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PubMed2026

The inoculum effect of methicillin-susceptible Staphylococcus aureus on cefazolin and other antimicrobial agents.

UNLABELLED: The inoculum effect (IE) refers to a reduced susceptibility of methicillin-susceptible Staphylococcus aureus (MSSA) to certain antibiotics under high bacterial inocula and may contribute to treatment failure. This exploratory study assessed IE prevalence among 234 nonduplicate MSSA isolates across 11 agents spanning major therapeutic classes, including cefazolin, and characterized IE-positive clones via whole-genome sequencing to inform clinical strategies. Minimum inhibitory concentrations (MICs) were determined by broth microdilution at standard and high inocula. Whole-genome sequencing was performed on IE-positive strains to identify β-lactamase types and conduct multilocus sequence typing. The highest prevalence of IE was observed for trimethoprim-sulfamethoxazole (9.4%), followed by erythromycin (8.8%), linezolid (6.8%), penicillin (6.1%), clindamycin (5.5%), vancomycin (3.8%), cefazolin (3.0%), levofloxacin (1.5%), tetracycline (0.5%), and oxacillin and gentamicin (0.0%). All cefazolin IE-positive strains carried blaZ type A, and ST25 was the most common sequence type (42.9%). For trimethoprim-sulfamethoxazole, erythromycin, and clindamycin IE, ST7 was the most common sequence type (22.7%, 26.7%, and 33.3%, respectively). ST1281 and ST188 were the predominant sequence types among strains exhibiting linezolid IE and vancomycin IE (25.0% and 33.3%, respectively). Among the 234 MSSA strains, 66.7% of ST59, 60.0% of ST25, 58.3% of ST5, and 54.2% of ST7 strains exhibited IE to at least one antimicrobial agent. Cefazolin IE was associated with blaZ type A, and ST5, ST7, ST59, and ST25 were the major sequence types associated with IE across the antimicrobial classes tested. IMPORTANCE: Methicillin-susceptible Staphylococcus aureus (MSSA) can show an inoculum effect on multiple antimicrobial agents, which may reduce antibiotic activity under high-burden conditions. In this study, MSSA isolates from Shanghai exhibited inoculum effects on several commonly used agents, although the overall detection rates were low. Cefazolin inoculum effect was specifically associated with blaZ type A, and several major sequence types were more likely to exhibit this phenotype. These findings improve our understanding of the epidemiology of the inoculum effect in MSSA and may help guide laboratory detection and antimicrobial treatment decisions.

Cefazolin↗
PubMed2026

Ceftriaxone for methicillin-susceptible Staphylococcus aureus bloodstream infections is associated with increased short-term mortality: a systematic review and meta-analysis.

BACKGROUND: Bloodstream infections (BSIs) by methicillin-susceptible Staphylococcus aureus (MSSA) are a significant cause of morbidity and mortality, traditionally treated with antistaphylococcal penicillins (ASPs) or cefazolin. Ceftriaxone has emerged as an alternative due to its once-daily dosing regimen and favourable safety profile; however, its efficacy compared to the standard of care (SoC) remains controversial. This evidence synthesis aimed to assess the role of ceftriaxone in treating MSSA-BSIs. METHODS: A systematic literature search was conducted in PubMed, Embase, and Scopus up to December 31, 2025 (PROSPERO protocol CRD42024595748). Studies comparing ceftriaxone to ASPs or cefazolin for MSSA-BSIs were included. Primary outcomes were 30-day and 90-day all-cause mortality . Pooled effect sizes with their 95% confidence intervals (CIs), were calculated using random-effects models, odds ratios (ORs) and mean differences (MDs) according to the type of outcome. RESULTS: Eleven studies totalling 2,568 patients were included. Ceftriaxone was associated with significantly increased 30-day mortality (OR 3.33; 95% CI: 2.17-5.10), although differences at 90 days were not significant (OR 1.71; 95% CI: 0.75-3.90). No significant differences were noted for clinical success (OR 0.49; 95% CI: 0.19-1.26), microbiological clearance (OR 1.66; 95% CI: 0.73-3.82). Adverse event rates were similar between groups. CONCLUSION: Given the availability of various alternatives and the consistent short-term mortality signal observed, routine use of ceftriaxone for MSSA-BSIs, especially as initial therapy, is not supported by current evidence. Only novel findings from randomized studies may change the place in therapy of the drug in this context.

