Antibiotics In Gram-positive Bacteria Research Articles

Advancements in Topical and Systemic Antibiotic Management for Burn Wounds: A Comprehensive Literature Review

Introduction: Antimicrobial treatment in burn patient include systemic and topical antibiotic care should be carefully deliberated to prevent the development of resistant organisms Methods: This literature review was compiled using information from numerous open access web databases. Data were compiled and analyzed. Results and Discussions: To prevent antibiotic resistance and prevent infection, the best prophylactic antibiotics for burn patients are topical antibiotics. However, for the treatment of patients with extensive burns or those with antibiotic resistance, especially antibiotics for gram-positive bacteria, systemic antibiotics can be used for treatment. Conclusion: The use of antibiotics in patients with burns can be adjusted to the patient's needs. surgeons may consider its use to prevent antibiotic resistance in patients.

Molecular typing of multidrug resistant bacteria isolated from health care professionals’ mobile phone: A pilot study in Jashore, Bangladesh

Background: Nowadays, Health Care Professionals’ (HCPs) are increasingly using mobile phones which may act as reservoirs and vector for transmission of pathogens. The presence of multidrug resistant nosocomial microbes on the surface of mobile phones used by HCPs in hospitals can pose a great public health threat. So, this research was conducted to identify the concerned multi-drug resistant (MDR) bacteria and also to explore the recent status of bacterial contamination on mobile phones of HCPs in the Jashore region of Bangladesh and determine their antibiotic resistance pattern. Methods: Swab samples of mobile phones were collected between June and September 2019 from 24 different users (i.e., manager, worker, doctor and nurse) associated to four distinct hospitals of Jashore region, Bangladesh. After suitable morphological and biochemical identification, we determined their antimicrobial susceptibility by Kirby- Bauer disc diffusion method by using 18 antibiotics for Gram positive bacteria and 19 antibiotics for Gram negative bacteria. Later, the MDR isolates were grouped by amplified ribosomal DNA restriction analysis (ARDRA) and 16S rRNA sequencing with phylogeny were performed to confirm the bacteria at species level. Results: A total of 38 bacterial isolates were obtained from the sample. Enterobacter spp. isolates showed maximum resistance against Amoxicillin, followed by Ampicillin and Aztreonam (80% each) and one isolate showed highest antibiotic resistance (15 out of 19) among all the isolates. In addition, Staphylococcus spp. and Exiguobacterium spp. isolates showed 100% resistance against Penicillin, Ampicillin, Oxacillin, Erythromycin, Lincomycin and Cefotaxime. On the contrary, all of the isolates of Escherichia spp., Bacillus spp., Proteus spp. were sensitive to all tested antibiotics. Surprisingly, 20 MDR isolates were showing resistance to at least 2 antibiotics. Subsequently, three distinct genera of these MDR isolates were identified by ARDRA; the strains Enterobacter cloacae (75%), Staphylococcus warneri (15%) and Exiguobacterium aurantiacum (10%) were confirmed by the 16S rRNA phylogenetic analysis. Conclusion: We found that cell phones can act as reservoirs of multidrug-resistant pathogens, causative agents for Hospital-acquired infections. An effective hygiene practice for health care personnel should be introduced to prevent the cross-contamination by their cell phone Bangladesh Journal of Medical Science Vol. 22 No. 03 July’23 Page : 643-656

Bacillus subtilis produces (p)ppGpp in response to the bacteriostatic antibiotic chloramphenicol to prevent its potential bactericidal effect.

Antibiotics combat bacteria through their bacteriostatic (by growth inhibition) or bactericidal (by killing bacteria) action. Mechanistically, it has been proposed that bactericidal antibiotics trigger cellular damage,while bacteriostatic antibiotics suppress cellular metabolism. Here, we demonstrate how the difference between bacteriostatic and bactericidal activities of the antibiotic chloramphenicol can be attributed to an antibiotic-induced bacterial protective response: the stringent response. Chloramphenicol targets the ribosome to inhibit the growth of the Gram-positive bacterium Bacillus subtilis. Intriguingly, we found that chloramphenicol becomes bactericidal in B. subtilis mutants unable to produce (p)ppGpp. We observed a similar (p)ppGpp-dependent bactericidal effect of chloramphenicol in the Gram-positive pathogen Enterococcus faecalis. In B. subtilis, chloramphenicol treatment induces (p)ppGpp accumulation through the action of the (p)ppGpp synthetase RelA. (p)ppGpp subsequently depletes the intracellular concentration of GTP and antagonizes GTP action. This GTP regulation is critical for preventing chloramphenicol from killing B. subtilis, as bypassing (p)ppGpp-dependent GTP regulation potentiates chloramphenicol killing, while reducing GTP synthesis increases survival. Finally, chloramphenicol treatment protects cells from the classical bactericidal antibiotic vancomycin, reminiscent of the clinical phenomenon of antibiotic antagonism. Taken together, our findings suggest a role of (p)ppGpp in the control of the bacteriostatic and bactericidal activity of antibiotics in Gram-positive bacteria, which can be exploited to potentiate the efficacy of existing antibiotics.

