Characterization of the resistome and predominant genetic lineages of Gram-positive bacteria causing keratitis

• Published in: Antimicrobial agents and chemotherapy Vol. 68; no. 3; p. e0124723
• Main Authors: André, Camille, Van Camp, Andrew G, Ung, Lawson, Gilmore, Michael S, Bispo, Paulo J M
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 06-03-2024
• Subjects: Anti-Bacterial Agents - pharmacology; Anti-Infective Agents; Azithromycin; Bacteriology; Drug Resistance, Bacterial - genetics; Fluoroquinolones; Humans; Macrolides; Mechanisms of Resistance; Methicillin-Resistant Staphylococcus aureus; Microbial Sensitivity Tests; Staphylococcal Infections - microbiology; Staphylococcus - genetics; Staphylococcus aureus; Streptococcus; Gram-positive bacteria; keratitis; genomics; resistome; antimicrobial resistance; MRSA
• ISSN: 0066-4804; 1098-6596; 1098-6596
• DOI: 10.1128/aac.01247-23

Bacterial keratitis is a vision-threatening infection mainly caused by Gram-positive bacteria (GPB). Antimicrobial therapy is commonly empirical using broad-spectrum agents with efficacy increasingly compromised by the emergence of antimicrobial resistance. We used a combination of phenotypic tests and genome sequencing to identify the predominant lineages of GPB causing keratitis and to characterize their antimicrobial resistance patterns. A total of 161 isolates, including
(
= 86), coagulase-negative staphylococci (CoNS;
= 34),
spp. (
= 34), and
(
= 7), were included. The population of
isolates consisted mainly of clonal complex 5 (CC5) (30.2%). Similarly, the population of
was homogenous with most of them belonging to CC2 (78.3%). Conversely, the genetic population of
was highly diverse. Resistance to first-line antibiotics was common among staphylococci, especially among CC5
. Methicillin-resistant
was commonly resistant to fluoroquinolones and azithromycin (78.6%) and tobramycin (57%). One-third of the CoNS were resistant to fluoroquinolones and 53% to azithromycin. Macrolide resistance was commonly caused by
genes in
,
and
in CoNS, and
) in streptococci. Aminoglycoside resistance in staphylococci was mainly associated with genes commonly found in mobile genetic elements and that encode for nucleotidyltransferases like
and
. Fluroquinolone-resistant staphylococci carried from 1 to 4 quinolone resistance-determining region mutations, mainly in the
and
genes. We found that GPB causing keratitis are associated with strains commonly resistant to first-line topical therapies, especially staphylococcal isolates that are frequently multidrug-resistant and associated with major hospital-adapted epidemic lineages.