Humans↗
PubMed1992

Development of new antibiotic resistance in methicillin-resistant but not methicillin-susceptible Staphylococcus aureus.

The frequency of infections caused by multidrug-resistant Staphylococcus aureus continues to increase while the numbers of alternative therapeutic agents remain limited. To investigate the changing patterns of in-vitro susceptibility of S. aureus to 16 antibiotics, 190 clinical isolates from two different years were studied. The MICs of methicillin-susceptible (MSSA) and methicillin-resistant (MRSA) strains isolated in 1987 were compared with those of similar numbers of strains isolated in 1989. For MRSA > or = 90% of isolates from both years were resistant to clindamycin, gentamicin and erythromycin. These strains remained highly susceptible to vancomycin (100%), minocycline (90%) and rifampicin (100%). The greatest increase in resistance was observed for ofloxacin (2% in 1987 vs 62% in 1989); cross-resistance to all of the quinolones tested was demonstrated. MSSA strains remained susceptible to vancomycin (100%), minocycline (98%), rifampicin (100%), clindamycin (90%), gentamicin (90%) and ciprofloxacin (98%). It is concluded that methicillin susceptibility is a useful marker for selecting potential agents for the treatment of infections caused by S. aureus. A combination of minocycline and rifampicin may be a useful alternative to vancomycin for treating MRSA infections.

Drug Resistance, Microbial↗
PubMed1992

In vitro activity of T-3761, a new fluoroquinolone.

The in vitro activity of T-3761, a new fluoroquinolone antimicrobial agent which has an oxazine ring structure with a cyclopropyl moiety at C-10, was compared with those of other agents against 2,854 clinical isolates. T-3761 had a broad spectrum of activity and had potent activity against gram-positive and -negative bacteria. The MICs of T-3761 against 90% of the methicillin-susceptible Staphylococcus aureus, methicillin-susceptible and -resistant Staphylococcus epidermidis, and Clostridium spp. tested were 0.39 to 6.25 micrograms/ml. Its activity was comparable to those of ciprofloxacin and ofloxacin and four- to eightfold greater than those of norfloxacin and fleroxacin, but its activity was two- to eightfold less than that of tosufloxacin. Some isolates of ciprofloxacin-resistant S. aureus (MIC of ciprofloxacin, greater than or equal to 3.13 micrograms/ml) were still susceptible to T-3761 (MIC of T-3761, less than or equal to 0.78 micrograms/ml). The MICs of T-3761 against 90% of the streptococci and enterococci tested were 3.13 to 100 micrograms/ml. Its activity was equal to or 2- or 4-fold greater than those of norfloxacin and fleroxacin, equal to or 2- or 4-fold less than those of ofloxacin and ciprofloxacin, and 4- to 16-fold less than that of tosufloxacin. The activity of T-3761 against gram-negative bacteria was usually fourfold greater than those of norfloxacin, ofloxacin, and fleroxacin. Many isolates which were resistant to nonfluoroquinolone agents, such as minocycline- or imipenem-resistant S. aureus, ceftazidime-resistant members of the family Enterobacteriaceae, gentamicin- or imipenem-resistant Pseudomonas aeruginosa, and ampicillin-resistant Haemophilus influenzae and Neisseria gonorrhoeae, were susceptible to T-3761. The MBCs of T-3761 were either equal to or twofold greater than the MICs. The number of viable cells decreased rapidly during incubation with T-3761 at one to four times the MIC. At a concentration of four times the MIC, the frequencies of appearance of spontaneous mutants resistant to T-3761 against S. aureus, Escherichia coli, Serratia marcescens, and P. aeruginosa were 2.2 x 10(-8) to less than or equal to 1.2 x 10(-9). The 50% inhibitory concentrations of T-3761 for DNA gyrases isolated from E. coli and P. aeruginosa were 0.88 and 1.9 micrograms/ml, respectively.

