Fusobacterium spp. are sensitive to penicillin.
Propionibacterium acnes is a gram-positive anaerobic cocci. It is part of the normal skin flora. Though the organism is usually a contaminant of blood and wound cultures, it can be the cause of serious life-threatening infections in the proper conditions. These infections include brain abscesses, osteomyelitis, subdural empyema, cerebral shunt infection, infective endocarditis, and parotid and dental infections.
