Persistence and evolution of Pseudomonas aeruginosa following initiation of highly effective modulator therapy in cystic fibrosis

Today, more than 90% of people with cystic fibrosis (pwCF) are eligible for the highly effective cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapy called elexacaftor/tezacaftor/ivacaftor (ETI) and its use is widespread. Given the drastic respiratory symptom improvement experienced by many post-ETI, clinical studies are already underway to reduce the number of respiratory therapies, including antibiotic regimens, that pwCF historically relied on to combat lung disease progression. Early studies suggest that bacterial burden in the lungs is reduced post-ETI, yet it is unknown how chronic Pseudomonas aeruginosa populations are impacted by ETI. We found that pwCF remain infected throughout their upper and lower respiratory tract with their same strain of P. aeruginosa post-ETI, and these strains continue to evolve in response to the newly CFTR-corrected airway. Our work underscores the continued importance of CF airway microbiology in the new era of highly effective CFTR modulator therapy.

IMPORTANCE

The highly effective cystic fibrosis transmembrane conductance regulator modulator therapy Elexakaftor/Tezacaftor/Ivacaftor (ETI) has changed cystic fibrosis (CF) disease for many people with cystic fibrosis. While respiratory symptoms are improved by ETI, we found that people with CF remain infected with Pseudomonas aeruginosa. How these persistent and evolving bacterial populations will impact the clinical manifestations of CF in the coming years remains to be seen, but the role and potentially changing face of infection in CF should not be discounted in the era of highly effective modulator therapy.

ID: 49: STUDY OF MINIMUM INHIBITORY CONCENTRATION OF CEFAZOLIN FOR METHICILLIN SENSITIVE STAPHYLOCOCCUS AUREUS AND CORRELATION WITH OXACILLIN SUSCEPTIBILITY

Background

Cefazolin, a first generation cephalosporin, has been used for the treatment of Methicillin Sensitive Staphylococcus aureus (MSSA) infections since the 1970s. There have now been reported cases of failed therapy with cefazolin. High-level β-lactamase producing strains of S. aureus can inactivate the susceptible β-lactam (cefazolin) at a rate high enough to overcome its antibacterial effect. These strains typically have a high Minimum Inhibitory Concentration (MIC) for cefazolin when a large inoculum is used. About 20% of MSSA isolates have been shown to have a substantial inoculum effect suggesting that cefazolin treatment might be associated with clinical failure in serious MSSA infections. The minimum inhibition concentration (MIC) for cefazolin is not provided on all standard sensitivity panels and susceptibility is extrapolated from the report on oxacillin. The goal of this study was to analyze the MIC of cefazolin for MSSA isolates to determine the correlation of cefazolin susceptibility and in vitro susceptibility of oxacillin. We also evaluated the MIC of alternative antibiotics as part of this study for use in patients that might be allergic to penicillin.

Method

Thirty two isolates of MSSA were randomly selected from repositories of isolates at Memorial Medical Center hospital's microbiology department from 2015. The isolates were from patients with a wide variety of diagnoses, including bacteremia, osteomyelitis and wound infections. S. aureus ATCC 29213 was used as controls. MICs were determined by a Kirby Bauer method for cefazolin and Epsilometer test for other antibiotics that were studied. Inocula were standardized using optical density measurements, with determinations of CFU/ml to determine the inoculum concentrations. IN addition to cefazolin, we obtained the MIC for daptomycin, oxacillin, ceftaroline and telavancin as well.

Results

Of the thirty two MSSA isolates tested, 100% were susceptible to cefazolin. The mean zone of inhibition (ZOI) was 29.18 with standard deviation of 3.67 for cefazolin (29–35 mm ZOI with ATCC strains of MSSA) . All the isolates were susceptible to Oxacillin with mean MIC of 0.7735 with standard deviation of 0.30. Daptomycin, ceftaroline and telavancin were 100% susceptible with mean MIC of 0.27, 0.25, and 0.07, respectively. All isolates were studied for the alternate antibiotics and no resistance was noted.

Conclusion

The MIC of cefazolin for MSSA determined by in vitro susceptibility to oxacillin was entirely in the susceptible range with 100% correlation. Daptomycin, ceftaroline and telavancin are suitable alternative antibiotics for treatment of patients with infections due to MSSA in whom anti-staphylococcal penicillins cannot be used due to penicillin allergic, intolerance, and/or non-availability since there is not much resistance to these antibiotics in MSSA.