Bacteriological profile and antibiogram analysis from a tertiary care centre in eastern India: Time to Act / ReAct

Development of antimicrobial resistance imposes a serious threat to the timely and efficient healing of mankind who fall prey to the infectious agents. It is increasingly being reported day by day throughout the world. Irrational and overuse of antibiotics coupled with unavailability of regional or local antibiogram aggravates the situation further.To understand and present the local antbiogram data for this region and bridge the existing knowledge gap about the same for this particular region.Two year data was retrospectively analyzed from a 750 bedded tertiary care centre.A total of 1143 non repeat isolates were studied, their antibiogram profiles were analyzed. Percentage of Gram negative bacteria obtained were 59.6%, while Gram Positive bacteria were obtained in 40.4% of the isolates. (22.8%) was the most common organism isolated, followed by Staphylococcus aureus (14.2%), Other sp(12.8%), sp(12.6%), (9.4%), and complex(7.4%), Miscellaneous Bacteria(13.4%). An alarming number of isolates were found to be Multidrug resistant isolates(MDRs). With the panel of antibiotics tested for Gram negative bacterial isolates, only Fosfomycin(1.5%), Nitrofurantoin(16%) & Chloramphenicol (19%) were the only antibiotics to exhibit <20% resistance. Antibiotics for Gram positive bacteria for which low resistance was observed were Vancomycin (0%), Linezolid (0.1%), Teicoplanin (<1%), Aminoglycosides (18%), Nitrofurantoin(15%), Chloramphenicol(6%) & Tetracyclines(11%). Extended Spectrum Beta lactamase(ESBL) prevalence was estimated to be 63.6% in , 82.4% in Klebsiellapneumoniae. Methicillin resistant Staphylococcus aureus (MRSA) was seen in 54% of the isolates, while Inducible clindamycin resistance was observed in 35.9% of the isolates.It is high time that we shift our focus from internationally and nationally available data on antibiogram to locally prevalent antibiotic resistance pattern. It will ensure faster patient recovery at a lesser cost and also prevent undue development of drug resistance.

Urgent need for novel antibiotics in Republic of Korea to combat multidrug-resistant bacteria.

Multidrug resistance in bacteria is an important issue and is increasing in frequency worldwide because of the limitations of therapeutic agents. From 2010 to 2019, 14 new systemic antibiotics received regulatory approval in the United States. However, few new antibiotics have been introduced in Republic of Korea to combat multidrug-resistant pathogens. Here, we introduce six novel antibiotics for Gram-positive bacteria and five for Gram-negative bacteria approved by the United States Food and Drug Administration and the European Medicines Agency from 2009 to October 2021, and recommend that they be approved for use in Republic of Korea at the earliest possible date.

Crystal structure and functional analysis of mycobacterial erythromycin resistance methyltransferase Erm38 reveals its RNA-binding site

Erythromycin resistance methyltransferases (Erms) confer resistance to macrolide, lincosamide, and streptogramin antibiotics in Gram-positive bacteria and mycobacteria. Although structural information for ErmAM, ErmC, and ErmE exists from Gram-positive bacteria, little is known about the Erms in mycobacteria, as there are limited biochemical data and no structures available. Here, we present crystal structures of Erm38 from Mycobacterium smegmatis in apoprotein and cofactor-bound forms. Based on structural analysis and mutagenesis, we identified several catalytically critical, positively charged residues at a putative RNA-binding site. We found that mutation of any of these sites is sufficient to abolish methylation activity, whereas the corresponding RNA-binding affinity of Erm38 remains unchanged. The methylation reaction thus appears to require a precise ensemble of amino acids to accurately position the RNA substrate, such that the target nucleotide can be methylated. In addition, we computationally constructed a model of Erm38 in complex with a 32-mer RNA substrate. This model shows the RNA substrate stably bound to Erm38 by a patch of positively charged residues. Furthermore, a π-π stacking interaction between a key aromatic residue of Erm38 and a target adenine of the RNA substrate forms a critical interaction needed for methylation. Taken together, these data provide valuable insights into Erm–RNA interactions, which will aid subsequent structure-based drug design efforts.

