Molecular analysis of methicillin-resistant Staphylococcus aureus as a causative agent of bronchopulmonary infection: relation to colonization in the upper respiratory tract

Successful infection control for a vancomycin-intermediate Staphylococcus aureus outbreak in an advanced emergency medical service centre

BACKGROUND

A vancomycin-intermediate Staphylococcus aureus (VISA) (vancomycin minimum inhibitory concentration: 4mg/L) outbreak occurred in an advanced emergency medical service centre [hereafter referred to as the intensive care unit (ICU)] between 2013 and 2014.

AIM

Our objective was to evaluate the infection control measures that were successful.

METHODS

Seventeen VISA strains were isolated from the sputum of 15 inpatients and the skin of two inpatients. Fourteen VISA strains were recognized as colonization. However, three VISA strains were isolated from the sputum of three inpatients with pneumonia. Environmental cultures were performed and VISA strains were detected in five of 65 sites. Pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST) was performed on 21 VISA strains.

FINDINGS

Molecular typing including PFGE and MLST showed that the patterns of 19 VISA strains were identical and those of the other two VISA strains were possibly related. This meant that a horizontal transmission of VISA strains had occurred in the ICU. In August 2013, the infection control team began interventions. However, new inpatients with VISA strains continued to appear. Therefore, in October 2013, the ICU was partially closed in order to try to prevent further horizontal transmission, and existing inpatients with the VISA strain were isolated. Although new cases quickly dissipated after the partial closure, it took approximately five months to eradicate the VISA outbreak.

CONCLUSION

Our data suggest that despite the employment of various other infection control measures, partial closure of the ICU was essential in terminating this VISA outbreak.

Infection control for a methicillin-resistant Staphylococcus aureus outbreak in an advanced emergency medical service center, as monitored by molecular analysis

A methicillin-resistant Staphylococcus aureus (MRSA) outbreak occurred in an advanced emergency medical service center between 2010 and 2011. Our objective was to evaluate the status of the MRSA outbreak, as monitored by molecular analysis. Twenty-eight MRSA strains were isolated from blood samples from 11 patients, from other specimens (pharynx, nasal cavity, etc.) from 12 patients, from two environmental samples, and from the skin, middle nasal meatus, and urine of one patient each from other wards. Pulsed-field gel electrophoresis (PFGE) was performed to evaluate horizontal transmission. Molecular typing by PFGE showed that the 28 MRSA strains presented 7 patterns in total, and that 11 of the MRSA strains had the same PGFE pattern. Unselective use of intranasal mupirocin ointment, MRSA monitoring for new inpatients, and prevention of direct or indirect contact infection were performed. However, the number of inpatients with MRSA did not quickly decrease, and additional molecular typing by PFGE showed that 10 of 19 MRSA strains found (5 of 6 from blood, 5 of 13 from other specimens) were the same as those found previously. Lectures and ward rounds were performed repeatedly, and staff participation in ward rounds was suggested. Finally, the number of inpatients with MRSA significantly decreased more than 6 months after the intervention. Although the MRSA outbreak was thought to have ended, follow-up molecular typing by PFGE showed that horizontal transmission persisted. Our data suggest that various combinations of infection control measures are essential when dealing with an MRSA outbreak, and monitoring by molecular analysis using PFGE is useful to identify the status of the outbreak.

Anti-staphylococcal potential of Callistemon rigidus

The last decade witnessed the emergence of Staphylococcus aureus- a versatile human pathogen, as a deadly superbug. The enormous genetic plasticity of the organism assists it to endlessly evolve resistance mechanisms against existing anti-infectives thus necessitating the need to control the spread of resistant staphylococcal isolates in hospitals and health care settings. This in turn demands the incessant exploration of newer biological matrices in search of diverse chemical entities with novel drug targets. Since time immemorial higher plants continue to be the best source of newer compounds with high therapeutic potential. Lead fractions from same or different plants can be developed into effective antibacterial polyherbal formulations. A lead fraction from methanolic extract of leaves of Callistemon rigidus exhibited a dose dependent antistaphylococcal activity during in vitro agar well assay against a panel of twenty seven clinical multidrug resistant S. aureus isolates. Further, minimal inhibitory concentration (MIC) evaluation by in vitro 96-well microplate based assay established a MIC range of 1.25–80 μg/ml as compared to 5–320 μg/ml of positive control, Cefuroxime sodium. The MIC50 and MIC90 of the methanolic lead fraction were 5 μg/ml and 40 μg/ml respectively. The present study thus signifies the vast potential of the lead fraction from Callistemon rigidus for future development into a herbal drug/ formulation and to impede global health crisis due to multidrug resistant Staphylococcus aureus.