Anti-Infective Agents↗
PubMed1992

Isolation and characterization of a Tn551-autolysis mutant of Staphylococcus aureus.

A Lyt- mutant with reduced autolytic activity was isolated after Tn551 mutagenesis of the methicillin-susceptible Staphylococcus aureus laboratory strain RN450. The Lyt- phenotype could be transferred back into the parent and into a variety of other S. aureus strains by transduction of the transposon marker. Southern analysis has located the Tn551 insert to a 3.2-kb HindIII DNA fragment on the SmaI B fragment of the staphylococcal chromosome. The Lyt- phenotype included reduced rates of cell wall turnover and autolysis induced by detergent or methicillin treatment; however, the rate of methicillin-induced killing was not affected. Peptidoglycans prepared from the parental and mutant cells showed identical muropeptide compositions, as resolved by a high-resolution high-pressure liquid chromatography technique. On the other hand, LiCl extracts of the mutant cells contained reduced amounts of total protein and lower specific cell wall-degrading activity compared with those of extracts of parental cells. The profile of bacteriolytic enzymes as detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed multiple band differences between mutant and parental cells; a major lytic band with properties characteristic of the staphylococcal endo-beta-N-acetylglucosaminidase was completely absent from the Lyt- cells. The Lyt- phenotype transduced into a series of methicillin-resistant strains of both homogeneous and heterogeneous phenotypes caused only a modest decrease in the level of methicillin resistance, as determined by population analysis.

Bacteriolysis↗
PubMed2025

Molecular landscape of methicillin-resistant Staphylococcus aureus strains in clinical infections from hospitals in Lagos, Nigeria.

BACKGROUND AND OBJECTIVES: Multidrug-resistant Staphylococcus aureus (MRSA) accounts for a significant proportion of antimicrobial resistance (AMR)-associated infections worldwide. This study investigated the molecular profile of MRSA in Nigeria, providing valuable genomic data to fill existing knowledge gaps and highlighting its importance in the context of the global AMR crisis. METHODS: A total of 107 isolates were obtained from patient samples, including wound swabs/pus (65 isolates, 60.7%), blood cultures (16 isolates, 15%), urine/urinary catheter (8 isolates, 7.5%) and other sources. Species identification was performed using MALDI-TOF, and antimicrobial susceptibility testing was performed using the VITEK®2 system. Genomic DNA was extracted and subjected to whole-genome sequencing using short-read Illumina technology. In addition, a subset of isolates underwent long-read sequencing using Oxford Nanopore technology. RESULTS: Among the 107 isolates, 63 (59%) were identified as MRSA, with 58 (92%) carrying the mecA gene. The MRSA isolates exhibited high resistance to non-β-lactam antibiotics, particularly trimethoprim/sulfamethoxazole (95.3%), erythromycin (76.6%), gentamicin (71.4%) and quinolones (69.8%). The most prevalent MRSA belonged to the Bengal Bay clone [t657/ST772/Staphylococcal Cassette Chromosome mec (SCCmec) V(5C2)/Panton-Valentine leukocidin (PVL) + methicillin-susceptible Staphylococcus aureus (MRSA)], followed by t4690/ST152/SCCmec Vc(5C2&5)/PVL + MRSA and ST8 (t008, n = 1; t064, n = 4)/SCCmec Vc(5C2&5). Phylogenetic analysis suggests both community/associated transmission and possible importation of strains. CONCLUSIONS: This study highlights the significant burden of MRSA in Nigeria, with the high-risk Bengal Bay MRSA clone as the most common strain. The widespread resistance to non-β-lactam antibiotics underscores the urgent need for enhanced surveillance, infection control and antibiotic stewardship to mitigate its spread.

Journal Article↗
PubMed1992

Multiple-dose pharmacokinetics of lomefloxacin: rationale for once-a-day dosing.

