We investigated the effects of bicarbonate on the growth of several different bacteria as well as its effects on biofilm formation and intracellular cAMP concentration in Pseudomonas aeruginosa. Biofilm formation was examined in 96-well plates, with or without bicarbonate. The cAMP production of bacteria was measured by a commercial assay kit. We found that NaHCO3 (100 mmol l-1) significantly inhibited, whereas NaCl (100 mmol l-1) did not influence the growth of planktonic bacteria. MIC and MBC measurements indicated that the effect of HCO3− is bacteriostatic rather than bactericidal. Moreover, NaHCO3 prevented biofilm formation as a function of concentration. Bicarbonate and alkalinization of external pH induced a significant increase in intracellular cAMP levels. In conclusion, HCO3− impedes the planktonic growth of different bacteria and impedes biofilm formation by P. aeruginosa that is associated with increased intracellular cAMP production. These findings suggest that aerosol inhalation therapy with HCO3− solutions may help improve respiratory hygiene in patients with cystic fibrosis and possibly other chronically infected lung diseases.

The purpose of this study was to investigate the impact of fluoroquinolone resistance on the existence and dynamic of MRSA clones. Resistance to ciprofloxacin was induced in strains of community-acquired (CA) MRSA from various sequence types and the fitness cost suffered by mutant derivatives measured in a propagation assay. In addition, the fitness of fluoroquinolone resistant health care-associated (HA) MRSA isolates from major clones prevalent in Hungary were compared with each other and with those of the CA-MRSA derivatives. The genetic background of fluoroquinolone resistance and fitness cost in CA-MRSA was investigated. The fitness cost observed in the CA-MRSA derivatives proved diverse; the derivatives of the ST30-MRSA-IV strain suffered significantly greater fitness cost than those of the ST8-MRSA-IV and ST80-MRSA-IV isolates. Strains from the New York-Japan (ST5-MRSA-II), South German (ST228-MRSA-I) and EMRSA-15 (ST22-MRSA-IV) HA-MRSA clones proved more viable than CA-MRSA derivatives with similar MIC values to ciprofloxacin and HA-MRSA strains from the Hungarian/Brazilian clone (ST239-MRSA-III). Our strains from the New York-Japan, South-German and EMRSA-15 clones seem to have a competitive edge over the tested CA-MRSA isolates in the health care setting. The greater fitness observed in our New York-Japan and South-German strains could account for the replacement by them of the Hungarian/Brazilian clone in Hungary about ten years ago. Alterations in relevant genes were detected. The Ser80 → Phe mutation in the grlA gene may have seriously compromised viability. Surprisingly silent nucleotide substitutions in the grlB gene seemed to impact fitness in derivatives of the ST30-MRSA-IV isolate.

Background Staphylococcus aureus bloodstream infections (BSI) cause significant morbidity and mortality due to the frequent antibiotic resistance, toxin and adhesin production of the bacterium. These characteristics differ significantly in methicillin resistant (MRSA) and methicillin sensitive S. aureus (MSSA) and also among isolates of different MRSA clones, contributing to the outcome of S. aureus bacteraemia. Methods In this study, all MRSA BSI isolates from Semmelweis University, Budapest, Hungary, isolated between 2011–2016 and the same number of matched MSSA (overall 306 isolates) were characterised in terms of antibiotic susceptibility, virulence genes, clonality and their association with all-cause 30-day mortality. Effect of patient related variables, such as age, gender and comorbidities were also investigated. Results ST22-MRSA-IV and ST5-MRSA-II were the most prevalent clones in our study. SCCmec I isolates showed the highest resistance rates and SCCmec II carried most virulence genes. Infections caused by SCCmec IV isolates were associated with the highest mortality rate (42.2%), despite the similar comorbidity rates of the different patient groups. All-cause 30-day mortality was 39.9% in the MRSA and 30.7% in the MSSA group. Increased teicoplanin MIC was associated with high mortality rate. Resistance to ciprofloxacin, erythromycin and clindamycin was common in MRSA, whereas MSSA isolates were more sensitive to all antibiotics with the exception of doxycycline. All MRSA isolates were sensitive to glycopeptides and linezolid; resistance to rifampicin and sulfamethoxazole-trimethoprim was low. MRSA isolates carried more adhesion genes, superantigens were more frequent in MSSA. Panton-Valentine leukocidin was found in 2.3% of the isolates. Conclusion This study provides insight into the clonal composition and associated mortality of BSI S. aureus isolates in Hungary. The results suggest that the outcome of the infection is determined by the antibiotic resistance, genotype of the bacterium, and patient-related factors; rather than the virulence factors carried by the bacteria.

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