Sepsis: Antibiotic Resistances of Gram-Positive and Gram-Negative Bacterial in a Tertiary Care Hospital

Introduction: Sepsis is a systemic infection that causes multiorgan failure and death. The death rate that is caused by sepsis is increasing. This high value of death has a correlation with the resistance of antibiotics. However, increased antibiotic resistance is not balanced with new research about antibiotics. As a consequence, it causes difficulties in handling sepsis patients who need antibiotic 1-2 hours after diagnosis is enforced. Methods: This was a descriptive study with case study design to analyze medical records of the patients, evaluating the pattern of bacterial resistance to antibiotic in 221 patients with sepsis with 240 blood isolates to identify. Results: From 221 patients identified as sepsis, there were 97 male patients (43.9%) and 124 female patients (56.1%), mostly between 18-59 years old (63.8%), with the highest level in female (54.8 %) and elderly (66.3%). The bacteria that caused the most sepsis were gram-positive. The most species in gram-positive are Staphylococcus haemolyticus (16.3%) and Staphylococcus aureus (12.5%), and the most species in gram-negative is Escheriichia coli (13.3%). The most sensitive antibiotics in gram-positive bacteria were Piperacillin-Tazobactam (100%), Daptomycin (99.2%), and Clindamycin (99.2%). The sensitive antibiotics in gram-negative bacteria were Amikacin (85.9%), Cefoperazone (84.6%), and Piperacillin-Tazobactam (84.1%). Conclusion: The most sensitive antibiotics in gram-positive bacteria were Piperacillin-Tazobactam, Daptomycin, and Clindamycin. The sensitive antibitics in gram-negative bacteria were Amikacin, Cefoperazone, and Piperacillin-Tazobactam.

Resistance status of antibiotics in Gram-positive bacteria isolated from acne lesions in İstanbul

Resistance status of antibiotics in Gram-positive bacteria isolated from acne lesions in İstanbul

Aerobic Bacteriological Profile and Antimicrobial Susceptibility Pattern in Postoperative Wound Infections at a Tertiary Care Hospital

Background: Postoperative wound infections are global problem in the field of surgery associated with long hospital stay, higher treatment expenditure, morbidity and mortality. The spectrum of infecting agents varies in each institution and same institution at different time points. Surveillance of surgical site infection with feedback of appropriate data to surgeons would be desirable to reduce surgical site infection rate. Hence we conducted this research to determine the prevalence and antimicrobial susceptibility patterns of aerobic bacteria in post surgical wound infected patients in ACS Medical College & Hospital, Chennai. Materials and Methods: Pus samples collected from the patients were processed using standard bacteriological methods to be used for bacterial isolation and Antimicrobial Susceptibility pattern. Results: Among the 102 pus samples, 61 (59.80%) had bacterial growth and in that 51(83.61%) were monomicrobial and 10(16.39%) were polymicrobial with a total of 73 bacterial isolates. Among the 73 bacterial isolates 33 (45.20%) were Gram positive cocci and 40 (54.80%) were Gram negative bacilli. The most common bacteria isolated was Staphylococcus aureus 19 (26.03%), followed by Escherichia coli 18 (24.65%) and Coagulase Negative Staphylococcus 11 (15.07%). Antibiotic susceptibility test of the isolates showed that Vancomycin (100%) and Linezolid (100%) followed by Amikacin (93.94%) were the most effective antibiotics for Gram positive bacteria and for Gram negative isolates Amikacin (85%), Cefaperazone-sulbactam (80%) and Gentamycin (77.5%) were found to be the most effective. Conclusion: Surveillance of the postoperative wound infection should be done in each and every hospital at regular intervals to evolve the control strategies and reduce the infection rate.

Quantitative proteomic view associated with resistance to clinically important antibiotics in Gram-positive bacteria: a systematic review.