Six dosage regimens of oral lomefloxacin, a new difluorinated quinolone, were given to healthy volunteer subjects for 7 days in a randomized, placebo-controlled trial to evaluate pharmacokinetics and tolerability and to determine the optimum dosage schedule. Single daily doses of lomefloxacin up to 800 mg and multiple doses up to 600 mg twice daily (1,200 mg/day) were well tolerated. At all dose levels and schedules, lomefloxacin was well absorbed and achieved peak plasma concentrations approximately 1 hour after administration. Urine concentrations were approximately 100 times the plasma concentrations. Elimination half-lives of 7-8 hours were found for all dosage regimens. Steady-state was achieved on the second day of dosing. Little accumulation was observed. A 400 mg oral dose provided a mean peak plasma concentration of 3.43 micrograms/mL, and trough concentrations at steady state that were above the minimum inhibitory concentration for 90% (MIC90) of most common Enterobacteriaceae. The 400 mg dose produced a urine concentration of greater than 80 micrograms/mL during the 12- to 24-hour period after the dose, thus exceeding the MIC90 for clinical isolates such as Pseudomonas aeruginosa, Serratia marcescens, and methicillin-susceptible and -resistant Staphylococcus aureus. There was good agreement between the results of this study and previously reported single-dose data. In summary, lomefloxacin's rapid absorption, long half-life, and high sustained plasma and urine concentrations should permit effective once-daily administration in many clinical situations.

Adolescent↗
PubMed1992

Antimicrobial activity of DU-6859, a new potent fluoroquinolone, against clinical isolates.

DU-6859, (-)-7-[(7S)-amino-5-azaspiro(2,4)heptan-5-yl]-8-chloro-6- fluoro-1-[(1R,2R)-cis-2-fluoro-1-cyclopropyl]-1,4-dihydro-4-oxoquinol one-3- carboxylic acid, is a new fluoroquinolone with antibacterial activity which is significantly better than those of currently available quinolones. The MICs for 90% of methicillin-susceptible and -resistant Staphylococcus aureus and Staphylococcus epidermidis clinical isolates (MIC90s) were 0.1, 3.13, 0.1, and 0.39 microgram/ml, respectively. MIC50s of DU-6859 against quinolone-resistant, methicillin-resistant S. aureus were 8-, 32-, 64-, and 128-fold lower than those of tosufloxacin and sparfloxacin, ofloxacin and fleroxacin, ciprofloxacin, and lomefloxacin, respectively. DU-6859 inhibited the growth of all strains of Streptococcus pneumoniae and Streptococcus pyogenes at 0.1 and 0.2 microgram/ml, respectively, and was more active against enterococci than the other quinolones tested. Although the activity of DU-6859 against Pseudomonas aeruginosa was roughly comparable to that of ciprofloxacin at the MIC50 level, it was fourfold more active than ciprofloxacin at the MIC90 level. DU-6859 was also more active against other glucose-nonfermenting bacteria, Haemophilus influenzae, Moraxella catarrhalis, and Neisseria gonorrhoeae, than the other drugs tested. Strains of Bacteroides fragilis and Peptostreptococcus spp. were susceptible to DU-6859; MIC90s were 0.39 and 0.2 microgram/ml, respectively. DU-6859 generally showed activities twofold or greater than those of ciprofloxacin and the other drugs against almost all members of the family Enterobacteriaceae. The action of DU-6859 against the clinical isolates was bactericidal at concentrations near the MICs. DU-6859 activity was not affected by different media, pH, inoculum size, or human serum but was decreased in human urine.

Anti-Infective Agents↗
PubMed1977

Reliability of the microdilution technic for detection of methicillin-resistant strains of staphylococcus aureus.

To determine whether the microdilution technic for antimicrobic susceptibility testing could detect the hetero-resistance of "methicillin"-resistant Staphylococcus aureus, 100 stock cultures (54 methicillin-susceptible and 46 methicillin-resistant) were tested against methicillin, oxacillin, nafcillin and cephalothin. Each drug was diluted in Mueller-Hinton broth and in Mueller-Hinton broth with 5% NaCl. Minimum inhibitory concentration (MIC) determinations were made after 20-24 hours at 35 C and again after 48 hours of incubation. With one exception, methicillin resistance was detected in Mueller-Hinton broth when the trays were reincubated and read after 48 hours. Earlier detection of methicillin resistance was possible when the penicillinase-stable penicillins were diluted in broth containing 5% NaCl. Further studies suggest that the addition of NaCl to the broth medium might improve the stabilities of methicillin, oxacillin, and nafcillin during storage of the frozen microdilution trays. Either nafcillin or oxacillin would appear to be the best representative of the penicillinase-stable penicillins. Standardized disk-diffusion tests with cephalothin disks indicated that most methicillin-resistant strains are susceptible to cephalothin. However, there is reason to believe that such in-vitro test results might be inappropriate. With microdilution tests, most methicillin-resistant isolates were more resistant to cephalothin than were the methicillin-susceptible strains, but the MIC's for both types of staphylococci were generally within the range of concentrations that can be obtained during therapy. The addition of NaCl to the microdilution tests with cephalothin did not alter the test results significantly.

Indicator Dilution Techniques↗
PubMed1992

In vitro activity of the new glycopeptide decaplanin.

The activity of decaplanin, a new glycopeptide, was compared to that of vancomycin, teicoplanin and daptomycin. Decaplanin was two- to four-fold less active than vancomycin, telcoplanin and daptomycin against Staphylococcus aureus and Staphylococcus epidermidis, with an MIC90 of 2 micrograms/ml for methicillin-susceptible and 4 micrograms/ml for methicillin-resistant isolates. Decaplanin had activity similar to that of vancomycin against Streptococcus pyogenes, Streptococcus agalactiae, group C and G streptococci, with an MIC90 of 0.12 micrograms/ml. It was less active than the other agents against the viridans group streptococci (MIC90 4 micrograms/ml). The activity of decaplanin against enterococci (MIC90 4 micrograms/ml) was similar to that of vancomycin. Clostridium spp. were inhibited by 0.5 micrograms/ml, peptostreptococci and peptococci by 0.25 microgram/ml. Decaplanin was active from pH 5.5 to 7.5. Inoculum size had a minimal effect on MICs, and increased concentrations of Ca2+ and Mg2+ and 50% serum did not alter MICs or MBCs.

Anti-Bacterial Agents↗
PubMed1978

Single and combination antibiotic therapy of Staphylococcus aureus experimental endocarditis: emergence of gentamicin-resistant mutants.

The efficacy of nafcillin and gentamicin used alone and in combination at doses giving serum concentrations comparable to those achieved in patients was studied in rabbits with experimental Staphylococcus aureus endocarditis. The organism used was a penicillinase-producing, methicillin-susceptible, clinical isolate. The addition of gentamicin to nafcillin significantly increased the rate of killing of organisms in valvular vegetations, compared to the effect of nafcillin alone. Gentamicin alone delayed mortality but was not effective in reducing the bacterial populations of the vegetations. Bacteremia persisted in the animals treated with gentamicin alone, in contrast to the groups treated with nafcillin or the combination. Selection of a subpopulation of aminoglycoside-resistant small-colony variants occurred in animals treated with gentamicin alone. This variant was subsequently employed in the rabbit model and produced endocarditis, metastatic infection, and bacteremia comparable to those caused by the parent strain. Animals with infection produced by the variant died later than animals infected by the parent strain. Nafcillin was equally effective in reducing the population of both parent and variant strains in vitro and in therapy of the infected animals. Population studies showed the variant to be a mutant emerging at a rate of 1.9 x 10(-7). It was shown to differ from the parent strain in coagulase and hemolysin production, colonial morphology, and aminoglycoside susceptibility, but was similar by light and electron microscopy and in phage type, pigmentation of colonies, deoxyribonuclease production, mannitol fermentation, and growth rate.

Animals↗
PubMed1992

Epidemiologic typing and delineation of genetic relatedness of methicillin-resistant Staphylococcus aureus by macrorestriction analysis of genomic DNA by using pulsed-field gel electrophoresis.

