P.O. Box 131375, Bryanston, 2074 Ground Floor, Block 5 Bryanston Gate, 170 Curzon Road Bryanston, Johannesburg, South Africa 804 Flatrock, Buiten Street, Cape Town, 8001 www.thistle.co.za Tel: +27 (011) 463 3260 Fax: +27 (011) 463 3036 Fax to Email: + 27 (0) 86‐538‐4484 e‐mail : [email protected] Please read this section first The HPCSA and the Med Tech Society have confirmed that this clinical case study, plus your routine review of your EQA reports from Thistle QA, should be documented as a “Journal Club” activity. This means that you must record those attending for CEU purposes. Thistle will not issue a certificate to cover these activities, nor send out “correct” answers to the CEU questions at the end of this case study. The Thistle QA CEU No is: MT-11/00142. Each attendee should claim THREE CEU points for completing this Quality Control Journal Club exercise, and retain a copy of the relevant Thistle QA Participation Certificate as proof of registration on a Thistle QA EQA. MICROBIOLOGY LEGEND CYCLE 31 ORGANISM 1 Eikenella corrodens E. corrodens is a pleomorphic bacillus that sometimes appears coccobacillary and typically creates a depression (or “pit”) in the agar on which it is growing. It grows in aerobic and anaerobic conditions, but requires an atmosphere enhanced by 3-10% carbon dioxide. The colonies are small and greyish, they produce a greenish discoloration of the underlying agar and smell faintly of bleach (hypochlorite). Only half produce the pitting of the agar that is considered characteristic. They are oxidase-positive, catalase-negative, urease-negative, indole-negative and reduce nitrate to nitrite. E. corrodens is a commensal of the human mouth and upper respiratory tract. It is an unusual cause of infection and when it is cultured it is most usually found mixed with other organisms. Infections most commonly occur in patients with cancers of the head and neck, but it is also common in human bite infections, especially “reverse bite”, “fight bite”, or “clenched fist injuries”. It also causes infections in insulin- dependent diabetics and intravenous drug users who lick their needles (“needle-licker’s osteomyelitis”). It is one of the HACEK group of infections which are a cause of culture-negative endocarditis. E. corrodens infections are typically indolent (the infection does not become clinically evident until a week or more after the injury). They also mimic anaerobic infection in being extremely foul-smelling. Microscopic Morphology Eikenella corrodens is a small, straight, non-spore forming, non-encapsulated, non-motile Gram-negative coccobacillus. The organism has a uniform morphology with rounded ends, although occasional short filaments of up to 12µm may be observed. In direct smears of clinical material, however, E. corrodens is more coccobacillary, resembeling Haemophilus species, and may even possess a capsule. Colonial Morphology E. corrodens is a facultative anaerobe. It grows in aerobic and anaerobic conditions, but requires an atmosphere enhanced by 3–10% carbon dioxide. After 48hours at 37°C, colonies are 0.5 to 2mm in diameter with clear centers. They are often surrounded by spreading growth. The colonies have a characteristic pitting or corroding appearance (hence, the specific epithet corrodens), although not all strains corrode the agar. Observation of pitting is facilitated by removal of the colonies with a swab, which reveals holes where the colonies were located. Pitting and non-pitting variants can occur in the same culture. Bacteria other than E. Corrodens can cause pitting of the agar surface, e.g. anaerobes in the Bacteroides ureolyticus group. Thistle QA is a SANAS accredited organisation, No: PTS0001 Accredited to ISO guide 43 and ILAC G13 Certificate available on request or at www.sanas.co.za P.O. Box 131375, Bryanston, 2074 Ground Floor, Block 5 Bryanston Gate, 170 Curzon Road Bryanston, Johannesburg, South Africa 804 Flatrock, Buiten Street, Cape Town, 8001 www.thistle.co.za Tel: +27 (011) 463 3260 Fax: +27 (011) 463 3036 Fax to Email: + 27 (0) 86‐538‐4484 e‐mail : [email protected] E. corrodens colonies may assume a slightly yellow hue after several days, which is best observed by dragging a white swab through some colonies; the yellow pigment will addhere to the swab. Although E. corrodens is non-motile, strains that corrode the agar produce a “twitching” motility. Colonies have a characteristic odour, described as smelling musty or resembling the smell of crackers, hypochlorite bleach, or mouse cages. E. Corrodens does not grow on MacConkey agar. Gram-stained Eikenella corrodens Pitting colonies of E. Corrodens on sheep blood agar after 72hours of incubation at 35°C in 5% to 7% CO2 Identification Generally, the organism is biochemically inactive, lacking oxidative and fermentative capabilities and failing to produce urease, indole or hydrogen sulfide (h2S). All isolates are oxidase positive and most isolates are capable of reducing nitrate to nitrite. Catalase is usually negative, although rare catalase-positive isolates may be encountered. Antimicrobial Susceptibility In vitro antimicrobial susceptibility studies indicate that E. corrodens infections can be successfully treated with a variety of agents including penicillin, ampicillin, amoxicillin, but not cephalothin or cefuroxime. Eikenella corrodens is susceptible in vitro to cefoxitin, ceftriaxone, cefotetan, ciprofloxacin, moxalactam, imipenem and tetracycline. Resistance to clindamycin, lincomycin, and metronizadole is constant, but variable with regard to aminoglycosides. Eikenella corrodens in vitro antibiotic susceptibility may be determined by disk-agar diffusion, agar dilution, and E-test methods. References 1. The Prokaryotes, Third Edition, Volume 5 - Edited by Martin M. Dworkin, Stanley Falkow, Eugene Rosenberg, Karl-Heinz Schleifer, Erko Stackebrandt 2. Laboratory Diagnosis of Infectious Diseases, Essentials of Diagnostic Microbiology- Paul G. Engelkirk, Janet L. Duben- Engelkirk ____________________________________________________________________________________________ Questions 1. Discuss the morphological characteristics of E. corrodens. 2. Discuss the role of E. corrodens in disease. 3. Discuss the antimicrobial susceptibility of E. corrodens. \ Thistle QA is a SANAS accredited organisation, No: PTS0001 Accredited to ISO guide 43 and ILAC G13 Certificate available on request or at www.sanas.co.za .