The increase of methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE) poses a worldwide and serious health threat. Although new antibiotics, such as daptomycin and linezolid, have been developed for the treatment of infections of Gram-positive pathogens, the emergence of daptomycin-resistant and linezolid-resistant strains during therapy has now increased clinical treatment failures. In the past few years, studies using quantitative proteomic methods have provided a considerable progress in understanding antibiotic resistance mechanisms. In this review, to understand the resistance mechanisms to four clinically important antibiotics (methicillin, vancomycin, linezolid, and daptomycin) used in the treatment of Gram-positive pathogens, we summarize recent advances in studies on resistance mechanisms using quantitative proteomic methods, and also examine proteins playing an important role in the bacterial mechanisms of resistance to the four antibiotics. Proteomic researches can identify proteins whose expression levels are changed in the resistance mechanism to only one antibiotic, such as LiaH in daptomycin resistance and PrsA in vancomycin resistance, and many proteins simultaneously involved in resistance mechanisms to various antibiotics. Most of resistance-related proteins, which are simultaneously associated with resistance mechanisms to several antibiotics, play important roles in regulating bacterial envelope biogenesis, or compensating for the fitness cost of antibiotic resistance. Therefore, proteomic data confirm that antibiotic resistance requires the fitness cost and the bacterial envelope is an important factor in antibiotic resistance.

Impact Of Systemic Antibiotic Prophylaxis In Hematopoietic Stem Cell Transplantation Recipients. A Meta-Analysis Of Randomized Controlled Trials

Objectives Fever during neutropenia occurs in > 90% and 80% of allogeneic and autologous hematopoietic stem cell transplantation (HSCT) recipients, respectively. Current guidelines recommend the prophylaxis with fluoroquinolones (FQs) in HSCT patients. Although there is evidence that antibiotic prophylaxis improve clinical outcome in patients with chemotherapy-induced neutropenia, prophylactic antibiotic therapy has not been thoroughly evaluated in HSCT recipients. Therefore, we performed a meta-analysis to evaluate the impact of systemic antibiotic prophylaxis in HSCT recipients on mortality, incidence of infection and related adverse events. Data sources We identified reports that were not restricted to those in English and not restricted to published trials through PubMed, the Cochrane Library, and references of identified studies. Review Methods We included prospective, randomized studies on systemic antibiotic prophylaxis in HSCT recipients. The outcome measures included the all-cause mortality, infection-related mortality, febrile episodes, incidence of clinically or microbiologically documented infection, bacteremia, or related adverse events. The summarized odds ratios (ORs) were calculated using the Mantel–Haenszel method and the DerSimonian–Laird method. Results Seventeen trials with 1453 patients (842 autologous and 407 allogeneic HSCT recipients) were included. The percentage of autologous and allogeneic HSCT recipients was not specified in 2 trials. Systemic antibiotic prophylaxis was compared with placebo or no prophylaxis in 10 trials and with non-absorbable antibiotic in 2 trials, respectively. Systemic antibiotics other than FQs were evaluated in five out of these 12 trials. Four trials evaluated the effect of addition of antibiotics for gram positive bacteria to FQs. Remaining 1 trial compared the two different systemic antibiotic regimens, FQs versus trimethoprim sulfamethoxazole. As a result, systemic antibiotic prophylaxis reduced the incidence of febrile episodes (OR 0.16; 95 percent confidence interval [CI], 0.09-0.30), clinically or microbiologically documented infection (OR 0.41; 95% CI 0.30-0.57) and bacteremia (OR 0.37; 95% CI 0.26-0.53) without the significant effect on all-cause mortality or infection-related mortality (OR 0.89; 95% CI 0.48-1.66, OR 1.37; 95% CI 0.50-3.76, respectively). Impact of prophylaxis with FQs on mortality was inconclusive because of small number of clinical trials evaluated. Adverse events increased in patients with systemic antibiotic prophylaxis compared to controls (OR 3.32; 95% CI 1.45-7.63). In meta-regression, percentage of allogeneic HSCT recipients was not associated with each outcome measure. With regard to the comparison between different prophylactic regimens, addition of antibiotics for gram positive bacteria to FQs decreased the incidence of bacteremia (OR 0.44; 0.24-0.80) without significant effects on all-cause mortality, infection related death and febrile episodes. There was not significant, but consistent decrease in clinically or microbiologically documented infection (OR 0.55; 95% CI 0.30-1.01). There was significant increase of adverse events in patients receiving addition of antibiotics for gram positive bacteria to FQs (OR 6.65; 95% CI 2.15-20.54). Conclusions Systemic antibiotic prophylaxis successfully reduced the incidence of infection in HSCT recipients. However, there was no significant impact on mortality. Impact of prophylaxis with FQs on mortality in HSCT recipients was inconclusive because of small number of trials evaluated. Disclosures: No relevant conflicts of interest to declare.

Prevalence of bacterial and antibiotic sensitivity in septicemia of neonates admitted to Kermanshah Imam Reza Hospital (2007-2008)

Background: Neonatal septicemia is an important cause of morbidity and mortality. The most common pathogens of bacterial sepsis and antibiotic sensitivity patterns may vary in different areas of the world. Understanding the etiology of bacteriological profiles is very important and helps to reduce the associated mortality. The aim of this study was to assess prevalence of bacterial and antibiotic sensitivity sepsis in neonates during 2007-2008. Methods: In this cross sectional descriptive study the information of neonates who have been admitted to Imam Reza Hospital were collected. Ninety out of 2175 admitted subjects had inclusive criteria including positive blood culture and clinical symptoms of fever, shock, hyporeflexia. Demographic data collected using questionnaires and SPSS version 15 was used for statistical analysis. Results: The prevalence of sepsis was 4.13%. 37.7% of bacteria were gram positive and 12 types of bacteria were isolated. The most common isolated microorganisms were staphylococcus aureus (31.1%) and Klebsiella Pneumoniae (16.7%). The mortality rate was 33.3%. The most sensitive antibiotics in gram positive bacteria were Ciprofloxacin(73.5%) , Imipenem(70.5%), Ceftriaxon (50%) and in gram negative bacteria Ciprofloxacin (76.8%), Imipenem (73.2%) and Co-Trimoxazole (44.6%).The most resistance antibiotic against gram positive bacteria were Co-Trimoxazole (35.3%), Gentamicin (32.4%), Ceftriaxon (29.4%) and in gram negative bacteria were, Ceftriaxon, Gentamicin, Cefotaxime (73.2%). Conclusions: It seems that Ciprofloxacin and Imipenem are the most appropriate antibiotics for experimental treatment prior to obtaining blood culture results in this hospital.

Evolution of peptidoglycan biosynthesis under the selective pressure of antibiotics in Gram-positive bacteria

Acquisition of resistance to the two classes of antibiotics therapeutically used against Gram-positive bacteria, the glycopeptides and the beta-lactams, has revealed an unexpected flexibility in the peptidoglycan assembly pathway. Glycopeptides select for diversification of the fifth position of stem pentapeptides because replacement of D-Ala by D-lactate or D-Ser at this position prevents binding of the drugs to peptidoglycan precursors. The substitution is generally well tolerated by the classical D,D-transpeptidases belonging to the penicillin-binding protein family, except by low-affinity enzymes. Total elimination of the fifth residue by a D,D-carboxypeptidase requires a novel cross-linking enzyme able to process the resulting tetrapeptide stems. This enzyme, an L,D-transpeptidase, confers cross-resistance to beta-lactams and glycopeptides. Diversification of the side chain of the precursors, presumably in response to the selective pressure of peptidoglycan endopeptidases, is controlled by aminoacyl transferases of the Fem family that redirect specific aminoacyl-tRNAs from translation to peptidoglycan synthesis. Diversification of the side chains has been accompanied by a parallel divergent evolution of the substrate specificity of the L,D-transpeptidases, in contrast to the D,D-transpeptidases, which display an unexpected broad specificity. This review focuses on the role of antibiotics in selecting or counter-selecting diversification of the structure of peptidoglycan precursors and their mode of polymerization.

Solving staphylococcal resistance to β-lactams

Class resistance to beta-lactam antibiotics in Gram-positive bacteria is mediated by structural changes in transpeptidase penicillin-binding proteins. These structural changes render a complex series of interactions between antibiotic and protein that are energetically unfavorable, such that the active site is inactivated not at all or too slowly to prevent cell-wall synthesis and bacterial growth. Determination of the crystal structure of the low-affinity penicillin-binding protein PBP2a, which mediates beta-lactam antibiotic resistance in staphylococci, has identified the molecular structures and interactions that are responsible for resistance. This information could be useful for designing beta-lactams to overcome these structural impediments, as well as resistance.