To evaluate the usefulness of phenotypic and genotypic analyses for the epidemiologic typing of methicillin-resistant Staphylococcus aureus (MRSA), we characterized 64 epidemic MRSA isolates and 10 sporadic methicillin-susceptible S. aureus isolates from a university hospital and 18 MRSA isolates from hospitals in different geographical areas. Chromosomal DNA macrorestriction analysis with SstII was resolved by pulsed-field gel electrophoresis and compared with antibiotype analysis, phage type analysis, and standard genomic DNA restriction analysis with BglII. Indices of the discriminatory ability of these methods were 0.982, 0.959, 0.947, and 0.959, respectively. Macrorestriction patterns of 94% of MRSA isolates from patients, personnel, and the environment associated with a nosocomial outbreak were closely related (similarity coefficient, 85 to 100%). In contrast, methicillin-susceptible S. aureus isolates showed a marked diversity of macrorestriction patterns (median similarity, 41%). MRSA isolates from other geographical areas showed diverse macrorestriction patterns, with the exception of four isolates displaying identical or closely related patterns; these isolates were associated with concurrent outbreaks in four other Belgian hospitals. A concordance of genomic DNA macrorestriction typing with phenotypic methods was observed for 60 to 65% of MRSA isolates, and a concordance with standard DNA restriction analysis was found for 79 to 98% of these isolates. In conclusion, genomic DNA macrorestriction analysis was a useful complement to phenotypic methods for delineating epidemic isolates of MRSA, for identifying their nosocomial reservoirs, and for tracing their intra- and interhospital spread. The genetic relatedness of MRSA isolates, as estimated by this technique, appeared to correlate with their space-time clustering.

Bacterial Typing Techniques↗
PubMed2026

Mocravimod as a repurposing drug against clinical isolates of Staphylococcus aureus by targeting cell membrane.

UNLABELLED: Staphylococcus aureus infections, particularly those caused by multidrug-resistant strains and associated with biofilm formation, pose a major therapeutic challenge in clinical practice. The objective of this study was to evaluate the antibacterial and antibiofilm activity of mocravimod (KRP-203), an FDA-approved S1P receptor modulator, against clinical S. aureus isolates and to explore its underlying mechanism of action. The antibacterial activity of KRP-203 was assessed against methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) using MIC determination, time-kill assays, and biofilm inhibition models. KRP-203 exhibited strong bactericidal activity against planktonic MSSA and MRSA, with MIC values ranging 6.25-50μM. Time-kill assays demonstrated rapid bacterial eradication at 8× MIC within 2 h, showing superior killing kinetics compared with vancomycin. At sub-inhibitory concentrations, KRP-203 inhibited biofilm formation by up to 70% and reduced viable bacterial counts in mature biofilms by >2.5 logs. To elucidate the antibacterial mechanism, whole-genome sequencing and quantitative proteomic analyses were performed. These analyses revealed mutations in membrane-associated genes, including glnQ and BCAT, and significant alterations in proteins related to membrane integrity and redox regulation. Consistently, functional assays confirmed that KRP-203 disrupts bacterial cell membrane, as evidenced by dose-dependent membrane depolarization, increased permeability, and direct binding to cardiolipin and phosphatidylglycerol. Molecular docking further predicted a favorable interaction between KRP-203 and GlnQ. In conclusion, KRP-203 demonstrated notable antibacterial and antibiofilm activity against S. aureus, likely through membrane integrity disruption. While these findings highlight its potential as a repurposed antibacterial agent, further studies are required to fully elucidate its molecular targets, optimize antibacterial efficacy, and evaluate its in vivo safety profile. IMPORTANCE: Antibiotic resistance and the formation of biofilms, which protect bacteria from medications and immunological responses, present the significant challenges for the clinical treatment of Staphylococcus aureus infections. This study reveals mocravimod hydrochloride (KRP-203), a clinically approved drug initially intended to treat leukemia, as a viable new candidate against S. aureus infection. KRP-203 quickly kills both drug-susceptible and resistant S. aureus, including difficult-to-treat biofilm-associated cells. Its membrane-disrupting activity quickly kills drug-resistant bacteria while also destroying biofilm formations, presenting a dual action rarely accomplished by conventional antibiotics. Critically, KRP-203's established safety profile in human studies may hasten its repurposing as a new weapon against biofilm-associated infections, providing possible solutions for chronic and drug-resistant S. aureus infections where existing treatments commonly fail.

Biofilms↗
PubMed1978

Use of a heavy inoculum in the in vitro evaluation of the anti-staphylococcal activity of 19 cephalosporins.

