Arcanobacterium haemolyticum (formerly Corynebacterium haemolyticum): Culture; Molecular diagnosis (PCR).
Arcanobacterium haemolyticum, formerly known as Corynebacterium hæmolyticum, is a gram-positive, catalase-negative, aerobic, beta-hemolytic and non-mobile bacillus. In cultures in blood agar produces hemolysis so it can be easily confused with Streptococcus pyogenes. The differences of microscopic morphology can be used to differentiate them initially, since Arcanobacterium has an elongated form of bacillus and Streptococcus has a round form of coccu. It often occurs in polymicrobial infections along with common respiratory pathogens such as streptococci, so it could be confused in cultures. Although A. haemolyticum is a beta-hemolytic organism, hemolysis is less defined than that of beta-hemolytic streptococci and can go unnoticed in culture with a huge growth of the flora of the commensal pharynx. The size of the colony and the degree of hemolysis vary considerably with the blood type of the culture media and the incubation atmosphere, in soybean tripticase agar with 5% horse blood, incubated for 48 hours with 5% atmosphere of CO2. It is resistant to bacitracin (<10 mm in diameter of the zone of inhibition with 0.04 U discs), so it is useful to detect its growth around discs with this antimicrobial. Inhibition of the hemolytic zone of Staphylococcus aureus (reverse CAMP test) is useful in its identification. It can cross-react with antisera against group B streptococci.
The pathogenicity of A. haemolyticum is related to hemolysin, a neuraminidase and a phospholipase D (PLD) that preferentially act on sphingomyelin. The latter produces tissue damage, but the role in the disease of the cytotoxic effect caused by this extracellular toxin has not been established. This phospholipase is a lipid hydrolyzing enzyme that damages the mammalian cell membrane, improves bacterial adhesion and promotes necrosis of the host cell after invasion and, therefore, may be important in the pathogenesis of the disease. Recently, a cholesterol-dependent cytolysin, designated arcanolysin, has been identified as a virulence determinant.
Unlike other bacteria that cause respiratory infections, its presence is rare in the pharynx of healthy people, so it is not considered part of the usual bacterial flora. Fundamentally, it causes upper respiratory mucosal infections such as pharyngitis and sinusitis, being responsible for 2.5% of pharyngitis. A. haemolyticum infection is more common in people aged 15 to 25 years and manifests as exudative pharyngitis and/or tonsillitis accompanied by cervical lymphadenopathy. Symptoms resemble those caused by β hemolytic streptococci or viral infections. Upper respiratory infections can also be accompanied by a skin rash in the chest, abdomen, neck and extremities in 20% to 25% of the cases, so that the possible confusion with streptococcal infections or penicillin allergy increases in patients treated with it antibiotic.
In addition to respiratory infections, this organism has been implicated as a cause of skin and soft tissue infections, including chronic ulceration, wound infection, soft tissue abscesses and cellulite. In skin infections, it is often isolated in association with other microorganisms, so the pathogenic importance is difficult to interpret.
Rarely, it has been implicated in systemic and deep infections, such as endocarditis, bacteraemia, severe sepsis, osteomyelitis, meningitis, brain abscess and pneumonia. These conditions occur mainly in patients with underlying predisposing diseases such as diabetes, alcoholism or malignant neoplasms treated with antineoplastic which are accompanied by immunosuppression.
A.haemolyticum isolated from humans is susceptible to erythromycin (proposed as a first-line drug), but clindamycin, gentamicin and cephalosporins are also recommended. However, many isolates are also sensitive to penicillins, other macrolides, carbapenems, rifampicin, glycopeptides and ciprofloxacin, but resistant to trimethoprim-sulfamethoxazole. Tetracycline resistance has been described in 34% of the isolates. Isolates resistant to vancomycin, macrolides, penicillin V and fluoroquinolones have been reported. However, bactericidal tests have shown that the majority of A. haemolyticum isolates are penicillin tolerant, which can lead to treatment failures.
Tests performed in IVAMI:
- Conventional culture and identification.
- Molecular diagnosis (PCR).
- Pharyngeal exudate or nasopharyngeal aspirate.
- Samples of skin and subcutaneous infections.
- Samples from other locations of suspected infections.
Samples storing and shipping conditions:
- Refrigerated (preferred) for less than 2 days.
- Frozen: more than 48 hours.
- Conventional culture and identification: 48 to 72 hours.
- PCR for molecular targets: 24 to 48 hours.
Cost of the test: