Mycobacterium abscessus wound infection

Mycobacterium fortuitum and Mycobacterium abscessus infections in the foot and ankle in two immunocompetent patients

Nontuberculous mycobacteria (NTM) infections of the musculoskeletal system are commonly missed due to its rarity and the absence of systemic symptoms. A high clinical index of suspicion is required to recognize such infections as they may occur in immunocompetent hosts. We present two cases of foot and ankle NTM infections involving Mycobacterium fortuitum and Mycobacterium abscessus in two such patients. The first case involves an 83-year old lady who presented with a two-month history of multiple foot abscesses initially treated at a rural hospital. She underwent drainage and debridement of her foot, with eventual cultures growing Pseudomonas aeruginosa and Mycobacterium abscessus. She was initially treated with clarithromycin and doxycycline. At one year follow-up review, her wound healed completely. The second case involves a 55-year old man who presented with infection following midfoot fusion and anterolateral thigh flap for an open complex fracture dislocation of his right foot. Cultures eventually grew Mycobacterium fortuitum and he was treated with cefoxitin, clarithromycin and doxycycline. 10 months after his initial injury, the infection has cleared and his flap was clean. Through these 2 cases, we hope to highlight the unusual presentations of such infections and illustrate that with a high initial index of suspicion and appropriate treatment, these infections can be treated successfully.

Mab_3168c, a putative acetyltransferase, enhances adherence, intracellular survival and antimicrobial resistance of Mycobacterium abscessus

Mycobacterium abscessus is a non-tuberculous mycobacterium. It can cause diseases in both immunosuppressed and immunocompetent patients and is highly resistant to multiple antimicrobial agents. M. abscessus displays two different colony morphology types: smooth and rough morphotypes. Cells with a rough morphotype are more virulent. The purpose of this study was to identify genes responsible for M. abscessus morphotype switching. With transposon mutagenesis, a mutant with a Tn5 inserted into the promoter region of the mab_3168c gene was found to switch its colonies from a rough to a smooth morphotype. This mutant had a higher sliding motility but a lower ability to form biofilms, aggregate in culture, and survive inside macrophages. Results of bioinformatic analyses suggest that the putative Mab_3168c protein is a member of the GCN5-related N-acetyltransferase superfamily. This prediction was supported by the demonstration that the mab_3168c gene conferred M. abscessus and M. smegmatis cells resistance to amikacin. The multiple roles of mab_3168c suggest that it could be a potential target for development of therapeutic regimens to treat diseases caused by M. abscessus.

Genetic analysis of new 16S rRNA mutations conferring aminoglycoside resistance in Mycobacterium abscessus

OBJECTIVES

We studied the development and fitness cost of 2-deoxystreptamine aminoglycoside resistance of Mycobacterium abscessus.

METHODS

Spontaneous 2-deoxystreptamine aminoglycoside-resistant mutants were selected and the frequency of their appearance was determined. The 3' part of the rrs gene was sequenced to characterize mutations. Additionally, we determined the MICs of aminoglycoside drugs for the different mutants obtained. The dominance/recessivity traits of the different mutations were examined and we explored the potential cost conferred by the mutations selected in vitro on the fitness of these isolates compared with the wild-type strain.

RESULTS

The in vitro mutation rate for 2-deoxystreptamine aminoglycoside resistance was ∼10(-7) mutations/cell division. In addition to the known rrs A→G substitution at position 1408 (Escherichia coli numbering), which confers kanamycin resistance (Kan(R)), three new substitutions in rrs were identified in M. abscessus Kan(R) mutants, i.e. T→A at 1406, C→T at 1409 and G→T at 1491. Heterodiploids carrying genomic mutations T→A at 1406 and A→G at 1408 with the wild-type rrs gene carried by the pNBV1 vector showed a resistant phenotype. In contrast, heterodiploids carrying genomic mutations C→T at 1409 and G→T at 1491 with the wild-type rrs gene carried by the pNBV1 vector had a susceptible phenotype. No burden on fitness was observed for the different mutations.

CONCLUSION

Mutations in the rrs gene that confer high-level 2-deoxystreptamine aminoglycoside resistance on M. abscessus differ in their dominance/recessivity traits and have no biological cost under our experimental conditions.

Culture-Negative Surgical Site Infections

BACKGROUND

The appearance of postoperative surgical site infection (SSI) in the absence of culturable bacterial pathogens is a common dilemma for the surgeon.

METHODS

The literature was searched through references to primary articles, as well as a MEDLINE review, for reports of culture-negative SSIs.

RESULTS

Potential causes of culture-negative SSIs include prior antimicrobial therapy; the presence of fastidious or slow-growing microorganisms such as mycobacteria, Mycoplasma spp., and Legionella spp.; infection caused by mundane bacteria that may be dismissed as "contaminants"; factitious infection; and others.

CONCLUSIONS

We review the recognized causes of "culture negative" SSIs and discuss the laboratory capabilities that may enhance recognition of many of these pathogens and management options.

Unusual infectious complications of dermatologic procedures

Because dermatologic procedures disrupt skin integrity, they alter the body's protective barrier and predispose individuals to cutaneous infection. Postoperative wound infections--even with common pathogens such as S. aureus--seldom complicate dermatologic procedures; however, unusual infections have been reported to complicate excisions, biopsies, skin grafts, chemical peels, dermabrasion, laser resurfacing, liposuction, blepharoplasty, and injections (eg, with anesthetic solutions or botulinum toxin). Numerous environmental and patient risk factors increase the rate of postoperative wound infections, but otherwise healthy individuals undergoing relatively simple procedures are sometimes affected. Obtaining a thorough patient, history (including history of prior HSV infection or any immunocompromising factors) is crucial. Patients should be warned of potential complications, particularly when they are undergoing cosmetic procedures. It is important to maintain a high index of suspicion for possible wound infection in all patients that extends several months postoperatively. Manifestations of unusual postoperative infections are highly variable, and they might be secondary to bacterial, fungal, viral, or parasitic pathogens. Bacterial lesions are often polymicrobial, and bacterial superinfection can exacerbate other wound complications such as HSV reactivation. Most wound infections remain localized, but occasionally systemic disease occurs. For example, cutaneous diphtheria or rapidly growing mycobacteria rarely disseminate, whereas TSS results in systemic disease caused by toxin release. Some unusual postsurgical infections are self-limited, but they can still be potentially life threatening or disfiguring. Antimicrobial prophylaxis might reduce the risk of wound infection in some cases. Clinicians can better care for patients by becoming familiar with the causes and clinical manifestations of unusual dermatologic postoperative wound infections (Table 1). Following the recognition of an infectious process, appropriate diagnostic procedures allow for pathogen identification and the prompt institution of indicated therapy.