The in vitro activity of 19 cephalosporins against 105 clinical isolates of Staphylococcus aureus and S. epidermidis was determined by using a heavy inoculum, i.e., 10(8) to 10(9) organisms per ml, to maximally challenge the antibiotics. The anti-staphylococcal activities of cephaloridine and 87/312 were consistently decreased by the use of a heavy inoculum when compared with the activity obtained with two less-concentrated inocula. The activity of most of the other compounds was also decreased with the use of a heavy inoculum, but this was observed only with selected isolates. Cephapirin, cephalothin, and cefazaflur were the most active drugs against the methicillin-susceptible isolates. Cephaloridine, cefamandole, cefazaflur, and 87/312 had substantial activity against methicillin-resistant staphylococci even with heavy inocula. With the exception of cefaclor against S. aureus, the orally absorbed cephalosporins were generally one-half to one-sixteenth as active as the parenterally administered cephalosporins. The median minimal inhibitory concentrations of five of the 12 parenteral cephalosporins were lower with the methicillin-susceptible S. aureus than with the methicillin-susceptible S. epidermidis strains.

Bacteriological Techniques↗
PubMed1992

In vitro antistaphylococcal activities of two investigative fluoroquinolones, CI-960 and WIN 57273, compared with those of ciprofloxacin, mupirocin (pseudomonic acid), and peptide-class antimicrobial agents.

By using broth microdilution, 373 clinical isolates of staphylococci were studied to determine their susceptibilities to CI-960, WIN 57273, ciprofloxacin, mupirocin, vancomycin, teicoplanin, and ramoplanin. Test strains comprised 179 strains of Staphylococcus aureus and 194 strains of coagulase-negative species. Strains of S. aureus were susceptible to CI-960, which had a mode MIC of 0.032 micrograms/ml and an MIC for 90% of the strains of 2 micrograms/ml. CI-960 was equally active against methicillin-susceptible and -resistant S. aureus strains as well as ciprofloxacin-resistant strains. Similarly, WIN 57273 was highly active, with a mode MIC of 0.008 micrograms/ml and an MIC for 90% of the strains of 1 micrograms/ml. No cross-resistance to CI-960 and WIN 57273 among ciprofloxacin-resistant strains was detected. Mupirocin was four- to eightfold more active than ramoplanin, vancomycin, and teicoplanin. With regard to coagulase-negative staphylococci, CI-960 and WIN 57273 were the most active of the test compounds, inhibiting all strains at 0.5 and 1 micrograms/ml, respectively. Against the same strains, mupirocin was fourfold more active than ramoplanin and eightfold more active than vancomycin. Five strains of S. haemolyticus were found to be resistant to ciprofloxacin, while resistance to teicoplanin was found among strains of S. epidermidis, S. haemolyticus, S. hominis, S. saprophyticus, S. simulans, S. warneri, and S. xylosus.

Anti-Infective Agents↗
PubMed2026

Large-scale genomic analysis places Chinese CC398 as a persistent human-associated MSSA lineage apart from the dominant global LA-MRSA clade.

Staphylococcus aureus clonal complex (CC)398 has emerged as a dominant livestock-associated methicillin-resistant S. aureus (LA-MRSA) lineage worldwide; however, its evolutionary trajectory and regional diversification remain incompletely understood. We developed a core-genome multilocus sequence typing (cgMLST) scheme with hierarchical clustering and applied it to over 30,000 S. aureus genomes, revealing frequent cross-border transmission of CC398. Subsequent time-calibrated phylogenetic analysis placed the most recent common ancestor at 1942 (95% CI: 1939-1945), with the human-to-livestock host jump around 1969 (95% CI: 1968-1972). Chinese CC398 exhibits a distinct trajectory: unlike the LA-MRSA lineages dominating Europe and North America, Chinese isolates are predominantly human-associated methicillin-susceptible S. aureus (HA-MSSA), forming unique East Asia-specific phylogroups (SAP1, SAP2, and AP1-AP3), with distinct resistance and virulence profiles. The LA lineage remains limited in China, with multinational mixed clusters emerging only after 2019. Analysis of global transmission networks revealed a significant correlation between LA-CC398 spread and international trade in fresh swine products, while no such correlation was observed for the human-associated lineage. Beyond the established lineage markers tet(M) and scn, our analysis identified additional differentially distributed genes, including cadC-a chromosomal cadmium resistance regulator-as a novel HA-lineage-enriched gene whose functional role in host adaptation remains to be determined. This study reveals that CC398 followed fundamentally different evolutionary paths in China versus Western countries, challenging a one-size-fits-all model of its dissemination.IMPORTANCEThis study illustrates how large-scale microbial genomics can resolve the evolutionary origins and regional diversification of bacterial pathogens. By applying a novel cgMLST scheme to over 30,000 S. aureus genomes, we show that CC398 followed fundamentally different evolutionary paths in China versus Western countries-challenging the prevailing model of uniform global dissemination-and that livestock-associated MRSA expansion is closely linked to international trade in fresh pork products. These findings highlight the need for integrated surveillance across human, animal, and trade interfaces to anticipate the emergence and spread of zoonotic pathogens.