Metallo-beta-lactamase producing gram-negative bacterial isolates

BACKGROUND

The global emergence of metallo-β-lactamase (MBL) producing bacterial isolates causing lower respiratory tract infection (LRTI) has resulted in fewer therapeutic options in treatment modalities. However, to our knowledge no studies regarding MBLs had been done so far in Nepal. Therefore, this study was carried out to assess the current level of MBL producing bacterial isolates in our setup.

METHODS

This was a cross-sectional study conducted over a period of six months (June to November 2008) at Bacteriology laboratory of a teaching hospital. A total of 1120 specimens representing lower respiratory tract (sputum, endotracheal secretion and bronchial washing) were processed from outpatients and inpatients, with suspected LRTI, at TUTH. The specimens were collected and processed according to the standard methodology. Combination disk method and Double disk synergy test methods were used for the detection of MBL producing isolates.

RESULTS

Respiratory pathogens were recovered from 497 (44.4%) of suspected cases. Among these, gram-negative bacteria were observed in 448 (84.0%). Multidrug resistance (MDR) was found in 286 (53.7%) of the total bacterial isolates. MBL was present in 6 (1.3%) of the total 448 gram-negative isolates. MBL was detected by both DDST and CD methods in 3 isolates each of Pseudomonas aeruginosa and Acinetobacter spp. from inpatients. All MBL producers were MDR.

CONCLUSIONS

MBL-producing gram negative bacteria were detected from LRTI isolates in this study and this data can be used as base-line information of this novel type of β-lactamase in our setup.

Granulocyte colony-stimulating factor dosing in pegylated interferon alpha-induced neutropenia and its impact on outcome of anti-HCV therapy

Many patients with chronic hepatitis C (HCV) infection undergoing treatment with pegylated interferon-alpha (PEG-IFN-alpha) and ribavirin develop neutropenia requiring dose reduction or granulocyte colony-stimulating factor (G-CSF) supplement. We analysed the database of patients who completed treatment for chronic HCV infection between 2003 and 2006. Patients with absolute neutrophil counts below 1000 cells/microL were initiated on G-CSF (G-CSF group) while a matching group of patients who received anti-HCV treatment without developing neutropenia were used as a control group (non-G-CSF group). Patients on the G-CSF arm were divided into two subgroups based on the timing of G-CSF administration relative to PEG-IFN-alpha administration. Of the 163 patients with HCV infection, 30 patients received G-CSF, most of who were maintained on 300 microg of G-CSF once a week. Administration of G-CSF 2 days before or after each dose of PEG-IFN-alpha did not make a significant difference in the neutrophil counts. In the G-CSF arm, 23 of 30 patients (77%) had undetectable end-of-treatment viral response which was comparable with 27 of 30 in the control group (90%; P = 0.17). There was no statistically significant difference in the sustained viral response between the two groups (61%vs 76%, P = 0.18). In most patients PEG-IFN-alpha induced neutropenia improved with a once-a-week dose of G-CSF with a comparable virological outcome. Timing of G-CSF administration did not make any significant impact on the patient's neutrophil counts but was better tolerated when given 2 days apart from PEG-IFN-alpha.

Lymphoproliferative responses to mitogens and prepared antigens of M. avium complex in patients with HIV infection

Published reports have demonstrated that antigens of Mycobacterium avium complex (MAC) can suppress the normal response to mitogens in lymphoproliferation assays. We therefore studied the lymphoproliferative (LP) function of PBMC from 55 HIV-infected patients and 16 controls in response to mitogens with and without MAC antigen. As expected, LP responses decline with progressive decline in CD4 count; MAC antigen in combination with PHA further suppresses that response in a dose-dependent manner. More relevant were the LP responses in those with CD4 counts less than 100. All patients with MAC disease had poor responses (stimulation index, SI < 10) to PHA or anti-CD3 with or without MAC antigen. Those who did not have nor subsequently developed MAC were both good (SI > 10) or poor responders (SI < 10). The suppressive effect of MAC on lymphocyte function may serve as a weak virulence factor which is only relevant in severely immunocompromised HIV patients.