Comparative genomics reveals the correlations of stress response genes and bacteriophages in developing antibiotic resistance of
Staphylococcus saprophyticus
Authors: Zhang Kailun , Potter Robert F. , Marino Jamie , Muenks Carol E. , Lammers Matthew G. , Dien Bard Jennifer , Dingle Tanis C. , Humphries Romney , Westblade Lars F. , Burnham Carey-Ann D. , Dantas Gautam 
Published: December 2023

Staphylococcus saprophyticus
is the leading Gram-positive cause of uncomplicated urinary tract infections. Recent reports of increasing antimicrobial resistance (AMR) in
S. saprophyticus
warrant investigation of its understudied resistance patterns. Here, we characterized a diverse collection of
S. saprophyticus
(
n
= 275) using comparative whole genome sequencing. We performed a phylogenetic analysis of core genes (1,646) to group our
S. saprophyticus
and investigated the distributions of antibiotic resistance genes (ARGs).
S. saprophyticus
isolates belonged to two previously characterized lineages, and 14.91% (41/275) demonstrated multidrug resistance. We compared antimicrobial susceptibility phenotypes of our
S. saprophyticus
with the presence of different ARGs and gene alleles. 29.8% (82/275) carried staphylococcal cassette chromosome mobile elements, among which 25.6% (21/82) were
mecA
+
. Penicillin resistance was associated with the presence of
mecA
or
blaZ
. The
mecA
gene could serve as a marker to infer cefoxitin and oxacillin resistance of
S. saprophyticus
, but the absence of this gene is not predictive of susceptibility. Utilizing computational modeling, we found several genes were associated with cefoxitin and oxacillin resistance in

mecA
−

isolates, some of which have predicted functions in stress response and cell wall synthesis. Furthermore, phenotype association analysis indicates ARGs against non-β-lactams reported in other staphylococci may serve as resistance determinants of
S. saprophyticus
. Lastly, we observed that two ARGs [
erm
and
erm (44)v
], carried by bacteriophages, were correlated with high phenotypic non-susceptibility against erythromycin (11/11 and 10/10) and clindamycin (11/11 and 10/10). The AMR-correlated genetic elements identified in this work can help to refine resistance prediction of
S. saprophyticus
during antibiotic treatment.

IMPORTANCE

Staphylococcus saprophyticus
is the second most common bacteria associated with urinary tract infections (UTIs) in women. The antimicrobial treatment regimen for uncomplicated UTI is normally nitrofurantoin, trimethoprim-sulfamethoxazole (TMP-SMX), or a fluoroquinolone without routine susceptibility testing of
S. saprophyticus
recovered from urine specimens. However, TMP-SMX-resistant
S. saprophyticus
has been detected recently in UTI patients, as well as in our cohort. Herein, we investigated the understudied resistance patterns of this pathogenic species by linking genomic antibiotic resistance gene (ARG) content to susceptibility phenotypes. We describe ARG associations with known and novel SCC
mec
configurations as well as phage elements in
S. saprophyticus
, which may serve as intervention or diagnostic targets to limit resistance transmission. Our analyses yielded a comprehensive database of phenotypic data associated with the ARG sequence in clinical
S. saprophyticus
isolates, which will be crucial for resistance surveillance and prediction to enable precise diagnosis and effective treatment of
S. saprophyticus
UTIs.