Prevalence and clinical associations of Staphylococcus aureus small-colony variant respiratory infection in children with cystic fibrosis (SCVSA): a multicentre, observational study

One of the most interesting features of Staphylococcus aureus is its ability to switch to a small colony variant (SCV). This switch allows the pathogen to survive periods of antibiotic treatment or pressure from the immune system of the host and further enables it to start the infection once again after the environmental stress declines. However, so far only little is known about this reversion back to the more virulent wild type phenotype. Therefore, this study aimed to analyze the frequency of reversion to the wild type phenotype of thymidine auxotroph S. aureus SCV isolates (TD-SCVs) obtained from patients with cystic fibrosis (CF). With the use of single cell starting cultures, the occurrence of the thymidine prototroph revertants was monitored. The underlying mutational cause of the SCVs and subsequent revertants were analyzed by sequencing the gene coding for thymidylate synthase (ThyA), whose mutations are known to produce thymidine auxotroph S. aureus SCV. In our study, the underlying mutational cause for the switch to the TD-SCV phenotype was primarily point mutations. Out of twelve isolates, seven isolates showed an occurrence of revertants with a frequency ranging from 90.06% to 0.16%. This high variability in the frequency of reversion to the wild type was not expected. However, this variability in the frequency of reversion may also be the key to successful re-infection of the host. Sometimes quick reversion to the wild type proves necessary for survival, whereas other times, staying hidden for a bit longer leads to success in re-colonization of the host.

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103 Linezolid resistance in methicillin-resistant small colony variant Staphylococcus aureus (MRSA-SCV) isolated from cystic fibrosis (CF) patients

Journal of Cystic Fibrosis ◽

10.1016/s1569-1993(17)30467-8 ◽

2017 ◽

Vol 16 ◽

pp. S91

Author(s):

P. Morelli ◽

R. Musumeci ◽

C. Cocuzza ◽

E. Calaresu ◽

R. Bandettini ◽

...

Keyword(s):

Cystic Fibrosis ◽

Staphylococcus Aureus ◽

Methicillin Resistant ◽

Small Colony Variant ◽

Linezolid Resistance ◽

Small Colony

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Intracellular Activity of Antibiotics in a Model of Human THP-1 Macrophages Infected by a Staphylococcus aureus Small-Colony Variant Strain Isolated from a Cystic Fibrosis Patient: Pharmacodynamic Evaluation and Comparison with Isogenic Normal-Phenotype and Revertant Strains

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01145-08 ◽

2009 ◽

Vol 53 (4) ◽

pp. 1434-1442 ◽

Cited By ~ 33

Author(s):

Hoang Anh Nguyen ◽

Olivier Denis ◽

Anne Vergison ◽

Anne Theunis ◽

Paul M. Tulkens ◽

...

Keyword(s):

Cystic Fibrosis ◽

Staphylococcus Aureus ◽

Cystic Fibrosis Patient ◽

Similar Reduction ◽

Small Colony Variant ◽

Normal Phenotype ◽

Intracellular Activity ◽

Static Effect ◽

Small Colony ◽

Confocal And Electron Microscopy

ABSTRACT Small-colony variant (SCV) strains of Staphylococcus aureus show reduced antibiotic susceptibility and intracellular persistence, potentially explaining therapeutic failures. The activities of oxacillin, fusidic acid, clindamycin, gentamicin, rifampin, vancomycin, linezolid, quinupristin-dalfopristin, daptomycin, tigecycline, moxifloxacin, telavancin, and oritavancin have been examined in THP-1 macrophages infected by a stable thymidine-dependent SCV strain in comparison with normal-phenotype and revertant isogenic strains isolated from the same cystic fibrosis patient. The SCV strain grew slowly extracellularly and intracellularly (1- and 0.2-log CFU increase in 24 h, respectively). In confocal and electron microscopy, SCV and the normal-phenotype bacteria remain confined in acid vacuoles. All antibiotics tested, except tigecycline, caused a net reduction in bacterial counts that was both time and concentration dependent. At an extracellular concentration corresponding to the maximum concentration in human serum (total drug), oritavancin caused a 2-log CFU reduction at 24 h; rifampin, moxifloxacin, and quinupristin-dalfopristin caused a similar reduction at 72 h; and all other antibiotics had only a static effect at 24 h and a 1-log CFU reduction at 72 h. In concentration dependence experiments, response to oritavancin was bimodal (two successive plateaus of −0.4 and −3.1 log CFU); tigecycline, moxifloxacin, and rifampin showed maximal effects of −1.1 to −1.7 log CFU; and the other antibiotics produced results of −0.6 log CFU or less. Addition of thymidine restored intracellular growth of the SCV strain but did not modify the activity of antibiotics (except quinupristin-dalfopristin). All drugs (except tigecycline and oritavancin) showed higher intracellular activity against normal or revertant phenotypes than against SCV strains. The data may help rationalizing the design of further studies with intracellular SCV strains.

