We described a case of severe pneumonia and pericarditis due to M. hominis in a previously healthy adolescent who completely recovered under doxycycline therapy. M. hominis was detected from the pleural and pericardial fluids by eubacterial PCR assay and subsequent specific PCR assay and culture. No alternative pathogen has been identified by culture, molecular or serological diagnostic procedures.
M. hominis may cause genital infections in adults and may be involved in neonatal infections. Serious extra-genital infections, such as brain abscess, pneumonia, mediastinitis, pericarditis, endocarditis, osteitis and arthritis, wound infections, peritonitis, and pyelonephritis have been reported, mainly in immunosuppressed patients [9–12]. However, such cases have also been described in immunocompetent patients, particularly in individuals with predisposing factors such as trauma, altered cardiorespiratory function and complicated urogenital manipulations or surgery.
Our review of the literature identified 11 cases of M. hominis pneumonia in immunocompetent patients (Additional file 1) [13–17].
Six cases occurred in patients with pre-existing co-morbidities (trauma or surgery, subarachnoid haemorrhage, and oesophageal carcinoma), one case in a pregnant woman, and four cases in patients with no known predisposing conditions.
Complete resolution has been described in the five patients who received antibiotic therapy active against M. hominis. In contrast, among those receiving an inadequate antibiotic therapy, four died and two recovered suggesting that untreated M. hominis infection may aggravates pre-existing conditions and lead to death.
Initially, our patient experienced a severe worsening of her clinical condition while on antibiotics active against common respiratory pathogens, but has fully recovered after receiving an antimicrobial drug active against M. hominis.
M. hominis may be an underestimated cause of severe pneumonia in previously healthy patients, particularly when other common etiological agents have been ruled out in those not responding to standard therapy.
The M. hominis strain isolated in our patient was susceptible to both tetracyclines and quinolones. We used a susceptibility assay based on breakpoint cut offs set according to the recommendations of the Clinical and Laboratory Standards Institute (CLSI) .
Unpublished data from our center on the antibiotic susceptibility of M. hominis strains isolated from the genital and respiratory tracts between 2000 and 2008 are in accordance with the data from the literature: 55% are susceptible to ciprofloxacin (5/9), 100% are susceptible to doxycycline (11/11), and 100% are resistant to clarithromycin (9/9).
M. hominis is intrinsically resistant to macrolides [19–21], and tetracyclines have been considered the drugs of choice. However, the therapeutic activity of tetracyclines may become unreliable due to resistance phenomena induced by previous antibiotic exposure. Moreover, they are no longer a valid therapeutic option in some areas [5, 7]. As no resistance to levofloxacin (or other newer fluoroquinolones) and clindamycin is yet identified, these drugs could be a suitable therapeutic alternative [5, 7, 20, 22, 23]. The increasing resistance of M. hominis strains to antibiotics makes guidance of therapy by in vitro susceptibility tests of paramount importance in invasive infections leading to life-threatening situations.