Oren Zimhony

Pyrazinoic Acid and Its n-Propyl Ester Inhibit Fatty Acid Synthase Type I in Replicating Tubercle Bacilli

ABSTRACT The activity of different analogs of pyrazinamide on Mycobacterium tuberculosis fatty acid synthase type I (FASI) in replicating bacilli was studied. Palmitic acid biosynthesis was diminished by 96% in bacilli treated with n-propyl pyrazinoate, 94% in bacilli treated with 5-chloro-pyrazinamide, and 97% in bacilli treated with pyrazinoic acid, the pharmacologically active agent of pyrazinamide. We conclude that the minimal structure of pyrazine ring with an acyl group is sufficient for FASI inhibition and antimycobacterial activity.

Characterization of Mycobacterium smegmatis expressing the Mycobacterium tuberculosis fatty acid synthase I (fas1) gene.

Unlike most other bacteria, mycobacteria make fatty acids with the multidomain enzyme eukaryote-like fatty acid synthase I (FASI). Previous studies have demonstrated that the tuberculosis drug pyrazinamide and 5-chloro-pyrazinamide target FASI activity. Biochemical studies have revealed that in addition to C(16:0), Mycobacterium tuberculosis FASI synthesizes C(26:0) fatty acid, while the Mycobacterium smegmatis enzyme makes C(24:0) fatty acid. In order to express M. tuberculosis FASI in a rapidly growing Mycobacterium and to characterize the M. tuberculosis FASI in vivo, we constructed an M. smegmatis Deltafas1 strain which contained the M. tuberculosis fas1 homologue. The M. smegmatis Deltafas1 (attB::M. tuberculosis fas1) strain grew more slowly than the parental M. smegmatis strain and was more susceptible to 5-chloro-pyrazinamide. Surprisingly, while the M. smegmatis Deltafas1 (attB::M. tuberculosis fas1) strain produced C(26:0), it predominantly produced C(24:0). These results suggest that the fatty acid elongation that produces C(24:0) or C(26:0) in vivo is due to a complex interaction among FASI, FabH, and FASII and possibly other systems and is not solely due to FASI elongation, as previously suggested by in vitro studies.

An effective intervention to limit the spread of an epidemic carbapenem-resistant Klebsiella pneumoniae strain in an acute care setting: From theory to practice

BACKGROUND The highly transmissible and virulent carbapenem-resistant Klebsiella pneumoniae (CRKP) KPC-3 strain has been spreading in our medical center and in other centers in Israel since 2006. An intervention that aimed to diminish its prevalence was constructed and applied in our institute. METHODS We analyzed the efficacy of the intervention during the years 2006-2010 using quasi-experimental methodology. The intervention included guidelines for patient isolation, cohorting, and environment cleaning; education of staff; and a computerized notification system that flags CRKP carriers and provides instructions. The efficacy of the program was evaluated through 3 quantifiable parameters: incidence of CRKP isolates from clinical samples, rate of cross-infections, and rate of screening for CRKP carriage in patients at risk identified by rectal samples. RESULTS The incidence of CRKP decreased by 16-fold (P < .001), and this decrease was sustained for 30 months. The rate of cross-infection decreased from 6% during 2007-2008 to 2.7% in 2009-2010 (P < .05). This period saw an increased rate of active surveillance for carriers, from 20% to 89%. CONCLUSIONS A comprehensive infection control program can contain an outbreak of the CRKP KPC-3 strain in acute care hospitals during a nationwide outbreak of this strain.

Treatment of Clostridium Difficile-Associated Diarrhea:

OBJECTIVE: To review the literature related to the treatment and infection control of Clostridium difficile-associated diarrhea (CDAD). DATA SOURCES: A MEDLINE search (1966–August 2001) of the English literature was conducted. DATA SYNTHESIS: C. difficile is a leading cause of antibiotic-related diarrhea. The clinical spectrum extends from simple diarrhea to fulminant colitis. Cessation of antibiotic therapy alone is sufficient for mild cases; however, the majority of cases require oral metronidazole as the drug of choice. Vancomycin orally is reserved for patients who have failed to respond to metronidazole, are pregnant, or are severely ill. There is an important role for infection control interventions. CONCLUSIONS: CDAD is a common infection. Appropriate antibiotic treatment and infection control policies can prevent the spread and reduce the morbidity associated with this disease.