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507: Establishing a mutant for modeling Staphylococcus aureus small colony–variant airway infection in cystic fibrosis

Journal of Cystic Fibrosis ◽

10.1016/s1569-1993(21)01931-7 ◽

2021 ◽

Vol 20 ◽

pp. S239-S240

Author(s):

G. Bollar ◽

J. Keith ◽

A. Oden ◽

M. Kiedrowski ◽

S. Birket

Keyword(s):

Cystic Fibrosis ◽

Staphylococcus Aureus ◽

Small Colony Variant ◽

Airway Infection ◽

Small Colony

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Persistent Infection with Small Colony Variant Strains of Staphylococcus aureus in Patients with Cystic Fibrosis

The Journal of Infectious Diseases ◽

10.1086/515238 ◽

1998 ◽

Vol 177 (4) ◽

pp. 1023-1029 ◽

Cited By ~ 223

Author(s):

B. Kahl ◽

M. Herrmann ◽

A. S. Everding ◽

H. G. Koch ◽

K. Becker ◽

...

Keyword(s):

Cystic Fibrosis ◽

Staphylococcus Aureus ◽

Persistent Infection ◽

Small Colony Variant ◽

Small Colony

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Increased Expression of Clumping Factor and Fibronectin-Binding Proteins by hemB Mutants of Staphylococcus aureus Expressing Small Colony Variant Phenotypes

Infection and Immunity ◽

10.1128/iai.70.10.5428-5437.2002 ◽

2002 ◽

Vol 70 (10) ◽

pp. 5428-5437 ◽

Cited By ~ 120

Author(s):

Pierre Vaudaux ◽

Patrice Francois ◽

Carmelo Bisognano ◽

William L. Kelley ◽

Daniel P. Lew ◽

...

Keyword(s):

Staphylococcus Aureus ◽

Surface Display ◽

Human Embryonic Kidney Cells ◽

Small Colony Variant ◽

Reverse Transcription Pcr ◽

Bacterial Adhesins ◽

Transport Chain ◽

Complete Restoration ◽

Small Colony ◽

Slow Growing

ABSTRACT Small colony variants (SCVs) of Staphylococcus aureus are slow-growing subpopulations that cause persistent and relapsing infections. The altered phenotype of SCV can arise from defects in menadione or hemin biosynthesis, which disrupt the electron transport chain and decrease ATP concentrations. With SCVs, virulence is altered by a decrease in exotoxin production and susceptibility to various antibiotics, allowing their intracellular survival. The expression of bacterial adhesins by SCVs is poorly documented. We tested fibrinogen- and fibronectin-mediated adhesion of a hemB mutant of S. aureus 8325-4 that is defective for hemin biosynthesis and exhibits a complete SCV phenotype. In this strain, adhesion to fibrinogen and fibronectin was significantly higher than that of its isogenic, normally growing parent and correlated with the increased surface display of these adhesins as assessed by flow cytometry. Real-time quantitative reverse transcription-PCR demonstrated increased expression of clfA and fnb genes by the hemB mutant compared to its isogenic parent. The influence of the hemB mutation on altered adhesin expression was confirmed by showing complete restoration of the wild-type adhesive phenotype in the hemB mutant, either by complementing with intact hemB or by supplementing the growth medium with hemin. Increased surface display of fibrinogen and fibronectin adhesins by the hemB mutation occurred independently from agr, a major regulatory locus of virulence factors in S. aureus. Both agr-positive and agr-lacking hemB mutants were also more efficiently internalized by human embryonic kidney cells than were their isogenic controls, presumably because of increased surface display of their fibronectin adhesins.

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