Persistence of Staphylococcus aureus L-form during experimental lung infection in rats

The course of pulmonary infection in rats infected by intranasal inoculation with a Staphylococcus aureus stable protoplast L-form was studied. Blood and bronchoalveolar samples were taken on days 3, 7, 14 and 30 after challenge and were investigated by microbiological, electron-microscopic, cytochemical and cytometric methods. The electron microscopic data and isolation of L-form cultures from bronchoalveolar samples at all experimental times demonstrated the ability of S. aureus L-form cells to internalize, replicate and persist in the lungs of infected rats to the end of the observation period, in contrast to the S. aureus parental form. It was found that persisting L-form evoked ineffectual phagocytose by alveolar macrophages and low but long-lasting inflammatory reaction in rats. The experimental model of pulmonary infection with S. aureus L-form suggests that the cell-wall-deficient bacterial forms may be involved in the pathogenesis of chronic and latent lung infections.

Significant reduction of nosocomial pneumonia after introduction of disinfection of upper airways using povidone-iodine in geriatric wards

We investigated the efficacy of disinfection of the upper airway using povidone-iodine against nosocomial pneumonia in geriatric wards. Cases of nosocomial pneumonia were retrospectively analyzed between January 1991 and March 1995 in geriatric wards (190 beds). Moreover, the relationship concerning methicillin-resistant Staphylococcus aureus (MRSA) isolates between patient and environment was investigated using pulsed-field gel electrophoresis (PFGE) with the SmaI restriction enzyme. The incidence of nosocomial pneumonia decreased significantly (p < 0.05). Major causative organisms of nosocomial pneumonia were MRSA and Pseudomonas aeruginosa, which significantly decreased. PFGE studies showed that the patterns of MRSA isolates show a strong association between patient and environment. Our study indicates that disinfection of the upper airways by povidone-iodine is very important in the prevention of nosocomial pneumonia in geriatric wards.

Molecular evidence that nasal carriage of Staphylococcus aureus plays a role in respiratory tract infections of critically ill patients

The relationship between nasal Staphylococcus aureus carriage and lower respiratory tract infections was studied in 16 critically ill patients. S. aureus strains from nasal and bronchial samples were characterized by pulsed-field gel electrophoresis. In all but one case, nasal and bronchial strains were genetically identical in the same patients.

Enterocolitis caused by methicillin-resistant Staphylococcus aureus: molecular characterization of respiratory and digestive tract isolates

We investigated the mechanism of outbreak of enterocolitis caused by methicillin-resistant Staphylococcus aureus (MRSA). Five epidemiological markers [coagulase type, enterotoxin type, toxic shock syndrome toxin-1 (TSST-1) production, beta-lactamase production and pulsed-field gel electrophoresis (PFGE)] of 45 strains of MRSA isolated simultaneously from the respiratory tract (nasal cavity and/or pharynx and/or sputum) and stool (plus one sample of gastric juice) in 13 patients (8 males and 5 females, mean age, 77.1 years) were compared retrospectively. Forty-four of the 45 isolates of MRSA were positive for enterotoxin C and TSST-1 production, and the remaining isolate was positive for enterotoxin A and negative for TSST-1 production. All isolates were coagulase type II, and 27 showed beta-lactamase production. The patterns of coagulase type, enterotoxin type, TSST-1 and beta-lactamase production of MRSA isolated from the respiratory tract were similar to those of MRSA isolated from the intestine in 12 of 13 patients. Molecular typing by PFGE demonstrated that the pattern of respiratory tract isolates was identical to those of stool isolates in 9 (69.2%), similar in 3 (23.1 %), and different in 1 (7.7%). The data suggested that enterocolitis might be caused by the MRSA colonized in the respiratory tract and incorporated into the digestive tracts. Therefore, we propose that early eradication of MRSA in the respiratory tract is important for protection of patients against the development of enterocolitis, particularly in susceptible patients, e.g., immunocompromised or pre-operated patients with digestive diseases, especially malignant disease.

Low concentrations of mupirocin in the pharynx following intranasal application may contribute to mupirocin resistance in methicillin-resistant Staphylococcus aureus

We describe a patient with methicillin-resistant Staphylococcus aureus (MRSA) colonizing the pharynx. The MIC of mupirocin was 0.25 microg/ml before treatment and increased after treatment to 8 microg/ml. Using pulsed-field gel electrophoresis, we confirmed that the genotypes of MRSA that colonized the pharynx before and after the use of mupirocin were identical. We measured the delivery of mupirocin to the pharynx in three normal volunteers and two patients. Low concentrations of mupirocin were present in the pharynx in all cases 10 min to 3 days after intranasal application. Our data suggested that low concentrations of the drug in the pharynx after intranasal application of mupirocin ointment might explain the selection of mupirocin resistance in MRSA.