Staphylococcus aureus↗
PubMed1992

Autolysis of methicillin-resistant and -susceptible Staphylococcus aureus.

The autolytic activities, including unstimulated, Triton X-100-stimulated, and daptomycin-induced, of various sets of methicillin-resistant and related methicillin-susceptible strains were compared. Faster rates of autolysis were noted in two heterogeneous methicillin-resistant transductants than in their methicillin-susceptible parental recipients, in a heterogeneous resistant strain than in a susceptible derivative created by chemical mutagenesis, and in a homogeneous resistant strain than in a derivative that had decreased methicillin resistance and was created by transposon Tn551 mutagenesis. These results suggest that the presence of the methicillin resistance region, mec, either directly or indirectly through an interaction with other host genes, confers a faster rate of autolysis on strains. Various auxilliary genes are known to affect methicillin resistance expression, and one of these genes, femA, was necessary for the expression of this faster rate of autolysis. These differences in autolytic activities were not observed in isolated crude cell walls retaining autolytic activities, suggesting different modes of regulation of autolysins in intact cells and isolated walls. In contrast, one homogeneous, highly resistant strain, DU4916, had a lower autolytic activity than did derived heterogeneous resistant and susceptible strains created by chemical mutagenesis and a strain that had decreased resistance and was created by transposon mutagenesis. Our observations suggest that methicillin resistance expression is associated with an enhanced rate of autolysis, in heterogeneous resistant strains at least.

Autolysis↗
PubMed1979

Modulation of protein A formation in Staphylococcus aureus by genetic determinants for methicillin resistance.

Many methicillin-resistant (Mec(r)) strains of Staphylococcus aureus either produce no protein A or secrete it extracellularly (S. Winblad and C. Ericson, Acta Pathol. Microbiol. Scand. Sect. B 81:150-156, 1973). We found that methicillin resistance and protein A production were apparently lost coordinately from the natively Mec(r) strain A676. Restoration of the genetic determinant for methicillin resistance (mec) by transduction or transformation restored protein A production. In two other Mec(r) strains, loss of mec was accompanied by marked reduction in protein A formation. Genetic transfer of mec to derivatives of S. aureus 8325 affected protein A formation differently with different mec determinants. Those derived from strain A676 and two other Mec(r) strains reduced the scanty amount of protein A produced by strain 8325 to even lower or undetectable levels, whereas mec from two more Mec(r) strains increased its protein A content. This "mec-effect," i.e., stimulation or inhibition of protein A formation dependent on the combination of host strain and mec determinant, was reduced in methicillin-susceptible (Mec(s)) mutants produced by ethyl methane sulfonate treatment of Mec(r) strains. The mec-effect reappeared in spontaneous revertants to methicillin resistance. Phenotypic reduction of methicillin resistance in Mec(r) strains grown at 44 degrees C was accompanied by reduction of the mec-effect on protein A, but it had no effect on protein A formation in Mec(s) strains. Two independent mutants of strain 8325 produced large amounts of protein A at rates that were unaffected by growth at 44 degrees C or by the introduction of mec determinants.

Genes↗