Pyrazinamide, but not pyrazinoic acid, is a competitive inhibitor of NADPH binding to Mycobacterium tuberculosis fatty acid synthase I

Pyrazinamide (PZA), an essential component of short-course anti-tuberculosis chemotherapy, was shown by Saturation Transfer Difference (STD) NMR methods to act as a competitive inhibitor of NADPH binding to purified Mycobacterium tuberculosis fatty acid synthase I (FAS I). Both PZA and pyrazinoic acid (POA) reversibly bind to FAS I but at different binding sites. The competitive binding of PZA and NADPH suggests potential FAS I binding sites. POA was not previously known to have any specific binding interactions. The STD NMR of NADPH bound to the mycobacterial FAS I was consistent with the orientation reported in published single crystal X-ray diffraction studies of fungal FAS I. Overall the differences in binding between PZA and POA are consistent with previous recognition of the importance of intracellular accumulation of POA for anti-mycobacterial activity.

Analogs of the antituberculous agent pyrazinamide are competitive inhibitors of NADPH binding to M. tuberculosis fatty acid synthase I.

Analogs of pyrazinamide (=pyrazine‐2‐carboxamide; PZA), an essential component of short‐course antituberculous chemotherapy, such as 5‐chloropyrazinamide (5‐Cl‐PZA) act as competitive inhibitors of NADPH binding to purified mycobacterial fatty acid synthase I (FAS I) as shown by Saturation Transfer Difference (STD) NMR studies. In addition, pyrazinoic acid esters (POE) and 5‐Cl‐POE reversibly bind to FAS I with the relatively greater affinity of longer‐chain esters for FAS I, clear from the STD amplification factors. The competitive binding of PZA and 5‐Cl‐PZA clearly illustrates that both agents bind FAS. In contrast to PZA, at low NADPH concentrations 5‐Cl‐PZA is a cooperative inhibitor of NADPH binding.

Structure-function analysis of the acyl carrier protein synthase (AcpS) from Mycobacterium tuberculosis.

We have solved the crystal structure of the acyl carrier protein synthase (AcpS) from Mycobacterium tuberculosis (Mtb) at 1.95 A resolution. AcpS, a 4-phosphopantetheinyl transferase, activates two distinct acyl carrier proteins (ACPs) that are present in fatty acid synthase (FAS) systems FAS-I and FAS-II, the ACP-I domain and the mycobacterial ACP-II protein (ACPM), respectively. Mtb, the causal agent of tuberculosis (TB), and all other members of the Corynebacterineae family are unique in possessing both FAS systems to produce and to elongate fatty acids to mycolic acids, the hallmark of mycobacterial cell wall. Various steps in this process are prime targets for first-line anti-TB agents. A comparison of the Mtb AcpS structure determined here with those of other AcpS proteins revealed unique structural features in Mtb AcpS, namely, the presence of an elongated helix followed by a flexible loop and a moderately electronegative surface unlike the positive surface common to other AcpSs. A structure-based sequence comparison between AcpS and its ACP substrates from various species demonstrated that the proteins of the Corynebacterineae family display high sequence conservation, forming a segregated subgroup of AcpS and ACPs. Analysis of the putative interactions between AcpS and ACPM from Mtb, based on a comparison with the complex structure from Bacillus subtilis, showed that the Mtb AcpS and ACPM lack the electrostatic complementarity observed in B. subtilis. Taken together, the common characteristic of the Corynebacterineae family is likely reflected in the participation of different residues and interactions used for binding the Mtb AcpS to ACP-I and ACPM. The distinct features and essentiality of AcpS, as well as the mode of interaction with ACPM and ACP-I in Mtb, could be exploited for the design of AcpS inhibitors, which, similarly to other inhibitors of fatty acid synthesis, are expected to be effective anti-TB-specific drugs.