Cellular impermeability and uptake of biocides and antibiotics in Gram-positive bacteria and mycobacteria

Gram-positive bacteria possess a permeable cell wall that usually does not restrict the penetration of antimicrobials. However, resistance due to restricted penetration can occur, as illustrated by vancomycin-intermediate resistant Staphylococcus aureus strains (VISA) which produce a markedly thickened cell wall. Alterations in these strains include increased amounts of nonamidated glutamine residues in the peptidoglycan and it is suggested that the resistance mechanism involves 'affinity trapping' of vancomycin in the thickened cell wall. VISA strains have reduced doubling times, lower sensitivity to lysostaphin and reduced autolytic activity, which may reflect changes in the D-alanyl ester content of the wall and membrane teichoic acids. Mycobacterial cell walls have a high lipid content, which is assumed to act as a major barrier to the penetration of antimicrobial agents. Relatively hydrophobic antibiotics such as rifampicin and fluoroquinolones may be able to cross the cell wall by diffusion through the hydrophobic bilayer composed of long chain length mycolic acids and glycolipids. Hydrophilic antibiotics and nutrients cannot diffuse across this layer and are thought to use porin channels which have been reported in many species of mycobacteria. The occurrence of porins in a lipid bilayer supports the view that the mycobacterial wall has an outer membrane analogous to that of gram-negative bacteria. However, mycobacterial porins are much less abundant than in the gram-negative outer membrane and allow only low rates of uptake for small hydrophilic nutrients and antibiotics.

Identification of a structural determinant for resistance to beta-lactam antibiotics in Gram-positive bacteria.

Streptococcus pneumoniae is the main causal agent of pathologies that are increasingly resistant to antibiotic treatment. Clinical resistance of S. pneumoniae to beta-lactam antibiotics is linked to multiple mutations of high molecular mass penicillin-binding proteins (H-PBPs), essential enzymes involved in the final steps of bacterial cell wall synthesis. H-PBPs from resistant bacteria have a reduced affinity for beta-lactam and a decreased hydrolytic activity on substrate analogues. In S. pneumoniae, the gene coding for one of these H-PBPs, PBP2x, is located in the cell division cluster (DCW). We present here structural evidence linking multiple beta-lactam resistance to amino acid substitutions in PBP2x within a buried cavity near the catalytic site that contains a structural water molecule. Site-directed mutation of amino acids in contact with this water molecule in the "sensitive" form of PBP2x produces mutants similar, in terms of beta-lactam affinity and substrate hydrolysis, to altered PBP2x produced in resistant clinical isolates. A reverse mutation in a PBP2x variant from a clinically important resistant clone increases the acylation efficiency for beta-lactams and substrate analogues. Furthermore, amino acid residues in contact with the structural water molecule are conserved in the equivalent H-PBPs of pathogenic Gram-positive cocci. We suggest that, probably via a local structural modification, the partial or complete loss of this water molecule reduces the acylation efficiency of PBP2x substrates to a point at which cell wall synthesis still occurs, but the sensitivity to therapeutic concentrations of beta-lactam antibiotics is lost.

Vancomycin-resistant Leuconostoc mesenteroides and Lactobacillus casei synthesize cytoplasmic peptidoglycan precursors that terminate in lactate.

The emergence of acquired high-level resistance among Enterococcus species has renewed interest in mechanisms of resistance to glycopeptide antibiotics in gram-positive bacteria. In Enterococcus faecalis and Enterococcus faecium, resistance is encoded by the van gene cluster and is due to the production of a peptidoglycan precursor terminating in D-alanyl-D-lactate, to which vancomycin does not bind. Most Leuconostoc and many Lactobacillus species are intrinsically resistant to high levels of glycopeptide antibiotics, but the mechanism of resistance has not been elucidated. To determine whether the mechanisms of resistance are similar in intrinsically resistant bacteria, cytoplasmic peptidoglycan precursors were isolated from Leuconostoc mesenteroides and Lactobacillus casei and analyzed by mass spectrometry, revealing structures consistent with UDP-N-acetylmuramyl-L-Ala-D-Glu-L-Lys-(L-Ala)-D-Ala-D-lactate and UDP-N-acetylmuramyl-L-Ala-D-Glu-L-Lys-D-Ala-D-lactate, respectively.