Mutually Exclusive Genotypes for Pyrazinamide and 5-Chloropyrazinamide Resistance Reveal a Potential Resistance-Proofing Strategy

ABSTRACT The pyrazinamide (PZA) analog 5-chloropyrazinamide (5-Cl PZA) is active against mycobacterial species, including PZA-resistant strains of Mycobacterium tuberculosis. In M. smegmatis, overexpression of the type 1 fatty acid synthase (FAS I) confers resistance to 5-Cl PZA, a potent FAS I inhibitor. Since M. tuberculosis and M. bovis cannot tolerate FAS I overexpression, 5-Cl PZA resistance mutations have yet to be described for tubercle bacilli. In an attempt to identify other factors that govern the activity of 5-Cl PZA, we selected for 5-Cl PZA-resistant isolates from a library of transposon-mutagenized M. smegmatis isolates. Here, we report that increased expression of the M. smegmatis pyrazinamidase PzaA confers resistance to 5-Cl PZA and susceptibility to PZA in M. smegmatis, M. tuberculosis, and M. bovis. In contrast, while ectopic overexpression of the M. tuberculosis pyrazinamidase PncA increases PZA susceptibility, this amidase does not mediate resistance to 5-Cl PZA. We conclude that PncA-independent turnover of 5-Cl PZA represents a potential mechanism of resistance to this compound for M. tuberculosis, which will likely translate into enhanced PZA susceptibility. Thus, countersusceptibility can be manipulated as a resistance-proofing strategy for PZA-based compounds when these agents are used simultaneously.

Aspergillus peritonitis in a lupus patient on chronic peritoneal dialysis

A woman on continuous ambulatory peritoneal dialysis (CAPD) due to renal failure in systemic lupus erythematosus (SLE) developed fungal peritonitis and survived following treatment with amphotericin B and removal of the dialysis catheter. The causative organism, Aspergillus fumigatus is very rare in fungal peritonitis and may be related in this case to the combination of SLE, end-stage renal disease (ESRD) and their treatment.

A nationwide surveillance of invasive pneumococcal disease in adults in Israel before an expected effect of PCV7

Pneumococcal infections in adults vary in severity and incidence is affected by childhood vaccination policy. Here, we try to define the host determinants and the interaction with specific serotypes that result in invasive pneumococcal disease (IPD) before an expected effect of pneumococcal conjugate vaccines. A nationwide active surveillance was initiated on July 2009, at the time of national implementation of PCV7 in Israel. The surveillance included all 27 laboratories and medical centers performing blood cultures in Israel, providing all blood and CSF pneumococcal isolates from persons ≥18y. Capture-recapture method assured that >95% of all cases were reported. IPD outcome and medical history were recorded and isolates were serotyped. Four hundred and sixty IPD cases were reported (annual incidence [/100,000] of 9.25). Incidence increased with age, from 2.6 among 18-34y to 66.8 among ≥85y. The most common diagnosis was pneumonia (72.4%), followed by bacteremia with no apparent focus (20.2%). Case fatality rate increased with age and number of comorbidities (34.5% for ≥75y or those with ≥3 comorbidities vs. 9.2-11.2% among <65y or those with no comorbidities; p=0.015). Variables independently associated with mortality were: age ≥75, chronic renal failure, malignancy, neurosurgery, alcohol abuse, multi-lobar pneumonia and sepsis with no apparent focus. The predominant serotypes in patients 18-49y were 1, 5, 8, 7F and 9V (constituting 56.3% in this age-group vs. 11.9% in ≥75y; p<0.01). The predominant serotypes among patients ≥75y were 3, 19A, 23F and 14 (40.3% of this age-group vs. 12.9% of 18-49y; p<0.01). Overall, PCV7 and PCV13 covered 25.6% and 63.7% of isolates, respectively, and 30.9% and 67.9% of isolates in mortality cases respectively. This nationwide active surveillance provides the baseline incidence, mortality rates and risk group distributions of IPD in adults before expected PCV effect.